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Bent-Shaped p-Type Small-Molecule Organic Semiconductors: A Molecular Design Strategy for Next-Generation Practical Applications

  • Toshihiro Okamoto*
    Toshihiro Okamoto
    Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    University of Tokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    PRESTO, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
    *[email protected]
    More by Toshihiro Okamoto
    Orcidhttp://orcid.org/0000-0002-4783-0621
    • , 
  • Craig P. Yu
    Craig P. Yu
    Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    More by Craig P. Yu
    Orcidhttp://orcid.org/0000-0002-1423-5244
    • , 
  • Chikahiko Mitsui
    Chikahiko Mitsui
    Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    More by Chikahiko Mitsui
    • , 
  • Masakazu Yamagishi
    Masakazu Yamagishi
    Department of Applied Chemistry and Chemical Engineering, National Institute of Technology, Toyama College, 13 Hongo-machi, Toyama City, Toyama 939-8630, Japan
    More by Masakazu Yamagishi
    • , 
  • Hiroyuki Ishii
    Hiroyuki Ishii
    Department of Applied Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
    More by Hiroyuki Ishii
    Orcidhttp://orcid.org/0000-0003-0644-1424
    • , and 
  • Jun Takeya
    Jun Takeya
    Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    University of Tokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    MANA, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 205-0044, Japan
    More by Jun Takeya
Cite this: J. Am. Chem. Soc. 2020, 142, 20, 9083–9096
Publication Date (Web):April 15, 2020
https://doi.org/10.1021/jacs.9b10450
Copyright © 2020 American Chemical Society
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Abstract

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Significant progress has been made in both molecular design and fundamental scientific understanding of organic semiconductors (OSCs) in recent years. Suitable charge-carrier mobilities (μ) have been obtained by many high-performance OSCs (μ > 10 cm2 V–1 s–1), but drawbacks remain, including low solution processability and poor thermal durability. In addition, since aggregation of OSCs involves weak intermolecular interactions, the molecules are perpetually in thermal motion, even in the solid state, which disrupts charge-carrier transport. These issues limit potential applications of OSCs. The present work examines a molecular design for hole-transporting (p-type) OSCs based on the “bent-shaped” geometry with specific molecular orbital configurations, which aims to enhance effective intermolecular orbital overlaps, stabilize crystal phases, suppress detrimental molecular motions in the solid state, and improve solution processability. The results indicated that such OSCs have high μ and suitable solution processability, and are resistant to ambient and thermal conditions, making them suitable for practical applications.

Introduction

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Organic semiconductors (OSCs) are of intense scientific and technological interest due to their potential incorporation in printable and flexible electronics, such as organic field-effect transistors (OFETs),(1−4) organic light-emitting diodes (OLEDs),(5,6) organic photovoltaics (OPVs),(7−11) and organic thermoelectrics (OTE).(12−15) In contrast to their inorganic semiconductor counterparts,(16) the functions of OSCs are governed by intermolecular charge transport between adjacent π-conjugated molecules, molecular geometry, and electronic characteristics.(17−26) Thus, rational, versatile molecular design could lead to the development of high-performance, printable OSCs that are suitable for large-scale industrial production.
The general requirements for printable, flexible electronic devices include (1) high chemical stability under ambient conditions without the need for special precautions, (2) high charge-carrier mobility (μ) that exceeds the performance of conventional amorphous silicon (e.g., 0.5–1.0 cm2 V–1 s–1)(27) and is competitive with that of metal-oxide semiconductors, (3) sufficient solubility in common organic solvents that allows low-cost solution processing for device fabrication, (4) high thermal durability (highly stable crystal phase above 150 °C to withstand fabrication processes),(28) and (5) facile synthetic routes for large-scale production.
To date, various molecular designs based on π-conjugated materials have been reported, with the aim of achieving the high performance required for the aforementioned applications.(29−40) Representative molecular designs in the literature have utilized linear or quasi-linear π-electron cores (π-cores) such as pentacene,(41) [1]benzothieno[3,2-b][1]benzothiophene (BTBT),(42) and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT)(43) as a means of obtaining effective intermolecular π-orbital overlaps necessary for charge transport in the solid state (Figure 1).(4,44) These π-cores aggregate through multiple intermolecular C–H···π, S···S, and S···π interactions and form two-dimensional (2D) herringbone (HB)-type packing structures that favor 2D charge carrier transport.(45) Various studies have also focused on side-chain engineering with bulky alkylsilyl,(46,47) linear alkyl,(48−52) and unsymmetrical substituents(53−57) in order to improve the solubility and tune the aggregated structures of these π-cores (Figure 1). As a result, high-performance and solution-processable OSCs with these substituted π-cores having excellent μ (>10 cm2 V–1 s–1) have been reported.(58−60) However, both linear and quasi-linear alkyl-substituted π-cores have exhibited phase transitions from crystalline to liquid crystalline or other crystal phases at temperatures around 90–130 °C,(42,61−63) leading to degradation of transistor performance at elevated temperatures during device fabrication. It has also been recently reported that unsymmetrical substituted BTBT analogues aggregate to form a highly crystalline liquid crystal phase.(53) These challenges associated with various representative OSCs illustrate that it is still difficult to simultaneously achieve sufficient solubility, thermal durability, and high μ with conventional molecular design strategies based on OSC π-cores.

Figure 1

Figure 1. Molecular structures of representative organic semiconductors.

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Recently, several fascinating studies have been reported concerning the detrimental effects of large-amplitude molecular motions on the performance of high-mobility OSCs such as pentacene and BTBT derivatives.(64−67) Sirringhaus and co-workers also suggested that the dynamic disorder of OSCs in the solid state might be the parameter having the most harmful effect on charge transport.(67) Hence, it is apparent that future rational molecular design not only should be guided by intramolecular characteristics or intermolecular orbital overlaps, but also must aim to reduce unfavorable molecular motions via unique π-core structures and effective side-chain engineering.
To meet all the aforementioned requirements for promising next-generation OSCs, our group has proposed a series of conceptually new bent-shaped π-cores.(68−73) The traditional linear and quasi-linear molecules have small radii of rotation and translation, which lead to low thermal durability as a result of constant molecular motions. In contrast, bent-shaped molecular geometries possess increased radii of rotation and translation, which suppress detrimental molecular motions in the solid state and simultaneously confer high μ and thermal durability (Figure 2).(74) Another feature of the bent-shaped geometry compared to conventional linear and quasi-linear geometries is an enhanced internal dipole moment resulting from reduced molecular symmetry. On this basis, we attempted to develop highly soluble π-cores that can be solution-processed to fabricate OFETs and that permit fine-tuning of molecular packing structures with further side-chain engineering. Our group has thus far synthesized a series of bent-shaped molecules, including first- and second-generation OSCs, as well as extended analogues. Sulfur atoms were incorporated into these compounds to allow tuning of the electronic structures (specifically, the highest occupied molecular orbital (HOMO) energy level) to achieve efficient hole injections during OFET operations under ambient conditions. In addition, the large HOMO coefficient of the sulfur atom produces favorable intermolecular short-range interactions with adjacent π-cores. These lead to large intermolecular orbital overlaps (increased transfer integral (t) values) and also suppress molecular motions in the solid state.

Figure 2

Figure 2. Molecular designs of first- and second-generation bent-shaped OSCs.

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Herein, we summarize our recent work regarding the molecular design of bent-shaped OSCs by providing a detailed analysis of the synthesis, aggregated structures (complemented by theoretical calculations), ionization potentials, thermal stabilities, and solubilities of these compounds. The OFET performances of these bent-shaped OSCs are also presented to demonstrate the effectiveness of the molecular designs. We hope that this work will assist future molecular design of OSCs toward the development of high-performance next-generation electronics materials.

Molecular Design

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First-Generation OSCs Based on V- and N-Shaped π-Cores

DNT-V

The V-shaped dinaphtho[2,3-b:2′,3′-d]thiophene (DNT-V) π-core was developed for p-channel OFET applications.(68)DNT-V features a thiophene in the center position that is fused by two naphthalene units on each side. The V-shaped molecular geometry and reduced molecular symmetry of this molecule produce an internal dipole moment that is not present in linear molecules, along with a stabilized crystalline phase (which suppresses molecular motions) and high solubility(75) in common organic solvents. Density functional theory (DFT) calculations revealed a delocalized distribution of HOMO coefficients across the backbone and a large HOMO coefficient of the sulfur atom (Figure 3a). The HOMO level of DNT-V was calculated to be −5.62 eV, which is higher than that of BTBT (−5.79 eV)(42) at the B3LYP/6-311G(d) level. In terms of reorganization energies for hole transport (λh), our calculations estimate a λh of 138 meV for DNT-V, which is significantly smaller than that for BTBT (226 meV) and almost equal to that of DNTT (130 meV).(76) The large HOMO coefficient for the sulfur atom suggests that the central sulfur-based heterocycle is different from thiophene. From the nucleus-independent chemical shift (NICS),(77,78) we hope to gain fundamental understanding on the molecular properties of such fused heterocyclic systems, as well as predict their molecular assemblies and charge transports. Indeed, NICS calculations showed that the central ring is more similar to the less aromatic compound 2,3,4,5-tetramethylenetetrahydrothiophene (thiophenoradialene)(79) (NICS(0) = −2.6 ppm) than to 2,3,4,5-tetramethylthiophene (NICS(0) = −11.6 ppm). Owing to this molecular feature, the large HOMO coefficient for sulfur can potentially contribute to significant intermolecular orbital overlaps that promote hole transports.

Figure 3

Figure 3. Molecular structures, NICS values (calculated at the HF/6-31+G(d)//B3LYP/6-31G(d) level), HOMO coefficients and energy levels, and dipole moments (calculated at the B3LYP/6-311G(d)//B3LYP/6-31G(d) level) of the (a) DNT-V, (b) DAT-V, (c) DNBDT-N, and (d) TBBT-V OSCs.

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DAT-V

The recent molecular design of dianthra[2,3-b:2′,3′]thiophene (DAT-V)(71) (Figure 3b) involves the expansion of π-conjugation from the dinaphthalene moiety of DNT-V to a dianthracene group while preserving the overall V-shaped geometry. DFT calculations demonstrate a highly delocalized distribution of HOMO coefficients across the backbone and a sizable HOMO coefficient for the sulfur atom that is similar to that of DNT-V. Extending the π-conjugation increases the calculated HOMO energy level of DAT-V to −5.32 eV, compared to −5.62 eV for DNT-V, which is expected to lower the injection barrier and threshold voltage in OFET operation. NICS calculations showed that the central sulfur-based heterocycle exhibits a much lower degree of aromaticity (NICS(0) = −2.1 ppm). Another attractive feature of the DAT-V π-core is the reduced λh value (99 meV), which is significantly smaller than those for DNT-V (138 meV) and DNTT (130 meV).(76)

DNBDT-N

The N-shaped (dinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DNBDT-N)(70) π-core (Figure 3c) is also considered as an extended V-shaped DNT-V π-core. DNBDT-N adopts a bent-shaped molecular geometry at two terminals that further suppresses molecular motions and stabilizes the crystal phase. The HOMO distribution of DNBDT-N is spread across the entire π-core, including a large coefficient of sulfur atoms. This scenario results in effective intermolecular orbital overlaps. The HOMO level calculated for DNBDT-N is −5.51 eV. This value is significantly higher than that for DNT-V and is attributed to the extended π-electron system of DNBDT-N. NICS calculations showed that the two heterocycle rings exhibit aromatic characteristics intermediate between those of thiophene and thiophenoradialene (NICS(0) = −4.9 ppm). In addition, the increased molecular weight of DNBDT-N compared to the smaller DNT-V molecule would also impart improved thermal durability to thin-film devices.

TBBT-V

The V-shaped thieno[3,2-f:4,5-f′]bis[1]benzothiophene (TBBT-V) molecule (Figure 3d) has electronic and geometric characteristics similar to those of DNT-V, although the outer aromatic units are changed from benzene to thiophene rings. One of the obvious advantages associated with this modification is the ease of functionalizing the more reactive thiophene units, whereas the terminal benzene groups of the DNT-V π-core cannot be selectively functionalized. The HOMO level of the TBBT-V π-core was determined to be −5.64 eV, which is the same as that of DNT-V. However, the terminal thiophene units of the parent TBBT-V can be readily functionalized. As an example, the HOMO level of methyl-substituted TBBT-V (Me-TBBT-V) is increased to −5.50 eV, and further fine-tuning of the HOMO levels can be achieved depending on the choice of substitution. NICS calculations for TBBT-V revealed that the central heterocycle ring exhibits higher aromaticity than the other V- and N-shaped π-cores (NICS(0) = −5.7 ppm). With the incorporation of thiophene in TBBT-V, a high internal dipole moment of 2.14 D is obtained, indicating the potential for device fabrication based on solution processing.

Second-Generation OSCs Based on W- and Zigzag-Shaped π-Cores

DNT-W

The molecular design of W-shaped dinaphtho[1,2-b:2′,1′-d]thiophene (DNT-W) (Figure 4) was inspired by the well-known picene backbone. Picene has been reported as a hole-transporting p-type OSC, although the performance of picene-based OFETs has been shown to be unstable under ambient conditions.(80−82) Moreover, the crystal structure of this compound suggests a relatively large displacement along the long axis, indicating the potential for significant variations in intermolecular orbital overlaps. Thus, we envisioned that a DNT-W π-core incorporating sulfur would provide effective and consistent intermolecular orbital overlaps as well as suppressed molecular motions. In fact, the HOMO and next HOMO (NHOMO) coefficients determined for DNT-W (EHOMO = −5.83 eV, ENHOMO = −5.86 eV) were determined to be almost degenerate. The calculation results show delocalized distributions of the HOMO and NHOMO and also a unique continuous NHOMO having a single phase over the entire π-core. Furthermore, NICS calculations for DNT-W determined that the central heterocycle ring has an almost aromatic character (NICS(0) = −7.3 ppm). These unique characteristics of DNT-W suggest that it will provide the required degree of orbital overlap and also give a well-anchored molecular assembly, leading to high μ.

Figure 4

Figure 4. Molecular structures, NICS(0) values (calculated at the HF/6-31+G(d)//B3LYP/6-31G(d) level), HOMO and NHOMO coefficients and their energy levels, and dipole moments (calculated at the B3LYP/6-311G(d)//B3LYP/6-31G(d) level) of V-, W-, and zigzag-shaped π-cores.

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ChDT

Our most recent zigzag-shaped π-core, chryseno[2,1-b:8,7-b′]dithiophene (ChDT), can be considered to be an extended version of DNT-W (Figure 4). In the case of ChDT, HOMO coefficients indicating the same phase (EHOMO = −5.68 eV) extend across the entire π-core, including the terminal thiophene sulfur atoms, which is the same as the NHOMO in DNT-W. NICS calculations for ChDT showed that the terminal heterocycle ring and other aromatic rings have the same aromatic character as benzene (NICS(0) = −9.2 ppm). The incorporation of two terminal thiophene units lowered the HOMO energy levels of ChDT derivatives, which is expected to promote hole injection and provide lower threshold voltages. These terminal thiophene groups also allow facile derivatizations due to the highly reactive α-positions.

Synthesis

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The synthetic route to DNT-V and its derivatives is illustrated in Scheme 1. Previously, the synthesis of a similar sulfur-bridged π-core was reported via a 10-step process, but gave only a 12% total yield.(83) In the present work, we developed a facile four-step synthesis to obtain the target compounds using the readily available compound 1 as a starting material. The first step features a selective ortho-lithiation with n-BuLi followed by a Fe(acac)3-catalyzed oxidative homocoupling to afford the dimerized 2 in good yield. After a demethylation reaction using BBr3, the sulfur atom is installed on the naphthalene dimer using thiocarbamoyl, followed by a solventless annulation via Newman–Kwart rearrangement(84) at 320 °C, to generate the target compound DNT-V in 42% total yield over four steps. Various alkyl-substituted DNT-V derivatives can be obtained by means of the same synthetic route using alkylated versions of 1 as starting materials.

Scheme 1

Scheme 1. Synthesis of DNT-V Derivativesa
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aReagents and conditions: (a) n-BuLi, Fe(acac)3, 0 °C to rt, 73% (R = C10H21); (b) BBr3, 0 °C to rt, 94% (R = H), 97% (R = C10H21); (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 78% (R = H), 75% (R = C10H21); (d) 300–320 °C, 81% (R = H), 77% (R = C10H21).

Recently, our group developed a simple alternative synthetic route that provides the DNT-V core in only three steps (Scheme 2). This process employs a modification of a previously reported strategy using compound 5 as the starting material to afford the key precursor 6 in excellent yield.(85) A subsequent reduction of the tetraone compound 7 with aqueous hydroiodic acid in acetic acid affords DNT-V in 97% yield, with a total yield of 77% over three steps. Thus, this represents an improvement compared to our previous route. Our current synthetic scheme also avoids the high-temperature Newman–Kwart rearrangement featured in the previous strategy. In addition, expensive transition metal catalysts such as palladium are not required, and the synthesis is well-suited to large-scale production.

Scheme 2

Scheme 2. Modified DNT-V Synthesisa
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aReagents and conditions: (a) (1) dithiooxamide, DMF, 55 °C, (2) Et3N, rt, 89%; (b) m-CPBA, CH2Cl2, 30 °C, 88%; (c) HI, AcOH, reflux, 97%.

Although a synthesis of DAT-V was previously reported,(86) we synthesized DAT-V via a process similar to that used to obtain DNT-V (Scheme 3). We employed the anthracene-based precursor 8 as the starting material and conducted a Fe(acac)3-catalyzed homocoupling to afford the dimer, followed by a demethylation with BBr3 to give compound 10 in excellent yield. From 11, we carried out a Newman–Kwart rearrangement to generate DAT-V in satisfactory yield.

Scheme 3

Scheme 3. Synthesis of DAT-Va
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aReagents and conditions: (a) n-BuLi, Fe(acac)3, 0 °C to rt, 52%; (b) BBr3, 0 °C to rt, 96%; (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 61%; (d) 300 °C, 68%.

DNBDT-N and decyl-substituted DNBDT-NW (C10-DNBDT-NW) were synthesized in a manner similar to that used for DNT-V and its derivatives (Scheme 4). From 1, selective lithiation with n-BuLi followed by transmetalation afforded the arylzinc intermediate, which was further reacted with 1,4-dibromo-2,5-dimethoxybenzene via Negishi cross-coupling to provide 12 in good yield. Subsequently, demethylation with BBr3 generated the tetra-hydroxyl intermediate 13 with subsequent installation of thiocarbamate groups. The target DNBDT-N derivatives were realized by the Newman–Kwart rearrangement under solventless conditions in 64–67% yield.

Scheme 4

Scheme 4. Synthesis of DNBDT-N Derivativesa
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aReagents and conditions: (a) (1) n-BuLi, ZnCl2, 0 °C to rt, (2) 1,4-dibromo-2,5-dimethoxybenzene, PdCl2(dppp), 50 °C, 87% (R = H), 85% (R = C10H21); (b) BBr3, 0 °C to rt, 81% (R = H), 92% (R = C10H21); (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 53% (R = H), 72% (R = C10H21); (d) 310–320 °C, 67% (R = H), 64% (R = C10H21).

The TBBT-V π-core was synthesized according to a procedure previously reported in the literature.(87) This parent π-core was then used to produce three derivatives: C10-TBBT-V, α-C10-Th-TBBT-V, and β-C10-Th-TBBT-V (Scheme 5). TBBT-V was brominated by sequential treatment with lithium 2,2,6,6-tetramethylpiperidide (to deprotonate the α-positions of the thiophene) and 1,2-dibromo-1,1,2,2-tetrachloroethane, to afford Br-TBBT-V. C10-TBBT-V was synthesized in 64% yield, whereas α-C10-Th-TBBT-V and β-C10-Th-TBBT-V were furnished in 86% and 92% yields, respectively. The facile reactions at the α-positions demonstrate the ease of functionalization of TBBT-V and the ready tuning of its molecular properties.

Scheme 5

Scheme 5. Synthesis of TBBT-V Derivativesa
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aReagents and conditions: (a) C10H21ZnCl2, PdCl2(dppf)·CH2Cl2, toluene, 70 °C, 64%; (b) (5-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 86%; (c) (4-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 92%.

DNT-W was furnished in a one-pot reaction according to a previously reported procedure.(88) The synthesis of ChDT (Scheme 6) started from compound 15, which was readily synthesized according to a literature procedure.(89) From 15, a halogen–lithium exchange and a transmetalation with zinc chloride were performed, followed by a Negishi cross-coupling to install the thiophene moieties, giving an overall yield of 79%. Facile removal of the trimethylsilyl protecting groups was carried out under basic conditions to give compound 17 in excellent yield. Subsequently, we used PtCl2 to catalyze the 6-exo-dig double cyclizations in DMF to furnish the ChDT π-core in satisfactory yield.(90) The α-positions of the thiophene were readily brominated by sequential treatments with lithium tetramethylpiperidide and 1,1,2,2-tetrachloro-1,2-dibromoethane to afford the key precursor Br-ChDT in 88% yield. Two ChDT derivatives, C10-ChDT and C10-Th-ChDT, were prepared using Negishi and Stille cross-coupling reactions, respectively, in excellent yields.

Scheme 6

Scheme 6. Synthesis of ChDT Derivativesa
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aReagents and conditions: (a) (1) n-BuLi, THF, −78 °C, (2) ZnCl2, THF, 0 °C, (3) 3-bromothiophene, Pd2(dba)3·CHCl3, THF, 50 °C, 79%; (b) K2CO3, MeOH, CH2Cl2, rt, 99%; (c) PtCl2, DMF, 80 °C, 58%; (d) (1) LiTMP, THF, −78 °C to −50 °C, (2) 1,2-dibromo-1,1,2,2-tetrachloroethane, −78 °C to rt, 88%; (e) C10H21ZnCl, PdCl2(dppf)·CH2Cl2, THF, 70 °C, 80%; (f) (4-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 81%.

Aggregated Structures, Theoretical Calculations, Thermal Stabilities, Ionization Potentials, and Solubilities

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Aggregated Structures and Theoretical Calculations

To understand the aggregated structures and charge-carrier transports of the current bent-shaped OSCs, we examined single crystals of the bent-shaped parent π-cores and their derivatives, grown by either physical vapor transport (PVT)(91,92) or solution techniques, using X-ray diffraction (XRD). A common feature observed in single crystals of V-shaped OSCs was their slightly bent geometries (Figure 5 and Table 1), which differ from the planar conformations suggested by DFT studies. The bent angles increased when substituents were added to the π-cores, as a result of increased attractive intermolecular interactions. N-shaped and second-generation zigzag-shaped OSCs were also observed. The bent geometry in these derivatives potentially allowed for C–H···π and S···π interactions between the prominent central sulfur atom and the adjacent backbone. As a result, higher degrees of intermolecular HOMO overlaps and greater suppression of molecular motions were realized, both of which improve charge-carrier transport and thermal durability.

Figure 5

Figure 5. Representative slightly bent geometries of C10-DNT-VW and C10-DNBDT-NW (front and side views) in single crystals.

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Table 1. Packing Modes and Twist Angles for V-, N-, and W-Shaped Derivatives
compoundpacking modebent angle (deg)
DNT-VHB13.9
C10-DNT-VWHB13.3
C10-DNT-VVHB18.0
DAT-VHB17.2
TBBT-VHB10.0
C10-TBBT-VHB11.3
DNBDT-Nπ–π stacking (π–π), slipped HB0.0
C10-DNBDT-NWHB9.7
DNT-WHB9.1
The parent DNT-V, DAT-V, and TBBT-V π-cores were found to adopt 2D HB packing structures, whereas the DNBDT-N demonstrated a less attractive one-dimensional (1D) π–π stacking motif that does not favor charge transport (Table 1). Following the incorporation of various substituents, the packing structures of the V-shaped OSCs were effectively modified to give high degrees of intermolecular orbital overlap, as indicated by the increased absolute t values (Table 2). As for the sign of t, the negative and positive intermolecular orbital overlaps result in positive and negative transfer integrals, respectively (Figure 6).

Figure 6

Figure 6. Relation between sign of transfer integral and intermolecular orbital overlap.

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Table 2. Summary of Transfer Integrals for V-Shaped Derivatives
  transfer integral, t (meV)b
compoundpacking mode and HB angle (deg)atHT|tHH||tTT|
DNT-VHB, 45.8°+374613
C10-DNT-VWHB, 45.3°+18c14c32c
+45d61d37d
C6-DNT-VWHB, 46.4°+44c63c36c
+19d10d17d
C10-DNT-VVHB, 36.0°+354215
DAT-VHB, 38.9°+41206.4
C10-TBBT-VHB, 43.6°+526710
a

Herringbone (HB) angles between two mean planes of the π-cores were 56.4° (at 293 K),(93) 52.5° (at 293 K),(43) and 51.1° (at 200 K)(52) for C8-BTBT, DNTT, and C10-DNTT as references.

b

Transfer integrals were calculated at the PBEPBE/6-31G(d) level.

c

Transfer integrals between HOMOs.

d

Transfer integrals between NHOMOs.

Both C10-DNT-VW and C6-DNT-VW had larger absolute t values than the DNT-V π-core, whereas C10-DNT-VV exhibited lower t values (Figure 7). Since C10- and C6-DNT-VW exhibit almost the same HOMO and NHOMO energy levels, the t values between these levels are estimated, and are listed in Table 2. The packing structures of the DNT-V series suggest that more effective intermolecular orbital overlaps were achieved by installing the alkyl chains in the VW fashion. As a consequence, the charge transport capabilities were significantly affected by the alkyl chain positions. Owing to the intrinsic disorder of the α-C10-Th-TBBT-V and β-C10-Th-TBBT-V, only C10-TBBT-V single crystals could be obtained from the TBBT-V series. The HB packing structure of the C10-TBBT-V showed a significantly larger t value in the head-to-tail (tHT) direction than in the head-to-head (tHH) and tail-to-tail (tTT) directions, suggesting anisotropic 2D charge-transport properties.

Figure 7

Figure 7. Representative packing structures and transfer integrals for (a) C10-DNT-VW and (b) C10-DNT-VV for their HOMOs (and NHOMO).

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Different from the 1D π–π stacking structure of DNDBT-N, C10-DNBDT-NW formed an HB motif with a layer-by-layer structure (Figure 8). The 2D cofacial molecular arrangement through strong π–π and C–H···π interactions resulted in equal t in the column and transverse directions (tc = +52 meV, tt = +51 meV), demonstrating favorable 2D charge-transport properties (Table 3).

Figure 8

Figure 8. Representative packing structures and transfer integrals for (a) DNBDT-N and (b) C10-DNBDT-NW.

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Table 3. Summary of Transfer Integrals for N-Shaped Derivatives
  transfer integral, t (meV)b
compoundpacking mode and HB angle (deg)atcolumn (tc)|ttrans| (|tt|)
DNBDT-Nπ–π and slipped HB, 126.5°+3.27.3
C10-DNBDT-NWHB, 46.7°+5251
a

Herringbone (HB) angles between two mean planes of the π-cores.

b

Transfer integrals were calculated at the PBEPBE/6-31Gd level.

The second-generation zigzag-shaped OSCs all exhibited HB packing structures in the crystalline state (Table 4). DNT-W showed reasonable positive t values in the head-to-tail (tHT) and tail-to-tail (tTT) directions, but larger absolute t values in the transverse head-to-head (tHH) direction (Figure 9). The ChDT derivatives showed strong intermolecular C–H···π and S···π interactions in the HB motif. The parent ChDT demonstrated large absolute t values in both the column (tc) and transverse (tt) directions, but adding C10-alkyl chains on both sides dramatically lowered the absolute t value in the transverse direction. Consequently, the C10-ChDT shows 1D charge transport. Although the tc and tt values for C10-Th-ChDT are well-balanced, these values are relatively small compared to other ChDT derivatives. Thus, the primary reason for the smaller absolute t values for C10-Th-ChDT is the much longer π–π stacking distance (6.90 Å) compared to ChDT (5.97 Å), due to the steric hindrance of the decylthienyl groups.

Figure 9

Figure 9. Representative packing structures and transfer integrals for (a) DNT-W, (b) C10-ChDT, and (c) C10-Th-ChDT.

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Table 4. Summary of (Top) Transfer Integrals of DNT-W and (Bottom) Transfer Integrals, Lattice Constants in the Column Direction, and Effective Masses for C10-ChDT, C10-Th-ChDT, and C10-DNBDT-NW
  transfer integral, t (meV)a
compoundpacking mode and HB angle (deg)atHT|tHH||tTT|
DNT-WHB, 41.6°+416240
 
  transfer integral, t (meV)b  
compoundpacking mode and HB angle (deg)atcolumn (tc)c|ttrans| (|tt|)lattice constant in the column direction, dc (Å)effective mass,cm||*/m0,dm⊥*/m0e
C10-ChDTHB, 89.2°–66224.8612.55, 17.2
C10-Th-ChDTHB, 39.2°+31246.8991.86, 5.85
C10-DNBDT-NWHB, 46.7°+52516.1271.31, 2.52
a

Herringbone (HB) angles between two mean planes of the π-core.

b

t values were calculated at the PBEPBE/6-31G(d) level.

c

m0 is the electron rest mass.

d

m* in the column direction.

e

m* in the transverse direction.

Experimental studies have revealed that OSCs having high μ show band transport characteristics,(59,70,74,94,95) with delocalized wave-like carriers over multiple molecules. Based on the band theory, the mobility μ of carrier with charge q is inversely proportional to the effective mass (m*) according to the following equation:where τ is the relaxation time. HOMO band structures, E(k), are obtained by the tight-binding approximation using t values. Effective masses of holes are calculated as the following equation along the respective directions:In the case of the HB-type packing structure studied herein, the top of the HOMO band is located on the Γ (k = 0) point, and the column direction exhibits the highest mobility, except for C10-ChDT. Therefore, we investigate 1/m* at the Γ point along the column direction, given by the following equation:Here, tcolumn (tc or tHT) and ttrans (tt or tHH, tTT) (see Figures 7–9) refer to the transfer integrals in the column (H-to-T) and transverse (H-to-H and T-to-T) directions of HB packing motif, respectively, and d refers to the lattice constant in the column direction. That is, the reciprocal of the effective mass is proportional to the transfer integral and the square of the lattice constant. In particular, tc is twice as effective as tt, and its sign (whether they are either positive or negative) is also important, as described in Figure 6.
Notably, the effective mass in the column and transverse directions (m||* and m⊥*) for C10-Th-ChDT (1.86 m0 and 5.85 m0) was found to be much smaller and more isotropic than for C10-ChDT (m||* = 2.55 m0 and 17.2 m0) and nearly comparable to that of C10-DNBDT-NW (m||* = 1.31 m0 and 2.52 m0) (see Figure 10). These data indicate that increasing the lattice constant of C10-Th-ChDT in the column direction compensates for the reduction of the transfer integral, resulting in a small effective mass.

Figure 10

Figure 10. HOMO band structures and effective masses of (a) C10-DNBDT-NW and (b) C10-ChDT. The origin of energy axis is set to HOMO level of the molecule. Insets show the first Brillouin zone with symmetry points of Γ(0,0,0), Y(0,π/b,0), Z(0,0,π/c), and S(0,π/b,π/c), where b and c are the lattice constants shown in Figures 8b and 9b. The column directions correspond to Γ–Z (C10-DNBDT-NW) and Γ–Y (C10-ChDT) directions in the reciprocal lattice.

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Motivated by the intriguing HOMO configuration of ChDT, we investigated the variance in t (Δt) values. It should be noted that the out-of-plane motion was the most prominent direction of molecular vibrations in the HB packing (Figure 11).(67) A smaller Δt of 5 meV was determined for ChDT, compared to those for DNTT (13 meV) and pentacene (29 meV) over the range of 0.13–0.18 Å. The small Δt for ChDT is a good indication of consistent intermolecular orbital overlaps in the solid state.

Figure 11

Figure 11. Values of t and Δt for ChDT, DNTT, and pentacene.

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Thermal Stability

One crucial benefit of the bent-shaped molecular design is the prevention of phase transitions at low temperatures by the suppression of molecular motions. Analysis of the DNT-V derivatives by thermogravimetry (TG) did not show any thermal decomposition before 500 °C. Differential scanning calorimetry (DSC) studies also demonstrated high phase transition temperatures of 202 and 151 °C for C6- and C10-DNT-VW, respectively, but a value of only 90 °C in the case of C10-DNT-VV. This lower temperature is attributed to the large displacements between adjacent molecules in the crystal packing structure of this compound, which result in reduced structural stability. The C10-DNBDT-NW showed higher phase transition and decomposition temperatures than the V-shaped C10-DNT-VW, resulting from the multiple intermolecular interactions and higher molecular weight of the former. C10-DNBDT-NW in a thin film device demonstrated no phase transition up to 200 °C. More importantly, C10-DNBDT-NW is a double V-shaped molecule, and thus should exhibit more effective suppression of molecular motions and stabilization of the crystalline phase compared to the DNT-V series. Both C10-TBBT-V and β-C10-Th-TBBT-V showed multiple phase transition peaks during differential thermal analyses, potentially due to their lower structural rigidity and intrinsic disordering. In contrast, α-C10-Th-TBBT-V showed a phase transition peak above 200 °C. The zigzag-shaped C10-ChDT and C10-Th-ChDT exhibited no phase transitions until above 250 °C. The excellent thermal stability of the current bent-shaped OSCs confirm their physical and chemical robustness, which would permit common purification techniques such as sublimation and PVT. These materials would also be expected to be thermally durable in the solid state.

Ionization Potentials

The electronic properties of these OSCs were further examined using photoelectron yield spectroscopy (PYS) to evaluate the ionization potential (IP) values. The resulting IP values were generally in good agreement with the HOMO energy levels calculated based on DFT. The DNT-V π-core was found to have a somewhat high IP of 5.72 eV, while extending the π-conjugation gave a considerably smaller IP of 5.21 eV for DAT-V. TBBT-V demonstrated an IP of 5.61 eV, similar to that for DNT-V. However, C10-TBBT-V, α-C10-Th-TBBT-V, and β-C10-Th-TBBT-V demonstrated effective tuning of the IP due to the synthetic versatility of the TBBT-V π-core, with values of 5.26, 5.10, and 5.01 eV, respectively. The IP value for the extended N-shaped C10-DNBDT-NW was 5.24 eV, which also indicates an improvement relative to the DNT-V series. The zigzag-shaped DNT-W showed a large IP of 5.87 eV as a result of its relatively short π-conjugation, while the extended analogues C10-ChDT and C10-Th-ChDT had values of 5.56 and 5.53 eV, respectively. Overall, these data confirm fine-tuning of the IP values of the current bent-shaped OSCs by modifying the π-conjugation length and varying the functional groups. Such modifications achieved air-stable p-type performance, and also would be expected to reduce the injection barrier and threshold voltage associated with OFET operations.

Solubility

In contrast to the poor solubility of unsubstituted linear and quasi-linear π-cores (e.g., <0.001 wt% in toluene for DNTT), DNT-V demonstrated superior solubility of up to 0.30 wt% in common organic solvents such as chloroform and toluene at room temperature. Alkyl-substituted DNT-V derivatives showed improved solubility, ranging from 0.38 to 1.53 wt% in the case of the DNT-VW series. In addition, extremely high solubilities in the range of 9.23–15.6 wt% were achieved with the DNT-VV derivative. The unsubstituted TBBT-V showed high solubility on the order of 0.1 wt% due to its large internal dipole moment, while C10-TBBT-V possessed the highest solubility of up to 1.1 wt%. Owing to the increased π-conjugation and molecular weight of DNBDT-N, the parent π-core exhibited limited solubility. However, the incorporation of C10-alkyl chains resulted in adequate solubility for C10-DNBDT-NW of up to 0.043 wt% in common organic solvents at a slightly elevated temperature. Having an equally extended π-conjugated system, C10-ChDT and C10-Th-ChDT showed higher solubilities of 0.068 and 0.13 wt% in toluene, respectively, than C10-DNBDT-NW. The high solubility and thermally stable crystal phases of the bent-shaped OSCs suggest that they show promises with regard to applications in thin-film OFET fabrication via solution-processing methods.

Summary of Properties

The bent-shaped OSCs presented herein exhibit unique NICS values, which suggest that the fused sulfur-containing heterocycles behave more like thiophenoradialene, rather than thiophene. The consequence of such behaviors is that the sulfur atom possesses protruding HOMO that are likely to reinforce the molecular assembly and charge transports. The aggregated structures of bent-shaped OSCs all exhibit some degree of nonplanarity, or bentness, which lead to enhancement of their intermolecular interactions in the favorable herringbone packing structures. Theoretical calculations of transfer integrals and effective masses suggest favorable charge transport properties that are promising for achieving high μ. Thermal studies suggest that the bent-shaped OSCs are thermally stable, and their crystal phases are thermally durable for sustaining elevated-temperature fabrication processes. Compared to the conventional linear and quasi-linear OSCs, the bent-shaped OSCs have their unique advantages to achieve high-performance and robust OSCs for future practical applications.

OFET Performance

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To evaluate the device performance of bent-shaped OSCs, single-crystalline-based bottom-gate/top-contact OFETs were fabricated using either manual lamination (ML) or the solution-processed edge-casting (EC) technique that our group previously developed(48−51) (Figure 12 and Supporting Information). These p-channel OFETs were produced by adding the strong electron acceptor F4-TCNQ between the OSC layer and the gold electrodes to reduce contact resistance. The transistors employed SiO2/Si substrates treated with heptadecafluorodecyltrimethoxysilane (F-DTS) in conjunction with the ML technique and either decyltrimethoxysilane (DTS) or β-phenylethyltrimethoxysilane (β-PTS) for the EC technique. All devices incorporating bent-shaped derivatives demonstrated air-stable p-channel OFET characteristics.

Figure 12

Figure 12. Schematic diagrams of (a) the manual lamination and (b) edge-casting techniques.

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The parent DNT-V single-crystalline thin-film OFET achieved a satisfactory μh of 1.5 cm2 V–1 s–1, which is similar to the value obtained for a vacuum-deposited polycrystalline thin-film OFET (1.1 cm2 V–1 s–1). [All reported μ values are summarized in Table 5.] The highest μh of 9.5 cm2 V–1 s–1 was demonstrated by single-crystalline C6-DNT-VW grown using the EC technique. This result was expected based on our transfer integral calculations, because this derivative possessed the largest absolute t values in all directions. The other C10-DNT-VW derivative exhibited a comparable maximum μh of 6.5 cm2 V–1 s–1, whereas C10-DNT-VV showed a μh of 1.0 cm2 V–1 s–1. Transmission XRD analyses confirmed that thin-film diffractions of the DNT-V series match with their single-crystal packing structures and that their crystal growth direction was along the b-axis (column) direction (Figure 7). Polycrystalline thin-film OFETs incorporating C6-DNT-VW and C10-DNT-VW fabricated by vacuum deposition also demonstrated decent μh values of 4.0 and 3.7 cm2 V–1 s–1, respectively. The trend of μh observed for the DNT-V derivatives was in perfect agreement with their t values. Moreover, C6-DNT-VW-based transistors demonstrated thermal resistance up to 150 °C.(68)
Table 5. Characteristics of Field-Effect Transistors with Bent-Shape π-Cores
compoundprocess,a SAM, and SiO2 thickness (nm)μmax (cm2/(V·s))μavg (cm2/(V·s))b
DNT-VVD,c DTS, 5001.10.91
DNT-VML, F-DTS, 5001.51.0
C6-DNT-VWVD,d DTS, 5003.73.6
C6-DNT-VWEC, β-PTS, 5009.56.2
C10-DNT-VVVD,d DTS, 5000.450.39
C10-DNT-VVEC, DTS, 5001.00.76
C10-DNT-VWVD,d DTS, 5004.03.6
C10-DNT-VWEC, DTS, 5006.54.0
DAT-VML, F-DTS, 5002.0n.a.e
C10-TBBT-VVD,d DTS, 2001.11.0
C10-TBBT-VDC, β-PTS, 2004.02.0
C10-TBBT-VEC, β-PTS, 2006.24.6
α-C10-Th-TBBT-VEC, β-PTS, 2000.550.53
β-C10-Th-TBBT-VEC, β-PTS, 2002.31.6
DNBDT-NML, F-DTS, 5000.06n.a.c
C10-DNBDT-NWEC, β-PTS, 1001612.1
DNT-WML, F-DTS, 5001.6n.a.e
ChDTML, F-DTS, 5003.1n.a.e
C10-ChDTEC, β-PTS, 5002.6n.a.e
C10-Th-ChDTEC, β-PTS, 50010n.a.e
C8-BTBTEC, DTS, 5005.0n.a.e
C10-DNTTGC, DTS, 500117.0
a

ML, manual lamination process; VD, vacuum deposition process; EC, edge-casting process; DC, drop-casting process; GC, gap-casting process.

b

μavg is the average of mobilities for more than 10 devices.

c

Data at substrate temperature (Tsub) of room temperature.

d

Data at Tsub of 100 °C.

e

μavg was not available because a sufficient number of devices was not evaluated.

PVT-grown single crystals of DAT-V were manually laminated on the OFET substrates. In view of the packing motif and charge transport direction of DAT-V, the OFET channel was constructed along the b-axis to maximize μh, with the assistance of in-plane XRD analysis. The highest μh of 2.0 cm2 V–1 s–1 was obtained with DAT-V. When OFET channels were constructed along the a axis, a lower μh of 1.1 cm2 V–1 s–1 was obtained.(71)
The highest μh of 6.2 cm2 V–1 s–1 was exhibited by the C10-TBBT-V single-crystalline OFET, while α-C10-Th-TBBT-V and β-C10-Th-TBBT-V produced mediocre μh values of 0.55 and 2.3 cm2 V–1 s–1, respectively. Although the C10-TBBT-V device demonstrated a slightly lower μh than C10-DNT-VW (6.5 cm2 V–1 s–1), it showed a lower threshold voltage of −20 to −15 V compared to C10-DNT-VW (−30 to −25 V). In addition, C10-TBBT-V demonstrated excellent solution-processability, and the resulting drop-cast thin-film transistor achieved a μh of 4.0 cm2 V–1 s–1. Owing to the extended π-conjugation of α-C10-Th-TBBT-V and β-C10-Th-TBBT-V, their transistor devices showed significantly lower threshold voltages of 0 to −10 V, albeit with relatively low μh. From the transmission XRD data, we confirmed that the solution-processed single-crystalline C10-TBBT-V thin film regained its single-crystal packing structure, and that the crystal growth direction was along the b-axis, as was also the case for the DNT-V series (column direction, Figure 7).
C10-DNBDT-NW formed excellent single-crystalline thin films using either the EC technique or the continuous EC technique over large areas.(48−51) Optical microscopic and atomic force microscopy images indicated a smooth crystal surface with steps having a height of one C10-DNBDT-NW molecule, indicating well-oriented crystalline films. (Figure 13a,b). Air-stable p-channel OFET performance was obtained using C10-DNBDT-NW with a maximum μh of 16 cm2 V–1 s–1 (Figure 13c,d). A large on/off ratio of 106 to 107 and a small threshold voltage of −10 to 0 V were also determined for the C10-DNBDT-NW device. The small threshold voltage for this material can be attributed to its low IP value (5.24 eV) resulting from the extended π-conjugated core. Moreover, C10-DNBDT-NW-based transistors demonstrated higher thermal resistance up to 200 °C. In addition, Hall effect measurements suggested significant hole diffusion. Thus, the C10-DNBDT-NW-based OSC exhibited a band transport mechanism with delocalized charge-carriers over the OSC layer.(94,95) Furthermore, we have recently reported that bending a flexible device incorporating a C10-DNBDT-NW single-crystalline film caused uniaxial lattice compression and led to a mobility increase of 70% under 3% strain. An in-depth analysis showed that this compression suppresses molecular motion.(96)

Figure 13

Figure 13. (a) Bottom-gate–top-contact device structure and packing structure of C10-DNBDT-NW on the substrate and (b) optical microscopy image. (c) Transfer and (d) output characteristics of the OFET based on a C10-DNBDT-NW single-crystalline film.

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DNT-W afforded flat platelet crystals when employing PVT, which could be simply laminated on substrates for OFET evaluation. The resulting DNT-W-based OFETs exhibited typical p-channel transfer and output characteristics with negligible hysteresis and an air-stable μh of 1.6 cm2 V–1 s–1. Despite the encouraging results obtained from our first second-generation zigzag-shaped DNT-W, the associated OFET suffered from a substantial threshold voltage (−50 V), a high injection barrier between the gold electrode and the semiconductor layer (due to the large IP value of 5.87 eV), and a μh insufficient for high-performance electronics. Recently, Yasuda and co-workers developed an original synthetic route for C8-substituted dinaphtho[1,2-b:2′,1-d]chalcogenophenes (DNE), including dinaphtho[1,2-b:2′,1-d]thiophene (DNT), dinaphtho[1,2-b:2′,1-d]selenophene (DNS), and dinaphtho[1,2-b:2′,1-d]tellurophene (DNTe).(97) Incorporation of the alkyl chain increased the solubility of these DNE derivatives such that solution-processing for device fabrication was viable. The introduction of tellurium in DNTe also effectively lowered its IP value to 5.24 eV. However, the threshold voltages of the C8-DNE series remained high.
In the case of the extended zigzag-shaped ChDT π-core, a decent μh of 3.1 cm2 V–1 s–1 was obtained from a single-crystalline thin film by the ML technique. It is worth noting that the threshold voltage for ChDT (−25 V) was found to be significantly improved compared to that for DNT-W due to its extended π-conjugation. C10-ChDT and C10-Th-ChDT both formed well-oriented single-crystalline thin films with smooth surfaces when applying the EC technique and showed maximum μh values of 2.6 and 10 cm2 V–1 s–1, respectively. The high μh exhibited by these ChDT derivatives may be correlated with their low Δt values, that the π-core is insensitive to detrimental molecular motions and shows consistent intermolecular orbital overlaps.
Thermal stress test of high-mobility C10-DNBDT-NW OSCs using solution-processed single-crystalline films on silicon substrates at 200 °C, were performed in transistors. To evaluate the thermal durability of C10-DNBDT-NW accurately, the transistors were prepared as follows: (1) The solution-processed single-crystalline films prepared by the edge-casting method were annealed at 200 °C for 10 min under nitrogen conditions. (2) After the film cooled to room temperature, the F4-TCNQ and gold electrodes were deposited. Notably, it was found that the mobility was unchanged, while the threshold voltage showed a slight positive shift. This might be due to the decrement of channel traps such as water and oxygen by annealing at high temperature. As a comparison, the other transistor was annealed at the same temperature after the F4-TCNQ and gold electrodes were deposited. In this case, the mobility was slightly decreased. This result might be attributed to the morphology change at the interface between OSC and F4-TCNQ. Therefore, the solution-processed single-crystalline film of C10-DNBDT-NW possesses thermal durability over 200 °C.

Conclusions and Future Perspectives

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In this Perspective, we have summarized recent advances in the development of bent-shaped OSCs for OFET applications. The bent-shaped molecules presented herein all demonstrated an excellent distribution of HOMO coefficients, leading to effective intermolecular orbital overlaps as well as electronic structures suitable for air-stable p-type OFET operation and charge injection. The incorporation of sulfur leads to a large HOMO coefficient for the sulfur atom that induces various heteroatom interactions and contributes to the reinforcement of the favorable HB packing structure in the solid state. It is apparent that the bent-shaped geometry contributes to the stabilization of the crystal phases of the OSCs, resulting in high thermal durability. Our work with V-shaped OSCs having bent-shaped geometries has mitigated various challenges associated with these compounds, such as low IP values, high OFET threshold voltages, poor thermal durability, and moderate charge mobilities. This was accomplished by extending the length of π-conjugation and alternating the type of bent shape. These endeavors provided a p-channel OFET mobility of 16 cm2 V–1 s–1 in conjunction with N-shaped OSCs, which is adequate for the development of applications such as radio frequency identifier tags. However, the performance of OSCs in transistors is still far inferior to that of inorganic semiconductors, such that OSCs remain best suited to applications in relatively low-end electronics. In addition, the range of high-performance electron-transporting n-type OSCs is still limited, and so there is an urgent need for the development of all-organic complementary logic circuits. To improve the carrier mobility for both p- and n-type OSCs, it is necessary to form a clearer understanding of molecular motion by studying OSCs that exhibit band-transport characteristics using techniques such as Raman spectroscopy, infrared spectroscopy, and neutron scattering. It is our hope that the bent-shaped OSCs described herein will provide insights into the design of molecular geometries and orbital configurations that are suitable for the advancement of the air-stable, thermally durable, high-performance n-type OSCs required for next-generation electronic materials.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.9b10450.

  • Video demonstrating the edge-casting technique (AVI)

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Author Information

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  • Corresponding Author
    • Toshihiro Okamoto - Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan;  University of Tokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan;  PRESTO, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan;  Orcidhttp://orcid.org/0000-0002-4783-0621;  Email: [email protected]
  • Authors
    • Craig P. Yu - Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan;  Orcidhttp://orcid.org/0000-0002-1423-5244
    • Chikahiko Mitsui - Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
    • Masakazu Yamagishi - Department of Applied Chemistry and Chemical Engineering, National Institute of Technology, Toyama College, 13 Hongo-machi, Toyama City, Toyama 939-8630, Japan
    • Hiroyuki Ishii - Department of Applied Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan;  Orcidhttp://orcid.org/0000-0003-0644-1424
    • Jun Takeya - Material Innovation Research Center (MIRC) and Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan;  University of Tokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan;  MANA, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 205-0044, Japan
  • Notes

    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the Japan Science and Technology Agency (JST) PRESTO programs “Molecular Technology and Creation of New Functions” (grant JPMJPR13K5 and JPMJPR12K2) and “Scientific Innovation for Energy Harvesting Technology” (grant JPMJPR17R2) as well as a Japan Society for the Promotion of Science (JSPS) KAKENHI grant-in-aid for Scientific Research B (no. 17H03104). C.P.Y. would also like to acknowledge support for his graduate work through a Todai Fellowship at the University of Tokyo. Finally, the authors thank R. Wang for performing additional DFT calculations.

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    Mechanical properties of organic semiconductors for stretchable, highly flexible, and mechanically robust electronics
    Root, Samuel E.; Savagatrup, Suchol; Printz, Adam D.; Rodriquez, Daniel; Lipomi, Darren J.
    Chemical Reviews (Washington, DC, United States) (2017), 117 (9), 6467-6499CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    Mech. deformability underpins many of the advantages of org. semiconductors. The mech. properties of these materials are, however, diverse, and the mol. characteristics that permit charge transport can render the materials stiff and brittle. This review is a comprehensive description of the mol. and morphol. parameters that govern the mech. properties of org. semiconductors. Particular attention is paid to ways in which mech. deformability and electronic performance can coexist. The review begins with a discussion of flexible and stretchable devices of all types, and in particular the unique characteristics of org. semiconductors. It then discusses the mech. properties most relevant to deformable devices. In particular, it describes how low modulus, good adhesion, and abs. extensibility prior to fracture enable robust performance, along with mech. "imperceptibility" if worn on the skin. A description of techniques of metrol. precedes a discussion of the mech. properties of three classes of org. semiconductors: π-conjugated polymers, small mols., and composites. The discussion of each class of materials focuses on mol. structure and how this structure (and postdeposition processing) influences the solid-state packing structure and thus the mech. properties. The review concludes with applications of org. semiconductor devices in which every component is intrinsically stretchable or highly flexible.
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    Mei, J.; Diao, Y.; Appleton, A. L.; Fang, L.; Bao, Z. Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors. J. Am. Chem. Soc. 2013, 135, 6724– 6746,  DOI: 10.1021/ja400881n
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    Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors
    Mei, Jianguo; Diao, Ying; Appleton, Anthony L.; Fang, Lei; Bao, Zhenan
    Journal of the American Chemical Society (2013), 135 (18), 6724-6746CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. The past couple of years have witnessed a remarkable burst in the development of org. field-effect transistors, with a no. of org. semiconductors surpassing the benchmark mobility of 10 cm2/(V·s). In this paper, we highlight some of the major milestones along the way to provide a historical view of org. field-effect transistor development, introduce the integrated mol. design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make org. field-effect transistors applicable in real applications.
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    Müllen, K.; Scherf, U. Organic Light-Emitting Devices: Synthesis, Properties and Applications; Wiley-VCH, 2006.
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    Burn, P. L.; Lo, S.-C.; Samuel, I. D. W. The Development of Light-Emitting Dendrimers for Displays. Adv. Mater. 2007, 19, 1675– 1688,  DOI: 10.1002/adma.200601592
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    The development of light-emitting dendrimers for displays
    Burn, Paul L.; Lo, Shih-Chun; Samuel, Ifor D. W.
    Advanced Materials (Weinheim, Germany) (2007), 19 (13), 1675-1688CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Dendrimers are now an important class of light-emitting material for use in org. light-emitting diodes (OLEDs). Dendrimers are branched macromols. that consist of a core, one or more dendrons, and surface groups. The different parts of the macromol. can be selected to give the desired optoelectronic and processing properties. The first light-emitting dendrimers were fluorescent but more recently highly efficient phosphorescent dendrimers have been developed. OLEDs contg. light-emitting dendrimers have been reported to have external quantum efficiencies of up to 16%. The soly. of the dendrimers opens the way for simple processing and a new class of flat-panel displays. In this review the authors show how the structure of the light-emitting dendrimers controls key features such as intermol. interactions and charge transport, which are important for all OLED materials. The advantages of the dendrimer architecture for phosphorescent emitters and the way the structure can be varied to enhance materials performance and device design are illustrated.
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    Ostroverkhova, O. Organic Optoelectronic Materials: Mechanisms and Applications. Chem. Rev. 2016, 116, 13279– 13412,  DOI: 10.1021/acs.chemrev.6b00127
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    Organic Optoelectronic Materials: Mechanisms and Applications
    Ostroverkhova, Oksana
    Chemical Reviews (Washington, DC, United States) (2016), 116 (22), 13279-13412CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Org. (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technol. promises include low cost of these materials and the possibility of their room-temp. deposition from soln. on large-area and/or flexible substrates. The article reviews the current understanding of the phys. mechanisms that det. the (opto)electronic properties of high-performance org. materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Addnl., it highlights the capabilities of various exptl. techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small mols. and on conjugated polymers are considered, and their applications in org. solar cells, photodetectors, and photorefractive devices are discussed.
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    Thompson, B. C.; Fréchet, J. M. J. Polymer-Fullerene Composite Solar Cells. Angew. Chem., Int. Ed. 2008, 47, 58– 77,  DOI: 10.1002/anie.200702506
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    Polymer-fullerene composite solar cells
    Thompson, Barry C.; Frechet, Jean M. J.
    Angewandte Chemie, International Edition (2008), 47 (1), 58-77CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Fossil fuel alternatives, such as solar energy, are moving to the forefront in a variety of research fields. Polymer-based org. photovoltaic systems hold the promise for a cost-effective, lightwt. solar energy conversion platform, which could benefit from simple soln. processing of the active layer. The function of such excitonic solar cells is based on photoinduced electron transfer from a donor to an acceptor. Fullerenes have become the ubiquitous acceptors because of their high electron affinity and ability to transport charge effectively. The most effective solar cells were made from bicontinuous polymer-fullerene composites, or so-called bulk heterojunctions. The best solar cells currently achieve an efficiency of ∼5%, thus significant advances in the fundamental understanding of the complex interplay between the active layer morphol. and electronic properties are required if this technol. is to find viable application.
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    Günes, S.; Neugebauer, H.; Sariciftci, N. S. Conjugated Polymer-Based Organic Solar Cells. Chem. Rev. 2007, 107, 1324– 1338,  DOI: 10.1021/cr050149z
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    Conjugated Polymer-Based Organic Solar Cells
    Guenes, Serap; Neugebauer, Helmut; Sariciftci, Niyazi Serdar
    Chemical Reviews (Washington, DC, United States) (2007), 107 (4), 1324-1338CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. A general introduction to the materials, prodn. techniques, working principles, crit. parameters, and stability of the org. solar cells is provided. Conjugated polymer/fullerene bulk heterojunction solar cells on polyphenylenevinylene (PPV) derivs./[1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61] (PCBM) fullerene derivs. and poly(3-hexylthiophene) (P3HT)/PCBM systems are discussed. Alternative approaches such as polymer/polymer solar cells and org./inorg. hybrid solar cells also receive attention. Routes for improvements and conclusions end the review.
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  10. 10
    Son, H. J.; He, F.; Carsten, B.; Yu, L. Are we there yet? Design of better conjugated polymers for polymer solar cells. J. Mater. Chem. 2011, 21, 18934– 18945,  DOI: 10.1039/c1jm12388b
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    Are we there yet? Design of better conjugated polymers for polymer solar cells
    Son, Hae Jung; He, Feng; Carsten, Bridget; Yu, Luping
    Journal of Materials Chemistry (2011), 21 (47), 18934-18945CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
    Over the last ten years, polymer solar cells have been developed as an attractive alternative to the traditional silicon photovoltaic devices. Remarkable progress has been made in polymer-fullerene solar cells and several polymers have shown power conversion efficiencies (PCEs) greater than 7%. The most important recent development has been the synthesis of new low bandgap polymers with optimal properties for the solar cells. Herein we provide an overview of the key strategies of optimization of HOMO (HOMO) and LUMO (LUMO) energy levels in the design of new low bandgap conjugated polymers. Detailed examples of representative donor polymers, the current state of the art in their solar cell performances and possible future directions for development of new polymers with improved efficiencies are discussed.
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    Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Synthesis of Conjugated Polymers for Organic Solar Cell Applications. Chem. Rev. 2009, 109, 5868– 5923,  DOI: 10.1021/cr900182s
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    11
    Synthesis of Conjugated Polymers for Organic Solar Cell Applications
    Cheng, Yen-Ju; Yang, Sheng-Hsiung; Hsu, Chain-Shu
    Chemical Reviews (Washington, DC, United States) (2009), 109 (11), 5868-5923CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review on synthesis of conjugated polymers for org. solar cells. Particular attention is focused on synthetic approaches directed toward making these polymers as well as highlighting the useful and important building blocks leading to the necessary monomers. The principle of mol. design with band gap engineering, structure-property relationships, and device performances are also discussed.
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  12. 12
    Chen, Y.; Zhao, Y.; Liang, Z. Solution processed organic thermoelectrics: towards flexible thermoelectric modules. Energy Environ. Sci. 2015, 8, 401– 422,  DOI: 10.1039/C4EE03297G
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    Solution processed organic thermoelectrics: towards flexible thermoelectric modules
    Chen, Yani; Zhao, Yan; Liang, Ziqi
    Energy & Environmental Science (2015), 8 (2), 401-422CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    A review. Org. semiconductor materials have advantages of low cost, light wt., mech. flexibility and low-temp. soln. processability over large areas, enabling the development of personal, portable, and flexible thermal modules. This review article summarizes the recent progress made in the area of org. thermoelecs. (TEs), including org. mol. structures, devices, characterization methods, and approaches to improve the performance. We begin with the discussion of each TE parameter and particularly their correlations in org. TEs. Then the TE applications of mol. org. semiconductors, poly(3,4-ethylenedioxythiophene), polymer nanostructures and mol. junctions are reviewed. Next we turn to highlight the nanocomposites of polymers and carbon nanotubes or nanocrystals, which lead to enhanced TEs. Interestingly, the merging of TEs and photovoltaics offers a new direction towards a great capability of elec. energy output. Crit. challenges of org. TE materials include stability, sample prepn. and measurement techniques, which are also discussed. Finally, the relationships among org. semiconductor structures, hybrid composites, doping states, film morphol. and TE performance are revealed, and a viable avenue is envisioned for synergistic optimization of org. TEs.
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  13. 13
    Park, T.; Park, C.; Kim, B.; Shin, H.; Kim, E. Flexible PEDOT electrodes with large thermoelectric power factors to generate electricity by the touch of fingertips. Energy Environ. Sci. 2013, 6, 788– 792,  DOI: 10.1039/c3ee23729j
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    13
    Flexible PEDOT electrodes with large thermoelectric power factors to generate electricity by the touch of fingertips
    Park, Teahoon; Park, Chihyun; Kim, Byeonggwan; Shin, Haejin; Kim, Eunkyoung
    Energy & Environmental Science (2013), 6 (3), 788-792CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    Highly conductive PEDOT films were prepd. by soln. casting polymn. using finely tuned oxidn. soln. and used as electrodes for the precise control of the oxidn. level of the polymer electrochem. They exhibited a large power factor of 1,270 μW m-1 K-2 and could be processed as flexible and cuttable thermoelec. films to generate electricity by fingertips.
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  14. 14
    Shi, K.; Zhang, F.; Di, C.-A.; Yan, T.-W.; Zou, Y.; Zhou, X.; Zhu, D.; Wang, J.-Y.; Pei, J. Toward High Performance n-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones. J. Am. Chem. Soc. 2015, 137, 6979– 6982,  DOI: 10.1021/jacs.5b00945
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    14
    Toward High Performance n-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones
    Shi, Ke; Zhang, Fengjiao; Di, Chong-An; Yan, Tian-Wei; Zou, Ye; Zhou, Xu; Zhu, Daoben; Wang, Jie-Yu; Pei, Jian
    Journal of the American Chemical Society (2015), 137 (22), 6979-6982CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Three n-type polymers BDPPV, ClBDPPV, and FBDPPV which exhibit outstanding elec. conductivities when mixed with an n-type dopant, N-DMBI ((4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine), in soln. High electron mobility and an efficient doping process endow FBDPPV with the highest elec. conductivities of 14 S cm-1 and power factors up to 28 μW m-1 K-2, which is the highest thermoelec. (TE) power factor that is reported for soln. processable n-type conjugated polymers. The authors' studies reveal that introduction of halogen atoms to the polymer backbones has a dramatic influence on not only the electron mobilities but also the doping levels, both of which are crit. to the elec. conductivities. This work suggests the significance of rational modification of polymer structures and opens the gate for applying the rapidly developed org. semiconductors with high carrier mobilities to thermoelec. field.
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  15. 15
    Schlitz, R. A.; Brunetti, F. G.; Glaudell, A. M.; Miller, P. L.; Brady, M. A.; Takacs, C. J.; Hawker, C. J.; Chabinyc, M. L. Solubility-Limited Extrinsic n-Type Doping of a High Electron Mobility Polymer for Thermoelectric Applications. Adv. Mater. 2014, 26, 2825– 2830,  DOI: 10.1002/adma.201304866
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    15
    Solubility-Limited Extrinsic n-type Doping of a High Electron Mobility Polymer for Thermoelectric Applications
    Schlitz, Ruth A.; Brunetti, Fulvio G.; Glaudell, Anne M.; Miller, P. Levi; Brady, Michael A.; Takacs, Christopher J.; Hawker, Craig J.; Chabinyc, Michael L.
    Advanced Materials (Weinheim, Germany) (2014), 26 (18), 2825-2830CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors have used both N-DMBI and a novel n-type dopant, N-DPBI, to dope P(NDIOD-T2) to conductivities 10"3 S/cm. The only one in one hundred mols. mixed with P(NDIOD-T2) in soln. ultimately contribute a mobile electron to the conduction band of the polymer. Few dopants are elec. active because N-DMBI and N-DPBI are insol. in P(NDIOD-T2) and aggregate on the top surface, leaving the polymer morphol. largely unchanged. The limitations of N-DBI dopants are likely due to this phase segregation and will depend upon the details of the phase diagram blend for any given polymer-dopant pair. Nonetheless, P(NDIOD-T2) exhibits a comparable Seebeck coeff., and thus thermoelec. power factor, to p-type polymers with similar conductivities. P(NDIOD-T2) is a promising candidate for org. thermoelecs. Rational engineering of dopant-polymer miscibility offers promise for greatly improved performance for org. thermoelec. materials with stable carrier concns. in the regime (-IO19-IO21 cm"3) required for most applications. The power factors achieved in this work are far from a fundamental limitation for electron-conducting orgs. and that the development of novel doping strategies with better miscibility offers the potential to optimize both th electron- and hole-transporting elements of thermoelec. generators and coolers for increased performance.
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    Lavieville, R.; Zhang, Y.; Casu, A.; Genovese, A.; Manna, L.; Di Fabrizio, E.; Krahne, R. Charge Transport in Nanoscale “All-Inorganic” Networks of Semiconductor Nanorods Linked by Metal Domains. ACS Nano 2012, 6, 2940– 2947,  DOI: 10.1021/nn3006625
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    16
    Charge Transport in Nanoscale All-Inorganic Networks of Semiconductor Nanorods Linked by Metal Domains
    Lavieville, Romain; Zhang, Yang; Casu, Alberto; Genovese, Alessandro; Manna, Liberato; Di Fabrizio, Enzo; Krahne, Roman
    ACS Nano (2012), 6 (4), 2940-2947CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Charge transport across metal-semiconductor interfaces at the nanoscale is a crucial issue in nanoelectronics. Chains of semiconductor nanorods linked by Au particles represent an ideal model system in this respect, because the metal-semiconductor interface is an intrinsic feature of the nanosystem and does not manifest solely as the contact to the macroscopic external electrodes. Here we investigate charge transport mechanisms in all-inorg. hybrid metal-semiconductor networks fabricated via self-assembly in soln., in which CdSe nanorods were linked to each other by Au nanoparticles. Thermal annealing of our devices changed the morphol. of the networks and resulted in the removal of small Au domains that were present on the lateral nanorod facets, and in ripening of the Au nanoparticles in the nanorod junctions with more homogeneous metal-semiconductor interfaces. In such thermally annealed devices the voltage dependence of the current at room temp. can be well described by a Schottky barrier lowering at a metal semiconductor contact under reverse bias, if the spherical shape of the gold nanoparticles is considered. In this case the natural logarithm of the current does not follow the square-root dependence of the voltage as in the bulk, but that of V2/3. From our fitting with this model we ext. the effective permittivity that agrees well with theor. predictions for the permittivity near the surface of CdSe nanorods. Furthermore, the annealing improved the network conductance at cryogenic temps., which could be related to the redn. of the no. of trap states.
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    Anthony, J. E. Functionalized Acenes and Heteroacenes for Organic Electronics. Chem. Rev. 2006, 106, 5028– 5048,  DOI: 10.1021/cr050966z
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    Functionalized acenes and heteroacenes for organic electronics
    Anthony, John E.
    Chemical Reviews (Washington, DC, United States) (2006), 106 (12), 5028-5048CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review on the functionalization of linearly fused arom. systems specifically for their application in electronic devices. The focus is on studies that deal with crystal structure/device property relationships in linearly fused acenes and heteroacenes.
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    Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J.-L. Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926– 952,  DOI: 10.1021/cr050140x
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    18
    Charge Transport in Organic Semiconductors
    Coropceanu, Veaceslav; Cornil, Jerome; Da Silva Filho, Demetrio A.; Olivier, Yoann; Silbey, Robert; Bredas, Jean-Luc
    Chemical Reviews (Washington, DC, United States) (2007), 107 (4), 926-952CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Both electron and hole transport in org. semiconductors are discussed.
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    Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Thienoacene-Based Organic Semiconductors. Adv. Mater. 2011, 23, 4347– 4370,  DOI: 10.1002/adma.201102007
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    Thienoacene-Based Organic Semiconductors
    Takimiya, Kazuo; Shinamura, Shoji; Osaka, Itaru; Miyazaki, Eigo
    Advanced Materials (Weinheim, Germany) (2011), 23 (38), 4347-4370CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Thienoacenes consist of fused thiophene rings in a ladder-type mol. structure and were intensively studied as potential org. semiconductors for org. field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar mol. structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chem. structures, and elucidates the mol. electronic structure of each class. The packing structures of thienoacenes and the thus-estd. solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the mol. structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relations in thienoacene-based org. semiconductors are discussed. The discussion provides insight into new mol. design strategies for the development of superior org. semiconductors.
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    Liu, C.; Huang, K.; Park, W.-T.; Li, M.; Yang, T.; Liu, X.; Liang, L.; Minari, T.; Noh, Y.-Y. A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers. Mater. Horiz. 2017, 4, 608– 618,  DOI: 10.1039/C7MH00091J
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    20
    A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers
    Liu, Chuan; Huang, Kairong; Park, Won-Tae; Li, Minmin; Yang, Tengzhou; Liu, Xuying; Liang, Lijuan; Minari, Takeo; Noh, Yong-Young
    Materials Horizons (2017), 4 (4), 608-618CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    The variety of charge transport theories for org. semiconductors (OSCs) raises the question of which models should be selected for each case, and there is a lack of generalized understanding regarding various OSCs over the full range of crystallinity from single crystal to amorphous. Here, we report that the generalized Einstein relation (GER) can unify various theor. models and predict charge transport in OSCs with various crystallinities, by altering the variance of the d. of states and the delocalization degree in a Gaussian-distributed d. of states. The GER also provides a good fitting to much of the exptl. data of temp.- and gate-voltage-dependent mobility for different OSCs in transistors. Consequently, disorders of charge transport in various OSCs can be directly compared in the same map, which reveals how energetic disorder and the delocalization degree det. charge transport in org. devices.
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  21. 21
    Ji, L.-F.; Fan, J.-X.; Qin, G.-Y.; Zhang, N.-X.; Lin, P.-P.; Ren, A.-M. Theoretical Study on the Electronic Structures and Charge Transport Properties of a Series of Rubrene Derivatives. J. Phys. Chem. C 2018, 122, 21226– 21238,  DOI: 10.1021/acs.jpcc.8b07018
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    21
    Theoretical Study on the Electronic Structures and Charge Transport Properties of a Series of Rubrene Derivatives
    Ji, Li-Fei; Fan, Jian-Xun; Qin, Gui-Ya; Zhang, Ning-Xi; Lin, Pan-Pan; Ren, Ai-Min
    Journal of Physical Chemistry C (2018), 122 (37), 21226-21238CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The charge transport properties of rubrene derivs. were systematically studied by d. functional theory and mol. dynamics (MD) simulations. Functionalizing electron-withdrawing groups (-CN, -CF3, or fluorination) on the peripheral phenyls not only enhance the chem. stability of materials but also favor electron injection by lowering the energy levels of frontier MOs and increasing the electron affinities. Derivs. 2-5 and 9, exhibiting packing motifs similar to rubrene but closer π-stacking distances, possess large hole and electron-transfer integrals, significant bandwidths, and small effective masses, suggesting excellent ambipolar semiconductor behavior. The max. hole(electron) mobilities in the Marcus hopping mechanism based on kinetic Monte Carlo simulation can reach 14.0-16.5(1.6-3.5) cm2 V-1 s-1. The antiparallel 2-dimensional brick stacking and twisted backbones of fluorinated derivs. 11 and 12 result in nearly 1-dimensional percolation network but balanced hole and electron transport property. In contrast, the parallel 2-dimensional brick stacking of 14 leads to 2-dimensional percolation network. Their max. hole and electron mobilities fall at 0.5-3.6 and 2.0-4.8 cm2 V-1 s-1. Also, MD simulations show that dynamic disorder is strongly detrimental to the hole transfer but has a little influence on the electron transfer for 1-5. Also, severe twist of backbones of 9 leads to almost 1 order of magnitude lowered mobility. The influences of different substituents on the mol. structure, packing motif, and intermol. reorganization energy are discussed.
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  22. 22
    Wang, Y.; Sun, L.; Wang, C.; Yang, F.; Ren, X.; Zhang, X.; Dong, H.; Hu, W. Organic crystalline materials in flexible electronics. Chem. Soc. Rev. 2019, 48, 1492– 1530,  DOI: 10.1039/C8CS00406D
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    Organic crystalline materials in flexible electronics
    Wang, Yu; Sun, Lingjie; Wang, Cong; Yang, Fangxu; Ren, Xiaochen; Zhang, Xiaotao; Dong, Huanli; Hu, Wenping
    Chemical Society Reviews (2019), 48 (6), 1492-1530CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance org. cryst. materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, mol. diversity, low-cost, soln. processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics. Meanwhile, OCMs also serve as a powerful tool to probe the intrinsic electronic and mech. properties of orgs. and reveal the flexible device physics for further guidance for flexible materials and device design. While the past decades have witnessed huge advances in OCM-based flexible electronics, this review is intended to provide a timely overview of this fascinating field. First, the crystal packing, charge transport, and assembly protocols of OCMs are introduced. State-of-the-art construction strategies for aligned/patterned OCM on/into flexible substrates are then discussed in detail. Following this, advanced OCM-based flexible devices and their potential applications are highlighted. Finally, future directions and opportunities for this field are proposed, in the hope of providing guidance for future research.
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  23. 23
    Gryn’ova, G.; Lin, K.-H.; Corminboeuf, C. Read between the Molecules: Computational Insights into Organic Semiconductors. J. Am. Chem. Soc. 2018, 140, 16370– 16386,  DOI: 10.1021/jacs.8b07985
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    23
    Read between the molecules: computational insights into organic semiconductors
    Gryn'ova, Ganna; Lin, Kun-Han; Corminboeuf, Clemence
    Journal of the American Chemical Society (2018), 140 (48), 16370-16386CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A review. The performance and key electronic properties of mol. org. semiconductors are dictated by the interplay between the chem. of the mol. core and the intermol. factors of which manipulation has inspired both experimentalists and theorists. This perspective presents major computational challenges and modern methodol. strategies to advance the field. The discussion ranges from insights and design principles at the quantum chem. level, in-depth atomistic modeling based on multiscale protocols, morphol. prediction and characterization as well as energy-property maps involving data-driven anal. A personal overview of the past achievements and future direction is also provided.
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  24. 24
    McGarry, K. A.; Xie, W.; Sutton, C.; Risko, C.; Wu, Y.; Young, V. G.; Brédas, J.-L.; Frisbie, C. D.; Douglas, C. J. Rubrene-Based Single-Crystal Organic Semiconductors: Synthesis, Electronic Structure, and Charge-Transport Properties. Chem. Mater. 2013, 25, 2254– 2263,  DOI: 10.1021/cm400736s
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    24
    Rubrene-Based Single-Crystal Organic Semiconductors: Synthesis, Electronic Structure, and Charge-Transport Properties
    McGarry, Kathryn A.; Xie, Wei; Sutton, Christopher; Risko, Chad; Wu, Yanfei; Young, Victor G., Jr.; Bredas, Jean-Luc; Frisbie, C. Daniel; Douglas, Christopher J.
    Chemistry of Materials (2013), 25 (11), 2254-2263CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Correlations among the mol. structure, crystal structure, electronic structure, and charge-carrier transport phenomena were derived from six congeners (2-7) of rubrene (1). The congeners were synthesized via a three-step route from known 6,11-dichloro-5,12-tetracenedione. After crystn., their packing structures were solved using single-crystal x-ray diffraction. Rubrenes 5-7 maintain the orthorhombic features of the parent rubrene (1) in their solid-state packing structures. Control of the packing structure in 5-7 provided the 1st series of systematically manipulated rubrenes that preserve the π-stacking motif of 1. D. functional theory calcns. were performed at the B3LYP/6-31G(d,p) level of theory to evaluate the geometric and electronic structure of each deriv. and reveal that key properties of rubrene (1) were maintained. Intermol. electronic couplings (transfer integrals) were calcd. for each deriv. to det. the propensity for charge-carrier transport. For rubrenes 5-7, evaluations of the transfer integrals and periodic electronic structures suggest these derivs. should exhibit transport characteristics equiv. to, or in some cases improved on, those of the parent rubrene (1), as well as the potential for ambipolar behavior. Single-crystal field-effect transistors were fabricated for 5-7, and these derivs. show ambipolar transport as predicted. Although device architecture has yet to be fully optimized, max. hole (electron) mobilities of 1.54 (0.28) cm2 V-1 s-1 were measured for rubrene 5. This work lays a foundation to improve the authors' understanding of charge-carrier transport phenomena in org. single-crystal semiconductors through the correlation of designed mol. and crystallog. changes to electronic and transport properties.
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    Giri, G.; Verploegen, E.; Mannsfeld, S. C. B.; Atahan-Evrenk, S.; Kim, D. H.; Lee, S. Y.; Becerril, H. A.; Aspuru-Guzik, A.; Toney, M. F.; Bao, Z. Tuning charge transport in solution-sheared organic semiconductors using lattice strain. Nature 2011, 480, 504,  DOI: 10.1038/nature10683
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    Tuning charge transport in solution-sheared organic semiconductors using lattice strain
    Giri, Gaurav; Verploegen, Eric; Mannsfeld, Stefan C. B.; Atahan-Evrenk, Sule; Kim, Do Hwan; Lee, Sang Yoon; Becerril, Hector A.; Aspuru-Guzik, Alan; Toney, Michael F.; Bao, Zhenan
    Nature (London, United Kingdom) (2011), 480 (7378), 504-508CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    A soln.-processing method known as soln. shearing was used to introduce lattice strain to org. semiconductors, thus improving charge carrier mobility.
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  26. 26
    Rühle, V.; Lukyanov, A.; May, F.; Schrader, M.; Vehoff, T.; Kirkpatrick, J.; Baumeier, B.; Andrienko, D. Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors. J. Chem. Theory Comput. 2011, 7, 3335– 3345,  DOI: 10.1021/ct200388s
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    26
    Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors
    Ruehle, Victor; Lukyanov, Alexander; May, Falk; Schrader, Manuel; Vehoff, Thorsten; Kirkpatrick, James; Baumeier, Bjoern; Andrienko, Denis
    Journal of Chemical Theory and Computation (2011), 7 (10), 3335-3345CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
    A review. Charge carrier dynamics in an org. semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the mols. The exact evaluation of these contributions in a mol. assembly is computationally prohibitive. Various, often semiempirical, approxns. are employed instead. The authors review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations, provide a uniform error control for the methods and a flexible platform for their development, and eventually allow in silico prescreening of org. semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum, a common org. semiconductor.
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    Nomura, K.; Ohta, H.; Takagi, A.; Kamiya, T.; Hirano, M.; Hosono, H. Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors. Nature 2004, 432, 488– 492,  DOI: 10.1038/nature03090
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    Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors
    Nomura, Kenji; Ohta, Hiromichi; Takagi, Akihiro; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo
    Nature (London, United Kingdom) (2004), 432 (7016), 488-492CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Transparent electronic devices formed on flexible substrates are expected to meet emerging technol. demands where silicon-based electronics cannot provide a soln. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and org. semiconductors have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven org. light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temp. and device performance. Here, we propose to solve this problem by using a novel semiconducting material, namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO), for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temp. and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit satn. mobilities of 6-9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.
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  28. 28
    Kuribara, K.; Wang, H.; Uchiyama, N.; Fukuda, K.; Yokota, T.; Zschieschang, U.; Jaye, C.; Fischer, D.; Klauk, H.; Yamamoto, T.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Sekitani, T.; Loo, Y.-L.; Someya, T. Organic transistors with high thermal stability for medical applications. Nat. Commun. 2012, 3, 723,  DOI: 10.1038/ncomms1721
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    Organic transistors with high thermal stability for medical applications
    Kuribara Kazunori; Wang He; Uchiyama Naoya; Fukuda Kenjiro; Yokota Tomoyuki; Zschieschang Ute; Jaye Cherno; Fischer Daniel; Klauk Hagen; Yamamoto Tatsuya; Takimiya Kazuo; Ikeda Masaaki; Kuwabara Hirokazu; Sekitani Tsuyoshi; Loo Yueh-Lin; Someya Takao
    Nature communications (2012), 3 (), 723 ISSN:.
    The excellent mechanical flexibility of organic electronic devices is expected to open up a range of new application opportunities in electronics, such as flexible displays, robotic sensors, and biological and medical electronic applications. However, one of the major remaining issues for organic devices is their instability, especially their thermal instability, because low melting temperatures and large thermal expansion coefficients of organic materials cause thermal degradation. Here we demonstrate the fabrication of flexible thin-film transistors with excellent thermal stability and their viability for biomedical sterilization processes. The organic thin-film transistors comprise a high-mobility organic semiconductor, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene, and thin gate dielectrics comprising a 2-nm-thick self-assembled monolayer and a 4-nm-thick aluminium oxide layer. The transistors exhibit a mobility of 1.2 cm(2) V(-1)s(-1) within a 2 V operation and are stable even after exposure to conditions typically used for medical sterilization.
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    Payne, M. M.; Parkin, S. R.; Anthony, J. E. Functionalized Higher Acenes: Hexacene and Heptacene. J. Am. Chem. Soc. 2005, 127, 8028– 8029,  DOI: 10.1021/ja051798v
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    Functionalized Higher Acenes: Hexacene and Heptacene
    Payne, Marcia M.; Parkin, Sean R.; Anthony, John E.
    Journal of the American Chemical Society (2005), 127 (22), 8028-8029CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We have extended our functionalization strategy for pentacene to the higher acenes hexacene and heptacene (I,II). Provided a large enough alkyne substituent is used, these large arom. rods are both stable and sol. and can be characterized spectroscopically as well as by single-crystal X-ray diffraction.
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    Tang, M. L.; Okamoto, T.; Bao, Z. High-Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur. J. Am. Chem. Soc. 2006, 128, 16002– 16003,  DOI: 10.1021/ja066824j
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    30
    High-Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur
    Tang, Ming L.; Okamoto, Toshihiro; Bao, Zhenan
    Journal of the American Chemical Society (2006), 128 (50), 16002-16003CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Two new linear acenes with fused thiophene units were synthesized. These acenes have conjugation lengths between anthracene and pentacene. Thin films of these linear mols. were characterized by UV spectroscopy, x-ray diffraction, at. force microscopy (AFM), and field-effect transistor measurements. Submonolayer AFM studies show growth that greatly resembles pentacene, while thin-film growth is dendritic. Mobilities ≤0.47 cm2 V-1 s-1 were found for the tetraceno[2,3-b]thiophene and are ≤0.15 cm2 V-1 s-1 for anthra[2,3-b]thiophene.
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    Wong, M. Y.; Hedley, G. J.; Xie, G.; Kölln, L. S.; Samuel, I. D. W.; Pertegás, A.; Bolink, H. J.; Zysman-Colman, E. Light-Emitting Electrochemical Cells and Solution-Processed Organic Light-Emitting Diodes Using Small Molecule Organic Thermally Activated Delayed Fluorescence Emitters. Chem. Mater. 2015, 27, 6535– 6542,  DOI: 10.1021/acs.chemmater.5b03245
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    31
    Light-Emitting Electrochemical Cells and Solution-Processed Organic Light-Emitting Diodes Using Small Molecule Organic Thermally Activated Delayed Fluorescence Emitters
    Wong, Michael Y.; Hedley, Gordon J.; Xie, Guohua; Kolln, Lisa S.; Samuel, Ifor D. W.; Pertegas, Antonio; Bolink, Henk J.; Zysman-Colman, Eli
    Chemistry of Materials (2015), 27 (19), 6535-6542CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Two novel charged org. thermally activated delayed fluorescence (TADF) emitters, 1 and 2, have been synthesized. Their TADF behavior is well-supported by the multiexponential decay of their emission (nanosecond and microsecond components) and the oxygen dependence of the photoluminescence quantum yields. Spin-coated electroluminescent devices have been fabricated to make light-emitting electrochem. cells (LEECs) and org. light-emitting diodes (OLEDs). The first example of a non-doped charged small org. mol. LEEC is reported and exhibited an external quantum efficiency (EQE) of 0.39% using 2. With a multilayer architecture, a soln.-processed OLED device using neat 2 as the emitting layer gave an EQE of 5.1%, the highest reported to date for a nondoped soln.-processed small mol. org. TADF OLED. These promising results open up a new area in light-emitting materials for the development of low-cost TADF LEECs.
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  32. 32
    Bin, H.; Yang, Y.; Zhang, Z.-G.; Ye, L.; Ghasemi, M.; Chen, S.; Zhang, Y.; Zhang, C.; Sun, C.; Xue, L.; Yang, C.; Ade, H.; Li, Y. 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor. J. Am. Chem. Soc. 2017, 139, 5085– 5094,  DOI: 10.1021/jacs.6b12826
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    9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor
    Bin, Haijun; Yang, Yankang; Zhang, Zhi-Guo; Ye, Long; Ghasemi, Masoud; Chen, Shanshan; Zhang, Yindong; Zhang, Chunfeng; Sun, Chenkai; Xue, Lingwei; Yang, Changduk; Ade, Harald; Li, Yongfang
    Journal of the American Chemical Society (2017), 139 (14), 5085-5094CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    In the last two years, polymer solar cells (PSCs) developed quickly with n-type org. semiconductor (n-OSs) as acceptor. In contrast, the research progress of nonfullerene org. solar cells (OSCs) with org. small mol. as donor and the n-OS as acceptor lags behind. Here, we synthesized a D-A structured medium bandgap org. small mol. H11 with bithienyl-benzodithiophene (BDTT) as central donor unit and fluorobenzotriazole as acceptor unit, and achieved a power conversion efficiency (PCE) of 9.73% for the all org. small mols. OSCs with H11 as donor and a low bandgap n-OS IDIC as acceptor. A control mol. H12 without thiophene conjugated side chains on the BDT unit was also synthesized for investigating the effect of the thiophene conjugated side chains on the photovoltaic performance of the p-type org. semiconductors (p-OSs). Compared with H12, the 2D-conjugated H11 with thiophene conjugated side chains shows intense absorption, low-lying HOMO energy level, higher hole mobility and ordered bimodal crystallite packing in the blend films. Moreover, a larger interaction parameter (χ) was obsd. in the H11 blends calcd. from Hansen soly. parameters and differential scanning calorimetry measurements. These special features combined with the complementary absorption of H11 donor and IDIC acceptor resulted in the best PCE of 9.73% for nonfullerene all small mol. OSCs up to date. Our results indicate that fluorobenzotriazole based 2D conjugated p-OSs are promising medium bandgap donors in the nonfullerene OSCs.
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    Lin, L.-Y.; Chen, Y.-H.; Huang, Z.-Y.; Lin, H.-W.; Chou, S.-H.; Lin, F.; Chen, C.-W.; Liu, Y.-H.; Wong, K.-T. A Low-Energy-Gap Organic Dye for High-Performance Small-Molecule Organic Solar Cells. J. Am. Chem. Soc. 2011, 133, 15822– 15825,  DOI: 10.1021/ja205126t
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    33
    A Low-Energy-Gap Organic Dye for High-Performance Small-Molecule Organic Solar Cells
    Lin, Li-Yen; Chen, Yi-Hong; Huang, Zheng-Yu; Lin, Hao-Wu; Chou, Shu-Hua; Lin, Francis; Chen, Chang-Wen; Liu, Yi-Hung; Wong, Ken-Tsung
    Journal of the American Chemical Society (2011), 133 (40), 15822-15825CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A novel donor-acceptor-acceptor (D-A-A) donor mol., DTDCTB, in which an electron-donating ditolylaminothienyl moiety and an electron-withdrawing dicyanovinylene moiety are bridged by another electron-accepting 2,1,3-benzothiadiazole block, was synthesized and characterized. A vacuum-deposited org. solar cell employing DTDCTB combined with the electron acceptor C70 achieved a record-high power conversion efficiency (PCE) of 5.81%. The respectable PCE is attributed to the solar spectral response extending to the near-IR region and the ultracompact absorption dipole stacking of the DTDCTB thin film.
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    Sun, Y.; Welch, G. C.; Leong, W. L.; Takacs, C. J.; Bazan, G. C.; Heeger, A. J. Solution-processed small-molecule solar cells with 6.7% efficiency. Nat. Mater. 2012, 11, 44,  DOI: 10.1038/nmat3160
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    Solution-processed small-molecule solar cells with 6.7% efficiency
    Sun, Yanming; Welch, Gregory C.; Leong, Wei Lin; Takacs, Christopher J.; Bazan, Guillermo C.; Heeger, Alan J.
    Nature Materials (2012), 11 (1), 44-48CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Org. photovoltaic devices that can be fabricated by simple processing techniques are under intense investigation in academic and industrial labs. because of their potential to enable mass prodn. of flexible and cost-effective devices. Most of the attention has been focused on soln.-processed polymer bulk-heterojunction solar cells. A combination of polymer design, morphol. control, structural insight and device engineering has led to power conversion efficiencies reaching the 6-8% range for conjugated polymer/fullerene blends. Soln.-processed small-mol. bulk-heterojunction solar cells have received less attention, and their efficiencies have remained below those of their polymeric counterparts. Here, we report efficient soln.-processed small-mol. bulk-heterojunction solar cells based on a new mol. donor, DTS(PTTh2)2. A record power conversion efficiency of 6.7% under air-mass 1.5G irradn. (100 mW/cm2) is achieved for small-mol. bulk-heterojunction devices from DTS(PTTh2)2:PC70BM (donor to acceptor ratio of 7:3). This high efficiency was obtained by using remarkably small percentages of solvent additive (0.25 vol.% of 1,8-diiodooctane) during the film-forming process, which leads to reduced domain sizes in the bulk-heterojunction layer. These results provide important progress for soln.-processed org. photovoltaics and demonstrate that solar cells fabricated from small donor mols. can compete with their polymeric counterparts.
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    Maliakal, A.; Raghavachari, K.; Katz, H.; Chandross, E.; Siegrist, T. Photochemical Stability of Pentacene and a Substituted Pentacene in Solution and in Thin Films. Chem. Mater. 2004, 16, 4980– 4986,  DOI: 10.1021/cm049060k
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    35
    Photochemical Stability of Pentacene and a Substituted Pentacene in Solution and in Thin Films
    Maliakal, Ashok; Raghavachari, Krishnan; Katz, Howard; Chandross, Edwin; Siegrist, Theo
    Chemistry of Materials (2004), 16 (24), 4980-4986CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The org. semiconductor pentacene (1) has shown the highest field effect mobilities in thin films of any org. semiconductor, yet suffers from instability toward oxidn. 6,13-Bis(triisopropylsilylethynyl)pentacene (2) has been reported as an interesting functionalized pentacene which is sol. in common org. solvents and exhibits high carrier mobility (>0.1 cm2/Vs) in thin film transistor devices. In our investigations of 2, we were surprised by its remarkable stability in soln. Using UV-vis spectroscopy we observe that under ambient light conditions, 2 is approx. 50× more stable toward degrdn. in air-satd. THF soln. as compared to unsubstituted pentacene. Previous investigators have implicated oxygen in the mechanism of photodegrdn. of pentacene. In this study, quantum chem. calcns. have been performed which demonstrate that alkynyl functionalization at the 6 and 13 positions reduces the rate of photooxidn. in two ways. First, alkynyl substitution reduces the triplet energy of 2 considerably, thereby preventing singlet oxygen sensitization. Second, alkynyl substitution lowers the LUMO energy for 2 as compared to that of pentacene. We propose that the lower LUMO energy hinders photooxidn. by reducing the rate of electron transfer from photoexcited 2 to oxygen. In thin films, pentacene is more stable to photooxidn. than 2 when exposed to UV irradn. The stabilization of pentacene in the solid state is discussed in the context of solid-state interactions.
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    Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. Synthesis, Morphology, and Field-Effect Mobility of Anthradithiophenes. J. Am. Chem. Soc. 1998, 120, 664– 672,  DOI: 10.1021/ja9728381
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    Synthesis, morphology, and field-effect mobility in anthradithiophenes
    Laquindanum, Joyce G.; Katz, Howard E.; Lovinger, Andrew J.
    Journal of the American Chemical Society (1998), 120 (4), 664-672CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The synthesis, thin-film morphol., and hole mobility in thin-film transistors (TFTs) of compds. based on the novel anthradithiophene (ADT) ring system are reported. The parent compd. and its 2,8-dihexyl, didodecyl, and dioctadecyl derivs. (DHADT, DDADT, and DOADT, resp.), synthesized via alkylated thiophene dicarboxaldehyde acetals, were investigated. They all form highly ordered polycryst. vacuum-evapd. films with mobilities as high as 0.15 cm2/V-s, as high as has ever been obsd. for a polycryst. org. material. DOADT exhibits a mobility of 0.06 cm2/V-s even though 70% of its mol. vol. is occupied by hydrocarbon chains. DHADT was cast from soln. under atm. conditions onto a TFT giving a mobility of 0.01-0.02 cm2/V-s. Thus, the alkylated ADTs combine a pentacene-like intrinsic mobility with greater soly. and oxidative stability.
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    Mishra, A.; Bäuerle, P. Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology. Angew. Chem., Int. Ed. 2012, 51, 2020– 2067,  DOI: 10.1002/anie.201102326
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    Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology
    Mishra, Amaresh; Baeuerle, Peter
    Angewandte Chemie, International Edition (2012), 51 (9), 2020-2067CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. This article, written from an org. chemist's point of view, provides an up-to-date overview of org. solar cells based on small mols. or oligomers as absorbers and describes devices that incorporate planar-heterojunctions and bulk heterojunctions between a donor (p-type semiconductor) and an acceptor (n-type semiconductor) material. The article pays particular attention to the design and development of mol. materials and their performance in corresponding devices. In recent years, a substantial amt. of both, academic and industrial research, has been directed towards org. solar cells, in an effort to develop new materials and to improve their tunability, processability, power conversion efficiency, and stability. On the eve of commercialization of org. solar cells, this review provides an overview of efficiencies attained with small mols./oligomers in org. solar cells and summarizes materials and device concepts developed over the last decade. Approaches to enhancing the efficiency of org. solar cells are analyzed.
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    Leung, L. M.; Lo, W. Y.; So, S. K.; Lee, K. M.; Choi, W. K. A High-Efficiency Blue Emitter for Small Molecule-Based Organic Light-Emitting Diode. J. Am. Chem. Soc. 2000, 122, 5640– 5641,  DOI: 10.1021/ja000927z
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    A High-Efficiency Blue Emitter for Small Molecule-Based Organic Light-Emitting Diode
    Leung, Louis M.; Lo, W. Y.; So, S. K.; Lee, K. M.; Choi, W. K.
    Journal of the American Chemical Society (2000), 122 (23), 5640-5641CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A bis(2-Me-8-quinolinolato)Al hydroxide complex (AlMq2OH) is also a high-efficiency blue dye with a single emission max. at 485 nm. The compd. has excellent thermal stability and can be processed similar to Alq3. The synthesis procedures are simple, using chems. that are readily available from com. sources. The blue-shift probably is a result of 2 conditions: (1) The Al complex is trivalent and (2) steric hindrance provided by the 2-Me groups on the 2-Me-8-quinolinol ligands weakened or prohibited the formation of Al-N bonds. Two multilayer small mol. OLEDs using either AlMq2OH or Alq3 as the emission layer were built and their characteristics compared. The OLED cell has a general structure of ITO (72 Ω/sq)/Cu(II) phthalocyanine (10 nm)/N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (50 nm)/emitter, AlMq2OH or Alq3 (80 nm)/Li-F (0.7 nm)/Al(80 nm). The AlMq2OH or Alq3 was evapd. from a homemade Mo boat at a deposition rate of 1 Å/s. At similar c.d. (80 mA/cm2), both the brightness and current efficiency of the AlMq2OH device was 3 times that of Alq3. The max. brightness of the AlMq2OH-based device is 14,000 cd/m at 480 mA/cm2, which is 1 of the highest-intensity blue emitter reported. The slightly higher turn-on voltage for the AlMq2OH device indicates that it has a higher energy barrier for charge injection. The UV-visible absorption, photoluminescence (PL) spectra of AlMq2OH solid thin film on quartz, and the electroluminescence (EL) spectrum of the AlMq2OH-based OLED are shown. Both the EL and PL spectrum of AlMq2OH have a similar shape, a single emission max. at 485 nm and a FWHM of 80 nm. The 50 nm blue-shift for the 2-Me-8-quinolinol based complex is consistent with similar dyes without the Al-N bonding. Steric hindrance was required to reduce the metal-N bonding, and therefore the required blue-shift was provided by the two 2-Me-8-quinolinol ligands, irresp. of the size of the third phenoxy group. The authors have also studied other Mq-based complexes using metals from groups III-B to IV-A. In general, the blue-shift is related to the size of the metal atom, its coordination no. and the acidity of the metal group. In general, divalent complexes have none or min. blue-shift, and the stability of the complexes decreased with an increase in the size of the metal atom. The AlMq2OH complex described here is among the highest-efficiency blue emitter reported, yet it can be processed using methods similar to that for Alq3. The complex itself is stable both under air and high temps. The TGA results of AlMq2OH compared to those for Alq3 under N2 atmosphere are shown. A yellowish side-product with EL and PL similar to that for Alq3, however, was collected during the train sublimation process. It has a lower mol. mass compared to that of AlMq2OH as obsd. from the lower temps. required for sublimation. Results from MS and elemental anal. indicated its chem. compn. was AlMq2, which may be a degrdn. product of the less stable AlMq2Ac. The reestablishment of the Al-N bonds after losing the third ligand confirmed that steric hindrance prohibiting the formation of metal-N bonding was the cause for the blue-shift.
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    Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Electron Transport Materials for Organic Light-Emitting Diodes. Chem. Mater. 2004, 16, 4556– 4573,  DOI: 10.1021/cm049473l
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    Electron Transport Materials for Organic Light-Emitting Diodes
    Kulkarni, Abhishek P.; Tonzola, Christopher J.; Babel, Amit; Jenekhe, Samson A.
    Chemistry of Materials (2004), 16 (23), 4556-4573CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    A review. A comprehensive review of the literature on electron transport materials (ETMs) used to enhance the performance of org. light-emitting diodes (OLEDs) is presented. The structure-property-performance relations of many classes of ETMs, both small-mol.- and polymer-based, that were widely used to improve OLED performance through control of charge injection, transport, and recombination are highlighted. The mol. architecture, electronic structure (electron affinity and ionization potential), thin film processing, thermal stability, morphol., and electron mobility of diverse org. ETMs are discussed and related to their effectiveness in improving OLED performance (efficiency, brightness, and drive voltage). Some issues relating to the exptl. procedures for the estn. of relevant material properties such as electron affinity and electron mobility are discussed. The design of multifunctional electroluminescent polymers whereby light emission and electron- and hole-transport properties are combined in 1 material to achieve efficient single-layer OLEDs is also discussed. The review concludes with a brief perspective on the challenges that future research should address.
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    Liu, Y.; Li, C.; Ren, Z.; Yan, S.; Bryce, M. R. All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Nat. Rev. Mater. 2018, 3, 18020,  DOI: 10.1038/natrevmats.2018.20
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    Liu, Yuchao; Li, Chensen; Ren, Zhongjie; Yan, Shouke; Bryce, Martin R.
    Nature Reviews Materials (2018), 3 (4), 18020CODEN: NRMADL; ISSN:2058-8437. (Nature Research)
    Thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both singlet and triplet excitons without noble metals, are emerging as next-generation org. electroluminescent materials. In the past few years, there have been rapid advances in mol. design criteria, our understanding of the photophysics underlying TADF and the applications of TADF materials as emitters in org. light-emitting diodes (OLEDs). This topic is set to remain at the forefront of research in optoelectronic org. materials for the foreseeable future. In this Review, we focus on state-of-the-art materials design and understanding of the photophys. processes, which are being leveraged to optimize the performance of OLED devices. Notably, we also appraise dendritic and polymeric TADF emitters - macromol. materials that offer the potential advantages of low cost, soln. processable and large-area OLED fabrication.
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    Klauk, H.; Halik, M.; Zschieschang, U.; Schmid, G.; Radlik, W.; Weber, W. High-mobility polymer gate dielectric pentacene thin film transistors. J. Appl. Phys. 2002, 92, 5259– 5263,  DOI: 10.1063/1.1511826
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    The authors have fabricated pentacene org. thin film transistors with spin-coated polymer gate dielec. layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent elec. characteristics, including carrier mobility as large as 3 cm2/Vs, subthreshold swing ≥1.2 V/decade, and on/off current ratio of 105. For comparison, the authors have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielec. and obtained carrier mobilities as large as 1 cm2/Vs and subthreshold swing ≥0.5 V/decade.
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    Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. Highly Soluble [1]Benzothieno[3,2-b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 15732– 15733,  DOI: 10.1021/ja074841i
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    Highly Soluble [1]Benzothieno[3,2-b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors
    Ebata, Hideaki; Izawa, Takafumi; Miyazaki, Eigo; Takimiya, Kazuo; Ikeda, Masaaki; Kuwabara, Hirokazu; Yui, Tatsuto
    Journal of the American Chemical Society (2007), 129 (51), 15732-15733CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    2,7-Dialkyl[1]benzothieno[3,2-b]benzothiophenes were tested as soln.-processible mol. semiconductors. Thin films of the org. semiconductors deposited on Si/SiO2 substrates by spin coating have well-ordered structures as confirmed by XRD anal. Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of ∼107.
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    Yamamoto, T.; Takimiya, K. Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2‘,3′-f]chalcogenopheno[3,2-b]chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224– 2225,  DOI: 10.1021/ja068429z
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    Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2',3'-f]chalcogenopheno[3,2-b]chalcogenophenes, and Their Application to Field-Effect Transistors
    Yamamoto, Tatsuya; Takimiya, Kazuo
    Journal of the American Chemical Society (2007), 129 (8), 2224-2225CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A facile three-step synthetic procedure for highly π-extended heteroarenes, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) and dinaphtho[2,3-b:2',3'-f]selenopheno[3,2-b]selenophene (DNSS), was established. Soln. UV-visible spectra and electrochem. indicated that they have relatively low-lying HOMO levels and large HOMO-LUMO energy gaps. OFET devices fabricated with evapd. thin-films of DNTT and DNSS showed excellent FET characteristics in air, and the highest field-effect mobility of DNTT- and DNSS-based OFETs is 2.9 and 1.9 cm2 V-1 s-1, resp.
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    Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics
    Wang, Chengliang; Dong, Huanli; Hu, Wenping; Liu, Yunqi; Zhu, Daoben
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    A review.
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    Curtis, M. David; Cao, Jie; Kampf, Jeff W.
    Journal of the American Chemical Society (2004), 126 (13), 4318-4328CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The solid-state structures of a series of bithiazole and thiophene oligomers, as well as a series of substituted pentacenes, are rationalized in terms of "pitch and roll" inclinations from an "ideal" cofacial π-stack. Pitch inclinations translate adjacent mols. relative to one another in the direction of the long mol. axis, whereas roll inclinations translate the mols. along the short mol. axis. Thus, moderately large pitch distortions preserve π-π interactions between adjacent mols., whereas roll translations greater than 2.5 Å essentially destroy π-π overlap between adjacent mols. The familiar herringbone packing is characterized by large roll distortions. It is shown that thiophenes tend to exhibit large roll translations, whereas thiazoles have small roll but large pitch translations. Substituted pentacenes tend to have both moderate pitch and roll distances. The relationship of mol. packing to transport properties is discussed.
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    Angewandte Chemie, International Edition (2011), 50 (31), 7013-7017, S7013/1-S7013/13CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The title compds. I (R = CHMe2, CHMeEt, cyclopentyl) were prepd. by alkylation of the corresponding quinones with alkynylsilanes followed by deoxygenation using SnCl2. The optoelectronic properties were explored via absorption and emission spectra, UV-Vis/NIR and EPR spectra. Crystallog. anal. revealed the presence of the conjugated nonacene chromophores.
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    A review. Acenes have long been the subject of intense study because of the unique electronic properties assocd. with their π-bond topol. Recent reports of impressive semiconductor properties of larger homologs have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purifn., as well as for fabricating org. electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in soln. These new functionalization strategies have recently gave acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as study of their assocd. structure/property relations.
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    Field-effect mobility as high as 5 cm2/(V s) is achieved in soln.-processed org. thin-film transistors with the development of a method for growing highly-oriented cryst. films of [1]benzothieno[3,2-b]benzothiophene derivs. A droplet of the soln. is sustained at an edge of a structure on an inclined substrate, so that the cryst. domain grows in the direction of inclination. The oriented growth realizes excellent mol. ordering that manifests itself in micrometer-scale mol. terraces on the surface as a result of the self-organizing function of the material. The unprecedented performance achieved using an easy fabrication process has increased attractiveness of org. thin-film transistors for industrial applications.
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    Alkylated Dinaphtho[2,3-b:2',3'-f]Thieno[3,2-b]Thiophenes (Cn-DNTTs): Organic Semiconductors for High-Performance Thin-Film Transistors
    Kang, Myeong Jin; Doi, Iori; Mori, Hiroki; Miyazaki, Eigo; Takimiya, Kazuo; Ikeda, Masaaki; Kuwabara, Hirokazu
    Advanced Materials (Weinheim, Germany) (2011), 23 (10), 1222-1225CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A series of Cn-DNTTs are synthesized and evaluated as p-channel org. semiconductors for vapor processed OTFTs. the OTFTs showed typical p-channel FET responses with good mobilities, and among them, the C10-DNTT-based devices gave the best TFT characteristics with mobilities of close to 8.0 cm2V-1s-1, which are among the highest ever reported for org. thin-film-based transistors. the present results indicate that the combination of a π-extended heteroarene core with long alkyl groups provide a chance to develop superior org. semiconductors. To elucidate the relationship between the electronic properties and the solid-state structure, the characterization of Cn-DNTT thin films as well as bulk single crystals is now being actively conducted in our group.
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    Iino, H.; Usui, T.; Hanna, J.-i. Liquid crystals for organic thin-film transistors. Nat. Commun. 2015, 6, 6828,  DOI: 10.1038/ncomms7828
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    Liquid crystals for organic thin-film transistors
    Iino, Hiroaki; Usui, Takayuki; Hanna, Jun-ichi
    Nature Communications (2015), 6 (), 6828CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Cryst. thin films of org. semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. However, there are currently two main problems, which are assocd. with inhomogeneity and poor thermal durability of these films. Here we report that liq. cryst. materials exhibiting a highly ordered liq. crystal phase of smectic E (SmE) can solve both these problems. We design a SmE liq. cryst. material, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), for FETs and synthesize it. This material provides uniform and molecularly flat polycryst. thin films reproducibly when SmE precursor thin films are crystd., and also exhibits high durability of films up to 200 °C. In addn., the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm2 V-1 s-1) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs. We anticipate the use of SmE liq. crystals in soln.-processed FETs may help overcome upcoming difficulties with novel technologies for printed electronics.
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  54. 54
    Inoue, S.; Minemawari, H.; Tsutsumi, J. y.; Chikamatsu, M.; Yamada, T.; Horiuchi, S.; Tanaka, M.; Kumai, R.; Yoneya, M.; Hasegawa, T. Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystals. Chem. Mater. 2015, 27, 3809– 3812,  DOI: 10.1021/acs.chemmater.5b00810
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    Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystals
    Inoue, Satoru; Minemawari, Hiromi; Tsutsumi, Jun'ya; Chikamatsu, Masayuki; Yamada, Toshikazu; Horiuchi, Sachio; Tanaka, Mutsuo; Kumai, Reiji; Yoneya, Makoto; Hasegawa, Tatsuo
    Chemistry of Materials (2015), 27 (11), 3809-3812CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The authors systematically studied the effects of the substituted alkyl chain length on soln.-processable layered cryst. org. semiconductors, 7-alkyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophenes (Ph-BTBT-Cn; 0 ≤ n ≤ 14). The solubilities of the compds. in org. solvents sharply increased with increasing alkyl chain length at n ≤ 3, but decreased gradually at 5 ≤ n; these latter compds. exhibit liq.-crystal phases at high temp. The properties are strongly correlated with the alkyl length dependence of the layered mol. packing, as revealed by single-crystal structural anal.: compds. with n ≤ 4 do not form independent alkyl chain layers, whereas those with 5 ≤ n form isomorphous bilayer-type crystal structures in which independent alkyl chain layers are formed and enhance the cohesive energy of the crystals.
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  55. 55
    He, K.; Li, W.; Tian, H.; Zhang, J.; Yan, D.; Geng, Y.; Wang, F. Asymmetric Conjugated Molecules Based on [1]Benzothieno[3,2-b][1]benzothiophene for High-Mobility Organic Thin-Film Transistors: Influence of Alkyl Chain Length. ACS Appl. Mater. Interfaces 2017, 9, 35427– 35436,  DOI: 10.1021/acsami.7b10675
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    55
    Asymmetric conjugated molecules based on [1]Benzothieno[3,2-b][1]benzothiophene for high-mobility organic thin-film transistors: influence of alkyl chain length
    He, Keqiang; Li, Weili; Tian, Hongkun; Zhang, Jidong; Yan, Donghang; Geng, Yanhou; Wang, Fosong
    ACS Applied Materials & Interfaces (2017), 9 (40), 35427-35436CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Herein, the authors report the synthesis and characterization of a series of [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based asym. conjugated mols., i.e., 2-(5-alkylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-Tn, in which T and n represent thiophene and the no. of carbons in the alkyl group, resp.). Alkyl chain length has a noticeable influence on the microstructures of vacuum-deposited films and therefore on the performance of the org. thin-film transistors (OTFTs). All mols. except for 2-(thiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-ethylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed OTFT mobilities above 5 cm2 V-1 s-1. 2-(5-Hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-heptylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed the greatest OTFT performance with reliable hole mobilities (μ) up to 10.5 cm2 V-1 s-1 because they formed highly ordered and homogeneous films with diminished grain boundaries.
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    Grigoriadis, C.; Niebel, C.; Ruzié, C.; Geerts, Y. H.; Floudas, G. Order, Viscoelastic, and Dielectric Properties of Symmetric and Asymmetric Alkyl[1]benzothieno[3,2-b][1]benzothiophenes. J. Phys. Chem. B 2014, 118, 1443– 1451,  DOI: 10.1021/jp412422e
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    56
    Order, Viscoelastic, and Dielectric Properties of Symmetric and Asymmetric Alkyl[1]benzothieno[3,2-b][1]benzothiophenes
    Grigoriadis, Christos; Niebel, Claude; Ruzie, Christian; Geerts, Yves H.; Floudas, George
    Journal of Physical Chemistry B (2014), 118 (5), 1443-1451CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    The morphol., the viscoelastic, the dielec. properties and the dynamics of phase transformation are studied in sym. and asym. substituted alkyl[1]benzothieno[3,2-b][1]benzothiophenes (C8-BTBT) by X-ray scattering, rheol., and dielec. spectroscopy (DS). The interlayer spacing reflects the mol. and supramol. ordering, resp., in the sym. and asym. substituted BTBTs. In the asym. BTBT, the core layer is double in size with a broader network of intermol. interactions though the increased S-S contacts that is prerequisite for the development of high performance OFET devices. Two crystal states with elastic and viscoelastic responses were identified in the sym. compd. In contrast, the SmA phase in the asym. compd. is a viscoelastic solid. A path-dependent dielec. environment with a switchable dielec. permittivity was found in both compds. by cooling below 0 °C with possible implications to charge transport. The kinetics of phase transformation to the cryst. and SmA phases revealed a nucleation and growth mechanism with rates dominated by the low activation barriers.
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  57. 57
    Inoue, S.; Shinamura, S.; Sadamitsu, Y.; Arai, S.; Horiuchi, S.; Yoneya, M.; Takimiya, K.; Hasegawa, T. Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors. Chem. Mater. 2018, 30, 5050– 5060,  DOI: 10.1021/acs.chemmater.8b01339
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    57
    Extended and modulated thienothiophenes for thermally durable and solution-processable organic semiconductors
    Inoue, Satoru; Shinamura, Shoji; Sadamitsu, Yuichi; Arai, Shunto; Horiuchi, Sachio; Yoneya, Makoto; Takimiya, Kazuo; Hasegawa, Tatsuo
    Chemistry of Materials (2018), 30 (15), 5050-5060CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Herein, we report the rational design of practical small-mol. org. semiconductors based on a π-electron skeleton of benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asym. substitutions with the Ph group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) and benzothieno[3,2-b]benzothiophene (BTBT), although the solvent soly. for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and Ph group remains extremely low. We show in the BTBT and BTNT derivs. that the tuning of the substituting position works to slightly bend the rodlike org. semiconductor mols. and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (b-LHB) packing for the asym. rodlike mols. This modification eventually leads to an increase in solvent soly., a decrease in phase transition temp., and the suppression of liq.-cryst. phases at high temps. By using the substituting effect, we successfully achieve the org. semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent soly. and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermol. transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact org. thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepd. films, because the thermal treatment stabilizes the b-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of org. semiconductor materials for practical printed electronics applications.
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    Diao, Y.; Tee, B. C. K.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C. B.; Bao, Z. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nat. Mater. 2013, 12, 665,  DOI: 10.1038/nmat3650
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    Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains
    Diao, Ying; Tee, Benjamin C.-K.; Giri, Gaurav; Xu, Jie; Kim, Do Hwan; Becerril, Hector A.; Stoltenberg, Randall M.; Lee, Tae Hoon; Xue, Gi; Mannsfeld, Stefan C. B.; Bao, Zhenan
    Nature Materials (2013), 12 (7), 665-671CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Soln. coating of org. semiconductors offers great potential for achieving low-cost manufg. of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale prodn. poses challenges to the control of thin-film morphol. Here, the authors report an approach-termed fluid-enhanced crystal engineering (FLUENCE)-that allows for a high degree of morphol. control of soln.-printed thin films. The authors designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, the authors demonstrate the fast coating and patterning of millimeter-wide, centimeter-long, highly aligned single-cryst. org. semiconductor thin films. In particular, the authors fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having nonequil. single-cryst. domains and an unprecedented av. and max. mobilities. FLUENCE of org. semiconductors with nonequil. single-cryst. domains may find use in the fabrication of high-performance, large-area printed electronics.
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    Nakayama, K.; Hirose, Y.; Soeda, J.; Yoshizumi, M.; Uemura, T.; Uno, M.; Li, W.; Kang, M. J.; Yamagishi, M.; Okada, Y.; Miyazaki, E.; Nakazawa, Y.; Nakao, A.; Takimiya, K.; Takeya, J. Patternable Solution-Crystallized Organic Transistors with High Charge Carrier Mobility. Adv. Mater. 2011, 23, 1626– 1629,  DOI: 10.1002/adma.201004387
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    Patternable Solution-Crystallized Organic Transistors with High Charge Carrier Mobility
    Nakayama, Kengo; Hirose, Yuri; Soeda, Junshi; Yoshizumi, Masahiro; Uemura, Takafumi; Uno, Mayumi; Li, Wanyan; Kang, Myeong Jin; Yamagishi, Masakazu; Okada, Yugo; Miyazaki, Eigo; Nakazawa, Yasuhiro; Nakao, Akiko; Takimiya, Kazuo; Takeya, Jun
    Advanced Materials (Weinheim, Germany) (2011), 23 (14), 1626-1629CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Newly developed arrays of patterned cryst. OFETs of air-stable compd. 2,9-didecyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C10-DNTT) formed from hot soln. are presented. A method of oriented growth is introduced to provide the single-cryst. films of C10-DNTT that regulates the crystg. direction and positions in a single process. The benchmark value, 10 cm2V-1s-1, of the charge mobility is achieved for the present OFETs, far exceeding the performance of former devices and opening a practical way to realize printed and flexible electronics with sufficient switching speed. The result is attributed to almost perfect mol. periodicity in the crystal films, which allows effective intermol. charge transport of the electrons.
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    Yuan, Y.; Giri, G.; Ayzner, A. L.; Zoombelt, A. P.; Mannsfeld, S. C. B.; Chen, J.; Nordlund, D.; Toney, M. F.; Huang, J.; Bao, Z. Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method. Nat. Commun. 2014, 5, 3005,  DOI: 10.1038/ncomms4005
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    Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method
    Yuan Yongbo; Huang Jinsong; Giri Gaurav; Zoombelt Arjan P; Bao Zhenan; Ayzner Alexander L; Mannsfeld Stefan C B; Nordlund Dennis; Toney Michael F; Chen Jihua
    Nature communications (2014), 5 (), 3005 ISSN:.
    Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.
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    Iino, H.; Kobori, T.; Hanna, J.-i. Improved thermal stability in organic FET fabricated with a soluble BTBT derivative. J. Non-Cryst. Solids 2012, 358, 2516– 2519,  DOI: 10.1016/j.jnoncrysol.2012.03.021
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    Improved thermal stability in organic FET fabricated with a soluble BTBT derivative
    Iino, Hiroaki; Kobori, Takeo; Hanna, Jun-ichi
    Journal of Non-Crystalline Solids (2012), 358 (17), 2516-2519CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)
    We have synthesized a new benzothienobenzothiophene (BTBT) deriv., 2-octylthienylbenzothienobenzothiophene having a highly ordered liq. crystal phase of smectic E (SmE) in the temp. range next to its crystal phase, fabricated its polycryst. thin films by spin-coating technique, and applied them to field effect transistors (FETs). Thanks to the liq. crystal phase as a precursor of polycryst. thin films, the resulting films were molecularly flat and uniform. The thermal stability of the thin films was very much improved compared with dialkyl BTBT derivs. because of the solid-like nature of the SmE phase up to 180 °C. The FETs fabricated with films after solvent vapor annealing with toluene showed high FET mobility of 1.4 ± 0.3 cm2/V s. As expected, the FETs were not destroyed by thermal load up to 150 °C. The FET mobility was recovered to 0.54 cm2/V s by the solvent vapor annealing, although the FET mobility was decreased by the thermal load. Highly ordered liq. cryst. phases provide us with easy fabrication of quality polycryst. thin films and high thermal stability of the polycryst. thin films.
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    Okamoto, K.; Kawamura, T.; Sone, M.; Ogino, K. Study on liquid crystallinity in 2,9-dialkylpentacenes. Liq. Cryst. 2007, 34, 1001– 1007,  DOI: 10.1080/02678290701478970
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    Study on liquid crystallinity in 2,9-dialkylpentacenes
    Okamoto, Kazuo; Kawamura, Takumi; Sone, Masato; Ogino, Kenji
    Liquid Crystals (2007), 34 (9), 1001-1007CODEN: LICRE6; ISSN:0267-8292. (Taylor & Francis Ltd.)
    A series of semiconducting and sym. 2,9-dialkylpentacenes was successfully synthesized via a five-step process and their structures confirmed by 1H NMR, IR and elemental analyses. Their liq. crystallinity was investigated by differential scanning calorimetry and polarizing optical microscopy. The introduction of alkyl chains also improved their soly. For alkyl chains longer than Bu, focal conic or baton texture was obsd., indicating the existence of an ordered smectic phase. Thermal analyses revealed that the both melting and smectic-isotropic transition temps. show an odd-even effect when the alkyl chain is larger than heptyl or octyl. The synthesized compds. are promising candidates for semiconductors in org. field-effect transistors because their liq. crystallinity allows easy mol. alignment in the device fabrication process.
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    A map of high-mobility molecular semiconductors
    Fratini, S.; Ciuchi, S.; Mayou, D.; Trambly de Laissardiere, G.; Troisi, A.
    Nature Materials (2017), 16 (10), 998-1002CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
    The charge mobility of mol. semiconductors is limited by the large fluctuation of intermol. transfer integrals, often referred to as off-diagonal dynamic disorder, which causes transient localization of the carriers' eigenstates. Using a recently developed theor. framework, the authors show here that the electronic structure of the mol. crystals dets. its sensitivity to intermol. fluctuations. The authors build a map of the transient localization lengths of high-mobility mol. semiconductors to identify what patterns of nearest-neighbor transfer integrals in the two-dimensional (2D) high-mobility plane protect the semiconductor from the effect of dynamic disorder and yield larger mobility. Such a map helps rationalizing the transport properties of the whole family of mol. semiconductors and is also used to demonstrate why common textbook approaches fail in describing this important class of materials. These results can be used to rapidly screen many compds. and design new ones with optimal transport characteristics.
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    Troisi, A.; Orlandi, G.; Anthony, J. E. Electronic Interactions and Thermal Disorder in Molecular Crystals Containing Cofacial Pentacene Units. Chem. Mater. 2005, 17, 5024– 5031,  DOI: 10.1021/cm051150h
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    Electronic Interactions and Thermal Disorder in Molecular Crystals Containing Cofacial Pentacene Units
    Troisi, Alessandro; Orlandi, Giorgio; Anthony, John E.
    Chemistry of Materials (2005), 17 (20), 5024-5031CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The authors computed the intermol. electronic coupling and the band structure of three pentacene derivs. that stack cofacially in one or two dimensions. The authors rationalize the results building a map of the coupling between HOMOs and LUMOs of isolated pentacene mols. as a function of the relative mol. orientation and finding the position on such map of the actual mol. pairs. The apparently chaotic dependence of the intermol. coupling from the crystal structure is explained, and directions for the design of materials with improved elec. transport properties are given. The authors run mol. dynamics simulations to explore the variation of the intermol. coupling due to the thermal motions. Even in the crystal phase, the limited conformational space explored at room temp. is large enough to produce consistent variation in the intermol. coupling. The consequences of this finding on the practicability of the transport properties of org. materials are analyzed.
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    Ciuchi, S.; Fratini, S. Electronic transport and quantum localization effects in organic semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 245201,  DOI: 10.1103/PhysRevB.86.245201
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    Electronic transport and quantum localization effects in organic semiconductors
    Ciuchi, S.; Fratini, S.
    Physical Review B: Condensed Matter and Materials Physics (2012), 86 (24), 245201/1-245201/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    We explore the charge transport mechanism in org. semiconductors based on a model that accounts for the thermal intermol. disorder at work in pure cryst. compds., as well as extrinsic sources of disorder that are present in current exptl. devices. Starting from the Kubo formula, we describe a theor. framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent cond. The electron mobility is then calcd. through a relaxation time approxn. that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a "transient localization" phenomenon is shown to be a general feature of org. semiconductors that is compatible with the bandlike temp. dependence of the mobility obsd. in pure compds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temp., which is progressively suppressed upon increasing the carrier concn., as is commonly obsd. in org. field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenol. considerations that are commonly used in the literature.
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    Illig, S.; Eggeman, A. S.; Troisi, A.; Jiang, L.; Warwick, C.; Nikolka, M.; Schweicher, G.; Yeates, S. G.; Henri Geerts, Y.; Anthony, J. E.; Sirringhaus, H. Reducing dynamic disorder in small-molecule organic semiconductors by suppressing large-amplitude thermal motions. Nat. Commun. 2016, 7, 10736,  DOI: 10.1038/ncomms10736
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    Reducing dynamic disorder in small-molecule organic semiconductors by suppressing large-amplitude thermal motions
    Illig, Steffen; Eggeman, Alexander S.; Troisi, Alessandro; Jiang, Lang; Warwick, Chris; Nikolka, Mark; Schweicher, Guillaume; Yeates, Stephen G.; Henri Geerts, Yves; Anthony, John E.; Sirringhaus, Henning
    Nature Communications (2016), 7 (), 10736CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Thermal vibrations and the dynamic disorder they create can detrimentally affect the transport properties of van der Waals bonded mol. semiconductors. The low-energy nature of these vibrations makes it difficult to access them exptl., which is why we still lack clear mol. design rules to control and reduce dynamic disorder. In this study we discuss the promising org. semiconductors rubrene, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothio-phene and 2,9-di-decyl-dinaphtho-[2,3-b:20,30-f]-thieno-[3,2-b]-thiophene in terms of an exceptionally low degree of dynamic disorder. In particular, we analyze diffuse scattering in transmission electron microscopy, to show that small mols. that have their side chains attached along the long axis of their conjugated core are better encapsulated in their crystal structure, which helps reduce large-amplitude thermal motions. Our work provides a general strategy for the design of new classes of very high mobility org. semiconductors with a low degree of dynamic disorder.
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  68. 68
    Okamoto, T.; Mitsui, C.; Yamagishi, M.; Nakahara, K.; Soeda, J.; Hirose, Y.; Miwa, K.; Sato, H.; Yamano, A.; Matsushita, T.; Uemura, T.; Takeya, J. V-shaped organic semiconductors with solution processability, high mobility, and high thermal durability. Adv. Mater. 2013, 25, 6392– 6397,  DOI: 10.1002/adma.201302086
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    V-Shaped Organic Semiconductors With Solution Processability, High Mobility, and High Thermal Durability
    Okamoto, Toshihiro; Mitsui, Chikahiko; Yamagishi, Masakazu; Nakahara, Katsumasa; Soeda, Junshi; Hirose, Yuri; Miwa, Kazumoto; Sato, Hiroyasu; Yamano, Akihito; Matsushita, Takeshi; Uemura, Takafumi; Takeya, Jun
    Advanced Materials (Weinheim, Germany) (2013), 25 (44), 6392-6397CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors have developed a new candidate for org. semiconductor materials that can be applied in a future printed electronics industry. By synthesizing the newly designed and conceptually unexplored V-shaped extended conjugated core of DNT-V, high-mobility charge transport and sufficient soly. have both been achieved, resulting in the prepn. of soln.-crystd. transistor devices exhibiting excellent performance, with the mobility reaching 9.5 cm2 V'1 s_1. A series of derivs. with alkyl chains became available through a mass-producible four-step synthetic route. In addn., the soln.-crystd. devices of the compd. exhibit high thermal durability up to 150 〈°C, which is also essential for practical usage. The authors detd. crystal packing and the resultant transfer integrals, with the results showing that the high carrier mobility is attributed to an almost optimized arrangement of the DNT-V cores to achieve the max. bandwidth.
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  69. 69
    Mitsui, C.; Okamoto, T.; Matsui, H.; Yamagishi, M.; Matsushita, T.; Soeda, J.; Miwa, K.; Sato, H.; Yamano, A.; Uemura, T.; Takeya, J. Dinaphtho[1,2b:2′,1’d]chalcogenophenes: Comprehensive Investigation of the Effect of the Chalcogen Atoms in the Phenacene-Type π Electronic Cores. Chem. Mater. 2013, 25, 3952– 3956,  DOI: 10.1021/cm303376g
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    69
    Dinaphtho[1,2b:2',1'd]chalcogenophenes: Comprehensive Investigation of the Effect of the Chalcogen Atoms in the Phenacene-Type π Electronic Cores
    Mitsui, Chikahiko; Okamoto, Toshihiro; Matsui, Hiroyuki; Yamagishi, Masakazu; Matsushita, Takeshi; Soeda, Junshi; Miwa, Kazumoto; Sato, Hiroyasu; Yamano, Akihito; Uemura, Takafumi; Takeya, Jun
    Chemistry of Materials (2013), 25 (20), 3952-3956CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    The authors report dinaphtho-[1,2-b:2',1'-d]-chalcogenophenes as a new class of highly potential p-type semiconductors. As the result of comprehensive studies including computational studies based on single-crystal structures successfully detd. by x-ray anal., the impacts of the chalcogen atoms are substantially manifested in their MOs, crystal packing structures, charge-transporting properties, and the device performances at the end. Among them, dinaphtho-[1,2-b:2',1'-d]-thiophene and dinaphtho-[1,2-b:2',1'-d]-selenophene achieved a hole mobility of up to 1.6 and 2.0 cm2 V-1 s-1, resp., accompanied by an Ion/Ioff ratio ≤104-105 in their single-crystal org. field-effect transistors. Such high performances are attributed to the large orbital coeff. on the chalcogen atoms and the ideal packing structures induced by chalcogen-bridged W-shaped mols.
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    Mitsui, C.; Okamoto, T.; Yamagishi, M.; Tsurumi, J.; Yoshimoto, K.; Nakahara, K.; Soeda, J.; Hirose, Y.; Sato, H.; Yamano, A.; Uemura, T.; Takeya, J. High-performance solution-processable N-shaped organic semiconducting materials with stabilized crystal phase. Adv. Mater. 2014, 26, 4546– 4551,  DOI: 10.1002/adma.201400289
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    High-Performance Solution-Processable N-Shaped Organic Semiconducting Materials with Stabilized Crystal Phase
    Mitsui, Chikahiko; Okamoto, Toshihiro; Yamagishi, Masakazu; Tsurumi, Junto; Yoshimoto, Kazumi; Nakahara, Katsumasa; Soeda, Junshi; Hirose, Yuri; Sato, Hiroyasu; Yamano, Akihito; Uemura, Takafumi; Takeya, Jun
    Advanced Materials (Weinheim, Germany) (2014), 26 (26), 4546-4551CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In this paper, authors report the synthesis, fundamental properties, single-crystal structures, and charge transporting capabilities of dinaphthol[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DNBDT) and C10-DNBDT-NW to understand clearly their potential usability as active semiconductors compared with V-shaped compds. The ionization potentials of DNBDT and C10-DNBDT-NW are 5.45 eV and 5.24 eV, resp., whose values are improved because of the extended π-electron system, as expected.
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    Mitsui, C.; Yamagishi, M.; Shikata, R.; Ishii, H.; Matsushita, T.; Nakahara, K.; Yano, M.; Sato, H.; Yamano, A.; Takeya, J.; Okamoto, T. Oxygen- and sulfur-bridged bianthracene V-shaped organic semiconductors. Bull. Chem. Soc. Jpn. 2017, 90, 931– 938,  DOI: 10.1246/bcsj.20170030
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    Oxygen- and sulfur-bridged bianthracene V-shaped organic semiconductors
    Mitsui, Chikahiko; Yamagishi, Masakazu; Shikata, Ryoji; Ishii, Hiroyuki; Matsushita, Takeshi; Nakahara, Katsumasa; Yano, Masafumi; Sato, Hiroyasu; Yamano, Akihito; Takeya, Jun; Okamoto, Toshihiro
    Bulletin of the Chemical Society of Japan (2017), 90 (8), 931-938CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
    A series of oxygen- and sulfur-bridged bianthracene V-shaped π-electronic cores are facilely synthesized (I; X = O, S). We clarify their fundamental properties and aggregated structures in single crystals as well as measure their transistor performances in single crystal field-effect transistors. Both V-shaped mols. possess bent structures induced by the intermol. interaction in a herringbone-packing manner. A theor. calcn. study reveals that the driving force of the bent structures originates from the strong dispersion energy. Addnl., the bent conformation plays a crucial role in the formation of a dense packing structure, resulting in an attractive intermol. overlap. An examn. of the charge transport indicates that the hole mobility is up to 2.0 cm2/Vs. Finally, to understand the anisotropies of the mobility in single crystals, the transistors are evaluated when the channel direction is either parallel or orthogonal to the column direction in the herring-bone packing along with their band structure calcns. Sulfur-bridged V-shaped π-electronic cores are more suitable for two-dimensional carrier-transport than oxygen-bridged analogs.
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    Mitsui, C.; Tsuyama, H.; Shikata, R.; Murata, Y.; Kuniyasu, H.; Yamagishi, M.; Ishii, H.; Yamamoto, A.; Hirose, Y.; Yano, M.; Takehara, T.; Suzuki, T.; Sato, H.; Yamano, A.; Fukuzaki, E.; Watanabe, T.; Usami, Y.; Takeya, J.; Okamoto, T. High performance solution-crystallized thin-film transistors based on V-shaped thieno[3,2-f:4,5-f’]bis[1]benzothiophene semiconductors. J. Mater. Chem. C 2017, 5, 1903– 1909,  DOI: 10.1039/C6TC04721A
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    High performance solution-crystallized thin-film transistors based on V-shaped thieno[3,2-f:4,5-f']bis[1]benzothiophene semiconductors
    Mitsui, Chikahiko; Tsuyama, Hiroaki; Shikata, Ryoji; Murata, Yoshinori; Kuniyasu, Hiroyuki; Yamagishi, Masakazu; Ishii, Hiroyuki; Yamamoto, Akito; Hirose, Yuri; Yano, Masafumi; Takehara, Tsunayoshi; Suzuki, Takeyuki; Sato, Hiroyasu; Yamano, Akihito; Fukuzaki, Eiji; Watanabe, Tetsuya; Usami, Yoshihisa; Takeya, Jun; Okamoto, Toshihiro
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (8), 1903-1909CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    A new class of soln.-processable thieno[3,2-f:4,5-f']bis[1]benzothiophene (TBBT-V) semiconductors are investigated. Semiconductors with decyl substituents and two kinds of π-extended decylthienyl substituents are facially derivatized from functionalized dibromo-substituted TBBT-Vvia either a Negishi or a Stille cross coupling procedure. The solubilities of TBBT-V semiconductors are somewhat higher than those of their previously developed dinaphtho[2,3-b:2',3'-d]thiophene (DNT-V) counterparts. Single crystal anal. together with a calcn. study on the transfer integral and the band structure in decyl-substituted TBBT-V (C10-TBBT-V) clarifies that these semiconductors form two-dimensionally ordered herringbone packing structures and the effective mass in the columnar direction rivals that of the previously developed decyl-substituted DNT-V. The carrier mobilities of TBBT-V derivs. in soln. grown into single-cryst. films are remarkable (up to 6.2 cm2 V-1 s-1). Furthermore, their operation voltages are apparently lower than those of previously developed DNT-V derivs. due to the optimized ionization potential of the TBBT-V core and further π-extension by substitution of the thienyl groups.
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    Yamamoto, A.; Murata, Y.; Mitsui, C.; Ishii, H.; Yamagishi, M.; Yano, M.; Sato, H.; Yamano, A.; Takeya, J.; Okamoto, T. Zigzag-Elongated Fused pi-Electronic Core: A Molecular Design Strategy to Maximize Charge-Carrier Mobility. Adv. Sci. 2018, 5, 1700317,  DOI: 10.1002/advs.201700317
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    Zigzag-Elongated Fused π-Electronic Core: A Molecular Design Strategy to Maximize Charge-Carrier Mobility
    Yamamoto Akito; Mitsui Chikahiko; Takeya Jun; Okamoto Toshihiro; Murata Yoshinori; Yano Masafumi; Ishii Hiroyuki; Yamagishi Masakazu; Sato Hiroyasu; Yamano Akihito; Okamoto Toshihiro
    Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2018), 5 (1), 1700317 ISSN:2198-3844.
    Printed and flexible electronics requires solution-processable organic semiconductors with a carrier mobility (μ) of ≈10 cm(2) V(-1) s(-1) as well as high chemical and thermal durability. In this study, chryseno[2,1-b:8,7-b']dithiophene (ChDT) and its derivatives, which have a zigzag-elongated fused π-electronic core (π-core) and a peculiar highest occupied molecular orbital (HOMO) configuration, are reported as materials with conceptually new semiconducting π-cores. ChDT and its derivatives are prepared by a versatile synthetic procedure. A comprehensive investigation reveals that the ChDT π-core exhibits increasing structural stability in the bulk crystal phase, and that it is unaffected by a variation of the transfer integral, induced by the perpetual molecular motion of organic materials owing to the combination of its molecular shape and its particular HOMO configuration. Notably, ChDT derivatives exhibit excellent chemical and thermal stability, high charge-carrier mobility under ambient conditions (μ ≤ 10 cm(2) V(-1) s(-1)), and a crystal phase that is highly stable, even at temperatures above 250 °C.
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    Tsurumi, J.; Matsui, H.; Kubo, T.; Hausermann, R.; Mitsui, C.; Okamoto, T.; Watanabe, S.; Takeya, J. Coexistence of ultra-long spin relaxation time and coherent charge transport in organic single-crystal semiconductors. Nat. Phys. 2017, 13, 994– 998,  DOI: 10.1038/nphys4217
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    Coexistence of ultra-long spin relaxation time and coherent charge transport in organic single-crystal semiconductors
    Tsurumi, Junto; Matsui, Hiroyuki; Kubo, Takayoshi; Hausermann, Roger; Mitsui, Chikahiko; Okamoto, Toshihiro; Watanabe, Shun; Takeya, Jun
    Nature Physics (2017), 13 (10), 994-998CODEN: NPAHAX; ISSN:1745-2473. (Nature Research)
    Coherent charge transport can occur in org. semiconductor crystals thanks to the highly periodic electrostatic potential-despite the weak van der Waals bonds. And as spin-orbit coupling is usually weak in org. materials, robust spin transport is expected, which is essential if they are to be exploited for spintronic applications. In such systems, momentum relaxation occurs via scattering events, which enables an intrinsic mobility to be defined for band-like charge transport, which is >10 cm2 V-1 s-1. In contrast, there are relatively few exptl. studies of the intrinsic spin relaxation for org. band-transport systems. Here, we demonstrate that the intrinsic spin relaxation in org. semiconductors is also caused by scattering events, with much less frequency than the momentum relaxation. Magnetotransport measurements and ESR spectroscopy consistently show a linear relationship between the two relaxation times over a wide temp. range, clearly manifesting the Elliott-Yafet type of spin relaxation mechanism. The coexistence of an ultra-long spin lifetime of milliseconds and the coherent band-like transport, resulting in a micrometer-scale spin diffusion length, constitutes a key step towards realizing spintronic devices based on org. single crystals.
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    Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; van Eikema Hommes, N. J. R. Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe. J. Am. Chem. Soc. 1996, 118, 6317– 6318,  DOI: 10.1021/ja960582d
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    Nucleus-independent chemical shifts: a simple and efficient aromaticity probe
    Schleyer, Paul v.R.; Maerker, Christoph; Dransfeld, Alk; Jiao, Haijun; van Eikema Hommes, Nicolaas J. R.
    Journal of the American Chemical Society (1996), 118 (26), 6317-6318CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Nucleus-independent chem. shifts (NICS), the neg. of the abs. magnetic shieldings (in ppm) computed at the ab initio GIAO-HF/6-31 + G* level at ring centers (non-weighted means of the heavy atom coordinates), are proposed as a simple and efficient magnetic probe for characterizing aromaticity and antiaromaticity. For a series of five membered heterocycles, NICS correlate with arom. stabilization energies, magnetic susceptibility exaltations, and geometric criteria of aromaticity. Arom. compds. have neg. NICS (e.g., -9.7 for benzene and -15.1 for pyrrole), whereas antiarom. systems, in contrast, exhibit pos. NICS values (18.1 for pentalene and 27.6 for cyclobutadiene). In addn., NICS can characterize the individual rings in polycyclic arom. (e.g., -19.7 and -7.0 for the five- and seven-membered rings in azulene) and antiarom. (e.g., -2.5 and 22.5 for the six- and four-membered rings in benzocyclobutadiene) systems as well as the spherical aromaticity of cage compds., e.g., closo-B12H122- (-34.4) and the 1,3-dehydro-5,7-adamantanediyl dication (-50.1). The C60 NICS confirm that the 5-rings are paramagnetic and the 6-rings are diamagnetic, but the magnitudes are not large.
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    Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 2005, 105, 3842– 3888,  DOI: 10.1021/cr030088+
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    Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion
    Chen, Zhongfang; Wannere, Chaitanya S.; Corminboeuf, Clemence; Puchta, Ralph; Schleyer, Paul von Rague
    Chemical Reviews (Washington, DC, United States) (2005), 105 (10), 3842-3888CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A comprehensive review is presented on nucleus-independent chem. shift as a criterion for aromaticity.
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    Münzel, N.; Kesper, K.; Schweig, A.; Specht, H. Detection of 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene. Tetrahedron Lett. 1988, 29, 6239– 6242,  DOI: 10.1016/S0040-4039(00)82314-X
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    Detection of 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene
    Muenzel, Norbert; Kesper, Karl; Schweig, Armin; Specht, Harald
    Tetrahedron Letters (1988), 29 (48), 6239-42CODEN: TELEAY; ISSN:0040-4039.
    The reactive species 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene were generated by pyrolytic elimination of HCl from their thiophene precursors.
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    Okamoto, H.; Kawasaki, N.; Kaji, Y.; Kubozono, Y.; Fujiwara, A.; Yamaji, M. Air-assisted High-performance Field-effect Transistor with Thin Films of Picene. J. Am. Chem. Soc. 2008, 130, 10470– 10471,  DOI: 10.1021/ja803291a
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    Air-assisted High-performance Field-effect Transistor with Thin Films of Picene
    Okamoto, Hideki; Kawasaki, Naoko; Kaji, Yumiko; Kubozono, Yoshihiro; Fujiwara, Akihiko; Yamaji, Minoru
    Journal of the American Chemical Society (2008), 130 (32), 10470-10471CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A field-effect transistor (FET) with thin films of picene has been fabricated on SiO2 gate dielec. The FET showed p-channel enhancement-type FET characteristics with the field-effect mobility of 1.1 cm2/(V·s) and the on-off ratio of >105. This excellent device performance was realized under atm. conditions. The field-effect mobility increased with an increase in temp., and the FET performance was improved by exposure to air or O2 for a long time. This result implies that this device is an air (O2)-assisted FET. The FET characteristics are discussed on the basis of structural topog. and the energy diagram of picene thin films.
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    Kawai, N.; Eguchi, R.; Goto, H.; Akaike, K.; Kaji, Y.; Kambe, T.; Fujiwara, A.; Kubozono, Y. Characteristics of Single Crystal Field-Effect Transistors with a New Type of Aromatic Hydrocarbon, Picene. J. Phys. Chem. C 2012, 116, 7983– 7988,  DOI: 10.1021/jp300052p
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    Characteristics of single crystal field-effect transistors with new type of aromatic hydrocarbon, picene
    Kawai, Nobuyuki; Eguchi, Ritsuko; Goto, Hidenori; Akaike, Kouki; Kaji, Yumiko; Kambe, Takashi; Fujiwara, Akihiko; Kubozono, Yoshihiro
    Journal of Physical Chemistry C (2012), 116 (14), 7983-7988CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Picene is a phenacene-type arom. hydrocarbon mol. with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liq. gate dielecs. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielec. and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V-1 s-1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liq. gate dielec., 1-butyl-3-Me imidazolium hexafluorophosphate, showing the field-effect mobility of 1.8 × 10-1 cm2 V-1 s-1 and low abs. value, 1.9 V, of threshold voltage.
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    De, A.; Ghosh, R.; Roychowdhury, S.; Roychowdhury, P. Structural analysis of picene, C22H14. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1985, 41, 907– 909,  DOI: 10.1107/S0108270185005959
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    Tedjamulia, M. L.; Tominaga, Y.; Castle, R. N.; Lee, M. L. The synthesis of dinaphthothiophenes. J. Heterocyclic Chem. 1983, 20, 1143– 1148,  DOI: 10.1002/jhet.5570200502
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    The synthesis of dinaphthothiophenes
    Tedjamulia, Marvin L.; Tominaga, Yoshinori; Castle, Raymond N.; Lee, Milton L.
    Journal of Heterocyclic Chemistry (1983), 20 (5), 1143-8CODEN: JHTCAD; ISSN:0022-152X.
    Dinaphtho[1,2-b:2',3'-d]thiophene, dinaphtho[2,1-b;2',3'-d]thiophene, dinaphtho-[1,2-b:1',2'-d]thiophene, dinaphtho[2,1-b; 1',2'-d]thiophene and dinaphtho[1,2-b:2',1'-d]thiophene were prepd.
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    Lloyd-Jones, G. C.; Moseley, J. D.; Renny, J. S. Mechanism and Application of the Newman-Kwart O→S Rearrangement of O-Aryl Thiocarbamates. Synthesis 2008, 2008, 661– 689,  DOI: 10.1055/s-2008-1032179
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    Shinamura, S.; Osaka, I.; Miyazaki, E.; Nakao, A.; Yamagishi, M.; Takeya, J.; Takimiya, K. Linear- and Angular-Shaped Naphthodithiophenes: Selective Synthesis, Properties, and Application to Organic Field-Effect Transistors. J. Am. Chem. Soc. 2011, 133, 5024– 5035,  DOI: 10.1021/ja110973m
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    Journal of the American Chemical Society (2011), 133 (13), 5024-5035CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A straightforward synthetic approach that exploits linear- and angular-shaped naphthodithiophenes (NDTs) being potential as new core structures for org. semiconductors is described. The newly established synthetic procedure involves 2 important steps; one is the chemoselective Sonogashira coupling reaction on the trifluoromethanesulfonyloxy site over the Br site enabling selective formation of o-bromoethynylbenzene substructures on the naphthalene core, and the other is a facile ring closing reaction of fused-thiophene rings from the o-bromoethynylbenzene substructures. As a result, 3 isomeric NDTs, naphtho[2,3-b:6,7-b']dithiophene, naphtho[2,3-b:7,6-b']dithiophenes, and naphtho[2,1-b:6,5-b']dithiophene, are selectively synthesized. Electrochem. and optical measurements of the parent NDTs indicated that the shape of the mols. plays an important role in detg. the electronic structure of the compds.; the linear-shaped NDTs formally isoelectronic with naphthacene have lower oxidn. potentials and more red shifted absorption bands than those of the angular-shaped NDTs isoelectronic with chrysene. On the contrary, the performance of the thin-film-based field-effect transistors (FETs) using the dioctyl or di-Ph derivs. were much influenced by the symmetry of the mols.; centrosym. derivs. tend to give higher mobility (up to 1.5 cm2 V-1 s-1) than axisym. ones (∼0.06 cm2 V-1 s-1), implying that the intermol. orbital overlap in the solid state is influenced by the symmetry of the mols. The present NDT cores, in particular the linear-shaped, centrosym. naphtho[2,3-b:6,7-b']dithiophene, are promising building blocks for the development of org. semiconducting materials.
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    Readily available biphenyl derivs. contg. an alkyne unit at one of their ortho-positions were converted into substituted phenanthrenes, e.g., I, on exposure to catalytic amts. of either PtCl2, AuCl, AuCl3, GaCl3 or InCl3 in toluene. This 6-endo-dig cyclization likely proceeded through initial π-complexation of the alkyne unit followed by interception of the resulting η2-metal species by the adjacent arene ring. The reaction was inherently modular, allowing for substantial structural variations and for the incorporation of substituents at any site of the phenanthrene product. Moreover, it was readily extended to the heterocyclic series as exemplified by the prepn. of benzoindoles, benzocarbazoles, naphthothiophenes, as well as bridgehead nitrogen heterocycles such as pyrrolo[1,2-a]quinolines, e.g., II. Depending on the chosen catalyst, biaryls bearing halo-alkyne units can either be converted into the corresponding 10-halo-phenanthrenes or into the isomeric 9-halo-phenanthrenes; in the latter case, the concomitant 1,2-halide shift was best explained by assuming a metal vinylidene species as the reactive intermediate. The scope of this method for the prepn. of polycyclic arenes was illustrated by the total synthesis of a series of polyoxygenated phenanthrenes that were close relatives of the anticancer agent combretastatin A-4, as well as by the total synthesis of the aporphine alkaloid O-methyl-dehydroisopiline and its naturally occurring sym. dimer.
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    Org. mol. semiconductors are soln. processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of org. semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel mol. and material design, and improved processing conditions. Here we show a method to increase the charge mobility in org. single-crystal field-effect transistors, by taking advantage of the inherent softness of org. semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm2 V-1 s-1 by 70% under 3% strain. In-depth anal. indicates that compressing the crystal structure directly restricts the vibration of the mols., thus suppresses dynamic disorder, a unique mechanism in org. semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance org. devices.
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    A series of π-conjugated 3,10-dialkyl-dinaphtho[1,2-b:2',1'-d]chalcogenophenes incorporating S, Se, and Te as the central chalcogen atom was newly synthesized, and their optoelectronic and charge-transport properties were systematically investigated. High carrier mobilities of up to 4.7 cm2 V-1 s-1 were achieved for soln.-processed org. field-effect transistors using these materials as p-channel org. semiconductors.
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  • Abstract

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    Figure 1

    Figure 1. Molecular structures of representative organic semiconductors.

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    Figure 2

    Figure 2. Molecular designs of first- and second-generation bent-shaped OSCs.

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    Figure 3

    Figure 3. Molecular structures, NICS values (calculated at the HF/6-31+G(d)//B3LYP/6-31G(d) level), HOMO coefficients and energy levels, and dipole moments (calculated at the B3LYP/6-311G(d)//B3LYP/6-31G(d) level) of the (a) DNT-V, (b) DAT-V, (c) DNBDT-N, and (d) TBBT-V OSCs.

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    Figure 4

    Figure 4. Molecular structures, NICS(0) values (calculated at the HF/6-31+G(d)//B3LYP/6-31G(d) level), HOMO and NHOMO coefficients and their energy levels, and dipole moments (calculated at the B3LYP/6-311G(d)//B3LYP/6-31G(d) level) of V-, W-, and zigzag-shaped π-cores.

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    Scheme 1

    Scheme 1. Synthesis of DNT-V Derivativesa
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    aReagents and conditions: (a) n-BuLi, Fe(acac)3, 0 °C to rt, 73% (R = C10H21); (b) BBr3, 0 °C to rt, 94% (R = H), 97% (R = C10H21); (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 78% (R = H), 75% (R = C10H21); (d) 300–320 °C, 81% (R = H), 77% (R = C10H21).

    Scheme 2

    Scheme 2. Modified DNT-V Synthesisa
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    aReagents and conditions: (a) (1) dithiooxamide, DMF, 55 °C, (2) Et3N, rt, 89%; (b) m-CPBA, CH2Cl2, 30 °C, 88%; (c) HI, AcOH, reflux, 97%.

    Scheme 3

    Scheme 3. Synthesis of DAT-Va
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    aReagents and conditions: (a) n-BuLi, Fe(acac)3, 0 °C to rt, 52%; (b) BBr3, 0 °C to rt, 96%; (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 61%; (d) 300 °C, 68%.

    Scheme 4

    Scheme 4. Synthesis of DNBDT-N Derivativesa
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    aReagents and conditions: (a) (1) n-BuLi, ZnCl2, 0 °C to rt, (2) 1,4-dibromo-2,5-dimethoxybenzene, PdCl2(dppp), 50 °C, 87% (R = H), 85% (R = C10H21); (b) BBr3, 0 °C to rt, 81% (R = H), 92% (R = C10H21); (c) dimethylcarbamyl chloride, Et3N, pyridine, THF, 65 °C, 53% (R = H), 72% (R = C10H21); (d) 310–320 °C, 67% (R = H), 64% (R = C10H21).

    Scheme 5

    Scheme 5. Synthesis of TBBT-V Derivativesa
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    aReagents and conditions: (a) C10H21ZnCl2, PdCl2(dppf)·CH2Cl2, toluene, 70 °C, 64%; (b) (5-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 86%; (c) (4-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 92%.

    Scheme 6

    Scheme 6. Synthesis of ChDT Derivativesa
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    aReagents and conditions: (a) (1) n-BuLi, THF, −78 °C, (2) ZnCl2, THF, 0 °C, (3) 3-bromothiophene, Pd2(dba)3·CHCl3, THF, 50 °C, 79%; (b) K2CO3, MeOH, CH2Cl2, rt, 99%; (c) PtCl2, DMF, 80 °C, 58%; (d) (1) LiTMP, THF, −78 °C to −50 °C, (2) 1,2-dibromo-1,1,2,2-tetrachloroethane, −78 °C to rt, 88%; (e) C10H21ZnCl, PdCl2(dppf)·CH2Cl2, THF, 70 °C, 80%; (f) (4-decylthiophen-2-yl)trimethylstannane, Pd(PPh3)4, LiCl, DMF, 100 °C, 81%.

    Figure 5

    Figure 5. Representative slightly bent geometries of C10-DNT-VW and C10-DNBDT-NW (front and side views) in single crystals.

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    Figure 6

    Figure 6. Relation between sign of transfer integral and intermolecular orbital overlap.

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    Figure 7

    Figure 7. Representative packing structures and transfer integrals for (a) C10-DNT-VW and (b) C10-DNT-VV for their HOMOs (and NHOMO).

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    Figure 8

    Figure 8. Representative packing structures and transfer integrals for (a) DNBDT-N and (b) C10-DNBDT-NW.

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    Figure 9

    Figure 9. Representative packing structures and transfer integrals for (a) DNT-W, (b) C10-ChDT, and (c) C10-Th-ChDT.

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    Figure 10

    Figure 10. HOMO band structures and effective masses of (a) C10-DNBDT-NW and (b) C10-ChDT. The origin of energy axis is set to HOMO level of the molecule. Insets show the first Brillouin zone with symmetry points of Γ(0,0,0), Y(0,π/b,0), Z(0,0,π/c), and S(0,π/b,π/c), where b and c are the lattice constants shown in Figures 8b and 9b. The column directions correspond to Γ–Z (C10-DNBDT-NW) and Γ–Y (C10-ChDT) directions in the reciprocal lattice.

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    Figure 11

    Figure 11. Values of t and Δt for ChDT, DNTT, and pentacene.

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    Figure 12

    Figure 12. Schematic diagrams of (a) the manual lamination and (b) edge-casting techniques.

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    Figure 13

    Figure 13. (a) Bottom-gate–top-contact device structure and packing structure of C10-DNBDT-NW on the substrate and (b) optical microscopy image. (c) Transfer and (d) output characteristics of the OFET based on a C10-DNBDT-NW single-crystalline film.

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      Shi, K.; Zhang, F.; Di, C.-A.; Yan, T.-W.; Zou, Y.; Zhou, X.; Zhu, D.; Wang, J.-Y.; Pei, J. Toward High Performance n-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones. J. Am. Chem. Soc. 2015, 137, 6979– 6982,  DOI: 10.1021/jacs.5b00945
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      14
      Toward High Performance n-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones
      Shi, Ke; Zhang, Fengjiao; Di, Chong-An; Yan, Tian-Wei; Zou, Ye; Zhou, Xu; Zhu, Daoben; Wang, Jie-Yu; Pei, Jian
      Journal of the American Chemical Society (2015), 137 (22), 6979-6982CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Three n-type polymers BDPPV, ClBDPPV, and FBDPPV which exhibit outstanding elec. conductivities when mixed with an n-type dopant, N-DMBI ((4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine), in soln. High electron mobility and an efficient doping process endow FBDPPV with the highest elec. conductivities of 14 S cm-1 and power factors up to 28 μW m-1 K-2, which is the highest thermoelec. (TE) power factor that is reported for soln. processable n-type conjugated polymers. The authors' studies reveal that introduction of halogen atoms to the polymer backbones has a dramatic influence on not only the electron mobilities but also the doping levels, both of which are crit. to the elec. conductivities. This work suggests the significance of rational modification of polymer structures and opens the gate for applying the rapidly developed org. semiconductors with high carrier mobilities to thermoelec. field.
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    15. 15
      Schlitz, R. A.; Brunetti, F. G.; Glaudell, A. M.; Miller, P. L.; Brady, M. A.; Takacs, C. J.; Hawker, C. J.; Chabinyc, M. L. Solubility-Limited Extrinsic n-Type Doping of a High Electron Mobility Polymer for Thermoelectric Applications. Adv. Mater. 2014, 26, 2825– 2830,  DOI: 10.1002/adma.201304866
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      15
      Solubility-Limited Extrinsic n-type Doping of a High Electron Mobility Polymer for Thermoelectric Applications
      Schlitz, Ruth A.; Brunetti, Fulvio G.; Glaudell, Anne M.; Miller, P. Levi; Brady, Michael A.; Takacs, Christopher J.; Hawker, Craig J.; Chabinyc, Michael L.
      Advanced Materials (Weinheim, Germany) (2014), 26 (18), 2825-2830CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors have used both N-DMBI and a novel n-type dopant, N-DPBI, to dope P(NDIOD-T2) to conductivities 10"3 S/cm. The only one in one hundred mols. mixed with P(NDIOD-T2) in soln. ultimately contribute a mobile electron to the conduction band of the polymer. Few dopants are elec. active because N-DMBI and N-DPBI are insol. in P(NDIOD-T2) and aggregate on the top surface, leaving the polymer morphol. largely unchanged. The limitations of N-DBI dopants are likely due to this phase segregation and will depend upon the details of the phase diagram blend for any given polymer-dopant pair. Nonetheless, P(NDIOD-T2) exhibits a comparable Seebeck coeff., and thus thermoelec. power factor, to p-type polymers with similar conductivities. P(NDIOD-T2) is a promising candidate for org. thermoelecs. Rational engineering of dopant-polymer miscibility offers promise for greatly improved performance for org. thermoelec. materials with stable carrier concns. in the regime (-IO19-IO21 cm"3) required for most applications. The power factors achieved in this work are far from a fundamental limitation for electron-conducting orgs. and that the development of novel doping strategies with better miscibility offers the potential to optimize both th electron- and hole-transporting elements of thermoelec. generators and coolers for increased performance.
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    16. 16
      Lavieville, R.; Zhang, Y.; Casu, A.; Genovese, A.; Manna, L.; Di Fabrizio, E.; Krahne, R. Charge Transport in Nanoscale “All-Inorganic” Networks of Semiconductor Nanorods Linked by Metal Domains. ACS Nano 2012, 6, 2940– 2947,  DOI: 10.1021/nn3006625
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      16
      Charge Transport in Nanoscale All-Inorganic Networks of Semiconductor Nanorods Linked by Metal Domains
      Lavieville, Romain; Zhang, Yang; Casu, Alberto; Genovese, Alessandro; Manna, Liberato; Di Fabrizio, Enzo; Krahne, Roman
      ACS Nano (2012), 6 (4), 2940-2947CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Charge transport across metal-semiconductor interfaces at the nanoscale is a crucial issue in nanoelectronics. Chains of semiconductor nanorods linked by Au particles represent an ideal model system in this respect, because the metal-semiconductor interface is an intrinsic feature of the nanosystem and does not manifest solely as the contact to the macroscopic external electrodes. Here we investigate charge transport mechanisms in all-inorg. hybrid metal-semiconductor networks fabricated via self-assembly in soln., in which CdSe nanorods were linked to each other by Au nanoparticles. Thermal annealing of our devices changed the morphol. of the networks and resulted in the removal of small Au domains that were present on the lateral nanorod facets, and in ripening of the Au nanoparticles in the nanorod junctions with more homogeneous metal-semiconductor interfaces. In such thermally annealed devices the voltage dependence of the current at room temp. can be well described by a Schottky barrier lowering at a metal semiconductor contact under reverse bias, if the spherical shape of the gold nanoparticles is considered. In this case the natural logarithm of the current does not follow the square-root dependence of the voltage as in the bulk, but that of V2/3. From our fitting with this model we ext. the effective permittivity that agrees well with theor. predictions for the permittivity near the surface of CdSe nanorods. Furthermore, the annealing improved the network conductance at cryogenic temps., which could be related to the redn. of the no. of trap states.
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    17. 17
      Anthony, J. E. Functionalized Acenes and Heteroacenes for Organic Electronics. Chem. Rev. 2006, 106, 5028– 5048,  DOI: 10.1021/cr050966z
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      17
      Functionalized acenes and heteroacenes for organic electronics
      Anthony, John E.
      Chemical Reviews (Washington, DC, United States) (2006), 106 (12), 5028-5048CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review on the functionalization of linearly fused arom. systems specifically for their application in electronic devices. The focus is on studies that deal with crystal structure/device property relationships in linearly fused acenes and heteroacenes.
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    18. 18
      Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J.-L. Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926– 952,  DOI: 10.1021/cr050140x
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      18
      Charge Transport in Organic Semiconductors
      Coropceanu, Veaceslav; Cornil, Jerome; Da Silva Filho, Demetrio A.; Olivier, Yoann; Silbey, Robert; Bredas, Jean-Luc
      Chemical Reviews (Washington, DC, United States) (2007), 107 (4), 926-952CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Both electron and hole transport in org. semiconductors are discussed.
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    19. 19
      Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Thienoacene-Based Organic Semiconductors. Adv. Mater. 2011, 23, 4347– 4370,  DOI: 10.1002/adma.201102007
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      19
      Thienoacene-Based Organic Semiconductors
      Takimiya, Kazuo; Shinamura, Shoji; Osaka, Itaru; Miyazaki, Eigo
      Advanced Materials (Weinheim, Germany) (2011), 23 (38), 4347-4370CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Thienoacenes consist of fused thiophene rings in a ladder-type mol. structure and were intensively studied as potential org. semiconductors for org. field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar mol. structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chem. structures, and elucidates the mol. electronic structure of each class. The packing structures of thienoacenes and the thus-estd. solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the mol. structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relations in thienoacene-based org. semiconductors are discussed. The discussion provides insight into new mol. design strategies for the development of superior org. semiconductors.
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    20. 20
      Liu, C.; Huang, K.; Park, W.-T.; Li, M.; Yang, T.; Liu, X.; Liang, L.; Minari, T.; Noh, Y.-Y. A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers. Mater. Horiz. 2017, 4, 608– 618,  DOI: 10.1039/C7MH00091J
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      20
      A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers
      Liu, Chuan; Huang, Kairong; Park, Won-Tae; Li, Minmin; Yang, Tengzhou; Liu, Xuying; Liang, Lijuan; Minari, Takeo; Noh, Yong-Young
      Materials Horizons (2017), 4 (4), 608-618CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
      The variety of charge transport theories for org. semiconductors (OSCs) raises the question of which models should be selected for each case, and there is a lack of generalized understanding regarding various OSCs over the full range of crystallinity from single crystal to amorphous. Here, we report that the generalized Einstein relation (GER) can unify various theor. models and predict charge transport in OSCs with various crystallinities, by altering the variance of the d. of states and the delocalization degree in a Gaussian-distributed d. of states. The GER also provides a good fitting to much of the exptl. data of temp.- and gate-voltage-dependent mobility for different OSCs in transistors. Consequently, disorders of charge transport in various OSCs can be directly compared in the same map, which reveals how energetic disorder and the delocalization degree det. charge transport in org. devices.
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    21. 21
      Ji, L.-F.; Fan, J.-X.; Qin, G.-Y.; Zhang, N.-X.; Lin, P.-P.; Ren, A.-M. Theoretical Study on the Electronic Structures and Charge Transport Properties of a Series of Rubrene Derivatives. J. Phys. Chem. C 2018, 122, 21226– 21238,  DOI: 10.1021/acs.jpcc.8b07018
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      21
      Theoretical Study on the Electronic Structures and Charge Transport Properties of a Series of Rubrene Derivatives
      Ji, Li-Fei; Fan, Jian-Xun; Qin, Gui-Ya; Zhang, Ning-Xi; Lin, Pan-Pan; Ren, Ai-Min
      Journal of Physical Chemistry C (2018), 122 (37), 21226-21238CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The charge transport properties of rubrene derivs. were systematically studied by d. functional theory and mol. dynamics (MD) simulations. Functionalizing electron-withdrawing groups (-CN, -CF3, or fluorination) on the peripheral phenyls not only enhance the chem. stability of materials but also favor electron injection by lowering the energy levels of frontier MOs and increasing the electron affinities. Derivs. 2-5 and 9, exhibiting packing motifs similar to rubrene but closer π-stacking distances, possess large hole and electron-transfer integrals, significant bandwidths, and small effective masses, suggesting excellent ambipolar semiconductor behavior. The max. hole(electron) mobilities in the Marcus hopping mechanism based on kinetic Monte Carlo simulation can reach 14.0-16.5(1.6-3.5) cm2 V-1 s-1. The antiparallel 2-dimensional brick stacking and twisted backbones of fluorinated derivs. 11 and 12 result in nearly 1-dimensional percolation network but balanced hole and electron transport property. In contrast, the parallel 2-dimensional brick stacking of 14 leads to 2-dimensional percolation network. Their max. hole and electron mobilities fall at 0.5-3.6 and 2.0-4.8 cm2 V-1 s-1. Also, MD simulations show that dynamic disorder is strongly detrimental to the hole transfer but has a little influence on the electron transfer for 1-5. Also, severe twist of backbones of 9 leads to almost 1 order of magnitude lowered mobility. The influences of different substituents on the mol. structure, packing motif, and intermol. reorganization energy are discussed.
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    22. 22
      Wang, Y.; Sun, L.; Wang, C.; Yang, F.; Ren, X.; Zhang, X.; Dong, H.; Hu, W. Organic crystalline materials in flexible electronics. Chem. Soc. Rev. 2019, 48, 1492– 1530,  DOI: 10.1039/C8CS00406D
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      22
      Organic crystalline materials in flexible electronics
      Wang, Yu; Sun, Lingjie; Wang, Cong; Yang, Fangxu; Ren, Xiaochen; Zhang, Xiaotao; Dong, Huanli; Hu, Wenping
      Chemical Society Reviews (2019), 48 (6), 1492-1530CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance org. cryst. materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, mol. diversity, low-cost, soln. processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics. Meanwhile, OCMs also serve as a powerful tool to probe the intrinsic electronic and mech. properties of orgs. and reveal the flexible device physics for further guidance for flexible materials and device design. While the past decades have witnessed huge advances in OCM-based flexible electronics, this review is intended to provide a timely overview of this fascinating field. First, the crystal packing, charge transport, and assembly protocols of OCMs are introduced. State-of-the-art construction strategies for aligned/patterned OCM on/into flexible substrates are then discussed in detail. Following this, advanced OCM-based flexible devices and their potential applications are highlighted. Finally, future directions and opportunities for this field are proposed, in the hope of providing guidance for future research.
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    23. 23
      Gryn’ova, G.; Lin, K.-H.; Corminboeuf, C. Read between the Molecules: Computational Insights into Organic Semiconductors. J. Am. Chem. Soc. 2018, 140, 16370– 16386,  DOI: 10.1021/jacs.8b07985
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      23
      Read between the molecules: computational insights into organic semiconductors
      Gryn'ova, Ganna; Lin, Kun-Han; Corminboeuf, Clemence
      Journal of the American Chemical Society (2018), 140 (48), 16370-16386CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A review. The performance and key electronic properties of mol. org. semiconductors are dictated by the interplay between the chem. of the mol. core and the intermol. factors of which manipulation has inspired both experimentalists and theorists. This perspective presents major computational challenges and modern methodol. strategies to advance the field. The discussion ranges from insights and design principles at the quantum chem. level, in-depth atomistic modeling based on multiscale protocols, morphol. prediction and characterization as well as energy-property maps involving data-driven anal. A personal overview of the past achievements and future direction is also provided.
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    24. 24
      McGarry, K. A.; Xie, W.; Sutton, C.; Risko, C.; Wu, Y.; Young, V. G.; Brédas, J.-L.; Frisbie, C. D.; Douglas, C. J. Rubrene-Based Single-Crystal Organic Semiconductors: Synthesis, Electronic Structure, and Charge-Transport Properties. Chem. Mater. 2013, 25, 2254– 2263,  DOI: 10.1021/cm400736s
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      24
      Rubrene-Based Single-Crystal Organic Semiconductors: Synthesis, Electronic Structure, and Charge-Transport Properties
      McGarry, Kathryn A.; Xie, Wei; Sutton, Christopher; Risko, Chad; Wu, Yanfei; Young, Victor G., Jr.; Bredas, Jean-Luc; Frisbie, C. Daniel; Douglas, Christopher J.
      Chemistry of Materials (2013), 25 (11), 2254-2263CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Correlations among the mol. structure, crystal structure, electronic structure, and charge-carrier transport phenomena were derived from six congeners (2-7) of rubrene (1). The congeners were synthesized via a three-step route from known 6,11-dichloro-5,12-tetracenedione. After crystn., their packing structures were solved using single-crystal x-ray diffraction. Rubrenes 5-7 maintain the orthorhombic features of the parent rubrene (1) in their solid-state packing structures. Control of the packing structure in 5-7 provided the 1st series of systematically manipulated rubrenes that preserve the π-stacking motif of 1. D. functional theory calcns. were performed at the B3LYP/6-31G(d,p) level of theory to evaluate the geometric and electronic structure of each deriv. and reveal that key properties of rubrene (1) were maintained. Intermol. electronic couplings (transfer integrals) were calcd. for each deriv. to det. the propensity for charge-carrier transport. For rubrenes 5-7, evaluations of the transfer integrals and periodic electronic structures suggest these derivs. should exhibit transport characteristics equiv. to, or in some cases improved on, those of the parent rubrene (1), as well as the potential for ambipolar behavior. Single-crystal field-effect transistors were fabricated for 5-7, and these derivs. show ambipolar transport as predicted. Although device architecture has yet to be fully optimized, max. hole (electron) mobilities of 1.54 (0.28) cm2 V-1 s-1 were measured for rubrene 5. This work lays a foundation to improve the authors' understanding of charge-carrier transport phenomena in org. single-crystal semiconductors through the correlation of designed mol. and crystallog. changes to electronic and transport properties.
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    25. 25
      Giri, G.; Verploegen, E.; Mannsfeld, S. C. B.; Atahan-Evrenk, S.; Kim, D. H.; Lee, S. Y.; Becerril, H. A.; Aspuru-Guzik, A.; Toney, M. F.; Bao, Z. Tuning charge transport in solution-sheared organic semiconductors using lattice strain. Nature 2011, 480, 504,  DOI: 10.1038/nature10683
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      25
      Tuning charge transport in solution-sheared organic semiconductors using lattice strain
      Giri, Gaurav; Verploegen, Eric; Mannsfeld, Stefan C. B.; Atahan-Evrenk, Sule; Kim, Do Hwan; Lee, Sang Yoon; Becerril, Hector A.; Aspuru-Guzik, Alan; Toney, Michael F.; Bao, Zhenan
      Nature (London, United Kingdom) (2011), 480 (7378), 504-508CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      A soln.-processing method known as soln. shearing was used to introduce lattice strain to org. semiconductors, thus improving charge carrier mobility.
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    26. 26
      Rühle, V.; Lukyanov, A.; May, F.; Schrader, M.; Vehoff, T.; Kirkpatrick, J.; Baumeier, B.; Andrienko, D. Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors. J. Chem. Theory Comput. 2011, 7, 3335– 3345,  DOI: 10.1021/ct200388s
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      26
      Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors
      Ruehle, Victor; Lukyanov, Alexander; May, Falk; Schrader, Manuel; Vehoff, Thorsten; Kirkpatrick, James; Baumeier, Bjoern; Andrienko, Denis
      Journal of Chemical Theory and Computation (2011), 7 (10), 3335-3345CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
      A review. Charge carrier dynamics in an org. semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the mols. The exact evaluation of these contributions in a mol. assembly is computationally prohibitive. Various, often semiempirical, approxns. are employed instead. The authors review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations, provide a uniform error control for the methods and a flexible platform for their development, and eventually allow in silico prescreening of org. semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum, a common org. semiconductor.
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    27. 27
      Nomura, K.; Ohta, H.; Takagi, A.; Kamiya, T.; Hirano, M.; Hosono, H. Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors. Nature 2004, 432, 488– 492,  DOI: 10.1038/nature03090
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      27
      Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors
      Nomura, Kenji; Ohta, Hiromichi; Takagi, Akihiro; Kamiya, Toshio; Hirano, Masahiro; Hosono, Hideo
      Nature (London, United Kingdom) (2004), 432 (7016), 488-492CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Transparent electronic devices formed on flexible substrates are expected to meet emerging technol. demands where silicon-based electronics cannot provide a soln. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and org. semiconductors have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven org. light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temp. and device performance. Here, we propose to solve this problem by using a novel semiconducting material, namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO), for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temp. and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit satn. mobilities of 6-9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.
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    28. 28
      Kuribara, K.; Wang, H.; Uchiyama, N.; Fukuda, K.; Yokota, T.; Zschieschang, U.; Jaye, C.; Fischer, D.; Klauk, H.; Yamamoto, T.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Sekitani, T.; Loo, Y.-L.; Someya, T. Organic transistors with high thermal stability for medical applications. Nat. Commun. 2012, 3, 723,  DOI: 10.1038/ncomms1721
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      28
      Organic transistors with high thermal stability for medical applications
      Kuribara Kazunori; Wang He; Uchiyama Naoya; Fukuda Kenjiro; Yokota Tomoyuki; Zschieschang Ute; Jaye Cherno; Fischer Daniel; Klauk Hagen; Yamamoto Tatsuya; Takimiya Kazuo; Ikeda Masaaki; Kuwabara Hirokazu; Sekitani Tsuyoshi; Loo Yueh-Lin; Someya Takao
      Nature communications (2012), 3 (), 723 ISSN:.
      The excellent mechanical flexibility of organic electronic devices is expected to open up a range of new application opportunities in electronics, such as flexible displays, robotic sensors, and biological and medical electronic applications. However, one of the major remaining issues for organic devices is their instability, especially their thermal instability, because low melting temperatures and large thermal expansion coefficients of organic materials cause thermal degradation. Here we demonstrate the fabrication of flexible thin-film transistors with excellent thermal stability and their viability for biomedical sterilization processes. The organic thin-film transistors comprise a high-mobility organic semiconductor, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene, and thin gate dielectrics comprising a 2-nm-thick self-assembled monolayer and a 4-nm-thick aluminium oxide layer. The transistors exhibit a mobility of 1.2 cm(2) V(-1)s(-1) within a 2 V operation and are stable even after exposure to conditions typically used for medical sterilization.
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    29. 29
      Payne, M. M.; Parkin, S. R.; Anthony, J. E. Functionalized Higher Acenes: Hexacene and Heptacene. J. Am. Chem. Soc. 2005, 127, 8028– 8029,  DOI: 10.1021/ja051798v
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      29
      Functionalized Higher Acenes: Hexacene and Heptacene
      Payne, Marcia M.; Parkin, Sean R.; Anthony, John E.
      Journal of the American Chemical Society (2005), 127 (22), 8028-8029CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We have extended our functionalization strategy for pentacene to the higher acenes hexacene and heptacene (I,II). Provided a large enough alkyne substituent is used, these large arom. rods are both stable and sol. and can be characterized spectroscopically as well as by single-crystal X-ray diffraction.
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    30. 30
      Tang, M. L.; Okamoto, T.; Bao, Z. High-Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur. J. Am. Chem. Soc. 2006, 128, 16002– 16003,  DOI: 10.1021/ja066824j
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      30
      High-Performance Organic Semiconductors: Asymmetric Linear Acenes Containing Sulphur
      Tang, Ming L.; Okamoto, Toshihiro; Bao, Zhenan
      Journal of the American Chemical Society (2006), 128 (50), 16002-16003CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Two new linear acenes with fused thiophene units were synthesized. These acenes have conjugation lengths between anthracene and pentacene. Thin films of these linear mols. were characterized by UV spectroscopy, x-ray diffraction, at. force microscopy (AFM), and field-effect transistor measurements. Submonolayer AFM studies show growth that greatly resembles pentacene, while thin-film growth is dendritic. Mobilities ≤0.47 cm2 V-1 s-1 were found for the tetraceno[2,3-b]thiophene and are ≤0.15 cm2 V-1 s-1 for anthra[2,3-b]thiophene.
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    31. 31
      Wong, M. Y.; Hedley, G. J.; Xie, G.; Kölln, L. S.; Samuel, I. D. W.; Pertegás, A.; Bolink, H. J.; Zysman-Colman, E. Light-Emitting Electrochemical Cells and Solution-Processed Organic Light-Emitting Diodes Using Small Molecule Organic Thermally Activated Delayed Fluorescence Emitters. Chem. Mater. 2015, 27, 6535– 6542,  DOI: 10.1021/acs.chemmater.5b03245
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      31
      Light-Emitting Electrochemical Cells and Solution-Processed Organic Light-Emitting Diodes Using Small Molecule Organic Thermally Activated Delayed Fluorescence Emitters
      Wong, Michael Y.; Hedley, Gordon J.; Xie, Guohua; Kolln, Lisa S.; Samuel, Ifor D. W.; Pertegas, Antonio; Bolink, Henk J.; Zysman-Colman, Eli
      Chemistry of Materials (2015), 27 (19), 6535-6542CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Two novel charged org. thermally activated delayed fluorescence (TADF) emitters, 1 and 2, have been synthesized. Their TADF behavior is well-supported by the multiexponential decay of their emission (nanosecond and microsecond components) and the oxygen dependence of the photoluminescence quantum yields. Spin-coated electroluminescent devices have been fabricated to make light-emitting electrochem. cells (LEECs) and org. light-emitting diodes (OLEDs). The first example of a non-doped charged small org. mol. LEEC is reported and exhibited an external quantum efficiency (EQE) of 0.39% using 2. With a multilayer architecture, a soln.-processed OLED device using neat 2 as the emitting layer gave an EQE of 5.1%, the highest reported to date for a nondoped soln.-processed small mol. org. TADF OLED. These promising results open up a new area in light-emitting materials for the development of low-cost TADF LEECs.
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    32. 32
      Bin, H.; Yang, Y.; Zhang, Z.-G.; Ye, L.; Ghasemi, M.; Chen, S.; Zhang, Y.; Zhang, C.; Sun, C.; Xue, L.; Yang, C.; Ade, H.; Li, Y. 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor. J. Am. Chem. Soc. 2017, 139, 5085– 5094,  DOI: 10.1021/jacs.6b12826
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      9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor
      Bin, Haijun; Yang, Yankang; Zhang, Zhi-Guo; Ye, Long; Ghasemi, Masoud; Chen, Shanshan; Zhang, Yindong; Zhang, Chunfeng; Sun, Chenkai; Xue, Lingwei; Yang, Changduk; Ade, Harald; Li, Yongfang
      Journal of the American Chemical Society (2017), 139 (14), 5085-5094CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      In the last two years, polymer solar cells (PSCs) developed quickly with n-type org. semiconductor (n-OSs) as acceptor. In contrast, the research progress of nonfullerene org. solar cells (OSCs) with org. small mol. as donor and the n-OS as acceptor lags behind. Here, we synthesized a D-A structured medium bandgap org. small mol. H11 with bithienyl-benzodithiophene (BDTT) as central donor unit and fluorobenzotriazole as acceptor unit, and achieved a power conversion efficiency (PCE) of 9.73% for the all org. small mols. OSCs with H11 as donor and a low bandgap n-OS IDIC as acceptor. A control mol. H12 without thiophene conjugated side chains on the BDT unit was also synthesized for investigating the effect of the thiophene conjugated side chains on the photovoltaic performance of the p-type org. semiconductors (p-OSs). Compared with H12, the 2D-conjugated H11 with thiophene conjugated side chains shows intense absorption, low-lying HOMO energy level, higher hole mobility and ordered bimodal crystallite packing in the blend films. Moreover, a larger interaction parameter (χ) was obsd. in the H11 blends calcd. from Hansen soly. parameters and differential scanning calorimetry measurements. These special features combined with the complementary absorption of H11 donor and IDIC acceptor resulted in the best PCE of 9.73% for nonfullerene all small mol. OSCs up to date. Our results indicate that fluorobenzotriazole based 2D conjugated p-OSs are promising medium bandgap donors in the nonfullerene OSCs.
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    33. 33
      Lin, L.-Y.; Chen, Y.-H.; Huang, Z.-Y.; Lin, H.-W.; Chou, S.-H.; Lin, F.; Chen, C.-W.; Liu, Y.-H.; Wong, K.-T. A Low-Energy-Gap Organic Dye for High-Performance Small-Molecule Organic Solar Cells. J. Am. Chem. Soc. 2011, 133, 15822– 15825,  DOI: 10.1021/ja205126t
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      A Low-Energy-Gap Organic Dye for High-Performance Small-Molecule Organic Solar Cells
      Lin, Li-Yen; Chen, Yi-Hong; Huang, Zheng-Yu; Lin, Hao-Wu; Chou, Shu-Hua; Lin, Francis; Chen, Chang-Wen; Liu, Yi-Hung; Wong, Ken-Tsung
      Journal of the American Chemical Society (2011), 133 (40), 15822-15825CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A novel donor-acceptor-acceptor (D-A-A) donor mol., DTDCTB, in which an electron-donating ditolylaminothienyl moiety and an electron-withdrawing dicyanovinylene moiety are bridged by another electron-accepting 2,1,3-benzothiadiazole block, was synthesized and characterized. A vacuum-deposited org. solar cell employing DTDCTB combined with the electron acceptor C70 achieved a record-high power conversion efficiency (PCE) of 5.81%. The respectable PCE is attributed to the solar spectral response extending to the near-IR region and the ultracompact absorption dipole stacking of the DTDCTB thin film.
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      Sun, Y.; Welch, G. C.; Leong, W. L.; Takacs, C. J.; Bazan, G. C.; Heeger, A. J. Solution-processed small-molecule solar cells with 6.7% efficiency. Nat. Mater. 2012, 11, 44,  DOI: 10.1038/nmat3160
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      Solution-processed small-molecule solar cells with 6.7% efficiency
      Sun, Yanming; Welch, Gregory C.; Leong, Wei Lin; Takacs, Christopher J.; Bazan, Guillermo C.; Heeger, Alan J.
      Nature Materials (2012), 11 (1), 44-48CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Org. photovoltaic devices that can be fabricated by simple processing techniques are under intense investigation in academic and industrial labs. because of their potential to enable mass prodn. of flexible and cost-effective devices. Most of the attention has been focused on soln.-processed polymer bulk-heterojunction solar cells. A combination of polymer design, morphol. control, structural insight and device engineering has led to power conversion efficiencies reaching the 6-8% range for conjugated polymer/fullerene blends. Soln.-processed small-mol. bulk-heterojunction solar cells have received less attention, and their efficiencies have remained below those of their polymeric counterparts. Here, we report efficient soln.-processed small-mol. bulk-heterojunction solar cells based on a new mol. donor, DTS(PTTh2)2. A record power conversion efficiency of 6.7% under air-mass 1.5G irradn. (100 mW/cm2) is achieved for small-mol. bulk-heterojunction devices from DTS(PTTh2)2:PC70BM (donor to acceptor ratio of 7:3). This high efficiency was obtained by using remarkably small percentages of solvent additive (0.25 vol.% of 1,8-diiodooctane) during the film-forming process, which leads to reduced domain sizes in the bulk-heterojunction layer. These results provide important progress for soln.-processed org. photovoltaics and demonstrate that solar cells fabricated from small donor mols. can compete with their polymeric counterparts.
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      Maliakal, A.; Raghavachari, K.; Katz, H.; Chandross, E.; Siegrist, T. Photochemical Stability of Pentacene and a Substituted Pentacene in Solution and in Thin Films. Chem. Mater. 2004, 16, 4980– 4986,  DOI: 10.1021/cm049060k
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      Photochemical Stability of Pentacene and a Substituted Pentacene in Solution and in Thin Films
      Maliakal, Ashok; Raghavachari, Krishnan; Katz, Howard; Chandross, Edwin; Siegrist, Theo
      Chemistry of Materials (2004), 16 (24), 4980-4986CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The org. semiconductor pentacene (1) has shown the highest field effect mobilities in thin films of any org. semiconductor, yet suffers from instability toward oxidn. 6,13-Bis(triisopropylsilylethynyl)pentacene (2) has been reported as an interesting functionalized pentacene which is sol. in common org. solvents and exhibits high carrier mobility (>0.1 cm2/Vs) in thin film transistor devices. In our investigations of 2, we were surprised by its remarkable stability in soln. Using UV-vis spectroscopy we observe that under ambient light conditions, 2 is approx. 50× more stable toward degrdn. in air-satd. THF soln. as compared to unsubstituted pentacene. Previous investigators have implicated oxygen in the mechanism of photodegrdn. of pentacene. In this study, quantum chem. calcns. have been performed which demonstrate that alkynyl functionalization at the 6 and 13 positions reduces the rate of photooxidn. in two ways. First, alkynyl substitution reduces the triplet energy of 2 considerably, thereby preventing singlet oxygen sensitization. Second, alkynyl substitution lowers the LUMO energy for 2 as compared to that of pentacene. We propose that the lower LUMO energy hinders photooxidn. by reducing the rate of electron transfer from photoexcited 2 to oxygen. In thin films, pentacene is more stable to photooxidn. than 2 when exposed to UV irradn. The stabilization of pentacene in the solid state is discussed in the context of solid-state interactions.
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      Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. Synthesis, Morphology, and Field-Effect Mobility of Anthradithiophenes. J. Am. Chem. Soc. 1998, 120, 664– 672,  DOI: 10.1021/ja9728381
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      Synthesis, morphology, and field-effect mobility in anthradithiophenes
      Laquindanum, Joyce G.; Katz, Howard E.; Lovinger, Andrew J.
      Journal of the American Chemical Society (1998), 120 (4), 664-672CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The synthesis, thin-film morphol., and hole mobility in thin-film transistors (TFTs) of compds. based on the novel anthradithiophene (ADT) ring system are reported. The parent compd. and its 2,8-dihexyl, didodecyl, and dioctadecyl derivs. (DHADT, DDADT, and DOADT, resp.), synthesized via alkylated thiophene dicarboxaldehyde acetals, were investigated. They all form highly ordered polycryst. vacuum-evapd. films with mobilities as high as 0.15 cm2/V-s, as high as has ever been obsd. for a polycryst. org. material. DOADT exhibits a mobility of 0.06 cm2/V-s even though 70% of its mol. vol. is occupied by hydrocarbon chains. DHADT was cast from soln. under atm. conditions onto a TFT giving a mobility of 0.01-0.02 cm2/V-s. Thus, the alkylated ADTs combine a pentacene-like intrinsic mobility with greater soly. and oxidative stability.
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      Mishra, A.; Bäuerle, P. Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology. Angew. Chem., Int. Ed. 2012, 51, 2020– 2067,  DOI: 10.1002/anie.201102326
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      Small Molecule Organic Semiconductors on the Move: Promises for Future Solar Energy Technology
      Mishra, Amaresh; Baeuerle, Peter
      Angewandte Chemie, International Edition (2012), 51 (9), 2020-2067CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. This article, written from an org. chemist's point of view, provides an up-to-date overview of org. solar cells based on small mols. or oligomers as absorbers and describes devices that incorporate planar-heterojunctions and bulk heterojunctions between a donor (p-type semiconductor) and an acceptor (n-type semiconductor) material. The article pays particular attention to the design and development of mol. materials and their performance in corresponding devices. In recent years, a substantial amt. of both, academic and industrial research, has been directed towards org. solar cells, in an effort to develop new materials and to improve their tunability, processability, power conversion efficiency, and stability. On the eve of commercialization of org. solar cells, this review provides an overview of efficiencies attained with small mols./oligomers in org. solar cells and summarizes materials and device concepts developed over the last decade. Approaches to enhancing the efficiency of org. solar cells are analyzed.
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      Leung, L. M.; Lo, W. Y.; So, S. K.; Lee, K. M.; Choi, W. K. A High-Efficiency Blue Emitter for Small Molecule-Based Organic Light-Emitting Diode. J. Am. Chem. Soc. 2000, 122, 5640– 5641,  DOI: 10.1021/ja000927z
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      A High-Efficiency Blue Emitter for Small Molecule-Based Organic Light-Emitting Diode
      Leung, Louis M.; Lo, W. Y.; So, S. K.; Lee, K. M.; Choi, W. K.
      Journal of the American Chemical Society (2000), 122 (23), 5640-5641CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A bis(2-Me-8-quinolinolato)Al hydroxide complex (AlMq2OH) is also a high-efficiency blue dye with a single emission max. at 485 nm. The compd. has excellent thermal stability and can be processed similar to Alq3. The synthesis procedures are simple, using chems. that are readily available from com. sources. The blue-shift probably is a result of 2 conditions: (1) The Al complex is trivalent and (2) steric hindrance provided by the 2-Me groups on the 2-Me-8-quinolinol ligands weakened or prohibited the formation of Al-N bonds. Two multilayer small mol. OLEDs using either AlMq2OH or Alq3 as the emission layer were built and their characteristics compared. The OLED cell has a general structure of ITO (72 Ω/sq)/Cu(II) phthalocyanine (10 nm)/N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (50 nm)/emitter, AlMq2OH or Alq3 (80 nm)/Li-F (0.7 nm)/Al(80 nm). The AlMq2OH or Alq3 was evapd. from a homemade Mo boat at a deposition rate of 1 Å/s. At similar c.d. (80 mA/cm2), both the brightness and current efficiency of the AlMq2OH device was 3 times that of Alq3. The max. brightness of the AlMq2OH-based device is 14,000 cd/m at 480 mA/cm2, which is 1 of the highest-intensity blue emitter reported. The slightly higher turn-on voltage for the AlMq2OH device indicates that it has a higher energy barrier for charge injection. The UV-visible absorption, photoluminescence (PL) spectra of AlMq2OH solid thin film on quartz, and the electroluminescence (EL) spectrum of the AlMq2OH-based OLED are shown. Both the EL and PL spectrum of AlMq2OH have a similar shape, a single emission max. at 485 nm and a FWHM of 80 nm. The 50 nm blue-shift for the 2-Me-8-quinolinol based complex is consistent with similar dyes without the Al-N bonding. Steric hindrance was required to reduce the metal-N bonding, and therefore the required blue-shift was provided by the two 2-Me-8-quinolinol ligands, irresp. of the size of the third phenoxy group. The authors have also studied other Mq-based complexes using metals from groups III-B to IV-A. In general, the blue-shift is related to the size of the metal atom, its coordination no. and the acidity of the metal group. In general, divalent complexes have none or min. blue-shift, and the stability of the complexes decreased with an increase in the size of the metal atom. The AlMq2OH complex described here is among the highest-efficiency blue emitter reported, yet it can be processed using methods similar to that for Alq3. The complex itself is stable both under air and high temps. The TGA results of AlMq2OH compared to those for Alq3 under N2 atmosphere are shown. A yellowish side-product with EL and PL similar to that for Alq3, however, was collected during the train sublimation process. It has a lower mol. mass compared to that of AlMq2OH as obsd. from the lower temps. required for sublimation. Results from MS and elemental anal. indicated its chem. compn. was AlMq2, which may be a degrdn. product of the less stable AlMq2Ac. The reestablishment of the Al-N bonds after losing the third ligand confirmed that steric hindrance prohibiting the formation of metal-N bonding was the cause for the blue-shift.
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      Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Electron Transport Materials for Organic Light-Emitting Diodes. Chem. Mater. 2004, 16, 4556– 4573,  DOI: 10.1021/cm049473l
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      Electron Transport Materials for Organic Light-Emitting Diodes
      Kulkarni, Abhishek P.; Tonzola, Christopher J.; Babel, Amit; Jenekhe, Samson A.
      Chemistry of Materials (2004), 16 (23), 4556-4573CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      A review. A comprehensive review of the literature on electron transport materials (ETMs) used to enhance the performance of org. light-emitting diodes (OLEDs) is presented. The structure-property-performance relations of many classes of ETMs, both small-mol.- and polymer-based, that were widely used to improve OLED performance through control of charge injection, transport, and recombination are highlighted. The mol. architecture, electronic structure (electron affinity and ionization potential), thin film processing, thermal stability, morphol., and electron mobility of diverse org. ETMs are discussed and related to their effectiveness in improving OLED performance (efficiency, brightness, and drive voltage). Some issues relating to the exptl. procedures for the estn. of relevant material properties such as electron affinity and electron mobility are discussed. The design of multifunctional electroluminescent polymers whereby light emission and electron- and hole-transport properties are combined in 1 material to achieve efficient single-layer OLEDs is also discussed. The review concludes with a brief perspective on the challenges that future research should address.
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      Liu, Y.; Li, C.; Ren, Z.; Yan, S.; Bryce, M. R. All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Nat. Rev. Mater. 2018, 3, 18020,  DOI: 10.1038/natrevmats.2018.20
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      All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes
      Liu, Yuchao; Li, Chensen; Ren, Zhongjie; Yan, Shouke; Bryce, Martin R.
      Nature Reviews Materials (2018), 3 (4), 18020CODEN: NRMADL; ISSN:2058-8437. (Nature Research)
      Thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both singlet and triplet excitons without noble metals, are emerging as next-generation org. electroluminescent materials. In the past few years, there have been rapid advances in mol. design criteria, our understanding of the photophysics underlying TADF and the applications of TADF materials as emitters in org. light-emitting diodes (OLEDs). This topic is set to remain at the forefront of research in optoelectronic org. materials for the foreseeable future. In this Review, we focus on state-of-the-art materials design and understanding of the photophys. processes, which are being leveraged to optimize the performance of OLED devices. Notably, we also appraise dendritic and polymeric TADF emitters - macromol. materials that offer the potential advantages of low cost, soln. processable and large-area OLED fabrication.
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      Klauk, H.; Halik, M.; Zschieschang, U.; Schmid, G.; Radlik, W.; Weber, W. High-mobility polymer gate dielectric pentacene thin film transistors. J. Appl. Phys. 2002, 92, 5259– 5263,  DOI: 10.1063/1.1511826
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      High-mobility polymer gate dielectric pentacene thin film transistors
      Klauk, Hagen; Halik, Marcus; Zschieschang, Ute; Schmid, Gunter; Radlik, Wolfgang; Weber, Werner
      Journal of Applied Physics (2002), 92 (9), 5259-5263CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      The authors have fabricated pentacene org. thin film transistors with spin-coated polymer gate dielec. layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent elec. characteristics, including carrier mobility as large as 3 cm2/Vs, subthreshold swing ≥1.2 V/decade, and on/off current ratio of 105. For comparison, the authors have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielec. and obtained carrier mobilities as large as 1 cm2/Vs and subthreshold swing ≥0.5 V/decade.
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      Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. Highly Soluble [1]Benzothieno[3,2-b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 15732– 15733,  DOI: 10.1021/ja074841i
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      Highly Soluble [1]Benzothieno[3,2-b]benzothiophene (BTBT) Derivatives for High-Performance, Solution-Processed Organic Field-Effect Transistors
      Ebata, Hideaki; Izawa, Takafumi; Miyazaki, Eigo; Takimiya, Kazuo; Ikeda, Masaaki; Kuwabara, Hirokazu; Yui, Tatsuto
      Journal of the American Chemical Society (2007), 129 (51), 15732-15733CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      2,7-Dialkyl[1]benzothieno[3,2-b]benzothiophenes were tested as soln.-processible mol. semiconductors. Thin films of the org. semiconductors deposited on Si/SiO2 substrates by spin coating have well-ordered structures as confirmed by XRD anal. Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of ∼107.
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      Yamamoto, T.; Takimiya, K. Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2‘,3′-f]chalcogenopheno[3,2-b]chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224– 2225,  DOI: 10.1021/ja068429z
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      Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3-b:2',3'-f]chalcogenopheno[3,2-b]chalcogenophenes, and Their Application to Field-Effect Transistors
      Yamamoto, Tatsuya; Takimiya, Kazuo
      Journal of the American Chemical Society (2007), 129 (8), 2224-2225CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A facile three-step synthetic procedure for highly π-extended heteroarenes, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) and dinaphtho[2,3-b:2',3'-f]selenopheno[3,2-b]selenophene (DNSS), was established. Soln. UV-visible spectra and electrochem. indicated that they have relatively low-lying HOMO levels and large HOMO-LUMO energy gaps. OFET devices fabricated with evapd. thin-films of DNTT and DNSS showed excellent FET characteristics in air, and the highest field-effect mobility of DNTT- and DNSS-based OFETs is 2.9 and 1.9 cm2 V-1 s-1, resp.
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    44. 44
      Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics. Chem. Rev. 2012, 112, 2208– 2267,  DOI: 10.1021/cr100380z
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      44
      Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics
      Wang, Chengliang; Dong, Huanli; Hu, Wenping; Liu, Yunqi; Zhu, Daoben
      Chemical Reviews (Washington, DC, United States) (2012), 112 (4), 2208-2267CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review.
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    45. 45
      Curtis, M. D.; Cao, J.; Kampf, J. W. Solid-State Packing of Conjugated Oligomers: From π-Stacks to the Herringbone Structure. J. Am. Chem. Soc. 2004, 126, 4318– 4328,  DOI: 10.1021/ja0397916
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      45
      Solid-State Packing of Conjugated Oligomers: From π-Stacks to the Herringbone Structure
      Curtis, M. David; Cao, Jie; Kampf, Jeff W.
      Journal of the American Chemical Society (2004), 126 (13), 4318-4328CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The solid-state structures of a series of bithiazole and thiophene oligomers, as well as a series of substituted pentacenes, are rationalized in terms of "pitch and roll" inclinations from an "ideal" cofacial π-stack. Pitch inclinations translate adjacent mols. relative to one another in the direction of the long mol. axis, whereas roll inclinations translate the mols. along the short mol. axis. Thus, moderately large pitch distortions preserve π-π interactions between adjacent mols., whereas roll translations greater than 2.5 Å essentially destroy π-π overlap between adjacent mols. The familiar herringbone packing is characterized by large roll distortions. It is shown that thiophenes tend to exhibit large roll translations, whereas thiazoles have small roll but large pitch translations. Substituted pentacenes tend to have both moderate pitch and roll distances. The relationship of mol. packing to transport properties is discussed.
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      Purushothaman, B.; Bruzek, M.; Parkin, S. R.; Miller, A.-F.; Anthony, J. E. Synthesis and Structural Characterization of Crystalline Nonacenes. Angew. Chem., Int. Ed. 2011, 50, 7013– 7017,  DOI: 10.1002/anie.201102671
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      Synthesis and Structural Characterization of Crystalline Nonacenes
      Purushothaman, Balaji; Bruzek, Matthew; Parkin, Sean R.; Miller, Anne-Frances; Anthony, John E.
      Angewandte Chemie, International Edition (2011), 50 (31), 7013-7017, S7013/1-S7013/13CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The title compds. I (R = CHMe2, CHMeEt, cyclopentyl) were prepd. by alkylation of the corresponding quinones with alkynylsilanes followed by deoxygenation using SnCl2. The optoelectronic properties were explored via absorption and emission spectra, UV-Vis/NIR and EPR spectra. Crystallog. anal. revealed the presence of the conjugated nonacene chromophores.
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      Anthony, J. E. The Larger Acenes: Versatile Organic Semiconductors. Angew. Chem., Int. Ed. 2008, 47, 452– 483,  DOI: 10.1002/anie.200604045
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      The larger acenes: versatile organic semiconductors
      Anthony, John E.
      Angewandte Chemie, International Edition (2008), 47 (3), 452-483CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Acenes have long been the subject of intense study because of the unique electronic properties assocd. with their π-bond topol. Recent reports of impressive semiconductor properties of larger homologs have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purifn., as well as for fabricating org. electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in soln. These new functionalization strategies have recently gave acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as study of their assocd. structure/property relations.
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      Uemura, T.; Hirose, Y.; Uno, M.; Takimiya, K.; Takeya, J. Very High Mobility in Solution-Processed Organic Thin-Film Transistors of Highly Ordered [1]Benzothieno[3,2-b]benzothiophene Derivatives. Appl. Phys. Express 2009, 2, 111501,  DOI: 10.1143/APEX.2.111501
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      48
      Very high mobility in solution-processed organic thin-film transistors of highly ordered [1]benzothieno[3,2-b]benzothiophene derivatives
      Uemura, Takafumi; Hirose, Yuri; Uno, Mayumi; Takimiya, Kazuo; Takeya, Jun
      Applied Physics Express (2009), 2 (11), 111501/1-111501/3CODEN: APEPC4; ISSN:1882-0778. (Japan Society of Applied Physics)
      Field-effect mobility as high as 5 cm2/(V s) is achieved in soln.-processed org. thin-film transistors with the development of a method for growing highly-oriented cryst. films of [1]benzothieno[3,2-b]benzothiophene derivs. A droplet of the soln. is sustained at an edge of a structure on an inclined substrate, so that the cryst. domain grows in the direction of inclination. The oriented growth realizes excellent mol. ordering that manifests itself in micrometer-scale mol. terraces on the surface as a result of the self-organizing function of the material. The unprecedented performance achieved using an easy fabrication process has increased attractiveness of org. thin-film transistors for industrial applications.
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      Soeda, J.; Uemura, T.; Okamoto, T.; Mitsui, C.; Yamagishi, M.; Takeya, J. Inch-Size Solution-Processed Single-Crystalline Films of High-Mobility Organic Semiconductors. Appl. Phys. Express 2013, 6, 076503,  DOI: 10.7567/APEX.6.076503
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      Inch-size solution-processed single-crystalline films of high-mobility organic semiconductors
      Soeda, Junshi; Uemura, Takafumi; Okamoto, Toshihiro; Mitsui, Chikahiko; Yamagishi, Masakazu; Takeya, Jun
      Applied Physics Express (2013), 6 (7), 076503/1-076503/4CODEN: APEPC4; ISSN:1882-0778. (Japan Society of Applied Physics)
      A method for continuously growing large-domain org. semiconductor crystals is developed to fabricate multi-array high-mobility org. transistors. An org. semiconductor soln. is held at the edge of a moving blade to grow a large-area cryst. thin film. The continuous evapn. of the solvent at around 100°C, while the soln. is supplied at the same rate, allows the org. crystals to grow steadily on the substrate to several inches in size. The performance of the arrays of field-effect transistors based on the large-domain crystal films is excellent, with mobility of 5-10 cm2V-1s-1.
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      Yamamura, A.; Watanabe, S.; Uno, M.; Mitani, M.; Mitsui, C.; Tsurumi, J.; Isahaya, N.; Kanaoka, Y.; Okamoto, T.; Takeya, J. Wafer-scale, layer-controlled organic single crystals for high-speed circuit operation. Sci. Adv. 2018, 4, eaao5758  DOI: 10.1126/sciadv.aao5758
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      Yamamura, A.; Matsui, H.; Uno, M.; Isahaya, N.; Tanaka, Y.; Kudo, M.; Ito, M.; Mitsui, C.; Okamoto, T.; Takeya, J. Painting Integrated Complementary Logic Circuits for Single-Crystal Organic Transistors: A Demonstration of a Digital Wireless Communication Sensing Tag. Adv. Electron. Mater. 2017, 3, 1600456,  DOI: 10.1002/aelm.201600456
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      Kang, M. J.; Doi, I.; Mori, H.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H. Alkylated Dinaphtho[2,3-b:2′,3′-f]Thieno[3,2-b]Thiophenes (Cn-DNTTs): Organic Semiconductors for High-Performance Thin-Film Transistors. Adv. Mater. 2011, 23, 1222– 1225,  DOI: 10.1002/adma.201001283
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      Alkylated Dinaphtho[2,3-b:2',3'-f]Thieno[3,2-b]Thiophenes (Cn-DNTTs): Organic Semiconductors for High-Performance Thin-Film Transistors
      Kang, Myeong Jin; Doi, Iori; Mori, Hiroki; Miyazaki, Eigo; Takimiya, Kazuo; Ikeda, Masaaki; Kuwabara, Hirokazu
      Advanced Materials (Weinheim, Germany) (2011), 23 (10), 1222-1225CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A series of Cn-DNTTs are synthesized and evaluated as p-channel org. semiconductors for vapor processed OTFTs. the OTFTs showed typical p-channel FET responses with good mobilities, and among them, the C10-DNTT-based devices gave the best TFT characteristics with mobilities of close to 8.0 cm2V-1s-1, which are among the highest ever reported for org. thin-film-based transistors. the present results indicate that the combination of a π-extended heteroarene core with long alkyl groups provide a chance to develop superior org. semiconductors. To elucidate the relationship between the electronic properties and the solid-state structure, the characterization of Cn-DNTT thin films as well as bulk single crystals is now being actively conducted in our group.
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      Iino, H.; Usui, T.; Hanna, J.-i. Liquid crystals for organic thin-film transistors. Nat. Commun. 2015, 6, 6828,  DOI: 10.1038/ncomms7828
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      Liquid crystals for organic thin-film transistors
      Iino, Hiroaki; Usui, Takayuki; Hanna, Jun-ichi
      Nature Communications (2015), 6 (), 6828CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Cryst. thin films of org. semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. However, there are currently two main problems, which are assocd. with inhomogeneity and poor thermal durability of these films. Here we report that liq. cryst. materials exhibiting a highly ordered liq. crystal phase of smectic E (SmE) can solve both these problems. We design a SmE liq. cryst. material, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), for FETs and synthesize it. This material provides uniform and molecularly flat polycryst. thin films reproducibly when SmE precursor thin films are crystd., and also exhibits high durability of films up to 200 °C. In addn., the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm2 V-1 s-1) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs. We anticipate the use of SmE liq. crystals in soln.-processed FETs may help overcome upcoming difficulties with novel technologies for printed electronics.
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    54. 54
      Inoue, S.; Minemawari, H.; Tsutsumi, J. y.; Chikamatsu, M.; Yamada, T.; Horiuchi, S.; Tanaka, M.; Kumai, R.; Yoneya, M.; Hasegawa, T. Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystals. Chem. Mater. 2015, 27, 3809– 3812,  DOI: 10.1021/acs.chemmater.5b00810
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      54
      Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystals
      Inoue, Satoru; Minemawari, Hiromi; Tsutsumi, Jun'ya; Chikamatsu, Masayuki; Yamada, Toshikazu; Horiuchi, Sachio; Tanaka, Mutsuo; Kumai, Reiji; Yoneya, Makoto; Hasegawa, Tatsuo
      Chemistry of Materials (2015), 27 (11), 3809-3812CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The authors systematically studied the effects of the substituted alkyl chain length on soln.-processable layered cryst. org. semiconductors, 7-alkyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophenes (Ph-BTBT-Cn; 0 ≤ n ≤ 14). The solubilities of the compds. in org. solvents sharply increased with increasing alkyl chain length at n ≤ 3, but decreased gradually at 5 ≤ n; these latter compds. exhibit liq.-crystal phases at high temp. The properties are strongly correlated with the alkyl length dependence of the layered mol. packing, as revealed by single-crystal structural anal.: compds. with n ≤ 4 do not form independent alkyl chain layers, whereas those with 5 ≤ n form isomorphous bilayer-type crystal structures in which independent alkyl chain layers are formed and enhance the cohesive energy of the crystals.
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    55. 55
      He, K.; Li, W.; Tian, H.; Zhang, J.; Yan, D.; Geng, Y.; Wang, F. Asymmetric Conjugated Molecules Based on [1]Benzothieno[3,2-b][1]benzothiophene for High-Mobility Organic Thin-Film Transistors: Influence of Alkyl Chain Length. ACS Appl. Mater. Interfaces 2017, 9, 35427– 35436,  DOI: 10.1021/acsami.7b10675
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      55
      Asymmetric conjugated molecules based on [1]Benzothieno[3,2-b][1]benzothiophene for high-mobility organic thin-film transistors: influence of alkyl chain length
      He, Keqiang; Li, Weili; Tian, Hongkun; Zhang, Jidong; Yan, Donghang; Geng, Yanhou; Wang, Fosong
      ACS Applied Materials & Interfaces (2017), 9 (40), 35427-35436CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Herein, the authors report the synthesis and characterization of a series of [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based asym. conjugated mols., i.e., 2-(5-alkylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-Tn, in which T and n represent thiophene and the no. of carbons in the alkyl group, resp.). Alkyl chain length has a noticeable influence on the microstructures of vacuum-deposited films and therefore on the performance of the org. thin-film transistors (OTFTs). All mols. except for 2-(thiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-ethylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed OTFT mobilities above 5 cm2 V-1 s-1. 2-(5-Hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-heptylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed the greatest OTFT performance with reliable hole mobilities (μ) up to 10.5 cm2 V-1 s-1 because they formed highly ordered and homogeneous films with diminished grain boundaries.
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    56. 56
      Grigoriadis, C.; Niebel, C.; Ruzié, C.; Geerts, Y. H.; Floudas, G. Order, Viscoelastic, and Dielectric Properties of Symmetric and Asymmetric Alkyl[1]benzothieno[3,2-b][1]benzothiophenes. J. Phys. Chem. B 2014, 118, 1443– 1451,  DOI: 10.1021/jp412422e
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      56
      Order, Viscoelastic, and Dielectric Properties of Symmetric and Asymmetric Alkyl[1]benzothieno[3,2-b][1]benzothiophenes
      Grigoriadis, Christos; Niebel, Claude; Ruzie, Christian; Geerts, Yves H.; Floudas, George
      Journal of Physical Chemistry B (2014), 118 (5), 1443-1451CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      The morphol., the viscoelastic, the dielec. properties and the dynamics of phase transformation are studied in sym. and asym. substituted alkyl[1]benzothieno[3,2-b][1]benzothiophenes (C8-BTBT) by X-ray scattering, rheol., and dielec. spectroscopy (DS). The interlayer spacing reflects the mol. and supramol. ordering, resp., in the sym. and asym. substituted BTBTs. In the asym. BTBT, the core layer is double in size with a broader network of intermol. interactions though the increased S-S contacts that is prerequisite for the development of high performance OFET devices. Two crystal states with elastic and viscoelastic responses were identified in the sym. compd. In contrast, the SmA phase in the asym. compd. is a viscoelastic solid. A path-dependent dielec. environment with a switchable dielec. permittivity was found in both compds. by cooling below 0 °C with possible implications to charge transport. The kinetics of phase transformation to the cryst. and SmA phases revealed a nucleation and growth mechanism with rates dominated by the low activation barriers.
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    57. 57
      Inoue, S.; Shinamura, S.; Sadamitsu, Y.; Arai, S.; Horiuchi, S.; Yoneya, M.; Takimiya, K.; Hasegawa, T. Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors. Chem. Mater. 2018, 30, 5050– 5060,  DOI: 10.1021/acs.chemmater.8b01339
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      57
      Extended and modulated thienothiophenes for thermally durable and solution-processable organic semiconductors
      Inoue, Satoru; Shinamura, Shoji; Sadamitsu, Yuichi; Arai, Shunto; Horiuchi, Sachio; Yoneya, Makoto; Takimiya, Kazuo; Hasegawa, Tatsuo
      Chemistry of Materials (2018), 30 (15), 5050-5060CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Herein, we report the rational design of practical small-mol. org. semiconductors based on a π-electron skeleton of benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asym. substitutions with the Ph group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) and benzothieno[3,2-b]benzothiophene (BTBT), although the solvent soly. for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and Ph group remains extremely low. We show in the BTBT and BTNT derivs. that the tuning of the substituting position works to slightly bend the rodlike org. semiconductor mols. and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (b-LHB) packing for the asym. rodlike mols. This modification eventually leads to an increase in solvent soly., a decrease in phase transition temp., and the suppression of liq.-cryst. phases at high temps. By using the substituting effect, we successfully achieve the org. semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent soly. and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermol. transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact org. thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepd. films, because the thermal treatment stabilizes the b-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of org. semiconductor materials for practical printed electronics applications.
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    58. 58
      Diao, Y.; Tee, B. C. K.; Giri, G.; Xu, J.; Kim, D. H.; Becerril, H. A.; Stoltenberg, R. M.; Lee, T. H.; Xue, G.; Mannsfeld, S. C. B.; Bao, Z. Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains. Nat. Mater. 2013, 12, 665,  DOI: 10.1038/nmat3650
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      58
      Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains
      Diao, Ying; Tee, Benjamin C.-K.; Giri, Gaurav; Xu, Jie; Kim, Do Hwan; Becerril, Hector A.; Stoltenberg, Randall M.; Lee, Tae Hoon; Xue, Gi; Mannsfeld, Stefan C. B.; Bao, Zhenan
      Nature Materials (2013), 12 (7), 665-671CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Soln. coating of org. semiconductors offers great potential for achieving low-cost manufg. of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale prodn. poses challenges to the control of thin-film morphol. Here, the authors report an approach-termed fluid-enhanced crystal engineering (FLUENCE)-that allows for a high degree of morphol. control of soln.-printed thin films. The authors designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, the authors demonstrate the fast coating and patterning of millimeter-wide, centimeter-long, highly aligned single-cryst. org. semiconductor thin films. In particular, the authors fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having nonequil. single-cryst. domains and an unprecedented av. and max. mobilities. FLUENCE of org. semiconductors with nonequil. single-cryst. domains may find use in the fabrication of high-performance, large-area printed electronics.
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    59. 59
      Nakayama, K.; Hirose, Y.; Soeda, J.; Yoshizumi, M.; Uemura, T.; Uno, M.; Li, W.; Kang, M. J.; Yamagishi, M.; Okada, Y.; Miyazaki, E.; Nakazawa, Y.; Nakao, A.; Takimiya, K.; Takeya, J. Patternable Solution-Crystallized Organic Transistors with High Charge Carrier Mobility. Adv. Mater. 2011, 23, 1626– 1629,  DOI: 10.1002/adma.201004387
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      59
      Patternable Solution-Crystallized Organic Transistors with High Charge Carrier Mobility
      Nakayama, Kengo; Hirose, Yuri; Soeda, Junshi; Yoshizumi, Masahiro; Uemura, Takafumi; Uno, Mayumi; Li, Wanyan; Kang, Myeong Jin; Yamagishi, Masakazu; Okada, Yugo; Miyazaki, Eigo; Nakazawa, Yasuhiro; Nakao, Akiko; Takimiya, Kazuo; Takeya, Jun
      Advanced Materials (Weinheim, Germany) (2011), 23 (14), 1626-1629CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Newly developed arrays of patterned cryst. OFETs of air-stable compd. 2,9-didecyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C10-DNTT) formed from hot soln. are presented. A method of oriented growth is introduced to provide the single-cryst. films of C10-DNTT that regulates the crystg. direction and positions in a single process. The benchmark value, 10 cm2V-1s-1, of the charge mobility is achieved for the present OFETs, far exceeding the performance of former devices and opening a practical way to realize printed and flexible electronics with sufficient switching speed. The result is attributed to almost perfect mol. periodicity in the crystal films, which allows effective intermol. charge transport of the electrons.
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    60. 60
      Yuan, Y.; Giri, G.; Ayzner, A. L.; Zoombelt, A. P.; Mannsfeld, S. C. B.; Chen, J.; Nordlund, D.; Toney, M. F.; Huang, J.; Bao, Z. Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method. Nat. Commun. 2014, 5, 3005,  DOI: 10.1038/ncomms4005
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      Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method
      Yuan Yongbo; Huang Jinsong; Giri Gaurav; Zoombelt Arjan P; Bao Zhenan; Ayzner Alexander L; Mannsfeld Stefan C B; Nordlund Dennis; Toney Michael F; Chen Jihua
      Nature communications (2014), 5 (), 3005 ISSN:.
      Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.
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      Iino, H.; Kobori, T.; Hanna, J.-i. Improved thermal stability in organic FET fabricated with a soluble BTBT derivative. J. Non-Cryst. Solids 2012, 358, 2516– 2519,  DOI: 10.1016/j.jnoncrysol.2012.03.021
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      Improved thermal stability in organic FET fabricated with a soluble BTBT derivative
      Iino, Hiroaki; Kobori, Takeo; Hanna, Jun-ichi
      Journal of Non-Crystalline Solids (2012), 358 (17), 2516-2519CODEN: JNCSBJ; ISSN:0022-3093. (Elsevier B.V.)
      We have synthesized a new benzothienobenzothiophene (BTBT) deriv., 2-octylthienylbenzothienobenzothiophene having a highly ordered liq. crystal phase of smectic E (SmE) in the temp. range next to its crystal phase, fabricated its polycryst. thin films by spin-coating technique, and applied them to field effect transistors (FETs). Thanks to the liq. crystal phase as a precursor of polycryst. thin films, the resulting films were molecularly flat and uniform. The thermal stability of the thin films was very much improved compared with dialkyl BTBT derivs. because of the solid-like nature of the SmE phase up to 180 °C. The FETs fabricated with films after solvent vapor annealing with toluene showed high FET mobility of 1.4 ± 0.3 cm2/V s. As expected, the FETs were not destroyed by thermal load up to 150 °C. The FET mobility was recovered to 0.54 cm2/V s by the solvent vapor annealing, although the FET mobility was decreased by the thermal load. Highly ordered liq. cryst. phases provide us with easy fabrication of quality polycryst. thin films and high thermal stability of the polycryst. thin films.
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      Okamoto, K.; Kawamura, T.; Sone, M.; Ogino, K. Study on liquid crystallinity in 2,9-dialkylpentacenes. Liq. Cryst. 2007, 34, 1001– 1007,  DOI: 10.1080/02678290701478970
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      Study on liquid crystallinity in 2,9-dialkylpentacenes
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      A series of semiconducting and sym. 2,9-dialkylpentacenes was successfully synthesized via a five-step process and their structures confirmed by 1H NMR, IR and elemental analyses. Their liq. crystallinity was investigated by differential scanning calorimetry and polarizing optical microscopy. The introduction of alkyl chains also improved their soly. For alkyl chains longer than Bu, focal conic or baton texture was obsd., indicating the existence of an ordered smectic phase. Thermal analyses revealed that the both melting and smectic-isotropic transition temps. show an odd-even effect when the alkyl chain is larger than heptyl or octyl. The synthesized compds. are promising candidates for semiconductors in org. field-effect transistors because their liq. crystallinity allows easy mol. alignment in the device fabrication process.
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      Fratini, S.; Ciuchi, S.; Mayou, D.; de Laissardière, G. T.; Troisi, A. A map of high-mobility molecular semiconductors. Nat. Mater. 2017, 16, 998,  DOI: 10.1038/nmat4970
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      A map of high-mobility molecular semiconductors
      Fratini, S.; Ciuchi, S.; Mayou, D.; Trambly de Laissardiere, G.; Troisi, A.
      Nature Materials (2017), 16 (10), 998-1002CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
      The charge mobility of mol. semiconductors is limited by the large fluctuation of intermol. transfer integrals, often referred to as off-diagonal dynamic disorder, which causes transient localization of the carriers' eigenstates. Using a recently developed theor. framework, the authors show here that the electronic structure of the mol. crystals dets. its sensitivity to intermol. fluctuations. The authors build a map of the transient localization lengths of high-mobility mol. semiconductors to identify what patterns of nearest-neighbor transfer integrals in the two-dimensional (2D) high-mobility plane protect the semiconductor from the effect of dynamic disorder and yield larger mobility. Such a map helps rationalizing the transport properties of the whole family of mol. semiconductors and is also used to demonstrate why common textbook approaches fail in describing this important class of materials. These results can be used to rapidly screen many compds. and design new ones with optimal transport characteristics.
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      Troisi, A.; Orlandi, G.; Anthony, J. E. Electronic Interactions and Thermal Disorder in Molecular Crystals Containing Cofacial Pentacene Units. Chem. Mater. 2005, 17, 5024– 5031,  DOI: 10.1021/cm051150h
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      Electronic Interactions and Thermal Disorder in Molecular Crystals Containing Cofacial Pentacene Units
      Troisi, Alessandro; Orlandi, Giorgio; Anthony, John E.
      Chemistry of Materials (2005), 17 (20), 5024-5031CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The authors computed the intermol. electronic coupling and the band structure of three pentacene derivs. that stack cofacially in one or two dimensions. The authors rationalize the results building a map of the coupling between HOMOs and LUMOs of isolated pentacene mols. as a function of the relative mol. orientation and finding the position on such map of the actual mol. pairs. The apparently chaotic dependence of the intermol. coupling from the crystal structure is explained, and directions for the design of materials with improved elec. transport properties are given. The authors run mol. dynamics simulations to explore the variation of the intermol. coupling due to the thermal motions. Even in the crystal phase, the limited conformational space explored at room temp. is large enough to produce consistent variation in the intermol. coupling. The consequences of this finding on the practicability of the transport properties of org. materials are analyzed.
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      Ciuchi, S.; Fratini, S. Electronic transport and quantum localization effects in organic semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 245201,  DOI: 10.1103/PhysRevB.86.245201
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      Electronic transport and quantum localization effects in organic semiconductors
      Ciuchi, S.; Fratini, S.
      Physical Review B: Condensed Matter and Materials Physics (2012), 86 (24), 245201/1-245201/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      We explore the charge transport mechanism in org. semiconductors based on a model that accounts for the thermal intermol. disorder at work in pure cryst. compds., as well as extrinsic sources of disorder that are present in current exptl. devices. Starting from the Kubo formula, we describe a theor. framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent cond. The electron mobility is then calcd. through a relaxation time approxn. that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a "transient localization" phenomenon is shown to be a general feature of org. semiconductors that is compatible with the bandlike temp. dependence of the mobility obsd. in pure compds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temp., which is progressively suppressed upon increasing the carrier concn., as is commonly obsd. in org. field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenol. considerations that are commonly used in the literature.
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      Illig, S.; Eggeman, A. S.; Troisi, A.; Jiang, L.; Warwick, C.; Nikolka, M.; Schweicher, G.; Yeates, S. G.; Henri Geerts, Y.; Anthony, J. E.; Sirringhaus, H. Reducing dynamic disorder in small-molecule organic semiconductors by suppressing large-amplitude thermal motions. Nat. Commun. 2016, 7, 10736,  DOI: 10.1038/ncomms10736
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      Reducing dynamic disorder in small-molecule organic semiconductors by suppressing large-amplitude thermal motions
      Illig, Steffen; Eggeman, Alexander S.; Troisi, Alessandro; Jiang, Lang; Warwick, Chris; Nikolka, Mark; Schweicher, Guillaume; Yeates, Stephen G.; Henri Geerts, Yves; Anthony, John E.; Sirringhaus, Henning
      Nature Communications (2016), 7 (), 10736CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Thermal vibrations and the dynamic disorder they create can detrimentally affect the transport properties of van der Waals bonded mol. semiconductors. The low-energy nature of these vibrations makes it difficult to access them exptl., which is why we still lack clear mol. design rules to control and reduce dynamic disorder. In this study we discuss the promising org. semiconductors rubrene, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothio-phene and 2,9-di-decyl-dinaphtho-[2,3-b:20,30-f]-thieno-[3,2-b]-thiophene in terms of an exceptionally low degree of dynamic disorder. In particular, we analyze diffuse scattering in transmission electron microscopy, to show that small mols. that have their side chains attached along the long axis of their conjugated core are better encapsulated in their crystal structure, which helps reduce large-amplitude thermal motions. Our work provides a general strategy for the design of new classes of very high mobility org. semiconductors with a low degree of dynamic disorder.
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      Okamoto, T.; Mitsui, C.; Yamagishi, M.; Nakahara, K.; Soeda, J.; Hirose, Y.; Miwa, K.; Sato, H.; Yamano, A.; Matsushita, T.; Uemura, T.; Takeya, J. V-shaped organic semiconductors with solution processability, high mobility, and high thermal durability. Adv. Mater. 2013, 25, 6392– 6397,  DOI: 10.1002/adma.201302086
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      V-Shaped Organic Semiconductors With Solution Processability, High Mobility, and High Thermal Durability
      Okamoto, Toshihiro; Mitsui, Chikahiko; Yamagishi, Masakazu; Nakahara, Katsumasa; Soeda, Junshi; Hirose, Yuri; Miwa, Kazumoto; Sato, Hiroyasu; Yamano, Akihito; Matsushita, Takeshi; Uemura, Takafumi; Takeya, Jun
      Advanced Materials (Weinheim, Germany) (2013), 25 (44), 6392-6397CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors have developed a new candidate for org. semiconductor materials that can be applied in a future printed electronics industry. By synthesizing the newly designed and conceptually unexplored V-shaped extended conjugated core of DNT-V, high-mobility charge transport and sufficient soly. have both been achieved, resulting in the prepn. of soln.-crystd. transistor devices exhibiting excellent performance, with the mobility reaching 9.5 cm2 V'1 s_1. A series of derivs. with alkyl chains became available through a mass-producible four-step synthetic route. In addn., the soln.-crystd. devices of the compd. exhibit high thermal durability up to 150 〈°C, which is also essential for practical usage. The authors detd. crystal packing and the resultant transfer integrals, with the results showing that the high carrier mobility is attributed to an almost optimized arrangement of the DNT-V cores to achieve the max. bandwidth.
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      Mitsui, C.; Okamoto, T.; Matsui, H.; Yamagishi, M.; Matsushita, T.; Soeda, J.; Miwa, K.; Sato, H.; Yamano, A.; Uemura, T.; Takeya, J. Dinaphtho[1,2b:2′,1’d]chalcogenophenes: Comprehensive Investigation of the Effect of the Chalcogen Atoms in the Phenacene-Type π Electronic Cores. Chem. Mater. 2013, 25, 3952– 3956,  DOI: 10.1021/cm303376g
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      Dinaphtho[1,2b:2',1'd]chalcogenophenes: Comprehensive Investigation of the Effect of the Chalcogen Atoms in the Phenacene-Type π Electronic Cores
      Mitsui, Chikahiko; Okamoto, Toshihiro; Matsui, Hiroyuki; Yamagishi, Masakazu; Matsushita, Takeshi; Soeda, Junshi; Miwa, Kazumoto; Sato, Hiroyasu; Yamano, Akihito; Uemura, Takafumi; Takeya, Jun
      Chemistry of Materials (2013), 25 (20), 3952-3956CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      The authors report dinaphtho-[1,2-b:2',1'-d]-chalcogenophenes as a new class of highly potential p-type semiconductors. As the result of comprehensive studies including computational studies based on single-crystal structures successfully detd. by x-ray anal., the impacts of the chalcogen atoms are substantially manifested in their MOs, crystal packing structures, charge-transporting properties, and the device performances at the end. Among them, dinaphtho-[1,2-b:2',1'-d]-thiophene and dinaphtho-[1,2-b:2',1'-d]-selenophene achieved a hole mobility of up to 1.6 and 2.0 cm2 V-1 s-1, resp., accompanied by an Ion/Ioff ratio ≤104-105 in their single-crystal org. field-effect transistors. Such high performances are attributed to the large orbital coeff. on the chalcogen atoms and the ideal packing structures induced by chalcogen-bridged W-shaped mols.
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      Mitsui, C.; Okamoto, T.; Yamagishi, M.; Tsurumi, J.; Yoshimoto, K.; Nakahara, K.; Soeda, J.; Hirose, Y.; Sato, H.; Yamano, A.; Uemura, T.; Takeya, J. High-performance solution-processable N-shaped organic semiconducting materials with stabilized crystal phase. Adv. Mater. 2014, 26, 4546– 4551,  DOI: 10.1002/adma.201400289
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      High-Performance Solution-Processable N-Shaped Organic Semiconducting Materials with Stabilized Crystal Phase
      Mitsui, Chikahiko; Okamoto, Toshihiro; Yamagishi, Masakazu; Tsurumi, Junto; Yoshimoto, Kazumi; Nakahara, Katsumasa; Soeda, Junshi; Hirose, Yuri; Sato, Hiroyasu; Yamano, Akihito; Uemura, Takafumi; Takeya, Jun
      Advanced Materials (Weinheim, Germany) (2014), 26 (26), 4546-4551CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In this paper, authors report the synthesis, fundamental properties, single-crystal structures, and charge transporting capabilities of dinaphthol[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DNBDT) and C10-DNBDT-NW to understand clearly their potential usability as active semiconductors compared with V-shaped compds. The ionization potentials of DNBDT and C10-DNBDT-NW are 5.45 eV and 5.24 eV, resp., whose values are improved because of the extended π-electron system, as expected.
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    71. 71
      Mitsui, C.; Yamagishi, M.; Shikata, R.; Ishii, H.; Matsushita, T.; Nakahara, K.; Yano, M.; Sato, H.; Yamano, A.; Takeya, J.; Okamoto, T. Oxygen- and sulfur-bridged bianthracene V-shaped organic semiconductors. Bull. Chem. Soc. Jpn. 2017, 90, 931– 938,  DOI: 10.1246/bcsj.20170030
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      Oxygen- and sulfur-bridged bianthracene V-shaped organic semiconductors
      Mitsui, Chikahiko; Yamagishi, Masakazu; Shikata, Ryoji; Ishii, Hiroyuki; Matsushita, Takeshi; Nakahara, Katsumasa; Yano, Masafumi; Sato, Hiroyasu; Yamano, Akihito; Takeya, Jun; Okamoto, Toshihiro
      Bulletin of the Chemical Society of Japan (2017), 90 (8), 931-938CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
      A series of oxygen- and sulfur-bridged bianthracene V-shaped π-electronic cores are facilely synthesized (I; X = O, S). We clarify their fundamental properties and aggregated structures in single crystals as well as measure their transistor performances in single crystal field-effect transistors. Both V-shaped mols. possess bent structures induced by the intermol. interaction in a herringbone-packing manner. A theor. calcn. study reveals that the driving force of the bent structures originates from the strong dispersion energy. Addnl., the bent conformation plays a crucial role in the formation of a dense packing structure, resulting in an attractive intermol. overlap. An examn. of the charge transport indicates that the hole mobility is up to 2.0 cm2/Vs. Finally, to understand the anisotropies of the mobility in single crystals, the transistors are evaluated when the channel direction is either parallel or orthogonal to the column direction in the herring-bone packing along with their band structure calcns. Sulfur-bridged V-shaped π-electronic cores are more suitable for two-dimensional carrier-transport than oxygen-bridged analogs.
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      Mitsui, C.; Tsuyama, H.; Shikata, R.; Murata, Y.; Kuniyasu, H.; Yamagishi, M.; Ishii, H.; Yamamoto, A.; Hirose, Y.; Yano, M.; Takehara, T.; Suzuki, T.; Sato, H.; Yamano, A.; Fukuzaki, E.; Watanabe, T.; Usami, Y.; Takeya, J.; Okamoto, T. High performance solution-crystallized thin-film transistors based on V-shaped thieno[3,2-f:4,5-f’]bis[1]benzothiophene semiconductors. J. Mater. Chem. C 2017, 5, 1903– 1909,  DOI: 10.1039/C6TC04721A
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      High performance solution-crystallized thin-film transistors based on V-shaped thieno[3,2-f:4,5-f']bis[1]benzothiophene semiconductors
      Mitsui, Chikahiko; Tsuyama, Hiroaki; Shikata, Ryoji; Murata, Yoshinori; Kuniyasu, Hiroyuki; Yamagishi, Masakazu; Ishii, Hiroyuki; Yamamoto, Akito; Hirose, Yuri; Yano, Masafumi; Takehara, Tsunayoshi; Suzuki, Takeyuki; Sato, Hiroyasu; Yamano, Akihito; Fukuzaki, Eiji; Watanabe, Tetsuya; Usami, Yoshihisa; Takeya, Jun; Okamoto, Toshihiro
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (8), 1903-1909CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      A new class of soln.-processable thieno[3,2-f:4,5-f']bis[1]benzothiophene (TBBT-V) semiconductors are investigated. Semiconductors with decyl substituents and two kinds of π-extended decylthienyl substituents are facially derivatized from functionalized dibromo-substituted TBBT-Vvia either a Negishi or a Stille cross coupling procedure. The solubilities of TBBT-V semiconductors are somewhat higher than those of their previously developed dinaphtho[2,3-b:2',3'-d]thiophene (DNT-V) counterparts. Single crystal anal. together with a calcn. study on the transfer integral and the band structure in decyl-substituted TBBT-V (C10-TBBT-V) clarifies that these semiconductors form two-dimensionally ordered herringbone packing structures and the effective mass in the columnar direction rivals that of the previously developed decyl-substituted DNT-V. The carrier mobilities of TBBT-V derivs. in soln. grown into single-cryst. films are remarkable (up to 6.2 cm2 V-1 s-1). Furthermore, their operation voltages are apparently lower than those of previously developed DNT-V derivs. due to the optimized ionization potential of the TBBT-V core and further π-extension by substitution of the thienyl groups.
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      Yamamoto, A.; Murata, Y.; Mitsui, C.; Ishii, H.; Yamagishi, M.; Yano, M.; Sato, H.; Yamano, A.; Takeya, J.; Okamoto, T. Zigzag-Elongated Fused pi-Electronic Core: A Molecular Design Strategy to Maximize Charge-Carrier Mobility. Adv. Sci. 2018, 5, 1700317,  DOI: 10.1002/advs.201700317
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      Zigzag-Elongated Fused π-Electronic Core: A Molecular Design Strategy to Maximize Charge-Carrier Mobility
      Yamamoto Akito; Mitsui Chikahiko; Takeya Jun; Okamoto Toshihiro; Murata Yoshinori; Yano Masafumi; Ishii Hiroyuki; Yamagishi Masakazu; Sato Hiroyasu; Yamano Akihito; Okamoto Toshihiro
      Advanced science (Weinheim, Baden-Wurttemberg, Germany) (2018), 5 (1), 1700317 ISSN:2198-3844.
      Printed and flexible electronics requires solution-processable organic semiconductors with a carrier mobility (μ) of ≈10 cm(2) V(-1) s(-1) as well as high chemical and thermal durability. In this study, chryseno[2,1-b:8,7-b']dithiophene (ChDT) and its derivatives, which have a zigzag-elongated fused π-electronic core (π-core) and a peculiar highest occupied molecular orbital (HOMO) configuration, are reported as materials with conceptually new semiconducting π-cores. ChDT and its derivatives are prepared by a versatile synthetic procedure. A comprehensive investigation reveals that the ChDT π-core exhibits increasing structural stability in the bulk crystal phase, and that it is unaffected by a variation of the transfer integral, induced by the perpetual molecular motion of organic materials owing to the combination of its molecular shape and its particular HOMO configuration. Notably, ChDT derivatives exhibit excellent chemical and thermal stability, high charge-carrier mobility under ambient conditions (μ ≤ 10 cm(2) V(-1) s(-1)), and a crystal phase that is highly stable, even at temperatures above 250 °C.
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      Tsurumi, J.; Matsui, H.; Kubo, T.; Hausermann, R.; Mitsui, C.; Okamoto, T.; Watanabe, S.; Takeya, J. Coexistence of ultra-long spin relaxation time and coherent charge transport in organic single-crystal semiconductors. Nat. Phys. 2017, 13, 994– 998,  DOI: 10.1038/nphys4217
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      Coexistence of ultra-long spin relaxation time and coherent charge transport in organic single-crystal semiconductors
      Tsurumi, Junto; Matsui, Hiroyuki; Kubo, Takayoshi; Hausermann, Roger; Mitsui, Chikahiko; Okamoto, Toshihiro; Watanabe, Shun; Takeya, Jun
      Nature Physics (2017), 13 (10), 994-998CODEN: NPAHAX; ISSN:1745-2473. (Nature Research)
      Coherent charge transport can occur in org. semiconductor crystals thanks to the highly periodic electrostatic potential-despite the weak van der Waals bonds. And as spin-orbit coupling is usually weak in org. materials, robust spin transport is expected, which is essential if they are to be exploited for spintronic applications. In such systems, momentum relaxation occurs via scattering events, which enables an intrinsic mobility to be defined for band-like charge transport, which is >10 cm2 V-1 s-1. In contrast, there are relatively few exptl. studies of the intrinsic spin relaxation for org. band-transport systems. Here, we demonstrate that the intrinsic spin relaxation in org. semiconductors is also caused by scattering events, with much less frequency than the momentum relaxation. Magnetotransport measurements and ESR spectroscopy consistently show a linear relationship between the two relaxation times over a wide temp. range, clearly manifesting the Elliott-Yafet type of spin relaxation mechanism. The coexistence of an ultra-long spin lifetime of milliseconds and the coherent band-like transport, resulting in a micrometer-scale spin diffusion length, constitutes a key step towards realizing spintronic devices based on org. single crystals.
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      Solubility Parameter. Bulletin of the American Group; International Institute for Conservation of Historic and Artistic Works, 1968; Vol. 8, pp 20– 24.
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      The reorganization energy was calculated based on the optimized structure by DFT at the B3LYP/6-31G(d) level.

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    77. 77
      Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; van Eikema Hommes, N. J. R. Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe. J. Am. Chem. Soc. 1996, 118, 6317– 6318,  DOI: 10.1021/ja960582d
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      Nucleus-independent chemical shifts: a simple and efficient aromaticity probe
      Schleyer, Paul v.R.; Maerker, Christoph; Dransfeld, Alk; Jiao, Haijun; van Eikema Hommes, Nicolaas J. R.
      Journal of the American Chemical Society (1996), 118 (26), 6317-6318CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Nucleus-independent chem. shifts (NICS), the neg. of the abs. magnetic shieldings (in ppm) computed at the ab initio GIAO-HF/6-31 + G* level at ring centers (non-weighted means of the heavy atom coordinates), are proposed as a simple and efficient magnetic probe for characterizing aromaticity and antiaromaticity. For a series of five membered heterocycles, NICS correlate with arom. stabilization energies, magnetic susceptibility exaltations, and geometric criteria of aromaticity. Arom. compds. have neg. NICS (e.g., -9.7 for benzene and -15.1 for pyrrole), whereas antiarom. systems, in contrast, exhibit pos. NICS values (18.1 for pentalene and 27.6 for cyclobutadiene). In addn., NICS can characterize the individual rings in polycyclic arom. (e.g., -19.7 and -7.0 for the five- and seven-membered rings in azulene) and antiarom. (e.g., -2.5 and 22.5 for the six- and four-membered rings in benzocyclobutadiene) systems as well as the spherical aromaticity of cage compds., e.g., closo-B12H122- (-34.4) and the 1,3-dehydro-5,7-adamantanediyl dication (-50.1). The C60 NICS confirm that the 5-rings are paramagnetic and the 6-rings are diamagnetic, but the magnitudes are not large.
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      Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion. Chem. Rev. 2005, 105, 3842– 3888,  DOI: 10.1021/cr030088+
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      Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion
      Chen, Zhongfang; Wannere, Chaitanya S.; Corminboeuf, Clemence; Puchta, Ralph; Schleyer, Paul von Rague
      Chemical Reviews (Washington, DC, United States) (2005), 105 (10), 3842-3888CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A comprehensive review is presented on nucleus-independent chem. shift as a criterion for aromaticity.
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      Münzel, N.; Kesper, K.; Schweig, A.; Specht, H. Detection of 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene. Tetrahedron Lett. 1988, 29, 6239– 6242,  DOI: 10.1016/S0040-4039(00)82314-X
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      Detection of 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene
      Muenzel, Norbert; Kesper, Karl; Schweig, Armin; Specht, Harald
      Tetrahedron Letters (1988), 29 (48), 6239-42CODEN: TELEAY; ISSN:0040-4039.
      The reactive species 2,5-dimethylene-2,5-dihydrothiophene and thiophenoradialene were generated by pyrolytic elimination of HCl from their thiophene precursors.
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      Okamoto, H.; Kawasaki, N.; Kaji, Y.; Kubozono, Y.; Fujiwara, A.; Yamaji, M. Air-assisted High-performance Field-effect Transistor with Thin Films of Picene. J. Am. Chem. Soc. 2008, 130, 10470– 10471,  DOI: 10.1021/ja803291a
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      Air-assisted High-performance Field-effect Transistor with Thin Films of Picene
      Okamoto, Hideki; Kawasaki, Naoko; Kaji, Yumiko; Kubozono, Yoshihiro; Fujiwara, Akihiko; Yamaji, Minoru
      Journal of the American Chemical Society (2008), 130 (32), 10470-10471CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A field-effect transistor (FET) with thin films of picene has been fabricated on SiO2 gate dielec. The FET showed p-channel enhancement-type FET characteristics with the field-effect mobility of 1.1 cm2/(V·s) and the on-off ratio of >105. This excellent device performance was realized under atm. conditions. The field-effect mobility increased with an increase in temp., and the FET performance was improved by exposure to air or O2 for a long time. This result implies that this device is an air (O2)-assisted FET. The FET characteristics are discussed on the basis of structural topog. and the energy diagram of picene thin films.
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      Kawai, N.; Eguchi, R.; Goto, H.; Akaike, K.; Kaji, Y.; Kambe, T.; Fujiwara, A.; Kubozono, Y. Characteristics of Single Crystal Field-Effect Transistors with a New Type of Aromatic Hydrocarbon, Picene. J. Phys. Chem. C 2012, 116, 7983– 7988,  DOI: 10.1021/jp300052p
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      Characteristics of single crystal field-effect transistors with new type of aromatic hydrocarbon, picene
      Kawai, Nobuyuki; Eguchi, Ritsuko; Goto, Hidenori; Akaike, Kouki; Kaji, Yumiko; Kambe, Takashi; Fujiwara, Akihiko; Kubozono, Yoshihiro
      Journal of Physical Chemistry C (2012), 116 (14), 7983-7988CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Picene is a phenacene-type arom. hydrocarbon mol. with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liq. gate dielecs. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielec. and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V-1 s-1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liq. gate dielec., 1-butyl-3-Me imidazolium hexafluorophosphate, showing the field-effect mobility of 1.8 × 10-1 cm2 V-1 s-1 and low abs. value, 1.9 V, of threshold voltage.
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      De, A.; Ghosh, R.; Roychowdhury, S.; Roychowdhury, P. Structural analysis of picene, C22H14. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1985, 41, 907– 909,  DOI: 10.1107/S0108270185005959
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      Tedjamulia, M. L.; Tominaga, Y.; Castle, R. N.; Lee, M. L. The synthesis of dinaphthothiophenes. J. Heterocyclic Chem. 1983, 20, 1143– 1148,  DOI: 10.1002/jhet.5570200502
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      The synthesis of dinaphthothiophenes
      Tedjamulia, Marvin L.; Tominaga, Yoshinori; Castle, Raymond N.; Lee, Milton L.
      Journal of Heterocyclic Chemistry (1983), 20 (5), 1143-8CODEN: JHTCAD; ISSN:0022-152X.
      Dinaphtho[1,2-b:2',3'-d]thiophene, dinaphtho[2,1-b;2',3'-d]thiophene, dinaphtho-[1,2-b:1',2'-d]thiophene, dinaphtho[2,1-b; 1',2'-d]thiophene and dinaphtho[1,2-b:2',1'-d]thiophene were prepd.
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      Lloyd-Jones, G. C.; Moseley, J. D.; Renny, J. S. Mechanism and Application of the Newman-Kwart O→S Rearrangement of O-Aryl Thiocarbamates. Synthesis 2008, 2008, 661– 689,  DOI: 10.1055/s-2008-1032179
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      Matsuoka, M.; Iwamoto, A.; Kitao, T. Reaction of 2, 3-dichloro-1, 4-naphthoquinone with dithiooxamide. Synthesis of dibenzo[b, i]thianthrene-5, 7, 12, 14-tetrone. J. Heterocycl. Chem. 1991, 28, 1445– 1447,  DOI: 10.1002/jhet.5570280543
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      Reaction of 2,3-dichloro-1,4-naphthoquinone with dithiooxamide. Synthesis of dibenzo[b,i]thianthrene-5,7,12,14-tetrone
      Matsuoka, Masaru; Iwamoto, Akihiro; Kitao, Teijiro
      Journal of Heterocyclic Chemistry (1991), 28 (5), 1445-7CODEN: JHTCAD; ISSN:0022-152X.
      The reaction of 2,3-dihalo-1,4-naphthoquinones with dithiooxamide gave dibenzo[b,i]thianthrene-5,7,12,14-tetrone in high yield but not 2,2'-bis(naphtho[2,3-d]thiazole-4,9-dione) as reported by A. R. Katritzky et al. (1989). A similar reaction of 3,4-dichloro-N-phenylmaleimide with dithiooxamide also gave the corresponding sulfur heterocycle but not the reported bisthiazole. The dyes are of interest for opto-electronic, etc., application.
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      De, P. K.; Neckers, D. C. Sulfur Containing Stable Unsubstituted Heptacene Analogs. Org. Lett. 2012, 14, 78– 81,  DOI: 10.1021/ol2028724
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      Sulfur Containing Stable Unsubstituted Heptacene Analogs
      De, Puran K.; Neckers, Douglas C.
      Organic Letters (2012), 14 (1), 78-81CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
      Methods to synthesize stable linear and a nonlinear unsubstituted heptacene analogs are discussed. No changes in the UV-visible absorption spectra in soln. over time for these materials indicate higher oxidative stability compared to analogous polyacenes.
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      Wex, B.; Kaafarani, B. R.; Kirschbaum, K.; Neckers, D. C. Synthesis of the anti and syn Isomers of Thieno[f, f‘]bis[1]benzothiophene. Comparison of the Optical and Electrochemical Properties of the anti and syn Isomers1. J. Org. Chem. 2005, 70, 4502– 4505,  DOI: 10.1021/jo048010w
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      Synthesis of the anti and syn Isomers of Thieno[f,f']bis[1]benzothiophene. Comparison of the Optical and Electrochemical Properties of the anti and syn Isomers
      Wex, Brigitte; Kaafarani, Bilal R.; Kirschbaum, Kristin; Neckers, Douglas C.
      Journal of Organic Chemistry (2005), 70 (11), 4502-4505CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      The isomer-pure synthesis of thieno[2,3-f:5,4-f']bis[1]benzothiophene I (X = S; Y = nothing) and thieno[3,2-f:4,5-f']bis[1]benzothiophene I (X = nothing; Y = S), the anti and syn isomers of a pentacyclic compd. consisting of alternating thiophene and benzene rings, is reported. The optical and electrochem. properties of these compds. are reported. In the anti isomer, the ribbon-like embedding of three thiophene units leads to a near-planar mol. with favorable π-π stacking behavior in the solid state as shown by X-ray crystal structure anal.
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    88. 88
      Armarego, W. L. F. The synthesis of two dinaphthothiophens. J. Chem. Soc. 1960, 433– 436,  DOI: 10.1039/jr9600000433
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      Synthesis of two dinaphthothiophenes
      Armarego, W. L. F.
      Journal of the Chemical Society (1960), (), 433-6CODEN: JCSOA9; ISSN:0368-1769.
      Dinaphtho[1,2-b:2',1'-d]-(I) and -[1,2-b:2',3'-d]thiophene (II) were synthesized. I was shown to be different from a S compd. isolated by Henriques [Ber. 27, 2993(1894)]. Na 2-iodonaphthalene-1-sulfonate (15 g.) ground with 8.8 g. PCl5, 5 ml. POCl3 added to start the reaction (completed in 1 hr. on the H2O bath), the mixt. poured into H2O at 0°, and the solid collected gave 14 g. 2-iodonaphthalene-1-sulfonyl chloride (III), m. 109-10° (ligroine). III (9 g.) heated 1 hr. with 2.6 g. PhOH in 10 ml. C5H5N, the soln. poured into refluxing H2O, and the ester isolated gave 8.4 g. Ph 2-iodonaphthalene-1-sulfonate (IV), prisms, m. 78-9° (MeOH). IV (10.4 g.) heated at 170-5° with 10 g. Cu bronze, the mixt. kept 15 min. at 210°, and extd. with PhCl gave 6.6 g. di-Ph 2,2'-binaphthyl-1,1'-disulfonate (V), rhombs, m. 210-11° (BuOH or AcOH). V (6.6 g.) refluxed 4 hrs. with 600 ml. BuOH contg. 2.14 g. Na, concd. in vacuo, poured into H2O, acidified to pH 2, extd. with Et2O, the aq. soln. neutralized, refluxed with C, filtered, and concd. (di-Na salt sepd. as an oil), the soln. evapd., and the sulfonate extd. from the residue with hot alc. gave 1.8 g. di-Na 2,2'-binaphthyl-1,1'-disulfonate (VI), plates. VI (1.4 g.) heated 1 hr. with an equal wt. of PCl5 gave 0.9 g. 2,2'-binaphthyl-1,1'-disulfonyl dichloride (VII), prisms, m. 236-7° (decompn.) (AcOH contg. 4% Ac2O). VII (431 mg.) in 30 ml. refluxing AcOH was treated with 20 ml. 55% Hl; after a few min. the dithiin started to sep. but the mixt. left overnight at room temp., poured into H2O, decolorized with SO2, and filtered gave 292 mg. dinaphtho[1,2-c:2',1'-e]dithiin (VIII), m. 195.5-6.0° (AcOH). VIII was insol. in alkali and unaffected by mild oxidizing agents. VIII (200 mg.) heated 1.5 hrs. at 260-80° with 400 mg. Cu bronze and the product crystd. gave 90 mg. I, plates, m. 255-6° (C6H6-ligroine), λ 262, 274.5, 284.5 mμ, log ε 4.8, 4.7, 4.7. Benzo[g]thianaphthene (2.15 g.) and 1.73 g. phthalic anhydride in 50 ml. PhNO2 treated 3 days at room temp. with 3.56 g. anhyd. AlCl3, mixed with 50 ml. 5N HCl, and steam distd. gave 2.9 g. acid (IX). IX heated 3 hrs. with 50 ml. polyphosphoric acid, poured into cold H2O, the solid collected, this solid refluxed 5 min. with 100 ml. NH4OH, and the residue sublimed at 250-300°/0.4 mm. gave 540 mg. dinaphtho[1,2-b:2',2'-d]thiophene-7,12-quinone (X), m. 299-300° (rapid heating). X (100 mg.) kept in air 5 min. with 1 g. Zn dust, 1 g. NaCl, and 5 g. anhyd. ZnCl2, placed in a metal bath at 180°, the temp. raised gradually to 320°, after 30 sec. at 320° the mixt. cooled to room temp., suspended in excess 5N HCl, filtered, after drying the residue dissolved in CHCl3, the mixt. filtered, concd., placed on Al2O3, and eluted gave 10 mg. II, flakes, m. 316-17°, λ 262, 269.7, and 279.8 mμ, log ε 4.7, 4.7, 4.9 (96% alc.). Sublimation of II at 250°/0.7 mm. and crystn. from alc. and then C6H6 gave chromatographically pure II. Refluxing II in xylene with excess Raney Ni 5 hrs. gave 2,2'-binaphthyl.
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    89. 89
      Shinamura, S.; Osaka, I.; Miyazaki, E.; Nakao, A.; Yamagishi, M.; Takeya, J.; Takimiya, K. Linear- and Angular-Shaped Naphthodithiophenes: Selective Synthesis, Properties, and Application to Organic Field-Effect Transistors. J. Am. Chem. Soc. 2011, 133, 5024– 5035,  DOI: 10.1021/ja110973m
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      Linear- and Angular-Shaped Naphthodithiophenes: Selective Synthesis, Properties, and Application to Organic Field-Effect Transistors
      Shinamura, Shoji; Osaka, Itaru; Miyazaki, Eigo; Nakao, Akiko; Yamagishi, Masakazu; Takeya, Jun; Takimiya, Kazuo
      Journal of the American Chemical Society (2011), 133 (13), 5024-5035CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A straightforward synthetic approach that exploits linear- and angular-shaped naphthodithiophenes (NDTs) being potential as new core structures for org. semiconductors is described. The newly established synthetic procedure involves 2 important steps; one is the chemoselective Sonogashira coupling reaction on the trifluoromethanesulfonyloxy site over the Br site enabling selective formation of o-bromoethynylbenzene substructures on the naphthalene core, and the other is a facile ring closing reaction of fused-thiophene rings from the o-bromoethynylbenzene substructures. As a result, 3 isomeric NDTs, naphtho[2,3-b:6,7-b']dithiophene, naphtho[2,3-b:7,6-b']dithiophenes, and naphtho[2,1-b:6,5-b']dithiophene, are selectively synthesized. Electrochem. and optical measurements of the parent NDTs indicated that the shape of the mols. plays an important role in detg. the electronic structure of the compds.; the linear-shaped NDTs formally isoelectronic with naphthacene have lower oxidn. potentials and more red shifted absorption bands than those of the angular-shaped NDTs isoelectronic with chrysene. On the contrary, the performance of the thin-film-based field-effect transistors (FETs) using the dioctyl or di-Ph derivs. were much influenced by the symmetry of the mols.; centrosym. derivs. tend to give higher mobility (up to 1.5 cm2 V-1 s-1) than axisym. ones (∼0.06 cm2 V-1 s-1), implying that the intermol. orbital overlap in the solid state is influenced by the symmetry of the mols. The present NDT cores, in particular the linear-shaped, centrosym. naphtho[2,3-b:6,7-b']dithiophene, are promising building blocks for the development of org. semiconducting materials.
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    90. 90
      Mamane, V.; Hannen, P.; Fürstner, A. Synthesis of Phenanthrenes and Polycyclic Heteroarenes by Transition-Metal Catalyzed Cycloisomerization Reactions. Chem. - Eur. J. 2004, 10, 4556– 4575,  DOI: 10.1002/chem.200400220
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      Synthesis of phenanthrenes and polycyclic heteroarenes by transition-metal catalyzed cycloisomerization reactions
      Mamane, Victor; Hannen, Peter; Fuerstner, Alois
      Chemistry - A European Journal (2004), 10 (18), 4556-4575CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Readily available biphenyl derivs. contg. an alkyne unit at one of their ortho-positions were converted into substituted phenanthrenes, e.g., I, on exposure to catalytic amts. of either PtCl2, AuCl, AuCl3, GaCl3 or InCl3 in toluene. This 6-endo-dig cyclization likely proceeded through initial π-complexation of the alkyne unit followed by interception of the resulting η2-metal species by the adjacent arene ring. The reaction was inherently modular, allowing for substantial structural variations and for the incorporation of substituents at any site of the phenanthrene product. Moreover, it was readily extended to the heterocyclic series as exemplified by the prepn. of benzoindoles, benzocarbazoles, naphthothiophenes, as well as bridgehead nitrogen heterocycles such as pyrrolo[1,2-a]quinolines, e.g., II. Depending on the chosen catalyst, biaryls bearing halo-alkyne units can either be converted into the corresponding 10-halo-phenanthrenes or into the isomeric 9-halo-phenanthrenes; in the latter case, the concomitant 1,2-halide shift was best explained by assuming a metal vinylidene species as the reactive intermediate. The scope of this method for the prepn. of polycyclic arenes was illustrated by the total synthesis of a series of polyoxygenated phenanthrenes that were close relatives of the anticancer agent combretastatin A-4, as well as by the total synthesis of the aporphine alkaloid O-methyl-dehydroisopiline and its naturally occurring sym. dimer.
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      Laudise, R. A.; Kloc, C.; Simpkins, P. G.; Siegrist, T. Physical vapor growth of organic semiconductors. J. Cryst. Growth 1998, 187, 449– 454,  DOI: 10.1016/S0022-0248(98)00034-7
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      Physical vapor growth of organic semiconductors
      Laudise, R. A.; Kloc, Ch.; Simpkins, P. G.; Siegrist, T.
      Journal of Crystal Growth (1998), 187 (3/4), 449-454CODEN: JCRGAE; ISSN:0022-0248. (Elsevier Science B.V.)
      Phys. vapor growth in horizontal and vertical systems was used to grow crystals of α-hexathiophene (α-6T), α-octithiophene (α-8T), α-quaterthiophene (α-4T), pentacene, anthracene and Cu phthalocyanine. Using 10-30 mg of starting material, mm-cm sized crystals, suitable for characterization measurements, were grown. New polymorphs of α-quaterthiophene (high temp., HT and low temp., LT) and pentacene were discovered. A horizontal geometry is advantageous because the fragile crystals are extd. more easily.
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      Kloc, C.; Simpkins, P. G.; Siegrist, T.; Laudise, R. A. Physical vapor growth of centimeter-sized crystals of α-hexathiophene. J. Cryst. Growth 1997, 182, 416– 427,  DOI: 10.1016/S0022-0248(97)00370-9
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXht1SgtbrM&md5=59a9f604b26f4c716d8783c931b6925d
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      Org. mol. semiconductors are soln. processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of org. semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel mol. and material design, and improved processing conditions. Here we show a method to increase the charge mobility in org. single-crystal field-effect transistors, by taking advantage of the inherent softness of org. semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm2 V-1 s-1 by 70% under 3% strain. In-depth anal. indicates that compressing the crystal structure directly restricts the vibration of the mols., thus suppresses dynamic disorder, a unique mechanism in org. semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance org. devices.
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      A series of π-conjugated 3,10-dialkyl-dinaphtho[1,2-b:2',1'-d]chalcogenophenes incorporating S, Se, and Te as the central chalcogen atom was newly synthesized, and their optoelectronic and charge-transport properties were systematically investigated. High carrier mobilities of up to 4.7 cm2 V-1 s-1 were achieved for soln.-processed org. field-effect transistors using these materials as p-channel org. semiconductors.
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