Molecular Photoswitching in Confined SpacesClick to copy article linkArticle link copied!
- Angela B. GrommetAngela B. GrommetDepartment of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, IsraelMore by Angela B. Grommet
- Lucia M. LeeLucia M. LeeDepartment of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, IsraelMore by Lucia M. Lee
- Rafal Klajn*Rafal Klajn*Email: [email protected]Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, IsraelMore by Rafal Klajn
Abstract
Conspectus
In nature, light is harvested by photoactive proteins to drive a range of biological processes, including photosynthesis, phototaxis, vision, and ultimately life. Bacteriorhodopsin, for example, is a protein embedded within archaeal cell membranes that binds the chromophore retinal within its hydrophobic pocket. Exposure to light triggers regioselective photoisomerization of the confined retinal, which in turn initiates a cascade of conformational changes within the protein, triggering proton flux against the concentration gradient, providing the microorganisms with the energy to live. We are inspired by these functions in nature to harness light energy using synthetic photoswitches under confinement. Like retinal, synthetic photoswitches require some degree of conformational flexibility to isomerize. In nature, the conformational change associated with retinal isomerization is accommodated by the structural flexibility of the opsin host, yet it results in steric communication between the chromophore and the protein. Similarly, we strive to design systems wherein isomerization of confined photoswitches results in steric communication between a photoswitch and its confining environment. To achieve this aim, a balance must be struck between molecular crowding and conformational freedom under confinement: too much crowding prevents switching, whereas too much freedom resembles switching of isolated molecules in solution, preventing communication.
In this Account, we discuss five classes of synthetic light-switchable compounds—diarylethenes, anthracenes, azobenzenes, spiropyrans, and donor–acceptor Stenhouse adducts—comparing their behaviors under confinement and in solution. The environments employed to confine these photoswitches are diverse, ranging from planar surfaces to nanosized cavities within coordination cages, nanoporous frameworks, and nanoparticle aggregates. The trends that emerge are primarily dependent on the nature of the photoswitch and not on the material used for confinement. In general, we find that photoswitches requiring less conformational freedom for switching are, as expected, more straightforward to isomerize reversibly under confinement. Because these compounds undergo only small structural changes upon isomerization, however, switching does not propagate into communication with their environment. Conversely, photoswitches that require more conformational freedom are more challenging to switch under confinement but also can influence system-wide behavior.
Although we are primarily interested in the effects of geometric constraints on photoswitching under confinement, additional effects inevitably emerge when a compound is removed from solution and placed within a new, more crowded environment. For instance, we have found that compounds that convert to zwitterionic isomers upon light irradiation often experience stabilization of these forms under confinement. This effect results from the mutual stabilization of zwitterions that are brought into close proximity on surfaces or within cavities. Furthermore, photoswitches can experience preorganization under confinement, influencing the selectivity and efficiency of their photoreactions. Because intermolecular interactions arising from confinement cannot be considered independently from the effects of geometric constraints, we describe all confinement effects concurrently throughout this Account.
Key References
Samanta, D.; Gemen, J.; Chu, Z.; Diskin-Posner, Y.; Shimon, L. J. W.; Klajn, R. Reversible photoswitching of encapsulated azobenzenes in water. Proc. Natl. Acad. Sci. U.S.A. 2018, 115, 9379–9384. A flexible Pd6L4coordination cage encapsulates structurally simple azobenzenes in a 2:1 ratio. Isomerization from trans- to cis-azobenzene results in a steric clash and expulsion of one guest from the cavity, offering an opportunity to translate light energy into system-wide communication. (1)Kundu, P. K.; Olsen, G. L.; Kiss, V.; Klajn, R. Nanoporous frameworks exhibiting multiple stimuli responsiveness. Nat. Commun. 2014, 5, 3588. The switching behavior of spiropyran within nanoporous frameworks is dependent on the density of the photochromic units. In less crowded frameworks, spiropyran switches reversibly as in solution; in more crowded frameworks, spiropyran converts spontaneously to merocyanine, driven by mutual stabilization of neighboring zwitterions. (2)Chu, Z.; Han, Y.; Bian, T.; De, S.; Král, P.; Klajn, R. Supramolecular Control of Azobenzene Switching on Nanoparticles. J. Am. Chem. Soc. 2019, 141, 1949–1960. Confinement of azobenzene on the surface of nanoparticles enables preorganization of these switches adjacent to background ligands that facilitate their isomerization. We also observe cooperative switching of neighboring azobenzenes within small aggregates on the nanoparticle surface. (3)Zhao, H.; Sen, S.; Udayabhaskararao, T.; Sawczyk, M.; Kučanda, K.; Manna, D.; Kundu, P. K.; Lee, J.-W.; Král, P.; Klajn, R. Reversible trapping and reaction acceleration within dynamically self-assembling nanoflasks. Nat. Nanotechnol. 2016, 11, 82–88. Reversible assembly of nanoparticles leads to the creation and destruction of confined environments, or “nanoflasks”, located interstitially within the aggregate. Preorganization of anthracenes within these nanoflasks results in reaction acceleration and regioselective photodimerization to the syn product. (4)
1. Introduction
Figure 1
Figure 1. (a) Light-induced regioselective isomerization of retinal within the binding pocket of bacteriorhodopsin. (b) Structure of bacteriorhodopsin with retinal buried inside its hydrophobic cavity. The arrows indicate the direction of light-induced proton transfer. (c) Binding of retinal (pink sticks with van der Waals radii shown as a transparent halo) encased within the hydrophobic cavity of bacteriorhodopsin (yellow). (d) Structural dynamics of retinal and its immediate surroundings captured by a femtosecond X-ray laser. The transition from trans-retinal to cis-retinal is mapped onto a dark-state model based on the difference Fourier electron density (Fobslight – Fobsdark) contoured at 4σ (yellow, negative; blue, positive). Adapted with permission from ref (5). Copyright 2018 American Association for the Advancement of Science.
2. Confined Diarylethenes
Figure 2
Figure 2. (a) Reversible photoisomerization of a diarylethene. The colored isomer featuring extensive conjugation of π electrons (here, the closed form) is shown in green. (b) Reversible light-induced deformation of a single crystal of a simple diarylethene (here, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene). (c) Reversible photoisomerization between dihydropyrene (DHP) and cyclophanediene (CPD). (d) Structural formula of coordination cage 1 used to investigate the behavior of photoswitchable molecules under confinement (left) and crystal structure of an inclusion complex of DHP inside cage 1 (right). (e) Gradual decomposition of DHP in pentane solution over 10 switching cycles. (f) Improved fatigue resistance of DHP⊂1 over 10 cycles under the same irradiation conditions. (b) Adapted with permission from ref (24). Copyright 2007 Springer Nature. (e, f) Adapted from ref (31). Copyright 2020 American Chemical Society.
3. Confined Anthracenes
Figure 3
Figure 3. (a) Reversible photodimerization of anthracene. (b) Proposed photoreaction of anthracene inside the cavity of ZIF-8. (c) Crystal structure of a ZIF-8 cavity encapsulating four molecules of anthracene. (d) UV/vis absorption spectra accompanying UV irradiation of ZIF-8 encapsulating anthracene. (e) Schematic illustration of light-induced trapping and increased reactivity of small molecules within colloidal crystals (“dynamically self-assembling nanoflasks”). (f) Electron micrographs (at different magnifications) of colloidal crystals prepared by exposing azobenzene-coated gold nanoparticles to UV light. (g) Accelerated photodimerization of 9-anthracenemethanol in the presence of photoresponsive nanoparticles. (h) Stereoselectivity in the dimerization of 9-anthracenemethanol in the presence and absence of photoresponsive nanoparticles. (i) Schematic illustration of the photoreaction of 9-(4-mercaptophenylethynyl)anthracene on a Au(111) surface. (j) Dependence of the anthracene dimerization yield on the curvature of the underlying nanoparticle. (c, d) Adapted with permission from ref (34). Copyright 2019 Wiley-VCH. (f–h) Adapted with permission from ref (4). Copyright 2016 Springer Nature. (i) Adapted with permission from ref (37). Copyright 2011 American Association for the Advancement of Science.
4. Confined Azo Compounds
Figure 4
Figure 4. (a) Reversible photoisomerization of azobenzene. (b) Structural formulas of azobenzene 2 and background ligand 3. (c) Snapshots from molecular dynamics simulations of a 2/3-coated gold nanoparticle in the trans and cis states of azobenzene. (d) Structural formulas of azobenzene 4 and background ligand 5. (3) (e) Proposed mechanism for accelerated azobenzene isomerization on a nanoparticle surface upon coadsorption with a hydroxy-terminated background ligand. (3) (f) Crystal structure of an inclusion complex comprising cage 1 and two molecules of tetra-o-fluoroazobenzene (6) (left) and the stepwise mechanism underlying the photoisomerization of 6 within the cavity of 1 (right). (c) Adapted from ref (3). Copyright 2019 American Chemical Society.
5. Confined Spiropyrans and DASA Switches
Figure 5
Figure 5. (a, b) Reversible photoisomerization of (a) spiropyran and (b) DASA. (c) Comparison of the kinetics of merocyanine→spiropyran back-isomerization in solution and on the surface of 2.6 nm gold nanoparticles (χ = 0.33). (d) Dependence of the kinetics of disassembly of gold nanoparticle aggregates on the spiropyran coverage. (e, f) Spontaneous bleaching of the open form of DASA on the surfaces of (e) 4.2 and (f) 8.6 nm magnetite nanoparticles. (g) TEM image of a spiropyran-incorporating framework. The arrows indicate individual nanopores. (h) Encapsulation of spiropyran 7 within cage 1 and the resulting crystal structure (hydrogen atoms of the cage have been omitted for clarity). (i) Mechanism of the light-induced decoloration of 7⊂1. (c, d) From ref (55). CC BY 3.0. (e, f) Adapted with permission from ref (57). Copyright 2017 Wiley-VCH. (g) From ref (2). CC BY NC ND 3.0.
6. Conclusion
Biographies
Angela B. Grommet
Angela B. Grommet received a Bachelor of Science with Honors from Kansas State University in 2013. She then moved to the University of Cambridge and conducted her doctoral research under the supervision of Jonathan Nitschke, employing coordination cages for the separation and transport of molecular cargo. Upon earning her Ph.D. in 2018, she was awarded a Zuckerman STEM Leadership Postdoctoral Fellowship and joined the group of Rafal Klajn at the Weizmann Institute of Science. She now focuses on utilizing confinement to modulate chemical reactivity.
Lucia M. Lee
Lucia M. Lee received a B.Sc. with Honors in 2011 from McMaster University, where she stayed as a Natural Sciences and Engineering Research Council (NSERC) doctoral student to study organochalcogen supramolecular building blocks under the mentorship of Ignacio Vargas-Baca. At the completion of her Ph.D. in 2017, she joined the group of Stefan Matile at the University of Geneva as a postdoctoral fellow to pursue studies on transmembrane anion transport using main-group supramolecular interactions. In 2019, she joined the Klajn group as a Zuckerman STEM Leadership Postdoctoral Fellow. Her current work involves using σ-hole interactions to guide the assembly of nanoparticles.
Rafal Klajn
Rafal Klajn completed his Ph.D. at Northwestern University in 2009 and joined the Department of Organic Chemistry at the Weizmann Institute of Science, where he is currently an Associate Professor. The interests of his research group revolve around supramolecular chemistry, photochromism, molecular switches, nanoscale self-assembly and reactivity, and the development of new stimuli-responsive and dissipative materials.
Acknowledgments
This work was supported by the European Research Council (Grant 336080). A.B.G. and L.M.L. acknowledge funding from the Zuckerman STEM Leadership Program.
References
This article references 71 other publications.
- 1Samanta, D.; Gemen, J.; Chu, Z.; Diskin-Posner, Y.; Shimon, L. J. W.; Klajn, R. Reversible photoswitching of encapsulated azobenzenes in water. Proc. Natl. Acad. Sci. U. S. A. 2018, 115, 9379– 9384, DOI: 10.1073/pnas.1712787115Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVKhurfO&md5=06b154f6f5783bdcc43a702bb08b39d4Reversible photoswitching of encapsulated azobenzenes in waterSamanta, Dipak; Gemen, Julius; Chu, Zonglin; Diskin-Posner, Yael; Shimon, Linda J. W.; Klajn, RafalProceedings of the National Academy of Sciences of the United States of America (2018), 115 (38), 9379-9384CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Efficient mol. switching in confined spaces is crit. for the successful development of artificial mol. machines. However, mol. switching events often entail large structural changes and therefore require conformational freedom, which is typically limited under confinement conditions. Here, we investigated the behavior of azobenzene-the key building block of light-controlled mol. machines-in a confined environment that is flexible and can adapt its shape to that of the bound guest. To this end, we encapsulated several structurally diverse azobenzenes within the cavity of a flexible, water-sol. coordination cage, and investigated their light-responsive behavior. Using UV/visible absorption spectroscopy and a combination of NMR methods, we showed that each of the encapsulated azobenzenes exhibited distinct switching properties. An azobenzene forming a 1:1 host-guest inclusion complex could be efficiently photoisomerized in a reversible fashion. In contrast, successful switching in inclusion complexes incorporating two azobenzene guests was dependent on the availability of free cages in the system, and it involved reversible trafficking of azobenzene between the cages. In the absence of extra cages, photoswitching was either suppressed or it involved expulsion of azobenzene from the cage and consequently its pptn. from the soln. This finding was utilized to develop an information storage medium in which messages could be written and erased in a reversible fashion using light.
- 2Kundu, P. K.; Olsen, G. L.; Kiss, V.; Klajn, R. Nanoporous frameworks exhibiting multiple stimuli responsiveness. Nat. Commun. 2014, 5, 3588, DOI: 10.1038/ncomms4588Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2cnhsF2jsg%253D%253D&md5=2a0ca98dcb275e4e9ee1d92819423bc5Nanoporous frameworks exhibiting multiple stimuli responsivenessKundu Pintu K; Klajn Rafal; Olsen Gregory L; Kiss VladimirNature communications (2014), 5 (), 3588 ISSN:.Nanoporous frameworks are polymeric materials built from rigid molecules, which give rise to their nanoporous structures with applications in gas sorption and storage, catalysis and others. Conceptually new applications could emerge, should these beneficial properties be manipulated by external stimuli in a reversible manner. One approach to render nanoporous frameworks responsive to external signals would be to immobilize molecular switches within their nanopores. Although the majority of molecular switches require conformational freedom to isomerize, and switching in the solid state is prohibited, the nanopores may provide enough room for the switches to efficiently isomerize. Here we describe two families of nanoporous materials incorporating the spiropyran molecular switch. These materials exhibit a variety of interesting properties, including reversible photochromism and acidochromism under solvent-free conditions, light-controlled capture and release of metal ions, as well reversible chromism induced by solvation/desolvation.
- 3Chu, Z.; Han, Y.; Bian, T.; De, S.; Král, P.; Klajn, R. Supramolecular Control of Azobenzene Switching on Nanoparticles. J. Am. Chem. Soc. 2019, 141, 1949– 1960, DOI: 10.1021/jacs.8b09638Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXkvFKk&md5=4d7b9f8e6f7e454c1a31d2eb7f63d206Supramolecular Control of Azobenzene Switching on NanoparticlesChu, Zonglin; Han, Yanxiao; Bian, Tong; De, Soumen; Kral, Petr; Klajn, RafalJournal of the American Chemical Society (2019), 141 (5), 1949-1960CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene's hydrophobic nature, most of these examples have been realized only in org. solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-sol. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amt. of azobenzene on the functionalized nanoparticles. Mol. dynamics simulations helped us to identify two distinct supramol. architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aq. solubilities. Azobenzenes adsorbed on these water-sol. nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aq. media and, in the long run, in biol. environments.
- 4Zhao, H.; Sen, S.; Udayabhaskararao, T.; Sawczyk, M.; Kučanda, K.; Manna, D.; Kundu, P. K.; Lee, J.-W.; Král, P.; Klajn, R. Reversible trapping and reaction acceleration within dynamically self-assembling nanoflasks. Nat. Nanotechnol. 2016, 11, 82– 88, DOI: 10.1038/nnano.2015.256Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVyhtrfF&md5=c71b923ef34cad1bdbb857f7eee92999Reversible trapping and reaction acceleration within dynamically self-assembling nanoflasksZhao, Hui; Sen, Soumyo; Udayabhaskararao, T.; Sawczyk, Michal; Kucanda, Kristina; Manna, Debasish; Kundu, Pintu K.; Lee, Ji-Woong; Kral, Petr; Klajn, RafalNature Nanotechnology (2016), 11 (1), 82-88CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The chem. behavior of mols. can be significantly modified by confinement to vols. comparable to the dimensions of the mols. Although such confined spaces can be found in various nanostructured materials, such as zeolites, nanoporous org. frameworks and colloidal nanocrystal assemblies, the slow diffusion of mols. in and out of these materials has greatly hampered studying the effect of confinement on their physicochem. properties. Here, we show that this diffusion limitation can be overcome by reversibly creating and destroying confined environments by means of UV and visible light irradn. We use colloidal nanocrystals functionalized with light-responsive ligands that readily self-assemble and trap various mols. from the surrounding bulk soln. Once trapped, these mols. can undergo chem. reactions with increased rates and with stereoselectivities significantly different from those in bulk soln. Illumination with visible light disassembles these nanoflasks, releasing the product in soln. and thereby establishes a catalytic cycle. These dynamic nanoflasks can be useful for studying chem. reactivities in confined environments and for synthesizing mols. that are otherwise hard to achieve in bulk soln.
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- 11Gonzalez, A.; Kengmana, E. S.; Fonseca, M. V.; Han, G. G. D. Solid-state photoswitching molecules: structural design for isomerization in condensed phase. Materials Today Adv. 2020, 6, 100058, DOI: 10.1016/j.mtadv.2020.100058Google ScholarThere is no corresponding record for this reference.
- 12Cohen, M. D.; Ron, I.; Schmidt, G. M. J.; Thomas, J. M. Photochemical Decoration of Dislocations inside Crystals of Acenaphthyne. Nature 1969, 224, 167– 168, DOI: 10.1038/224167a0Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXmvVCn&md5=794e08e122c4411969d26bf29ffec840Photochemical decoration of dislocations inside crystals of acenaphthyleneCohen, Mendel David; Ron, I.; Schmidt, Gerhardt M. J.; Thomas, John MeurigNature (London, United Kingdom) (1969), 224 (5215), 167-8CODEN: NATUAS; ISSN:0028-0836.The solid in which dislocations were revealed, acenaphthylene (I), dimerizes under irradn. at ∼300 nm to yield a trans dimer (II). II is orthorhombic pseudotetragonal with a 7.82, b 7.85, and c 14.04 Å; the space group is Pba21 or Pbma; d. = 1.17 for Z = 4; the m.p. is 307°. Thin (∼0.01 cm) single crystals of I were prepd. from slowly cooled melts and irradiated for several hr at 0° (to suppress sublimation and thermal polymn. of the monomer). The interior of the crystal was illuminated by transmitted polarized light, or by reflected uv light. The strictly crystallographic nature of the aligned II nuclei and tendency for the anthracene photodimer to crystallize at dislocation cores (J. M. Thomas, et al., 1967) are evidence that the patterns revealed are due to locked-in dislocation networks and to terraces which are produced by dislocation glide. Cross-slip freely occurs in I and is probably the principal mechanism for dislocation multiplication in this solid. Screw dislocations are not strongly preferred over edge dislocations. For all the obsd. angles of intersections, it was possible to suggest an internally consistent set of planes in which dislocations glide relatively freely.
- 13Wang, R.; Iyoda, T.; Jiang, L.; Tryk, D. A.; Hashimoto, K.; Fujishima, A. Structural investigation of azobenzene-containing self-assembled monolayer films. J. Electroanal. Chem. 1997, 438, 213– 219, DOI: 10.1016/S0022-0728(96)05031-0Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXktVCju7Y%253D&md5=cad1c1339f47bf32e70feabb2d590b2cStructural investigation of azobenzene-containing self-assembled monolayer filmsWang, Rong; Iyoda, Tomokazu; Jiang, Lei; Tryk, Donald A.; Hashimoto, Kazuhito; Fujishima, AkiraJournal of Electroanalytical Chemistry (1997), 438 (1-2), 213-219CODEN: JECHES ISSN:. (Elsevier Science S.A.)An azobenzene-terminated long chain alkane-thiol was used for self-assembly onto Au substrates. A remarkable lack of activity for trans-to-cis photoisomerization in the film was quant. evaluated using a combined photochem.-electrochem. method. Film structure was then examd. using UV-visible spectroscopy and at. force microscopy (AFM). Results indicated the azobenzene-contg. mols. were extraordinarily densely packed in the self-assembled monolayer. A pinwheel structure, in which the long axes of azobenzene moieties were parallel to each other and the neighboring short axes were mutually perpendicular to each other, was supported by UV-visible and IR evidence and was obsd. directly with AFM. This structure is consistent with the dense packing. By comparing the structure of the same mol. in the cryst. state, it was obsd. that the pinwheel structure can be ascribed to a combination of covalent bonding between the S head-groups of the mol. and Au atoms of the substrate, strong van der Waals interaction of the alkane chains, and interactions between neighboring azobenzene moieties.
- 14Klajn, R. Immobilized azobenzenes for the construction of photoresponsive materials. Pure Appl. Chem. 2010, 82, 2247– 2279, DOI: 10.1351/PAC-CON-10-09-04Google ScholarThere is no corresponding record for this reference.
- 15Kusukawa, T.; Fujita, M. Ship-in-a-Bottle” Formation of Stable Hydrophobic Dimers of cis-Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination Nanocage. J. Am. Chem. Soc. 1999, 121, 1397– 1398, DOI: 10.1021/ja9837295Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvFCrtw%253D%253D&md5=88dc88b5795487a78f96109d578d09e7"Ship-in-a-Bottle" Formation of Stable Hydrophobic Dimers of cis-Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination NanocageKusukawa, Takahiro; Fujita, MakotoJournal of the American Chemical Society (1999), 121 (6), 1397-1398CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The cage compd. [Pd6(en)6L4](NO3)12 (I) (L = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) is capable of selective enclathration of C-shaped mols. as hydrophobic dimers, such as cis-azobenzenes and cis-stilbenes to give I.2Q (Q = cis-p-methylazobenzene, cis-p-methylstilbene, cis-p-methoxystilbene, cis-azobenzene and cis-bis(4-methoxyphenyl)ethane). The ship-in-a-bottle assembly of the hydrophobic dimer in the cage is suggested by NMR data.
- 16Moldt, T.; Brete, D.; Przyrembel, D.; Das, S.; Goldman, J. R.; Kundu, P. K.; Gahl, C.; Klajn, R.; Weinelt, M. Tailoring the Properties of Surface-Immobilized Azobenzenes by Monolayer Dilution and Surface Curvature. Langmuir 2015, 31, 1048– 1057, DOI: 10.1021/la504291nGoogle Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitFOgtr7N&md5=ae4f32a585066c4e127fe2b9ea88e2ffTailoring the Properties of Surface-Immobilized Azobenzenes by Monolayer Dilution and Surface CurvatureMoldt, Thomas; Brete, Daniel; Przyrembel, Daniel; Das, Sanjib; Goldman, Joel R.; Kundu, Pintu K.; Gahl, Cornelius; Klajn, Rafal; Weinelt, MartinLangmuir (2015), 31 (3), 1048-1057CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Photoswitching in densely packed azobenzene self-assembled monolayers (SAMs) is strongly affected by steric constraints and excitonic coupling between neighboring chromophores. Therefore, control of the chromophore d. is essential for enhancing and manipulating the photoisomerization yield. The authors compared two methods to achieve this goal, first assembling monocomponent azobenzene-alkanethiolate SAMs on gold nanoparticles of varying size. Then mixed SAMs of azobenzene-alkanethiolates and "dummy" alkanethiolates were prepd. on planar substrates. Both methods led to a gradual decrease of the chromophore d. and enable efficient photoswitching with low-power light sources. X-ray spectroscopy revealed that coadsorption from soln. yields mixts. with tunable compn. The orientation of the chromophores with respect to the surface normal changed from a tilted to an upright position with increasing azobenzene d. For both systems, optical spectroscopy revealed a pronounced excitonic shift that increased with the chromophore d. In spite of exciting the optical transition of the monomer, the main spectral change in mixed SAMs occurred in the excitonic band. The photoisomerization yield decreased only slightly by increasing the azobenzene-alkanethiolate d., and we obsd. photoswitching even with minor dilns. Unlike in soln., azobenzene in the planar SAM could be switched back almost completely by optical excitation from the cis to the original trans state within a short time scale. These observations indicate cooperativity in the photoswitching process of mixed SAMs.
- 17Moldt, T.; Przyrembel, D.; Schulze, M.; Bronsch, W.; Boie, L.; Brete, D.; Gahl, C.; Klajn, R.; Tegeder, P.; Weinelt, M. Differing Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in Vacuum. Langmuir 2016, 32, 10795– 10801, DOI: 10.1021/acs.langmuir.6b01690Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFOkt73N&md5=6f6f22a01204d21ff3d61b3f8965ac7fDiffering Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in VacuumMoldt, Thomas; Przyrembel, Daniel; Schulze, Michael; Bronsch, Wibke; Boie, Larissa; Brete, Daniel; Gahl, Cornelius; Klajn, Rafal; Tegeder, Petra; Weinelt, MartinLangmuir (2016), 32 (42), 10795-10801CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Azobenzenealkanethiols in self-assembled monolayers (SAMs) on Au(111) exhibit reversible trans-cis photoisomerization when dild. with alkanethiol spacers. Using these mixed SAMs, the authors show switching of the linear optical and second-harmonic response. The effective switching of these surface optical properties relies on a reasonably large cross section and a high photoisomerization yield as well as a long lifetime of the metastable cis isomer. The switching process was quantified by X-ray absorption spectra. The cross sections for the trans-cis and cis-trans photoisomerization with 365 and 455 nm light, resp., are 1 order of magnitude smaller than in soln. In vacuum, the 365 nm photostationary state comprises 50-74% of the mols. in the cis form, limited by their rapid thermal isomerization back to the trans state. In contrast, the 455 nm photostationary state contains nearly 100% trans-azobenzene. We detd. time consts. for the thermal cis-trans isomerization of only a few minutes in vacuum and in a dry nitrogen atm. but of more than 1 day in ambient air. Our results suggest that adventitious water adsorbed on the surface of the SAM stabilizes the polar cis configuration of azobenzene under ambient conditions. The back reaction rate consts. differing by 2 orders of magnitude underline the huge influence of the environment and, accordingly, its importance when comparing various expts.
- 18Han, M.; Ishikawa, D.; Honda, T.; Ito, E.; Hara, M. Light-driven molecular switches in azobenzene self-assembled monolayers: effect of molecular structure on reversible photoisomerization and stable cis state. Chem. Commun. 2010, 46, 3598– 3600, DOI: 10.1039/b921801gGoogle Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlvVSkur8%253D&md5=6ba0d6cfc33615a6fcd02af345b42f62Light-driven molecular switches in azobenzene self-assembled monolayers: effect of molecular structure on reversible photoisomerization and stable cis stateHan, Mina; Ishikawa, Daisuke; Honda, Takumu; Ito, Eisuke; Hara, MasahikoChemical Communications (Cambridge, United Kingdom) (2010), 46 (20), 3598-3600CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Both the reversible trans ↔ cis photoisomerization and slow thermal back cis-to-trans isomerization of azobenzene-functionalized self-assembled monolayers on gold surfaces have been achieved by rationally designed single-component azobenzene thiol.
- 19Santos Hurtado, C.; Bastien, G.; Mašát, M.; Štoček, J. R.; Dračínský, M.; Rončević, I.; Císařová, I.; Rogers, C. T.; Kaleta, J. Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV–vis and NMR Spectroscopy. J. Am. Chem. Soc. 2020, 142, 9337– 9351, DOI: 10.1021/jacs.0c01753Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXot1Wlsrs%253D&md5=58c1587e20ffafc3a9f63ffa5f3ac902Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV-vis and NMR SpectroscopySantos Hurtado, Carina; Bastien, Guillaume; Masat, Milan; Stocek, Jakub Radek; Dracinsky, Martin; Roncevic, Igor; Cisarova, Ivana; Rogers, Charles T.; Kaleta, JiriJournal of the American Chemical Society (2020), 142 (20), 9337-9351CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Using solid-state 15N NMR spectroscopy, the cis/trans isomerization in a two-dimensional (2-D) array of surface-mounted azobenzene-based switches was detected for the first time. In order to achieve this, a new class of rod-shaped mol. switches, suitable for formation of 2-D regular arrays on large facets of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) nanocrystals, was synthesized. A mechanochem. approach was used to prep. corresponding host-guest surface inclusions in a TPP matrix. Comparison of thermal steps in soln. and supramol. surface inclusions revealed that switching of individual mols. is not compromised by the close proximity of neighbors.
- 20Negishi, Y.; Kamimura, U.; Ide, M.; Hirayama, M. A photoresponsive Au25 nanocluster protected by azobenzene derivative thiolates. Nanoscale 2012, 4, 4263– 4268, DOI: 10.1039/c2nr30830dGoogle Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XptlWnt70%253D&md5=d7dd917db4fb1da0b975febe79b9ddb5A photoresponsive Au25 nanocluster protected by azobenzene derivative thiolatesNegishi, Yuichi; Kamimura, Ukyo; Ide, Mao; Hirayama, MichiyoNanoscale (2012), 4 (14), 4263-4268CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)An Au25 cluster protected by azobenzene deriv. thiolates (S-Az) ([Au25(S-Az)18]-) was synthesized with the aim of producing a photoresponsive Au25 cluster. The matrix-assisted laser desorption/ionization mass spectrum of the product revealed that [Au25(S-Az)18]- was synthesized in high purity. Optical absorption spectra of [Au25(S-Az)18]- obtained before and after photoirradn. suggest that the azobenzenes in the ligands of Au25(S-Az)18 isomerize with an efficiency of nearly 100%, both from the trans to cis conformation and from the cis to trans conformation. Furthermore, the redox potential and optical absorption of Au25(S-Az)18 change reversibly due to photoisomerization of azobenzenes.
- 21Dolgopolova, E. A.; Berseneva, A. A.; Faillace, M. S.; Ejegbavwo, O. A.; Leith, G. A.; Choi, S. W.; Gregory, H. N.; Rice, A. M.; Smith, M. D.; Chruszcz, M.; Garashchuk, S.; Mythreye, K.; Shustova, N. B. Confinement-Driven Photophysics in Cages, Covalent–Organic Frameworks, Metal–Organic Frameworks, and DNA. J. Am. Chem. Soc. 2020, 142, 4769– 4783, DOI: 10.1021/jacs.9b13505Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjsVOns74%253D&md5=997b2ba493960570ec3ad5cdc493dad8Confinement-driven photophysics in cages, covalent-organic frameworks, metal-organic frameworks, and DNADolgopolova, Ekaterina A.; Berseneva, Anna A.; Faillace, Martin S.; Ejegbavwo, Otega A.; Leith, Gabrielle A.; Choi, Seok W.; Gregory, Haley N.; Rice, Allison M.; Smith, Mark D.; Chruszcz, Maksymilian; Garashchuk, Sophya; Mythreye, Karthikeyan; Shustova, Natalia B.Journal of the American Chemical Society (2020), 142 (10), 4769-4783CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photophysics tunability through alteration of framework aperture (metal-org. framework (MOF) = variable; guest = const.) was probed for the first time in comparison with previously explored concepts (MOF = const.; guest = variable). In particular, anal. of the confinement effect on a photophys. response of integrated 5-(3-chlorobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one (Cl-BI) chromophore allowed us to establish a photophysics-aperture relationship. To shed light on the obsd. correlation, the framework confined environment was replicated using a mol. cage, Pd6(TPT)4 (TPT = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine), thus allowing for utilization of crystallog., spectroscopy, and theor. simulations to reveal the effect a confined space has on the chromophore's mol. conformation (including disruption of strong hydrogen bonding and novel conformer formation) and any assocd. changes on a photophys. response. Furthermore, the chosen Cl-oHBI@Pd6(TPT)4 (Cl-oHBI = 5-(5-chloro-2-hydroxybenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one, chromophore) system was applied as a tool for targeted cargo delivery of a chromophore to the confined space of DNA, which resulted in promotion of chromophore-DNA interactions through a well-established intercalation mechanism. Moreover, the developed principles were applied toward utilizing a HBI-based chromophore as a fluorescent probe on the example of macrophage cells. For the first time, suppression of non-radiative decay pathways of a chromophore was tested by anchoring the chromophore to a framework metal node, portending a potential avenue to develop an alternative to natural biomarkers. Overall, these studies are among the first attempts to demonstrate the unrevealed potential of a confined scaffold environment for tailoring a material's photophys. response.
- 22Danowski, W.; van Leeuwen, T.; Abdolahzadeh, S.; Roke, D.; Browne, W. R.; Wezenberg, S.; Feringa, B. L. Unidirectional rotary motion in a metal–organic framework. Nat. Nanotechnol. 2019, 14, 488– 494, DOI: 10.1038/s41565-019-0401-6Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms1Ogtrk%253D&md5=861d9bbbd1eafb32a0004a698d9d741aUnidirectional rotary motion in a metal-organic frameworkDanowski, Wojciech; van Leeuwen, Thomas; Abdolahzadeh, Shaghayegh; Roke, Diederik; Browne, Wesley R.; Wezenberg, Sander J.; Feringa, Ben L.Nature Nanotechnology (2019), 14 (5), 488-494CODEN: NNAABX; ISSN:1748-3387. (Nature Research)Overcrowded alkene-based light-driven mol. motors are able to perform large-amplitude repetitive unidirectional rotations. Their behavior is well understood in soln. However, Brownian motion precludes the precise positioning at the nanoscale needed to harness cooperative action. Here, authors demonstrate mol. motors organized in cryst. metal-org. frameworks (MOFs). The motor unit becomes a part of the org. linker (or strut), and its spatial arrangement is elucidated through powder and single-crystal x-ray analyses and polarized optical and Raman microscopies. They confirm that the light-driven unidirectional rotation of the motor units is retained in the MOF framework and that the motors can operate in the solid state with similar rotary speed (rate of thermal helix inversion) to that in soln. These 'moto-MOFs' could in the future be used to control dynamic function in cryst. materials.
- 23Samanta, D.; Galaktionova, D.; Gemen, J.; Shimon, L. J. W.; Diskin-Posner, Y.; Avram, L.; Král, P.; Klajn, R. Reversible chromism of spiropyran in the cavity of a flexible coordination cage. Nat. Commun. 2018, 9, 641, DOI: 10.1038/s41467-017-02715-6Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MrhtlCgtw%253D%253D&md5=3b0b16177f47ce496acec9a361e4cd0bReversible chromism of spiropyran in the cavity of a flexible coordination cageSamanta Dipak; Gemen Julius; Klajn Rafal; Galaktionova Daria; Kral Petr; Shimon Linda J W; Diskin-Posner Yael; Avram Liat; Kral Petr; Kral PetrNature communications (2018), 9 (1), 641 ISSN:.Confining molecules to volumes only slightly larger than the molecules themselves can profoundly alter their properties. Molecular switches-entities that can be toggled between two or more forms upon exposure to an external stimulus-often require conformational freedom to isomerize. Therefore, placing these switches in confined spaces can render them non-operational. To preserve the switchability of these species under confinement, we work with a water-soluble coordination cage that is flexible enough to adapt its shape to the conformation of the encapsulated guest. We show that owing to its flexibility, the cage is not only capable of accommodating-and solubilizing in water-several light-responsive spiropyran-based molecular switches, but, more importantly, it also provides an environment suitable for the efficient, reversible photoisomerization of the bound guests. Our findings pave the way towards studying various molecular switching processes in confined environments.
- 24Kobatake, S.; Takami, S.; Muto, H.; Ishikawa, T.; Irie, M. Rapid and reversible shape changes of molecular crystals on photoirradiation. Nature 2007, 446, 778– 781, DOI: 10.1038/nature05669Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktVeqtrc%253D&md5=1aaa9a8858aa3c0c0f115bccd466626eRapid and reversible shape changes of molecular crystals on photoirradiationKobatake, Seiya; Takami, Shizuka; Muto, Hiroaki; Ishikawa, Tomoyuki; Irie, MasahiroNature (London, United Kingdom) (2007), 446 (7137), 778-781CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)The development of actuators based on materials that reversibly change shape and/or size in response to external stimuli has attracted interest for some time. A particularly intriguing possibility is offered by light-responsive materials, which allow remote operation without the need for direct contact to the actuator. The photoresponse of these materials is based on the photoisomerization of constituent mols. (typically trans-cis isomerization of azobenzene chromophores), which gives rise to mol. motions and thereby deforms the bulk material. This effect has been used to create light-deformable polymer films and gels, but the response of these systems is relatively slow. The authors report that mol. crystals based on diarylethene chromophores and with sizes ranging from 10 to 100 μm exhibit rapid and reversible macroscopic changes in shape and size induced by UV and visible light. The authors find that on exposure to UV light, a single crystal of 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene changes from a square shape to a lozenge shape, whereas a rectangular single crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene contracts by about 5-7 per cent. The deformed crystals are thermally stable, and switch back to their original state on irradn. with visible light. The authors find that the authors crystals respond in about 25 μs (i.e., about five orders of magnitude faster than the response time of the azobenzene-based polymer systems) and that they can move microscopic objects, making them promising materials for possible light-driven actuator applications.
- 25Jia, C.; Migliore, A.; Xin, N.; Huang, S.; Wang, J.; Yang, Q.; Wang, S.; Chen, H.; Wang, D.; Feng, B.; Liu, Z.; Zhang, G.; Qu, D.-H.; Tian, H.; Ratner, M. A.; Xu, H. Q.; Nitzan, A.; Guo, X. Covalently bonded single-molecule junctions with stable and reversible photoswitched conductivity. Science 2016, 352, 1443– 1445, DOI: 10.1126/science.aaf6298Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslOqs74%253D&md5=6ecca36730ce7856881ee196592a0b74Covalently bonded single-molecule junctions with stable and reversible photoswitched conductivityJia, Chuancheng; Migliore, Agostino; Xin, Na; Huang, Shaoyun; Wang, Jinying; Yang, Qi; Wang, Shuopei; Chen, Hongliang; Wang, Duoming; Feng, Boyong; Liu, Zhirong; Zhang, Guangyu; Qu, Da-Hui; Tian, He; Ratner, Mark A.; Xu, H. Q.; Nitzan, Abraham; Guo, XuefengScience (Washington, DC, United States) (2016), 352 (6292), 1443-1445CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Through mol. engineering, single diarylethenes were covalently sandwiched between graphene electrodes to form stable mol. conduction junctions. Our exptl. and theor. studies of these junctions consistently show and interpret reversible conductance photoswitching at room temp. and stochastic switching between different conductive states at low temp. at a single-mol. level. We demonstrate a fully reversible, two-mode, single-mol. elec. switch with unprecedented levels of accuracy (on/off ratio of ∼100), stability (over a year), and reproducibility (46 devices with more than 100 cycles for photoswitching and ∼105 to 106 cycles for stochastic switching).
- 26Katsonis, N.; Kudernac, T.; Walko, M.; van der Molen, S. J.; van Wees, B. J.; Feringa, B. L. Reversible Conductance Switching of Single Diarylethenes on a Gold Surface. Adv. Mater. 2006, 18, 1397– 1400, DOI: 10.1002/adma.200600210Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XlvVOgtbg%253D&md5=524f3a095bc0c232341fa58990057b85Reversible conductance switching of single diarylethenes on a gold surfaceKatsonis, Nathalie; Kudernac, Tibor; Walko, Martin; van der Molen, Sense Jan; van Wees, Bart J.; Feringa, Ben L.Advanced Materials (Weinheim, Germany) (2006), 18 (11), 1397-1400CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Light-controlled conductance switching of diarylethenes attached to Au(111) is reported. First, scanning tunneling microscopy is used to demonstrate reversible photoswitching for individual mols. Second, reversible switching in self-assembled monolayers is established by means of optical spectroscopy.
- 27Arramel; Pijper, T. C.; Kudernac, T.; Katsonis, N.; van der Maas, M.; Feringa, B. L.; van Wees, B. J. Reversible light induced conductance switching of asymmetric diarylethenes on gold: surface and electronic studies. Nanoscale 2013, 5, 9277– 9282, DOI: 10.1039/c3nr00832kGoogle Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVers7vE&md5=d16605e471a455f35650d33e60f5afdeReversible light induced conductance switching of asymmetric diarylethenes on gold. Surface and electronic studiesArramel; Pijper, Thomas C.; Kudernac, Tibor; Katsonis, Nathalie; van der Maas, Minko; Feringa, Ben L.; van Wees, Bart J.Nanoscale (2013), 5 (19), 9277-9282CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)We report on the light-induced switching of conductance of a new generation of diarylethene switches embedded in an insulating matrix of dodecanethiol on Au(111), by scanning tunneling microscopy (STM). The diarylethene switches we synthesize and study are modified diarylethenes where the thiophene unit at one side of the mol. backbone introduces an intrinsic asymmetry into the switch, which is expected to influence its photo-conductance properties. We show that reversible conversion between 2 distinguishable conductance states can be controlled via photoisomerization of the switches by alternative irradn. with UV (λ = 313 nm) or visible (λ > 420 nm) light. We addressed this phenomenon by STM in ambient conditions, based on switching of the apparent height of the mols. which convert from 4-6 Å in their closed form to 0-1 Å in their open form. Furthermore, the levels of the frontier MO levels (HOMO and LUMO) were evaluated for these asym. switches by scanning tunneling spectroscopy at 77 K, which allowed us to det. a HOMO-LUMO energy gap of 2.24 eV.
- 28Hou, L.; Leydecker, T.; Zhang, X.; Rekab, W.; Herder, M.; Cendra, C.; Hecht, S.; McCulloch, I.; Salleo, A.; Orgiu, E.; Samorì, P. Engineering Optically Switchable Transistors with Improved Performance by Controlling Interactions of Diarylethenes in Polymer Matrices. J. Am. Chem. Soc. 2020, 142, 11050– 11059, DOI: 10.1021/jacs.0c02961Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOmtLbF&md5=80eef9df218b4cc3dd01acfa61e1ea53Engineering Optically Switchable Transistors with Improved Performance by Controlling Interactions of Diarylethenes in Polymer MatricesHou, Lili; Leydecker, Tim; Zhang, Xiaoyan; Rekab, Wassima; Herder, Martin; Cendra, Camila; Hecht, Stefan; McCulloch, Iain; Salleo, Alberto; Orgiu, Emanuele; Samori, PaoloJournal of the American Chemical Society (2020), 142 (25), 11050-11059CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The integration of photochromic mols. into semiconducting polymer matrixes via blending has recently attracted a great deal of attention, as it provides the means to reversibly modulate the output signal of electronic devices by using light as a remote control. However, the structural and electronic interactions between photochromic mols. and semiconducting polymers are far from being fully understood. Here we perform a comparative investigation by combining two photochromic diarylethene moieties possessing similar energy levels yet different propensity to aggregate with five prototypical polymer semiconductors exhibiting different energy levels and structural order, ranging from amorphous to semicryst. Our in-depth photochem., structural, morphol., and elec. characterization reveals that the photoresponsive behavior of thin-film transistors including polymer/diarylethenes blends as the active layer is governed by a complex interplay between the relative position of the energy levels and the polymer matrix microstructure. By matching the energy levels and optimizing the mol. packing, high-performance optically switchable org. thin-film transistors were fabricated. These findings represent a major step forward in the fabrication of light-responsive org. devices.
- 29Sciascia, C.; Castagna, R.; Dekermenjian, M.; Martel, R.; Srimath Kandada, A. R.; Di Fonzo, F.; Bianco, A.; Bertarelli, C.; Meneghetti, M.; Lanzani, G. Light-Controlled Resistance Modulation in a Photochromic Diarylethene–Carbon Nanotube Blend. J. Phys. Chem. C 2012, 116, 19483– 19489, DOI: 10.1021/jp212231jGoogle Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFOisr3I&md5=c638be080c1a6839df81e2396b919b66Light-Controlled Resistance Modulation in a Photochromic Diarylethene-Carbon Nanotube BlendSciascia, Calogero; Castagna, Rossella; Dekermenjian, Maria; Martel, Richard; Srimath Kandada, Ajay R.; Di Fonzo, Fabio; Bianco, Andrea; Bertarelli, Chiara; Meneghetti, Moreno; Lanzani, GuglielmoJournal of Physical Chemistry C (2012), 116 (36), 19483-19489CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Photochromic mols. are part of a large class of materials in which light stimulus not only induces a color variation but also affects other physicochem. properties. However, the change of bulk elec. properties (e.g., elec. cond.) via light excitation remains difficult to control because the intrinsically switchable mols. may lose their functionality when wired with conductive electrodes. In contrast with previous work based on single mols., here the authors demonstrate a facile and accessible wet-chem. method to produce light-induced elec. switching. The elec. cond. of a photochromic blend composed of diarylethene polymer and single-walled carbon nanotubes (SWNTs) is reversibly tuned according with UV-vis excitation. The devices present good thermal stability and remarkable fatigue resistance under ambient conditions. Supported by elec. and spectroscopic evidence, the authors show that the intertube elec. coupling, mediated by the light-induced electrocyclization of the diarylethene unit, is the mechanism responsible for the modulation.
- 30El Gemayel, M.; Börjesson, K.; Herder, M.; Duong, D. T.; Hutchison, J. A.; Ruzié, C.; Schweicher, G.; Salleo, A.; Geerts, Y.; Hecht, S.; Orgiu, E.; Samorì, P. Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matrices. Nat. Commun. 2015, 6, 6330, DOI: 10.1038/ncomms7330Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtF2lurfN&md5=e35fbc381f15dafa589cc965ab143585Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matricesEl Gemayel, Mirella; Borjesson, Karl; Herder, Martin; Duong, Duc T.; Hutchison, James A.; Ruzie, Christian; Schweicher, Guillaume; Salleo, Alberto; Geerts, Yves; Hecht, Stefan; Orgiu, Emanuele; Samori, PaoloNature Communications (2015), 6 (), 6330CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The fabrication of multifunctional high-performance org. thin-film transistors as key elements in future logic circuits is a major research challenge. Here we demonstrate that a photoresponsive bi-functional field-effect transistor with carrier mobilities exceeding 0.2 cm2 V-1 s-1 can be developed by incorporating photochromic mols. into an org. semiconductor matrix via a single-step soln. processing deposition of a two components blend. Tuning the interactions between the photochromic diarylethene system and the org. semiconductor is achieved via ad-hoc side functionalization of the diarylethene. Thereby, a large-scale phase-segregation can be avoided and superior miscibility is provided, while retaining optimal π-π stacking to warrant efficient charge transport and to attenuate the effect of photoinduced switching on the extent of current modulation. This leads to enhanced elec. performance of transistors incorporating small conjugated mols. as compared with polymeric semiconductors. These findings are of interest for the development of high-performing optically gated electronic devices.
- 31Canton, M.; Grommet, A. B.; Pesce, L.; Gemen, J.; Li, S.; Diskin-Posner, Y.; Credi, A.; Pavan, G. M.; Andréasson, J.; Klajn, R. Improving Fatigue Resistance of Dihydropyrene by Encapsulating within a Coordination Cage. J. Am. Chem. Soc. 2020, 142, 14557– 14565, DOI: 10.1021/jacs.0c06146Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhsFOlu7rO&md5=4da6ff40387d24c9d3a2cd41deba9a2bImproving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination CageCanton, Martina; Grommet, Angela B.; Pesce, Luca; Gemen, Julius; Li, Shiming; Diskin-Posner, Yael; Credi, Alberto; Pavan, Giovanni M.; Andreasson, Joakim; Klajn, RafalJournal of the American Chemical Society (2020), 142 (34), 14557-14565CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photochromic mols. undergo reversible isomerization upon irradn. with light at different wavelengths, a process that can alter their phys. and chem. properties. For instance, dihydropyrene (DHP) is a deep-colored compd. that isomerizes to light-brown cyclophanediene (CPD) upon irradn. with visible light. CPD can then isomerize back to DHP upon irradn. with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimol. events involving this unstable intermediate thus result in rapid decompn. and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a PdII6L4 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although mol. confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic mols., but may also increase the amt. of product obtainable from traditionally low-yielding org. reactions.
- 32Samanta, D.; Mukherjee, S.; Patil, Y. P.; Mukherjee, P. S. Self-Assembled Pd6 Open Cage with Triimidazole Walls and the Use of Its Confined Nanospace for Catalytic Knoevenagel- and Diels–Alder Reactions in Aqueous Medium. Chem. - Eur. J. 2012, 18, 12322– 12329, DOI: 10.1002/chem.201201679Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht1Wktr7N&md5=6b0e91194f096995c78a8959f1f6d0a1Self-Assembled Pd6 Open Cage with Triimidazole Walls and the Use of Its Confined Nanospace for Catalytic Knoevenagel- and Diels-Alder Reactions in Aqueous MediumSamanta, Dipak; Mukherjee, Sandip; Patil, Yogesh P.; Mukherjee, Partha SarathiChemistry - A European Journal (2012), 18 (39), 12322-12329, S12322/1-S12322/13CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)The two-component self-assembly of a 90° PdII acceptor and a triimidazole donor gave a water-sol. semi-cylindrical cage with a hydrophobic cavity, which was sep. crystd. with hydrophilic- and hydrophobic guests. The parent cage was found to catalyze the Knoevenagel condensation reaction of arom. mono-aldehydes with active methylene compds., such as Meldrum's acid or 1,3-dimethylbarbituric acid. The confined hydrophobic nanospace within this cage was also used in the catalytic Diels-Alder reactions of 9-(hydroxymethyl)anthracene with N-phenylmaleimide or N-cyclohexylmaleimide.
- 33Sheepwash, M. A. L.; Mitchell, R. H.; Bohne, C. Mechanistic Insights into the Photochromism of trans-10b,10c-Dimethyl-10b,10c-dihydropyrene Derivatives. J. Am. Chem. Soc. 2002, 124, 4693– 4700, DOI: 10.1021/ja017229eGoogle Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XisFyhu7o%253D&md5=d8d2cc3b9339b8d40be8fa821030686dMechanistic insights into the photochromism of trans-10b,10c-dimethyl-10b,10c-dihydropyrene derivativesSheepwash, Molina A. L.; Mitchell, Reginald H.; Bohne, CorneliaJournal of the American Chemical Society (2002), 124 (17), 4693-4700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A series of dimethyldihydropyrene derivs. was studied to elucidate the photochem. mechanism assocd. with the switching between the dimethyldihydropyrene (DHP, closed) and metacyclophanediene (CPD, open) forms of the mol. Quantum yields of ring opening and closure, fluorescence quantum yields and lifetimes, as well as laser flash photolysis studies were performed to establish the effect of substituents on the switching efficiency. Ring opening of the DHPs occurs from the first singlet excited state. The low quantum yields for the ring opening reaction obsd. (≤0.042) are a consequence of the low rate const. (≤1.7 × 107 s-1) for this process. The quantum yields for ring closure of the CPD were detd. for select compds. and were of the order of 0.1-0.4. These results show that the efficiency for ring opening of this class of compds. is intrinsically low, but can be modulated to some extent by the introduction of substituents. These properties should be taken into account when considering what type of photoswitching devices DHPs might be useful for.
- 34Tu, M.; Reinsch, H.; Rodríguez-Hermida, S.; Verbeke, R.; Stassin, T.; Egger, W.; Dickmann, M.; Dieu, B.; Hofkens, J.; Vankelecom, I. F. J.; Stock, N.; Ameloot, R. Reversible Optical Writing and Data Storage in an Anthracene-Loaded Metal–Organic Framework. Angew. Chem., Int. Ed. 2019, 58, 2423– 2427, DOI: 10.1002/anie.201813996Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFSgsrk%253D&md5=9b99639d7890b79d1749d766cdfddbd1Reversible Optical Writing and Data Storage in an Anthracene-Loaded Metal-Organic FrameworkTu, Min; Reinsch, Helge; Rodriguez-Hermida, Sabina; Verbeke, Rhea; Stassin, Timothee; Egger, Werner; Dickmann, Marcel; Dieu, Bjorn; Hofkens, Johan; Vankelecom, Ivo F. J.; Stock, Norbert; Ameloot, RobAngewandte Chemie, International Edition (2019), 58 (8), 2423-2427CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Metal-org. frameworks (MOFs) enable the design of host-guest systems with specific properties. In this work, we show how the confinement of anthracene in a well-chosen MOF host leads to reversible yellow-to-purple photoswitching of the fluorescence emission. This behavior has not been obsd. before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host-guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and vol. as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.
- 35Becker, H. D.; Andersson, K. Photochemical Diels–Alder dimerization of 9-phenylethylnylanthracene. J. Photochem. 1984, 26, 75– 77, DOI: 10.1016/0047-2670(84)85029-7Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXlvFSrsL0%253D&md5=b2e55371f49d57cd44f25176e78baf66Photochemical Diels-Alder dimerization of 9-phenylethynylanthraceneBecker, Hans Dieter; Andersson, KjellJournal of Photochemistry (1984), 26 (1), 75-7CODEN: JPCMAE; ISSN:0047-2670.Crystallog. indicates that the title reaction of I (R = PhC≡C) (II) gives the Diels-Alder adduct III (R = PhC≡C, R1 = 9-anthracenyl) via a centrosym. complex. Similar attempted reactions of RC≡CH (R = H, Ph) to anthracene gave only dianthracene. The electron stoichiometry, the regiochem., and mechanism of the reaction, and the photochem. excitation and conjugation in II are discussed.
- 36Das, S.; Okamura, N.; Yagi, S.; Ajayaghosh, A. Supramolecular Gel Phase Controlled [4 + 2] Diels–Alder Photocycloaddition for Electroplex Mediated White Electroluminescence. J. Am. Chem. Soc. 2019, 141, 5635– 5639, DOI: 10.1021/jacs.9b00955Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXmtlWisb8%253D&md5=ac1e76d5581b33823043f80eba56413bSupramolecular Gel Phase Controlled [4 + 2] Diels-Alder Photocycloaddition for Electroplex Mediated White ElectroluminescenceDas, Satyajit; Okamura, Naoki; Yagi, Shigeyuki; Ajayaghosh, AyyappanpillaiJournal of the American Chemical Society (2019), 141 (14), 5635-5639CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Diels-Alder photocycloaddn. of 9-phenylethynylanthracene results in multiple [4 + 2] and [4 + 4] cycloaddn. products in soln., which can be controlled to form specific products under a restricted environment. We have exploited the gel phase of a 9-phenylethynylanthracence deriv. as a confined medium to specifically yield the [4 + 2] cycloadduct in >90% yield. The photocycloadduct (anti-form) exhibited a blue emission with CIE chromaticity of x = 0.16/y = 0.16. Construction of an org. light emitting device with the photocycloadduct, using a carbazole-based hole transporting host, resulted in white light emission with a CIE chromaticity of x = 0.33/y = 0.32. This observation not only highlights the use of gel chem. to achieve the otherwise difficult to obtain photoproducts but also underlines their potential in optoelectronic device fabrication.
- 37Kim, M.; Hohman, J. N.; Cao, Y.; Houk, K. N.; Ma, H.; Jen, A. K.-Y.; Weiss, P. S. Creating Favorable Geometries for Directing Organic Photoreactions in Alkanethiolate Monolayers. Science 2011, 331, 1312– 1315, DOI: 10.1126/science.1200830Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXivVWksbw%253D&md5=c68f7297fe13dc70152f2ee1f8ee0e24Creating Favorable Geometries for Directing Organic Photoreactions in Alkanethiolate MonolayersKim, Moonhee; Hohman, J. Nathan; Cao, Yang; Houk, Kendall N.; Ma, Hong; Jen, Alex K.-Y.; Weiss, Paul S.Science (Washington, DC, United States) (2011), 331 (6022), 1312-1315CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The products of photoreactions of conjugated org. mols. may be allowed by selection rules but not obsd. in soln. reactions because of unfavorable reaction geometries. We have used defect sites in self-assembled alkanethiolate monolayers on gold surfaces to direct geometrically unfavorable photochem. reactions between individual org. mols. High cond. and stochastic switching of anthracene-terminated phenylethynylthiolates within alkanethiolate monolayers, as well as in situ photochem. transformations, have been obsd. and distinguished with the scanning tunneling microscope (STM). UV light absorbed during imaging increases the apparent heights of excited mols. in STM images, a direct manifestation of probing electronically excited states.
- 38Zheng, Y. B.; Payton, J. L.; Song, T.-B.; Pathem, B. K.; Zhao, Y.; Ma, H.; Yang, Y.; Jensen, L.; Jen, A. K.-Y.; Weiss, P. S. Surface-Enhanced Raman Spectroscopy To Probe Photoreaction Pathways and Kinetics of Isolated Reactants on Surfaces: Flat versus Curved Substrates. Nano Lett. 2012, 12, 5362– 5368, DOI: 10.1021/nl302750dGoogle Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtlGnu7jE&md5=2c41e912afcbb13d3db25c42094404a8Surface-Enhanced Raman Spectroscopy To Probe Photoreaction Pathways and Kinetics of Isolated Reactants on Surfaces: Flat versus Curved SubstratesZheng, Yue Bing; Payton, John L.; Song, Tze-Bin; Pathem, Bala Krishna; Zhao, Yuxi; Ma, Hong; Yang, Yang; Jensen, Lasse; Jen, Alex K.-Y.; Weiss, Paul S.Nano Letters (2012), 12 (10), 5362-5368CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The authors identify and control the photoreaction paths of self-assembled monolayers (SAMs) of thiolate-linked anthracene phenylethynyl mols. on Au substrate surfaces, and study the effects of nanoscale morphol. of substrates on regioselective photoreactions. Two types of morphologies, atomically flat and curved, are produced on Au surfaces by controlling substrate structure and metal deposition. The authors employ surface-enhanced Raman spectroscopy (SERS), combined with Raman mode analyses using d. functional theory, to identify the different photoreaction paths and to track the photoreaction kinetics and efficiencies of mols. in monolayers. The SAMs on curved surfaces exhibit dramatically lower regioselective photoreaction kinetics and efficiencies than those on atomically flat surfaces. This result is attributed to the increased intermol. distances and variable orientations on the curved surfaces. Better understanding of the morphol. effects of substrates will enable control of nanoparticle functionalization in ligand exchange in targeted delivery of therapeutics and theranostics and in catalysis.
- 39Zdobinsky, T.; Sankar Maiti, P.; Klajn, R. Support Curvature and Conformational Freedom Control Chemical Reactivity of Immobilized Species. J. Am. Chem. Soc. 2014, 136, 2711– 2714, DOI: 10.1021/ja411573aGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c3kslCnsQ%253D%253D&md5=29f29254961ffbffb578b2c5ed8cd1feSupport curvature and conformational freedom control chemical reactivity of immobilized speciesZdobinsky Tino; Maiti Pradipta Sankar; Klajn RafalJournal of the American Chemical Society (2014), 136 (7), 2711-4 ISSN:.We show that bimolecular reactions between species confined to the surfaces of nanoparticles can be manipulated by the nature of the linker, as well as by the curvature of the underlying particles.
- 40Muraoka, T.; Kinbara, K.; Aida, T. Mechanical twisting of a guest by a photoresponsive host. Nature 2006, 440, 512– 515, DOI: 10.1038/nature04635Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xis1OlsL8%253D&md5=e1f15a4cff1979a22c9c68c901583350Mechanical twisting of a guest by a photoresponsive hostMuraoka, Takahiro; Kinbara, Kazushi; Aida, TakuzoNature (London, United Kingdom) (2006), 440 (7083), 512-515CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Mol. analogs of a variety of mech. devices such as shuttles, brakes, unidirectional rotors and tweezers have been created. But these 'mol. machines' have not yet been used to mech. manipulate a second mol. in a controlled and reversible manner. Here we show that light-induced scissor-like conformational changes of one mol. can give rise to mech. twisting of a non-covalently bound guest mol. To realize this coupling of mol. motions, we use a previously designed system: a ferrocene moiety with an azobenzene strap, each end of which is attached to one of the two cyclopentadienyl rings of the ferrocene unit, acts as a pivot so that photoisomerization of the strap rotates the ferrocene rings relative to each other and thereby also changes the relative position of two 'pedal' moieties attached to the ferrocene rings. We translate this effect into intermol. coupling of motion by endowing the pedals with binding sites, which allow the host system to form a stable complex with a bidentate rotor mol. Using CD spectroscopy, we show that the photoinduced conformational changes of the host are indeed transmitted and induce mech. twisting of the rotor mol. This design concept, which significantly extends the successful coupling of motion beyond the intramol. level seen in synthetic allosteric receptors, might allow for the remote control of mol. events in larger interlocked mol. systems.
- 41Coskun, A.; Friedman, D. C.; Li, H.; Patel, K.; Khatib, H. A.; Stoddart, J. F. A Light-Gated STOP–GO Molecular Shuttle. J. Am. Chem. Soc. 2009, 131, 2493– 2495, DOI: 10.1021/ja809225eGoogle Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFegsL0%253D&md5=fe810aa73641e162aabce83d1132412cA light-gated STOP-GO molecular shuttleCoskun, Ali; Friedman, Douglas C.; Li, Hao; Patel, Kaushik; Khatib, Hussam A.; Stoddart, J. FraserJournal of the American Chemical Society (2009), 131 (7), 2493-2495CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Degenerate [2]rotaxanes, with their two identical binding sites, generally exhibit equil. dynamics with free energies of activation (ΔG‡) for the shuttling process starting as low as 10 kcal/mol-1. This ΔG‡ value can be raised quite dramatically by inserting "speed bumps" in the form of steric and/or electrostatic barriers into the linkers between the two identical binding sites. In our more recent research targeted toward the exploitation of the 4,4'-azobiphenyloxy unit (ABP) as a light-operated gate, we decided to introduce (i) four Me groups on the one hand and (ii) four fluorine atoms on the other, at the 3,5,3',5'-positions of the ABP units to curtail binding by the CBPQT4+ ring if not sterically in the case of (i), then electronically in the case of (ii). The first approach led to a gate (ABP-Me4) that remains closed all the time, whereas the second approach affords a gate (ABP-F4) that we can close with UV light and open with visible light. Herein, we show how light can be used, in conjunction with thermal energy, to raise and lower the free energy barrier at will and, in so doing, impart STOP and GO instructions upon the operation of a mol. shuttle.
- 42Pace, G.; Ferri, V.; Grave, C.; Elbing, M.; von Hänisch, C.; Zharnikov, M.; Mayor, M.; Rampi, M. A.; Samorì, P. Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 9937– 9942, DOI: 10.1073/pnas.0703748104Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmvVChtrg%253D&md5=6793d00b61e29b13a81f632c2451223eCooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayersPace, Giuseppina; Ferri, Violetta; Grave, Christian; Elbing, Mark; von Haenisch, Carsten; Zharnikov, Michael; Mayor, Marcel; Rampi, Maria Anita; Samori, PaoloProceedings of the National Academy of Sciences of the United States of America (2007), 104 (24), 9937-9942CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Photochromic systems can convert light energy into mech. energy, thus they can be used as building blocks for the fabrication of prototypes of mol. devices that are based on the photomech. effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged mols. The authors show by scanning tunneling microscopy imaging the photochem. switching of a new terminally thiolated azobiphenyl rigid rod mol. Interestingly, the switching of entire mol. 2D cryst. domains is obsd., which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-d. data storage.
- 43Fredy, J. W.; Méndez-Ardoy, A.; Kwangmettatam, S.; Bochicchio, D.; Matt, B.; Stuart, M. C. A.; Huskens, J.; Katsonis, N.; Pavan, G. M.; Kudernac, T. Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 11850– 11855, DOI: 10.1073/pnas.1711184114Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1aju7fK&md5=83b78a7ce199f1a688d87f3e8fc02d13Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubulesFredy, Jean W.; Mendez-Ardoy, Alejandro; Kwangmettatam, Supaporn; Bochicchio, Davide; Matt, Benjamin; Stuart, Marc C. A.; Huskens, Jurriaan; Katsonis, Nathalie; Pavan, Giovanni M.; Kudernac, TiborProceedings of the National Academy of Sciences of the United States of America (2017), 114 (45), 11850-11855CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Chemists have created mol. machines and switches with specific mech. responses that were typically demonstrated in soln., where mech. relevant motion is dissipated in the Brownian storm. The next challenge consists of designing specific mechanisms through which the action of individual mols. is transmitted to a supramol. architecture, with a sense of directionality. Cellular microtubules are capable of meeting such a challenge. While their capacity to generate pushing forces by ratcheting growth is well known, conversely these versatile machines can also pull microscopic objects apart through a burst of their rigid tubular structure. One essential feature of this disassembling mechanism is the accumulation of strain in the tubules, which develops when tubulin dimers change shape, triggered by a hydrolysis event. We envision a strategy toward supramol. machines generating directional pulling forces by harnessing the mech. purposeful motion of mol. switches in supramol. tubules. Here, we report on wholly synthetic, water-sol., and chiral tubules that incorporate photoswitchable building blocks in their supramol. architecture. Under illumination, these tubules display a nonlinear operation mode, by which light is transformed into units of strain by the shape changes of individual switches, until a threshold is reached and the tubules unleash the strain energy. The operation of this wholly synthetic and stripped-down system compares to the conformational wave by which cellular microtubules disassemble. Addnl., atomistic simulations provide mol. insight into how strain accumulates to induce destabilization. Our findings pave the way toward supramol. machines that would photogenerate pulling forces, at the nanoscale and beyond.
- 44Bochicchio, D.; Kwangmettatam, S.; Kudernac, T.; Pavan, G. M. How Defects Control the Out-of-Equilibrium Dissipative Evolution of a Supramolecular Tubule. ACS Nano 2019, 13, 4322– 4334, DOI: 10.1021/acsnano.8b09523Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXltFCjsbw%253D&md5=460309c10a44f9a043042ad25bf9c31fHow Defects Control the Out-of-Equilibrium Dissipative Evolution of a Supramolecular TubuleBochicchio, Davide; Kwangmettatam, Supaporn; Kudernac, Tibor; Pavan, Giovanni M.ACS Nano (2019), 13 (4), 4322-4334CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Supramol. architectures that work out-of-equil. or that can change in specific ways when absorbing external energy are ubiquitous in nature. Gaining the ability to create via self-assembly artificial materials possessing such fascinating behaviors would have a major impact in many fields. However, the rational design of similar dynamic structures requires to understand and, even more challenging, to learn how to master the mol. mechanisms governing how the assembled systems evolve far from the equil. Typically, this represents a daunting challenge due to the limited mol. insight that can be obtained by the expts. or by classical modeling approaches. Here we combine coarse-grained mol. models and advanced simulation approaches to study at submol. (<5 Å) resoln. a supramol. tubule, which breaks and disassembles upon absorption of light energy triggering isomerization of its azobenzene-contg. monomers. Our approach allows us to investigate the mol. mechanism of monomer transition in the assembly and to elucidate the kinetic process for the accumulation of the transitions in the system. Despite the stochastic nature of the excitation process, we demonstrate how these tubules preferentially dissipate the absorbed energy locally via the amplification of defects in their supramol. structure. We find that this constitutes the best kinetic pathway for accumulating monomer transitions in the system, which dets. the dynamic evolution out-of-equil. and the brittle behavior of the assembly under perturbed conditions. Thanks to the flexibility of our models, we finally come out with a general principle, where defects explain and control the brittle/soft behavior of such light-responsive assemblies.
- 45Chu, Z.; Klajn, R. Polysilsesquioxane Nanowire Networks as an “Artificial Solvent” for Reversible Operation of Photochromic Molecules. Nano Lett. 2019, 19, 7106– 7111, DOI: 10.1021/acs.nanolett.9b02642Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvVWksr3E&md5=0986b73d0572a35ba8429a664f022e6cPolysilsesquioxane nanowire networks as an artificial solvent for reversible operation of photochromic moleculesChu, Zonglin; Klajn, RafalNano Letters (2019), 19 (10), 7106-7111CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Efficient isomerization of photochromic mols. often requires conformational freedom and is typically not available under solvent-free conditions. Here, we report a general methodol. allowing for reversible switching of such mols. on the surfaces of solid materials. Our method is based on dispersing photochromic compds. within polysilsesquioxane nanowire networks (PNNs), which can be fabricated as transparent, highly porous, micrometer-thick layers on various substrates. We found that azobenzene switching within the PNNs proceeded unusually fast compared with the same mols. in liq. solvents. Efficient isomerization of another photochromic system, spiropyran, from a colorless to a colored form was used to create reversible images in PNN-coated glass. The coloration reaction could be induced with sunlight and is of interest for developing "smart" windows.
- 46Akiyama, H.; Tamada, K.; Nagasawa, J.; Abe, K.; Tamaki, T. Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para Substituted Azobenzenes. J. Phys. Chem. B 2003, 107, 130– 135, DOI: 10.1021/jp026103gGoogle Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptFOhurc%253D&md5=10dbc902e8a58c91506c76f3091d2413Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para-Substituted AzobenzenesAkiyama, Haruhisa; Tamada, Kaoru; Nagasawa, Junichi; Abe, Koji; Tamaki, TakashiJournal of Physical Chemistry B (2003), 107 (1), 130-135CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)Asym. dialkyl disulfides with a para-substituted azobenzene (i.e., 4-substituted 4'-(12-(dodecyldithio)dodecyloxy)azobenzenes) produced photoresponsive self-assembled monolayers (SAMs) on Au (111) surfaces. IR reflection absorption (IR-RA) spectroscopy and reflection UV and visible (visible) light absorption spectroscopy gave information on the mol. orientational order of the adsorbates in the SAMs. The photoreactivity was studied using dynamic contact-angle measurements with a Wilhelmy-type surface balance. The structure and photoreactivity of the SAMs were dependent on the substituent at the para position of an azobenzene moiety. Relatively ordered structures in the methylene parts and the photoisomerization of azobenzene moieties were obsd. for the SAMs formed from the hexyl- and the nonsubstituted azobenzene disulfides. However, a less-ordered SAM structure was seen for the cyanoazobenzene disulfide SAM, and the photoresponse is rather unstable.
- 47Titov, E.; Granucci, G.; Götze, J. P.; Persico, M.; Saalfrank, P. Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects. J. Phys. Chem. Lett. 2016, 7, 3591– 3596, DOI: 10.1021/acs.jpclett.6b01401Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOqu7rP&md5=acdc1bc0bd1dff46f544dbd93b00e7abDynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric EffectsTitov, Evgenii; Granucci, Giovanni; Goetze, Jan Philipp; Persico, Maurizio; Saalfrank, PeterJournal of Physical Chemistry Letters (2016), 7 (18), 3591-3596CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)While azobenzenes readily photoswitch in soln., their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. The authors address these possibilities by means of nonadiabatic mol. dynamics with trajectory surface hopping calcns., investigating the trans → cis isomerization of azobenzene after excitation into the ππ* absorption band. The authors consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of addnl. azobenzene mols., imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, mol. switch. Simulations reveal that in comparison to the single mol. the quantum yield of the trans → cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implications of dimerization and steric constraints are also discussed.
- 48Cantatore, V.; Granucci, G.; Rousseau, G.; Padula, G.; Persico, M. Photoisomerization of Self-Assembled Monolayers of Azobiphenyls: Simulations Highlight the Role of Packing and Defects. J. Phys. Chem. Lett. 2016, 7, 4027– 4031, DOI: 10.1021/acs.jpclett.6b02018Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKmsbzL&md5=818e9627fa0b614ba68cfd437a6b3b31Photoisomerization of Self-Assembled Monolayers of Azobiphenyls: Simulations Highlight the Role of Packing and DefectsCantatore, Valentina; Granucci, Giovanni; Rousseau, Guillaume; Padula, Giancarlo; Persico, MaurizioJournal of Physical Chemistry Letters (2016), 7 (19), 4027-4031CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We present surface hopping simulations of the photodynamics of self-assembled monolayers (SAMs) of 4'-(biphenyl-4-ylazo)-biphenyl-4-thiol (ABPT) on Au(111). We show that trans → cis photoisomerization is suppressed because of steric hindrance in a well-ordered SAM. Photoisomerization is instead viable in the presence of defects. Two particularly important defects are the boundaries between domains of trans-ABPT mols. leaning in different directions (a line defect) and single cis mols. embedded in a SAM of trans (a point defect). Our findings explain the cooperative behavior obsd. during the photoisomerization of a trans-ABPT SAM, leading to large domains of pure cis and trans isomers. The line and point defects are predicted to produce different patterns of cis-ABPT mols. during the early stages of the photoconversion.
- 49Lai, C.-Y.; Raj, G.; Liepuoniute, I.; Chiesa, M.; Naumov, P. Direct Observation of Photoinduced trans–cis Isomerization on Azobenzene Single Crystal. Cryst. Growth Des. 2017, 17, 3306– 3312, DOI: 10.1021/acs.cgd.7b00288Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmvVGntb8%253D&md5=4b9c4a50d264173c0caaf415173af248Direct observation of photoinduced trans-cis isomerization on azobenzene single crystalLai, Chia-Yun; Raj, Gijo; Liepuoniute, Ieva; Chiesa, Matteo; Naumov, PanceCrystal Growth & Design (2017), 17 (6), 3306-3312CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)Photoexcitation can lead to either homogeneous or heterogeneous transformations of a reactive surface. Homogeneous transformations result in a statistical mixt. of reactants and products, whereas the outcome of heterogeneous transformations is a coexistence of macroscopic reactant and product domains, sepd. by a phase boundary. Heterogeneous photoinduced changes are also typically restricted to the surface, have individual phase structures that are inaccessible with classical diffraction methods, and possess surface properties that cannot readily be measured by the traditional wetting (water contact angle) technique. In this study, we demonstrate application of Atomic Force Microscopy (AFM) to obtain high spatial resoln. surface energy distribution in the trans and cis domains on the surface of azobenzene single crystal. UV excitation of single crystals of 3',4'-dimethyl-4-(dimethylamino)azobenzene results in domino-like trans-to-cis isomerization on their surface. In the AFM phase channel, this affords contrasting domains with different physicochem. properties. Small amplitude small set point (SASS) method and bimodal AFM operated in the attractive regime provide maps of the tip-sample adhesion force and the Hamaker const., resp. The results show that the Hamaker const. of the cis domains (∼1 × 10-19 J) is higher than that of the trans domains (∼7 × 10-20 J). After UV irradn., the calcd. surface energies of the domains were ∼40% higher based on the Hamaker const. Within a broader context, the results presented here demonstrate the potency of AFM-based surface-sensitive techniques for probing of the dynamic changes in surface properties upon photoinduced isomerization of mol. switches.
- 50Pesce, L.; Perego, C.; Grommet, A. B.; Klajn, R.; Pavan, G. M. Molecular Factors Controlling the Isomerization of Azobenzenes in the Cavity of a Flexible Coordination Cage. J. Am. Chem. Soc. 2020, 142, 9792– 9802, DOI: 10.1021/jacs.0c03444Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXosVSitLk%253D&md5=574e6fde7deb3487e1d3fdf3bc028414Molecular Factors Controlling the Isomerization of Azobenzenes in the Cavity of a Flexible Coordination CagePesce, Luca; Perego, Claudio; Grommet, Angela B.; Klajn, Rafal; Pavan, Giovanni M.Journal of the American Chemical Society (2020), 142 (21), 9792-9802CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photoswitchable mols. are employed for many applications, from the development of active materials to the design of stimuli-responsive mol. systems and light-powered mol. machines. To fully exploit their potential, we must learn ways to control the mechanism and kinetics of their photoinduced isomerization. One possible strategy involves confinement of photoresponsive switches such as azobenzenes or spiropyrans within crowded mol. environments, which may allow control over their light-induced conversion. However, the mol. factors that influence and control the switching process under realistic conditions and within dynamic mol. regimes often remain difficult to ascertain. As a case study, here we have employed mol. models to probe the isomerization of azobenzene guests within a Pd(II)-based coordination cage host in water. Atomistic mol. dynamics and metadynamics simulations allow us to characterize the flexibility of the cage in the solvent, the (rare) guest encapsulation and release events, and the relative probability/kinetics of light-induced isomerization of azobenzene analogs in these host-guest systems. In this way, we can reconstruct the mechanism of azobenzene switching inside the cage cavity and explore key mol. factors that may control this event. We obtain a mol.-level insight on the effects of crowding and host-guest interactions on azobenzene isomerization. The detailed picture elucidated by this study may enable the rational design of photoswitchable systems whose reactivity can be controlled via host-guest interactions.
- 51Hanopolskyi, A. I.; De, S.; Białek, M. J.; Diskin-Posner, Y.; Avram, L.; Feller, M.; Klajn, R. Reversible switching of arylazopyrazole within a metal–organic cage. Beilstein J. Org. Chem. 2019, 15, 2398– 2407, DOI: 10.3762/bjoc.15.232Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVyqtrrF&md5=cbb6c6d63b6c9ac9390e546946b42355Reversible switching of arylazopyrazole within a metal-organic cageHanopolskyi, Anton I.; De, Soumen; Bialek, Michal J.; Diskin-Posner, Yael; Avram, Liat; Feller, Moran; Klajn, RafalBeilstein Journal of Organic Chemistry (2019), 15 (), 2398-2407CODEN: BJOCBH; ISSN:1860-5397. (Beilstein-Institut zur Foerderung der Chemischen Wissenschaften)Arylazopyrazoles represent a new family of mol. photoswitches characterized by a near-quant. conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd-imidazole coordination. Owing to its high water soly., the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not sol. in water. NMR spectroscopy and X-ray crystallog. have independently demonstrated that each cage can encapsulate two mols. of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calcns. suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage.
- 52Klajn, R. Spiropyran-based dynamic materials. Chem. Soc. Rev. 2014, 43, 148– 184, DOI: 10.1039/C3CS60181AGoogle Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVGktLvK&md5=3f1e3c4f172f5d1da08476ecc2344df1Spiropyran-based dynamic materialsKlajn, RafalChemical Society Reviews (2014), 43 (1), 148-184CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A review. In the past few years, spiropyran has emerged as the mol. of choice for the construction of novel dynamic materials. This unique mol. switch undergoes structural isomerization in response to a variety of orthogonal stimuli, e.g. light, temp., metal ions, redox potential, and mech. stress. Incorporation of this switch onto macromol. supports or inorg. scaffolds allows for the creation of robust dynamic materials. This review discusses the synthesis, switching conditions and use of dynamic materials in which spiropyran has been attached to the surfaces of polymers, biomacromols., inorg. nanoparticles, as well as solid surfaces. The resulting materials show fascinating properties whereby the state of the switch intimately affects a multitude of useful properties of the support. The utility of the spiropyran switch will undoubtedly endow these materials with far-reaching applications in the near future.
- 53Lerch, M. M.; Wezenberg, S. J.; Szymanski, W.; Feringa, B. L. Unraveling the Photoswitching Mechanism in Donor–Acceptor Stenhouse Adducts. J. Am. Chem. Soc. 2016, 138, 6344– 6347, DOI: 10.1021/jacs.6b01722Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntlCmtrY%253D&md5=65feb79220cf86d96a790eba76e25989Unraveling the Photoswitching Mechanism in Donor-Acceptor Stenhouse AdductsLerch, Michael M.; Wezenberg, Sander J.; Szymanski, Wiktor; Feringa, Ben L.Journal of the American Chemical Society (2016), 138 (20), 6344-6347CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The photoswitching mechanism of donor-acceptor Stenhouse adducts (DASA), a recently reported class of photoswitches, is shown to proceed via E-Z photoisomerization followed by a thermal, con-rotatory 4π-electrocyclization. The photogenerated intermediate is manifested by a bathochromically shifted band in the visible absorption spectrum of the DASA. The identification of the role of this intermediate reveals a key step in the photoswitching mechanism that is essential to the rational design of switching properties via structural modification.
- 54Udayabhaskararao, T.; Kundu, P. K.; Ahrens, J.; Klajn, R. Reversible Photoisomerization of Spiropyran on the Surfaces of Au25 Nanoclusters. ChemPhysChem 2016, 17, 1805– 1809, DOI: 10.1002/cphc.201500897Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVOlt7bE&md5=0f960ed916622e9cfd46878a0538360fReversible Photoisomerization of Spiropyran on the Surfaces of Au25 NanoclustersUdayabhaskararao, T.; Kundu, Pintu K.; Ahrens, Johannes; Klajn, RafalChemPhysChem (2016), 17 (12), 1805-1809CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Au25 nanoclusters functionalized with a spiropyran mol. switch are synthesized via a ligand-exchange reaction at low temp. The resulting nanoclusters are characterized by optical and NMR spectroscopies as well as by mass spectrometry. Spiropyran bound to nanoclusters isomerizes in a reversible fashion when exposed to UV and visible light, and its properties are similar to those of free spiropyran mols. in soln. The reversible photoisomerization entails the modulation of fluorescence as well as the light-controlled self-assembly of nanoclusters.
- 55Kundu, P. K.; Das, S.; Ahrens, J.; Klajn, R. Controlling the lifetimes of dynamic nanoparticle aggregates by spiropyran functionalization. Nanoscale 2016, 8, 19280– 19286, DOI: 10.1039/C6NR05959GGoogle Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs12ks7vE&md5=32fefcef4721fc7416cbd081f8a94f0aControlling the lifetimes of dynamic nanoparticle aggregates by spiropyran functionalizationKundu, Pintu K.; Das, Sanjib; Ahrens, Johannes; Klajn, RafalNanoscale (2016), 8 (46), 19280-19286CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Novel light-responsive nanoparticles were synthesized by decorating the surfaces of gold and silver nanoparticles with a nitrospiropyran mol. photoswitch. Upon exposure to UV light in nonpolar solvents, these nanoparticles self-assembled to afford spherical aggregates, which disassembled rapidly when the UV stimulus was turned off. The sizes of these aggregates depended on the nanoparticle concn., and their lifetimes could be controlled by adjusting the surface concn. of nitrospiropyran on the nanoparticles. The conformational flexibility of nitrospiropyran, which was altered by modifying the structure of the background ligand, had a profound impact on the self-assembly process. By coating the nanoparticles with a spiropyran lacking the nitro group, a conceptually different self-assembly system, relying on a reversible proton transfer, was realized. The resulting particles spontaneously (in the dark) assembled into aggregates that could be readily disassembled upon exposure to blue light.
- 56Cabrera, I.; Krongauz, V. Dynamic ordering of aggregated mesomorphic macromolecules. Nature 1987, 326, 582– 585, DOI: 10.1038/326582a0Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsFGjtL4%253D&md5=5d7144fd237e14e35d1e1c6aff9c1be9Dynamic ordering of aggregated mesomorphic macromoleculesCabrera, Ivan; Krongauz, ValeriNature (London, United Kingdom) (1987), 326 (6113), 582-5CODEN: NATUAS; ISSN:0028-0836.Structural transformations in a thermotropic liq.-cryst. copolymer of I and CH2:CHCO2(CH2)6O-p-C6H4CO2-p-C6H4CN caused by shearing or other mech. perturbations resulted in restoration of parallel arrangement of the mesogenic groups as well as reconstruction of the main chain conformation. Phys. crosslinking due to aggregation of the merocyanine dye moieties (from thermal conversion of the spiropyran side groups) in I led to network formation which was responsible for the appearance of a new rheo-optical effect obsd. above the clearing point.
- 57Ahrens, J.; Bian, T.; Vexler, T.; Klajn, R. Irreversible Bleaching of Donor–Acceptor Stenhouse Adducts on the Surfaces of Magnetite Nanoparticles. ChemPhotoChem 2017, 1, 230– 236, DOI: 10.1002/cptc.201700009Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KgtbvM&md5=3184f957d41f8cc6202120b2f1b58b49Irreversible Bleaching of Donor-Acceptor Stenhouse Adducts on the Surfaces of Magnetite NanoparticlesAhrens, Johannes; Bian, Tong; Vexler, Tom; Klajn, RafalChemPhotoChem (2017), 1 (5), 230-236CODEN: CHEMYH ISSN:. (Wiley-VCH Verlag GmbH & Co. KGaA)Two novel donor-acceptor Stenhouse adducts (DASAs) featuring the catechol moiety were synthesized and characterized. Both compds. bind strongly to the surfaces of magnetite nanoparticles. An adrenaline-derived DASA renders the particles insol. in all common solvents, likely because of poor solvation of the zwitterionic isomer generated on the nanoparticle surfaces. Well-sol. nanoparticles were successfully obtained using dopamine-derived DASA equipped with a long alkyl chain. Upon its attachment to nanoparticles, this DASA undergoes an irreversible decoloration reaction owing to the formation of the zwitterionic form. The reaction follows first-order kinetics and proceeds more rapidly on large nanoparticles. Interestingly, decoloration can be suppressed in the presence of free DASA mols. in soln. or at high nanoparticle concns.
- 58Williams, D. E.; Martin, C. R.; Dolgopolova, E. A.; Swifton, A.; Godfrey, D. C.; Ejegbavwo, O. A.; Pellechia, P. J.; Smith, M. D.; Shustova, N. B. Flipping the Switch: Fast Photoisomerization in a Confined Environment. J. Am. Chem. Soc. 2018, 140, 7611– 7622, DOI: 10.1021/jacs.8b02994Google Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVags77O&md5=137454435f0af95aa275c1cc53a77e04Flipping the Switch: Fast Photoisomerization in a Confined EnvironmentWilliams, Derek E.; Martin, Corey R.; Dolgopolova, Ekaterina A.; Swifton, Anton; Godfrey, Danielle C.; Ejegbavwo, Otega A.; Pellechia, Perry J.; Smith, Mark D.; Shustova, Natalia B.Journal of the American Chemical Society (2018), 140 (24), 7611-7622CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Stimuli-responsive materials are vital for addressing emerging demands in the advanced technol. sector as well as current industrial challenges. Here, we report for the first time that coordinative integration of photoresponsive building blocks possessing photochromic spiropyran and diarylethene moieties within a rigid scaffold of metal-org. frameworks (MOFs) could control photophysics, in particular, cycloreversion kinetics, with a level of control that is not accessible in the solid state or soln. On the series of photoactive materials, we demonstrated for the first time that photoisomerization rates of photochromic compds. could be tuned within almost 2 orders of magnitude. Moreover, cycloreversion rates of photoresponsive derivs. could be modulated as a function of the framework structure. Furthermore, through MOF engineering we were able to achieve complete isomerization for coordinatively immobilized spiropyran derivs., typically exhibiting limited photoswitching behavior in the solid state. For instance, spectroscopic anal. revealed that the novel monosubstituted spiropyran deriv. grafted to the backbone of the MOF pillar exhibits a remarkable photoisomerization rate of 0.16 s-1, typical for cycloreversion in soln. We also applied the acquired fundamental principles toward mapping of changes in material properties, which could provide a pathway for monitoring material aging or structural deterioration.
- 59Wang, Z.; Müller, K.; Valášek, M.; Grosjean, S.; Bräse, S.; Wöll, C.; Mayor, M.; Heinke, L. Series of Photoswitchable Azobenzene-Containing Metal–Organic Frameworks with Variable Adsorption Switching Effect. J. Phys. Chem. C 2018, 122, 19044– 19050, DOI: 10.1021/acs.jpcc.8b05843Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlGit7%252FK&md5=15950da71da18498ef1517f39f0706d4Series of Photoswitchable Azobenzene-Containing Metal-Organic Frameworks with Variable Adsorption Switching EffectWang, Zhengbang; Mueller, Kai; Valasek, Michal; Grosjean, Sylvain; Braese, Stefan; Woell, Christof; Mayor, Marcel; Heinke, LarsJournal of Physical Chemistry C (2018), 122 (33), 19044-19050CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Nanoporous metal-org. frameworks (MOFs) equipped with light-responsive azobenzene pendant groups present a novel family of smart materials, enabling advanced applications like switchable guest adsorption, membranes with tunable mol. sepn. factors, and photoswitchable proton conduction. Although it is obvious that for small pore sizes, steric constraints may prohibit azobenzene switching, guidelines for optimizing the MOF architecture to achieve large switching effects have not yet been established. Here, a series of five different photoswitchable azobenzene-contg. pillared-layer MOF structures is presented. The switching effect is quantified by the light-induced increase of the uptake amt. of butanol as the probe mol. For fast and reproducible measurements, thin well-defined MOF films, referred to as surface-mounted MOFs (SURMOFs), were used in combination with a quartz crystal microbalance. Although the series comprises similar MOF structures, the magnitude of the switching effect considerably differs, here by a factor of 5. The uptake data show that, rather than the pore size or the no. of azobenzene mols. per pore, the d. of azobenzene per pore vol. is crucial. The finding that a large switching effect is reached for a high d. of azobenzene moieties per MOF unit cell provides the basis for further applications of photoswitchable MOFs and SURMOFs.
- 60Müller, K.; Helfferich, J.; Zhao, F. L.; Verma, R.; Kanj, A. B.; Meded, V.; Bléger, D.; Wenzel, W.; Heinke, L. Switching the Proton Conduction in Nanoporous, Crystalline Materials by Light. Adv. Mater. 2018, 30, 1706551, DOI: 10.1002/adma.201706551Google ScholarThere is no corresponding record for this reference.
- 61Castiglioni, F.; Danowski, W.; Perego, J.; Leung, F. K.-C.; Sozzani, P.; Bracco, S.; Wezenberg, S. J.; Comotti, A.; Feringa, B. L. Modulation of porosity in a solid material enabled by bulk photoisomerization of an overcrowded alkene. Nat. Chem. 2020, 12, 595– 602, DOI: 10.1038/s41557-020-0493-5Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1KgtbvF&md5=69f6f01350338226fd63708acf633d12Modulation of porosity in a solid material enabled by bulk photoisomerization of an overcrowded alkeneCastiglioni, Fabio; Danowski, Wojciech; Perego, Jacopo; Leung, Franco King-Chi; Sozzani, Piero; Bracco, Silvia; Wezenberg, Sander J.; Comotti, Angiolina; Feringa, Ben L.Nature Chemistry (2020), 12 (7), 595-602CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)The incorporation of photoswitchable mols. into solid-state materials holds promise for the fabrication of responsive materials, the properties of which can be controlled on-demand. However, the possible applications of these materials are limited due to the restrictions imposed by the solid-state environment on the incorporated photoswitches, which render the photoisomerization inefficient. Here we present responsive porous switchable framework materials based on a bistable chiroptical overcrowded alkene incorporated in the backbone of a rigid arom. framework. As a consequence of the high intrinsic porosity, the resulting framework readily responds to a light stimulus, as demonstrated by solid-state Raman and reflectance spectroscopies. Solid-state 13C NMR spectroscopy highlights an efficient and quant. bulk photoisomerization of the incorporated light-responsive overcrowded olefins in the solid material. Taking advantage of the quant. photoisomerization, the porosity of the framework and the consequent gas adsorption can be reversibly modulated in response to light and heat.
- 62Saha, R.; Devaraj, A.; Bhattacharyya, S.; Das, S.; Zangrando, E.; Mukherjee, P. S. Unusual Behavior of Donor–Acceptor Stenhouse Adducts in Confined Space of a Water-Soluble PdII8 Molecular Vessel. J. Am. Chem. Soc. 2019, 141, 8638– 8645, DOI: 10.1021/jacs.9b03924Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXovVKntrg%253D&md5=2d54830caa9d553dc369eeb47256e18aUnusual Behavior of Donor-Acceptor Stenhouse Adducts in Confined Space of a Water-Soluble PdII8 Molecular VesselSaha, Rupak; Devaraj, Anthonisamy; Bhattacharyya, Soumalya; Das, Soumik; Zangrando, Ennio; Mukherjee, Partha SarathiJournal of the American Chemical Society (2019), 141 (21), 8638-8645CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Donor-acceptor Stenhouse adducts (DASA) are new-generation photochromic compds. discovered recently. DASA exist normally in open form (blue/violet) and readily convert to cyclic (light yellow/colorless) zwitterionic form reversibly in the presence of green light in toluene/dioxane. In aq. medium, the open form is not stable and converts to the cyclic zwitterionic form irreversibly. We report here a new self-assembled Pd8 mol. vessel (MV) that can stabilize and store the open form of DASA even in aq. medium. Reaction of the 90° acceptor cis-(tmeda)Pd(NO3)2 (M) [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] with a sym. tetraimidazole donor (L, 3,3',5,5'-tetra(1H-imidazol-1-yl)-1,1'-biphenyl) in a 2:1 molar ratio yielded a water-sol. [8+4] self-assembled M8L4 mol. barrel (MV). This barrel (MV) is found to be a potential mol. vessel to store and stabilize the open forms of DASA in aq. medium over the more stable zwitterionic cyclic form, while in the absence of the barrel the same DASA exist in cyclic zwitterionic form in aq. medium. The hydrophobic interaction between the cavity and the open form of DASA mols. benefits reaching an out-of-equil. or reverse equil. state in aq. medium. The presence of excess MV could even drive the conversion of the stable cyclic form to the open form in aq. medium. The host-guest complex is stable upon irradiating with green light. To the best of our knowledge, this is the first successful attempt to stabilize the open form of DASA mols. in aq. medium and the first report on the fate of DASA in a confined space discrete mol. architecture. Furthermore, the mol. vessel has been utilized for catalytic Michael addn. reactions of a series of nitrostyrene derivs. with 1,3-indandione in aq. medium.
- 63Singh, G.; Chan, H.; Baskin, A.; Gelman, E.; Repnin, N.; Král, P.; Klajn, R. Self-assembly of magnetite nanocubes into helical superstructures. Science 2014, 345, 1149– 1153, DOI: 10.1126/science.1254132Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVGhtLbJ&md5=41873b1ec6481770bbd5fc02430c433cSelf-assembly of magnetite nanocubes into helical superstructuresSingh, Gurvinder; Chan, Henry; Baskin, Artem; Gelman, Elijah; Repnin, Nikita; Kral, Petr; Klajn, RafalScience (Washington, DC, United States) (2014), 345 (6201), 1149-1153CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Organizing inorg. nanocrystals into complex architectures is challenging and typically relies on preexisting templates, such as properly folded DNA or polypeptide chains. We found that under carefully controlled conditions, cubic nanocrystals of magnetite self-assemble into arrays of helical superstructures in a template-free manner with >99% yield. Computer simulations revealed that the formation of helixes is detd. by the interplay of van der Waals and magnetic dipole-dipole interactions, Zeeman coupling, and entropic forces and can be attributed to spontaneous formation of chiral nanocube clusters. Neighboring helixes within their densely packed ensembles tended to adopt the same handedness to maximize packing, thus revealing a novel mechanism of symmetry breaking and chirality amplification.
- 64Sawczyk, M.; Klajn, R. Out-of-Equilibrium Aggregates and Coatings during Seeded Growth of Metallic Nanoparticles. J. Am. Chem. Soc. 2017, 139, 17973– 17978, DOI: 10.1021/jacs.7b09111Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2gu7fO&md5=00cf9c36e2f21a4b446c54605268dcd6Out-of-Equilibrium Aggregates and Coatings during Seeded Growth of Metallic NanoparticlesSawczyk, Michal; Klajn, RafalJournal of the American Chemical Society (2017), 139 (49), 17973-17978CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Although dissipative self-assembly is ubiquitous, where it gives rise to structures and functions crit. to life, examples of artificial systems featuring this mode of self-assembly are rare. Here, the authors identify the presence of ephemeral assemblies during seeded growth of Au nanoparticles. In this process, hydrazine reduces Au(III) ions, which attach to the existing nanoparticles seeds. The attachment is accompanied by a local increase in the concn. of a surfactant, which therefore forms a bilayer on nanoparticle surfaces, inducing their assembly. The resulting aggregates gradually disassemble as the surfactant concn. throughout the soln. equilibrates. The lifetimes of the out-of-equil. aggregates depend on and can be controlled by the size of the constituent nanoparticles. The authors demonstrate the utility of the out-of-equil. aggregates to form transient reflective coatings on polar surfaces.
- 65Udayabhaskararao, T.; Altantzis, T.; Houben, L.; Coronado-Puchau, M.; Langer, J.; Popovitz-Biro, R.; Liz-Marzán, L. M.; Vuković, L.; Král, P.; Bals, S.; Klajn, R. Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices. Science 2017, 358, 514– 518, DOI: 10.1126/science.aan6046Google Scholar65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslSgsb7I&md5=cb2cb80da91ead2c9e6698d496ba91dcTunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlatticesUdayabhaskararao, Thumu; Altantzis, Thomas; Houben, Lothar; Coronado-Puchau, Marc; Langer, Judith; Popovitz-Biro, Ronit; Liz-Marzan, Luis M.; Vukovic, Lela; Kral, Petr; Bals, Sara; Klajn, RafalScience (Washington, DC, United States) (2017), 358 (6362), 514-518CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Self-assembly of inorg. nanoparticles has been used to prep. many different colloidal crystals, but almost invariably with the restriction that these particles must be densely packed. This work showed non-close-packed nanoparticle arrays can be fabricated by selectively removing one of two components comprising binary nanoparticle superlattices. First, a variety of binary nanoparticle superlattices were prepd. at an liq./air interface, including several previously unknown arrangements. Mol. dynamics simulations showed the particular role of the liq. in templating superlattice formation not achievable by self-assembly in bulk soln. Second, upon stabilization, all these binary superlattices could be transformed into distinct nanoallotropes/nanoporous materials of the same chem. compn. but differing in their nanoscale architectures.
- 66Amdursky, N.; Kundu, P. K.; Ahrens, J.; Huppert, D.; Klajn, R. Noncovalent Interactions with Proteins Modify the Physicochemical Properties of a Molecular Switch. ChemPlusChem 2016, 81, 44– 48, DOI: 10.1002/cplu.201500417Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemtL3N&md5=f44f9ba03632a8b7861db598a7caa8c6Noncovalent Interactions with Proteins Modify the Physicochemical Properties of a Molecular SwitchAmdursky, Nadav; Kundu, Pintu K.; Ahrens, Johannes; Huppert, Dan; Klajn, RafalChemPlusChem (2016), 81 (1), 44-48CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)It is reported that spiropyran-a widely investigated mol. photoswitch-can be stabilized in aq. environments in the presence of a variety of proteins, including human serum albumin, insulin fibrils, lysozyme, and glucose oxidase. The optical properties of the complexed photoswitch are protein dependent, with human serum albumin providing the spiropyran with emission features previously obsd. for a photoswitch confined in media of high viscosity. Despite being bound to the protein mols., spiropyran can undergo a ring-opening reaction upon exposure to UV light. This photoisomerization process can affect the properties of the proteins: here, it is shown that the elec. conduction through human serum albumin to which the spiropyran is bound increases following the ring-opening reaction.
- 67Bian, T.; Chu, Z.; Klajn, R. The Many Ways to Assemble Nanoparticles Using Light. Adv. Mater. 2020, 32, 1905866, DOI: 10.1002/adma.201905866Google Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFequr7P&md5=b32f318d96c4963cc0e3dc61f14d0125The Many Ways to Assemble Nanoparticles Using LightBian, Tong; Chu, Zonglin; Klajn, RafalAdvanced Materials (Weinheim, Germany) (2020), 32 (20), 1905866CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. The ability to reversibly assemble nanoparticles using light is both fundamentally interesting and important for applications ranging from reversible data storage to controlled drug delivery. Here, the diverse approaches that have so far been developed to control the self-assembly of nanoparticles using light are reviewed and compared. These approaches include functionalizing nanoparticles with monolayers of photoresponsive mols., placing them in photoresponsive media capable of reversibly protonating the particles under light, and decorating plasmonic nanoparticles with thermoresponsive polymers, to name just a few. The applicability of these methods to larger, micrometer-sized particles is also discussed. Finally, several perspectives on further developments in the field are offered.
- 68Manna, D.; Udayabhaskararao, T.; Zhao, H.; Klajn, R. Orthogonal Light-Induced Self-Assembly of Nanoparticles using Differently Substituted Azobenzenes. Angew. Chem., Int. Ed. 2015, 54, 12394– 12397, DOI: 10.1002/anie.201502419Google Scholar68https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVClsLw%253D&md5=7ed3d2d8934ef7f40cc778683922d74cOrthogonal Light-Induced Self-Assembly of Nanoparticles using Differently Substituted AzobenzenesManna, Debasish; Udayabhaskararao, Thumu; Zhao, Hui; Klajn, RafalAngewandte Chemie, International Edition (2015), 54 (42), 12394-12397CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Precise control of the self-assembly of selected components within complex mixts. is a challenging goal whose realization is important for fabricating novel nanomaterials. Herein we show that by decorating the surfaces of metallic nanoparticles with differently substituted azobenzenes, it is possible to modulate the wavelength of light at which the self-assembly of these nanoparticles is induced. Exposing a mixt. of two types of nanoparticles, each functionalized with a different azobenzene, to UV or blue light induces the selective self-assembly of only one type of nanoparticles. Irradn. with the other wavelength triggers the disassembly of the aggregates, and the simultaneous self-assembly of nanoparticles of the other type. By placing both types of azobenzenes on the same nanoparticles, we created unique materials ("frustrated" nanoparticles) whose self-assembly is induced irresp. of the wavelength of the incident light.
- 69Das, S.; Ranjan, P.; Maiti, P. S.; Singh, G.; Leitus, G.; Klajn, R. Dual-Responsive Nanoparticles and their Self-Assembly. Adv. Mater. 2013, 25, 422– 426, DOI: 10.1002/adma.201201734Google Scholar69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht12jtr3E&md5=10d7e0a453e95435bae2d8916f21bcefDual-Responsive Nanoparticles and their Self-AssemblyDas, Sanjib; Ranjan, Priyadarshi; Maiti, Pradipta Sankar; Singh, Gurvinder; Leitus, Gregory; Klajn, RafalAdvanced Materials (Weinheim, Germany) (2013), 25 (3), 422-426CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors have demonstrated that self-assembly of nanoparticles (NPs) can be controlled independently and/or cooperatively by light and magnetic field. This methodol. could be used to fabricate devices whose electronic properties could independently be modulated using these two orthogonal types of external stimuli. In the context of self-assembly, the results reported can be used to construct dynamically self-assembling magnetic objects which can be guided, using external magnetic fields, to desired locations, where their disassembly can be initiated at will, using visible light. The authors expect that in the long run, this strategy will enable controlled capture, delivery, and release of mol./nanosized cargo.
- 70Chovnik, O.; Balgley, R.; Goldman, J. R.; Klajn, R. Dynamically Self-Assembling Carriers Enable Guiding of Diamagnetic Particles by Weak Magnets. J. Am. Chem. Soc. 2012, 134, 19564– 19567, DOI: 10.1021/ja309633vGoogle Scholar70https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCgsb7J&md5=788b86033c58bb1bfde1dcbff822b6b7Dynamically Self-Assembling Carriers Enable Guiding of Diamagnetic Particles by Weak MagnetsChovnik, Olga; Balgley, Renata; Goldman, Joel R.; Klajn, RafalJournal of the American Chemical Society (2012), 134 (48), 19564-19567CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Diamagnetic particles can be remotely manipulated by a magnet by the reversible adsorption of dual-responsive, light-switchable/superparamagnetic nanoparticles down to their surface. Adsorption occurs upon exposure to UV light, and can be reversed thermally or by ambient light. The dynamic self-assembly of thin films of the dual-responsive nanoparticles induces attractive interactions between diamagnetic particles. Catalytic amts. of the dual-responsive nanoparticles are sufficient to magnetically guide and deliver the diamagnetic particles to desired locations, where they can then be released by disassembling the dynamic layers of superparamagnetic nanoparticles with visible light.
- 71Lee, J.-W.; Klajn, R. Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2. Chem. Commun. 2015, 51, 2036– 2039, DOI: 10.1039/C4CC08541HGoogle Scholar71https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvF2jtrvK&md5=61087db3b48da505da5c85bf36d59252Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2Lee, Ji-Woong; Klajn, RafalChemical Communications (Cambridge, United Kingdom) (2015), 51 (11), 2036-2039CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Metallic nanoparticles co-functionalized with monolayers of UV- and CO2-sensitive ligands were prepd. and shown to respond to these two types of stimuli reversibly and in an orthogonal fashion. The compn. of the coating could be tailored to yield nanoparticles capable of aggregating exclusively when both UV and CO2 were applied at the same time, analogously to the behavior of an AND logic gate.
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Abstract
Figure 1
Figure 1. (a) Light-induced regioselective isomerization of retinal within the binding pocket of bacteriorhodopsin. (b) Structure of bacteriorhodopsin with retinal buried inside its hydrophobic cavity. The arrows indicate the direction of light-induced proton transfer. (c) Binding of retinal (pink sticks with van der Waals radii shown as a transparent halo) encased within the hydrophobic cavity of bacteriorhodopsin (yellow). (d) Structural dynamics of retinal and its immediate surroundings captured by a femtosecond X-ray laser. The transition from trans-retinal to cis-retinal is mapped onto a dark-state model based on the difference Fourier electron density (Fobslight – Fobsdark) contoured at 4σ (yellow, negative; blue, positive). Adapted with permission from ref (5). Copyright 2018 American Association for the Advancement of Science.
Figure 2
Figure 2. (a) Reversible photoisomerization of a diarylethene. The colored isomer featuring extensive conjugation of π electrons (here, the closed form) is shown in green. (b) Reversible light-induced deformation of a single crystal of a simple diarylethene (here, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene). (c) Reversible photoisomerization between dihydropyrene (DHP) and cyclophanediene (CPD). (d) Structural formula of coordination cage 1 used to investigate the behavior of photoswitchable molecules under confinement (left) and crystal structure of an inclusion complex of DHP inside cage 1 (right). (e) Gradual decomposition of DHP in pentane solution over 10 switching cycles. (f) Improved fatigue resistance of DHP⊂1 over 10 cycles under the same irradiation conditions. (b) Adapted with permission from ref (24). Copyright 2007 Springer Nature. (e, f) Adapted from ref (31). Copyright 2020 American Chemical Society.
Figure 3
Figure 3. (a) Reversible photodimerization of anthracene. (b) Proposed photoreaction of anthracene inside the cavity of ZIF-8. (c) Crystal structure of a ZIF-8 cavity encapsulating four molecules of anthracene. (d) UV/vis absorption spectra accompanying UV irradiation of ZIF-8 encapsulating anthracene. (e) Schematic illustration of light-induced trapping and increased reactivity of small molecules within colloidal crystals (“dynamically self-assembling nanoflasks”). (f) Electron micrographs (at different magnifications) of colloidal crystals prepared by exposing azobenzene-coated gold nanoparticles to UV light. (g) Accelerated photodimerization of 9-anthracenemethanol in the presence of photoresponsive nanoparticles. (h) Stereoselectivity in the dimerization of 9-anthracenemethanol in the presence and absence of photoresponsive nanoparticles. (i) Schematic illustration of the photoreaction of 9-(4-mercaptophenylethynyl)anthracene on a Au(111) surface. (j) Dependence of the anthracene dimerization yield on the curvature of the underlying nanoparticle. (c, d) Adapted with permission from ref (34). Copyright 2019 Wiley-VCH. (f–h) Adapted with permission from ref (4). Copyright 2016 Springer Nature. (i) Adapted with permission from ref (37). Copyright 2011 American Association for the Advancement of Science.
Figure 4
Figure 4. (a) Reversible photoisomerization of azobenzene. (b) Structural formulas of azobenzene 2 and background ligand 3. (c) Snapshots from molecular dynamics simulations of a 2/3-coated gold nanoparticle in the trans and cis states of azobenzene. (d) Structural formulas of azobenzene 4 and background ligand 5. (3) (e) Proposed mechanism for accelerated azobenzene isomerization on a nanoparticle surface upon coadsorption with a hydroxy-terminated background ligand. (3) (f) Crystal structure of an inclusion complex comprising cage 1 and two molecules of tetra-o-fluoroazobenzene (6) (left) and the stepwise mechanism underlying the photoisomerization of 6 within the cavity of 1 (right). (c) Adapted from ref (3). Copyright 2019 American Chemical Society.
Figure 5
Figure 5. (a, b) Reversible photoisomerization of (a) spiropyran and (b) DASA. (c) Comparison of the kinetics of merocyanine→spiropyran back-isomerization in solution and on the surface of 2.6 nm gold nanoparticles (χ = 0.33). (d) Dependence of the kinetics of disassembly of gold nanoparticle aggregates on the spiropyran coverage. (e, f) Spontaneous bleaching of the open form of DASA on the surfaces of (e) 4.2 and (f) 8.6 nm magnetite nanoparticles. (g) TEM image of a spiropyran-incorporating framework. The arrows indicate individual nanopores. (h) Encapsulation of spiropyran 7 within cage 1 and the resulting crystal structure (hydrogen atoms of the cage have been omitted for clarity). (i) Mechanism of the light-induced decoloration of 7⊂1. (c, d) From ref (55). CC BY 3.0. (e, f) Adapted with permission from ref (57). Copyright 2017 Wiley-VCH. (g) From ref (2). CC BY NC ND 3.0.
References
This article references 71 other publications.
- 1Samanta, D.; Gemen, J.; Chu, Z.; Diskin-Posner, Y.; Shimon, L. J. W.; Klajn, R. Reversible photoswitching of encapsulated azobenzenes in water. Proc. Natl. Acad. Sci. U. S. A. 2018, 115, 9379– 9384, DOI: 10.1073/pnas.17127871151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitVKhurfO&md5=06b154f6f5783bdcc43a702bb08b39d4Reversible photoswitching of encapsulated azobenzenes in waterSamanta, Dipak; Gemen, Julius; Chu, Zonglin; Diskin-Posner, Yael; Shimon, Linda J. W.; Klajn, RafalProceedings of the National Academy of Sciences of the United States of America (2018), 115 (38), 9379-9384CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Efficient mol. switching in confined spaces is crit. for the successful development of artificial mol. machines. However, mol. switching events often entail large structural changes and therefore require conformational freedom, which is typically limited under confinement conditions. Here, we investigated the behavior of azobenzene-the key building block of light-controlled mol. machines-in a confined environment that is flexible and can adapt its shape to that of the bound guest. To this end, we encapsulated several structurally diverse azobenzenes within the cavity of a flexible, water-sol. coordination cage, and investigated their light-responsive behavior. Using UV/visible absorption spectroscopy and a combination of NMR methods, we showed that each of the encapsulated azobenzenes exhibited distinct switching properties. An azobenzene forming a 1:1 host-guest inclusion complex could be efficiently photoisomerized in a reversible fashion. In contrast, successful switching in inclusion complexes incorporating two azobenzene guests was dependent on the availability of free cages in the system, and it involved reversible trafficking of azobenzene between the cages. In the absence of extra cages, photoswitching was either suppressed or it involved expulsion of azobenzene from the cage and consequently its pptn. from the soln. This finding was utilized to develop an information storage medium in which messages could be written and erased in a reversible fashion using light.
- 2Kundu, P. K.; Olsen, G. L.; Kiss, V.; Klajn, R. Nanoporous frameworks exhibiting multiple stimuli responsiveness. Nat. Commun. 2014, 5, 3588, DOI: 10.1038/ncomms45882https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2cnhsF2jsg%253D%253D&md5=2a0ca98dcb275e4e9ee1d92819423bc5Nanoporous frameworks exhibiting multiple stimuli responsivenessKundu Pintu K; Klajn Rafal; Olsen Gregory L; Kiss VladimirNature communications (2014), 5 (), 3588 ISSN:.Nanoporous frameworks are polymeric materials built from rigid molecules, which give rise to their nanoporous structures with applications in gas sorption and storage, catalysis and others. Conceptually new applications could emerge, should these beneficial properties be manipulated by external stimuli in a reversible manner. One approach to render nanoporous frameworks responsive to external signals would be to immobilize molecular switches within their nanopores. Although the majority of molecular switches require conformational freedom to isomerize, and switching in the solid state is prohibited, the nanopores may provide enough room for the switches to efficiently isomerize. Here we describe two families of nanoporous materials incorporating the spiropyran molecular switch. These materials exhibit a variety of interesting properties, including reversible photochromism and acidochromism under solvent-free conditions, light-controlled capture and release of metal ions, as well reversible chromism induced by solvation/desolvation.
- 3Chu, Z.; Han, Y.; Bian, T.; De, S.; Král, P.; Klajn, R. Supramolecular Control of Azobenzene Switching on Nanoparticles. J. Am. Chem. Soc. 2019, 141, 1949– 1960, DOI: 10.1021/jacs.8b096383https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXkvFKk&md5=4d7b9f8e6f7e454c1a31d2eb7f63d206Supramolecular Control of Azobenzene Switching on NanoparticlesChu, Zonglin; Han, Yanxiao; Bian, Tong; De, Soumen; Kral, Petr; Klajn, RafalJournal of the American Chemical Society (2019), 141 (5), 1949-1960CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene's hydrophobic nature, most of these examples have been realized only in org. solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-sol. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amt. of azobenzene on the functionalized nanoparticles. Mol. dynamics simulations helped us to identify two distinct supramol. architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aq. solubilities. Azobenzenes adsorbed on these water-sol. nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aq. media and, in the long run, in biol. environments.
- 4Zhao, H.; Sen, S.; Udayabhaskararao, T.; Sawczyk, M.; Kučanda, K.; Manna, D.; Kundu, P. K.; Lee, J.-W.; Král, P.; Klajn, R. Reversible trapping and reaction acceleration within dynamically self-assembling nanoflasks. Nat. Nanotechnol. 2016, 11, 82– 88, DOI: 10.1038/nnano.2015.2564https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVyhtrfF&md5=c71b923ef34cad1bdbb857f7eee92999Reversible trapping and reaction acceleration within dynamically self-assembling nanoflasksZhao, Hui; Sen, Soumyo; Udayabhaskararao, T.; Sawczyk, Michal; Kucanda, Kristina; Manna, Debasish; Kundu, Pintu K.; Lee, Ji-Woong; Kral, Petr; Klajn, RafalNature Nanotechnology (2016), 11 (1), 82-88CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The chem. behavior of mols. can be significantly modified by confinement to vols. comparable to the dimensions of the mols. Although such confined spaces can be found in various nanostructured materials, such as zeolites, nanoporous org. frameworks and colloidal nanocrystal assemblies, the slow diffusion of mols. in and out of these materials has greatly hampered studying the effect of confinement on their physicochem. properties. Here, we show that this diffusion limitation can be overcome by reversibly creating and destroying confined environments by means of UV and visible light irradn. We use colloidal nanocrystals functionalized with light-responsive ligands that readily self-assemble and trap various mols. from the surrounding bulk soln. Once trapped, these mols. can undergo chem. reactions with increased rates and with stereoselectivities significantly different from those in bulk soln. Illumination with visible light disassembles these nanoflasks, releasing the product in soln. and thereby establishes a catalytic cycle. These dynamic nanoflasks can be useful for studying chem. reactivities in confined environments and for synthesizing mols. that are otherwise hard to achieve in bulk soln.
- 5Nogly, P.; Weinert, T.; James, D.; Carbajo, S.; Ozerov, D.; Furrer, A.; Gashi, D.; Borin, V.; Skopintsev, P.; Jaeger, K.; Nass, K.; Båth, P.; Bosman, R.; Koglin, J.; Seaberg, M.; Lane, T.; Kekilli, D.; Brünle, S.; Tanaka, T.; Wu, W.; Milne, C.; White, T.; Barty, A.; Weierstall, U.; Panneels, V.; Nango, E.; Iwata, S.; Hunter, M.; Schapiro, I.; Schertler, G.; Neutze, R.; Standfuss, J. Retinal isomerization in bacteriorhodopsin captured by a femtosecond X-ray laser. Science 2018, 361, eaat0094, DOI: 10.1126/science.aat0094There is no corresponding record for this reference.
- 6Shichida, Y.; Matsuyama, T. Evolution of opsins and phototransduction. Philos. Trans. R. Soc., B 2009, 364, 2881– 2895, DOI: 10.1098/rstb.2009.00516https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1Wis77L&md5=8408e9594cf807da0a8d134074b097f0Evolution of opsins and phototransductionShichida, Yoshinori; Matsuyama, TakePhilosophical Transactions of the Royal Society, B: Biological Sciences (2009), 364 (1531), 2881-2895CODEN: PTRBAE; ISSN:0962-8436. (Royal Society)A review. Opsins are the universal photoreceptor mols. of all visual systems in the animal kingdom. They can change their conformation from a resting state to a signaling state upon light absorption, which activates the G protein, thereby resulting in a signaling cascade that produces physiol. responses. This process of capturing a photon and transforming it into a physiol. response is known as phototransduction. Recent cloning techniques have revealed the rich and diverse nature of these mols., found in organisms ranging from jellyfish to humans, functioning in visual and non-visual phototransduction systems and photoisomerases. Here we describe the diversity of these proteins and their role in phototransduction. Then we explore the mol. properties of opsins, by analyzing site-directed mutants, strategically designed by phylogenetic comparison. This site-directed mutant approach led us to identify many key features in the evolution of the photoreceptor mols. In particular, we will discuss the evolution of the counterion, the redn. of agonist binding to the receptor, and the mol. properties that characterize rod opsins apart from cone opsins. We will show how the advances in mol. biol. and biophysics have given us insights into how evolution works at the mol. level.
- 7Weinert, T.; Skopintsev, P.; James, D.; Dworkowski, F.; Panepucci, E.; Kekilli, D.; Furrer, A.; Brünle, S.; Mous, S.; Ozerov, D.; Nogly, P.; Wang, M. T.; Standfuss, J. Proton uptake mechanism in bacteriorhodopsin captured by serial synchrotron crystallography. Science 2019, 365, 61– 65, DOI: 10.1126/science.aaw86347https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlWjtbjE&md5=d4da9d49767d85485ea9b17bf3404a42Proton uptake mechanism in bacteriorhodopsin captured by serial synchrotron crystallographyWeinert, Tobias; Skopintsev, Petr; James, Daniel; Dworkowski, Florian; Panepucci, Ezequiel; Kekilli, Demet; Furrer, Antonia; Bruenle, Steffen; Mous, Sandra; Ozerov, Dmitry; Nogly, Przemyslaw; Wang, Meitian; Standfuss, JoergScience (Washington, DC, United States) (2019), 365 (6448), 61-65CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Proteins are dynamic. Rearrangements of side chains, secondary structure, and entire domains gate functional transitions on time scales ranging from picoseconds to milliseconds. Weinert et al. used time-resolved serial crystallog. to study large conformational changes in the proton pump bacteriorhodopsin that allow for redistribution of protons during the pumping cycle. They adapted methods used for x-ray free electron lasers to synchrotron x-ray sources. Large loop movements and a chain of water mols. were central to regenerating the starting state of bacteriorhodopsin.
- 8Grommet, A. B.; Feller, M.; Klajn, R. Chemical reactivity under nanoconfinement. Nat. Nanotechnol. 2020, 15, 256– 271, DOI: 10.1038/s41565-020-0652-28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnsVCksrc%253D&md5=4b13eb6c35cc698dd64118b477884f1dChemical reactivity under nanoconfinementGrommet, Angela B.; Feller, Moran; Klajn, RafalNature Nanotechnology (2020), 15 (4), 256-271CODEN: NNAABX; ISSN:1748-3387. (Nature Research)A review. Confining mols. can fundamentally change their chem. and phys. properties. Confinement effects are considered instrumental at various stages of the origins of life, and life continues to rely on layers of compartmentalization to maintain an out-of-equil. state and efficiently synthesize complex biomols. under mild conditions. As interest in synthetic confined systems grows, we are realizing that the principles governing reactivity under confinement are the same in abiol. systems as they are in nature. In this Review, we categorize the ways in which nanoconfinement effects impact chem. reactivity in synthetic systems. Under nanoconfinement, chem. properties can be modulated to increase reaction rates, enhance selectivity and stabilize reactive species. Confinement effects also lead to changes in phys. properties. The fluorescence of light emitters, the colors of dyes and electronic communication between electroactive species can all be tuned under confinement. Within each of these categories, we elucidate design principles and strategies that are widely applicable across a range of confined systems, specifically highlighting examples of different nanocompartments that influence reactivity in similar ways.
- 9Nakano, S.; Miyoshi, D.; Sugimoto, N. Effects of Molecular Crowding on the Structures, Interactions, and Functions of Nucleic Acids. Chem. Rev. 2014, 114, 2733– 2758, DOI: 10.1021/cr400113m9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFOntLjF&md5=289fa514fecb5ac40b5adfc1eab34256Effects of Molecular Crowding on the Structures, Interactions, and Functions of Nucleic AcidsNakano, Shu-ichi; Miyoshi, Daisuke; Sugimoto, NaokiChemical Reviews (Washington, DC, United States) (2014), 114 (5), 2733-2758CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Recent progresses in microscopy and spectroscopy technologies for intracellular measurements, quant. studies using exptl. model systems, and computer simulations have led to an improved understanding of the interactions and reactions of nucleic acids under the macromol. crowding and small-mol. crowding conditions, which are the central theme of this review.
- 10Banks, D. S.; Fradin, C. Anomalous Diffusion of Proteins Due to Molecular Crowding. Biophys. J. 2005, 89, 2960– 2971, DOI: 10.1529/biophysj.104.05107810https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXht1WmurjE&md5=744ff30c81166c3394c5b5ea43792706Anomalous diffusion of proteins due to molecular crowdingBanks, Daniel S.; Fradin, CecileBiophysical Journal (2005), 89 (5), 2960-2971CODEN: BIOJAU; ISSN:0006-3495. (Biophysical Society)We have studied the diffusion of tracer proteins in highly concd. random-coil polymer and globular protein solns. imitating the crowded conditions encountered in cellular environments. Using fluorescence correlation spectroscopy, we measured the anomalous diffusion exponent α characterizing the dependence of the mean square displacement of the tracer proteins on time, 〈R2(t)〉 ∼ tα. We obsd. that the diffusion of proteins in dextran solns. with concns. up to 400 g/l is subdiffusive (α < 1) even at low obstacle concn. The anomalous diffusion exponent α decreases continuously with increasing obstacle concn. and mol. wt., but does not depend on buffer ionic strength, neither does it depend strongly on soln. temp. At very high random-coil polymer concns., α reaches a limit value of α1 ≈ 3/4, which we take to be the signature of a coupling between the motions of the tracer proteins and the segments of the dextran chains. A similar, although less pronounced, subdiffusive behavior is obsd. for the diffusion of streptavidin in concd. globular protein solns. These observations indicate that protein diffusion in the cell cytoplasm and nucleus should be anomalous as well, with consequences for measurements of solute diffusion coeffs. in cells and for the modeling of cellular processes relying on diffusion.
- 11Gonzalez, A.; Kengmana, E. S.; Fonseca, M. V.; Han, G. G. D. Solid-state photoswitching molecules: structural design for isomerization in condensed phase. Materials Today Adv. 2020, 6, 100058, DOI: 10.1016/j.mtadv.2020.100058There is no corresponding record for this reference.
- 12Cohen, M. D.; Ron, I.; Schmidt, G. M. J.; Thomas, J. M. Photochemical Decoration of Dislocations inside Crystals of Acenaphthyne. Nature 1969, 224, 167– 168, DOI: 10.1038/224167a012https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3cXmvVCn&md5=794e08e122c4411969d26bf29ffec840Photochemical decoration of dislocations inside crystals of acenaphthyleneCohen, Mendel David; Ron, I.; Schmidt, Gerhardt M. J.; Thomas, John MeurigNature (London, United Kingdom) (1969), 224 (5215), 167-8CODEN: NATUAS; ISSN:0028-0836.The solid in which dislocations were revealed, acenaphthylene (I), dimerizes under irradn. at ∼300 nm to yield a trans dimer (II). II is orthorhombic pseudotetragonal with a 7.82, b 7.85, and c 14.04 Å; the space group is Pba21 or Pbma; d. = 1.17 for Z = 4; the m.p. is 307°. Thin (∼0.01 cm) single crystals of I were prepd. from slowly cooled melts and irradiated for several hr at 0° (to suppress sublimation and thermal polymn. of the monomer). The interior of the crystal was illuminated by transmitted polarized light, or by reflected uv light. The strictly crystallographic nature of the aligned II nuclei and tendency for the anthracene photodimer to crystallize at dislocation cores (J. M. Thomas, et al., 1967) are evidence that the patterns revealed are due to locked-in dislocation networks and to terraces which are produced by dislocation glide. Cross-slip freely occurs in I and is probably the principal mechanism for dislocation multiplication in this solid. Screw dislocations are not strongly preferred over edge dislocations. For all the obsd. angles of intersections, it was possible to suggest an internally consistent set of planes in which dislocations glide relatively freely.
- 13Wang, R.; Iyoda, T.; Jiang, L.; Tryk, D. A.; Hashimoto, K.; Fujishima, A. Structural investigation of azobenzene-containing self-assembled monolayer films. J. Electroanal. Chem. 1997, 438, 213– 219, DOI: 10.1016/S0022-0728(96)05031-013https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXktVCju7Y%253D&md5=cad1c1339f47bf32e70feabb2d590b2cStructural investigation of azobenzene-containing self-assembled monolayer filmsWang, Rong; Iyoda, Tomokazu; Jiang, Lei; Tryk, Donald A.; Hashimoto, Kazuhito; Fujishima, AkiraJournal of Electroanalytical Chemistry (1997), 438 (1-2), 213-219CODEN: JECHES ISSN:. (Elsevier Science S.A.)An azobenzene-terminated long chain alkane-thiol was used for self-assembly onto Au substrates. A remarkable lack of activity for trans-to-cis photoisomerization in the film was quant. evaluated using a combined photochem.-electrochem. method. Film structure was then examd. using UV-visible spectroscopy and at. force microscopy (AFM). Results indicated the azobenzene-contg. mols. were extraordinarily densely packed in the self-assembled monolayer. A pinwheel structure, in which the long axes of azobenzene moieties were parallel to each other and the neighboring short axes were mutually perpendicular to each other, was supported by UV-visible and IR evidence and was obsd. directly with AFM. This structure is consistent with the dense packing. By comparing the structure of the same mol. in the cryst. state, it was obsd. that the pinwheel structure can be ascribed to a combination of covalent bonding between the S head-groups of the mol. and Au atoms of the substrate, strong van der Waals interaction of the alkane chains, and interactions between neighboring azobenzene moieties.
- 14Klajn, R. Immobilized azobenzenes for the construction of photoresponsive materials. Pure Appl. Chem. 2010, 82, 2247– 2279, DOI: 10.1351/PAC-CON-10-09-04There is no corresponding record for this reference.
- 15Kusukawa, T.; Fujita, M. Ship-in-a-Bottle” Formation of Stable Hydrophobic Dimers of cis-Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination Nanocage. J. Am. Chem. Soc. 1999, 121, 1397– 1398, DOI: 10.1021/ja983729515https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvFCrtw%253D%253D&md5=88dc88b5795487a78f96109d578d09e7"Ship-in-a-Bottle" Formation of Stable Hydrophobic Dimers of cis-Azobenzene and -Stilbene Derivatives in a Self-Assembled Coordination NanocageKusukawa, Takahiro; Fujita, MakotoJournal of the American Chemical Society (1999), 121 (6), 1397-1398CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The cage compd. [Pd6(en)6L4](NO3)12 (I) (L = 2,4,6-tris(4-pyridyl)-1,3,5-triazine) is capable of selective enclathration of C-shaped mols. as hydrophobic dimers, such as cis-azobenzenes and cis-stilbenes to give I.2Q (Q = cis-p-methylazobenzene, cis-p-methylstilbene, cis-p-methoxystilbene, cis-azobenzene and cis-bis(4-methoxyphenyl)ethane). The ship-in-a-bottle assembly of the hydrophobic dimer in the cage is suggested by NMR data.
- 16Moldt, T.; Brete, D.; Przyrembel, D.; Das, S.; Goldman, J. R.; Kundu, P. K.; Gahl, C.; Klajn, R.; Weinelt, M. Tailoring the Properties of Surface-Immobilized Azobenzenes by Monolayer Dilution and Surface Curvature. Langmuir 2015, 31, 1048– 1057, DOI: 10.1021/la504291n16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitFOgtr7N&md5=ae4f32a585066c4e127fe2b9ea88e2ffTailoring the Properties of Surface-Immobilized Azobenzenes by Monolayer Dilution and Surface CurvatureMoldt, Thomas; Brete, Daniel; Przyrembel, Daniel; Das, Sanjib; Goldman, Joel R.; Kundu, Pintu K.; Gahl, Cornelius; Klajn, Rafal; Weinelt, MartinLangmuir (2015), 31 (3), 1048-1057CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Photoswitching in densely packed azobenzene self-assembled monolayers (SAMs) is strongly affected by steric constraints and excitonic coupling between neighboring chromophores. Therefore, control of the chromophore d. is essential for enhancing and manipulating the photoisomerization yield. The authors compared two methods to achieve this goal, first assembling monocomponent azobenzene-alkanethiolate SAMs on gold nanoparticles of varying size. Then mixed SAMs of azobenzene-alkanethiolates and "dummy" alkanethiolates were prepd. on planar substrates. Both methods led to a gradual decrease of the chromophore d. and enable efficient photoswitching with low-power light sources. X-ray spectroscopy revealed that coadsorption from soln. yields mixts. with tunable compn. The orientation of the chromophores with respect to the surface normal changed from a tilted to an upright position with increasing azobenzene d. For both systems, optical spectroscopy revealed a pronounced excitonic shift that increased with the chromophore d. In spite of exciting the optical transition of the monomer, the main spectral change in mixed SAMs occurred in the excitonic band. The photoisomerization yield decreased only slightly by increasing the azobenzene-alkanethiolate d., and we obsd. photoswitching even with minor dilns. Unlike in soln., azobenzene in the planar SAM could be switched back almost completely by optical excitation from the cis to the original trans state within a short time scale. These observations indicate cooperativity in the photoswitching process of mixed SAMs.
- 17Moldt, T.; Przyrembel, D.; Schulze, M.; Bronsch, W.; Boie, L.; Brete, D.; Gahl, C.; Klajn, R.; Tegeder, P.; Weinelt, M. Differing Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in Vacuum. Langmuir 2016, 32, 10795– 10801, DOI: 10.1021/acs.langmuir.6b0169017https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFOkt73N&md5=6f6f22a01204d21ff3d61b3f8965ac7fDiffering Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in VacuumMoldt, Thomas; Przyrembel, Daniel; Schulze, Michael; Bronsch, Wibke; Boie, Larissa; Brete, Daniel; Gahl, Cornelius; Klajn, Rafal; Tegeder, Petra; Weinelt, MartinLangmuir (2016), 32 (42), 10795-10801CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)Azobenzenealkanethiols in self-assembled monolayers (SAMs) on Au(111) exhibit reversible trans-cis photoisomerization when dild. with alkanethiol spacers. Using these mixed SAMs, the authors show switching of the linear optical and second-harmonic response. The effective switching of these surface optical properties relies on a reasonably large cross section and a high photoisomerization yield as well as a long lifetime of the metastable cis isomer. The switching process was quantified by X-ray absorption spectra. The cross sections for the trans-cis and cis-trans photoisomerization with 365 and 455 nm light, resp., are 1 order of magnitude smaller than in soln. In vacuum, the 365 nm photostationary state comprises 50-74% of the mols. in the cis form, limited by their rapid thermal isomerization back to the trans state. In contrast, the 455 nm photostationary state contains nearly 100% trans-azobenzene. We detd. time consts. for the thermal cis-trans isomerization of only a few minutes in vacuum and in a dry nitrogen atm. but of more than 1 day in ambient air. Our results suggest that adventitious water adsorbed on the surface of the SAM stabilizes the polar cis configuration of azobenzene under ambient conditions. The back reaction rate consts. differing by 2 orders of magnitude underline the huge influence of the environment and, accordingly, its importance when comparing various expts.
- 18Han, M.; Ishikawa, D.; Honda, T.; Ito, E.; Hara, M. Light-driven molecular switches in azobenzene self-assembled monolayers: effect of molecular structure on reversible photoisomerization and stable cis state. Chem. Commun. 2010, 46, 3598– 3600, DOI: 10.1039/b921801g18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXlvVSkur8%253D&md5=6ba0d6cfc33615a6fcd02af345b42f62Light-driven molecular switches in azobenzene self-assembled monolayers: effect of molecular structure on reversible photoisomerization and stable cis stateHan, Mina; Ishikawa, Daisuke; Honda, Takumu; Ito, Eisuke; Hara, MasahikoChemical Communications (Cambridge, United Kingdom) (2010), 46 (20), 3598-3600CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Both the reversible trans ↔ cis photoisomerization and slow thermal back cis-to-trans isomerization of azobenzene-functionalized self-assembled monolayers on gold surfaces have been achieved by rationally designed single-component azobenzene thiol.
- 19Santos Hurtado, C.; Bastien, G.; Mašát, M.; Štoček, J. R.; Dračínský, M.; Rončević, I.; Císařová, I.; Rogers, C. T.; Kaleta, J. Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV–vis and NMR Spectroscopy. J. Am. Chem. Soc. 2020, 142, 9337– 9351, DOI: 10.1021/jacs.0c0175319https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXot1Wlsrs%253D&md5=58c1587e20ffafc3a9f63ffa5f3ac902Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV-vis and NMR SpectroscopySantos Hurtado, Carina; Bastien, Guillaume; Masat, Milan; Stocek, Jakub Radek; Dracinsky, Martin; Roncevic, Igor; Cisarova, Ivana; Rogers, Charles T.; Kaleta, JiriJournal of the American Chemical Society (2020), 142 (20), 9337-9351CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Using solid-state 15N NMR spectroscopy, the cis/trans isomerization in a two-dimensional (2-D) array of surface-mounted azobenzene-based switches was detected for the first time. In order to achieve this, a new class of rod-shaped mol. switches, suitable for formation of 2-D regular arrays on large facets of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) nanocrystals, was synthesized. A mechanochem. approach was used to prep. corresponding host-guest surface inclusions in a TPP matrix. Comparison of thermal steps in soln. and supramol. surface inclusions revealed that switching of individual mols. is not compromised by the close proximity of neighbors.
- 20Negishi, Y.; Kamimura, U.; Ide, M.; Hirayama, M. A photoresponsive Au25 nanocluster protected by azobenzene derivative thiolates. Nanoscale 2012, 4, 4263– 4268, DOI: 10.1039/c2nr30830d20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XptlWnt70%253D&md5=d7dd917db4fb1da0b975febe79b9ddb5A photoresponsive Au25 nanocluster protected by azobenzene derivative thiolatesNegishi, Yuichi; Kamimura, Ukyo; Ide, Mao; Hirayama, MichiyoNanoscale (2012), 4 (14), 4263-4268CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)An Au25 cluster protected by azobenzene deriv. thiolates (S-Az) ([Au25(S-Az)18]-) was synthesized with the aim of producing a photoresponsive Au25 cluster. The matrix-assisted laser desorption/ionization mass spectrum of the product revealed that [Au25(S-Az)18]- was synthesized in high purity. Optical absorption spectra of [Au25(S-Az)18]- obtained before and after photoirradn. suggest that the azobenzenes in the ligands of Au25(S-Az)18 isomerize with an efficiency of nearly 100%, both from the trans to cis conformation and from the cis to trans conformation. Furthermore, the redox potential and optical absorption of Au25(S-Az)18 change reversibly due to photoisomerization of azobenzenes.
- 21Dolgopolova, E. A.; Berseneva, A. A.; Faillace, M. S.; Ejegbavwo, O. A.; Leith, G. A.; Choi, S. W.; Gregory, H. N.; Rice, A. M.; Smith, M. D.; Chruszcz, M.; Garashchuk, S.; Mythreye, K.; Shustova, N. B. Confinement-Driven Photophysics in Cages, Covalent–Organic Frameworks, Metal–Organic Frameworks, and DNA. J. Am. Chem. Soc. 2020, 142, 4769– 4783, DOI: 10.1021/jacs.9b1350521https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjsVOns74%253D&md5=997b2ba493960570ec3ad5cdc493dad8Confinement-driven photophysics in cages, covalent-organic frameworks, metal-organic frameworks, and DNADolgopolova, Ekaterina A.; Berseneva, Anna A.; Faillace, Martin S.; Ejegbavwo, Otega A.; Leith, Gabrielle A.; Choi, Seok W.; Gregory, Haley N.; Rice, Allison M.; Smith, Mark D.; Chruszcz, Maksymilian; Garashchuk, Sophya; Mythreye, Karthikeyan; Shustova, Natalia B.Journal of the American Chemical Society (2020), 142 (10), 4769-4783CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photophysics tunability through alteration of framework aperture (metal-org. framework (MOF) = variable; guest = const.) was probed for the first time in comparison with previously explored concepts (MOF = const.; guest = variable). In particular, anal. of the confinement effect on a photophys. response of integrated 5-(3-chlorobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one (Cl-BI) chromophore allowed us to establish a photophysics-aperture relationship. To shed light on the obsd. correlation, the framework confined environment was replicated using a mol. cage, Pd6(TPT)4 (TPT = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine), thus allowing for utilization of crystallog., spectroscopy, and theor. simulations to reveal the effect a confined space has on the chromophore's mol. conformation (including disruption of strong hydrogen bonding and novel conformer formation) and any assocd. changes on a photophys. response. Furthermore, the chosen Cl-oHBI@Pd6(TPT)4 (Cl-oHBI = 5-(5-chloro-2-hydroxybenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one, chromophore) system was applied as a tool for targeted cargo delivery of a chromophore to the confined space of DNA, which resulted in promotion of chromophore-DNA interactions through a well-established intercalation mechanism. Moreover, the developed principles were applied toward utilizing a HBI-based chromophore as a fluorescent probe on the example of macrophage cells. For the first time, suppression of non-radiative decay pathways of a chromophore was tested by anchoring the chromophore to a framework metal node, portending a potential avenue to develop an alternative to natural biomarkers. Overall, these studies are among the first attempts to demonstrate the unrevealed potential of a confined scaffold environment for tailoring a material's photophys. response.
- 22Danowski, W.; van Leeuwen, T.; Abdolahzadeh, S.; Roke, D.; Browne, W. R.; Wezenberg, S.; Feringa, B. L. Unidirectional rotary motion in a metal–organic framework. Nat. Nanotechnol. 2019, 14, 488– 494, DOI: 10.1038/s41565-019-0401-622https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXms1Ogtrk%253D&md5=861d9bbbd1eafb32a0004a698d9d741aUnidirectional rotary motion in a metal-organic frameworkDanowski, Wojciech; van Leeuwen, Thomas; Abdolahzadeh, Shaghayegh; Roke, Diederik; Browne, Wesley R.; Wezenberg, Sander J.; Feringa, Ben L.Nature Nanotechnology (2019), 14 (5), 488-494CODEN: NNAABX; ISSN:1748-3387. (Nature Research)Overcrowded alkene-based light-driven mol. motors are able to perform large-amplitude repetitive unidirectional rotations. Their behavior is well understood in soln. However, Brownian motion precludes the precise positioning at the nanoscale needed to harness cooperative action. Here, authors demonstrate mol. motors organized in cryst. metal-org. frameworks (MOFs). The motor unit becomes a part of the org. linker (or strut), and its spatial arrangement is elucidated through powder and single-crystal x-ray analyses and polarized optical and Raman microscopies. They confirm that the light-driven unidirectional rotation of the motor units is retained in the MOF framework and that the motors can operate in the solid state with similar rotary speed (rate of thermal helix inversion) to that in soln. These 'moto-MOFs' could in the future be used to control dynamic function in cryst. materials.
- 23Samanta, D.; Galaktionova, D.; Gemen, J.; Shimon, L. J. W.; Diskin-Posner, Y.; Avram, L.; Král, P.; Klajn, R. Reversible chromism of spiropyran in the cavity of a flexible coordination cage. Nat. Commun. 2018, 9, 641, DOI: 10.1038/s41467-017-02715-623https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MrhtlCgtw%253D%253D&md5=3b0b16177f47ce496acec9a361e4cd0bReversible chromism of spiropyran in the cavity of a flexible coordination cageSamanta Dipak; Gemen Julius; Klajn Rafal; Galaktionova Daria; Kral Petr; Shimon Linda J W; Diskin-Posner Yael; Avram Liat; Kral Petr; Kral PetrNature communications (2018), 9 (1), 641 ISSN:.Confining molecules to volumes only slightly larger than the molecules themselves can profoundly alter their properties. Molecular switches-entities that can be toggled between two or more forms upon exposure to an external stimulus-often require conformational freedom to isomerize. Therefore, placing these switches in confined spaces can render them non-operational. To preserve the switchability of these species under confinement, we work with a water-soluble coordination cage that is flexible enough to adapt its shape to the conformation of the encapsulated guest. We show that owing to its flexibility, the cage is not only capable of accommodating-and solubilizing in water-several light-responsive spiropyran-based molecular switches, but, more importantly, it also provides an environment suitable for the efficient, reversible photoisomerization of the bound guests. Our findings pave the way towards studying various molecular switching processes in confined environments.
- 24Kobatake, S.; Takami, S.; Muto, H.; Ishikawa, T.; Irie, M. Rapid and reversible shape changes of molecular crystals on photoirradiation. Nature 2007, 446, 778– 781, DOI: 10.1038/nature0566924https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktVeqtrc%253D&md5=1aaa9a8858aa3c0c0f115bccd466626eRapid and reversible shape changes of molecular crystals on photoirradiationKobatake, Seiya; Takami, Shizuka; Muto, Hiroaki; Ishikawa, Tomoyuki; Irie, MasahiroNature (London, United Kingdom) (2007), 446 (7137), 778-781CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)The development of actuators based on materials that reversibly change shape and/or size in response to external stimuli has attracted interest for some time. A particularly intriguing possibility is offered by light-responsive materials, which allow remote operation without the need for direct contact to the actuator. The photoresponse of these materials is based on the photoisomerization of constituent mols. (typically trans-cis isomerization of azobenzene chromophores), which gives rise to mol. motions and thereby deforms the bulk material. This effect has been used to create light-deformable polymer films and gels, but the response of these systems is relatively slow. The authors report that mol. crystals based on diarylethene chromophores and with sizes ranging from 10 to 100 μm exhibit rapid and reversible macroscopic changes in shape and size induced by UV and visible light. The authors find that on exposure to UV light, a single crystal of 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene changes from a square shape to a lozenge shape, whereas a rectangular single crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene contracts by about 5-7 per cent. The deformed crystals are thermally stable, and switch back to their original state on irradn. with visible light. The authors find that the authors crystals respond in about 25 μs (i.e., about five orders of magnitude faster than the response time of the azobenzene-based polymer systems) and that they can move microscopic objects, making them promising materials for possible light-driven actuator applications.
- 25Jia, C.; Migliore, A.; Xin, N.; Huang, S.; Wang, J.; Yang, Q.; Wang, S.; Chen, H.; Wang, D.; Feng, B.; Liu, Z.; Zhang, G.; Qu, D.-H.; Tian, H.; Ratner, M. A.; Xu, H. Q.; Nitzan, A.; Guo, X. Covalently bonded single-molecule junctions with stable and reversible photoswitched conductivity. Science 2016, 352, 1443– 1445, DOI: 10.1126/science.aaf629825https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XpslOqs74%253D&md5=6ecca36730ce7856881ee196592a0b74Covalently bonded single-molecule junctions with stable and reversible photoswitched conductivityJia, Chuancheng; Migliore, Agostino; Xin, Na; Huang, Shaoyun; Wang, Jinying; Yang, Qi; Wang, Shuopei; Chen, Hongliang; Wang, Duoming; Feng, Boyong; Liu, Zhirong; Zhang, Guangyu; Qu, Da-Hui; Tian, He; Ratner, Mark A.; Xu, H. Q.; Nitzan, Abraham; Guo, XuefengScience (Washington, DC, United States) (2016), 352 (6292), 1443-1445CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Through mol. engineering, single diarylethenes were covalently sandwiched between graphene electrodes to form stable mol. conduction junctions. Our exptl. and theor. studies of these junctions consistently show and interpret reversible conductance photoswitching at room temp. and stochastic switching between different conductive states at low temp. at a single-mol. level. We demonstrate a fully reversible, two-mode, single-mol. elec. switch with unprecedented levels of accuracy (on/off ratio of ∼100), stability (over a year), and reproducibility (46 devices with more than 100 cycles for photoswitching and ∼105 to 106 cycles for stochastic switching).
- 26Katsonis, N.; Kudernac, T.; Walko, M.; van der Molen, S. J.; van Wees, B. J.; Feringa, B. L. Reversible Conductance Switching of Single Diarylethenes on a Gold Surface. Adv. Mater. 2006, 18, 1397– 1400, DOI: 10.1002/adma.20060021026https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XlvVOgtbg%253D&md5=524f3a095bc0c232341fa58990057b85Reversible conductance switching of single diarylethenes on a gold surfaceKatsonis, Nathalie; Kudernac, Tibor; Walko, Martin; van der Molen, Sense Jan; van Wees, Bart J.; Feringa, Ben L.Advanced Materials (Weinheim, Germany) (2006), 18 (11), 1397-1400CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Light-controlled conductance switching of diarylethenes attached to Au(111) is reported. First, scanning tunneling microscopy is used to demonstrate reversible photoswitching for individual mols. Second, reversible switching in self-assembled monolayers is established by means of optical spectroscopy.
- 27Arramel; Pijper, T. C.; Kudernac, T.; Katsonis, N.; van der Maas, M.; Feringa, B. L.; van Wees, B. J. Reversible light induced conductance switching of asymmetric diarylethenes on gold: surface and electronic studies. Nanoscale 2013, 5, 9277– 9282, DOI: 10.1039/c3nr00832k27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVers7vE&md5=d16605e471a455f35650d33e60f5afdeReversible light induced conductance switching of asymmetric diarylethenes on gold. Surface and electronic studiesArramel; Pijper, Thomas C.; Kudernac, Tibor; Katsonis, Nathalie; van der Maas, Minko; Feringa, Ben L.; van Wees, Bart J.Nanoscale (2013), 5 (19), 9277-9282CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)We report on the light-induced switching of conductance of a new generation of diarylethene switches embedded in an insulating matrix of dodecanethiol on Au(111), by scanning tunneling microscopy (STM). The diarylethene switches we synthesize and study are modified diarylethenes where the thiophene unit at one side of the mol. backbone introduces an intrinsic asymmetry into the switch, which is expected to influence its photo-conductance properties. We show that reversible conversion between 2 distinguishable conductance states can be controlled via photoisomerization of the switches by alternative irradn. with UV (λ = 313 nm) or visible (λ > 420 nm) light. We addressed this phenomenon by STM in ambient conditions, based on switching of the apparent height of the mols. which convert from 4-6 Å in their closed form to 0-1 Å in their open form. Furthermore, the levels of the frontier MO levels (HOMO and LUMO) were evaluated for these asym. switches by scanning tunneling spectroscopy at 77 K, which allowed us to det. a HOMO-LUMO energy gap of 2.24 eV.
- 28Hou, L.; Leydecker, T.; Zhang, X.; Rekab, W.; Herder, M.; Cendra, C.; Hecht, S.; McCulloch, I.; Salleo, A.; Orgiu, E.; Samorì, P. Engineering Optically Switchable Transistors with Improved Performance by Controlling Interactions of Diarylethenes in Polymer Matrices. J. Am. Chem. Soc. 2020, 142, 11050– 11059, DOI: 10.1021/jacs.0c0296128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOmtLbF&md5=80eef9df218b4cc3dd01acfa61e1ea53Engineering Optically Switchable Transistors with Improved Performance by Controlling Interactions of Diarylethenes in Polymer MatricesHou, Lili; Leydecker, Tim; Zhang, Xiaoyan; Rekab, Wassima; Herder, Martin; Cendra, Camila; Hecht, Stefan; McCulloch, Iain; Salleo, Alberto; Orgiu, Emanuele; Samori, PaoloJournal of the American Chemical Society (2020), 142 (25), 11050-11059CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The integration of photochromic mols. into semiconducting polymer matrixes via blending has recently attracted a great deal of attention, as it provides the means to reversibly modulate the output signal of electronic devices by using light as a remote control. However, the structural and electronic interactions between photochromic mols. and semiconducting polymers are far from being fully understood. Here we perform a comparative investigation by combining two photochromic diarylethene moieties possessing similar energy levels yet different propensity to aggregate with five prototypical polymer semiconductors exhibiting different energy levels and structural order, ranging from amorphous to semicryst. Our in-depth photochem., structural, morphol., and elec. characterization reveals that the photoresponsive behavior of thin-film transistors including polymer/diarylethenes blends as the active layer is governed by a complex interplay between the relative position of the energy levels and the polymer matrix microstructure. By matching the energy levels and optimizing the mol. packing, high-performance optically switchable org. thin-film transistors were fabricated. These findings represent a major step forward in the fabrication of light-responsive org. devices.
- 29Sciascia, C.; Castagna, R.; Dekermenjian, M.; Martel, R.; Srimath Kandada, A. R.; Di Fonzo, F.; Bianco, A.; Bertarelli, C.; Meneghetti, M.; Lanzani, G. Light-Controlled Resistance Modulation in a Photochromic Diarylethene–Carbon Nanotube Blend. J. Phys. Chem. C 2012, 116, 19483– 19489, DOI: 10.1021/jp212231j29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFOisr3I&md5=c638be080c1a6839df81e2396b919b66Light-Controlled Resistance Modulation in a Photochromic Diarylethene-Carbon Nanotube BlendSciascia, Calogero; Castagna, Rossella; Dekermenjian, Maria; Martel, Richard; Srimath Kandada, Ajay R.; Di Fonzo, Fabio; Bianco, Andrea; Bertarelli, Chiara; Meneghetti, Moreno; Lanzani, GuglielmoJournal of Physical Chemistry C (2012), 116 (36), 19483-19489CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Photochromic mols. are part of a large class of materials in which light stimulus not only induces a color variation but also affects other physicochem. properties. However, the change of bulk elec. properties (e.g., elec. cond.) via light excitation remains difficult to control because the intrinsically switchable mols. may lose their functionality when wired with conductive electrodes. In contrast with previous work based on single mols., here the authors demonstrate a facile and accessible wet-chem. method to produce light-induced elec. switching. The elec. cond. of a photochromic blend composed of diarylethene polymer and single-walled carbon nanotubes (SWNTs) is reversibly tuned according with UV-vis excitation. The devices present good thermal stability and remarkable fatigue resistance under ambient conditions. Supported by elec. and spectroscopic evidence, the authors show that the intertube elec. coupling, mediated by the light-induced electrocyclization of the diarylethene unit, is the mechanism responsible for the modulation.
- 30El Gemayel, M.; Börjesson, K.; Herder, M.; Duong, D. T.; Hutchison, J. A.; Ruzié, C.; Schweicher, G.; Salleo, A.; Geerts, Y.; Hecht, S.; Orgiu, E.; Samorì, P. Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matrices. Nat. Commun. 2015, 6, 6330, DOI: 10.1038/ncomms733030https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtF2lurfN&md5=e35fbc381f15dafa589cc965ab143585Optically switchable transistors by simple incorporation of photochromic systems into small-molecule semiconducting matricesEl Gemayel, Mirella; Borjesson, Karl; Herder, Martin; Duong, Duc T.; Hutchison, James A.; Ruzie, Christian; Schweicher, Guillaume; Salleo, Alberto; Geerts, Yves; Hecht, Stefan; Orgiu, Emanuele; Samori, PaoloNature Communications (2015), 6 (), 6330CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The fabrication of multifunctional high-performance org. thin-film transistors as key elements in future logic circuits is a major research challenge. Here we demonstrate that a photoresponsive bi-functional field-effect transistor with carrier mobilities exceeding 0.2 cm2 V-1 s-1 can be developed by incorporating photochromic mols. into an org. semiconductor matrix via a single-step soln. processing deposition of a two components blend. Tuning the interactions between the photochromic diarylethene system and the org. semiconductor is achieved via ad-hoc side functionalization of the diarylethene. Thereby, a large-scale phase-segregation can be avoided and superior miscibility is provided, while retaining optimal π-π stacking to warrant efficient charge transport and to attenuate the effect of photoinduced switching on the extent of current modulation. This leads to enhanced elec. performance of transistors incorporating small conjugated mols. as compared with polymeric semiconductors. These findings are of interest for the development of high-performing optically gated electronic devices.
- 31Canton, M.; Grommet, A. B.; Pesce, L.; Gemen, J.; Li, S.; Diskin-Posner, Y.; Credi, A.; Pavan, G. M.; Andréasson, J.; Klajn, R. Improving Fatigue Resistance of Dihydropyrene by Encapsulating within a Coordination Cage. J. Am. Chem. Soc. 2020, 142, 14557– 14565, DOI: 10.1021/jacs.0c0614631https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhsFOlu7rO&md5=4da6ff40387d24c9d3a2cd41deba9a2bImproving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination CageCanton, Martina; Grommet, Angela B.; Pesce, Luca; Gemen, Julius; Li, Shiming; Diskin-Posner, Yael; Credi, Alberto; Pavan, Giovanni M.; Andreasson, Joakim; Klajn, RafalJournal of the American Chemical Society (2020), 142 (34), 14557-14565CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photochromic mols. undergo reversible isomerization upon irradn. with light at different wavelengths, a process that can alter their phys. and chem. properties. For instance, dihydropyrene (DHP) is a deep-colored compd. that isomerizes to light-brown cyclophanediene (CPD) upon irradn. with visible light. CPD can then isomerize back to DHP upon irradn. with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimol. events involving this unstable intermediate thus result in rapid decompn. and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a PdII6L4 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although mol. confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic mols., but may also increase the amt. of product obtainable from traditionally low-yielding org. reactions.
- 32Samanta, D.; Mukherjee, S.; Patil, Y. P.; Mukherjee, P. S. Self-Assembled Pd6 Open Cage with Triimidazole Walls and the Use of Its Confined Nanospace for Catalytic Knoevenagel- and Diels–Alder Reactions in Aqueous Medium. Chem. - Eur. J. 2012, 18, 12322– 12329, DOI: 10.1002/chem.20120167932https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht1Wktr7N&md5=6b0e91194f096995c78a8959f1f6d0a1Self-Assembled Pd6 Open Cage with Triimidazole Walls and the Use of Its Confined Nanospace for Catalytic Knoevenagel- and Diels-Alder Reactions in Aqueous MediumSamanta, Dipak; Mukherjee, Sandip; Patil, Yogesh P.; Mukherjee, Partha SarathiChemistry - A European Journal (2012), 18 (39), 12322-12329, S12322/1-S12322/13CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)The two-component self-assembly of a 90° PdII acceptor and a triimidazole donor gave a water-sol. semi-cylindrical cage with a hydrophobic cavity, which was sep. crystd. with hydrophilic- and hydrophobic guests. The parent cage was found to catalyze the Knoevenagel condensation reaction of arom. mono-aldehydes with active methylene compds., such as Meldrum's acid or 1,3-dimethylbarbituric acid. The confined hydrophobic nanospace within this cage was also used in the catalytic Diels-Alder reactions of 9-(hydroxymethyl)anthracene with N-phenylmaleimide or N-cyclohexylmaleimide.
- 33Sheepwash, M. A. L.; Mitchell, R. H.; Bohne, C. Mechanistic Insights into the Photochromism of trans-10b,10c-Dimethyl-10b,10c-dihydropyrene Derivatives. J. Am. Chem. Soc. 2002, 124, 4693– 4700, DOI: 10.1021/ja017229e33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XisFyhu7o%253D&md5=d8d2cc3b9339b8d40be8fa821030686dMechanistic insights into the photochromism of trans-10b,10c-dimethyl-10b,10c-dihydropyrene derivativesSheepwash, Molina A. L.; Mitchell, Reginald H.; Bohne, CorneliaJournal of the American Chemical Society (2002), 124 (17), 4693-4700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)A series of dimethyldihydropyrene derivs. was studied to elucidate the photochem. mechanism assocd. with the switching between the dimethyldihydropyrene (DHP, closed) and metacyclophanediene (CPD, open) forms of the mol. Quantum yields of ring opening and closure, fluorescence quantum yields and lifetimes, as well as laser flash photolysis studies were performed to establish the effect of substituents on the switching efficiency. Ring opening of the DHPs occurs from the first singlet excited state. The low quantum yields for the ring opening reaction obsd. (≤0.042) are a consequence of the low rate const. (≤1.7 × 107 s-1) for this process. The quantum yields for ring closure of the CPD were detd. for select compds. and were of the order of 0.1-0.4. These results show that the efficiency for ring opening of this class of compds. is intrinsically low, but can be modulated to some extent by the introduction of substituents. These properties should be taken into account when considering what type of photoswitching devices DHPs might be useful for.
- 34Tu, M.; Reinsch, H.; Rodríguez-Hermida, S.; Verbeke, R.; Stassin, T.; Egger, W.; Dickmann, M.; Dieu, B.; Hofkens, J.; Vankelecom, I. F. J.; Stock, N.; Ameloot, R. Reversible Optical Writing and Data Storage in an Anthracene-Loaded Metal–Organic Framework. Angew. Chem., Int. Ed. 2019, 58, 2423– 2427, DOI: 10.1002/anie.20181399634https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFSgsrk%253D&md5=9b99639d7890b79d1749d766cdfddbd1Reversible Optical Writing and Data Storage in an Anthracene-Loaded Metal-Organic FrameworkTu, Min; Reinsch, Helge; Rodriguez-Hermida, Sabina; Verbeke, Rhea; Stassin, Timothee; Egger, Werner; Dickmann, Marcel; Dieu, Bjorn; Hofkens, Johan; Vankelecom, Ivo F. J.; Stock, Norbert; Ameloot, RobAngewandte Chemie, International Edition (2019), 58 (8), 2423-2427CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Metal-org. frameworks (MOFs) enable the design of host-guest systems with specific properties. In this work, we show how the confinement of anthracene in a well-chosen MOF host leads to reversible yellow-to-purple photoswitching of the fluorescence emission. This behavior has not been obsd. before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host-guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and vol. as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.
- 35Becker, H. D.; Andersson, K. Photochemical Diels–Alder dimerization of 9-phenylethylnylanthracene. J. Photochem. 1984, 26, 75– 77, DOI: 10.1016/0047-2670(84)85029-735https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2cXlvFSrsL0%253D&md5=b2e55371f49d57cd44f25176e78baf66Photochemical Diels-Alder dimerization of 9-phenylethynylanthraceneBecker, Hans Dieter; Andersson, KjellJournal of Photochemistry (1984), 26 (1), 75-7CODEN: JPCMAE; ISSN:0047-2670.Crystallog. indicates that the title reaction of I (R = PhC≡C) (II) gives the Diels-Alder adduct III (R = PhC≡C, R1 = 9-anthracenyl) via a centrosym. complex. Similar attempted reactions of RC≡CH (R = H, Ph) to anthracene gave only dianthracene. The electron stoichiometry, the regiochem., and mechanism of the reaction, and the photochem. excitation and conjugation in II are discussed.
- 36Das, S.; Okamura, N.; Yagi, S.; Ajayaghosh, A. Supramolecular Gel Phase Controlled [4 + 2] Diels–Alder Photocycloaddition for Electroplex Mediated White Electroluminescence. J. Am. Chem. Soc. 2019, 141, 5635– 5639, DOI: 10.1021/jacs.9b0095536https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXmtlWisb8%253D&md5=ac1e76d5581b33823043f80eba56413bSupramolecular Gel Phase Controlled [4 + 2] Diels-Alder Photocycloaddition for Electroplex Mediated White ElectroluminescenceDas, Satyajit; Okamura, Naoki; Yagi, Shigeyuki; Ajayaghosh, AyyappanpillaiJournal of the American Chemical Society (2019), 141 (14), 5635-5639CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Diels-Alder photocycloaddn. of 9-phenylethynylanthracene results in multiple [4 + 2] and [4 + 4] cycloaddn. products in soln., which can be controlled to form specific products under a restricted environment. We have exploited the gel phase of a 9-phenylethynylanthracence deriv. as a confined medium to specifically yield the [4 + 2] cycloadduct in >90% yield. The photocycloadduct (anti-form) exhibited a blue emission with CIE chromaticity of x = 0.16/y = 0.16. Construction of an org. light emitting device with the photocycloadduct, using a carbazole-based hole transporting host, resulted in white light emission with a CIE chromaticity of x = 0.33/y = 0.32. This observation not only highlights the use of gel chem. to achieve the otherwise difficult to obtain photoproducts but also underlines their potential in optoelectronic device fabrication.
- 37Kim, M.; Hohman, J. N.; Cao, Y.; Houk, K. N.; Ma, H.; Jen, A. K.-Y.; Weiss, P. S. Creating Favorable Geometries for Directing Organic Photoreactions in Alkanethiolate Monolayers. Science 2011, 331, 1312– 1315, DOI: 10.1126/science.120083037https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXivVWksbw%253D&md5=c68f7297fe13dc70152f2ee1f8ee0e24Creating Favorable Geometries for Directing Organic Photoreactions in Alkanethiolate MonolayersKim, Moonhee; Hohman, J. Nathan; Cao, Yang; Houk, Kendall N.; Ma, Hong; Jen, Alex K.-Y.; Weiss, Paul S.Science (Washington, DC, United States) (2011), 331 (6022), 1312-1315CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The products of photoreactions of conjugated org. mols. may be allowed by selection rules but not obsd. in soln. reactions because of unfavorable reaction geometries. We have used defect sites in self-assembled alkanethiolate monolayers on gold surfaces to direct geometrically unfavorable photochem. reactions between individual org. mols. High cond. and stochastic switching of anthracene-terminated phenylethynylthiolates within alkanethiolate monolayers, as well as in situ photochem. transformations, have been obsd. and distinguished with the scanning tunneling microscope (STM). UV light absorbed during imaging increases the apparent heights of excited mols. in STM images, a direct manifestation of probing electronically excited states.
- 38Zheng, Y. B.; Payton, J. L.; Song, T.-B.; Pathem, B. K.; Zhao, Y.; Ma, H.; Yang, Y.; Jensen, L.; Jen, A. K.-Y.; Weiss, P. S. Surface-Enhanced Raman Spectroscopy To Probe Photoreaction Pathways and Kinetics of Isolated Reactants on Surfaces: Flat versus Curved Substrates. Nano Lett. 2012, 12, 5362– 5368, DOI: 10.1021/nl302750d38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtlGnu7jE&md5=2c41e912afcbb13d3db25c42094404a8Surface-Enhanced Raman Spectroscopy To Probe Photoreaction Pathways and Kinetics of Isolated Reactants on Surfaces: Flat versus Curved SubstratesZheng, Yue Bing; Payton, John L.; Song, Tze-Bin; Pathem, Bala Krishna; Zhao, Yuxi; Ma, Hong; Yang, Yang; Jensen, Lasse; Jen, Alex K.-Y.; Weiss, Paul S.Nano Letters (2012), 12 (10), 5362-5368CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The authors identify and control the photoreaction paths of self-assembled monolayers (SAMs) of thiolate-linked anthracene phenylethynyl mols. on Au substrate surfaces, and study the effects of nanoscale morphol. of substrates on regioselective photoreactions. Two types of morphologies, atomically flat and curved, are produced on Au surfaces by controlling substrate structure and metal deposition. The authors employ surface-enhanced Raman spectroscopy (SERS), combined with Raman mode analyses using d. functional theory, to identify the different photoreaction paths and to track the photoreaction kinetics and efficiencies of mols. in monolayers. The SAMs on curved surfaces exhibit dramatically lower regioselective photoreaction kinetics and efficiencies than those on atomically flat surfaces. This result is attributed to the increased intermol. distances and variable orientations on the curved surfaces. Better understanding of the morphol. effects of substrates will enable control of nanoparticle functionalization in ligand exchange in targeted delivery of therapeutics and theranostics and in catalysis.
- 39Zdobinsky, T.; Sankar Maiti, P.; Klajn, R. Support Curvature and Conformational Freedom Control Chemical Reactivity of Immobilized Species. J. Am. Chem. Soc. 2014, 136, 2711– 2714, DOI: 10.1021/ja411573a39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2c3kslCnsQ%253D%253D&md5=29f29254961ffbffb578b2c5ed8cd1feSupport curvature and conformational freedom control chemical reactivity of immobilized speciesZdobinsky Tino; Maiti Pradipta Sankar; Klajn RafalJournal of the American Chemical Society (2014), 136 (7), 2711-4 ISSN:.We show that bimolecular reactions between species confined to the surfaces of nanoparticles can be manipulated by the nature of the linker, as well as by the curvature of the underlying particles.
- 40Muraoka, T.; Kinbara, K.; Aida, T. Mechanical twisting of a guest by a photoresponsive host. Nature 2006, 440, 512– 515, DOI: 10.1038/nature0463540https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28Xis1OlsL8%253D&md5=e1f15a4cff1979a22c9c68c901583350Mechanical twisting of a guest by a photoresponsive hostMuraoka, Takahiro; Kinbara, Kazushi; Aida, TakuzoNature (London, United Kingdom) (2006), 440 (7083), 512-515CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Mol. analogs of a variety of mech. devices such as shuttles, brakes, unidirectional rotors and tweezers have been created. But these 'mol. machines' have not yet been used to mech. manipulate a second mol. in a controlled and reversible manner. Here we show that light-induced scissor-like conformational changes of one mol. can give rise to mech. twisting of a non-covalently bound guest mol. To realize this coupling of mol. motions, we use a previously designed system: a ferrocene moiety with an azobenzene strap, each end of which is attached to one of the two cyclopentadienyl rings of the ferrocene unit, acts as a pivot so that photoisomerization of the strap rotates the ferrocene rings relative to each other and thereby also changes the relative position of two 'pedal' moieties attached to the ferrocene rings. We translate this effect into intermol. coupling of motion by endowing the pedals with binding sites, which allow the host system to form a stable complex with a bidentate rotor mol. Using CD spectroscopy, we show that the photoinduced conformational changes of the host are indeed transmitted and induce mech. twisting of the rotor mol. This design concept, which significantly extends the successful coupling of motion beyond the intramol. level seen in synthetic allosteric receptors, might allow for the remote control of mol. events in larger interlocked mol. systems.
- 41Coskun, A.; Friedman, D. C.; Li, H.; Patel, K.; Khatib, H. A.; Stoddart, J. F. A Light-Gated STOP–GO Molecular Shuttle. J. Am. Chem. Soc. 2009, 131, 2493– 2495, DOI: 10.1021/ja809225e41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFegsL0%253D&md5=fe810aa73641e162aabce83d1132412cA light-gated STOP-GO molecular shuttleCoskun, Ali; Friedman, Douglas C.; Li, Hao; Patel, Kaushik; Khatib, Hussam A.; Stoddart, J. FraserJournal of the American Chemical Society (2009), 131 (7), 2493-2495CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Degenerate [2]rotaxanes, with their two identical binding sites, generally exhibit equil. dynamics with free energies of activation (ΔG‡) for the shuttling process starting as low as 10 kcal/mol-1. This ΔG‡ value can be raised quite dramatically by inserting "speed bumps" in the form of steric and/or electrostatic barriers into the linkers between the two identical binding sites. In our more recent research targeted toward the exploitation of the 4,4'-azobiphenyloxy unit (ABP) as a light-operated gate, we decided to introduce (i) four Me groups on the one hand and (ii) four fluorine atoms on the other, at the 3,5,3',5'-positions of the ABP units to curtail binding by the CBPQT4+ ring if not sterically in the case of (i), then electronically in the case of (ii). The first approach led to a gate (ABP-Me4) that remains closed all the time, whereas the second approach affords a gate (ABP-F4) that we can close with UV light and open with visible light. Herein, we show how light can be used, in conjunction with thermal energy, to raise and lower the free energy barrier at will and, in so doing, impart STOP and GO instructions upon the operation of a mol. shuttle.
- 42Pace, G.; Ferri, V.; Grave, C.; Elbing, M.; von Hänisch, C.; Zharnikov, M.; Mayor, M.; Rampi, M. A.; Samorì, P. Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 9937– 9942, DOI: 10.1073/pnas.070374810442https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmvVChtrg%253D&md5=6793d00b61e29b13a81f632c2451223eCooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayersPace, Giuseppina; Ferri, Violetta; Grave, Christian; Elbing, Mark; von Haenisch, Carsten; Zharnikov, Michael; Mayor, Marcel; Rampi, Maria Anita; Samori, PaoloProceedings of the National Academy of Sciences of the United States of America (2007), 104 (24), 9937-9942CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Photochromic systems can convert light energy into mech. energy, thus they can be used as building blocks for the fabrication of prototypes of mol. devices that are based on the photomech. effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged mols. The authors show by scanning tunneling microscopy imaging the photochem. switching of a new terminally thiolated azobiphenyl rigid rod mol. Interestingly, the switching of entire mol. 2D cryst. domains is obsd., which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-d. data storage.
- 43Fredy, J. W.; Méndez-Ardoy, A.; Kwangmettatam, S.; Bochicchio, D.; Matt, B.; Stuart, M. C. A.; Huskens, J.; Katsonis, N.; Pavan, G. M.; Kudernac, T. Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubules. Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 11850– 11855, DOI: 10.1073/pnas.171118411443https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1aju7fK&md5=83b78a7ce199f1a688d87f3e8fc02d13Molecular photoswitches mediating the strain-driven disassembly of supramolecular tubulesFredy, Jean W.; Mendez-Ardoy, Alejandro; Kwangmettatam, Supaporn; Bochicchio, Davide; Matt, Benjamin; Stuart, Marc C. A.; Huskens, Jurriaan; Katsonis, Nathalie; Pavan, Giovanni M.; Kudernac, TiborProceedings of the National Academy of Sciences of the United States of America (2017), 114 (45), 11850-11855CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Chemists have created mol. machines and switches with specific mech. responses that were typically demonstrated in soln., where mech. relevant motion is dissipated in the Brownian storm. The next challenge consists of designing specific mechanisms through which the action of individual mols. is transmitted to a supramol. architecture, with a sense of directionality. Cellular microtubules are capable of meeting such a challenge. While their capacity to generate pushing forces by ratcheting growth is well known, conversely these versatile machines can also pull microscopic objects apart through a burst of their rigid tubular structure. One essential feature of this disassembling mechanism is the accumulation of strain in the tubules, which develops when tubulin dimers change shape, triggered by a hydrolysis event. We envision a strategy toward supramol. machines generating directional pulling forces by harnessing the mech. purposeful motion of mol. switches in supramol. tubules. Here, we report on wholly synthetic, water-sol., and chiral tubules that incorporate photoswitchable building blocks in their supramol. architecture. Under illumination, these tubules display a nonlinear operation mode, by which light is transformed into units of strain by the shape changes of individual switches, until a threshold is reached and the tubules unleash the strain energy. The operation of this wholly synthetic and stripped-down system compares to the conformational wave by which cellular microtubules disassemble. Addnl., atomistic simulations provide mol. insight into how strain accumulates to induce destabilization. Our findings pave the way toward supramol. machines that would photogenerate pulling forces, at the nanoscale and beyond.
- 44Bochicchio, D.; Kwangmettatam, S.; Kudernac, T.; Pavan, G. M. How Defects Control the Out-of-Equilibrium Dissipative Evolution of a Supramolecular Tubule. ACS Nano 2019, 13, 4322– 4334, DOI: 10.1021/acsnano.8b0952344https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXltFCjsbw%253D&md5=460309c10a44f9a043042ad25bf9c31fHow Defects Control the Out-of-Equilibrium Dissipative Evolution of a Supramolecular TubuleBochicchio, Davide; Kwangmettatam, Supaporn; Kudernac, Tibor; Pavan, Giovanni M.ACS Nano (2019), 13 (4), 4322-4334CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)Supramol. architectures that work out-of-equil. or that can change in specific ways when absorbing external energy are ubiquitous in nature. Gaining the ability to create via self-assembly artificial materials possessing such fascinating behaviors would have a major impact in many fields. However, the rational design of similar dynamic structures requires to understand and, even more challenging, to learn how to master the mol. mechanisms governing how the assembled systems evolve far from the equil. Typically, this represents a daunting challenge due to the limited mol. insight that can be obtained by the expts. or by classical modeling approaches. Here we combine coarse-grained mol. models and advanced simulation approaches to study at submol. (<5 Å) resoln. a supramol. tubule, which breaks and disassembles upon absorption of light energy triggering isomerization of its azobenzene-contg. monomers. Our approach allows us to investigate the mol. mechanism of monomer transition in the assembly and to elucidate the kinetic process for the accumulation of the transitions in the system. Despite the stochastic nature of the excitation process, we demonstrate how these tubules preferentially dissipate the absorbed energy locally via the amplification of defects in their supramol. structure. We find that this constitutes the best kinetic pathway for accumulating monomer transitions in the system, which dets. the dynamic evolution out-of-equil. and the brittle behavior of the assembly under perturbed conditions. Thanks to the flexibility of our models, we finally come out with a general principle, where defects explain and control the brittle/soft behavior of such light-responsive assemblies.
- 45Chu, Z.; Klajn, R. Polysilsesquioxane Nanowire Networks as an “Artificial Solvent” for Reversible Operation of Photochromic Molecules. Nano Lett. 2019, 19, 7106– 7111, DOI: 10.1021/acs.nanolett.9b0264245https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvVWksr3E&md5=0986b73d0572a35ba8429a664f022e6cPolysilsesquioxane nanowire networks as an artificial solvent for reversible operation of photochromic moleculesChu, Zonglin; Klajn, RafalNano Letters (2019), 19 (10), 7106-7111CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Efficient isomerization of photochromic mols. often requires conformational freedom and is typically not available under solvent-free conditions. Here, we report a general methodol. allowing for reversible switching of such mols. on the surfaces of solid materials. Our method is based on dispersing photochromic compds. within polysilsesquioxane nanowire networks (PNNs), which can be fabricated as transparent, highly porous, micrometer-thick layers on various substrates. We found that azobenzene switching within the PNNs proceeded unusually fast compared with the same mols. in liq. solvents. Efficient isomerization of another photochromic system, spiropyran, from a colorless to a colored form was used to create reversible images in PNN-coated glass. The coloration reaction could be induced with sunlight and is of interest for developing "smart" windows.
- 46Akiyama, H.; Tamada, K.; Nagasawa, J.; Abe, K.; Tamaki, T. Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para Substituted Azobenzenes. J. Phys. Chem. B 2003, 107, 130– 135, DOI: 10.1021/jp026103g46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptFOhurc%253D&md5=10dbc902e8a58c91506c76f3091d2413Photoreactivity in Self-Assembled Monolayers Formed from Asymmetric Disulfides Having para-Substituted AzobenzenesAkiyama, Haruhisa; Tamada, Kaoru; Nagasawa, Junichi; Abe, Koji; Tamaki, TakashiJournal of Physical Chemistry B (2003), 107 (1), 130-135CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)Asym. dialkyl disulfides with a para-substituted azobenzene (i.e., 4-substituted 4'-(12-(dodecyldithio)dodecyloxy)azobenzenes) produced photoresponsive self-assembled monolayers (SAMs) on Au (111) surfaces. IR reflection absorption (IR-RA) spectroscopy and reflection UV and visible (visible) light absorption spectroscopy gave information on the mol. orientational order of the adsorbates in the SAMs. The photoreactivity was studied using dynamic contact-angle measurements with a Wilhelmy-type surface balance. The structure and photoreactivity of the SAMs were dependent on the substituent at the para position of an azobenzene moiety. Relatively ordered structures in the methylene parts and the photoisomerization of azobenzene moieties were obsd. for the SAMs formed from the hexyl- and the nonsubstituted azobenzene disulfides. However, a less-ordered SAM structure was seen for the cyanoazobenzene disulfide SAM, and the photoresponse is rather unstable.
- 47Titov, E.; Granucci, G.; Götze, J. P.; Persico, M.; Saalfrank, P. Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects. J. Phys. Chem. Lett. 2016, 7, 3591– 3596, DOI: 10.1021/acs.jpclett.6b0140147https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlOqu7rP&md5=acdc1bc0bd1dff46f544dbd93b00e7abDynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric EffectsTitov, Evgenii; Granucci, Giovanni; Goetze, Jan Philipp; Persico, Maurizio; Saalfrank, PeterJournal of Physical Chemistry Letters (2016), 7 (18), 3591-3596CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)While azobenzenes readily photoswitch in soln., their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. The authors address these possibilities by means of nonadiabatic mol. dynamics with trajectory surface hopping calcns., investigating the trans → cis isomerization of azobenzene after excitation into the ππ* absorption band. The authors consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of addnl. azobenzene mols., imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, mol. switch. Simulations reveal that in comparison to the single mol. the quantum yield of the trans → cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implications of dimerization and steric constraints are also discussed.
- 48Cantatore, V.; Granucci, G.; Rousseau, G.; Padula, G.; Persico, M. Photoisomerization of Self-Assembled Monolayers of Azobiphenyls: Simulations Highlight the Role of Packing and Defects. J. Phys. Chem. Lett. 2016, 7, 4027– 4031, DOI: 10.1021/acs.jpclett.6b0201848https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsFKmsbzL&md5=818e9627fa0b614ba68cfd437a6b3b31Photoisomerization of Self-Assembled Monolayers of Azobiphenyls: Simulations Highlight the Role of Packing and DefectsCantatore, Valentina; Granucci, Giovanni; Rousseau, Guillaume; Padula, Giancarlo; Persico, MaurizioJournal of Physical Chemistry Letters (2016), 7 (19), 4027-4031CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)We present surface hopping simulations of the photodynamics of self-assembled monolayers (SAMs) of 4'-(biphenyl-4-ylazo)-biphenyl-4-thiol (ABPT) on Au(111). We show that trans → cis photoisomerization is suppressed because of steric hindrance in a well-ordered SAM. Photoisomerization is instead viable in the presence of defects. Two particularly important defects are the boundaries between domains of trans-ABPT mols. leaning in different directions (a line defect) and single cis mols. embedded in a SAM of trans (a point defect). Our findings explain the cooperative behavior obsd. during the photoisomerization of a trans-ABPT SAM, leading to large domains of pure cis and trans isomers. The line and point defects are predicted to produce different patterns of cis-ABPT mols. during the early stages of the photoconversion.
- 49Lai, C.-Y.; Raj, G.; Liepuoniute, I.; Chiesa, M.; Naumov, P. Direct Observation of Photoinduced trans–cis Isomerization on Azobenzene Single Crystal. Cryst. Growth Des. 2017, 17, 3306– 3312, DOI: 10.1021/acs.cgd.7b0028849https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmvVGntb8%253D&md5=4b9c4a50d264173c0caaf415173af248Direct observation of photoinduced trans-cis isomerization on azobenzene single crystalLai, Chia-Yun; Raj, Gijo; Liepuoniute, Ieva; Chiesa, Matteo; Naumov, PanceCrystal Growth & Design (2017), 17 (6), 3306-3312CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)Photoexcitation can lead to either homogeneous or heterogeneous transformations of a reactive surface. Homogeneous transformations result in a statistical mixt. of reactants and products, whereas the outcome of heterogeneous transformations is a coexistence of macroscopic reactant and product domains, sepd. by a phase boundary. Heterogeneous photoinduced changes are also typically restricted to the surface, have individual phase structures that are inaccessible with classical diffraction methods, and possess surface properties that cannot readily be measured by the traditional wetting (water contact angle) technique. In this study, we demonstrate application of Atomic Force Microscopy (AFM) to obtain high spatial resoln. surface energy distribution in the trans and cis domains on the surface of azobenzene single crystal. UV excitation of single crystals of 3',4'-dimethyl-4-(dimethylamino)azobenzene results in domino-like trans-to-cis isomerization on their surface. In the AFM phase channel, this affords contrasting domains with different physicochem. properties. Small amplitude small set point (SASS) method and bimodal AFM operated in the attractive regime provide maps of the tip-sample adhesion force and the Hamaker const., resp. The results show that the Hamaker const. of the cis domains (∼1 × 10-19 J) is higher than that of the trans domains (∼7 × 10-20 J). After UV irradn., the calcd. surface energies of the domains were ∼40% higher based on the Hamaker const. Within a broader context, the results presented here demonstrate the potency of AFM-based surface-sensitive techniques for probing of the dynamic changes in surface properties upon photoinduced isomerization of mol. switches.
- 50Pesce, L.; Perego, C.; Grommet, A. B.; Klajn, R.; Pavan, G. M. Molecular Factors Controlling the Isomerization of Azobenzenes in the Cavity of a Flexible Coordination Cage. J. Am. Chem. Soc. 2020, 142, 9792– 9802, DOI: 10.1021/jacs.0c0344450https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXosVSitLk%253D&md5=574e6fde7deb3487e1d3fdf3bc028414Molecular Factors Controlling the Isomerization of Azobenzenes in the Cavity of a Flexible Coordination CagePesce, Luca; Perego, Claudio; Grommet, Angela B.; Klajn, Rafal; Pavan, Giovanni M.Journal of the American Chemical Society (2020), 142 (21), 9792-9802CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Photoswitchable mols. are employed for many applications, from the development of active materials to the design of stimuli-responsive mol. systems and light-powered mol. machines. To fully exploit their potential, we must learn ways to control the mechanism and kinetics of their photoinduced isomerization. One possible strategy involves confinement of photoresponsive switches such as azobenzenes or spiropyrans within crowded mol. environments, which may allow control over their light-induced conversion. However, the mol. factors that influence and control the switching process under realistic conditions and within dynamic mol. regimes often remain difficult to ascertain. As a case study, here we have employed mol. models to probe the isomerization of azobenzene guests within a Pd(II)-based coordination cage host in water. Atomistic mol. dynamics and metadynamics simulations allow us to characterize the flexibility of the cage in the solvent, the (rare) guest encapsulation and release events, and the relative probability/kinetics of light-induced isomerization of azobenzene analogs in these host-guest systems. In this way, we can reconstruct the mechanism of azobenzene switching inside the cage cavity and explore key mol. factors that may control this event. We obtain a mol.-level insight on the effects of crowding and host-guest interactions on azobenzene isomerization. The detailed picture elucidated by this study may enable the rational design of photoswitchable systems whose reactivity can be controlled via host-guest interactions.
- 51Hanopolskyi, A. I.; De, S.; Białek, M. J.; Diskin-Posner, Y.; Avram, L.; Feller, M.; Klajn, R. Reversible switching of arylazopyrazole within a metal–organic cage. Beilstein J. Org. Chem. 2019, 15, 2398– 2407, DOI: 10.3762/bjoc.15.23251https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVyqtrrF&md5=cbb6c6d63b6c9ac9390e546946b42355Reversible switching of arylazopyrazole within a metal-organic cageHanopolskyi, Anton I.; De, Soumen; Bialek, Michal J.; Diskin-Posner, Yael; Avram, Liat; Feller, Moran; Klajn, RafalBeilstein Journal of Organic Chemistry (2019), 15 (), 2398-2407CODEN: BJOCBH; ISSN:1860-5397. (Beilstein-Institut zur Foerderung der Chemischen Wissenschaften)Arylazopyrazoles represent a new family of mol. photoswitches characterized by a near-quant. conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd-imidazole coordination. Owing to its high water soly., the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not sol. in water. NMR spectroscopy and X-ray crystallog. have independently demonstrated that each cage can encapsulate two mols. of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calcns. suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage.
- 52Klajn, R. Spiropyran-based dynamic materials. Chem. Soc. Rev. 2014, 43, 148– 184, DOI: 10.1039/C3CS60181A52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvVGktLvK&md5=3f1e3c4f172f5d1da08476ecc2344df1Spiropyran-based dynamic materialsKlajn, RafalChemical Society Reviews (2014), 43 (1), 148-184CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)A review. In the past few years, spiropyran has emerged as the mol. of choice for the construction of novel dynamic materials. This unique mol. switch undergoes structural isomerization in response to a variety of orthogonal stimuli, e.g. light, temp., metal ions, redox potential, and mech. stress. Incorporation of this switch onto macromol. supports or inorg. scaffolds allows for the creation of robust dynamic materials. This review discusses the synthesis, switching conditions and use of dynamic materials in which spiropyran has been attached to the surfaces of polymers, biomacromols., inorg. nanoparticles, as well as solid surfaces. The resulting materials show fascinating properties whereby the state of the switch intimately affects a multitude of useful properties of the support. The utility of the spiropyran switch will undoubtedly endow these materials with far-reaching applications in the near future.
- 53Lerch, M. M.; Wezenberg, S. J.; Szymanski, W.; Feringa, B. L. Unraveling the Photoswitching Mechanism in Donor–Acceptor Stenhouse Adducts. J. Am. Chem. Soc. 2016, 138, 6344– 6347, DOI: 10.1021/jacs.6b0172253https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntlCmtrY%253D&md5=65feb79220cf86d96a790eba76e25989Unraveling the Photoswitching Mechanism in Donor-Acceptor Stenhouse AdductsLerch, Michael M.; Wezenberg, Sander J.; Szymanski, Wiktor; Feringa, Ben L.Journal of the American Chemical Society (2016), 138 (20), 6344-6347CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The photoswitching mechanism of donor-acceptor Stenhouse adducts (DASA), a recently reported class of photoswitches, is shown to proceed via E-Z photoisomerization followed by a thermal, con-rotatory 4π-electrocyclization. The photogenerated intermediate is manifested by a bathochromically shifted band in the visible absorption spectrum of the DASA. The identification of the role of this intermediate reveals a key step in the photoswitching mechanism that is essential to the rational design of switching properties via structural modification.
- 54Udayabhaskararao, T.; Kundu, P. K.; Ahrens, J.; Klajn, R. Reversible Photoisomerization of Spiropyran on the Surfaces of Au25 Nanoclusters. ChemPhysChem 2016, 17, 1805– 1809, DOI: 10.1002/cphc.20150089754https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvVOlt7bE&md5=0f960ed916622e9cfd46878a0538360fReversible Photoisomerization of Spiropyran on the Surfaces of Au25 NanoclustersUdayabhaskararao, T.; Kundu, Pintu K.; Ahrens, Johannes; Klajn, RafalChemPhysChem (2016), 17 (12), 1805-1809CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)Au25 nanoclusters functionalized with a spiropyran mol. switch are synthesized via a ligand-exchange reaction at low temp. The resulting nanoclusters are characterized by optical and NMR spectroscopies as well as by mass spectrometry. Spiropyran bound to nanoclusters isomerizes in a reversible fashion when exposed to UV and visible light, and its properties are similar to those of free spiropyran mols. in soln. The reversible photoisomerization entails the modulation of fluorescence as well as the light-controlled self-assembly of nanoclusters.
- 55Kundu, P. K.; Das, S.; Ahrens, J.; Klajn, R. Controlling the lifetimes of dynamic nanoparticle aggregates by spiropyran functionalization. Nanoscale 2016, 8, 19280– 19286, DOI: 10.1039/C6NR05959G55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs12ks7vE&md5=32fefcef4721fc7416cbd081f8a94f0aControlling the lifetimes of dynamic nanoparticle aggregates by spiropyran functionalizationKundu, Pintu K.; Das, Sanjib; Ahrens, Johannes; Klajn, RafalNanoscale (2016), 8 (46), 19280-19286CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)Novel light-responsive nanoparticles were synthesized by decorating the surfaces of gold and silver nanoparticles with a nitrospiropyran mol. photoswitch. Upon exposure to UV light in nonpolar solvents, these nanoparticles self-assembled to afford spherical aggregates, which disassembled rapidly when the UV stimulus was turned off. The sizes of these aggregates depended on the nanoparticle concn., and their lifetimes could be controlled by adjusting the surface concn. of nitrospiropyran on the nanoparticles. The conformational flexibility of nitrospiropyran, which was altered by modifying the structure of the background ligand, had a profound impact on the self-assembly process. By coating the nanoparticles with a spiropyran lacking the nitro group, a conceptually different self-assembly system, relying on a reversible proton transfer, was realized. The resulting particles spontaneously (in the dark) assembled into aggregates that could be readily disassembled upon exposure to blue light.
- 56Cabrera, I.; Krongauz, V. Dynamic ordering of aggregated mesomorphic macromolecules. Nature 1987, 326, 582– 585, DOI: 10.1038/326582a056https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsFGjtL4%253D&md5=5d7144fd237e14e35d1e1c6aff9c1be9Dynamic ordering of aggregated mesomorphic macromoleculesCabrera, Ivan; Krongauz, ValeriNature (London, United Kingdom) (1987), 326 (6113), 582-5CODEN: NATUAS; ISSN:0028-0836.Structural transformations in a thermotropic liq.-cryst. copolymer of I and CH2:CHCO2(CH2)6O-p-C6H4CO2-p-C6H4CN caused by shearing or other mech. perturbations resulted in restoration of parallel arrangement of the mesogenic groups as well as reconstruction of the main chain conformation. Phys. crosslinking due to aggregation of the merocyanine dye moieties (from thermal conversion of the spiropyran side groups) in I led to network formation which was responsible for the appearance of a new rheo-optical effect obsd. above the clearing point.
- 57Ahrens, J.; Bian, T.; Vexler, T.; Klajn, R. Irreversible Bleaching of Donor–Acceptor Stenhouse Adducts on the Surfaces of Magnetite Nanoparticles. ChemPhotoChem 2017, 1, 230– 236, DOI: 10.1002/cptc.20170000957https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1KgtbvM&md5=3184f957d41f8cc6202120b2f1b58b49Irreversible Bleaching of Donor-Acceptor Stenhouse Adducts on the Surfaces of Magnetite NanoparticlesAhrens, Johannes; Bian, Tong; Vexler, Tom; Klajn, RafalChemPhotoChem (2017), 1 (5), 230-236CODEN: CHEMYH ISSN:. (Wiley-VCH Verlag GmbH & Co. KGaA)Two novel donor-acceptor Stenhouse adducts (DASAs) featuring the catechol moiety were synthesized and characterized. Both compds. bind strongly to the surfaces of magnetite nanoparticles. An adrenaline-derived DASA renders the particles insol. in all common solvents, likely because of poor solvation of the zwitterionic isomer generated on the nanoparticle surfaces. Well-sol. nanoparticles were successfully obtained using dopamine-derived DASA equipped with a long alkyl chain. Upon its attachment to nanoparticles, this DASA undergoes an irreversible decoloration reaction owing to the formation of the zwitterionic form. The reaction follows first-order kinetics and proceeds more rapidly on large nanoparticles. Interestingly, decoloration can be suppressed in the presence of free DASA mols. in soln. or at high nanoparticle concns.
- 58Williams, D. E.; Martin, C. R.; Dolgopolova, E. A.; Swifton, A.; Godfrey, D. C.; Ejegbavwo, O. A.; Pellechia, P. J.; Smith, M. D.; Shustova, N. B. Flipping the Switch: Fast Photoisomerization in a Confined Environment. J. Am. Chem. Soc. 2018, 140, 7611– 7622, DOI: 10.1021/jacs.8b0299458https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVags77O&md5=137454435f0af95aa275c1cc53a77e04Flipping the Switch: Fast Photoisomerization in a Confined EnvironmentWilliams, Derek E.; Martin, Corey R.; Dolgopolova, Ekaterina A.; Swifton, Anton; Godfrey, Danielle C.; Ejegbavwo, Otega A.; Pellechia, Perry J.; Smith, Mark D.; Shustova, Natalia B.Journal of the American Chemical Society (2018), 140 (24), 7611-7622CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Stimuli-responsive materials are vital for addressing emerging demands in the advanced technol. sector as well as current industrial challenges. Here, we report for the first time that coordinative integration of photoresponsive building blocks possessing photochromic spiropyran and diarylethene moieties within a rigid scaffold of metal-org. frameworks (MOFs) could control photophysics, in particular, cycloreversion kinetics, with a level of control that is not accessible in the solid state or soln. On the series of photoactive materials, we demonstrated for the first time that photoisomerization rates of photochromic compds. could be tuned within almost 2 orders of magnitude. Moreover, cycloreversion rates of photoresponsive derivs. could be modulated as a function of the framework structure. Furthermore, through MOF engineering we were able to achieve complete isomerization for coordinatively immobilized spiropyran derivs., typically exhibiting limited photoswitching behavior in the solid state. For instance, spectroscopic anal. revealed that the novel monosubstituted spiropyran deriv. grafted to the backbone of the MOF pillar exhibits a remarkable photoisomerization rate of 0.16 s-1, typical for cycloreversion in soln. We also applied the acquired fundamental principles toward mapping of changes in material properties, which could provide a pathway for monitoring material aging or structural deterioration.
- 59Wang, Z.; Müller, K.; Valášek, M.; Grosjean, S.; Bräse, S.; Wöll, C.; Mayor, M.; Heinke, L. Series of Photoswitchable Azobenzene-Containing Metal–Organic Frameworks with Variable Adsorption Switching Effect. J. Phys. Chem. C 2018, 122, 19044– 19050, DOI: 10.1021/acs.jpcc.8b0584359https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtlGit7%252FK&md5=15950da71da18498ef1517f39f0706d4Series of Photoswitchable Azobenzene-Containing Metal-Organic Frameworks with Variable Adsorption Switching EffectWang, Zhengbang; Mueller, Kai; Valasek, Michal; Grosjean, Sylvain; Braese, Stefan; Woell, Christof; Mayor, Marcel; Heinke, LarsJournal of Physical Chemistry C (2018), 122 (33), 19044-19050CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Nanoporous metal-org. frameworks (MOFs) equipped with light-responsive azobenzene pendant groups present a novel family of smart materials, enabling advanced applications like switchable guest adsorption, membranes with tunable mol. sepn. factors, and photoswitchable proton conduction. Although it is obvious that for small pore sizes, steric constraints may prohibit azobenzene switching, guidelines for optimizing the MOF architecture to achieve large switching effects have not yet been established. Here, a series of five different photoswitchable azobenzene-contg. pillared-layer MOF structures is presented. The switching effect is quantified by the light-induced increase of the uptake amt. of butanol as the probe mol. For fast and reproducible measurements, thin well-defined MOF films, referred to as surface-mounted MOFs (SURMOFs), were used in combination with a quartz crystal microbalance. Although the series comprises similar MOF structures, the magnitude of the switching effect considerably differs, here by a factor of 5. The uptake data show that, rather than the pore size or the no. of azobenzene mols. per pore, the d. of azobenzene per pore vol. is crucial. The finding that a large switching effect is reached for a high d. of azobenzene moieties per MOF unit cell provides the basis for further applications of photoswitchable MOFs and SURMOFs.
- 60Müller, K.; Helfferich, J.; Zhao, F. L.; Verma, R.; Kanj, A. B.; Meded, V.; Bléger, D.; Wenzel, W.; Heinke, L. Switching the Proton Conduction in Nanoporous, Crystalline Materials by Light. Adv. Mater. 2018, 30, 1706551, DOI: 10.1002/adma.201706551There is no corresponding record for this reference.
- 61Castiglioni, F.; Danowski, W.; Perego, J.; Leung, F. K.-C.; Sozzani, P.; Bracco, S.; Wezenberg, S. J.; Comotti, A.; Feringa, B. L. Modulation of porosity in a solid material enabled by bulk photoisomerization of an overcrowded alkene. Nat. Chem. 2020, 12, 595– 602, DOI: 10.1038/s41557-020-0493-561https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1KgtbvF&md5=69f6f01350338226fd63708acf633d12Modulation of porosity in a solid material enabled by bulk photoisomerization of an overcrowded alkeneCastiglioni, Fabio; Danowski, Wojciech; Perego, Jacopo; Leung, Franco King-Chi; Sozzani, Piero; Bracco, Silvia; Wezenberg, Sander J.; Comotti, Angiolina; Feringa, Ben L.Nature Chemistry (2020), 12 (7), 595-602CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)The incorporation of photoswitchable mols. into solid-state materials holds promise for the fabrication of responsive materials, the properties of which can be controlled on-demand. However, the possible applications of these materials are limited due to the restrictions imposed by the solid-state environment on the incorporated photoswitches, which render the photoisomerization inefficient. Here we present responsive porous switchable framework materials based on a bistable chiroptical overcrowded alkene incorporated in the backbone of a rigid arom. framework. As a consequence of the high intrinsic porosity, the resulting framework readily responds to a light stimulus, as demonstrated by solid-state Raman and reflectance spectroscopies. Solid-state 13C NMR spectroscopy highlights an efficient and quant. bulk photoisomerization of the incorporated light-responsive overcrowded olefins in the solid material. Taking advantage of the quant. photoisomerization, the porosity of the framework and the consequent gas adsorption can be reversibly modulated in response to light and heat.
- 62Saha, R.; Devaraj, A.; Bhattacharyya, S.; Das, S.; Zangrando, E.; Mukherjee, P. S. Unusual Behavior of Donor–Acceptor Stenhouse Adducts in Confined Space of a Water-Soluble PdII8 Molecular Vessel. J. Am. Chem. Soc. 2019, 141, 8638– 8645, DOI: 10.1021/jacs.9b0392462https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXovVKntrg%253D&md5=2d54830caa9d553dc369eeb47256e18aUnusual Behavior of Donor-Acceptor Stenhouse Adducts in Confined Space of a Water-Soluble PdII8 Molecular VesselSaha, Rupak; Devaraj, Anthonisamy; Bhattacharyya, Soumalya; Das, Soumik; Zangrando, Ennio; Mukherjee, Partha SarathiJournal of the American Chemical Society (2019), 141 (21), 8638-8645CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Donor-acceptor Stenhouse adducts (DASA) are new-generation photochromic compds. discovered recently. DASA exist normally in open form (blue/violet) and readily convert to cyclic (light yellow/colorless) zwitterionic form reversibly in the presence of green light in toluene/dioxane. In aq. medium, the open form is not stable and converts to the cyclic zwitterionic form irreversibly. We report here a new self-assembled Pd8 mol. vessel (MV) that can stabilize and store the open form of DASA even in aq. medium. Reaction of the 90° acceptor cis-(tmeda)Pd(NO3)2 (M) [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] with a sym. tetraimidazole donor (L, 3,3',5,5'-tetra(1H-imidazol-1-yl)-1,1'-biphenyl) in a 2:1 molar ratio yielded a water-sol. [8+4] self-assembled M8L4 mol. barrel (MV). This barrel (MV) is found to be a potential mol. vessel to store and stabilize the open forms of DASA in aq. medium over the more stable zwitterionic cyclic form, while in the absence of the barrel the same DASA exist in cyclic zwitterionic form in aq. medium. The hydrophobic interaction between the cavity and the open form of DASA mols. benefits reaching an out-of-equil. or reverse equil. state in aq. medium. The presence of excess MV could even drive the conversion of the stable cyclic form to the open form in aq. medium. The host-guest complex is stable upon irradiating with green light. To the best of our knowledge, this is the first successful attempt to stabilize the open form of DASA mols. in aq. medium and the first report on the fate of DASA in a confined space discrete mol. architecture. Furthermore, the mol. vessel has been utilized for catalytic Michael addn. reactions of a series of nitrostyrene derivs. with 1,3-indandione in aq. medium.
- 63Singh, G.; Chan, H.; Baskin, A.; Gelman, E.; Repnin, N.; Král, P.; Klajn, R. Self-assembly of magnetite nanocubes into helical superstructures. Science 2014, 345, 1149– 1153, DOI: 10.1126/science.125413263https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVGhtLbJ&md5=41873b1ec6481770bbd5fc02430c433cSelf-assembly of magnetite nanocubes into helical superstructuresSingh, Gurvinder; Chan, Henry; Baskin, Artem; Gelman, Elijah; Repnin, Nikita; Kral, Petr; Klajn, RafalScience (Washington, DC, United States) (2014), 345 (6201), 1149-1153CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Organizing inorg. nanocrystals into complex architectures is challenging and typically relies on preexisting templates, such as properly folded DNA or polypeptide chains. We found that under carefully controlled conditions, cubic nanocrystals of magnetite self-assemble into arrays of helical superstructures in a template-free manner with >99% yield. Computer simulations revealed that the formation of helixes is detd. by the interplay of van der Waals and magnetic dipole-dipole interactions, Zeeman coupling, and entropic forces and can be attributed to spontaneous formation of chiral nanocube clusters. Neighboring helixes within their densely packed ensembles tended to adopt the same handedness to maximize packing, thus revealing a novel mechanism of symmetry breaking and chirality amplification.
- 64Sawczyk, M.; Klajn, R. Out-of-Equilibrium Aggregates and Coatings during Seeded Growth of Metallic Nanoparticles. J. Am. Chem. Soc. 2017, 139, 17973– 17978, DOI: 10.1021/jacs.7b0911164https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvV2gu7fO&md5=00cf9c36e2f21a4b446c54605268dcd6Out-of-Equilibrium Aggregates and Coatings during Seeded Growth of Metallic NanoparticlesSawczyk, Michal; Klajn, RafalJournal of the American Chemical Society (2017), 139 (49), 17973-17978CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Although dissipative self-assembly is ubiquitous, where it gives rise to structures and functions crit. to life, examples of artificial systems featuring this mode of self-assembly are rare. Here, the authors identify the presence of ephemeral assemblies during seeded growth of Au nanoparticles. In this process, hydrazine reduces Au(III) ions, which attach to the existing nanoparticles seeds. The attachment is accompanied by a local increase in the concn. of a surfactant, which therefore forms a bilayer on nanoparticle surfaces, inducing their assembly. The resulting aggregates gradually disassemble as the surfactant concn. throughout the soln. equilibrates. The lifetimes of the out-of-equil. aggregates depend on and can be controlled by the size of the constituent nanoparticles. The authors demonstrate the utility of the out-of-equil. aggregates to form transient reflective coatings on polar surfaces.
- 65Udayabhaskararao, T.; Altantzis, T.; Houben, L.; Coronado-Puchau, M.; Langer, J.; Popovitz-Biro, R.; Liz-Marzán, L. M.; Vuković, L.; Král, P.; Bals, S.; Klajn, R. Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices. Science 2017, 358, 514– 518, DOI: 10.1126/science.aan604665https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhslSgsb7I&md5=cb2cb80da91ead2c9e6698d496ba91dcTunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlatticesUdayabhaskararao, Thumu; Altantzis, Thomas; Houben, Lothar; Coronado-Puchau, Marc; Langer, Judith; Popovitz-Biro, Ronit; Liz-Marzan, Luis M.; Vukovic, Lela; Kral, Petr; Bals, Sara; Klajn, RafalScience (Washington, DC, United States) (2017), 358 (6362), 514-518CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Self-assembly of inorg. nanoparticles has been used to prep. many different colloidal crystals, but almost invariably with the restriction that these particles must be densely packed. This work showed non-close-packed nanoparticle arrays can be fabricated by selectively removing one of two components comprising binary nanoparticle superlattices. First, a variety of binary nanoparticle superlattices were prepd. at an liq./air interface, including several previously unknown arrangements. Mol. dynamics simulations showed the particular role of the liq. in templating superlattice formation not achievable by self-assembly in bulk soln. Second, upon stabilization, all these binary superlattices could be transformed into distinct nanoallotropes/nanoporous materials of the same chem. compn. but differing in their nanoscale architectures.
- 66Amdursky, N.; Kundu, P. K.; Ahrens, J.; Huppert, D.; Klajn, R. Noncovalent Interactions with Proteins Modify the Physicochemical Properties of a Molecular Switch. ChemPlusChem 2016, 81, 44– 48, DOI: 10.1002/cplu.20150041766https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemtL3N&md5=f44f9ba03632a8b7861db598a7caa8c6Noncovalent Interactions with Proteins Modify the Physicochemical Properties of a Molecular SwitchAmdursky, Nadav; Kundu, Pintu K.; Ahrens, Johannes; Huppert, Dan; Klajn, RafalChemPlusChem (2016), 81 (1), 44-48CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)It is reported that spiropyran-a widely investigated mol. photoswitch-can be stabilized in aq. environments in the presence of a variety of proteins, including human serum albumin, insulin fibrils, lysozyme, and glucose oxidase. The optical properties of the complexed photoswitch are protein dependent, with human serum albumin providing the spiropyran with emission features previously obsd. for a photoswitch confined in media of high viscosity. Despite being bound to the protein mols., spiropyran can undergo a ring-opening reaction upon exposure to UV light. This photoisomerization process can affect the properties of the proteins: here, it is shown that the elec. conduction through human serum albumin to which the spiropyran is bound increases following the ring-opening reaction.
- 67Bian, T.; Chu, Z.; Klajn, R. The Many Ways to Assemble Nanoparticles Using Light. Adv. Mater. 2020, 32, 1905866, DOI: 10.1002/adma.20190586667https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFequr7P&md5=b32f318d96c4963cc0e3dc61f14d0125The Many Ways to Assemble Nanoparticles Using LightBian, Tong; Chu, Zonglin; Klajn, RafalAdvanced Materials (Weinheim, Germany) (2020), 32 (20), 1905866CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. The ability to reversibly assemble nanoparticles using light is both fundamentally interesting and important for applications ranging from reversible data storage to controlled drug delivery. Here, the diverse approaches that have so far been developed to control the self-assembly of nanoparticles using light are reviewed and compared. These approaches include functionalizing nanoparticles with monolayers of photoresponsive mols., placing them in photoresponsive media capable of reversibly protonating the particles under light, and decorating plasmonic nanoparticles with thermoresponsive polymers, to name just a few. The applicability of these methods to larger, micrometer-sized particles is also discussed. Finally, several perspectives on further developments in the field are offered.
- 68Manna, D.; Udayabhaskararao, T.; Zhao, H.; Klajn, R. Orthogonal Light-Induced Self-Assembly of Nanoparticles using Differently Substituted Azobenzenes. Angew. Chem., Int. Ed. 2015, 54, 12394– 12397, DOI: 10.1002/anie.20150241968https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXotVClsLw%253D&md5=7ed3d2d8934ef7f40cc778683922d74cOrthogonal Light-Induced Self-Assembly of Nanoparticles using Differently Substituted AzobenzenesManna, Debasish; Udayabhaskararao, Thumu; Zhao, Hui; Klajn, RafalAngewandte Chemie, International Edition (2015), 54 (42), 12394-12397CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Precise control of the self-assembly of selected components within complex mixts. is a challenging goal whose realization is important for fabricating novel nanomaterials. Herein we show that by decorating the surfaces of metallic nanoparticles with differently substituted azobenzenes, it is possible to modulate the wavelength of light at which the self-assembly of these nanoparticles is induced. Exposing a mixt. of two types of nanoparticles, each functionalized with a different azobenzene, to UV or blue light induces the selective self-assembly of only one type of nanoparticles. Irradn. with the other wavelength triggers the disassembly of the aggregates, and the simultaneous self-assembly of nanoparticles of the other type. By placing both types of azobenzenes on the same nanoparticles, we created unique materials ("frustrated" nanoparticles) whose self-assembly is induced irresp. of the wavelength of the incident light.
- 69Das, S.; Ranjan, P.; Maiti, P. S.; Singh, G.; Leitus, G.; Klajn, R. Dual-Responsive Nanoparticles and their Self-Assembly. Adv. Mater. 2013, 25, 422– 426, DOI: 10.1002/adma.20120173469https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xht12jtr3E&md5=10d7e0a453e95435bae2d8916f21bcefDual-Responsive Nanoparticles and their Self-AssemblyDas, Sanjib; Ranjan, Priyadarshi; Maiti, Pradipta Sankar; Singh, Gurvinder; Leitus, Gregory; Klajn, RafalAdvanced Materials (Weinheim, Germany) (2013), 25 (3), 422-426CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)The authors have demonstrated that self-assembly of nanoparticles (NPs) can be controlled independently and/or cooperatively by light and magnetic field. This methodol. could be used to fabricate devices whose electronic properties could independently be modulated using these two orthogonal types of external stimuli. In the context of self-assembly, the results reported can be used to construct dynamically self-assembling magnetic objects which can be guided, using external magnetic fields, to desired locations, where their disassembly can be initiated at will, using visible light. The authors expect that in the long run, this strategy will enable controlled capture, delivery, and release of mol./nanosized cargo.
- 70Chovnik, O.; Balgley, R.; Goldman, J. R.; Klajn, R. Dynamically Self-Assembling Carriers Enable Guiding of Diamagnetic Particles by Weak Magnets. J. Am. Chem. Soc. 2012, 134, 19564– 19567, DOI: 10.1021/ja309633v70https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCgsb7J&md5=788b86033c58bb1bfde1dcbff822b6b7Dynamically Self-Assembling Carriers Enable Guiding of Diamagnetic Particles by Weak MagnetsChovnik, Olga; Balgley, Renata; Goldman, Joel R.; Klajn, RafalJournal of the American Chemical Society (2012), 134 (48), 19564-19567CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Diamagnetic particles can be remotely manipulated by a magnet by the reversible adsorption of dual-responsive, light-switchable/superparamagnetic nanoparticles down to their surface. Adsorption occurs upon exposure to UV light, and can be reversed thermally or by ambient light. The dynamic self-assembly of thin films of the dual-responsive nanoparticles induces attractive interactions between diamagnetic particles. Catalytic amts. of the dual-responsive nanoparticles are sufficient to magnetically guide and deliver the diamagnetic particles to desired locations, where they can then be released by disassembling the dynamic layers of superparamagnetic nanoparticles with visible light.
- 71Lee, J.-W.; Klajn, R. Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2. Chem. Commun. 2015, 51, 2036– 2039, DOI: 10.1039/C4CC08541H71https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvF2jtrvK&md5=61087db3b48da505da5c85bf36d59252Dual-responsive nanoparticles that aggregate under the simultaneous action of light and CO2Lee, Ji-Woong; Klajn, RafalChemical Communications (Cambridge, United Kingdom) (2015), 51 (11), 2036-2039CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Metallic nanoparticles co-functionalized with monolayers of UV- and CO2-sensitive ligands were prepd. and shown to respond to these two types of stimuli reversibly and in an orthogonal fashion. The compn. of the coating could be tailored to yield nanoparticles capable of aggregating exclusively when both UV and CO2 were applied at the same time, analogously to the behavior of an AND logic gate.