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Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies
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Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies
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  • Carla Cunha
    Carla Cunha
    CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, Coimbra 3004-535, Portugal
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  • Andrea Pinto
    Andrea Pinto
    Departament de Química Inorgànica i Orgànica, Secció de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1−11, Barcelona E-08028, Spain
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  • Adelino Galvão
    Adelino Galvão
    Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049 001 Lisboa, Portugal
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  • Laura Rodríguez*
    Laura Rodríguez
    Departament de Química Inorgànica i Orgànica, Secció de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1−11, Barcelona E-08028, Spain
    Institut de Nanociència i Nanotecnologia. Universitat de Barcelona, Barcelona 08028, Spain
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-1289-1587
  • J. Sérgio Seixas de Melo*
    J. Sérgio Seixas de Melo
    CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, Coimbra 3004-535, Portugal
    *Email: [email protected]
    More by J. Sérgio Seixas de Melo
    Orcidhttps://orcid.org/0000-0001-9708-5079
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Inorganic Chemistry

Cite this: Inorg. Chem. 2022, 61, 18, 6964–6976
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https://doi.org/10.1021/acs.inorgchem.2c00366
Published April 27, 2022

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Abstract

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Aggregation-induced emission (AIE) has gained a remarkable amount of interest in the past 20 years, but the majority of the studies are based on organic structures. Herein, three dinuclear gold(I) complexes, with the general formula [PPh2XPPh2-Au2-Coum2], where the Au(I) atom is linked to three different diphosphanes [PPh2XPPh2; DPPM for X = CH2 (1.1), DPPP for X = (CH2)3 (1.2), and DPPA for X = C≡C (1.3)] and the propynyloxycoumarin precursor (1, 4-methyl-substituted coumarin), have been synthesized. The compounds present AIE characteristics, AIEgens, with high luminescence quantum yields in the solid state when they are compared to dilute solutions. Photophysical studies (steady-state and time-resolved fluorescence) were obtained, with AIE being observed with the three gold(I) complexes in acetonitrile/water mixtures. This was further corroborated with dynamic light scattering measurements. Time-dependent density functional theory (TDDFT) electronic calculations show that the compounds have different syn and anti conformations (relative to the coumarin core) with 1.1 syn and 1.2 and 1.3 both anti. From time-resolved fluorescence experiments, the augment in the contribution of the longer decay component is found to be associated with the emission of the aggregate (AIE effect) and its nature (involving a dimer) rationalized from TDDFT electronic calculations.

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Published ASAP on April 27, 2022; Revised April 28, 2022 to correct production error in Table 2.

Synopsis

Aggregation-induced emission (AIE) found with three dinuclear gold(I) complexes [PPh2XPPh2-Au2-Coum2], where X = DPPM (1.1), DPPP (1.2), and DPPA (1.3). This was obtained from steady-state and time-resolved fluorescence experiments in acetonitrile/water mixtures, further complemented by dynamic light scattering experiments. Different syn and anti conformations are found and the double-exponential decay associated with the emission of the aggregate (AIE effect) and its nature (involving a dimer) rationalized from time-dependent density functional theory electronic calculations.

Introduction

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Since the pioneering study of Tang and co-workers, there has been a substantial increase in the number of luminescent compounds with aggregation-induced emission (AIE) properties (AIEgens). (1−7) One current strategy to improve the luminescence emission in the solid state involves the development of structures, whereby when molecular movements, free motion, or internal rotation (loose bolt or rigid rotor effects) of a molecule are restricted, the radiative deactivation increases because of a decrease of the radiatiotionless deactivation channel. (7) This is valid for excited singlet and triplet states. (8−10) AIEgens, such as tetraphenylethylene (TPE), show weak emissions in dilute solutions (good solvents) but emit intensely when they aggregate and, usually, also in the solid state (aggregates). The AIE effect has been linked to the restriction in intramolecular rotations, by aggregate formation, of the emissive molecules, which efficiently limits the radiationless energy deactivation, enhancing the radiative decay. (7,11) With AIEgens, the particular shape of the TPE units prevents luminogens from packing (in the luminescence loss π–π stacking), while the intramolecular rotations (an efficient route for radiationless deactivation through the loose bolt effect) are physically constrained in the condensed phase. Aggregates typically have dimensions around 100 nm, and its luminescence efficiency is also found to depend on the degree of crystallinity.
A growing interest in organometallic complexes has been observed in the past 2 decades mainly because of their potential use in a variety of applications; in particular, gold(I)-derived complexes represent an area of research that is emerging mainly because of their luminescent properties, both in the solid state and in solution. (12−15) Gold(I) complexes are particularly interesting because of the structural characteristics of their ligands but also because of the possible establishment of AuI···AuI interactions (an aurophilicity phenomenon), (12,16−18) which can modulate and give the resulting assembly properties and various potential applications in, for example, drugs, photodynamic therapy (PDT) agents, and sensors. (19−23) This interaction (aurophilicity) can be of intramolecular or intermolecular origin, and the ideal distance for such an interaction to be significant must be lower than, or close to, the sum of the van der Waals radii (3.32 Å), (24,25) and the energy of these bonds is analogous to that of strong hydrogen bonds (5–10 kcal/mol). (24,26) This synergy can provide additional stability to the complexes derived from gold(I). (27) Self-assembly in supramolecular aggregates can facilitate other types of interactions between ligands, including π–π-stacking interactions, that can also involve “neighboring” complexes, which, in turn, can lead to new emission bands, as a result of AIE. (6,28−31) In this context, this class of compounds is one of the most promising in the current panorama of materials science. (24,26) The luminescent properties of alkynylgold(I) complexes have grown significantly in the past several years. (27,32) The general strategy for obtaining luminescent alkynylgold(I) complexes relies on the fact that the ligand is actually a luminophore of its own, whose emission in the triplet state increases strongly as a consequence of the heavy effect induced by gold. (27,29) This, in turn, facilitates access to excited triplet states by increasing the spin–orbit coupling (SOC), thus favoring the S1∼∼→T1 intersystem crossing pathway. (8,23,30,32)
Inclusion of the phosphane ligands allows the introduction of complementary electronic properties, together with several different types of coordination geometries, in transition-metal centers, improving the predictable physical and chemical properties of these new complexes. (33−35) Additionally, gold(I) complexes can display dual luminescence at room temperature with emission efficiencies that depend significantly on the structure of the molecule. (31,34,36)
Despite some recent publications reporting gold(I) AIEgen complexes, with relevant works pointing to a diverse number of applications, (31,37−41) including the potential to reach an efficient low dose of X-ray-induced PDT, (42) only a very limited number of these offer a rationale of the observed phenomena with different techniques. In previous works of our group, we have investigated the alkynylcoumarin ligand, which presents different electron-donating and electron-withdrawing substituents and the water-soluble phosphane spacers 1,3,5-triaza-7-phosphaadamantane (PTA) and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA). (32) The 7-substituted coumarin chromophore (with the substitution of O–R, with R = alkyl group, in the 7 position) displays high fluorescence emission, making it highly appropriate to be investigated with fluorescence techniques. (32) In this work, we describe the synthesis and analytical and photophysical (including steady-state and time-resolved data) characterization of a series of dinuclear gold(I) complexes constituted by an alkynyl-4-methylcoumarin ligand and diphosphanes with various lengths and flexibilities (1.1, 1.2, and 1.3 in Scheme 1). In addition, dynamic light scattering (DLS) and time-dependent density functional theory (TDDFT) electronic calculations were performed, aiming to shed light on the nature of the aggregates.

Scheme 1

Scheme 1. General Synthetic Routes, Structures, and Acronyms of Alkynylcoumarin Dinuclear Gold(I) Complexes [Au (C≡C13H9O3)(PPh2XPPh2)]2 [PPh2XPPh2 = DPPM for X = (CH2) (1.1), DPPP for X = (CH2)3 (1.2), and DPPA for X = C≡C (1.3)]
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Results and Discussion

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Synthesis and Structural Characterization

Three different organometallic dinuclear gold(I) complexes containing the diphosphanes DPPM (1.1), DPPP (1.2), and DPPA (1.3) were synthesized. This required the previous synthesis of the polymer [Au(C≡C13H9O3)]n (1a) from deprotonation of the propargyloxycoumarin ligand and a subsequent reaction with AuCl(tht), as the gold(I) source (Scheme 1). Correct formation of the compound was evidenced by the disappearance of the terminal alkynyl proton of the organic chromophore (∼3303 cm–1) and the presence of the C≡C vibration (∼2935 cm–1) in the IR spectrum (Figures S1 and S2). Then, a dichloromethane suspension of 1a was stirred with the different phosphanes (PPh2XPPh2) in a 2:1 ratio (Scheme 1), and the reaction was kept under stirring for 60 min at room temperature. Coordination of the corresponding diphosphanes (DPPM, DPPP, and DPPA) gave pale-yellow (1.1) and white (1.2 and 1.3) solutions that yielded the corresponding complexes in moderate yields after concentration and precipitation with n-hexane (∼50–70%).
Characterization of 1.1, 1.2, and 1.3 was obtained from different spectroscopic techniques (IR and 1H and 31P NMR spectroscopy and positive-ion electrospray ionization mass spectrometry [ESI-MS(+)], which concluded with the successful synthesis of the complexes. The corresponding 1H NMR spectra show the characteristic protons of the organic ligand, together with the characteristic protons of the different diphosphanes (Figures S3–S5). Furthermore, the methylene protons, close to the alkynyl group, are detected as a singlet instead of the doublet recorded in the organic ligand due to coordination to the metal atom. 31P NMR obtained in CDCl3 typically shows signals at 31.0, 34.3, and 17.0 ppm, which are ca. 50 ppm downfield-shifted compared with the free diphosphane, as expected for coordination to the gold(I) atom (Figures S6–S8). From IR spectroscopy, the characteristic v(C≡C) vibration was also observed at 2130 cm–1. Formation of the gold(I) complexes was finally confirmed by ESI-MS(+) measurements, with the detection of the corresponding molecular peaks [M + Na]+ and [M + K]+ of the protonated species for all complexes (Figures S9–S11).

Electronic Spectral Characterization

The three dinuclear gold(I) complexes 1.1, 1.2, and 1.3 and the propynyloxycoumarin ligand 1 were further investigated, aiming to clarify the effect of the diphosphanes and the presence of gold(I) atoms on the photophysical properties and the presence of AIE. Figure 1 represents both the absorption and fluorescence emission spectra of 1.1, 1.2, and 1.3, together with the corresponding data of 1 in different organic solvents and in the solid state (thin films) at room temperature (293 K). The relevant electronic spectral parameters (including the absorption, fluorescence, and phosphorescence emission wavelength maxima, fluorescence quantum yields, and Stokes shifts) are summarized in Table 1. The data for 1, which was previously studied, are included for comparison. (32)

Figure 1

Figure 1. Absorption and fluorescence emission spectra of the dinuclear gold(I) complexes (1.1, 1.2, and 1.3) with the parent compound (1) in MeCN, 2-MeTHF, and thin films. Vertical dashed lines are just guides to the eye. Color legend for lines: absorption and emission spectra of 1, orange; 1.1, purple; 1.2, blue; 1.3, dark green.

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Table 1. Spectroscopic Data (Including Wavelength Absorption λabs, Fluorescence λem, and Phosphorescence Emission Maxima λPh), Together with the Fluorescence Quantum Yields ϕF (in the Presence of Molecular Oxygen, O2, and Saturated Nitrogen, N2 sat.) and Stokes Shift ΔSS (cm–1), for the Gold(I) Complexes 1.1, 1.2, and 1.3 and Ligand 1 in Different Organic Solvents (Dioxane, Dx, 2-Methyltetrahydrofuran, 2-MeTHF, Dimethylformamide, DMF, and Acetonitrile, MeCN) and in the Solid State (Thin Films)
   293 K77 K
 solventε′aλabs (nm)λem (nm)ΔSS (cm–1)ϕF(O2)ϕF(N2 sat.)λPh (nm)
1Dx2.2531737649500.0120.015 
 2-MeTHF7.5831837144920.0100.014489a
 DMF36.731637449080.0210.027 
 MeCNa37.531637449080.0130.016 
 film 32138048370.181  
1.1Dx2.2531337552820.0110.014 
 2-MeTHF7.5832038049340.0120.015490
 DMF36.731937748230.0230.025 
 MeCN37.531837346810.0100.013 
 film 32539554530.054  
1.2Dx2.2532037445120.0180.023 
 2-MeTHF7.5831837749210.0150.022489
 DMF36.732037646540.0180.023 
 MeCN37.531437652510.0110.013 
 film 32539353240.122  
1.3Dx2.2532137444150.0230.029 
 2-MeTHF7.5831837849920.0130.015488
 DMF36.732137544860.0250.032 
 MeCN37.531937446100.0120.013 
 film 32539252590.113  
a

For 1 in MeCN and 2-MeTHF, the data are from ref (32).

In organic solvents, the gold(I) complexes display a strong absorption band at ∼320 nm, attributed to the coumarin chromophoric unit (32) and also indicative of a minor influence of the two gold atoms, and of the diphosphane units, on the electronic properties of the complexes. Hence, as previously observed for 1, (32) the band at ∼320 nm is assigned to a π → π* transition of the coumarin chromophoric unit, i.e., to intraligand electronic transitions. (43−46) This is corroborated from TDDFT theoretical calculations, which indicate that the relevant electronic transitions are located in the coumarin part of the molecule (see below). By changing the solvent’s polarity, here mirrored from the dielectric constant ε, the absorption spectral profile and maxima are found to be identical, as illustrated by the behavior in 2-methyltetrahydrofuran (2-MeTHF; ε = 7.58) and acetonitrile (MeCN; ε =37.5) (Figure 1 and Table 1).
The emission spectra show a broad emission band with maxima at 375–400 nm, again associated with the emission of 1. (43−45) Excitation spectra, obtained by collection at the emission wavelength maxima (see the vertical dashed lines in Figure 1), match the absorption of 1, indicative of this core structure being in the origin of the emission. From the summarized spectral data (Table 1) of 1, 1.1, 1.2, and 1.3, it can be seen that their absorption and emission spectra are identical, thus showing that the spectral properties are basically those of the alkynylcoumarin percursor 1.
In the solid state (thin films), a broader absorption with a ∼8–13 nm red shift of the absorption maxima is observed upon comparison with the spectra in solution (Figure 1). In general, similar spectroscopic features are observed in different solvents. Additionally, the fluorescence quantum yields (ϕF) show that the compounds weakly fluoresce in a solution of good solvents, with values ranging from 1 to 3%, becoming moderately emissive in the solid state (thin films) with values of 5–12% (Table 1).
Upon a change from the solution to the solid state, broadening of the absorption band and the red shift of both the absorption and emission maxima are indicative of emissive aggregates in thin films with enhancement of the fluorescence quantum yield (AIE effect).
Time-resolved fluorescence studies were further conducted to gain deeper insight into deactivation of the first singlet excited state of the studied compounds in solution (Figure 2). The fluorescence decays were analyzed with sums of exponentials, according to eq 1,
(1)
where τi are the decay times and ai are the preexponential factors that represent the contribution of each exponential term for t = 0. The fractional contribution of each species (Ci) was determined using eq 2, (47)
(2)
with n the number of exponential terms, ai the contribution of each of the exponential terms for t = 0, and τi the respective decay time. The data are summarized in Table S1 and Figure 2. The fluorescence decays of 1 were fitted to a single-exponential decay (with values ranging from 0.017 to 0.066 ns depending on the solvent), whereas that for the gold(I) complexes, in all solvents, the decays were found to be biexponential, with decay time values of 0.042–0.149 ns (τ1) and 0.116–0.430 ns (τ2). Furthermore, the amplitude (normalized preexponential factor) associated with the shorter decay time (ai1) is, in all solvents, found with the major contribution (Table S1). The second component, associated with the longer decay time (τ2) and with a smaller contribution (% C2), is, as will be rationalized in detail, also with the TDDFT data, with simulated structures of dimeric species (see the next section), attributed to the presence of ground-state aggregates.

Figure 2

Figure 2. Fluorescence decays for the gold(I) complexes (1.1, 1.2, and 1.3) and 1 in dimethylformamide at T = 293 K with λexc = 268 nm and λem = 375 nm. The quality of the analysis is judged by the presentation of the weighted residuals, autocorrelation functions (A.C.), and χ2 values. The decay with the black dashed line is the IRF obtained with a scatter solution (see the Experimental Section).

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Because the chromophoric and fluorogenic units in the complexes is the coumarin 1 ligand, the absence of even vestigial amounts of this compound in solutions of 1.1, 1.2, and 1.3 was indicated by the clearly different nature of the fluorescence decays. Indeed, besides the fact that for 1 the decay is single-exponential, in contrast with the gold(I) complexes, where it is double-exponential, the shorter component, τ1, is clearly much shorter in the precursor ligand 1, 66 ps, than in 1.1, 1.2, and 1.3, with ∼140 ps (Figure 2).
Phosphorescence emission spectra and lifetimes for the three gold(I) complexes were obtained in 2-MeTHF at low temperature (77 K; Figure 3). The spectra were obtained with a pulsed xenon lamp and delays after the flash (DAF) of 0.0 and 0.5 ms. The assignment of the phosphorescence emission band was carried out with DAF = 0.5 ms, which is also accompanied by the appearance of a red-shifted emission band when it is compared to the characteristic fluorescence band in 2-MeTHF (Figure S12). The phosphorescence emission bands of the different gold(I) complexes are found to be independent of the excitation wavelength, fully overlapped, displaying a vibronically structured band centered at ∼490 nm (Figure 3 A), and are attributed to a 3π,π* state localized on the coumarin chromophoric unit. (32) From the large Stokes shift observed and the long excited-state phosphorescence lifetimes (∼1.2 s; Figure 3 B), the triplet state has 3π,π* character, with high phosphorescence quantum yields (Table 2).

Figure 3

Figure 3. (A) Normalized phosphorescence emission spectra (λexc = 320 nm; DAF = 0.5 ms) and (B) decays (λem = 490 nm) for the gold(I) complexes 1.1, 1.2, and 1.3 in 2-MeTHF at T = 77 K.

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Table 2. Photophysical Data Including Quantum Yields (Fluorescence ϕF, Phosphorescence τPh, and Singlet Oxygen Sensitization Fluorescence ϕΔ) and Phosphorescence Lifetimes (τPh) Obtained in MeCN at 293 K and in 2-MeTHF at Low Temperature (77 K) for 1.1, 1.2, 1.3, and 1
 77 K  
 ϕFϕPhϕF + ϕPhτPh (s)ϕΔ
1a0.6770.1980.8751.06 
1.10.4260.2690.6951.140.021
1.20.4900.1720.6621.170.022
1.30.4660.1930.6591.190.029
a

For 1 in MeCN and 2-MeTHF, the data are from ref (32).

The efficiency of singlet oxygen sensitization was obtained by measurement of the O2 phosphorescence emission (at 1270 nm) in aerated MeCN solutions, resulting in triplet energy transfer from 1.1, 1.2, and 1.3 to molecular singlet oxygen. The obtained values of the singlet oxygen sensitization quantum yields (ϕΔ) were found to vary between 0.021 and 0.029 (Table 2), thus showing no appreciable changes among them. From the data, it can be concluded that the introduction of different phosphanes (DPPM, DPPP, and DPPA) and two gold(I) atoms does not have a significant impact on the singlet oxygen sensitization efficiency. Nevertheless, the presence of gold(I) is relevant for populating T1. Indeed, singlet oxygen generation could not be detected for 1─therefore with nonsignificant population of the triplet state at room temperature─despite the ∼20% yield for phosphorescence (Table 1). Remember that ϕΔ is obtained at 293 K but ϕPh at 77 K. By a comparison of previously investigated alkynylcoumarin gold(I) complexes with PTA and DAPTA phosphane linkers, with the 3-chlorocoumarin ligand derivative, ϕΔ values of 0.12 and 0.18 were obtained, making them good singlet oxygen sensitizers, (32) the herein investigated gold complexes all display much lower values, likely because of the fact that a more efficient radiative deactivation channel is now present (Table 2).
From the overall photophysical data, some relevant aspects should be highlighted at this stage: (i) similar ϕF values (0.010–0.016) were observed in the presence and absence of oxygen; (ii) low quantum singlet oxygen sensitization was observed for 1.1, 1.2, and 1.3, while no singlet oxygen sensitization effect was detected for 1; (iii) the total emission, resulting from the fluorescence and phosphorescence quantum yields ϕF + ϕPh in Table 2 is, at 77 K, high and higher than 66%, thus showing that the radiative processes dominate, at low temperatures, the deactivation of the excited state. Furthermore, at 77 K, the ratio ϕPh/ϕF decreases from 1 (ϕPh/ϕF = 3.4) to 1.1 (ϕPh/ϕF = 1.6) to 1.2 (ϕPh/ϕF = 2.8) to 1.3 (ϕPh/ϕF = 2.4), mirroring the contribution of the heavy atom effect, which favors the intersystem crossing quantum yield (increase of the SOC contribution due to the heavy atom effect promoted by the gold atom) and decreases ϕF in the gold(I) complexes (increase in the population of T1). This effect is particularly notorious with the phosphorescence value of 1.1, which is higher than all of the others, indicating not only a more effective SOC due to the aurophilic effect, as predicted from TDDFT studies, but also a more efficient radiative deactivation of 1.1.

AIE Studies

AIE occurrence in the gold(I) complexes 1.1, 1.2, and 1.3 and model compound 1 was investigated in MeCN/water mixtures (fw is the volume percentage of water in MeCN/water mixtures). Figure 4 (left panel) shows the fluorescence emission spectra of 1.1, 1.2, 1.3, and 1 in MeCN/water mixtures. The absorption spectra in MeCN/water mixtures are represented in Figure S13.

Figure 4

Figure 4. Fluorescence emission spectra (left panel) with pictures obtained under UV irradiation (with λexc = 254 nm) and correlation of the emission area (right panel) with increasing water fractions (fw) in MeCN/water mixtures for the three alkynylcoumarin dinuclear gold(I) complexes 1.1, 1.2, and 1.3 and the ligand 1.

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In MeCN/water mixtures, the fluorescence emission is seen to be clearly enhanced with the mixtures containing a high fraction of water. With an increase of the water percentage in the mixture, there is a continuing increase in the total fluorescence quantum yield up to water fraction values of 50% (1.2 and 1.3) and 60% (1.1). Moreover, in the case of 1.1, a small blue shift is also observed in the emission spectra for the mixtures with a 40–90% water content. Indeed, the gradual addition of water to the MeCN solutions increases the solvent polarity and medium viscosity while decreasing the solvation power of the solution. Consequently, total emission is ruled out by the solvent, with ϕF increasing in MeCN (1.1, 0.010; 1.2, 0.011; 1.3, 0.012) to the 20:80 MeCN/water (% v/v) mixture (1.1, 0.089; 1.2, 0.140; 1.3, 0.119), i.e., an increment of 5–10 times depending on the compound and solvent mixture. With 1, the increase in the fluorescence intensity with the water fraction is different from the pattern found for 1.1, 1.2, and 1.3 and not due to the AIE effect (Figure 4). Indeed, DFT and TDDFT calculations indicate a close proximity between, and mixing of, the two lowest-lying S1 (π,π*) and S2 (with an n,π* contribution) for 1. The increase of the solvent polarity raises the energetic gap relative to the S1 (π,π*) and S2 (n,π*) states, thus decreasing the mixing of these states with an increase of the more polar solvent water in MeCN/water mixtures (with increasing fw), leading to S1 (π,π*) absent of a mixture with S2 of forbidden nature, being responsible for the increase of the resulting fluorescence emission. (48,49)

DLS Experiments in Mixtures of Good/Bad Solvents

DLS experiments, performed in order to evaluate the formation and size of the aggregates in MeCN/water mixtures (Figure 5), corroborate their formation in MeCN/water mixtures and the decrease of the average size for fw > 75%, in agreement with the observed decrease of the emission intensity (Figure 4). With 1, no aggregates could be found.

Figure 5

Figure 5. DLS particle size distribution curves obtained in MeCN/water mixtures (>75–95% H2O, v/v) for the gold(I) complexes 1.1, 1.2, and 1.3. From top to bottom, fw increases.

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Dependence with fw of the Time-Resolved Fluorescence Data

The time-resolved fluorescence emission in MeCN/water mixtures (Figures S14–S19) is again shown, as in organic solvents, to be fitted to single-exponential (for 1) and double-exponential (for 1.1, 1.2, and 1.3) decay laws, with the decay time values increasing with fw (Table S2 and Figures S14–S19). It is very interesting to see that, with 1.1, 1.2, and 1.3, the increase of fw leads to a decrease of the preexponential factor associated with the shorter decay time (τ1) and a concomitant increase of the preexponential factor associated with the longer component (τ2) (Figures S15, S17, and S19). The increase in the τ2 contribution (as seen by % C2) is also associated with an increase of the fluorescence quantum yield (Figure 4). Moreover, aggregates are already present in the ground state, which is particularly evident with excitation at 268 nm (Table S1). The second decay component is consequently assigned to the emissive aggregates and, thus, the shortest (τ1) decay time to the emission of monomeric (isolated) species. The monomer has lifetimes varying from 0.076 to 0.257 ns, whereas the lifetimes of the aggregates vary from 0.204 to 0.792 ns. Moreover, the preexponential (ai2) value, associated with the aggregates, increases concomitantly with fw. This can also be correlated with the DLS experiments, demonstrating the presence of a higher number of fluorescent aggregates at high fw values (Figures 5 and S14–S19). This is further rationalized from TDDFT electronic calculations, namely, on the type of interaction established between the molecules (see the next section).

TDDFT Theoretical Studies

Theoretical DFT studies were performed in order to rationalize and better understand the experimental data, in particular the electronic properties of 1, 1.1, 1.2, and 1.3. The ground-state-optimized geometry structures were calculated together with the relevant highest occupied and lowest unoccupied molecular orbital energy levels and the electronic transitions (obtained by TDDFT) using the same level of theory, DFT//LC-BPBE(ω=0.2)/SBKJC (Stevens–Bash–Krauss–Jasien–Cundari). These results were compared to the experimental data. Frequency analyses for each compound were also computed and no imaginary frequencies were observed, which indicates that the structure of each one of the molecules corresponds, at least, to a local minimum on the potential energy surface (PES).
Model compounds, with phosphane phenyl rings replaced by hydrogen atoms, were used to probe different conformational structures of the dinuclear gold(I) complexes 1.1, 1.2, and 1.3. For DPPM, the most common structure, reported from different literature studies, involves the syn conformation with the Au–P chromophores in parallel orientation. In contrast, with DPPP and DPPA, it is the anti conformation, with Au–P chromophores in antiparallel positions, which is the most energetically favorable and therefore the most likely to be observed. (19,50,51) From simple structure representations, conformers with anti and syn configurations can be easily drawn and their energy calculated (Figure S20). Among the different investigated structures (many others not depicted in Figure S20 have been considered in the calculations; see Figures S21–S23) and after verification of which structure (and conformation) is more stable for each compound, the different possible molecular geometries were optimized by DFT calculations and the main transitions, predicted for both absorption and emission, were analyzed. Figure 6 shows the most energetically stable structural conformer for 1.1, 1.2, and 1.3.

Figure 6

Figure 6. Energetically more favorable molecular structures, obtained from TDDFT calculations, for 1.1 (syn), 1.2 (anti), and 1.3 (anti).

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From all of the above and considering the spectral and structural characteristics of these conformers, the following aspects should be highlighted: (i) In DPPM, the syn conformation is found to be the most stable configuration, whereas for DPPP and DPPA, it is the anti conformation, with the Au–P chromophores in antiparallel positions to each other (Figures S21–S23). (ii) Structurally, compound 1.1 is expected to exhibit, in all solvents, aurophilic interactions. Indeed, from the data in Table S4, it is possible to observe that the bonding distances between the two gold atoms in compound 1.1, considering different solvation environments, are on the order of 2.991–3.016 Å. These values suggest the formation of aurophilic interactions in all solvents. Furthermore, the results obtained for the binding distance AuI···AuI are in good agreement with literature values. (24,25,51) (iii) Two pairs of nearly degenerate absorption bands (located in each of the two chromophores) are predicted: an intense band, in the range 310–314 nm, and a much less intense band, in the range 278–288 nm (depending on the ligand and solvent; see Table S3 for further details). With all compounds, the more intense (strong) band is essentially considered to be a π → π* transition located in the coumarin core, whereas the less intense (weak) band depicts significant charge-transfer character from the gold ethylene to the coumarin chromophore (MLCT). Considering the experimental data and TDDFT calculations that predict this transition with low f values (f < 0.05; Table S3; the contribution of this MLCT band is almost negligible, with the exception of 1.1, which is likely to be associated with the aurophilic effect involving the proximity of the gold atoms). (32,52) (iv) Calculations predict an emission band at 360 nm slightly blue-shifted (∼16 nm) compared to the experimental values of 373–376 nm (in MeCN; Table S5). From the representative orbital contours for each of these two transitions/bands (Figures S24–S26) for 1.1, 1.2, and 1.3, in vacuum, the nature of the MLCT and aurophilic interactions can be further visualized. Additionally, triplet states are predicted to emit in the ∼460 nm range, with a 30 nm difference relative to the experimental value (490 nm in 2-MeTHF; Table S5).

AIE Effect Probed by TDDFT: Rationalizing the Double-Exponential Decay in MeCN/Water Mixtures

Although there is almost total qualitative equivalence between the experimental data and computed values for the absorption and emission spectra, an explanation for the observed time-resolved fluorescence studies (single exponential for 1 and double exponential for the gold(I) complexes, in particular in MeCN/water mixtures) is still missing. As a result of the high energy difference between the different possible conformers, only a single conformer could be found at room temperature (Figure 6), therefore failing to rationalize the biexponential nature of the fluorescence decays as being the result of the presence of two stable conformers. The nature of the double-exponential decays will therefore be rationalized in the following paragraphs and essentially involve the formation of an emissive aggregate coexisting with a monomer.
As shown above, model compounds with phosphane phenyl rings were replaced by hydrogen atoms, and their geometry was optimized; the computed absorption and emission maxima showed no substantial deviations (less than 2 nm) from the gold(I) complexes (Figures S24–S26). These simpler models were used to probe the different dimer/aggregate conformational structures of the complexes (Figure 7). The analysis was followed by the use of the most stable conformer to promote aggregate, in this case the simpler dimer, formation. Two dimers, of 1.1, 1.2, and 1.3, with distinct orientations were explored: one of the dimers is oriented by the {P–Au–C≡C} fragments in parallel (“Dimer A”), whereas the other structure is oriented with parallel coumarin ring moieties (“Dimer B”) (Figure 7). DFT electronic calculations on the nature of the excited states of these two dimers allow us to conclude that “Dimer B” should be considered as more suitable because there is a lowering of its energy in comparison with the monomeric species (isolated molecule; Figure 7).

Figure 7

Figure 7. TDDFT absorption spectra of two dimers of 1.1, 1.2, and 1.3, respectively, with different orientations and of the monomer and both dimers. Color legend: black, monomer; orange, “Dimer A”; blue, “Dimer B”.

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This additional dimer (or aggregate species)─in addition to the monomer─now accounts for the observed biexponential decays. TDDFT-generated absorption spectra of the aggregate (in the present cases well accounted as a dimer, “Dimer B”; Figure 7) show that a new absorption band, ca. 5 nm (1.1), 10 nm (1.2), and 5 nm (1.3) red-shifted relative to the monomer band, is observed. This “Dimer B” band involves the contribution of the molecular orbitals located in the two stacked coumarins (resulting from π–π stacking involving two coumarin rings but from different monomer units; Figures S27–S29). Experimentally (Figure 1), this new band is observed as a shoulder of the main transition (π → π*), with molecular orbitals located in the terminal coumarin cores.

Conclusions

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Three propargyloxycoumarin diphosphane gold(I) complexes (1.1, 1.2, and 1.3), investigated in MeCN/water mixtures and in the solid state (thin film), have shown the AIE effect to be absent in the organic precursor, the propynyloxycoumarin ligand (1), by the absence of aggregates (from DLS) and by a single-exponential fluorescence decay, in contrast with the double-exponential decay found for 1.1, 1.2, and 1.3. The overall behavior is rationalized with TDDFT calculations, leading to different favorable syn (1.1) and anti (1.2 and 1.3) conformers and the formation of an emissive aggregate “dimer” with an antiparallel orientation of the coumarin rings (chromophoric unit). This is further cosubstantiated from DLS measurements, showing an increase of the molecular volume resulting from π–π stacking between the two coumarin rings and from time-resolved fluorescence data, where aggregates coexist with monomer species with different decay times. The presence of the two gold atoms, together with the change in size and flexibility of the different phosphanes, does not determine the dominant interaction responsible for the aggregate emission. Larger aggregates can be built from the dimer structure of the different gold(I) complexes. However, the chromophoric unit, responsible for the absorption and emission properties, should be considered to be that of the dimer, thus showing that larger aggregates essentially behave as if they are this species.

Experimental Section

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General Procedures

For the synthetic procedures, all operations were performed under prepurified dinitrogen using standard Schlenk techniques. Solvents were distilled from the appropriate drying agents. The commercial reagents bis(diphenylphospino)methane (DPPM), 1,3-bis(diphenylphospino)propane (DPPP), and bis(diphenylphospino)acetylene (DPPA) were used as received from Sigma-Aldrich. Literature methods were used to prepare the synthesis of 4-methyl-7-(prop-2-in-1-yloxy)-1-benzopyran-2-one. (52)
The solvents were of spectroscopic or equivalent grade and were used as received. MeCN/water solutions were prepared using deionized water (18.2 MΩ·cm at 25 °C; Milli-Q, Millipore). For the photophysical experiments, removal of the oxygen dissolved in the solutions was performed by bubbling the solutions with a stream of argon or nitrogen for approximately 20–30 min in a home-built quartz cuvette described elsewhere. (53) All measured solutions were freshly prepared (within 1 day).

Physical Measurements

IR spectra were recorded with a Nicolet FT-IR 520 spectrophotometer. 1H NMR [δ(TMS) = 0.0 ppm; TMS = tetramethylsilane] and 31P NMR [δ(85% H3PO4) = 0.0 ppm] spectra were obtained on Varian Mercury 400 and Bruker 400 (Universitat de Barcelona) spectrometers. Positive-ion-mode electrospray ionization mass spectrometry [ESI-MS(+)] spectra were recorded on a Fisons VG Quatro spectrometer. Chemical shifts are given in δ (ppm) relative to TMS (1H) or CDCl3 (31P), and coupling constants J are given in hertz. The multiplicity is expressed as s (singlet), d (doublet), and m (multiplet). Numbering schemes for the compounds characterized are displayed in Scheme 1. Absorption spectra were obtained in a 5 or 10 mm quartz cuvette in MeCN on a Shimadzu UV-2600 spectrophotometer. Fluorescence emission spectra were obtained with a fluorescence quartz cuvette of 5 or 10 mm path length using a Horiba-Jobin-Vonn Fluorolog 3.22 or a Fluoromax spectrometer. Phosphorescence spectra and decays were obtained with the D1934 unit of a Horiba-Jobin-Vonn Fluorolog 3.22 spectrometer using a pulsed xenon lamp. Fluorescence and phosphorescence spectra were corrected for the wavelength response of the system.

Determination of the Emission Quantum Yields

The fluorescence quantum yields for the solid and solution samples were obtained by an absolute method using a Hamamatsu Quantaurus QY model C11437 absolute photoluminescence quantum yield spectrometer (integration sphere). The absorption of the solutions was kept under 0.1 at the excitation wavelength to avoid the inner filter effect. (54) For the solid-state samples (thin films), the fluorescence quantum yields were obtained with the same Hamamatsu Quantaurus QY integration sphere.

Determination of the Emission Singlet Oxygen Quantum Yields

The phosphorescence of singlet oxygen at room temperature was detected at an emission wavelength of 1270 nm with a Horiba-Jobin-Ivon SPEX Fluorolog 3.22 spectrofluorimeter using a Hamamatsu R5509-42 photomultiplier cooled with liquid nitrogen. A Schott RG1000 filter, to eliminate all of the first-harmonic contributions of the sensitizer emission in the region below 850 m, from the IR signal, was used. The singlet oxygen formation quantum yield was subsequently determined by direct measurement of the phosphorescence signal at 1270 nm, Emission1270 nm (in eq 3), following irradiation of the aerated solution of the samples in MeCN. The standard used was 1H-phenal-1-one in MeCN (ϕΔ= 0.98), (55) and using eq 3, the singlet oxygen formation quantum yield of our compounds was obtained.
(3)
where ϕΔref stands for the singlet oxygen formation quantum yield of the reference compound.

Time-Resolved Fluorescence Measurements

Fluorescence decays were obtained with a home-built picosecond time-correlated single-photon-counting (TCSPC) apparatus, described in detail elsewhere. (56) The equipment can be briefly described as follows: excitation was obtained from a picosecond Spectra Physics mode-lock Tsunami laser (Ti:sapphire) model 3950 (80 MHz repetition rate; tuning range 700–1000 nm), which was pumped by a continuous-wave solid-state Millennia Pro-10s laser (532 nm), and the third harmonic with a wavelength of 275 nm was generated with a Spectra Physics GWU-23PS component. An Oriel Cornerstone 260 monochromator and a Hamamatsu multichannel photomultiplier (R3809U-50) were used for emission wavelength selection and signal detection. The signal acquisition and data processing were performed with a Becker & Hickl SPC-630 TCSPC module. Fluorescence decays and instrumental response functions (IRFs) were collected using 1024 or 4096 channels in time scales varying from 3.26 to 6.4 ps/channel scale, until 5000 counts were reached. The full width at half-maximum (fwhm) of the IRF was 25 ps. Deconvolution of the fluorescence decay curves was performed using the modulating function method in the SAND (57) program by Striker et al., which further allows a value of ca. 10% of the fwhm (∼2 ps) as the time resolution of the equipment with this excitation source.

DLS Measurements

DLS studies were performed using a Zetasizer Nano ZS (Malvem Panalytical). The size distribution of the aggregates was measured in a 10 mm quartz cuvette with a final volume of 1 mL, at 20 °C, in three consecutive runs of the same sample. The refractive index and viscosity of the MeCN/water mixtures were determined in advance at the experiment temperature and seen to be in agreement with those found in the literature for different reported temperatures. (58)

Sample Preparation

A 3 mL stock solution of all compounds in MeCN with an absorption of 0.5–0.6 (at 320 nm) in a 10 mm quartz cuvette was prepared. An aliquot (200 μL) of the stock solution was transferred to a 2 mL volumetric flask. After the appropriate amount of MeCN was added, water was added to furnish mixtures with different water fractions (fw = 0–90% by volume) with the same compound concentrations. The photophysical studies of the resultant mixtures were performed immediately after the sample preparation.
Thin films from the compounds were obtained using a desktop precision spin-coating system, model P6700 series from Speedline Technologies, as described elsewhere. (59) Briefly described, thin films from the samples were obtained by the deposition of ca. 50 μL from a solution of the compounds into a circular sapphire substrate (10 mm diameter), followed by spin coating (2500 rpm) in a nitrogen-saturated atmosphere (2 psi). The solutions for spin coating were prepared by adding 2 mg of the samples to 200 μL of a chloroform solution containing 15 mg of Zeonex. Before the film deposition procedure was performed, the solutions were stirred overnight at room temperature.

TDDFT Calculations

All theoretical calculations were of the DFT type and were carried out using GAMESS-US, version R3. (60) A range-corrected LC-BPBE (ω = 0.20 au–1) functional, as implemented in GAMESS-US, (60) was used in both ground- and excited-state calculations. TDDFT calculations, with similar functionals, were used to probe the excited-state PES. A solvent was included using the polarizable continuum model with the solvation model density to add corrections for cavitation, dispersion, and solvent structure. In TDDFT calculation of the Franck–Condon excitations, the dielectric constant of the solvent was split into a “bulk” component and a fast component, which is essentially the square of the refractive index. Under “adiabatic” conditions, only the static dielectric constant was used. DFT and TDDFT calculations, for location of the critical points, were carried out using SBKJC effective core potentials for nonvalence electrons, with a split-31G for valence electrons. (61−63) The results obtained with the LC-BPBE(20) functional are essentially unscaled raw data from calculations; for the S0 → Sn transitions, a small correction, which results in the subtraction of 0.05 eV to account for the difference between the zero point and the first vibronic level, was considered. TDDFT calculations (using the same functional and basis set as those in the previous calculations) were performed for the resulting optimized geometries to predict the vertical electronic excitation energies. Molecular orbital contours were plotted using the ChemCraft 1.7 program. The frequency analysis for each compound was also computed and did not yield any imaginary frequencies, indicating that the structure of each molecule corresponds to at least a local minimum on the PES.

Synthesis of the Propynyloxycoumarin Ligand (1)

The organic alkynyl ligand was prepared by a method previously reported in the literature. (52)

Synthesis of [Au(C≡C13H9O3)]n (1a)

The organic alkynyl ligand 1 (51 mg, 0.238 mmol) was dissolved in dichloromethane (10 mL) and allowed to stir for 10 min. A sodium acetate base (49 mg, 0.595 mmol), previously dissolved in methanol, was added at the stoichiometry of 1:2.5. The solid AuCl(tht), in a 1:1 stoichiometry (72 mg, 0.225 mmol), was transferred to the reaction mixture which was allowed to stir for approximately 30 min. The product was filtered and dried under vacuum. A white solid was obtained in 80% yield.
IR (KBr, cm–1): 2022 (C≡C), 1716 (C═O).

Synthesis of [Au{4-methyl-7-(prop-2-in-1-yloxy)-1-benzopyran-2-one} (DPPM)]2 (1.1)

Solid DPPM (15 mg, 0.04 mmol) was added to a suspension of 1a (31 mg, 0.15 mmol) in dichloromethane (15 mL). After 60 min of stirring at room temperature, the resulting pale-yellow solution was concentrated (5 mL), and n-hexane (15 mL) was added to precipitate a pale-yellow solid, which was obtained in 56% yield (26 mg).
1H NMR (CDCl3): δ 7.56–7.47 (m, 8H, HorthoPh), 7.43–7.30 (m, 14H, Hmeta,paraPh + 2O–C–CH–CH), 7.01–6.95 (m, 4H, 2O–C–CH–CH + O–C–CH–C), 6.06 (q, 2H, J = 21.0 Hz, CO–CH–C), 4.91 (s, 4H, 2CH2), 3.54 (t, J = 10.8 Hz, 2H), 2.34 (s, 6H, 2CH3). 31P{1H} NMR (CDCl3): δ 31.0. IR (KBr, cm–1): 2131 (C≡C), 1709 (C═O). HRESI-MS(+): m/z 1227.1474 ([M + Na]+, calcd m/z 1227.1523), 1243.1244 ([M + K]+, calcd m/z 1243.1263).

Synthesis of [Au{4-methyl-7-(prop-2-in-1-yloxy)-1-benzopyran-2-one} (DPPP)]2 (1.2)

The same synthesis as that of 1.1 was used in the preparation of this compound, but DPPP (15 mg, 0.04 mmol) was used instead of DPPM. A pale-yellow solid was obtained in 66% yield (30 mg).
1H NMR (CDCl3): δ 7.65–7.62 (m, 8H, HorthoPh), 7.60–7.39 (m, 14H, Hmeta,paraPh + 2O–C–CH–CH), 7.05–6.96 (m, 4H, 2O–C–CH–CH + O–C–CH–C), 6.11 (q, 2H, J = 21.5 Hz, CO–CH–C), 4.90 (s, 4H, 2CH2), 2.73 (m, 4H), 2.36 (s, 6H, 2CH3), 1.87 (m, 2H). 31P{1H NMR (CDCl3): δ 34.3. IR (KBr, cm–1): 2135 (C≡C), 1704 (C═O). HRESI-MS(+): m/z 1233.1971 ([M + H]+, calcd m/z 1233.2017), 1255.1862 ([M + Na]+, calcd m/z 1255.1836), 1271.1528 ([M + K]+, calcd m/z 1271.1576), 2482.4192 ([2M + NH4]+, calcd m/z 2482.4227), 2487.3756 ([2M + Na]+, calcd m/z 2487.378).

Synthesis of [Au{4-methyl-7-(prop-2-in-1-yloxy)-1-benzopyran-2-one} (DPPA)]2 (1.3)

The same synthesis as that of 1.1 was used in the preparation of this compound, but DPPA (15 mg, 0.04 mmol) was used instead of DPPM. A pale-yellow solid was obtained in 48% yield (23 mg).
1H NMR (CDCl3): δ 7.74–7.69 (m, 8H, HorthoPh), 7.55–7.48 (m, 14H, Hmeta,paraPh + 2O–C–CH–CH), 7.06–6.96 (m, 4H, 2O–C–CH–CH + O–C–CH–C), 6.13 (q, 2H, J = 21.7 Hz, CO–CH–C), 4.91 (s, 4H, 2CH2), 2.39 (s, 6H, 2CH3). 31P{1H} NMR (CDCl3): 17.0. IR (KBr, cm–1): 2137 (C≡C), 1710 (C═O). HRESI-MS(+): m/z 1237.1323 ([M + Na]+, calcd m/z 1237.1367), 1253.1056 ([M + K]+, calcd m/z 1253.1106), 2446.326 ([2M + NH4]+, calcd m/z 2446.3288), 2451.281 ([2M + Na]+, calcd m/z 2451.2841).

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c00366.

  • Photoluminescence spectra of gold(I) complexes in MeCN/water mixtures, particle size distribution studies of gold(I) complexes in MeCN/water mixtures, 1H and 31P NMR and ESI-MS(+) spectra, and DFT/LC-BPBE(ω=0.2)/SBKJC-optimized ground-state geometries of the coumarin and dinuclear gold(I) complexes (PDF)

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Author Information

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  • Corresponding Authors
  • Authors
    • Carla Cunha - CQC-IMS, Department of Chemistry, University of Coimbra, Rua Larga, Coimbra 3004-535, Portugal
    • Andrea Pinto - Departament de Química Inorgànica i Orgànica, Secció de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1−11, Barcelona E-08028, Spain
    • Adelino Galvão - Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049 001 Lisboa, Portugal
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Financial support from the FCT (Portuguese Science Foundation) and Compete Centro 2020 (Project “Hylight”, PTDC/QUI-QFI/31625/2017) and Centro de Química de Coimbra (through FCT Projects UIDB/00313/2020 and UIDP/00313/2020) is acknowledged. We also acknowledge funding by Fundo Europeu de Desenvolvimento Regional (FEDER) through Programa Operacional Factores de Competitividade (COMPETE) and Project ROTEIRO/0152/2013. The authors are grateful for Project PID2019-104121GB-I00, funded by Ministerio de Ciencia e Innovación of Spain (MCIN/AEI/10.13039/501100011033). The research leading to these results received funding from Laserlab-Europe (Grant Agreement 284464, EC’s Seventh Framework Programme). C.C. thanks the FCT for a Ph.D. Grant, with ref. 2020.09661.BD.

References

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This article references 63 other publications.

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    A review. Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this crit. review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure-property relationships are derived. Through mechanistic decipherment of the photophys. processes, structural design strategies for generating new AIE luminogens are developed. Technol., esp. optoelectronic and biol., applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 refs.).
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  7. 7
    Rodrigues, A. C. B.; Seixas de Melo, J. S. In Aggregation-Induced Emission; Tang, Y., Tang, B. Z., Ed.; Springer International Publishing, 2022; pp 209− 246.
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  8. 8
    Aguiló, E.; Moro, A. J.; Gavara, R.; Alfonso, I.; Pérez, Y.; Zaccaria, F.; Guerra, C. l. F.; Malfois, M.; Baucells, C.; Ferrer, M.; Lima, J. C.; Rodríguez, L. Reversible self-assembly of water-soluble Gold (I) complexes. Inorg. Chem. 2018, 57 (3), 1017– 1028,  DOI: 10.1021/acs.inorgchem.7b02343
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    Reversible self-assembly of water-soluble gold(I) complexes
    Aguilo, Elisabet; Moro, Artur J.; Gavara, Raquel; Alfonso, Ignacio; Perez, Yolanda; Zaccaria, Francesco; Guerra, Celia Fonseca; Malfois, Marc; Baucells, Clara; Ferrer, Montserrat; Lima, Joao Carlos; Rodriguez, Laura
    Inorganic Chemistry (2018), 57 (3), 1017-1028CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The reaction of the gold polymers contg. bipyridyl and terpyridyl units, [Au(C≡CC15H10N3)]n and [Au(C≡CC10H7N2)]n, with the water-sol. phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H2O) and DMSO (DMSO), through different intermol. interactions, with an impact on the obsd. luminescence displayed by the supramol. assemblies. A detailed anal. carried out by NMR studies performed in different DMSO/deuterated H2O mixts. indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramol. environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from d. functional theory calcns. carried out in DMSO and H2O. Small-angle X-ray scattering (SAXS) expts. performed in the same mixt. of solvents are in agreement with the formation of aggregates in all cases. The arom. units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramol. assemblies. Interaction with the Zn2+ cation is obsd. to disassemble the aggregates, while encapsulating agents competing for Zn2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramol. assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn2+.
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  9. 9
    Lázaro, A.; Cunha, C.; Bosque, R.; Pina, J.; Ward, J. S.; Truong, K.-N.; Rissanen, K.; Lima, J. C.; Crespo, M.; Seixas de Melo, J. S.; Rodríguez, L. Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt (II) Complexes with Aromatic Alkynyl Ligands. Inorg. Chem. 2020, 59 (12), 8220– 8230,  DOI: 10.1021/acs.inorgchem.0c00577
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    9
    Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt(II) Complexes with Aromatic Alkynyl Ligands
    Lazaro, Ariadna; Cunha, Carla; Bosque, Ramon; Pina, Joao; Ward, Jas S.; Truong, Khai-Nghi; Rissanen, Kari; Lima, Joao Carlos; Crespo, Margarita; Seixas de Melo, J. Sergio; Rodriguez, Laura
    Inorganic Chemistry (2020), 59 (12), 8220-8230CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Platinum acetylide imine-amine complexes I (Ar = Ph, 4-FC6H4, 3-thienyl, 2-naphthyl, 9-phenanthryl) were prepd. and examd. for their photoluminescence, photophys. properties and catalysis of photochem. singlet oxygen prodn. The synthesis of five novel cyclometalated platinum(II) compds. contg. five different alkynyl-chromophores was achieved by the reaction of the previously synthesized Pt-Cl cyclometalated compd. (1) with the corresponding RC≡CH by a Sonogashira reaction. It was obsd. that the spectral and photophys. characteristics of the cyclometalated platinum(II) complexes (Pt-Ar) are essentially assocd. with the platinum-cyclometalated unit. Room-temp. emission of the Pt-Ar complexes was attributed to phosphorescence in agreement with DFT calcns. Broad nanosecond (ns)-transient absorption spectra were obsd. with decays approx. identical to those obtained from the emission of the triplet state. From the femtosecond-transient absorption (fs-TA) data, two main excited-state decay components were identified: one in the order of a few picoseconds was assigned to fast intersystem crossing to populate the triplet excited-state and the second (hundreds of ns) was assocd. with the decay of the transient triplet state. In general, efficient singlet oxygen photosensitization quantum yields were obsd. from the triplet state of these complexes. Platinum cyclometalated compds. contg. alkynyl chromophores have been synthesized and fully characterized. The X-ray crystal structures of three of the complexes do not show Pt···Pt contacts. Their photophys. properties have been studied in detail, showing room-temp. phosphorescence (RTP) and efficient 1O2 prodn.
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  10. 10
    Arsenault, N. E.; Xu, Z.; Wolf, M. O. Lewis Pair-Functionalized Pt (II) Complexes with Tunable Emission Color and Triplet-State Properties. Inorg. Chem. 2022, 61, 2804,  DOI: 10.1021/acs.inorgchem.1c03174
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    10
    Lewis Pair-Functionalized Pt(II) Complexes with Tunable Emission Color and Triplet-State Properties
    Arsenault, Nicole E.; Xu, Zhen; Wolf, Michael O.
    Inorganic Chemistry (2022), 61 (6), 2804-2812CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Two emissive Pt(II) complexes contg. dynamic "flexible" Lewis pair (FlexLP) ligands are reported. The FlexLP ligand encompasses a diphenylphosphine oxide Lewis base and a dimesitylborane Lewis acid attached to a bithiophene scaffold, which can switch between an open unbound Lewis pair and a bound P-O-B Lewis adduct depending on the hydrogen bond-donating (HBD) strength of the solvent. [Pt(FlexLP)2] contains two FlexLP ligands, and [Pt(FlexLP)(Py)] contains one FlexLP ligand and one pyrene ligand. UV-vis absorption and fluorescence studies demonstrate that the FlexLP ligands switch between the open Lewis pair and the closed Lewis adduct in MeOH, a strong HBD solvent, and acetone, a weak HBD solvent, resp., and exhibit tunable emission color depending on the acetone/MeOH solvent ratio. Transient absorption spectroscopy reveals a large difference in the triplet-state lifetime depending on the conformation of the FlexLP ligands for both complexes. In the closed form, the triplet-state lifetimes of the two complexes are over an order of magnitude longer compared to that of the complexes in the open conformation. Calcns. of optimized geometries suggest that this difference in triplet-state lifetime is due to a difference in the thiophene-thiophene torsion angle between the two conformations.
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  11. 11
    Pina, J.; Rodrigues, A. C. B.; Alnady, M.; Dong, W.; Scherf, U.; Seixas de Melo, J. S. Restricted Aggregate Formation on Tetraphenylethene-Substituted Polythiophenes. J. Phys. Chem. C 2020, 124 (25), 13956– 13965,  DOI: 10.1021/acs.jpcc.9b10908
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    11
    Restricted Aggregate Formation on Tetraphenylethene-Substituted Polythiophenes
    Pina, Joao; Rodrigues, Ana Clara B.; Alnady, Mohamed; Dong, Wenyue; Scherf, Ullrich; Seixas de Melo, J. Sergio
    Journal of Physical Chemistry C (2020), 124 (25), 13956-13965CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Two new polythiophenes functionalized with different degrees of tetraphenylethene, TPE, side groups (with TPE moieties at each thiophene unit, homoPT, and one in which only each second thiophene unit carries a TPE side chain, coPT) were successfully synthesized and characterized together with a poly(3-hexylthiophene) with similar av. mol. wt. and a tetraphenylethene-thiophene model compd. The study aimed to understand the role of the sterically bulky TPE pendant groups on the inhibition of intra- and/or interchain packing (aggregation) of these conjugated polymers. For the tetraphenylethene-thiophene model, compd. aggregation induced emission (AIE) is active for water fractions ≥ 90%. An opposite behavior is found for the polythiophenes (homoPT and coPT) where aggregation caused quenching (ACQ) was found to occur both in soln. and in the solid state. For the polythiophene with the higher degree of TPE labeling, homoPT, the amt. of ACQ is significantly decreased. This is attributed to the high TPE substitution d. in the polymer which promotes a more twisted conformation of the polymer backbone as the emissive chromophore. For the TPE-polythiophenes, only the energy migration mechanism was found to be active since the bulky TPE substituents restrict the polymer's intramol. motions. The exptl. observations of a small shift in the emission spectra of homoPT and significant hindering of ACQ on going from soln. to the solid state explain the absence of intermol. interactions together with the restriction of intramol. rotations.
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    Yam, V. W.-W.; Cheng, E. C.-C. Highlights on the recent advances in gold chemistry─a photophysical perspective. Chem. Soc. Rev. 2008, 37 (9), 1806– 1813,  DOI: 10.1039/b708615f
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    Highlights on the recent advances in gold chemistry-a photophysical perspective
    Yam, Vivian Wing-Wah; Cheng, Eddie Chung-Chin
    Chemical Society Reviews (2008), 37 (9), 1806-1813CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review; the presence of inter- and/or intra-mol. aurophilic interactions among the closed-shell gold(I) centers in various systems has been studied from various aspects, including synthetic, spectroscopic and theor. approaches. The employment of different ligands can impose a significant influence on these factors and give rise to new complexes with interesting structural and photophys. properties. In this tutorial review, a no. of recent examples are selected to illustrate the fascinating properties and chem., as well as versatility of gold(I) in these aspects and their potential applications to newcomers in this field. An emerging class of luminescent gold(III) complexes is also described.
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    Rodríguez, L.; Ferrer, M.; Crehuet, R.; Anglada, J.; Lima, J. C. Correlation between photophysical parameters and gold–gold distances in gold (I)(4-Pyridyl) ethynyl complexes. Inorg. Chem. 2012, 51 (14), 7636– 7641,  DOI: 10.1021/ic300609f
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    Correlation between Photophysical Parameters and Gold-Gold Distances in Gold(I) (4-Pyridyl)ethynyl Complexes
    Rodriguez, Laura; Ferrer, Montserrat; Crehuet, Ramon; Anglada, Josep; Lima, Joao Carlos
    Inorganic Chemistry (2012), 51 (14), 7636-7641CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The systematic anal. of the luminescence of a series of alkynyl gold derivs. with general formulas [(diphos)(AuC≡Cpy)2] (diphosphane =2,2'-bis(diphenylphosphanyl)propane or dppip (1), bis(diphenylphosphanyl)acetylene or dppa (2), 1,2-bis(diphenylphosphanyl)ethane or dppe (3) and 1,4-bis(diphenylphosphanyl)butane or dppb, (4), has shown a straightforward correlation between the Au(I)···Au(I) distance and the emission quantum yields and decaytimes. The anal. of the decaytimes, quantum yields and thus, the corresponding calcd. rate consts. demonstrated the existence of a correlation between Au(I)···Au(I) distance and the radiative rate const. for the deactivation of the emissive triplet states. It was concluded that the increased emission of these compds. results from the increase in spin-orbit coupling that favors the spin forbidden transition to the singlet ground state.
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    Blanco, M. C.; Camara, J.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Lopez-de-Luzuriaga, J. M.; Olmos, M. E.; Villacampa, M. D. Luminescent homo-and heteropolynuclear gold complexes stabilized by a unique acetylide fragment. Organometallics 2012, 31 (7), 2597– 2605,  DOI: 10.1021/om200397t
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    Luminescent Homo- and Heteropolynuclear Gold Complexes Stabilized by a Unique Acetylide Fragment
    Blanco, M. Carmen; Camara, Jessica; Gimeno, M. Concepcion; Jones, Peter G.; Laguna, Antonio; Lopez-de-Luzuriaga, Jose M.; Olmos, M. Elena; Villacampa, M. Dolores
    Organometallics (2012), 31 (7), 2597-2605CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
    The authors describe the reactivity of the Au acetylide derivs. [Au(C≡CR)(PPh3)] (R = Ph, 2-pyridyl). Reactions of these complexes with fragments [M(PPh3)2]+ (M = Au, Ag, Cu) afford novel discrete mols. stabilized not only by interactions with the triple bond but also by the formation of strong metal-Au interactions. The crystal structures of the Au-Au and Au-Ag species confirm their similar behavior, while x-ray diffraction establishes a different arrangement for the Cu complex with pyridine acetylide as a consequence of the coordination of this metal center to the N atom of pyridine and to the carbons of the alkyne. The luminescent properties of the complexes were studied.
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    Kathewad, N.; Kumar, N.; Dasgupta, R.; Ghosh, M.; Pal, S.; Khan, S. The syntheses and photophysical properties of PNP-based Au (i) complexes with strong intramolecular Au··· Au interactions. Dalton Trans. 2019, 48 (21), 7274– 7280,  DOI: 10.1039/C8DT04471F
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    The syntheses and photophysical properties of PNP-based Au(I) complexes with strong intramolecular Au···Au interactions
    Kathewad, Neha; Kumar, Nandha; Dasgupta, Rajarshi; Ghosh, Moushakhi; Pal, Shiv; Khan, Shabana
    Dalton Transactions (2019), 48 (21), 7274-7280CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    Herein the authors report the syntheses, x-ray structures and photophys. studies of the dinuclear dimeric gold(I) complexes [ClAu(C6H5N)(PPh2)2]2 (1), [Au(C6H5N)(PPh2)2]2[SbF6]2 (2) and [Au(2,6-Me2C6H3N)(PPh2)2]2[SbF6]2 (4). The authors used ligands with different substituents to see the effect of the substituents on the photophys. properties. All these complexes feature strong intramol. Au···Au interactions (2.7987-3.0056 Å) and exhibit excellent luminescence properties with high quantum yields as well as different colors of emission.
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    Sculfort, S.; Braunstein, P. Intramolecular d10–d10 interactions in heterometallic clusters of the transition metals. Chem. Soc. Rev. 2011, 40 (5), 2741– 2760,  DOI: 10.1039/c0cs00102c
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    Intramolecular d10-d10 interactions in heterometallic clusters of the transition metals
    Sculfort, Sabrina; Braunstein, Pierre
    Chemical Society Reviews (2011), 40 (5), 2741-2760CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Weak attractive interactions between closed shell metal ions have been increasingly studied in the last few years and are generally designated as metallophilic interactions. They are best evidenced in the solid state where structural data obtained by X-ray diffraction provide precise information about the distance between the metals involved. The strength of such metal-metal interactions has been compared to that of hydrogen bonding (ca. 7-11 kcal mol-1) and is clearly sufficient to bring about novel bonding and structural features and confer interesting phys. properties such as luminescence, polychromism, magnetism or one-dimensional elec. cond. The Cu(i)-Cu(i), Ag(i)-Ag(i) and Au(i)-Au(i) interactions have been increasingly obsd. and the latter have certainly been the most studied. Early qual. analyses of the aurophilic attraction focused on Au-Au bonding originating from 6s, 6p and 5d orbital mixing. Numerous theor. studies on metallophilic interactions continue to be carried out at various levels of sophistication which take into account relativistic and correlation effects to describe these van der Waals-type interactions. In this crit. review, we would like to focus on the synthesis and structures of heterometallic clusters of the transition metals in which intra- rather than intermol. d10-d10 interactions are at work, in order to limit the role of packing effects. We wish to provide the reader with a comparative overview of the metal core structures resulting from or favoring metallophilic interactions but do not intend to provide a comprehensive coverage of the literature. We will first examine heterometallic clusters displaying homometallic and then heterometallic d10-d10 interactions. Although the focus of this review is on d10-d10 interactions involving metals from the group 11, we shall also briefly examine for comparison some complexes displaying intramol. d10-d10 interactions involving metals from other groups (188 refs.).
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    Schmidbaur, H.; Schier, A. Aurophilic interactions as a subject of current research: an up-date. Chem. Soc. Rev. 2012, 41 (1), 370– 412,  DOI: 10.1039/C1CS15182G
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    Aurophilic interactions as a subject of current research: an up-date
    Schmidbaur, Hubert; Schier, Annette
    Chemical Society Reviews (2012), 41 (1), 370-412CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Recently accumulated exptl. evidence for aurophilic interactions in and between mol. Au(I) compds. and the results of pertinent theor. calcns. are reviewed for the period from 2007 to mid-2011. The influence of the intra- and intermol. bonding contacts between the closed-shell metal centers, Au-Au, on the mol. and crystal structures, and the consequences of these effects for the chem. and phys. properties of Au compds. are summarized for the various classes of mono- and polynuclear systems. The literature survey builds on the contents of previous reviews and relates new exptl. and theor. findings to earlier observations (353 refs.).
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    Schmidbaur, H.; Schier, A. A briefing on aurophilicity. Chem. Soc. Rev. 2008, 37 (9), 1931– 1951,  DOI: 10.1039/b708845k
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    A briefing on aurophilicity
    Schmidbaur, Hubert; Schier, Annette
    Chemical Society Reviews (2008), 37 (9), 1931-1951CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. There is now compelling exptl. evidence for the existence of specific intra- and intermol. bonding between seemingly closed-shell gold(i) centers (5d10) which manifests itself in all areas of gold chem. This "aurophilic interaction", which had not been predicted by conventional valence theory, was found to be assocd. with binding energies in some cases exceeding even those of strong hydrogen bonds and therefore to be highly significant in co-detg. mol. structure and dynamics. In high-level theor. treatments the attraction is rationalized as a "super van der Waals bonding" based on particularly strong relativistic, dispersion and correlation effects (crit. review, 265 refs.).
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    Lima, J. C.; Rodriguez, L. Applications of gold (I) alkynyl systems: a growing field to explore. Chem. Soc. Rev. 2011, 40 (11), 5442– 5456,  DOI: 10.1039/c1cs15123a
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    Applications of gold(I) alkynyl systems: a growing field to explore
    Lima, Joao Carlos; Rodriguez, Laura
    Chemical Society Reviews (2011), 40 (11), 5442-5456CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Gold(I) alkynyl complexes present a growing research field with respect to their very wide range of applications in different areas such as luminescence, mol. recognition, optical switches, electronics and catalysis. Biol. applications are also being developed in the recent years, where these complexes are used as therapeutic agents against different illnesses such as cancer cells or malaria. Related to luminescence, a general overview of the different states responsible for the obsd. emission is also included in this crit. review. In some cases, the assignment is complicated due to the influence of the gold(I) atom and its capability to form metal···metal interactions (aurophilicity). Although an extensive discussion has been found in the literature related to the luminescent properties of these complexes, to the best of our knowledge there are not reports covering the span of their very interesting applications. The widespread research fields where this kind of complexes could present a key role is presented in this review (119 refs.).
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    Zhao, Q.; Huang, C.; Li, F. Phosphorescent heavy-metal complexes for bioimaging. Chem. Soc. Rev. 2011, 40 (5), 2508– 2524,  DOI: 10.1039/c0cs00114g
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    Phosphorescent heavy-metal complexes for bioimaging
    Zhao, Qiang; Huang, Chunhui; Li, Fuyou
    Chemical Society Reviews (2011), 40 (5), 2508-2524CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. The application of phosphorescent heavy-metal complexes with d6, d8 and d10 electron configurations for bioimaging is a new and promising research field and has been attracting increasing interest. In this crit. review, we systematically evaluate the advantages of phosphorescent heavy-metal complexes as bioimaging probes, including their photophys. properties, cytotoxicity and cellular uptake mechanisms. The progress of research into the use of phosphorescent heavy-metal complexes for staining different compartments of cells, monitoring intracellular functional species, providing targeted bioimaging, two-photon bioimaging, small-animal bioimaging, multimodal bioimaging and time-resolved bioimaging is summarized. In addn., several possible future directions in this field are also discussed (133 refs.).
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    Zhou, G.-J.; Wong, W.-Y. Organometallic acetylides of Pt II, Au I and Hg II as new generation optical power limiting materials. Chem. Soc. Rev. 2011, 40 (5), 2541– 2566,  DOI: 10.1039/c0cs00094a
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    Organometallic acetylides of PtII, AuI and HgII as new generation optical power limiting materials
    Zhou, Gui-Jiang; Wong, Wai-Yeung
    Chemical Society Reviews (2011), 40 (5), 2541-2566CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compds. which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metalated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good soln. processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This crit. review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compds. Strategies including copolymn. with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophys. behavior and improve the resulting OPL responses. Special emphasis is placed on the structure-OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 refs.).
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    Aguiló, E.; Soler, L.; Casanovas, A.; Moro, A. J.; Lima, J. C.; Rodríguez, L.; Llorca, J. Gold (I)-complex–titania hybrid photocatalyst for hydrogen production. ChemCatChem. 2017, 9 (17), 3289– 3292,  DOI: 10.1002/cctc.201700518
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    Gold(I)-Complex-Titania Hybrid Photocatalyst for Hydrogen Production
    Aguilo, Elisabet; Soler, Lluis; Casanovas, Albert; Moro, Artur J.; Lima, Joao Carlos; Rodriguez, Laura; Llorca, Jordi
    ChemCatChem (2017), 9 (17), 3289-3292CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The integration of TiO2 with a AuI complex contg. a thiocoumarin moiety resulted in a very efficient photocatalyst for the generation of H2. The mol. structure of the complex was preserved under the photoreaction owing to the strong AuI-S bond. The AuI complex played a determinant role in the photogeneration of H2 by accepting the photoinduced electrons originated in TiO2 upon light exposure. This is the first example of a AuI complex semiconductor hybrid photocatalyst. The rate of H2 generation under dynamic conditions from water/ethanol is approx. one order of magnitude superior on a metal basis to that obtained over conventional TiO2 decorated with Au metal nanoparticles.
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    Hobbollahi, E.; List, M.; Redhammer, G.; Zabel, M.; Monkowius, U. Structural and photophysical characterization of gold (I) complexes bearing naphthyl chromophores. Inorg. Chem. Commun. 2016, 65, 24– 27,  DOI: 10.1016/j.inoche.2016.01.009
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    Structural and photophysical characterization of gold(I) complexes bearing naphthyl chromophores
    Hobbollahi, Elnaz; List, Manuela; Redhammer, Guenther; Zabel, Manfred; Monkowius, Uwe
    Inorganic Chemistry Communications (2016), 65 (), 24-27CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
    The authors prepd. two chlorido-Au(I) complexes L-Au-Cl bearing a naphthyl moiety. Complex 1 with L = tris(1-naphthyl)phosphine shows std. linear coordination without further aggregation in the solid state. Complex 2 with L = 2-naphthyl isonitrile is engaged in a complex network of aurophilic and π-π interactions. The two complexes show similar luminescence behavior in soln. at room temp. with both intraligand fluorescence and phosphorescence. At 77 K the emission spectra are dominated by intraligand phosphorescence, which is typical of Au complexes with extended π-chromophores.
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    Schmidbaur, H. The aurophilicity phenomenon: a decade of experimental findings, theoretical concepts and emerging applications. Gold Bulletin 2000, 33 (1), 3– 10,  DOI: 10.1007/BF03215477
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    The aurophilicity phenomenon: a decade of experimental findings, theoretical concepts and emerging applications
    Schmidbaur, Hubert
    Gold Bulletin (London) (2000), 33 (1), 3-10CODEN: GOBUFW; ISSN:1027-8591. (World Gold Council)
    A review, with 111 refs., discusses aurophilicity. The term aurophilicity was introduced in 1989 to describe phenomena in the structural chem. of Au which could not be readily rationalized by conventional concepts of chem. bonding. In the following decade the aurophilicity concept was widely applied and supported by the results of many exptl. as well as theor. studies. It will be carried over into the new millennium as a continued incentive for studies that will help in the understanding of the unique properties of Au.
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    Bondi, A. V. van der Waals Volumes and Radii. J. Chem. Phys. 1964, 68 (3), 441– 451,  DOI: 10.1021/j100785a001
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    van der Waals volumes and radii
    Bondi, A.
    Journal of Physical Chemistry (1964), 68 (3), 441-51CODEN: JPCHAX; ISSN:0022-3654.
    Intermol. van der Waals radii of the nonmetallic elements were assembled into a list of recommended values for vol. calcns. These values were arrived at by selecting from the most reliable x-ray diffraction data those which could be reconciled with crystal d. at 0°K. (to give reasonable packing d.), gas kinetic collision cross section, crit. d., and with liquid state properties. A qual. understanding of the nature of van der Waals radii is provided by correlation with the de Broglie wavelength of the outermost valence electron. Tentative values for the van der Waals radii of metallic elements in organometallic compds. are proposed. A list of increments for the vol. of mols. impenetrable to thermal collision, the so-called van der Waals vol., and of the corresponding increments in area per mol. is given.
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    Gavara, R.; Llorca, J.; Lima, J. C.; Rodríguez, L. A luminescent hydrogel based on a new Au (I) complex. Chem. Commun. 2013, 49 (1), 72– 74,  DOI: 10.1039/C2CC37262B
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    A luminescent hydrogel based on a new Au(I) complex
    Gavara, Raquel; Llorca, Jordi; Lima, Joao Carlos; Rodriguez, Laura
    Chemical Communications (Cambridge, United Kingdom) (2013), 49 (1), 72-74CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The reaction of the H2O sol. phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) with [Au(C≡C-C5H4N)]n yields the highly luminescent H2O sol. [(PTA)Au(4-pyridylethynyl)] complex. A detailed anal. of the compd. shows the formation of gel structure giving rise to long fibers, being the 1st example reported with such a simple structure.
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    Moro, A. J.; Avó, J.; Malfois, M.; Zaccaria, F.; Fonseca Guerra, C.; Caparrós, F. J.; Rodríguez, L.; Lima, J. C. Aggregation induced emission of a new naphthyridine-ethynyl–gold (I) complex as a potential tool for sensing guanosine nucleotides in aqueous media. Dalton Trans. 2020, 49 (1), 171– 178,  DOI: 10.1039/C9DT04162A
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    Aggregation induced emission of a new naphthyridine-ethynyl-gold(I) complex as a potential tool for sensing guanosine nucleotides in aqueous media
    Moro, Artur J.; Avo, Joao; Malfois, Marc; Zaccaria, Francesco; Fonseca Guerra, Celia; Caparros, Francisco J.; Rodriguez, Laura; Lima, Joao Carlos
    Dalton Transactions (2020), 49 (1), 171-178CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    A new organometallic alkynyl-gold(I) complex capable of exhibiting aggregation induced emission was designed and synthesized. The linear complex structure possesses a central Au(I) atom, bearing two axial ligands: (1) 1,3,5-triaza-7-phosphaadamantane and (2) 2-acetamido-7-ethynyl-1,8-naphthyridine. While the former accounts for its partial soly. in an aq. environment, the latter acts as a receptor unit for binding guanosine nucleotides and derivs. via multiple hydrogen bonding interactions. At high concns., aggregation of the complex was obsd. by the formation of new absorption (λmax ∼ 400 nm) and emission bands (550-700 nm). Formation of aggregates of ca. 60 nm diam. was confirmed by Small Angle X-ray Scattering (SAXS). Disruption of the aggregates in the presence of guanosine derivs. resulted in a ratiometric signal with apparent assocn. consts. in the order of 105 M-1 and high sensitivity (around 63% signal change) which are, to the best of our knowledge, in line with the highest values recorded for nucleotide sensors based on hydrogen bonding and capable of working in water. Computational studies indicate the presence of addnl. hydrogen bonding interactions that account for the strong binding of the Au(I) complex to phosphorylated guanosine nucleotides.
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    Tubaro, C.; Baron, M.; Costante, M.; Basato, M.; Biffis, A.; Gennaro, A.; Isse, A. A.; Graiff, C.; Accorsi, G. Dinuclear gold (I) complexes with propylene bridged N-heterocyclic dicarbene ligands: Synthesis, structures, and trends in reactivities and properties. Dalton Trans. 2013, 42 (30), 10952– 10963,  DOI: 10.1039/c3dt51260f
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    Dinuclear gold(I) complexes with propylene bridged N-heterocyclic dicarbene ligands: synthesis, structures, and trends in reactivities and properties
    Tubaro, Cristina; Baron, Marco; Costante, Michele; Basato, Marino; Biffis, Andrea; Gennaro, Armando; Isse, Abdirisak Ahmed; Graiff, Claudia; Accorsi, Gianluca
    Dalton Transactions (2013), 42 (30), 10952-10963CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    Four novel dinuclear N-heterocyclic dicarbene Au(I) complexes with a propylene linker between the carbene moieties were synthesized and their luminescence and electrochem. properties, together with their reactivity towards Br oxidative addn., were screened. The mol. structures of two complexes were detd. by x-ray crystallog. All the complexes emit in the solid state in the blue-green spectral range (400-500 nm) with appreciable intensities (Φem up to ≈10%). In cyclic voltammetry, the Au(I)/Au(0) peak splits at low temp. into two sep. peaks relative to the couples Au(I)-Au(I)/Au(i)-Au(0) and Au(I)-Au(0)/Au(0)-Au(0), thus indicating the presence of an Au···Au interaction in the dinuclear complex. Oxidative addn. of Br affords as a major or unique product Au(II)-Au(II) complexes most likely as a consequence of the interaction between the two Au centers favored by the propylene linker.
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    Luo, Z.; Yuan, X.; Yu, Y.; Zhang, Q.; Leong, D. T.; Lee, J. Y.; Xie, J. From aggregation-induced emission of Au (I)–thiolate complexes to ultrabright Au (0)@ Au (I)–thiolate core–shell nanoclusters. J. Am. Chem. Soc. 2012, 134 (40), 16662– 16670,  DOI: 10.1021/ja306199p
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    From Aggregation-Induced Emission of Au(I)-Thiolate Complexes to Ultrabright Au(0)@Au(I)-Thiolate Core-Shell Nanoclusters
    Luo, Zhentao; Yuan, Xun; Yu, Yue; Zhang, Qingbo; Leong, David Tai; Lee, Jim Yang; Xie, Jianping
    Journal of the American Chemical Society (2012), 134 (40), 16662-16670CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    A fundamental understanding of the luminescence of Au-thiolate nanoclusters (NCs), such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I)-thiolate complexes: strong luminescence emission by the mechanism of aggregation-induced emission (AIE). The AIE property of the complexes was then used to develop a simple 1-pot synthesis of highly luminescent Au-thiolate NCs with a quantum yield of ∼15%. Key strategy was to induce the controlled aggregation of Au(I)-thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I)-thiolate core-shell NCs where strong luminescence was generated by the AIE of Au(I)-thiolate complexes on the NC surface. The authors were able to extend the synthetic strategy to other thiolate ligands with added functionalities (as custom-designed peptides). The discovery (e.g., identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.
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  30. 30
    Au, V. K.-M.; Tsang, D. P.-K.; Wong, K. M.-C.; Chan, M.-Y.; Zhu, N.; Yam, V. W.-W. Functionalized bis-cyclometalated alkynylgold (III) complexes: synthesis, characterization, electrochemistry, photophysics, photochemistry, and electroluminescence studies. Inorg. Chem. 2013, 52 (21), 12713– 12725,  DOI: 10.1021/ic4019212
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    Functionalized Bis-Cyclometalated Alkynylgold(III) Complexes: Synthesis, Characterization, Electrochemistry, Photophysics, Photochemistry, and Electroluminescence Studies
    Au, Vonika Ka-Man; Tsang, Daniel Ping-Kuen; Wong, Keith Man-Chung; Chan, Mei-Yee; Zhu, Nianyong; Yam, Vivian Wing-Wah
    Inorganic Chemistry (2013), 52 (21), 12713-12725CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    A series of luminescent alkynylgold(III) complexes contg. various tridentate bis-cyclometalating ligands derived from 2,6-diphenylpyridine (R-C-N-C), [Au(R-C-N-C)(C≡C-C6H4-R')] has been successfully synthesized and characterized. Complexes 1 and 6 have been detd. by x-ray crystallog. Electrochem. studies show a ligand-centered redn. that originated from the tridentate R-C-N-C pincer ligands and an alkynyl-centered oxidn. The photophys. properties of the complexes have been studied in detail by electronic absorption and emission studies. Tunable photoluminescence behaviors have been obsd., with the emission maxima spanning through the visible region from 476 to 669 nm in dichloromethane at room temp., and the complexes were also emissive in various media at both room and low temps. Transient absorption studies have been conducted to investigate the excited state properties of the complexes. Furthermore, selected complexes have been incorporated into the emissive layer (EML) of org. light-emitting devices (OLEDs) and have demonstrated interesting electroluminescence.
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    Pinto, A.; Svahn, N.; Lima, J. C.; Rodríguez, L. Aggregation induced emission of gold (I) complexes in water or water mixtures. Dalton Trans. 2017, 46 (34), 11125– 11139,  DOI: 10.1039/C7DT02349A
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    Aggregation induced emission of gold(I) complexes in water or water mixtures
    Pinto, Andrea; Svahn, Noora; Lima, Joao Carlos; Rodriguez, Laura
    Dalton Transactions (2017), 46 (34), 11125-11139CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    A review. Gold(I) complexes are an expanding area of study due to the possibility of giving rise to supramol. aggregates with particular morphologies that can be modulated together with their luminescent properties. A detailed study was carried out for gold(I) complexes that self-assemble in aq. media (in pure water or in mixts. of water and org. solvents in different proportions). The majority of the examples reported until now were found in mixts. of water and DMSO, acetone, DMF or acetonitrile. The addn. of cations to a soln. of gold(I) complexes was obsd. to show a direct impact on the resulting process of aggregation. The use of perhalogenated ligands together with isocyanide moieties should be highlighted to promote the resulting self-organization. Nevertheless, other ligands like alkynyls or carbenes also promote self-assembly. A careful anal. of the data shows that aurophilic interactions have a key role in the formation of the resulting aggregates and in the enhancement of luminescence (aggregation induced emission, AIE).
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  32. 32
    Pinto, A.; Cunha, C.; Aullón, G.; Lima, J. C.; Rodríguez, L.; Seixas de Melo, J. S. Comprehensive Investigation of the Photophysical Properties of Alkynylcoumarin Gold(I) Complexes. J. Chem. Phys. B 2021, 125 (42), 11751– 11760,  DOI: 10.1021/acs.jpcb.1c07985
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    Comprehensive investigation of the photophysical properties of alkynylcoumarin gold(I) complexes
    Pinto, Andrea; Cunha, Carla; Aullon, Gabriel; Lima, Joao Carlos; Rodriguez, Laura; Seixas de Melo, J. Sergio
    Journal of Physical Chemistry B (2021), 125 (42), 11751-11760CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    Six gold(I) complexes (R3P-Au-Coum) contg. three different alkynylcoumarin chromophores (Coum) with different electron-donating and electron-withdrawing characteristics and two different water-sol. phosphanes (PR3 = PTA (a) and DAPTA (b)) have been synthesized (1a,b, unsubstituted coumarin; 2a,b, 4-Me substituted coumarin; 3a,b, 3-chloro and 4-Me substituted coumarin). A comprehensive study of the photophys. properties of the R3P-Au-Coum, together with their propynyloxycoumarin precursors 1-3, was performed in soln. at room and low temps. Spectral and photophys. characteristics of the R3P-Au-Coum essentially depend on the electronic characteristics of the propynyloxycoumarin ligand. The presence of the Au(I) atom was found to be responsible for an increase of the intersystem crossing, with triplet state quantum yield values, .vphi.T, ranging from ~ 0.05 to 0.35 and high coumarin phosphorescence quantum yield values for derivs. 1 and 2; fluorescence dominates the deactivation in derivs. 3. Efficient singlet oxygen photosensitization was obsd. for the new compds. 3a,b. From TDDFT calcns., the relevant HOMO and LUMO of the compds., i.e., those involved in the transitions, are dominated by the frontier orbitals assocd. with the coumarin core. The Au(I)-phosphane structure introduces a new transition assigned to an intraligand transition involving the phosphane ligand, and π(C≡C) system, to the p orbitals of phosphorus and gold atoms.
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    Pandey, M. K.; Kunchur, H. S.; Mondal, D.; Radhakrishna, L.; Kote, B. S.; Balakrishna, M. S. Rare Au··· H Interactions in Gold (I) Complexes of Bulky Phosphines Derived from 2, 6-Dibenzhydryl-4-methylphenyl Core. Inorg. Chem. 2020, 59 (6), 3642– 3658,  DOI: 10.1021/acs.inorgchem.9b03207
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    Rare Au···H Interactions in Gold(I) Complexes of Bulky Phosphines Derived from 2,6-Dibenzhydryl-4-methylphenyl Core
    Pandey, Madhusudan K.; Kunchur, Harish S.; Mondal, Dipanjan; Radhakrishna, Latchupatula; Kote, Basvaraj S.; Balakrishna, Maravanji S.
    Inorganic Chemistry (2020), 59 (6), 3642-3658CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Gold(I) complexes of sterically demanding phosphines derived from 2,6-dibenzhydryl-4-methylphenyl core viz: 2,6-dibenzhydryl-N,N-bis((diphenylphosphane)-methyl)-4-methylaniline (1), (2,6-dibenzhydryl-4-methylphenyl)-diphenylphosphane (2), N-(2,6-dibenzhydryl-4-methylphenyl)-1,1-diphenylphosphanamine (3), and (2,6-dibenzhydryl-4-methylphenoxy)-diphenylphosphane (4) are described. The reaction of 1 with 2 equiv of [AuCl(SMe2)] in dichloromethane yielded [{AuCl}2{Ar*N(CH2PPh2)2}] (5), which on further treatment with 2 equiv of AgSbF6 and 1 equiv of 1 produced 12-membered dimeric complex [Au2{μ-(Ar*N(CH2PPh2)2)2}][(SbF6)2] (6). A similar reaction of 5 with AgSbF6 in CH3CN afforded [{Au(NCCH3)}2{Ar*N(CH2PPh2)2}][(SbF6)2] (7). Equimolar reactions of bulky phosphines 2, 3, and 4 with [AuCl(SMe2)] resulted in [AuCl(PPh2Ar*)] (8), [AuCl(PPh2NHAr*)] (9), and [AuCl(PPh2OAr*)] (10). Complexes 9 and 10 on treatment with AgSbF6 in CH3CN produced the cationic complexes [Au(NCCH3)(PPh2NHAr*)][(SbF6)] (11) and [Au(NCCH3)(PPh2OAr*)][(SbF6)] (12), resp. The mol. structure of complex 6 revealed the presence of a strong intramol. aurophilic interaction with a Au···Au distance of 2.9720(4) Å. Careful anal. of mol. structure of 5 revealed the presence of rare Au···H-C (sp3) interactions between the gold(I) atom and one of the methylene protons of -NCH2PPh2 groups. The soln. 1H NMR signals of the methylene protons of 5 showed a considerable downfield shift (∼1 ppm) compared to that of the free ligand indicating their interactions (Au···H) with the Au atom. Complexes 8 and 10 also showed Au···H interactions in their mol. structures. The existence of the Au···H interaction was studied by variable temp. 1H NMR data in the case of complex 5 and further evinced by the QTAIM anal. in complexes 5, 8, and 10. This paper describes the synthesis of sterically demanding phosphines derived from the 2,6-dibenzhydryl-4-methylphenyl core and their AuI complexes. The AuI complexes show Au···H interactions in their mol. structures which were also supported by 1H NMR studies in the soln. state.
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    Pujadas, M.; Rodríguez, L. Luminescent phosphine gold (I) alkynyl complexes. Highlights from 2010 to 2018. Coord. Chem. Rev. 2020, 408, 213179,  DOI: 10.1016/j.ccr.2020.213179
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    Luminescent phosphine gold(I) alkynyl complexes. Highlights from 2010 to 2018
    Pujadas, Marc; Rodriguez, Laura
    Coordination Chemistry Reviews (2020), 408 (), 213179CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    An overview of the homometallic phosphine-Au(I)alkynyl complexes reported in the literature from 2010 to 2018 have been collected and reported in this review article. They have been classified for better understanding, between mononuclear and polynuclear compds. Their luminescent properties have been discussed along the text and the specific absorption and emission data collected in Annex I. This type of compds. are being used for a wide range of applications in fields such as biomedicine, chemosensors or luminescent materials among others and their interest is increasing in the last years. Some particular examples have been also selected herein.
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    Blanco, M. C.; Gimeno, M.; Fernández-Moreira, V.; Cámara, J.; Laguna, A. Gold (I), Phosphanes, and Alkynyls: The Perfect Allies in the Search for Luminescent Compounds. Eur. J. Inorg. Chem. 2018, 2018, 2762,  DOI: 10.1002/ejic.201701256
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    Gold(I), Phosphanes, and Alkynyls: The Perfect Allies in the Search for Luminescent Compounds
    Blanco, M. Carmen; Camara, Jessica; Fernandez-Moreira, Vanesa; Laguna, Antonio; Gimeno, M. Concepcion
    European Journal of Inorganic Chemistry (2018), 2018 (24), 2762-2767CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A family of mixed phosphane/alkynyl gold(I) complexes was prepd. by addn. of PPh3 or PPh2py to suspensions of the polymeric species [Au(C≡CR)n] [R = Ph, 2-pyridyl (py)] and [Au2{C≡C(CH2)3C≡C}]n. The resulting complexes are luminescent both at room and low temp., in soln. and in the solid state. The emissions are assigned to intraligand transitions assocd. with the C≡C moieties or related to 3[σ(Au-P)→π*(C≡Cpy)] transitions. The crystal structure of dinuclear complex [Au2{C≡C(CH2)3C≡C}(PPh2py)2] shows the presence of dimers stabilized by intermol. aurophilic interactions.
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    Chen, Z.; Huang, P.-S.; Li, Z.; Yin, J.; Yu, G.-A.; Liu, S. H. Triisocyano-based trinuclear gold (I) complexes with aggregation-induced emission (AIE) and mechanochromic luminescence characteristics. Inorg. Chim. Acta 2015, 432, 192– 197,  DOI: 10.1016/j.ica.2015.04.016
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    Triisocyano-based trinuclear gold(I) complexes with aggregation-induced emission (AIE) and mechanochromic luminescence characteristics
    Chen, Zhao; Huang, Peng-Shou; Li, Zheng; Yin, Jun; Yu, Guang-Ao; Liu, Sheng Hua
    Inorganica Chimica Acta (2015), 432 (), 192-197CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
    Three novel trinuclear Au(I) complexes were designed and synthesized. These Au(I) complexes exhibit aggregation-induced emission characteristics. The luminescence properties of these luminogens show off-on green fluorescence in response to mech. grinding. The changing of weak multiple intermol. C-H···F or π-π interactions, or the formation of aurophilic interactions are possibly responsible for their mechanochromism phenomena.
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    Wu, Z. N.; Yao, Q. F.; Chai, O. J. H.; Ding, N.; Xu, W.; Zang, S. Q.; Xie, J. P. Unraveling the Impact of Gold(I)-Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters. Angew. Chem. 2020, 59 (25), 9934– 9939,  DOI: 10.1002/anie.201916675
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    Unraveling the Impact of Gold(I)-Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters
    Wu, Zhennan; Yao, Qiaofeng; Chai, Osburg Jin Huang; Ding, Nan; Xu, Wen; Zang, Shuangquan; Xie, Jianping
    Angewandte Chemie, International Edition (2020), 59 (25), 9934-9939CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Aggregation-induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. The impact of surface AuI-thiolate motifs on the AIE properties of Au NCs is revealed, by using H2O-sol. glutathione (GSH)-coordinated Au complexes and NCs as a model ([Au10SR10], [Au15SR13], [Au18SR14], and [Au25SR18]-, SR = thiolate ligand). Spectroscopic studies show that the emission wavelength of Au NCs is adjustable from visible to the near-IR II (NIR-II) region by controlling the length of the AuI-SR motifs on the NC surface. Decreasing the length of AuI-SR motifs also changes the origin of cluster luminescence from AIE-type phosphorescence to Au0-core-dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in soln.
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    Zheng, L. B.; Ye, X. Y.; Qi, P.; Zhang, D.; Sun, Y. Fluorometric detection of sulfate-reducing bacteria via the aggregation-induced emission of glutathione-gold(I) complexes. Microchim. Acta 2019, 186 (6). DOI: 10.1007/s00604-019-3427-4
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    Shu, T.; Cheng, X. J.; Wang, J. X.; Lin, X. F.; Zhou, Z. P.; Su, L.; Zhang, X. J. Synthesis of Luminescent Gold Nanoclusters Embedded Goose Feathers for Facile Preparation of Au(I) Complexes with Aggregation-Induced Emission. ACS Sustainable Chem. Eng. 2019, 7 (1), 592– 598,  DOI: 10.1021/acssuschemeng.8b04124
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    Synthesis of Luminescent Gold Nanoclusters Embedded Goose Feathers for Facile Preparation of Au(I) Complexes with Aggregation-Induced Emission
    Shu, Tong; Cheng, Xiaojun; Wang, Jianxing; Lin, Xiangfang; Zhou, Ziping; Su, Lei; Zhang, Xueji
    ACS Sustainable Chemistry & Engineering (2019), 7 (1), 592-598CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
    A new kind of luminescent hybrid materials based on ultrasmall nanomaterials, i.e., Au nanoclusters (AuNCs) and goose feathers, precious gifts from nature, was successfully synthesized. Goose feathers possess high sp. surface area due to their hierarchical structure and are mainly composed of thiol-rich proteins, for example, keratin, which can reduce Au(III) and encapsulate the formed AuNCs in a large scale. The resultant golden feathers exhibit bright red luminescence under UV light, of which the substructures, i.e., barbs and barbules, were sufficiently stained with red-emitting AuNCs. Also, the AuNC-stained feathers maintain almost unchanged structure (solid and hierarchical) and intact chem. compn. The features of such AuNC/feather hybrids, for example, bulk, high sp. surface, inspired one to develop a facile method to prep. various valuable debris from AuNC-based etching, i.e., Au(I) complexes with aggregation-induced emission (AIE). The authors selected tris(2-carboxyethyl)phosphine and cysteamine as etchants, resp., which were previously reported to be able to synthesize AIE-featured Au(I) complexes through etching AuNCs protected by sol. protein. Conveniently, in this approach, the protein-free Au(I) complexes in soln. can be attained simply by taking out with bare hand. After cation aggregation inducer was added, for example, Cd2+, the nonemitting soln. can generate bright luminescence, demonstrating the feasibility to synthesize the precious AIE-type Au(I) complexes. This study not only boosts the development of luminescent Au materials through rational use of natural product, enriching the library of Au nanomaterials, but also definitely provides a new view of nanoclusters as reagents to prep. other noble materials.
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    Wang, X. Y.; Zhang, J.; Dong, Y. B.; Zhang, Y. Y.; Yin, J.; Liu, S. H. Different structures modulated mechanochromism and aggregation-induced emission in a series of Gold(I) complexes. Dyes Pigm. 2018, 156, 74– 81,  DOI: 10.1016/j.dyepig.2018.03.062
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    Different structures modulated mechanochromism and aggregation-induced emission in a series of Gold(I) complexes
    Wang, Xiao-Yan; Zhang, Jing; Dong, Yu-Bao; Zhang, Yiyue; Yin, Jun; Liu, Sheng Hua
    Dyes and Pigments (2018), 156 (), 74-81CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
    Five novel Au(I) complexes with various isocyanide ligands were synthesized and characterized in the present work. The introduction of different terminal ligands endows distinct diverse properties onto the complexes: (i) alkyl modified complexes exhibit tricolor or bicolor mechanochromic behaviors due to the loose packing formed through weak intermol. C-H···F interactions, while aryl bridged complexes are not mechano-responsive with tight π-π stackings; (ii) all the target complexes present prominent but different aggregation-induced emission (AIE) characteristics caused by the inherent difference in their structures. Therefore, the above Au(I) complexes are anticipated to be used as fluorescent detectors and mechanosensors.
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    Chen, Z.; Liu, G.; Pu, S. Z.; Liu, S. H. Carbazole-based aggregation-induced emission (AIE)-active gold(I) complex: Persistent room-temperature phosphorescence, reversible mechanochromism and vapochromism characteristics. Dyes Pigm. 2017, 143, 409– 415,  DOI: 10.1016/j.dyepig.2017.05.003
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    41
    Carbazole-based aggregation-induced emission (AIE)-active gold(I) complex: Persistent room-temperature phosphorescence, reversible mechanochromism and vapochromism characteristics
    Chen, Zhao; Liu, Gang; Pu, Shouzhi; Liu, Sheng Hua
    Dyes and Pigments (2017), 143 (), 409-415CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
    A carbazole-based gold(I) complex 1 (I) was successfully synthesized. Its structure was characterized by NMR spectroscopy, elemental anal. and single crystal x-ray diffractometry. Its aggregation-induced emission behavior was studied by UV/visible, photoluminescence spectroscopy and scanning electron microscope. Its solid-state mechanochromic and thin-film vapochromic luminescence behaviors were also studied by photoluminescence spectroscopy. Luminogen 1 showed obvious aggregation-induced emission property. Furthermore, 1 also exhibited reversible high-contrast mechanochromic and vapochromic luminescence behaviors. More interestingly, 1 can emit persistent room-temp. phosphorescence with a solid-state emission lifetime up to 86.84 ms, which is the highest lifetime value among all the reported gold(I) complexes so far. To the best of the authors' knowledge, the gold(I) complex is the first example of an AIE-active luminogen with persistent room-temp. phosphorescence, reversible mechanochromism and vapochromism characteristics.
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    Sun, W. J.; Luo, L.; Feng, Y. S.; Cai, Y. T.; Zhuang, Y. X.; Xie, R. J.; Chen, X. Y.; Chen, H. M. Aggregation-Induced Emission Gold Clustoluminogens for Enhanced Low-Dose X-ray-Induced Photodynamic Therapy. Angew. Chem. 2020, 59 (25), 9914– 9921,  DOI: 10.1002/anie.201908712
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    42
    Aggregation-Induced Emission Gold Clustoluminogens for Enhanced Low-Dose X-ray-Induced Photodynamic Therapy
    Sun, Wenjing; Luo, Li; Feng, Yushuo; Cai, Yuting; Zhuang, Yixi; Xie, Rong-Jun; Chen, Xiaoyuan; Chen, Hongmin
    Angewandte Chemie, International Edition (2020), 59 (25), 9914-9921CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The use of gold nanoparticles as radiosensitizers is an effective way to boost the killing efficacy of radiotherapy while drastically limiting the received dose and reducing the possible damage to normal tissues. Herein, we designed aggregation-induced emission gold clustoluminogens (AIE-Au) to achieve efficient low-dose X-ray-induced photodynamic therapy (X-PDT) with negligible side effects. The aggregates of glutathione-protected gold clusters (GCs) assembled through a cationic polymer enhanced the X-ray-excited luminescence by 5.2-fold. Under low-dose X-ray irradn., AIE-Au strongly absorbed X-rays and efficiently generated hydroxyl radicals, which enhanced the radiotherapy effect. Addnl., X-ray-induced luminescence excited the conjugated photosensitizers, resulting in a PDT effect. The in vitro and in vivo expts. demonstrated that AIE-Au effectively triggered the generation of reactive oxygen species with an order-of-magnitude redn. in the X-ray dose, enabling highly effective cancer treatment.
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    Seixas de Melo, J. S.; Cabral, C.; Lima, J. C.; Macanita, A. L. Characterization of the singlet and triplet excited states of 3-chloro-4-methylumbelliferone. J. Chem. Phys. A 2011, 115 (30), 8392– 8398,  DOI: 10.1021/jp204354x
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    Characterization of the Singlet and Triplet Excited States of 3-Chloro-4-methylumbelliferone
    Seixas de Melo, J. Sergio; Cabral, Catarina; Lima, Joao C.; Macanita, Antonio L.
    Journal of Physical Chemistry A (2011), 115 (30), 8392-8398CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    An extensive photophys. characterization of 3-chloro-4-methylumbelliferone (3Cl4MU) in the ground-state, S0, first excited singlet state, S1, and lowest triplet state, T1, was undertaken in water, neutral ethanol, acidified ethanol, and basified ethanol. Quant. measurements of quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion, and singlet oxygen formation) together with lifetimes were obtained at room and low temp. in water, dioxane/water mixts., and alcs. The different transient species were assigned and a general kinetic scheme is presented, summarizing the excited-state multiequil. of 3Cl4MU. In water, the equil. is restricted to neutral (N*) and anionic (A*) species, both in the ground (pKa = 7.2) and first excited singlet states (pKa* = 0.5). In dioxane/water mixts. (pH ca. 6), substantial changes of the kinetics of the S1 state were obsd. with the appearance of an addnl. tautomeric T* species. In low water content mixts. (mixt. 9:1 v:v), only the neutral (N*) and tautomeric (T*) forms of 3Cl4MU are obsd., whereas at higher water content mixts. (water mole fraction superior to 0.45), all three species N*, T*, and A* coexist in the excited state. In the triplet state, in the nonprotic and nonpolar solvent dioxane, the obsd. transient signals were assigned as the triplet-triplet transition of the neutral form, N*T1 → N*Tn. In water, two transient species were obsd. and are assigned as the triplets of the neutral N*T1 and the anionic form, A*T1 (also obtained in basified ethanol). The phosphorescence spectra and decays of 3Cl4MU, in neutral, acidified, and basified solns., demonstrate that only these two species N*T1 and A*T1 exist in the lowest lying triplet state, T1. The radiative channel was found dominant for the deactivation of the anionic species, whereas with the neutral the S1 (symbol) S0 internal conversion competes with fluorescence. For both N* and A* the intersystem crossing yield represents a minor deactivation channel for S1.
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    Oliveira, E.; Capelo, J. L.; Lima, J. C.; Lodeiro, C. Novel emissive bio-inspired non-proteinogenic coumarin-alanine amino acid: fluorescent probe for polyfunctional systems. Amino Acids 2012, 43 (4), 1779– 1790,  DOI: 10.1007/s00726-012-1262-6
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    Novel emissive bio-inspired non-proteinogenic coumarin-alanine amino acid: fluorescent probe for polyfunctional systems
    Oliveira, Elisabete; Capelo, Jose Luis; Lima, Joao Carlos; Lodeiro, Carlos
    Amino Acids (2012), 43 (4), 1779-1790CODEN: AACIE6; ISSN:0939-4451. (SpringerWienNewYork)
    Two new bio-inspired non-proteinogenic compds. L1 and L2, contg. coumarin and/or acridine chromophores and bearing as spacer an alanine amino acid were successfully synthesized and fully characterized by elemental anal., 1H and 13C NMR, IR spectroscopy (KBr disks), m.p., ESI-TOF (electrospray ionization-time of flight-mass), UV-vis absorption and emission spectroscopy, fluorescence quantum yields and lifetime measurements. A relative fluorescence quantum yield of 0.02 was detd. for both compds. In L2 the presence of an intramol. energy transfer from the coumarin to the acridine unit was obsd. L1 and L2 are quite sensitive to the basicity of the environment. At alk. values both compds. show a strong quenching in the fluorescence emission, attributed to the photoinduced electron transfer (PET). However, both deprotonated forms recover the emission with the addn. of Zn2+, Cd2+ and Al3+ metal ions. As multifunctional emissive probes, the titrn. of L1 and L2 with lanthanides (III), Eu3+ and Tb3+ was also explored as new visible bio-probes in the absence and in the presence of liposomes. In a liposomal environment a lower energy transfer was obsd.
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    Heldt, J. R.; Heldt, J.; Stoń, M.; Diehl, H. A. Photophysical properties of 4-alkyl-and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time. Spectrochimica Acta Part A 1995, 51 (9), 1549– 1563,  DOI: 10.1016/0584-8539(95)01467-9
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    Photophysical properties of 4-alkyl- and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time
    Heldt, Janina R.; Heldt, Jozef; Ston, Marek; Diehl, Horst A.
    Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (1995), 51A (9), 1549-63CODEN: SAMCAS; ISSN:0584-8539. (Elsevier)
    4-Alkyl- and 7-alkoxycoumarin derivs. have been investigated for their spectroscopic properties in three different solvents. The substitutions are Me, Et, Pr and Bu groups. Absorption and emission spectra, quantum yields and mean fluorescence decay times have been detd. The spectroscopic studies together with calcns. of the radiative transition probabilities indicate that the 4-alkyl- and 7-alkoxy substituents do not change the symmetry of the electronic cloud of the coumarin skeleton. The changes obsd. for the rates of radiative transitions and also for the positions of the absorption and emission maxima can be explained by changes in the mol. electronic transition moment, caused by the weak donation potential of the substituents. A strong dependence of the quantum yields and mean fluorescence decay times on solvent viscosity has been found, leading to the suggestion that torsional rotations of the alkyl and alkoxy substituents significantly increase the internal non-radiative energy conversion rate.
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    Seixas de Melo, J. S.; Fernandes, P. F. Spectroscopy and photophysics of 4-and 7-hydroxycoumarins and their thione analogs. J. Mol. Struct. 2001, 565, 69– 78,  DOI: 10.1016/S0022-2860(01)00458-6
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    Spectroscopy and photophysics of 4- and 7-hydroxycoumarins and their thione analogs
    Seixas de Melo, J.; Fernandes, P. F.
    Journal of Molecular Structure (2001), 565-566 (), 69-78CODEN: JMOSB4; ISSN:0022-2860. (Elsevier Science B.V.)
    Acid-base equil. were studied for 4-hydroxycoumarin, 7-hydroxy-4-methylcoumarin and their thione derivs. in different media for their ground and lowest energy singlet and triplet excited states. The ethoxylated and/or methoxylated derivs. were also investigated. Characterization involves fluorescence spectra, quantum yields, lifetimes, phosphorescence spectra, lifetimes, and triplet-triplet absorption spectra. From their pKa values it was found that 4- and 7-hydroxycoumarins are more acidic in their lowest excited singlet states than in S0. The origin and character of the lowest singlet and triplet excited states is discussed.
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  47. 47
    de Castro, C. S.; Cova, T. F.; Pais, A. C.; Pinheiro, D.; Nunez, C.; Lodeiro, C.; Seixas de Melo, J. S. Probing metal cations with two new Schiff base bischromophoric pyrene based chemosensors: Synthesis, photophysics and interactions patterns. Dyes Pigm. 2016, 134, 601– 612,  DOI: 10.1016/j.dyepig.2016.08.016
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    Probing metal cations with two new Schiff base bischromophoric pyrene based chemosensors: Synthesis, photophysics and interactions patterns
    de Castro, Catherine S.; Cova, Tania F. G. G.; Pais, Alberto C. C.; Pinheiro, Daniela; Nunez, Cristina; Lodeiro, Carlos; Seixas de Melo, J. Sergio
    Dyes and Pigments (2016), 134 (), 601-612CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
    Two new pyrene chemosensors (bipyrenyl ligands L1 and L2) were synthesized, fully characterized and their sensing ability towards metal cations (Cu2+, Ag+, Pb2+, Zn2+, Cd2+ and Hg2+) was studied by absorption and fluorescence (steady-state and time-resolved) techniques in soln. The absorption spectra of the two free ligands displays a single band (attributed to the monomer absorption) whereas the emission spectra show two bands, which were attributed to the emission of the monomer and dimer. For L1, time-resolved fluorescence measurements indicate a single component that becomes double exponential when the metal ion (in the studied case, Pb2+) is added. From both steady-state and time-resolved data this dimer likely involves the interaction of two pyrene units, but the absence of a rising component in the fluorescence decays discards the possibility of the presence of a dynamic excimer. Upon addn. of a metal ion, this band changes in shape mirroring the fact that a new complex, involving the metal ion and the ligand, is formed. From the overall spectroscopic and photophys. data rationalized by Hierarchical Cluster Anal. (HCA) and Principal Component Anal. (PCA) both L1 and L2 ligands are able to discriminate Ag+ and Pb2+ from all the other metal ions, with L2 displaying a higher sensing ability (as seen from HCA/PCA anal.) towards Pb2+. This global approach, joining spectral and photophys. data with multivariate anal., showed to constitute a powerful tool for revealing important patterns in this type of system.
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    Seixas de Melo, J. S.; Becker, R. S.; Macanita, A. L. Photophysical behavior of coumarins as a function of substitution and solvent: experimental evidence for the existence of a lowest lying 1 (n, pi.*) state. J. Chem. Phys. 1994, 98 (24), 6054– 6058,  DOI: 10.1021/j100075a002
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    Photophysical Behavior of Coumarins as a Function of Substitution and Solvent: Experimental Evidence for the Existence of a Lowest Lying 1(n,π*) State
    Seixas de Melo, J. Sergio; Becker, Ralph S.; Macanita, Antonio L.
    Journal of Physical Chemistry (1994), 98 (24), 6054-8CODEN: JPCHAX; ISSN:0022-3654.
    The nature of the lowest excited state for coumarin and some derivs. was investigated using steady-state and time-resolved fluorescence data at room temp., as well as fluorescence anisotropy at 77 K in nonpolar and polar solvents in conjunction with theor. data obtained with different methods: INDO/S-CI, CNDO/S-CI, MNDO-CI, and AM1-CI. The results show that S1 is actually n,π* for coumarin in any solvent. Substitution with methoxy and Me and/or chlorine and/or an increase of solvent polarity reduces the energy gap between the S1 (n,π*) and S2 (π,π*) states, promoting the mixing of these states and finally inducing inversion to S1 (π,π*) with trisubstitution and for the disubstituted case in dioxane-water (1:4). The presence of a lowest lying S1 (n,π*) mediates a large degree of radiationless processes in the singlet manifold.
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    Seixas de Melo, J. S.; Becker, R. S.; Elisei, F.; Maçanita, A. The photophysical behavior of 3-chloro-7-methoxy-4-methylcoumarin related to the energy separation of the two lowest-lying singlet excited states. J. Chem. Phys. 1997, 107 (16), 6062– 6069,  DOI: 10.1063/1.474274
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    The photophysical behavior of 3-chloro-7-methoxy-4-methylcoumarin related to the energy separation of the two lowest-lying singlet excited states
    Seixas de Melo, J.; Becker, Ralph S.; Elisei, Fausto; Macanita, A. L.
    Journal of Chemical Physics (1997), 107 (16), 6062-6069CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    The photophys. behavior of 3-chloro-7-methoxy-4-methylcoumarin (ClMMC) was studied as a function of the solvent and temp. The radiative lifetime τF0 = 1/kF is essentially solvent independent and its value (≈4.6 ns) is totally commensurate with the fluorescence originating from a 1(π,π*) state as the lowest excited state. From the fluorescence data obtained in 24 solvents plus nine solvent mixts., and the triplet formation quantum yields for three representative solvents, it was found that the internal conversion rate const. (kIC) dictates the photophys. behavior of ClMMC and changes of two orders of magnitude occur from nonpolar to polar solvents. From the temp. dependence (20 to -100 °C) of the fluorescence lifetimes in five solvents it was found that a change of the internal conversion rate const. of the same order of magnitude occurred as above. The rate consts. and the activation energies for the radiationless processes were detd. The results show that the reason for the dramatic variation of kIC is the fact that when the S2(n,π*) state is close lying to S1(π,π*), there is a decrease of the activation energy of the internal conversion process (S1∼∼→S0). Increasing solvent polarity increases the energy gap between these states, and decreases the magnitude of the effect. Decreasing the temp. to sufficiently low values, disables the deactivation channel. The interpretation of the foregoing results can be satisfied by either a model involving a fast equil. between two close lying S2 and S1 states or in terms of the so-called "proximity effect.".
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    Bardají, M.; Teresa de la Cruz, M.; Jones, P. G.; Laguna, A.; Martínez, J.; Dolores Villacampa, M. Luminescent dinuclear gold complexes of bis (diphenylphosphano) acetylene. Inorg. Chim. Acta 2005, 358 (5), 1365– 1372,  DOI: 10.1016/j.ica.2004.05.017
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    Luminescent dinuclear gold complexes of bis(diphenylphosphano)acetylene
    Bardaji, Manuel; de la Cruz, M. Teresa; Jones, Peter G.; Laguna, Antonio; Martinez, Julia; Villacampa, M. Dolores
    Inorganica Chimica Acta (2005), 358 (5), 1365-1372CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
    The authors synthesized dinuclear Au(I) derivs. with the diphosphine bis(diphenylphosphino)acetylene (dppa), [(AuX)2(μ-dppa)] (I; X = Cl, C6F5, SC6F5, S2CN(CH2Ph)2). X-ray structure detns. for I (X = = Cl, C6F5, SC6F5)reveal a linear geometry for the Au centers. There are no intramol. Au-Au interactions, although for X = Cl intermol. Au(I)-Au(I) interactions of 3.0694(4) Å lead to an infinite twisted chain; the further presence of C-H···Cl contacts leads to a more complex three-dimensional structure. All the derivs. are luminescent in the solid state at low temp. in the range 455-593 nm; most of them are emissive at room temp. in the range 470-598 nm. The authors also prepd. the dinuclear Au(III) deriv. [(Au(C6F5)3)2(μ-dppa)]. Finally, the authors prepd. [(AuCl)2(μ-dppa)3], which forms a cage with two tetrahedrally coordinated Au(I) centers at the apical positions bridged by three rigid diphosphine ligands, with a helical twist of 26.2°, and a Au-Au distance of 5.769 Å. The Au(III) and the four-coordinate Au(I) derivs. are not luminescent.
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    Ferrer, M.; Gutiérrez, A.; Rodríguez, L.; Rossell, O.; Lima, J. C.; Font-Bardia, M.; Solans, X. Study of the Effect of the Phosphane Bridging Chain Nature on the Structural and Photophysical Properties of a Series of Gold(I) Ethynylpyridine Complexes; Wiley-VCH Verlag: Weinheim, Germany, 2008.
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    Arcau, J.; Andermark, V.; Aguiló, E.; Gandioso, A.; Moro, A.; Cetina, M.; Lima, J. C.; Rissanen, K.; Ott, I.; Rodríguez, L. Luminescent alkynyl-gold (I) coumarin derivatives and their biological activity. Dalton Trans. 2014, 43 (11), 4426– 4436,  DOI: 10.1039/C3DT52594E
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    Luminescent alkynyl-gold(I) coumarin derivatives and their biological activity
    Arcau, Julia; Andermark, Vincent; Aguilo, Elisabet; Gandioso, Albert; Moro, Artur; Cetina, Mario; Lima, Joao Carlos; Rissanen, Kari; Ott, Ingo; Rodriguez, Laura
    Dalton Transactions (2014), 43 (11), 4426-4436CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    The synthesis and characterization of three propynyloxycoumarins are reported in this work together with the formation of three different series of gold(I) organometallic complexes. Neutral complexes are constituted by water sol. phosphines (PTA and DAPTA) which confer water soly. to them. The x-ray crystal structure of 7-(prop-2-in-1-yloxy)-1-benzopyran-2-one and its corresponding dialkynyl complex is also shown and the formation of rectangular dimers for the gold deriv. in the solid state can be obsd. A detailed anal. of the absorption and emission spectra of both ligands and complexes allows us to attribute the luminescent behavior to the coumarin org. ligand. Moreover, the presence of the gold(I) metal atom seems to be responsible for an increase of coumarin phosphorescence emission. The biol. activity of the complexes showed that the anionic complexes triggered strong cytotoxic effects in two different cell lines whereas the neutral gold alkynyl complexes led to lower effects against tumor cell growth. Thioredoxin reductase (TrxR) inhibition was very strong in the case of the neutral complexes (IC50 values below 0.1 μM) but moderate for the anionic complexes (IC50 values above 0.8 μM).
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    The influence of oxygen on the lifetime of luminescent probes. A simple device for degassing solutions for fluorescence measurements
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  1. Carla Cunha, Mariana Peixoto, José A. Paixão, Marta Pineiro, J. Sérgio Seixas de Melo. Tuning the AIE Properties of Di-tert-Butyl-diphenyldibenzofulvene Derivatives. The Journal of Physical Chemistry C 2024, 128 (3) , 1156-1164. https://doi.org/10.1021/acs.jpcc.3c06436
  2. Guillermo Romo-Islas, Jas S. Ward, Kari Rissanen, Laura Rodríguez. Heterometallic Au(I)–Cu(I) Clusters: Luminescence Studies and 1O2 Production. Inorganic Chemistry 2023, 62 (21) , 8101-8111. https://doi.org/10.1021/acs.inorgchem.3c00046
  3. Andrea Pinto, Alejandro Llanos, Rosa M. Gomila, Antonio Frontera, Laura Rodríguez. Ligand and Gold(I) Fluorescein–AIEgens as Photosensitizers in Solution and Doped Polymers. Inorganic Chemistry 2023, 62 (19) , 7131-7140. https://doi.org/10.1021/acs.inorgchem.3c00197
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  6. Ana Clara B. Rodrigues, Susana M. M. Lopes, Carla Cunha, João Braz, Teresa M. V. D. Pinho e Melo, J. Sérgio Seixas de Melo, Marta Pineiro. The role of solvents and concentrations in the properties of oxime bearing A 2 B corroles. Physical Chemistry Chemical Physics 2023, 163 https://doi.org/10.1039/D2CP05941J
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  • Abstract

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    Scheme 1

    Scheme 1. General Synthetic Routes, Structures, and Acronyms of Alkynylcoumarin Dinuclear Gold(I) Complexes [Au (C≡C13H9O3)(PPh2XPPh2)]2 [PPh2XPPh2 = DPPM for X = (CH2) (1.1), DPPP for X = (CH2)3 (1.2), and DPPA for X = C≡C (1.3)]
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    Figure 1

    Figure 1. Absorption and fluorescence emission spectra of the dinuclear gold(I) complexes (1.1, 1.2, and 1.3) with the parent compound (1) in MeCN, 2-MeTHF, and thin films. Vertical dashed lines are just guides to the eye. Color legend for lines: absorption and emission spectra of 1, orange; 1.1, purple; 1.2, blue; 1.3, dark green.

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    Figure 2

    Figure 2. Fluorescence decays for the gold(I) complexes (1.1, 1.2, and 1.3) and 1 in dimethylformamide at T = 293 K with λexc = 268 nm and λem = 375 nm. The quality of the analysis is judged by the presentation of the weighted residuals, autocorrelation functions (A.C.), and χ2 values. The decay with the black dashed line is the IRF obtained with a scatter solution (see the Experimental Section).

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    Figure 3

    Figure 3. (A) Normalized phosphorescence emission spectra (λexc = 320 nm; DAF = 0.5 ms) and (B) decays (λem = 490 nm) for the gold(I) complexes 1.1, 1.2, and 1.3 in 2-MeTHF at T = 77 K.

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    Figure 4

    Figure 4. Fluorescence emission spectra (left panel) with pictures obtained under UV irradiation (with λexc = 254 nm) and correlation of the emission area (right panel) with increasing water fractions (fw) in MeCN/water mixtures for the three alkynylcoumarin dinuclear gold(I) complexes 1.1, 1.2, and 1.3 and the ligand 1.

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    Figure 5

    Figure 5. DLS particle size distribution curves obtained in MeCN/water mixtures (>75–95% H2O, v/v) for the gold(I) complexes 1.1, 1.2, and 1.3. From top to bottom, fw increases.

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    Figure 6

    Figure 6. Energetically more favorable molecular structures, obtained from TDDFT calculations, for 1.1 (syn), 1.2 (anti), and 1.3 (anti).

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    Figure 7

    Figure 7. TDDFT absorption spectra of two dimers of 1.1, 1.2, and 1.3, respectively, with different orientations and of the monomer and both dimers. Color legend: black, monomer; orange, “Dimer A”; blue, “Dimer B”.

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      Suzuki, S.; Sasaki, S.; Sairi, A. S.; Iwai, R.; Tang, B. Z.; Konishi, G.-I. Principles of Aggregation-Induced Emission: Design of Deactivation Pathways for Advanced AIEgens and Applications. Angew. Chem. 2020, 59 (25), 9856– 9867,  DOI: 10.1002/anie.202000940
      2
      Principles of Aggregation-Induced Emission: Design of Deactivation Pathways for Advanced AIEgens and Applications
      Suzuki, Satoshi; Sasaki, Shunsuke; Sairi, Amir Sharidan; Iwai, Riki; Tang, Ben Zhong; Konishi, Gen-ichi
      Angewandte Chemie, International Edition (2020), 59 (25), 9856-9867CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Twenty years ago, the concept of aggregation-induced emission (AIE) was proposed, and this unique luminescent property has attracted scientific interest ever since. However, AIE denominates only the phenomenon, while the details of its underlying guiding principles remain to be elucidated. This minireview discusses the basic principles of AIE based on our previous mechanistic study of the photophys. behavior of 9,10-bis(N,N-dialkylamino)anthracene (BDAA) and the corresponding mechanistic anal. by quantum chem. calcns. BDAA comprises an anthracene core and small electron donors, which allows the quantum chem. aspects of AIE to be discussed. The key factor for AIE is the control over the non-radiative decay (deactivation) pathway, which can be visualized by considering the conical intersection (CI) on a potential energy surface. Controlling the conical intersection (CI) on the potential energy surface enables the sep. formation of fluorescent (CI:high) and non-fluorescent (CI:low) mols. [control of conical intersection accessibility (CCIA)]. The novelty and originality of AIE in the field of photochem. lies in the creation of functionality by design and in the active control over deactivation pathways. Moreover, we provide a new design strategy for AIE luminogens (AIEgens) and discuss selected examples.
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    3. 3
      Rodrigues, A. C. B.; Pina, J.; Seixas de Melo, J. S. Structure-relation properties of N-substituted phenothiazines in solution and solid state: Photophysical, photostability and aggregation-induced emission studies. J. Mol. Liq. 2020, 317, 113966,  DOI: 10.1016/j.molliq.2020.113966
      There is no corresponding record for this reference.
    4. 4
      Rodrigues, A. C. B.; Pina, J.; Dong, W.; Forster, M.; Scherf, U.; Seixas de Melo, J. S. Aggregation-Induced Emission in Phenothiazine–TPE and -TPAN Polymers. Macromolecules 2018, 51 (21), 8501– 8512,  DOI: 10.1021/acs.macromol.8b01758
      4
      Aggregation-Induced Emission in Phenothiazine-TPE and -TPAN Polymers
      Rodrigues, Ana Clara B.; Pina, Joao; Dong, Wenyue; Forster, Michael; Scherf, Ullrich; Seixas de Melo, J. Sergio
      Macromolecules (Washington, DC, United States) (2018), 51 (21), 8501-8512CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Two phenothiazine-based polymers-tetraphenylethylene- (PTzTPE) and triphenylacrylonitrile-substituted (PTzTPAN) polyphenothiazines-were studied in org. solvents, solid state, and THF:water and dioxane:water mixts. to investigate the occurrence of aggregation-induced emission (AIE). It is shown that AIE is present for the PTzTPE and PTzTPAN polymers in THF:water mixts., although to a lesser extent in the latter case. The emission of PTzTPE was found to display the simultaneous emission of locally excited (LE) and charge transfer (CT) states with emission maxima at ∼480 and ∼640 nm, resp. Dynamic light scattering measurements in THF:water mixts. point out to the formation of small nanoaggregates in which the polymers likely adopt a collapsed structure. The overall effect of the restriction of mol. movements of TPE or TPAN units and the poly(phenothiazine) backbone (thus leading to the enhancing of the excited state radiative channel over the internal conversion deactivation channel through the redn. of the "loose bolt" or free rotor effect), together with the decrease of the CT contribution with the increase of the water fraction was assocd. with the AIE effect obsd. in THF:water mixts. For PTzTPE in dioxane:water mixts. an opposite effect, i.e., an aggregation caused quenching (ACQ), is obsd. with the increment of water fraction, fw, in the mixt. (.vphi.F decreasing from 0.14 in pure dioxane to 0.042 for fw = 90%). This selective AIE behavior in specific solvents was attributed to the conversion of emissive LE states into dark CT states. DFT calcns. of the phenothiazine-TPE and -TPA trimer units confirm the bent butterfly shape generally adopted by the phenothiazine moiety and the excited state charge transfer from the phenothiazine donor to the side-chain acceptor units.
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    5. 5
      Dong, W.; Pina, J.; Pan, Y.; Preis, E.; Seixas de Melo, J. S.; Scherf, U. Polycarbazoles and polytriphenylamines showing aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) behavior for the optical detection of nitroaromatic compounds. Polymer 2015, 76, 173– 181,  DOI: 10.1016/j.polymer.2015.08.064
      5
      Polycarbazoles and polytriphenylamines showing aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) behavior for the optical detection of nitroaromatic compounds
      Dong, Wenyue; Pina, Joao; Pan, Yuyu; Preis, Eduard; Seixas de Melo, J. Sergio; Scherf, Ullrich
      Polymer (2015), 76 (), 173-181CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      Acceptor-substituted polycarbazoles (PCzTPAN) and polytriphenylamines (PTPATPAN) bearing electron-deficient 2,3,3-triphenylacrylonitrile (TPAN) side groups were successfully synthesized. Both of them are aggregation-induced emission (AIE)-active and show intramol. charge transfer (ICT) behavior. PCzTPAN and PTPATPAN aggregates in 90% water/THF were used for the detection of 1,3,5-trinitrobenzene (TNB) as prototypical nitroarom. compd. They show amplified PL quenching upon addn. of TNB with a max. quenching const. of 5.5 × 105 M-1. As addnl. application example, the detection of the glass transition temp. of polystyrene (PS) was accomplished for PTPATPAN blended into PS at doping concns. of 0.1-1.0%.
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    6. 6
      Hong, Y.; Lam, J. W.; Tang, B. Z. Aggregation-induced emission. Chem. Soc. Rev. 2011, 40 (11), 5361– 5388,  DOI: 10.1039/c1cs15113d
      6
      Aggregation-induced emission
      Hong, Yuning; Lam, Jacky W. Y.; Tang, Ben Zhong
      Chemical Society Reviews (2011), 40 (11), 5361-5388CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this crit. review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure-property relationships are derived. Through mechanistic decipherment of the photophys. processes, structural design strategies for generating new AIE luminogens are developed. Technol., esp. optoelectronic and biol., applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 refs.).
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    7. 7
      Rodrigues, A. C. B.; Seixas de Melo, J. S. In Aggregation-Induced Emission; Tang, Y., Tang, B. Z., Ed.; Springer International Publishing, 2022; pp 209− 246.
      There is no corresponding record for this reference.
    8. 8
      Aguiló, E.; Moro, A. J.; Gavara, R.; Alfonso, I.; Pérez, Y.; Zaccaria, F.; Guerra, C. l. F.; Malfois, M.; Baucells, C.; Ferrer, M.; Lima, J. C.; Rodríguez, L. Reversible self-assembly of water-soluble Gold (I) complexes. Inorg. Chem. 2018, 57 (3), 1017– 1028,  DOI: 10.1021/acs.inorgchem.7b02343
      8
      Reversible self-assembly of water-soluble gold(I) complexes
      Aguilo, Elisabet; Moro, Artur J.; Gavara, Raquel; Alfonso, Ignacio; Perez, Yolanda; Zaccaria, Francesco; Guerra, Celia Fonseca; Malfois, Marc; Baucells, Clara; Ferrer, Montserrat; Lima, Joao Carlos; Rodriguez, Laura
      Inorganic Chemistry (2018), 57 (3), 1017-1028CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The reaction of the gold polymers contg. bipyridyl and terpyridyl units, [Au(C≡CC15H10N3)]n and [Au(C≡CC10H7N2)]n, with the water-sol. phosphines 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane gives rise to the formation of four gold(I) alkynyl complexes that self-assemble in water (H2O) and DMSO (DMSO), through different intermol. interactions, with an impact on the obsd. luminescence displayed by the supramol. assemblies. A detailed anal. carried out by NMR studies performed in different DMSO/deuterated H2O mixts. indicates the presence of two different assembly modes in the aggregates: (i) chain assemblies, which are based mainly on aurophilic interactions, and (ii) stacked assemblies, which are based on Au···π and π···π interactions. These different supramol. environments can also be detected by their intrinsic optical properties (differences in absorption and emission spectra) and are predicted by the changes in the relative binding energy from d. functional theory calcns. carried out in DMSO and H2O. Small-angle X-ray scattering (SAXS) expts. performed in the same mixt. of solvents are in agreement with the formation of aggregates in all cases. The arom. units chosen, bipyridine and terpyridine, allow the use of external stimuli to reversibly change the aggregation state of the supramol. assemblies. Interaction with the Zn2+ cation is obsd. to disassemble the aggregates, while encapsulating agents competing for Zn2+ complexation revert the process to the aggregation stage, as verified by SAXS and NMR. The adaptive nature of the supramol. assemblies to the metal-ion content is accompanied by significant changes in the absorption and emission spectra, signaling the aggregation state and also the content on Zn2+.
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    9. 9
      Lázaro, A.; Cunha, C.; Bosque, R.; Pina, J.; Ward, J. S.; Truong, K.-N.; Rissanen, K.; Lima, J. C.; Crespo, M.; Seixas de Melo, J. S.; Rodríguez, L. Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt (II) Complexes with Aromatic Alkynyl Ligands. Inorg. Chem. 2020, 59 (12), 8220– 8230,  DOI: 10.1021/acs.inorgchem.0c00577
      9
      Room-Temperature Phosphorescence and Efficient Singlet Oxygen Production by Cyclometalated Pt(II) Complexes with Aromatic Alkynyl Ligands
      Lazaro, Ariadna; Cunha, Carla; Bosque, Ramon; Pina, Joao; Ward, Jas S.; Truong, Khai-Nghi; Rissanen, Kari; Lima, Joao Carlos; Crespo, Margarita; Seixas de Melo, J. Sergio; Rodriguez, Laura
      Inorganic Chemistry (2020), 59 (12), 8220-8230CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Platinum acetylide imine-amine complexes I (Ar = Ph, 4-FC6H4, 3-thienyl, 2-naphthyl, 9-phenanthryl) were prepd. and examd. for their photoluminescence, photophys. properties and catalysis of photochem. singlet oxygen prodn. The synthesis of five novel cyclometalated platinum(II) compds. contg. five different alkynyl-chromophores was achieved by the reaction of the previously synthesized Pt-Cl cyclometalated compd. (1) with the corresponding RC≡CH by a Sonogashira reaction. It was obsd. that the spectral and photophys. characteristics of the cyclometalated platinum(II) complexes (Pt-Ar) are essentially assocd. with the platinum-cyclometalated unit. Room-temp. emission of the Pt-Ar complexes was attributed to phosphorescence in agreement with DFT calcns. Broad nanosecond (ns)-transient absorption spectra were obsd. with decays approx. identical to those obtained from the emission of the triplet state. From the femtosecond-transient absorption (fs-TA) data, two main excited-state decay components were identified: one in the order of a few picoseconds was assigned to fast intersystem crossing to populate the triplet excited-state and the second (hundreds of ns) was assocd. with the decay of the transient triplet state. In general, efficient singlet oxygen photosensitization quantum yields were obsd. from the triplet state of these complexes. Platinum cyclometalated compds. contg. alkynyl chromophores have been synthesized and fully characterized. The X-ray crystal structures of three of the complexes do not show Pt···Pt contacts. Their photophys. properties have been studied in detail, showing room-temp. phosphorescence (RTP) and efficient 1O2 prodn.
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    10. 10
      Arsenault, N. E.; Xu, Z.; Wolf, M. O. Lewis Pair-Functionalized Pt (II) Complexes with Tunable Emission Color and Triplet-State Properties. Inorg. Chem. 2022, 61, 2804,  DOI: 10.1021/acs.inorgchem.1c03174
      10
      Lewis Pair-Functionalized Pt(II) Complexes with Tunable Emission Color and Triplet-State Properties
      Arsenault, Nicole E.; Xu, Zhen; Wolf, Michael O.
      Inorganic Chemistry (2022), 61 (6), 2804-2812CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Two emissive Pt(II) complexes contg. dynamic "flexible" Lewis pair (FlexLP) ligands are reported. The FlexLP ligand encompasses a diphenylphosphine oxide Lewis base and a dimesitylborane Lewis acid attached to a bithiophene scaffold, which can switch between an open unbound Lewis pair and a bound P-O-B Lewis adduct depending on the hydrogen bond-donating (HBD) strength of the solvent. [Pt(FlexLP)2] contains two FlexLP ligands, and [Pt(FlexLP)(Py)] contains one FlexLP ligand and one pyrene ligand. UV-vis absorption and fluorescence studies demonstrate that the FlexLP ligands switch between the open Lewis pair and the closed Lewis adduct in MeOH, a strong HBD solvent, and acetone, a weak HBD solvent, resp., and exhibit tunable emission color depending on the acetone/MeOH solvent ratio. Transient absorption spectroscopy reveals a large difference in the triplet-state lifetime depending on the conformation of the FlexLP ligands for both complexes. In the closed form, the triplet-state lifetimes of the two complexes are over an order of magnitude longer compared to that of the complexes in the open conformation. Calcns. of optimized geometries suggest that this difference in triplet-state lifetime is due to a difference in the thiophene-thiophene torsion angle between the two conformations.
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    11. 11
      Pina, J.; Rodrigues, A. C. B.; Alnady, M.; Dong, W.; Scherf, U.; Seixas de Melo, J. S. Restricted Aggregate Formation on Tetraphenylethene-Substituted Polythiophenes. J. Phys. Chem. C 2020, 124 (25), 13956– 13965,  DOI: 10.1021/acs.jpcc.9b10908
      11
      Restricted Aggregate Formation on Tetraphenylethene-Substituted Polythiophenes
      Pina, Joao; Rodrigues, Ana Clara B.; Alnady, Mohamed; Dong, Wenyue; Scherf, Ullrich; Seixas de Melo, J. Sergio
      Journal of Physical Chemistry C (2020), 124 (25), 13956-13965CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Two new polythiophenes functionalized with different degrees of tetraphenylethene, TPE, side groups (with TPE moieties at each thiophene unit, homoPT, and one in which only each second thiophene unit carries a TPE side chain, coPT) were successfully synthesized and characterized together with a poly(3-hexylthiophene) with similar av. mol. wt. and a tetraphenylethene-thiophene model compd. The study aimed to understand the role of the sterically bulky TPE pendant groups on the inhibition of intra- and/or interchain packing (aggregation) of these conjugated polymers. For the tetraphenylethene-thiophene model, compd. aggregation induced emission (AIE) is active for water fractions ≥ 90%. An opposite behavior is found for the polythiophenes (homoPT and coPT) where aggregation caused quenching (ACQ) was found to occur both in soln. and in the solid state. For the polythiophene with the higher degree of TPE labeling, homoPT, the amt. of ACQ is significantly decreased. This is attributed to the high TPE substitution d. in the polymer which promotes a more twisted conformation of the polymer backbone as the emissive chromophore. For the TPE-polythiophenes, only the energy migration mechanism was found to be active since the bulky TPE substituents restrict the polymer's intramol. motions. The exptl. observations of a small shift in the emission spectra of homoPT and significant hindering of ACQ on going from soln. to the solid state explain the absence of intermol. interactions together with the restriction of intramol. rotations.
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    12. 12
      Yam, V. W.-W.; Cheng, E. C.-C. Highlights on the recent advances in gold chemistry─a photophysical perspective. Chem. Soc. Rev. 2008, 37 (9), 1806– 1813,  DOI: 10.1039/b708615f
      12
      Highlights on the recent advances in gold chemistry-a photophysical perspective
      Yam, Vivian Wing-Wah; Cheng, Eddie Chung-Chin
      Chemical Society Reviews (2008), 37 (9), 1806-1813CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review; the presence of inter- and/or intra-mol. aurophilic interactions among the closed-shell gold(I) centers in various systems has been studied from various aspects, including synthetic, spectroscopic and theor. approaches. The employment of different ligands can impose a significant influence on these factors and give rise to new complexes with interesting structural and photophys. properties. In this tutorial review, a no. of recent examples are selected to illustrate the fascinating properties and chem., as well as versatility of gold(I) in these aspects and their potential applications to newcomers in this field. An emerging class of luminescent gold(III) complexes is also described.
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    13. 13
      Rodríguez, L.; Ferrer, M.; Crehuet, R.; Anglada, J.; Lima, J. C. Correlation between photophysical parameters and gold–gold distances in gold (I)(4-Pyridyl) ethynyl complexes. Inorg. Chem. 2012, 51 (14), 7636– 7641,  DOI: 10.1021/ic300609f
      13
      Correlation between Photophysical Parameters and Gold-Gold Distances in Gold(I) (4-Pyridyl)ethynyl Complexes
      Rodriguez, Laura; Ferrer, Montserrat; Crehuet, Ramon; Anglada, Josep; Lima, Joao Carlos
      Inorganic Chemistry (2012), 51 (14), 7636-7641CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The systematic anal. of the luminescence of a series of alkynyl gold derivs. with general formulas [(diphos)(AuC≡Cpy)2] (diphosphane =2,2'-bis(diphenylphosphanyl)propane or dppip (1), bis(diphenylphosphanyl)acetylene or dppa (2), 1,2-bis(diphenylphosphanyl)ethane or dppe (3) and 1,4-bis(diphenylphosphanyl)butane or dppb, (4), has shown a straightforward correlation between the Au(I)···Au(I) distance and the emission quantum yields and decaytimes. The anal. of the decaytimes, quantum yields and thus, the corresponding calcd. rate consts. demonstrated the existence of a correlation between Au(I)···Au(I) distance and the radiative rate const. for the deactivation of the emissive triplet states. It was concluded that the increased emission of these compds. results from the increase in spin-orbit coupling that favors the spin forbidden transition to the singlet ground state.
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    14. 14
      Blanco, M. C.; Camara, J.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Lopez-de-Luzuriaga, J. M.; Olmos, M. E.; Villacampa, M. D. Luminescent homo-and heteropolynuclear gold complexes stabilized by a unique acetylide fragment. Organometallics 2012, 31 (7), 2597– 2605,  DOI: 10.1021/om200397t
      14
      Luminescent Homo- and Heteropolynuclear Gold Complexes Stabilized by a Unique Acetylide Fragment
      Blanco, M. Carmen; Camara, Jessica; Gimeno, M. Concepcion; Jones, Peter G.; Laguna, Antonio; Lopez-de-Luzuriaga, Jose M.; Olmos, M. Elena; Villacampa, M. Dolores
      Organometallics (2012), 31 (7), 2597-2605CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
      The authors describe the reactivity of the Au acetylide derivs. [Au(C≡CR)(PPh3)] (R = Ph, 2-pyridyl). Reactions of these complexes with fragments [M(PPh3)2]+ (M = Au, Ag, Cu) afford novel discrete mols. stabilized not only by interactions with the triple bond but also by the formation of strong metal-Au interactions. The crystal structures of the Au-Au and Au-Ag species confirm their similar behavior, while x-ray diffraction establishes a different arrangement for the Cu complex with pyridine acetylide as a consequence of the coordination of this metal center to the N atom of pyridine and to the carbons of the alkyne. The luminescent properties of the complexes were studied.
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    15. 15
      Kathewad, N.; Kumar, N.; Dasgupta, R.; Ghosh, M.; Pal, S.; Khan, S. The syntheses and photophysical properties of PNP-based Au (i) complexes with strong intramolecular Au··· Au interactions. Dalton Trans. 2019, 48 (21), 7274– 7280,  DOI: 10.1039/C8DT04471F
      15
      The syntheses and photophysical properties of PNP-based Au(I) complexes with strong intramolecular Au···Au interactions
      Kathewad, Neha; Kumar, Nandha; Dasgupta, Rajarshi; Ghosh, Moushakhi; Pal, Shiv; Khan, Shabana
      Dalton Transactions (2019), 48 (21), 7274-7280CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      Herein the authors report the syntheses, x-ray structures and photophys. studies of the dinuclear dimeric gold(I) complexes [ClAu(C6H5N)(PPh2)2]2 (1), [Au(C6H5N)(PPh2)2]2[SbF6]2 (2) and [Au(2,6-Me2C6H3N)(PPh2)2]2[SbF6]2 (4). The authors used ligands with different substituents to see the effect of the substituents on the photophys. properties. All these complexes feature strong intramol. Au···Au interactions (2.7987-3.0056 Å) and exhibit excellent luminescence properties with high quantum yields as well as different colors of emission.
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    16. 16
      Sculfort, S.; Braunstein, P. Intramolecular d10–d10 interactions in heterometallic clusters of the transition metals. Chem. Soc. Rev. 2011, 40 (5), 2741– 2760,  DOI: 10.1039/c0cs00102c
      16
      Intramolecular d10-d10 interactions in heterometallic clusters of the transition metals
      Sculfort, Sabrina; Braunstein, Pierre
      Chemical Society Reviews (2011), 40 (5), 2741-2760CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Weak attractive interactions between closed shell metal ions have been increasingly studied in the last few years and are generally designated as metallophilic interactions. They are best evidenced in the solid state where structural data obtained by X-ray diffraction provide precise information about the distance between the metals involved. The strength of such metal-metal interactions has been compared to that of hydrogen bonding (ca. 7-11 kcal mol-1) and is clearly sufficient to bring about novel bonding and structural features and confer interesting phys. properties such as luminescence, polychromism, magnetism or one-dimensional elec. cond. The Cu(i)-Cu(i), Ag(i)-Ag(i) and Au(i)-Au(i) interactions have been increasingly obsd. and the latter have certainly been the most studied. Early qual. analyses of the aurophilic attraction focused on Au-Au bonding originating from 6s, 6p and 5d orbital mixing. Numerous theor. studies on metallophilic interactions continue to be carried out at various levels of sophistication which take into account relativistic and correlation effects to describe these van der Waals-type interactions. In this crit. review, we would like to focus on the synthesis and structures of heterometallic clusters of the transition metals in which intra- rather than intermol. d10-d10 interactions are at work, in order to limit the role of packing effects. We wish to provide the reader with a comparative overview of the metal core structures resulting from or favoring metallophilic interactions but do not intend to provide a comprehensive coverage of the literature. We will first examine heterometallic clusters displaying homometallic and then heterometallic d10-d10 interactions. Although the focus of this review is on d10-d10 interactions involving metals from the group 11, we shall also briefly examine for comparison some complexes displaying intramol. d10-d10 interactions involving metals from other groups (188 refs.).
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    17. 17
      Schmidbaur, H.; Schier, A. Aurophilic interactions as a subject of current research: an up-date. Chem. Soc. Rev. 2012, 41 (1), 370– 412,  DOI: 10.1039/C1CS15182G
      17
      Aurophilic interactions as a subject of current research: an up-date
      Schmidbaur, Hubert; Schier, Annette
      Chemical Society Reviews (2012), 41 (1), 370-412CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Recently accumulated exptl. evidence for aurophilic interactions in and between mol. Au(I) compds. and the results of pertinent theor. calcns. are reviewed for the period from 2007 to mid-2011. The influence of the intra- and intermol. bonding contacts between the closed-shell metal centers, Au-Au, on the mol. and crystal structures, and the consequences of these effects for the chem. and phys. properties of Au compds. are summarized for the various classes of mono- and polynuclear systems. The literature survey builds on the contents of previous reviews and relates new exptl. and theor. findings to earlier observations (353 refs.).
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    18. 18
      Schmidbaur, H.; Schier, A. A briefing on aurophilicity. Chem. Soc. Rev. 2008, 37 (9), 1931– 1951,  DOI: 10.1039/b708845k
      18
      A briefing on aurophilicity
      Schmidbaur, Hubert; Schier, Annette
      Chemical Society Reviews (2008), 37 (9), 1931-1951CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. There is now compelling exptl. evidence for the existence of specific intra- and intermol. bonding between seemingly closed-shell gold(i) centers (5d10) which manifests itself in all areas of gold chem. This "aurophilic interaction", which had not been predicted by conventional valence theory, was found to be assocd. with binding energies in some cases exceeding even those of strong hydrogen bonds and therefore to be highly significant in co-detg. mol. structure and dynamics. In high-level theor. treatments the attraction is rationalized as a "super van der Waals bonding" based on particularly strong relativistic, dispersion and correlation effects (crit. review, 265 refs.).
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    19. 19
      Lima, J. C.; Rodriguez, L. Applications of gold (I) alkynyl systems: a growing field to explore. Chem. Soc. Rev. 2011, 40 (11), 5442– 5456,  DOI: 10.1039/c1cs15123a
      19
      Applications of gold(I) alkynyl systems: a growing field to explore
      Lima, Joao Carlos; Rodriguez, Laura
      Chemical Society Reviews (2011), 40 (11), 5442-5456CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Gold(I) alkynyl complexes present a growing research field with respect to their very wide range of applications in different areas such as luminescence, mol. recognition, optical switches, electronics and catalysis. Biol. applications are also being developed in the recent years, where these complexes are used as therapeutic agents against different illnesses such as cancer cells or malaria. Related to luminescence, a general overview of the different states responsible for the obsd. emission is also included in this crit. review. In some cases, the assignment is complicated due to the influence of the gold(I) atom and its capability to form metal···metal interactions (aurophilicity). Although an extensive discussion has been found in the literature related to the luminescent properties of these complexes, to the best of our knowledge there are not reports covering the span of their very interesting applications. The widespread research fields where this kind of complexes could present a key role is presented in this review (119 refs.).
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    20. 20
      Zhao, Q.; Huang, C.; Li, F. Phosphorescent heavy-metal complexes for bioimaging. Chem. Soc. Rev. 2011, 40 (5), 2508– 2524,  DOI: 10.1039/c0cs00114g
      20
      Phosphorescent heavy-metal complexes for bioimaging
      Zhao, Qiang; Huang, Chunhui; Li, Fuyou
      Chemical Society Reviews (2011), 40 (5), 2508-2524CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. The application of phosphorescent heavy-metal complexes with d6, d8 and d10 electron configurations for bioimaging is a new and promising research field and has been attracting increasing interest. In this crit. review, we systematically evaluate the advantages of phosphorescent heavy-metal complexes as bioimaging probes, including their photophys. properties, cytotoxicity and cellular uptake mechanisms. The progress of research into the use of phosphorescent heavy-metal complexes for staining different compartments of cells, monitoring intracellular functional species, providing targeted bioimaging, two-photon bioimaging, small-animal bioimaging, multimodal bioimaging and time-resolved bioimaging is summarized. In addn., several possible future directions in this field are also discussed (133 refs.).
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    21. 21
      Zhou, G.-J.; Wong, W.-Y. Organometallic acetylides of Pt II, Au I and Hg II as new generation optical power limiting materials. Chem. Soc. Rev. 2011, 40 (5), 2541– 2566,  DOI: 10.1039/c0cs00094a
      21
      Organometallic acetylides of PtII, AuI and HgII as new generation optical power limiting materials
      Zhou, Gui-Jiang; Wong, Wai-Yeung
      Chemical Society Reviews (2011), 40 (5), 2541-2566CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compds. which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metalated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good soln. processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This crit. review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compds. Strategies including copolymn. with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophys. behavior and improve the resulting OPL responses. Special emphasis is placed on the structure-OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 refs.).
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    22. 22
      Aguiló, E.; Soler, L.; Casanovas, A.; Moro, A. J.; Lima, J. C.; Rodríguez, L.; Llorca, J. Gold (I)-complex–titania hybrid photocatalyst for hydrogen production. ChemCatChem. 2017, 9 (17), 3289– 3292,  DOI: 10.1002/cctc.201700518
      22
      Gold(I)-Complex-Titania Hybrid Photocatalyst for Hydrogen Production
      Aguilo, Elisabet; Soler, Lluis; Casanovas, Albert; Moro, Artur J.; Lima, Joao Carlos; Rodriguez, Laura; Llorca, Jordi
      ChemCatChem (2017), 9 (17), 3289-3292CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The integration of TiO2 with a AuI complex contg. a thiocoumarin moiety resulted in a very efficient photocatalyst for the generation of H2. The mol. structure of the complex was preserved under the photoreaction owing to the strong AuI-S bond. The AuI complex played a determinant role in the photogeneration of H2 by accepting the photoinduced electrons originated in TiO2 upon light exposure. This is the first example of a AuI complex semiconductor hybrid photocatalyst. The rate of H2 generation under dynamic conditions from water/ethanol is approx. one order of magnitude superior on a metal basis to that obtained over conventional TiO2 decorated with Au metal nanoparticles.
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    23. 23
      Hobbollahi, E.; List, M.; Redhammer, G.; Zabel, M.; Monkowius, U. Structural and photophysical characterization of gold (I) complexes bearing naphthyl chromophores. Inorg. Chem. Commun. 2016, 65, 24– 27,  DOI: 10.1016/j.inoche.2016.01.009
      23
      Structural and photophysical characterization of gold(I) complexes bearing naphthyl chromophores
      Hobbollahi, Elnaz; List, Manuela; Redhammer, Guenther; Zabel, Manfred; Monkowius, Uwe
      Inorganic Chemistry Communications (2016), 65 (), 24-27CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
      The authors prepd. two chlorido-Au(I) complexes L-Au-Cl bearing a naphthyl moiety. Complex 1 with L = tris(1-naphthyl)phosphine shows std. linear coordination without further aggregation in the solid state. Complex 2 with L = 2-naphthyl isonitrile is engaged in a complex network of aurophilic and π-π interactions. The two complexes show similar luminescence behavior in soln. at room temp. with both intraligand fluorescence and phosphorescence. At 77 K the emission spectra are dominated by intraligand phosphorescence, which is typical of Au complexes with extended π-chromophores.
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    24. 24
      Schmidbaur, H. The aurophilicity phenomenon: a decade of experimental findings, theoretical concepts and emerging applications. Gold Bulletin 2000, 33 (1), 3– 10,  DOI: 10.1007/BF03215477
      24
      The aurophilicity phenomenon: a decade of experimental findings, theoretical concepts and emerging applications
      Schmidbaur, Hubert
      Gold Bulletin (London) (2000), 33 (1), 3-10CODEN: GOBUFW; ISSN:1027-8591. (World Gold Council)
      A review, with 111 refs., discusses aurophilicity. The term aurophilicity was introduced in 1989 to describe phenomena in the structural chem. of Au which could not be readily rationalized by conventional concepts of chem. bonding. In the following decade the aurophilicity concept was widely applied and supported by the results of many exptl. as well as theor. studies. It will be carried over into the new millennium as a continued incentive for studies that will help in the understanding of the unique properties of Au.
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    25. 25
      Bondi, A. V. van der Waals Volumes and Radii. J. Chem. Phys. 1964, 68 (3), 441– 451,  DOI: 10.1021/j100785a001
      25
      van der Waals volumes and radii
      Bondi, A.
      Journal of Physical Chemistry (1964), 68 (3), 441-51CODEN: JPCHAX; ISSN:0022-3654.
      Intermol. van der Waals radii of the nonmetallic elements were assembled into a list of recommended values for vol. calcns. These values were arrived at by selecting from the most reliable x-ray diffraction data those which could be reconciled with crystal d. at 0°K. (to give reasonable packing d.), gas kinetic collision cross section, crit. d., and with liquid state properties. A qual. understanding of the nature of van der Waals radii is provided by correlation with the de Broglie wavelength of the outermost valence electron. Tentative values for the van der Waals radii of metallic elements in organometallic compds. are proposed. A list of increments for the vol. of mols. impenetrable to thermal collision, the so-called van der Waals vol., and of the corresponding increments in area per mol. is given.
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    26. 26
      Gavara, R.; Llorca, J.; Lima, J. C.; Rodríguez, L. A luminescent hydrogel based on a new Au (I) complex. Chem. Commun. 2013, 49 (1), 72– 74,  DOI: 10.1039/C2CC37262B
      26
      A luminescent hydrogel based on a new Au(I) complex
      Gavara, Raquel; Llorca, Jordi; Lima, Joao Carlos; Rodriguez, Laura
      Chemical Communications (Cambridge, United Kingdom) (2013), 49 (1), 72-74CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The reaction of the H2O sol. phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) with [Au(C≡C-C5H4N)]n yields the highly luminescent H2O sol. [(PTA)Au(4-pyridylethynyl)] complex. A detailed anal. of the compd. shows the formation of gel structure giving rise to long fibers, being the 1st example reported with such a simple structure.
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    27. 27
      Moro, A. J.; Avó, J.; Malfois, M.; Zaccaria, F.; Fonseca Guerra, C.; Caparrós, F. J.; Rodríguez, L.; Lima, J. C. Aggregation induced emission of a new naphthyridine-ethynyl–gold (I) complex as a potential tool for sensing guanosine nucleotides in aqueous media. Dalton Trans. 2020, 49 (1), 171– 178,  DOI: 10.1039/C9DT04162A
      27
      Aggregation induced emission of a new naphthyridine-ethynyl-gold(I) complex as a potential tool for sensing guanosine nucleotides in aqueous media
      Moro, Artur J.; Avo, Joao; Malfois, Marc; Zaccaria, Francesco; Fonseca Guerra, Celia; Caparros, Francisco J.; Rodriguez, Laura; Lima, Joao Carlos
      Dalton Transactions (2020), 49 (1), 171-178CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      A new organometallic alkynyl-gold(I) complex capable of exhibiting aggregation induced emission was designed and synthesized. The linear complex structure possesses a central Au(I) atom, bearing two axial ligands: (1) 1,3,5-triaza-7-phosphaadamantane and (2) 2-acetamido-7-ethynyl-1,8-naphthyridine. While the former accounts for its partial soly. in an aq. environment, the latter acts as a receptor unit for binding guanosine nucleotides and derivs. via multiple hydrogen bonding interactions. At high concns., aggregation of the complex was obsd. by the formation of new absorption (λmax ∼ 400 nm) and emission bands (550-700 nm). Formation of aggregates of ca. 60 nm diam. was confirmed by Small Angle X-ray Scattering (SAXS). Disruption of the aggregates in the presence of guanosine derivs. resulted in a ratiometric signal with apparent assocn. consts. in the order of 105 M-1 and high sensitivity (around 63% signal change) which are, to the best of our knowledge, in line with the highest values recorded for nucleotide sensors based on hydrogen bonding and capable of working in water. Computational studies indicate the presence of addnl. hydrogen bonding interactions that account for the strong binding of the Au(I) complex to phosphorylated guanosine nucleotides.
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    28. 28
      Tubaro, C.; Baron, M.; Costante, M.; Basato, M.; Biffis, A.; Gennaro, A.; Isse, A. A.; Graiff, C.; Accorsi, G. Dinuclear gold (I) complexes with propylene bridged N-heterocyclic dicarbene ligands: Synthesis, structures, and trends in reactivities and properties. Dalton Trans. 2013, 42 (30), 10952– 10963,  DOI: 10.1039/c3dt51260f
      28
      Dinuclear gold(I) complexes with propylene bridged N-heterocyclic dicarbene ligands: synthesis, structures, and trends in reactivities and properties
      Tubaro, Cristina; Baron, Marco; Costante, Michele; Basato, Marino; Biffis, Andrea; Gennaro, Armando; Isse, Abdirisak Ahmed; Graiff, Claudia; Accorsi, Gianluca
      Dalton Transactions (2013), 42 (30), 10952-10963CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      Four novel dinuclear N-heterocyclic dicarbene Au(I) complexes with a propylene linker between the carbene moieties were synthesized and their luminescence and electrochem. properties, together with their reactivity towards Br oxidative addn., were screened. The mol. structures of two complexes were detd. by x-ray crystallog. All the complexes emit in the solid state in the blue-green spectral range (400-500 nm) with appreciable intensities (Φem up to ≈10%). In cyclic voltammetry, the Au(I)/Au(0) peak splits at low temp. into two sep. peaks relative to the couples Au(I)-Au(I)/Au(i)-Au(0) and Au(I)-Au(0)/Au(0)-Au(0), thus indicating the presence of an Au···Au interaction in the dinuclear complex. Oxidative addn. of Br affords as a major or unique product Au(II)-Au(II) complexes most likely as a consequence of the interaction between the two Au centers favored by the propylene linker.
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    29. 29
      Luo, Z.; Yuan, X.; Yu, Y.; Zhang, Q.; Leong, D. T.; Lee, J. Y.; Xie, J. From aggregation-induced emission of Au (I)–thiolate complexes to ultrabright Au (0)@ Au (I)–thiolate core–shell nanoclusters. J. Am. Chem. Soc. 2012, 134 (40), 16662– 16670,  DOI: 10.1021/ja306199p
      29
      From Aggregation-Induced Emission of Au(I)-Thiolate Complexes to Ultrabright Au(0)@Au(I)-Thiolate Core-Shell Nanoclusters
      Luo, Zhentao; Yuan, Xun; Yu, Yue; Zhang, Qingbo; Leong, David Tai; Lee, Jim Yang; Xie, Jianping
      Journal of the American Chemical Society (2012), 134 (40), 16662-16670CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      A fundamental understanding of the luminescence of Au-thiolate nanoclusters (NCs), such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I)-thiolate complexes: strong luminescence emission by the mechanism of aggregation-induced emission (AIE). The AIE property of the complexes was then used to develop a simple 1-pot synthesis of highly luminescent Au-thiolate NCs with a quantum yield of ∼15%. Key strategy was to induce the controlled aggregation of Au(I)-thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I)-thiolate core-shell NCs where strong luminescence was generated by the AIE of Au(I)-thiolate complexes on the NC surface. The authors were able to extend the synthetic strategy to other thiolate ligands with added functionalities (as custom-designed peptides). The discovery (e.g., identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.
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    30. 30
      Au, V. K.-M.; Tsang, D. P.-K.; Wong, K. M.-C.; Chan, M.-Y.; Zhu, N.; Yam, V. W.-W. Functionalized bis-cyclometalated alkynylgold (III) complexes: synthesis, characterization, electrochemistry, photophysics, photochemistry, and electroluminescence studies. Inorg. Chem. 2013, 52 (21), 12713– 12725,  DOI: 10.1021/ic4019212
      30
      Functionalized Bis-Cyclometalated Alkynylgold(III) Complexes: Synthesis, Characterization, Electrochemistry, Photophysics, Photochemistry, and Electroluminescence Studies
      Au, Vonika Ka-Man; Tsang, Daniel Ping-Kuen; Wong, Keith Man-Chung; Chan, Mei-Yee; Zhu, Nianyong; Yam, Vivian Wing-Wah
      Inorganic Chemistry (2013), 52 (21), 12713-12725CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      A series of luminescent alkynylgold(III) complexes contg. various tridentate bis-cyclometalating ligands derived from 2,6-diphenylpyridine (R-C-N-C), [Au(R-C-N-C)(C≡C-C6H4-R')] has been successfully synthesized and characterized. Complexes 1 and 6 have been detd. by x-ray crystallog. Electrochem. studies show a ligand-centered redn. that originated from the tridentate R-C-N-C pincer ligands and an alkynyl-centered oxidn. The photophys. properties of the complexes have been studied in detail by electronic absorption and emission studies. Tunable photoluminescence behaviors have been obsd., with the emission maxima spanning through the visible region from 476 to 669 nm in dichloromethane at room temp., and the complexes were also emissive in various media at both room and low temps. Transient absorption studies have been conducted to investigate the excited state properties of the complexes. Furthermore, selected complexes have been incorporated into the emissive layer (EML) of org. light-emitting devices (OLEDs) and have demonstrated interesting electroluminescence.
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    31. 31
      Pinto, A.; Svahn, N.; Lima, J. C.; Rodríguez, L. Aggregation induced emission of gold (I) complexes in water or water mixtures. Dalton Trans. 2017, 46 (34), 11125– 11139,  DOI: 10.1039/C7DT02349A
      31
      Aggregation induced emission of gold(I) complexes in water or water mixtures
      Pinto, Andrea; Svahn, Noora; Lima, Joao Carlos; Rodriguez, Laura
      Dalton Transactions (2017), 46 (34), 11125-11139CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      A review. Gold(I) complexes are an expanding area of study due to the possibility of giving rise to supramol. aggregates with particular morphologies that can be modulated together with their luminescent properties. A detailed study was carried out for gold(I) complexes that self-assemble in aq. media (in pure water or in mixts. of water and org. solvents in different proportions). The majority of the examples reported until now were found in mixts. of water and DMSO, acetone, DMF or acetonitrile. The addn. of cations to a soln. of gold(I) complexes was obsd. to show a direct impact on the resulting process of aggregation. The use of perhalogenated ligands together with isocyanide moieties should be highlighted to promote the resulting self-organization. Nevertheless, other ligands like alkynyls or carbenes also promote self-assembly. A careful anal. of the data shows that aurophilic interactions have a key role in the formation of the resulting aggregates and in the enhancement of luminescence (aggregation induced emission, AIE).
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    32. 32
      Pinto, A.; Cunha, C.; Aullón, G.; Lima, J. C.; Rodríguez, L.; Seixas de Melo, J. S. Comprehensive Investigation of the Photophysical Properties of Alkynylcoumarin Gold(I) Complexes. J. Chem. Phys. B 2021, 125 (42), 11751– 11760,  DOI: 10.1021/acs.jpcb.1c07985
      32
      Comprehensive investigation of the photophysical properties of alkynylcoumarin gold(I) complexes
      Pinto, Andrea; Cunha, Carla; Aullon, Gabriel; Lima, Joao Carlos; Rodriguez, Laura; Seixas de Melo, J. Sergio
      Journal of Physical Chemistry B (2021), 125 (42), 11751-11760CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      Six gold(I) complexes (R3P-Au-Coum) contg. three different alkynylcoumarin chromophores (Coum) with different electron-donating and electron-withdrawing characteristics and two different water-sol. phosphanes (PR3 = PTA (a) and DAPTA (b)) have been synthesized (1a,b, unsubstituted coumarin; 2a,b, 4-Me substituted coumarin; 3a,b, 3-chloro and 4-Me substituted coumarin). A comprehensive study of the photophys. properties of the R3P-Au-Coum, together with their propynyloxycoumarin precursors 1-3, was performed in soln. at room and low temps. Spectral and photophys. characteristics of the R3P-Au-Coum essentially depend on the electronic characteristics of the propynyloxycoumarin ligand. The presence of the Au(I) atom was found to be responsible for an increase of the intersystem crossing, with triplet state quantum yield values, .vphi.T, ranging from ~ 0.05 to 0.35 and high coumarin phosphorescence quantum yield values for derivs. 1 and 2; fluorescence dominates the deactivation in derivs. 3. Efficient singlet oxygen photosensitization was obsd. for the new compds. 3a,b. From TDDFT calcns., the relevant HOMO and LUMO of the compds., i.e., those involved in the transitions, are dominated by the frontier orbitals assocd. with the coumarin core. The Au(I)-phosphane structure introduces a new transition assigned to an intraligand transition involving the phosphane ligand, and π(C≡C) system, to the p orbitals of phosphorus and gold atoms.
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    33. 33
      Pandey, M. K.; Kunchur, H. S.; Mondal, D.; Radhakrishna, L.; Kote, B. S.; Balakrishna, M. S. Rare Au··· H Interactions in Gold (I) Complexes of Bulky Phosphines Derived from 2, 6-Dibenzhydryl-4-methylphenyl Core. Inorg. Chem. 2020, 59 (6), 3642– 3658,  DOI: 10.1021/acs.inorgchem.9b03207
      33
      Rare Au···H Interactions in Gold(I) Complexes of Bulky Phosphines Derived from 2,6-Dibenzhydryl-4-methylphenyl Core
      Pandey, Madhusudan K.; Kunchur, Harish S.; Mondal, Dipanjan; Radhakrishna, Latchupatula; Kote, Basvaraj S.; Balakrishna, Maravanji S.
      Inorganic Chemistry (2020), 59 (6), 3642-3658CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Gold(I) complexes of sterically demanding phosphines derived from 2,6-dibenzhydryl-4-methylphenyl core viz: 2,6-dibenzhydryl-N,N-bis((diphenylphosphane)-methyl)-4-methylaniline (1), (2,6-dibenzhydryl-4-methylphenyl)-diphenylphosphane (2), N-(2,6-dibenzhydryl-4-methylphenyl)-1,1-diphenylphosphanamine (3), and (2,6-dibenzhydryl-4-methylphenoxy)-diphenylphosphane (4) are described. The reaction of 1 with 2 equiv of [AuCl(SMe2)] in dichloromethane yielded [{AuCl}2{Ar*N(CH2PPh2)2}] (5), which on further treatment with 2 equiv of AgSbF6 and 1 equiv of 1 produced 12-membered dimeric complex [Au2{μ-(Ar*N(CH2PPh2)2)2}][(SbF6)2] (6). A similar reaction of 5 with AgSbF6 in CH3CN afforded [{Au(NCCH3)}2{Ar*N(CH2PPh2)2}][(SbF6)2] (7). Equimolar reactions of bulky phosphines 2, 3, and 4 with [AuCl(SMe2)] resulted in [AuCl(PPh2Ar*)] (8), [AuCl(PPh2NHAr*)] (9), and [AuCl(PPh2OAr*)] (10). Complexes 9 and 10 on treatment with AgSbF6 in CH3CN produced the cationic complexes [Au(NCCH3)(PPh2NHAr*)][(SbF6)] (11) and [Au(NCCH3)(PPh2OAr*)][(SbF6)] (12), resp. The mol. structure of complex 6 revealed the presence of a strong intramol. aurophilic interaction with a Au···Au distance of 2.9720(4) Å. Careful anal. of mol. structure of 5 revealed the presence of rare Au···H-C (sp3) interactions between the gold(I) atom and one of the methylene protons of -NCH2PPh2 groups. The soln. 1H NMR signals of the methylene protons of 5 showed a considerable downfield shift (∼1 ppm) compared to that of the free ligand indicating their interactions (Au···H) with the Au atom. Complexes 8 and 10 also showed Au···H interactions in their mol. structures. The existence of the Au···H interaction was studied by variable temp. 1H NMR data in the case of complex 5 and further evinced by the QTAIM anal. in complexes 5, 8, and 10. This paper describes the synthesis of sterically demanding phosphines derived from the 2,6-dibenzhydryl-4-methylphenyl core and their AuI complexes. The AuI complexes show Au···H interactions in their mol. structures which were also supported by 1H NMR studies in the soln. state.
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    34. 34
      Pujadas, M.; Rodríguez, L. Luminescent phosphine gold (I) alkynyl complexes. Highlights from 2010 to 2018. Coord. Chem. Rev. 2020, 408, 213179,  DOI: 10.1016/j.ccr.2020.213179
      34
      Luminescent phosphine gold(I) alkynyl complexes. Highlights from 2010 to 2018
      Pujadas, Marc; Rodriguez, Laura
      Coordination Chemistry Reviews (2020), 408 (), 213179CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      An overview of the homometallic phosphine-Au(I)alkynyl complexes reported in the literature from 2010 to 2018 have been collected and reported in this review article. They have been classified for better understanding, between mononuclear and polynuclear compds. Their luminescent properties have been discussed along the text and the specific absorption and emission data collected in Annex I. This type of compds. are being used for a wide range of applications in fields such as biomedicine, chemosensors or luminescent materials among others and their interest is increasing in the last years. Some particular examples have been also selected herein.
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    35. 35
      Blanco, M. C.; Gimeno, M.; Fernández-Moreira, V.; Cámara, J.; Laguna, A. Gold (I), Phosphanes, and Alkynyls: The Perfect Allies in the Search for Luminescent Compounds. Eur. J. Inorg. Chem. 2018, 2018, 2762,  DOI: 10.1002/ejic.201701256
      35
      Gold(I), Phosphanes, and Alkynyls: The Perfect Allies in the Search for Luminescent Compounds
      Blanco, M. Carmen; Camara, Jessica; Fernandez-Moreira, Vanesa; Laguna, Antonio; Gimeno, M. Concepcion
      European Journal of Inorganic Chemistry (2018), 2018 (24), 2762-2767CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A family of mixed phosphane/alkynyl gold(I) complexes was prepd. by addn. of PPh3 or PPh2py to suspensions of the polymeric species [Au(C≡CR)n] [R = Ph, 2-pyridyl (py)] and [Au2{C≡C(CH2)3C≡C}]n. The resulting complexes are luminescent both at room and low temp., in soln. and in the solid state. The emissions are assigned to intraligand transitions assocd. with the C≡C moieties or related to 3[σ(Au-P)→π*(C≡Cpy)] transitions. The crystal structure of dinuclear complex [Au2{C≡C(CH2)3C≡C}(PPh2py)2] shows the presence of dimers stabilized by intermol. aurophilic interactions.
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    36. 36
      Chen, Z.; Huang, P.-S.; Li, Z.; Yin, J.; Yu, G.-A.; Liu, S. H. Triisocyano-based trinuclear gold (I) complexes with aggregation-induced emission (AIE) and mechanochromic luminescence characteristics. Inorg. Chim. Acta 2015, 432, 192– 197,  DOI: 10.1016/j.ica.2015.04.016
      36
      Triisocyano-based trinuclear gold(I) complexes with aggregation-induced emission (AIE) and mechanochromic luminescence characteristics
      Chen, Zhao; Huang, Peng-Shou; Li, Zheng; Yin, Jun; Yu, Guang-Ao; Liu, Sheng Hua
      Inorganica Chimica Acta (2015), 432 (), 192-197CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
      Three novel trinuclear Au(I) complexes were designed and synthesized. These Au(I) complexes exhibit aggregation-induced emission characteristics. The luminescence properties of these luminogens show off-on green fluorescence in response to mech. grinding. The changing of weak multiple intermol. C-H···F or π-π interactions, or the formation of aurophilic interactions are possibly responsible for their mechanochromism phenomena.
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    37. 37
      Wu, Z. N.; Yao, Q. F.; Chai, O. J. H.; Ding, N.; Xu, W.; Zang, S. Q.; Xie, J. P. Unraveling the Impact of Gold(I)-Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters. Angew. Chem. 2020, 59 (25), 9934– 9939,  DOI: 10.1002/anie.201916675
      37
      Unraveling the Impact of Gold(I)-Thiolate Motifs on the Aggregation-Induced Emission of Gold Nanoclusters
      Wu, Zhennan; Yao, Qiaofeng; Chai, Osburg Jin Huang; Ding, Nan; Xu, Wen; Zang, Shuangquan; Xie, Jianping
      Angewandte Chemie, International Edition (2020), 59 (25), 9934-9939CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Aggregation-induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. The impact of surface AuI-thiolate motifs on the AIE properties of Au NCs is revealed, by using H2O-sol. glutathione (GSH)-coordinated Au complexes and NCs as a model ([Au10SR10], [Au15SR13], [Au18SR14], and [Au25SR18]-, SR = thiolate ligand). Spectroscopic studies show that the emission wavelength of Au NCs is adjustable from visible to the near-IR II (NIR-II) region by controlling the length of the AuI-SR motifs on the NC surface. Decreasing the length of AuI-SR motifs also changes the origin of cluster luminescence from AIE-type phosphorescence to Au0-core-dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in soln.
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    38. 38
      Zheng, L. B.; Ye, X. Y.; Qi, P.; Zhang, D.; Sun, Y. Fluorometric detection of sulfate-reducing bacteria via the aggregation-induced emission of glutathione-gold(I) complexes. Microchim. Acta 2019, 186 (6). DOI: 10.1007/s00604-019-3427-4
      There is no corresponding record for this reference.
    39. 39
      Shu, T.; Cheng, X. J.; Wang, J. X.; Lin, X. F.; Zhou, Z. P.; Su, L.; Zhang, X. J. Synthesis of Luminescent Gold Nanoclusters Embedded Goose Feathers for Facile Preparation of Au(I) Complexes with Aggregation-Induced Emission. ACS Sustainable Chem. Eng. 2019, 7 (1), 592– 598,  DOI: 10.1021/acssuschemeng.8b04124
      39
      Synthesis of Luminescent Gold Nanoclusters Embedded Goose Feathers for Facile Preparation of Au(I) Complexes with Aggregation-Induced Emission
      Shu, Tong; Cheng, Xiaojun; Wang, Jianxing; Lin, Xiangfang; Zhou, Ziping; Su, Lei; Zhang, Xueji
      ACS Sustainable Chemistry & Engineering (2019), 7 (1), 592-598CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
      A new kind of luminescent hybrid materials based on ultrasmall nanomaterials, i.e., Au nanoclusters (AuNCs) and goose feathers, precious gifts from nature, was successfully synthesized. Goose feathers possess high sp. surface area due to their hierarchical structure and are mainly composed of thiol-rich proteins, for example, keratin, which can reduce Au(III) and encapsulate the formed AuNCs in a large scale. The resultant golden feathers exhibit bright red luminescence under UV light, of which the substructures, i.e., barbs and barbules, were sufficiently stained with red-emitting AuNCs. Also, the AuNC-stained feathers maintain almost unchanged structure (solid and hierarchical) and intact chem. compn. The features of such AuNC/feather hybrids, for example, bulk, high sp. surface, inspired one to develop a facile method to prep. various valuable debris from AuNC-based etching, i.e., Au(I) complexes with aggregation-induced emission (AIE). The authors selected tris(2-carboxyethyl)phosphine and cysteamine as etchants, resp., which were previously reported to be able to synthesize AIE-featured Au(I) complexes through etching AuNCs protected by sol. protein. Conveniently, in this approach, the protein-free Au(I) complexes in soln. can be attained simply by taking out with bare hand. After cation aggregation inducer was added, for example, Cd2+, the nonemitting soln. can generate bright luminescence, demonstrating the feasibility to synthesize the precious AIE-type Au(I) complexes. This study not only boosts the development of luminescent Au materials through rational use of natural product, enriching the library of Au nanomaterials, but also definitely provides a new view of nanoclusters as reagents to prep. other noble materials.
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    40. 40
      Wang, X. Y.; Zhang, J.; Dong, Y. B.; Zhang, Y. Y.; Yin, J.; Liu, S. H. Different structures modulated mechanochromism and aggregation-induced emission in a series of Gold(I) complexes. Dyes Pigm. 2018, 156, 74– 81,  DOI: 10.1016/j.dyepig.2018.03.062
      40
      Different structures modulated mechanochromism and aggregation-induced emission in a series of Gold(I) complexes
      Wang, Xiao-Yan; Zhang, Jing; Dong, Yu-Bao; Zhang, Yiyue; Yin, Jun; Liu, Sheng Hua
      Dyes and Pigments (2018), 156 (), 74-81CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
      Five novel Au(I) complexes with various isocyanide ligands were synthesized and characterized in the present work. The introduction of different terminal ligands endows distinct diverse properties onto the complexes: (i) alkyl modified complexes exhibit tricolor or bicolor mechanochromic behaviors due to the loose packing formed through weak intermol. C-H···F interactions, while aryl bridged complexes are not mechano-responsive with tight π-π stackings; (ii) all the target complexes present prominent but different aggregation-induced emission (AIE) characteristics caused by the inherent difference in their structures. Therefore, the above Au(I) complexes are anticipated to be used as fluorescent detectors and mechanosensors.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXnt1ehtbs%253D&md5=8ecf4704898554a4e4b9e68c6693b1fd
    41. 41
      Chen, Z.; Liu, G.; Pu, S. Z.; Liu, S. H. Carbazole-based aggregation-induced emission (AIE)-active gold(I) complex: Persistent room-temperature phosphorescence, reversible mechanochromism and vapochromism characteristics. Dyes Pigm. 2017, 143, 409– 415,  DOI: 10.1016/j.dyepig.2017.05.003
      41
      Carbazole-based aggregation-induced emission (AIE)-active gold(I) complex: Persistent room-temperature phosphorescence, reversible mechanochromism and vapochromism characteristics
      Chen, Zhao; Liu, Gang; Pu, Shouzhi; Liu, Sheng Hua
      Dyes and Pigments (2017), 143 (), 409-415CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
      A carbazole-based gold(I) complex 1 (I) was successfully synthesized. Its structure was characterized by NMR spectroscopy, elemental anal. and single crystal x-ray diffractometry. Its aggregation-induced emission behavior was studied by UV/visible, photoluminescence spectroscopy and scanning electron microscope. Its solid-state mechanochromic and thin-film vapochromic luminescence behaviors were also studied by photoluminescence spectroscopy. Luminogen 1 showed obvious aggregation-induced emission property. Furthermore, 1 also exhibited reversible high-contrast mechanochromic and vapochromic luminescence behaviors. More interestingly, 1 can emit persistent room-temp. phosphorescence with a solid-state emission lifetime up to 86.84 ms, which is the highest lifetime value among all the reported gold(I) complexes so far. To the best of the authors' knowledge, the gold(I) complex is the first example of an AIE-active luminogen with persistent room-temp. phosphorescence, reversible mechanochromism and vapochromism characteristics.
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    42. 42
      Sun, W. J.; Luo, L.; Feng, Y. S.; Cai, Y. T.; Zhuang, Y. X.; Xie, R. J.; Chen, X. Y.; Chen, H. M. Aggregation-Induced Emission Gold Clustoluminogens for Enhanced Low-Dose X-ray-Induced Photodynamic Therapy. Angew. Chem. 2020, 59 (25), 9914– 9921,  DOI: 10.1002/anie.201908712
      42
      Aggregation-Induced Emission Gold Clustoluminogens for Enhanced Low-Dose X-ray-Induced Photodynamic Therapy
      Sun, Wenjing; Luo, Li; Feng, Yushuo; Cai, Yuting; Zhuang, Yixi; Xie, Rong-Jun; Chen, Xiaoyuan; Chen, Hongmin
      Angewandte Chemie, International Edition (2020), 59 (25), 9914-9921CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The use of gold nanoparticles as radiosensitizers is an effective way to boost the killing efficacy of radiotherapy while drastically limiting the received dose and reducing the possible damage to normal tissues. Herein, we designed aggregation-induced emission gold clustoluminogens (AIE-Au) to achieve efficient low-dose X-ray-induced photodynamic therapy (X-PDT) with negligible side effects. The aggregates of glutathione-protected gold clusters (GCs) assembled through a cationic polymer enhanced the X-ray-excited luminescence by 5.2-fold. Under low-dose X-ray irradn., AIE-Au strongly absorbed X-rays and efficiently generated hydroxyl radicals, which enhanced the radiotherapy effect. Addnl., X-ray-induced luminescence excited the conjugated photosensitizers, resulting in a PDT effect. The in vitro and in vivo expts. demonstrated that AIE-Au effectively triggered the generation of reactive oxygen species with an order-of-magnitude redn. in the X-ray dose, enabling highly effective cancer treatment.
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    43. 43
      Seixas de Melo, J. S.; Cabral, C.; Lima, J. C.; Macanita, A. L. Characterization of the singlet and triplet excited states of 3-chloro-4-methylumbelliferone. J. Chem. Phys. A 2011, 115 (30), 8392– 8398,  DOI: 10.1021/jp204354x
      43
      Characterization of the Singlet and Triplet Excited States of 3-Chloro-4-methylumbelliferone
      Seixas de Melo, J. Sergio; Cabral, Catarina; Lima, Joao C.; Macanita, Antonio L.
      Journal of Physical Chemistry A (2011), 115 (30), 8392-8398CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      An extensive photophys. characterization of 3-chloro-4-methylumbelliferone (3Cl4MU) in the ground-state, S0, first excited singlet state, S1, and lowest triplet state, T1, was undertaken in water, neutral ethanol, acidified ethanol, and basified ethanol. Quant. measurements of quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion, and singlet oxygen formation) together with lifetimes were obtained at room and low temp. in water, dioxane/water mixts., and alcs. The different transient species were assigned and a general kinetic scheme is presented, summarizing the excited-state multiequil. of 3Cl4MU. In water, the equil. is restricted to neutral (N*) and anionic (A*) species, both in the ground (pKa = 7.2) and first excited singlet states (pKa* = 0.5). In dioxane/water mixts. (pH ca. 6), substantial changes of the kinetics of the S1 state were obsd. with the appearance of an addnl. tautomeric T* species. In low water content mixts. (mixt. 9:1 v:v), only the neutral (N*) and tautomeric (T*) forms of 3Cl4MU are obsd., whereas at higher water content mixts. (water mole fraction superior to 0.45), all three species N*, T*, and A* coexist in the excited state. In the triplet state, in the nonprotic and nonpolar solvent dioxane, the obsd. transient signals were assigned as the triplet-triplet transition of the neutral form, N*T1 → N*Tn. In water, two transient species were obsd. and are assigned as the triplets of the neutral N*T1 and the anionic form, A*T1 (also obtained in basified ethanol). The phosphorescence spectra and decays of 3Cl4MU, in neutral, acidified, and basified solns., demonstrate that only these two species N*T1 and A*T1 exist in the lowest lying triplet state, T1. The radiative channel was found dominant for the deactivation of the anionic species, whereas with the neutral the S1 (symbol) S0 internal conversion competes with fluorescence. For both N* and A* the intersystem crossing yield represents a minor deactivation channel for S1.
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    44. 44
      Oliveira, E.; Capelo, J. L.; Lima, J. C.; Lodeiro, C. Novel emissive bio-inspired non-proteinogenic coumarin-alanine amino acid: fluorescent probe for polyfunctional systems. Amino Acids 2012, 43 (4), 1779– 1790,  DOI: 10.1007/s00726-012-1262-6
      44
      Novel emissive bio-inspired non-proteinogenic coumarin-alanine amino acid: fluorescent probe for polyfunctional systems
      Oliveira, Elisabete; Capelo, Jose Luis; Lima, Joao Carlos; Lodeiro, Carlos
      Amino Acids (2012), 43 (4), 1779-1790CODEN: AACIE6; ISSN:0939-4451. (SpringerWienNewYork)
      Two new bio-inspired non-proteinogenic compds. L1 and L2, contg. coumarin and/or acridine chromophores and bearing as spacer an alanine amino acid were successfully synthesized and fully characterized by elemental anal., 1H and 13C NMR, IR spectroscopy (KBr disks), m.p., ESI-TOF (electrospray ionization-time of flight-mass), UV-vis absorption and emission spectroscopy, fluorescence quantum yields and lifetime measurements. A relative fluorescence quantum yield of 0.02 was detd. for both compds. In L2 the presence of an intramol. energy transfer from the coumarin to the acridine unit was obsd. L1 and L2 are quite sensitive to the basicity of the environment. At alk. values both compds. show a strong quenching in the fluorescence emission, attributed to the photoinduced electron transfer (PET). However, both deprotonated forms recover the emission with the addn. of Zn2+, Cd2+ and Al3+ metal ions. As multifunctional emissive probes, the titrn. of L1 and L2 with lanthanides (III), Eu3+ and Tb3+ was also explored as new visible bio-probes in the absence and in the presence of liposomes. In a liposomal environment a lower energy transfer was obsd.
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    45. 45
      Heldt, J. R.; Heldt, J.; Stoń, M.; Diehl, H. A. Photophysical properties of 4-alkyl-and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time. Spectrochimica Acta Part A 1995, 51 (9), 1549– 1563,  DOI: 10.1016/0584-8539(95)01467-9
      45
      Photophysical properties of 4-alkyl- and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time
      Heldt, Janina R.; Heldt, Jozef; Ston, Marek; Diehl, Horst A.
      Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy (1995), 51A (9), 1549-63CODEN: SAMCAS; ISSN:0584-8539. (Elsevier)
      4-Alkyl- and 7-alkoxycoumarin derivs. have been investigated for their spectroscopic properties in three different solvents. The substitutions are Me, Et, Pr and Bu groups. Absorption and emission spectra, quantum yields and mean fluorescence decay times have been detd. The spectroscopic studies together with calcns. of the radiative transition probabilities indicate that the 4-alkyl- and 7-alkoxy substituents do not change the symmetry of the electronic cloud of the coumarin skeleton. The changes obsd. for the rates of radiative transitions and also for the positions of the absorption and emission maxima can be explained by changes in the mol. electronic transition moment, caused by the weak donation potential of the substituents. A strong dependence of the quantum yields and mean fluorescence decay times on solvent viscosity has been found, leading to the suggestion that torsional rotations of the alkyl and alkoxy substituents significantly increase the internal non-radiative energy conversion rate.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXos1Skurk%253D&md5=a379cbae2d5b5ac3e1ec9e2923f7ca55
    46. 46
      Seixas de Melo, J. S.; Fernandes, P. F. Spectroscopy and photophysics of 4-and 7-hydroxycoumarins and their thione analogs. J. Mol. Struct. 2001, 565, 69– 78,  DOI: 10.1016/S0022-2860(01)00458-6
      46
      Spectroscopy and photophysics of 4- and 7-hydroxycoumarins and their thione analogs
      Seixas de Melo, J.; Fernandes, P. F.
      Journal of Molecular Structure (2001), 565-566 (), 69-78CODEN: JMOSB4; ISSN:0022-2860. (Elsevier Science B.V.)
      Acid-base equil. were studied for 4-hydroxycoumarin, 7-hydroxy-4-methylcoumarin and their thione derivs. in different media for their ground and lowest energy singlet and triplet excited states. The ethoxylated and/or methoxylated derivs. were also investigated. Characterization involves fluorescence spectra, quantum yields, lifetimes, phosphorescence spectra, lifetimes, and triplet-triplet absorption spectra. From their pKa values it was found that 4- and 7-hydroxycoumarins are more acidic in their lowest excited singlet states than in S0. The origin and character of the lowest singlet and triplet excited states is discussed.
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    47. 47
      de Castro, C. S.; Cova, T. F.; Pais, A. C.; Pinheiro, D.; Nunez, C.; Lodeiro, C.; Seixas de Melo, J. S. Probing metal cations with two new Schiff base bischromophoric pyrene based chemosensors: Synthesis, photophysics and interactions patterns. Dyes Pigm. 2016, 134, 601– 612,  DOI: 10.1016/j.dyepig.2016.08.016
      47
      Probing metal cations with two new Schiff base bischromophoric pyrene based chemosensors: Synthesis, photophysics and interactions patterns
      de Castro, Catherine S.; Cova, Tania F. G. G.; Pais, Alberto C. C.; Pinheiro, Daniela; Nunez, Cristina; Lodeiro, Carlos; Seixas de Melo, J. Sergio
      Dyes and Pigments (2016), 134 (), 601-612CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
      Two new pyrene chemosensors (bipyrenyl ligands L1 and L2) were synthesized, fully characterized and their sensing ability towards metal cations (Cu2+, Ag+, Pb2+, Zn2+, Cd2+ and Hg2+) was studied by absorption and fluorescence (steady-state and time-resolved) techniques in soln. The absorption spectra of the two free ligands displays a single band (attributed to the monomer absorption) whereas the emission spectra show two bands, which were attributed to the emission of the monomer and dimer. For L1, time-resolved fluorescence measurements indicate a single component that becomes double exponential when the metal ion (in the studied case, Pb2+) is added. From both steady-state and time-resolved data this dimer likely involves the interaction of two pyrene units, but the absence of a rising component in the fluorescence decays discards the possibility of the presence of a dynamic excimer. Upon addn. of a metal ion, this band changes in shape mirroring the fact that a new complex, involving the metal ion and the ligand, is formed. From the overall spectroscopic and photophys. data rationalized by Hierarchical Cluster Anal. (HCA) and Principal Component Anal. (PCA) both L1 and L2 ligands are able to discriminate Ag+ and Pb2+ from all the other metal ions, with L2 displaying a higher sensing ability (as seen from HCA/PCA anal.) towards Pb2+. This global approach, joining spectral and photophys. data with multivariate anal., showed to constitute a powerful tool for revealing important patterns in this type of system.
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    48. 48
      Seixas de Melo, J. S.; Becker, R. S.; Macanita, A. L. Photophysical behavior of coumarins as a function of substitution and solvent: experimental evidence for the existence of a lowest lying 1 (n, pi.*) state. J. Chem. Phys. 1994, 98 (24), 6054– 6058,  DOI: 10.1021/j100075a002
      48
      Photophysical Behavior of Coumarins as a Function of Substitution and Solvent: Experimental Evidence for the Existence of a Lowest Lying 1(n,π*) State
      Seixas de Melo, J. Sergio; Becker, Ralph S.; Macanita, Antonio L.
      Journal of Physical Chemistry (1994), 98 (24), 6054-8CODEN: JPCHAX; ISSN:0022-3654.
      The nature of the lowest excited state for coumarin and some derivs. was investigated using steady-state and time-resolved fluorescence data at room temp., as well as fluorescence anisotropy at 77 K in nonpolar and polar solvents in conjunction with theor. data obtained with different methods: INDO/S-CI, CNDO/S-CI, MNDO-CI, and AM1-CI. The results show that S1 is actually n,π* for coumarin in any solvent. Substitution with methoxy and Me and/or chlorine and/or an increase of solvent polarity reduces the energy gap between the S1 (n,π*) and S2 (π,π*) states, promoting the mixing of these states and finally inducing inversion to S1 (π,π*) with trisubstitution and for the disubstituted case in dioxane-water (1:4). The presence of a lowest lying S1 (n,π*) mediates a large degree of radiationless processes in the singlet manifold.
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    49. 49
      Seixas de Melo, J. S.; Becker, R. S.; Elisei, F.; Maçanita, A. The photophysical behavior of 3-chloro-7-methoxy-4-methylcoumarin related to the energy separation of the two lowest-lying singlet excited states. J. Chem. Phys. 1997, 107 (16), 6062– 6069,  DOI: 10.1063/1.474274
      49
      The photophysical behavior of 3-chloro-7-methoxy-4-methylcoumarin related to the energy separation of the two lowest-lying singlet excited states
      Seixas de Melo, J.; Becker, Ralph S.; Elisei, Fausto; Macanita, A. L.
      Journal of Chemical Physics (1997), 107 (16), 6062-6069CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The photophys. behavior of 3-chloro-7-methoxy-4-methylcoumarin (ClMMC) was studied as a function of the solvent and temp. The radiative lifetime τF0 = 1/kF is essentially solvent independent and its value (≈4.6 ns) is totally commensurate with the fluorescence originating from a 1(π,π*) state as the lowest excited state. From the fluorescence data obtained in 24 solvents plus nine solvent mixts., and the triplet formation quantum yields for three representative solvents, it was found that the internal conversion rate const. (kIC) dictates the photophys. behavior of ClMMC and changes of two orders of magnitude occur from nonpolar to polar solvents. From the temp. dependence (20 to -100 °C) of the fluorescence lifetimes in five solvents it was found that a change of the internal conversion rate const. of the same order of magnitude occurred as above. The rate consts. and the activation energies for the radiationless processes were detd. The results show that the reason for the dramatic variation of kIC is the fact that when the S2(n,π*) state is close lying to S1(π,π*), there is a decrease of the activation energy of the internal conversion process (S1∼∼→S0). Increasing solvent polarity increases the energy gap between these states, and decreases the magnitude of the effect. Decreasing the temp. to sufficiently low values, disables the deactivation channel. The interpretation of the foregoing results can be satisfied by either a model involving a fast equil. between two close lying S2 and S1 states or in terms of the so-called "proximity effect.".
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    50. 50
      Bardají, M.; Teresa de la Cruz, M.; Jones, P. G.; Laguna, A.; Martínez, J.; Dolores Villacampa, M. Luminescent dinuclear gold complexes of bis (diphenylphosphano) acetylene. Inorg. Chim. Acta 2005, 358 (5), 1365– 1372,  DOI: 10.1016/j.ica.2004.05.017
      50
      Luminescent dinuclear gold complexes of bis(diphenylphosphano)acetylene
      Bardaji, Manuel; de la Cruz, M. Teresa; Jones, Peter G.; Laguna, Antonio; Martinez, Julia; Villacampa, M. Dolores
      Inorganica Chimica Acta (2005), 358 (5), 1365-1372CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
      The authors synthesized dinuclear Au(I) derivs. with the diphosphine bis(diphenylphosphino)acetylene (dppa), [(AuX)2(μ-dppa)] (I; X = Cl, C6F5, SC6F5, S2CN(CH2Ph)2). X-ray structure detns. for I (X = = Cl, C6F5, SC6F5)reveal a linear geometry for the Au centers. There are no intramol. Au-Au interactions, although for X = Cl intermol. Au(I)-Au(I) interactions of 3.0694(4) Å lead to an infinite twisted chain; the further presence of C-H···Cl contacts leads to a more complex three-dimensional structure. All the derivs. are luminescent in the solid state at low temp. in the range 455-593 nm; most of them are emissive at room temp. in the range 470-598 nm. The authors also prepd. the dinuclear Au(III) deriv. [(Au(C6F5)3)2(μ-dppa)]. Finally, the authors prepd. [(AuCl)2(μ-dppa)3], which forms a cage with two tetrahedrally coordinated Au(I) centers at the apical positions bridged by three rigid diphosphine ligands, with a helical twist of 26.2°, and a Au-Au distance of 5.769 Å. The Au(III) and the four-coordinate Au(I) derivs. are not luminescent.
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    51. 51
      Ferrer, M.; Gutiérrez, A.; Rodríguez, L.; Rossell, O.; Lima, J. C.; Font-Bardia, M.; Solans, X. Study of the Effect of the Phosphane Bridging Chain Nature on the Structural and Photophysical Properties of a Series of Gold(I) Ethynylpyridine Complexes; Wiley-VCH Verlag: Weinheim, Germany, 2008.
      There is no corresponding record for this reference.
    52. 52
      Arcau, J.; Andermark, V.; Aguiló, E.; Gandioso, A.; Moro, A.; Cetina, M.; Lima, J. C.; Rissanen, K.; Ott, I.; Rodríguez, L. Luminescent alkynyl-gold (I) coumarin derivatives and their biological activity. Dalton Trans. 2014, 43 (11), 4426– 4436,  DOI: 10.1039/C3DT52594E
      52
      Luminescent alkynyl-gold(I) coumarin derivatives and their biological activity
      Arcau, Julia; Andermark, Vincent; Aguilo, Elisabet; Gandioso, Albert; Moro, Artur; Cetina, Mario; Lima, Joao Carlos; Rissanen, Kari; Ott, Ingo; Rodriguez, Laura
      Dalton Transactions (2014), 43 (11), 4426-4436CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      The synthesis and characterization of three propynyloxycoumarins are reported in this work together with the formation of three different series of gold(I) organometallic complexes. Neutral complexes are constituted by water sol. phosphines (PTA and DAPTA) which confer water soly. to them. The x-ray crystal structure of 7-(prop-2-in-1-yloxy)-1-benzopyran-2-one and its corresponding dialkynyl complex is also shown and the formation of rectangular dimers for the gold deriv. in the solid state can be obsd. A detailed anal. of the absorption and emission spectra of both ligands and complexes allows us to attribute the luminescent behavior to the coumarin org. ligand. Moreover, the presence of the gold(I) metal atom seems to be responsible for an increase of coumarin phosphorescence emission. The biol. activity of the complexes showed that the anionic complexes triggered strong cytotoxic effects in two different cell lines whereas the neutral gold alkynyl complexes led to lower effects against tumor cell growth. Thioredoxin reductase (TrxR) inhibition was very strong in the case of the neutral complexes (IC50 values below 0.1 μM) but moderate for the anionic complexes (IC50 values above 0.8 μM).
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    53. 53
      Seixas de Melo, J. S. The influence of oxygen on the lifetime of luminescent probes. A simple device for degassing solutions for fluorescence measurements. Chem. Educ. 2005, 10 (05), 29– 35
      53
      The influence of oxygen on the lifetime of luminescent probes. A simple device for degassing solutions for fluorescence measurements
      Seixas de Melo, Joao
      Chemical Educator (2005), 10 (1), 29-35CODEN: CHEDF5; ISSN:1430-4171. (Chemical Educator)
      The lifetime of an emissive species is one fundamental characteristic assocd. with its emission. Degassing solns. (by removing or replacing of oxygen with another gas) is a crit. exptl. procedure for time-resolved fluorescence studies. It is generally considered that oxygen is a strong quencher of fluorescent probes, in particular of those with long lifetimes. The importance of efficient deoxygenation for luminescence measurements is discussed and, in addn., a simple device for conducting this procedure is described. This can replace the use of freeze-pump-thaw cycles in vacuum-scaled cuvettes, avoiding both working with high-vacuum conditions and handling low-temp. systems. The simple design of the fluorescence cell consists of two Teflon stopcocks with a ring-sealed immersion tube and a fitting for a purging gas. The cuvette is novel and is useful in various situations particularly those where stringent degassing is required. The effect of variable oxygen concns. on the fluorescence decays is described and some common examples are used to illustrate this point and to test the reliability of the fluorescence lifetimes obtained with the device. The control of this variable is important for any type of expt. involving fluorescence.
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    54. 54
      Magde, D.; Wong, R.; Seybold, P. G. Fluorescence quantum yields and their relation to lifetimes of rhodamine 6G and fluorescein in nine solvents: Improved absolute standards for quantum yields¶. Photochem. Photobiol. 2002, 75 (4), 327– 334,  DOI: 10.1562/0031-8655(2002)075<0327:FQYATR>2.0.CO;2
      54
      Fluorescence quantum yields and their relation to lifetimes of rhodamine 6G and fluorescein in nine solvents: improved absolute standards for quantum yields
      Magde, Douglas; Wong, Roger; Seybold, Paul G.
      Photochemistry and Photobiology (2002), 75 (4), 327-334CODEN: PHCBAP; ISSN:0031-8655. (American Society for Photobiology)
      Abs. fluorescence quantum yields are reported for the rhodamine 6G cation and the fluorescein dianion dyes in nine hydroxyl-contg. solvents. This information is combined with previously reported fluorescence lifetimes to deduce radiative and nonradiative decay rates. Along the alc. series from methanol to octanol, rhodamine 6G displays an increasing radiative rate, in parallel with the square of the refractive index increase, and a slightly decreasing nonradiative rate. Fluorescein is different: the apparent radiative rate actually decreases, suggesting that the emissive species is perturbed in some fashion. For both dyes, fluorescence yields are enhanced in D2O, rising to 0.98, in parallel with a corresponding increase in lifetimes. Protonated solvents invariably give shorter lifetimes and lower quantum yields, contrary to some previous speculation. From this work and an anal. of existing literature values, more precise values have been obtained for two previously proposed abs. quantum yield stds. The yield of fluorescein in 0.1 N aq. NaOH is 0.925 ± 0.015, and for rhodamine 6G in ethanol, it is 0.950 ± 0.015. In both cases, the solns. are assumed to be in the limit of low concn., excited close to their long-wave absorption band and at room temp. but may be either air-satd. or free of oxygen.
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    55. 55
      Kristiansen, M.; Scurlock, R. D.; Iu, K. K.; Ogilby, P. R. Charge-transfer state and singlet oxygen (1. DELTA. g O2) production in photoexcited organic molecule-molecular oxygen complexes. J. Phys. Chem. 1991, 95 (13), 5190– 5197,  DOI: 10.1021/j100166a051
      55
      Charge-transfer state and singlet oxygen (1Δg O2) production in photoexcited organic molecule-molecular oxygen complexes
      Kristiansen, Marianne; Scurlock, Rodger D.; Iu, Kai Kong; Ogilby, Peter R.
      Journal of Physical Chemistry (1991), 95 (13), 5190-7CODEN: JPCHAX; ISSN:0022-3654.
      A mol. was chosen whose CT state energy is substantially higher than that of 3M1. Relative 1Δg O2 and 1M1 yields were detd. upon (1) photolysis into the M-O2 CT band of 1-methylnaphthalene and (2) 3Σg- O2 quenching of triplet 1-methylnaphthalene, which was independently produced. In nonpolar solvents, 1Δg O2 and 3M1 yields were independent of the *(M-O2) prodn. method, indicating that relaxation of the 1,3CT states to the 1,3(3M1...3Σg- O2) states is very efficient. In a polar solvent where the CT state is more stable, the data indicate that direct coupling between the CT and ground-state surface [3(1M0...3Σg- O2] may increase. CT-mediated indirect coupling of the 1,3(3M1...3Σg- O2), and other M-O2 excited states, to the ground-state surface should also increase in a polar solvent. 1Δg O2 quantum yields obtained upon direct photolysis (1M0 → 1M1) of 6 arom. hydrocarbons support this interpretation. The data are consistent with a model for oxygen-induced intersystem crossing in org. mols. in which coupling between singlet and triplet states is facilitated by mixing with a CT state.
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    56. 56
      Prusti, B.; Chakravarty, M. An electron-rich small AIEgen as a solid platform for the selective and ultrasensitive on-site visual detection of TNT in the solid, solution and vapor states. Analyst 2020, 145 (5), 1687– 1694,  DOI: 10.1039/C9AN02334H
      56
      An electron-rich small AIEgen as a solid platform for the selective and ultrasensitive on-site visual detection of TNT in the solid, solution and vapor states
      Prusti, Banchhanidhi; Chakravarty, Manab
      Analyst (Cambridge, United Kingdom) (2020), 145 (5), 1687-1694CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
      Promising research on AIEgen (aggregation-induced emission active fluorogens)-based sensors for the detection of explosives (mostly picric acid) is primarily dominated by polymeric mols. However, herein, we report the ability of a recently developed anthracene-based electron-rich π-conjugate as a small and suitable AIEgen for the selective and sensitive detection of 2,4,6-trinitrotoluene (TNT) through fluorescence (PL) quenching. This fluorophore consists of trimethoxybenzene-linked anthranyl-π-phenothiazine, which is recognized as a significantly electron-rich AIEgen suitable for the selective detection of TNT detection. The detection of TNT was performed in the solid, liq. and vapor states using this AIEgen in the aggregate or solid-state. The detection limit in the soln. state was measured to be 3.2 × 10-9 M. When this fluorophore was impregnated on a paper strip for on-site visual detection, TNT was detected up to the 10-14 M level by the naked eye using a 365 nm UV-torch. The paper strip was also successfully used to detect TNT in the vapor state. This application was further extended to detect TNT in field soil. The detection of TNT by replacing trimethoxybenzene in the fluorophore with dimethoxy or monomethoxy was a failure, indicating the requirement of an adequate electron-rich system. Unlike the previous report with static quenching as the main reason for TNT detection, our exptl. observations demonstrated the participation of favorable photo-induced electron transfer (PET) between TNT and the fluorophore as the origin of the PL quenching.
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    57. 57
      Striker, G.; Subramaniam, V.; Seidel, C. A.; Volkmer, A. Photochromicity and fluorescence lifetimes of green fluorescent protein. J. Phys. Chem. B 1999, 103 (40), 8612– 8617,  DOI: 10.1021/jp991425e
      57
      Photochromicity and Fluorescence Lifetimes of Green Fluorescent Protein
      Striker, George; Subramaniam, Vinod; Seidel, Claus A. M.; Volkmer, Andreas
      Journal of Physical Chemistry B (1999), 103 (40), 8612-8617CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      The green fluorescent protein (GFP) of the bioluminescent jellyfish Aequorea and its mutants have gained widespread usage as an indicator of structure and function within cells. Proton transfer has been implicated in the complex photophysics of the wild-type mol., exhibiting a protonated A species excited at 400 nm, and two deprotonated excited-state species I* and B* with red-shifted excitation ∼475 nm. Photochromicity between the protonated and deprotonated species has been reported upon 400 nm excitation. Using precise time-resolved spectroscopy, we have been able to distinguish the fluorescence lifetimes of the I and B species (∼3.3 and ∼2.8 ns, resp.) and show that the irreversible photochromicity which we observe is due to formation in the excited state of the B species, which cannot return to other species in the ground state. The ground state A and I species are in thermal equil. Anisotropy measurements indicate that the chromophore lies rigidly in the mol. with a rotational correlation time of ∼15.5 ns, as is to be expected for a mol. of this size. Time-resolved measurements of enhanced yellow fluorescent protein (EYFP) and red-shifted green fluorescent protein (RSGFP) were also analyzed.
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    58. 58
      Jiang, R.; Liu, M.; Chen, T.; Huang, H.; Huang, Q.; Tian, J.; Wen, Y.; Cao, Q.-y.; Zhang, X.; Wei, Y. Facile construction and biological imaging of cross-linked fluorescent organic nanoparticles with aggregation-induced emission feature through a catalyst-free azide-alkyne click reaction. Dyes Pigm. 2018, 148, 52– 60,  DOI: 10.1016/j.dyepig.2017.09.005
      58
      Facile construction and biological imaging of cross-linked fluorescent organic nanoparticles with aggregation-induced emission feature through a catalyst-free azide-alkyne click reaction
      Jiang, Ruming; Liu, Meiying; Chen, Tingting; Huang, Hongye; Huang, Qiang; Tian, Jianwen; Wen, Yuanqing; Cao, Qian-yong; Zhang, Xiaoyong; Wei, Yen
      Dyes and Pigments (2018), 148 (), 52-60CODEN: DYPIDX; ISSN:0143-7208. (Elsevier Ltd.)
      The research in fluorescent org. nanoparticles (FONs) with aggregation-induced emission (AIE) feature shows an upward trend due to their outstanding optical properties and potential biomedical applications. In this work, a novel strategy has been developed for the first time through a catalyst-free azide-alkyne click reaction, which could directly conjugate azide contg. polymers (PEGMA-AGE-N3) and alkyne terminating AIE dye (named as PhE-OE) under mild exptl. conditions. The final PEGMA-AGE-PhE copolymers contg. AIE-active dye could self-assemble into FONs with intense fluorescence owing to their AIE feature. These PEGMA-AGE-PhE FONs were characterized by a series of characterization techniques in details. The cell viability as well as cell uptake behavior of PEGMA-AGE-PhE FONs was also examd. to evaluate their potential for biomedical applications. We demonstrated that the catalyst-free azide-alkyne click reaction is effective for fabrication of AIE-active FONs and these AIE-active FONs showed high water dispersity and AIE feature. Moreover, the PEGMA-AGE-PhE FONs also exhibited low cytotoxicity and great potential for biol. imaging. Taken together, a facile catalyst-free azide-alkyne click reaction with high efficiency has been developed for the prepn. of AIE-active FONs, which showed excellent physicochem. properties for biol. imaging applications.
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    59. 59
      Pina, J.; Seixas de Melo, J. S.; Burrows, H.; Bilge, A.; Farrell, T.; Forster, M.; Scherf, U. Spectral and photophysical studies on cruciform oligothiophenes in solution and the solid state. J. Phys. Chem. B 2006, 110 (31), 15100– 15106,  DOI: 10.1021/jp060707t
      59
      Spectral and Photophysical Studies on Cruciform Oligothiophenes in Solution and the Solid State
      Pina, J.; Seixas de Melo, J.; Burrows, H. D.; Bilge, A.; Farrell, T.; Forster, M.; Scherf, U.
      Journal of Physical Chemistry B (2006), 110 (31), 15100-15106CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The photophys. and spectroscopic properties of a new class of oligothiophene derivs., designated as cruciform oligomers, have been investigated in soln. (room and low temp.) and in the solid state (as thin films in Zeonex matrixes). The study comprises absorption, emission, and triplet-triplet absorption spectra, together with quant. measurements of quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation) and lifetimes. The overall data allow the detn. of the rate consts. for all decay processes. From these, several conclusions are drawn. First, in soln., the main deactivation channels for the compds. are the radiationless processes: S1 S0 internal conversion and S1 T1 intersystem crossing. Second, in general, in the solid state, the fluorescence quantum yields decrease relative to soln. A comparison is made with the analogous linear α-oligothiophenes, revealing a lower fluorescence quantum efficiency and, in contrast to the normal oligothiophenes, that internal conversion is an important channel for the deactivation of the singlet excited state. Replacement of thiophene by 1,4-phenylene units in the longer-sized cruciform oligomer increases the fluorescence efficiency. The highly efficient generation of singlet oxygen through energy transfer from the triplet state (SΔ ≈ 1) provides support for the measured intersystem crossing quantum yields and suggests that reaction with this may be an important pathway to consider for degrdn. of devices produced with these compds.
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    60. 60
      Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus, T. L.; Dupuis, M.; Montgomery, J. A. General atomic and molecular electronic structure system. J. Comput. Chem. 1993, 14 (11), 1347– 1363,  DOI: 10.1002/jcc.540141112
      60
      General atomic and molecular electronic structure system
      Schmidt, Michael W.; Baldridge, Kim K.; Boatz, Jerry A.; Elbert, Steven T.; Gordon, Mark S.; Jensen, Jan H.; Koseki, Shiro; Matsunaga, Nikita; Nguyen, Kiet A.; et al.
      Journal of Computational Chemistry (1993), 14 (11), 1347-63CODEN: JCCHDD; ISSN:0192-8651.
      A description of the ab initio quantum chem. package GAMESS is presented. Chem. systems contg. atoms through Rn can be treated with wave functions ranging from the simplest closed-shell case up to a general MCSCF case, permitting calcns. at the necessary level of sophistication. Emphasis is given to novel features of the program. The parallelization strategy used in the RHF, ROHF, UHF, and GVB sections of the program is described, and detailed speedup results are given. Parallel calcns. can be run on ordinary workstations as well as dedicated parallel machines.
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    61. 61
      Cundari, T. R.; Stevens, W. J. Effective core potential methods for the lanthanides. J. Chem. Phys. 1993, 98 (7), 5555– 5565,  DOI: 10.1063/1.464902
      61
      Effective-core-potential methods for the lanthanides
      Cundari, Thomas R.; Stevens, Walter J.
      Journal of Chemical Physics (1993), 98 (7), 5555-65CODEN: JCPSA6; ISSN:0021-9606.
      A complete set of effective core potentials (ECPs) and valence basis sets for the lanthanides (Ce to Lu) were derived. These ECPs are consistent not only within the lanthanide series, but also with the third-row transition metals which bracket them. A 46-electron core was chosen to provide the best compromise between computational savings and chem. accuracy. Thus, the 5s and 5p are included as "outer" core while all lower energy AOs were replaced with the ECP. Generator states were chosen from the most chem. relevant +3 and +2 oxidn. states. The greatest error vs highly accurate numerical potential/large, even-tempered basis set calcns. results from replacement of the large, even-tempered basis sets with more compact representations. However, the agreement among at. calcns. remains excellent with both basis set sizes, for a variety of spin and oxidn. states, with a significant savings in time for the optimized valence basis set. The compact representation of the ECPs and valence basis sets will eventually encourage their use by computational chemists to further explore the bonding and reactivity of lanthanide complexes.
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    62. 62
      Stevens, W. J.; Krauss, M.; Basch, H.; Jasien, P. G. Relativistic compact effective potentials and efficient, shared-exponent basis sets for the third-, fourth-, and fifth-row atoms. CAN. J. CHEM. 1992, 70 (2), 612– 630,  DOI: 10.1139/v92-085
      62
      Relativistic compact effective potentials and efficient, shared-exponent basis sets for the third-, fourth-, and fifth-row atoms
      Stevens, Walter J.; Krauss, Morris; Basch, Harold; Jasien, Paul G.
      Canadian Journal of Chemistry (1992), 70 (2), 612-30CODEN: CJCHAG; ISSN:0008-4042.
      Relativistic compact effective potentials (RCEP), which replace the at. core electrons in mol. calcns., have been derived from numerical Dirac-Fock at. wavefunctions using shape-consistent valence pseudo-orbitals and an optimizing procedure based on an energy-overlap functional. Potentials are presented for the third-, fourth-, and fifth-row atoms of the Periodic Table (excluding the lanthanide series). The efficiency of mol. calcns. is enhanced by using compact Gaussian expansions (no more than three terms) to represent the radial components of the potentials, and energy-optimized, shared-exponent, contracted-Gaussian AO basis sets. Transferability of the potentials has been tested by comparing calcd. at. excitation energies and ionization potentials with values obtained from numerical relativistic Hartree-Fock calcns. For the alkali and alk. earth atoms, core polarization potentials (CPP) have been derived which may be added to the RCEP to make possible accurate mol. calcns. without explicitly including core-valence correlating configurations in the wavefunction.
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    63. 63
      Stevens, W. J.; Basch, H.; Krauss, M. Compact effective potentials and efficient shared-exponent basis sets for the first-and second-row atoms. J. Chem. Phys. 1984, 81 (12), 6026– 6033,  DOI: 10.1063/1.447604
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    • Photoluminescence spectra of gold(I) complexes in MeCN/water mixtures, particle size distribution studies of gold(I) complexes in MeCN/water mixtures, 1H and 31P NMR and ESI-MS(+) spectra, and DFT/LC-BPBE(ω=0.2)/SBKJC-optimized ground-state geometries of the coumarin and dinuclear gold(I) complexes (PDF)


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