Solvent Dependent Excited State Behaviors of Luminescent Gold(I)–Silver(I) Cluster with Hypercoordinated Carbon

Abstract

Polynuclear Au(I) complexes continues to attract considerable attention because of their bright emissions in the visible wavelength, which hold promise in applications in luminescence, fluorescence sensing, and bioimaging. Despite various spectroscopic investigations on their steady state properties, detailed understanding of the origin of their emissions and excited state relaxations is still lacking. Here, we report femtosecond time-resolved transient absorption experiments combined with quantum chemical calculations on a brightly emissive [Au 6 Ag 2 (C)(dppy) 6 ](BF 4 ) 4 cluster in different solvents. Global analysis on the transient absorption spectra based on a sequential model gives three spectral components: (1) excited state absorption (ESA) of 1 MLCT Au state (τ = 1−3 ps);(2) ESA of 3 MLCT Au state (τ = 11−40 ps), and (3) ESA of 3 MLCT Ag state (long-lived). By variation of the solvent's polarity and hydrogen bonding ability, the relative population of the triplet MLCT states and the emission properties can be modulated. Especially in methanol, an additional site specific O−H···π bond is formed between methanol molecules and aromatic rings of ligands, which enhances the ultrafast nonradiative decay from the hydrogen bond stabilized 3 MLCT Au state and reduces the population of the emissive 3 MLCT Ag state. The results presented here about the excited state dynamics of luminescent gold(I)− silver(I) cluster allow a deeper insight into the origin of their emissions by monitoring the population of the emissive 3 MLCT Ag state and dark 3 MLCT Au state in different environments.

Full Protection of Intensely Luminescent Gold(I)–Silver(I) Cluster by Phosphine Ligands and Inorganic Anions

“…Owing to the poor solubility of 2 and 3 in dichloromethane,t he crystalline clusters are dissolved in dichloromethane/methanol = 1:1( v:v) in the photophysical studies.A si llustrated in Figure 5, the solution of 2 emits in the orange-red region, with emission maxima at 603 nm. [35] Note that clusters 2 and 3 in CH 2 Cl 2 /CH 3 OH are very stable in air, and solutions of 2 and 3 were still brightly emissive after being kept in the dark for months.F urthermore,n os ignificant emission intensity decrease was observed even after the solution with concentration of 1.0 10 À5 mol L À1 had been exposed under a3 00 WHglamp for 60 min in air. Cluster 3 emits bright yellow light with l max at 557 nm, and the quantum yield is determined to be 92 %, which is av ery It is interesting that 3 exhibits much higher QY in solution than in the solid state.T his is probably due to self-quenching as ar esult of intermolecular interactions in solid state.…”

“…[34] Compared to [(C)(Audppy) 6 Ag 2 ](BF 4 ) 4 ,w hose QY was measured to be 29 %i nd ichloromethane,t he relative weak luminescence of 2 in CH 2 Cl 2 /CH 3 OH = 1:1( v:v) (poor solubility in neat CH 2 Cl 2 )i sd ue to polarity and hydrogen bonding ability of CH 3 OH employed in the study. [35] Note that clusters 2 and 3 in CH 2 Cl 2 /CH 3 OH are very stable in air, and solutions of 2 and 3 were still brightly emissive after being kept in the dark for months.F urthermore,n os ignificant emission intensity decrease was observed even after the solution with concentration of 1.0 10 À5 mol L À1 had been exposed under a3 00 WHglamp for 60 min in air.…”

A Controlled Route to a Luminescent 3 d10–5 d10 Sulfido Cluster Containing Unique AuCu2(μ3‐S) Motifs

“…Such spectral features are common in the chemistry of phenylphosphine‐ and thiophenolate‐containing gold(I) clusters . The low energy shoulder is usually ascribed to ligand‐to‐metal or metal‐to‐ligand charge transfer, depending on the electron donating/withdrawing properties of the ligand . In addition to metal‐to‐ligand (Cu + →P) character, induced by the electron withdrawing phosphine ligand, the low energy shoulder in 2 is also thought to have interligand (S 2− →P) character.…”

“…[16] The low energy shoulder is usually ascribed to ligand-to-metal or metal-to-ligand charget ransfer,d ependingo nt he electron donating/withdrawing properties of the ligand. [17] In addition to metal-to-ligand (Cu + !P) character,i nduced by the electron withdrawing phosphine ligand,t he low energy shoulder in 2 is Scheme1.Synthesis of 1a, 1b and 2:i )1molar equiv LiESiMe 3 ,THF;i i) 1 molar equivCuOAc, 1.5 molare quiv dppm,T HF.THF = tetrahydrofuran. (8): P1-Au1 2.2585(9), Au1-S1 2.3232(9), Au1-Cu1 2.8663(8), Au2-Cu2 2.9174(8) Au1-Cu2 i 2.8539(8), Au2-Cu1 i 2.8418(7), S1-Cu1 2.160(1), S2-Cu12.164(1), Cu1-Cu2 2.9019(8) Cu1-Cu2 i 2.906(1);P1-Au1-S1172.58 (3), Au1-S1-Cu1 79.39(3), Cu1-S2-Cu2 i 84.33(4), S1-Cu1-S2 175.51 (4).…”

Ligand and Solvent Effects on the Structural and Optical Properties of Au13L8 3+ Clusters: a Density Functional Theory Study

“…Besides the ligand influence, it has been reported that the solvent effect also affects the structural, electronic and optical properties of gold clusters. [38][39][40][41][42][43] From the structural point of view, Jiang et al 39 showed that solvents with higher polarity tend to form thiolate clusters with smaller sizes due to hydrogen bonding interactions. Recently, Thanthirige et al 43 observed the characteristics of the absorption spectra of bi-icosahedral Au 25 clusters in ethanol and toluene, under different temperatures.…”