文摘
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 [Au6Ag2(C)(dppy)6](BF4)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 1MLCTAu state (蟿 = 1鈥? ps); (2) ESA of 3MLCTAu state (蟿 = 11鈥?0 ps), and (3) ESA of 3MLCTAg state (long-lived). By variation of the solvent鈥檚 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鈥揌路路路蟺 bond is formed between methanol molecules and aromatic rings of ligands, which enhances the ultrafast nonradiative decay from the hydrogen bond stabilized 3MLCTAu state and reduces the population of the emissive 3MLCTAg state. The results presented here about the excited state dynamics of luminescent gold(I)鈥搒ilver(I) cluster allow a deeper insight into the origin of their emissions by monitoring the population of the emissive 3MLCTAg state and dark 3MLCTAu state in different environments.