부산대학교 도서관

Thiolate-stabilized Au nanoclusters (NCs) have attracted considerable interest because of their unique properties and promising applications. However, there are still challenges in fully understanding the involved mechanisms of their electronic structure and optical properties. Here, we have focused primarily on bovine serum albumin (BSA)-protected Au25(SR)18NCs to gain deep insight into their electronic structure by creating quantum beats in fluorescence dynamics with multiple pulse excitations. The electronic oscillations among degenerate excited states have been successfully generated and systematically investigated. The visibility of quantum beats demonstrates an insensitivity to the excitation wavelength, excitation power, and solution temperature but is very sensitive to the emission wavelength, the population of triplet states, and the number of Au atoms. The generated oscillations in fluorescence dynamics by sequential pulse excitations clearly reveal the existence of long-lived degenerate triplet states in the electronic structure of Au25(SR)18NCs. There are three typical frequencies of 1.79 ± 0.01 GHz, 2.64 ± 0.05 GHz, and 3.87 ± 0.03 GHz determined from the Fourier transform analysis of the oscillation profile, suggesting the electronic superimpositions and energetic differences among the degenerate triplet states. These findings are significant for deep understanding of the relationship between the electronic structure and photophysical properties of BSA-protected Au25(SR)18NCs.