Realizing Visible Photoactivity of Metal Nanoparticles: Excited-State Behavior and Electron-Transfer Properties of Silver (Ag8) Clusters

Silver nanoclusters complexed with dihydrolipoic acid (DHLA) exhibit molecular-like excited-state properties with well-defined absorption and emission features. The 1.8 nm diameter Ag nanoparticles capped with Ag-8 clusters exhibit fluorescence maximum at 660 nm with a quantum yield of 0.07%. Although the excited state is relatively short-lived (tau 130 ps), it exhibits significant photochemical reactivity. By introducing MV2+ as a probe, we have succeeded in elucidating the interfacial electron transfer dynamics of Ag nanoclusters. The formation of MV+center dot as the electron-transfer product with a rate constant of 2.74 x 10(10) s(-1) confirms the ability of these metal clusters to participate in the photocatalytic reduction process. Basic understanding of excited-state processes in fluorescent metal clusters paves the way toward the development of biological probes, sensors, and catalysts in energy conversion devices.