Photomediated Oxidation of Atomically Precise Au25(SC2H4Ph)18(-) Nanoclusters

The anionic charge of atomically precise Au25(SC2H4Ph)18(-) nanoclusters (abbreviated as Au25(-)) is thought to facilitate the adsorption and activation of molecular species. We used optical spectroscopy, nonaqueous electrochemistry, and density functional theory to study the interaction between Au25(-) and O2. Surprisingly, the oxidation of Au25(-) by O2 was not a spontaneous process. Rather, Au25(-)-O2 charge transfer was found to be a photomediated process dependent on the relative energies of the Au25(-) LUMO and the O2 electron-accepting level. Photomediated charge transfer was not restricted to one particular electron accepting molecule or solvent system, and this phenomenon likely extends to other Au25(-)-adsorbate systems with appropriate electron donor-acceptor energy levels. These findings underscore the significant and sometimes overlooked way that photophysical processes can influence the chemistry of ligand-protected clusters. In a broader sense, the identification of photochemical pathways may help develop new cluster-adsorbate models and expand the range of catalytic reactions available to these materials.