Plasmonic Switching: Hole Transfer Opens an Electron-Transfer Channel in Plasmon-Driven Reactions

Plasmon excitation and decay in gold nanoparticles (AuNPs) generates hot charge carriers that transfer to surface molecules and cause chemical transformation. We reveal that both electron- and hole-transfer channels must be open for reactions to occur. Furthermore, electron-transfer reactions can be switched on or off by a hole-transfer reaction. The reduction of 4-nitrobenzenethiol (NBT) to 4,4′-dimercaptoazobenzene (DMAB) via electron transfer from AuNPs to NBT does not occur in nanogaps between AuNPs and Au films with NBT alone. However, DMAB appears when NBT is mixed with 4-mercaptobenzoic acid (MBA), which undergoes decarboxylation by plasmon-induced hole transfer. The electron-transfer reaction yield is linearly correlated with the hole-transfer reaction yield. In contrast, when pairing NBT with molecules that are unreactive to plasmon excitation, electron transfer to NBT does not occur. Balancing the transfer of charge acts as a plasmonic switch for reaction pathways.