Noncanonical Electron Donor-Acceptor Model: Photoinduced Charge Transfer Between Metal-Based Photocatalyst and Inorganic Base

The fundamental transitions of metal-based photocatalysts from ground to excited states are typically metal-to-ligand or ligand-to-metal charge transfer, which require high-energy visible-light absorption. Herein, we describe a noncanonical electron donor–acceptor model between the cheap inorganic base phosphates/carbonate and the robust iridium/ruthenium-based polypyridyl photocatalysts using a lower energy visible light instead of popular blue light through in-depth theoretical calculations and experimental findings. The generated phosphate/carbonate radical can dominate the radical C(sp3)-H. The currently popular view is that the reductive quenching of excited photocatalysts is mediated by Br−/Cl− when Br−/Cl− and phosphate/carbonate are both present in a photocatalytic system. By contrast, this EDA complex model is more reasonable and promising than Br−/Cl− quenching pattern because of the ability to harvest lower-energy light. These mechanistic insights will provide practical guidance for the activation of inert chemical bonds under lower-energy photocatalytic conditions.