A Small Organic Molecular Catalyst with Efficient Electron Accumulation for Near-unity CO2 Photoreduction

Molecular catalysis is of great interest to CO2 photoreduction. Various transition metal complexes have been developed as efficient molecular catalysts. However, it remains a challenge to catalyze CO2 reduction by a small organic molecular photocatalyst, as the accumulation of multiple electrons in a small organic molecule is normally difficult for CO2 reduction. We report herein a small organic molecular catalyst can be used for selective reduction of CO2 to CO under visible light irradiation. The turnover number (TON) of CO formation is found to be 400 +/- 26 with near 100% selectivity in DMF/H2O medium. UV-Vis absorption spectroscopy, density functional theory (DFT) calculations, and spectroelectrochemical studies demonstrate that the organic molecular catalyst is capable of accumulating electrons through a 2e(-) reduced product which shows good stability and is responsible for interacting with CO2. These findings elucidate an accessible way to develop purely organic molecular catalysts for CO2 reduction by strengthening the electron accumulation.