Ligand-based electron transfer enables molecular polypyridyl Zn(II) complexes for efficient photocatalytic CO2 reduction

Electron transfer process plays a critical role in photocatalytic CO2 reduction. Owing to low redox activity of Zn (II) cation under catalytic conditions, it remains a challenge to use Zn(II) complexes as efficient molecular catalysts for CO2 photoreduction. Herein, we overcome the obstacle and demonstrate two polypyridyl Zn(II) complexes can be utilized for selective photoreduction of CO2 to CO. Thanks to more efficient ligand-based electron transfer, the polypyridyl Zn(II) complex modified with electron-donating carbazole groups displays a higher TON of CO up to 116 than the other unsubstituted polypyridyl Zn(II) complex, which is among the most efficient Zn(II) complexes molecular catalysts in CO2 photoreduction. Photocatalytic mechanism has been studied by UV-vis absorption spectroscopy and computational calculations. These results show a promising way to develop Zn(II) complexes for efficient CO2 photoreduction through ligand modification and ligand-based electron transfer.