Role of excited-state hydrogen bonding in CO 2 photoreduction catalyzed by sodium magnesium chlorophyll.

In this paper, we report a joint experimental and computational study to elaborate the mechanism for the photocatalytic CO ₂ reduction reaction (CO ₂ RR). Experimental results indicate that the catalyst (sodium magnesium chlorophyll, MgChlNa ₂ ), which has a well-defined structure for calculation and understanding, can achieve the photoreduction of CO ₂ to CO only using water as a dispersant, without adding any photosensitizer or sacrificial agent. Subsequently, a series of structural models of the hydrogen-bonded complexes of the catalyst were constructed and outlined via utilizing density functional theory (DFT) calculations, including photophysical and photochemical processes. The results confirm that the rate-limiting step of the whole CO ₂ RR was the intersystem crossing process. The electron and proton transfers involved in photophysical and photochemical processes are induced by hydrogen bonds in the excited states. The combination of experiments and calculations will provide an important reference for the design of high-efficiency photocatalysts in the photocatalytic CO ₂ RR.