Unveiling the key role of excited-state hydrogen bonding in homogeneous photocatalytic CO2 reduction

In this paper, we investigated the role of excited-state hydrogen bonding in the photocatalytic carbon dioxide reduction reaction (CO2RR) utilizing Rose Bengal as a catalyst, through a combined experimental and theoretical approach. Experiments validated the successful conversion of CO2 to CO in a homogeneous aqueous solution system under light irradiation, without additional photosensitizers or sacrificial agents. Theoretically, the DFT/TDDFT calculations modeled the catalyst-reactants as a hydrogen-bonded complex (HBC), understanding the energy, hydrogen, and electron transfer mechanisms induced by excited-state hydrogen bonding. Combining the photophysical and photochemical insights revealed the complete catalytic cycle, identifying the water oxidation process as the rate-limiting step in the entire photocatalytic CO2RR process. Experimental and computational results provide molecular-level insights into the structure–activity relationships. This work enhances comprehension of the pivotal role of excited-state hydrogen bonding and holds significant reference value for enhancing the conversion efficiency in the photocatalytic CO2RR.