Reduction of CO2 in the presence of light via excited-state hydride transfer reaction in a NADPH-inspired derivative.

The photo-catalytic reduction of CO2 into chemical feedstocks using solar energy has attracted vast interest in environmental science because of global warming. Based on our previous study on the CO2 complex with one of the benzimidazoline (BI) derivatives, we explore the photochemical reduction of CO2 in one of the benzimidazoline derivatives (1,3-dimethyl-5,6-diol-2,3-dihydro-1H-benzimidazole) by quantum-chemical methods. Our results reveal that carbon dioxide can be reduced to formate (HCOO-) by a hydride transfer reaction in the excited state of this complex of benzimidazoline derivative and CO2. While the ground-state hydride transfer reaction in this complex exhibits a substantial barrier, a charge-transfer can occur in the first singlet excited state of the complex in the UV-A region (326 nm), and after overcoming a moderate barrier (∼0.4 eV) the system can have access to the products. The interaction with a polar solvent decreases further the barrier such that the reaction in dimethyl sulfoxide can proceed with a negligibly small barrier (∼0.1 eV) or in a nearly barrierless manner. Our results show that this benzimidazoline derivative may act as a catalyst in the photoreduction of CO2.