Prolonging the Triplet State Lifetimes of Rhenium Complexes with Imidazole-Pyridine Framework for Efficient CO2 Photoreduction

The photocatalytic reduction of CO2 into fuels offers the prospect for creating a new CO2 economy. Harnessing visible light-driven CO2-to-CO reduction mediated by the long-lived triplet excited state of rhenium(I) tricarbonyl complexes is a challenging approach. We here develop a series of new mononuclear rhenium(I) tricarbonyl complexes (Re-1-Re-4) based on the imidazole-pyridine skeleton for photo-driven CO2 reduction. These catalysts are featured by combining pyridyl-imidazole with the aromatic ring and different pendant organic groups onto the N1 position of 1,3-imidazole unit, which display phosphorescence under Ar-saturated solution even at ambient conditions. By contrast, {Re[9-(pyren-1-yl)-10-(pyridin-2-yl)-9H-pyreno[4,5-d]imidazole)](CO)(3)Cl} (Re-4) by introducing pyrene ring at the N1 position of pyrene-fused imidazole unit exhibits superior catalytic performance with a higher turnover number for CO (TONCO=124) and >99.9 % selectivity, primarily ascribed to the strong visible light-harvesting ability, long-lived triplet lifetimes (164.2 mu s) and large reductive quenching constant. Moreover, the rhenium(I) tricarbonyl complexes derived from pi-extended pyrene chromophore exhibit a long lifetime corresponding to its ligand-localized triplet state ((IL)-I-3) evidenced from spectroscopic investigations and DFT calculations.

Automated summary

The study focuses on the photocatalytic reduction of CO2 into fuels using rhenium(I) tricarbonyl complexes. New mononuclear rhenium(I) tricarbonyl complexes based on the imidazole-pyridine skeleton were developed for this purpose, displaying phosphorescence even in Ar-saturated solution. Among them, a specific complex exhibited superior catalytic performance with high CO turnover number and selectivity, attributed to its strong visible light-harvesting ability and long-lived triplet lifetimes.