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

Graphical CO 2 photoreduction : A series of new mononuclear rhenium(I) complexes with imidazole-pyridine framework based on the long-lived excited triplet state exhibit satisfactory stability and catalytic efficiency in photoreduction of CO 2 to CO. This work emphasizes the practice and importance of tailored photocatalyst design on molecular level, representing appealing and potentially applications for phosphorescent catalysts in CO 2 reduction to solar fuels. The photocatalytic reduction of CO 2 into fuels offers the prospect for creating a new CO 2 economy. Harnessing visible light-driven CO 2 -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 CO 2 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 (TON CO =124) and >99.9 % selectivity, primarily ascribed to the strong visible light-harvesting ability, long-lived triplet lifetimes (164.2 μs) and large reductive quenching constant. Moreover, the rhenium(I) tricarbonyl complexes derived from π-extended pyrene chromophore exhibit a long lifetime corresponding to its ligand-localized triplet state ( 3 IL) evidenced from spectroscopic investigations and DFT calculations.