Photochemical CO₂ Reduction Driven by Water-Soluble Copper(I) Photosensitizer with the Catalysis Accelerated by Multi-Electron Chargeable Cobalt Porphyrin

Without using precious elements, a highly efficient and selective molecular-based photocatalytic system for CO 2 -to-CO conversion in fully aqueous media has been developed. Our copper(I)-based water-soluble photosensitizer ( CuPS ) preserves its highly luminescent and long-lived excited state even in aqueous media. The CuPS -driven CO 2 reduction catalyzed by a water-soluble cobalt porphyrin possessing four N -methylpyridinium acceptors at the meso positions ( CoTMPyP ) achieves the highest catalytic activity among those reported for aqueous systems: TON CO = 2680 and TOF CO max = 1600–2600 h –1 with Sel CO2 = 77–90% (selectivity for CO vs H 2 ). The observed photocatalytic enhancement is discussed in terms of the 6-electron chargeable character of CoTMPyP, permitting its rapid release of CO via reduction of Co II to Co I by intramolecular electron transfer from the reducing equivalent stored at one of the acceptors.