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 CO2-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 CO2 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: TONCO = 2680 and TOFCOmax = 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.