Integrating Light-Harvesting, Electron-Accumulating, and Proton-Supply Functions Into a Single Catalyst for Efficient CO2 Reduction

The development of efficient molecular catalysts for photochemical CO₂ reduction is a central challenge in artificial photosynthesis. The efficiency of this reaction depends on three critical elementary processes, namely light harvesting, electron transfer, and proton transfer. To realize efficient catalysts, the catalytic system for photochemical CO₂ reduction should include following three functions: light-harvesting, electron-accumulating, and proton-supply. However, creating a single molecular system that simultaneously integrates all three functions remains challenging. In this study, a novel iron porphyrin complex, 5,10,15,20-tetrakis[4-(N-(pentan-3-yl)-1,4,5,8-naphthalenetetracarboxylic diimide-N-yl)phenyl] porphyrinato iron(III) chloride (FeNDI), was developed which successfully incorporates these three key functions through the incorporation of naphthalene diimide (NDI) moieties at the porphyrin meso-positions. FeNDI exhibits intrinsic light-harvesting ability, enabling the reaction to proceed without external photosensitizers. Additionally, it demonstrates electron-accumulating ability, which enhances catalytic durability, while also exhibiting proton-supply ability, which allows the interaction between the coordinated CO₂ species and proton-supplying sites. Consequently, this complex achieved a turnover number of 611 for CO production, which is the highest value reported to date among relevant systems. This study therefore demonstrates the successful integration of all the three essential functions into a single catalyst molecule, offering a powerful strategy for the design of high-performance solar energy conversion systems.