Design and Construction of Noble-Metal-Free Porphyrin-Based Light-Harvesting Antennas for Efficient NADH Generation

Porphyrin-based artificial photosystems capable of converting solar light to chemical energy provide an encouraging strategy to alleviate energy and environmental problems. However, over-reliance on precious electron mediators (e.g., rhodium complexes) and electron separators (e.g., Pt nanoparticles) limits their extensive applications in artificial photosynthesis. Herein, we designed and constructed novel noble-metal-free porphyrin-based light-harvesting antennas (TPPS/Cd) via Cd²⁺-bridged aggregation and metalation of tetrakis­(4-sulfonatophenyl)­porphine (TPPS). The TPPS/Cd antennas exhibited high photocatalytic activity in converting visible light to chemical energy in reduced nicotinamide adenine dinucleotide phosphate (NADH). The yield of NADH reached 60.0% without any noble metals, far beyond those of the TPPS monomer (15.8%) and its Pt complexes (TPPS/Pt, 36.7%). The in-depth analysis of the results indicates that the Cd²⁺-bridged coordination (pyridinic-N···Cd²⁺···–SO₃^–) is essential to the porphyrin J-aggregates, while the formation of metalloporphyrin (Cd@TPPS) from the intermediates (Cd@TPPS-2H) is responsible for their activity enhancement, which greatly facilitates spatial charge separation and transfer by the establishment of delocalized π systems. This work developed a metal-bridged coordination-driven strategy for porphyrin J-aggregates to exceed the environmental pH limits and made a promising step toward noble-metal-free porphyrin-based light-harvesting antennas with high photocatalytic performance and excellent stability.