Dual Porphyrin Sensitized Photocatalytic System for Visible-Light-Driven CO₂ Reduction

Dye-sensitized photocatalysis offers a powerful strategy for combining the molecular selectivity of transition-metal catalysts with the robustness and charge-separation capabilities of semiconductor materials. Herein, we report a dual porphyrin-sensitized TiO₂ platform for visible-light-driven CO₂ reduction, integrating a Zn-porphyrin photosensitizer with newly designed Fe-porphyrin catalysts bearing urea-based secondary-sphere functionalities. These hydrogen-bonding motifs promote CO₂ preorganization and stabilization of key reduced intermediates at the metal center. Systematic comparison of homogeneous and heterogeneous systems reveals a pronounced enhancement in activity and durability upon immobilization onto TiO₂ nanoparticles. Optimization studies demonstrate that catalytic activity is strongly governed by both sacrificial electron donor (SED) availability and proton concentration. Under anhydrous conditions, increased SED concentration boosts turnover numbers, while the introduction of controlled amounts of water enhances proton-coupled electron transfer but ultimately compromises catalyst stability at higher concentrations. Under optimized conditions, the best-performing assembly achieves turnover numbers (TONs) exceeding 15,000 after 96 h of irradiation, representing, to the best of our knowledge, the highest reported TON for Fe-porphyrin-based dye-sensitized photocatalytic systems (DSPs). These findings highlight the delicate balance between electron and proton management in dye-sensitized architectures and provide key design principles for developing durable and efficient molecular-semiconductor hybrids for solar-driven CO₂ conversion.