Electron Cloud Density Modulation in Three-Dimensional Porphyrin-Based Covalent Organic Frameworks for Enhanced Photocatalytic CO₂ Reduction

Covalent organic frameworks (COFs), with their tunable structures and defined active sites, hold promise for photocatalytic reduction of CO2 reduction. Systematic modulation of linker electron cloud density represents a critical strategy for optimizing the catalytic performance of COF-based photocatalysts, yet this approach faces several challenges. In this work, we employed 8-connected porphyrin as a building block to synthesize three distinct three-dimensional (3D) COF materials through the adjustment of the length and functional groups of the biconnected units. The synthesized 3D COFs exhibited varying catalytic activities for photocatalytic CO2 conversion. Notably, COF-3-Co, which incorporates the benzimidazole unit (BFBie), demonstrated the best CO production yield and selectivity. Combined experimental and theoretical investigations revealed that the high electron cloud density of the BFBie unit effectively facilitated electron transfer, thereby significantly enhancing the photocatalytic activity. The findings presented herein provide valuable insights into the rational design and synthesis of efficient COF-based photocatalysts for the reduction of CO2.