In Situ Integration of Metallic Catalytic Sites and Photosensitive Centers within Covalent Organic Frameworks for the Enhanced Photocatalytic Reduction of CO₂

Covalent organic frameworks (COFs) are a promising platform for heterogeneous photocatalysis due to their stability and design diversity, but their potential is often restricted by unmanageable targeted excitation and charge transfer. Herein, a bimetallic COF integrating photosensitizers and catalytic sites is designed to facilitate locally ultrafast charge transfer, aiming to improve the photocatalytic reduction of CO₂. The strategy uses a "one-pot" method to synthesize the bimetallic COF (termed PBCOF_RuRe) through in situ Schiff-base condensation of Pyrene with MBpy (M = Ru, Re) units. In this structure, Ru and Re are anchored within bipyridine as the photosensitive center and catalytic site, respectively. The bimetallic architecture of PBCOF_RuRe significantly boosts the photocatalytic efficiency for CO₂ reduction, achieving an impressive CO yield of 8306.6 µmol g^-1 h^-1 with 99.8% selectivity, surpassing most reported COF materials. This improvement is attributed to the localized ultrafast charge transfer (0.23 ps) from Ru to Re, as demonstrated by femtosecond transient absorption spectroscopy (TAS). Further investigations demonstrate its heterogeneous feature, showcasing exceptional long-term stability and recyclability. This study represents a versatile approach for designing bimetallic COFs with ultrafast charge transfer, paving the pathway for advancements in artificial photosynthesis.