Tailoring 3D COFs with vinyl motifs boosts intramolecular electron transfer for photocatalytic CO2 reduction to HCOOH

Solar-driven photocatalytic CO₂ conversion into value-added fuels has emerged as a pivotal strategy for sustainable energy development, where rationally designed covalent organic frameworks (COFs) demonstrate unprecedented potential in orchestrating controllable photoreduction processes. The precise integration of tri-functional motifs with light-harvesting, catalytic and electron-storing in framework of COFs can enable synergistic enhancement of charge carrier separation kinetics and photocatalytic reduction efficacy. Herein, a novel metal-free imine-linked ternary 3D COFs (named COF-TAPP-TVBT) with triazine, porphyrin and alkenyl groups, which can achieve the photoreduction reaction of CO₂ to HCOOH under visible-light, was synthesized. Combined experiments and theoretical calculations, porphyrin unit functions as dual-functional centers for both photocatalytic activity and photosensitization, while triazine and alkenyl groups can facilitate electron-hole separation and suppress carrier recombination. DFT calculations provides further confirmation that the TAPP moiety as the dominant catalytic active site in COF-TAPP-TVBT, with mechanistic insights revealing that hydrogen adsorption near within the active microenvironment enhanced CO₂ adsorption, while the synergistic interplay between alkenyl and triazine rings promotes accelerated electron transfer pathways. This study establishes a 3D-COFs photocatalyst for CO₂RR, while providing fundamental insights at the molecular level into the structure–activity correlations and charge carriers within multi-component synergy.