Synergistic Modulation of Photoexcitation Dynamics and Catalytic Site Activation in Covalent Organic Frameworks through Doebner Nonconjugated Modification for Boosting Photocatalytic CO ₂ Reduction

The development of metal-free covalent organic frameworks (COFs) for photocatalytic CO₂ reduction faces a critical challenge in establishing an efficient synergistic mechanism between photogenerated carrier dynamics and catalytic site activity. Herein, we demonstrate the enhancing effect of Doebner locally nonconjugated modification on the photocatalytic performance of imine-based COFs to address this issue. The resultant locally nonconjugated TAPT-TT-HQ achieves an outstanding CO production rate of 247 ± 15 µmol g^-1 h^-1 with water as hole scavenger, approximately twice that of conjugated TAPT-TT-Q and eight times that higher than pristine TAPT-TT. This performance places it among the top-performing metal-free COFs photocatalysts reported to date. Combined experimental analyses and density functional theory (DFT) calculations attribute the superior performance of TAPT-TT-HQ to the synergistic effects of multiple factors induced by nonconjugated Doebner modification: effective carrier separation and transfer mediated by unique photoexcitation dynamics, activated carboxylic acid site with a lowered energy barrier for ^*COOH intermediate formation, and improved CO₂ adsorption capacity. This work comprehensively clarifies the influence mechanism of Doebner nonconjugated modification on the photocatalytic performance of COFs in CO₂ reduction, establishing locally nonconjugated modification as a novel design strategy for CO₂ photoreduction catalysts, which breaks away from the dependency on conjugated systems.