Protonation-Enhanced Pyridine-Imine Synergy in Covalent Organic Frameworks for Efficient Photocatalytic H2O2 Synthesis.

Covalent organic frameworks (COFs) have emerged as promising photocatalysts for H2O2 generation, leveraging their tunable electronic structures and inherent porosity to simultaneously optimize light absorption and reactant diffusion. However, their performance is limited by inefficient charge separation. Herein, we report a protonated, pyridinic nitrogen-incorporated imine-linked COF, designated TAPB-BTPA-H, which is obtained via the acid protonation of a pristine COF synthesized from 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-tris(2-formylpyridin-5-yl)benzene. This modified framework exhibits a remarkable H2O2 production rate of 2776 μmol g-1 h-1, representing a 4.1-fold enhancement over its neutral nonpyridinic counterpart. Crucially, the photocatalytic activity can be fully restored through reprotonation. The high performance is attributed to the synergistic effects between the protonated pyridinic nitrogen and the imine backbone. Combined experimental and density functional theory (DFT) calculations reveal that protonation induces a fundamental electronic restructuring, wherein the protonated pyridinic nitrogen acts as an efficient electron sink, maintaining strong electronic coupling with adjacent imine linkages. This targeted modification not only facilitates charge separation and enhances surface hydrophilicity, but also critically lowers the Gibbs free energy barrier for the rate-determining O2 to *OOH conversion. These findings establish protonated heteroatoms as a powerful design principle for creating intramolecular electron sinks, providing a general strategy for developing high-performance COF photocatalysts for various applications.