Engineering photocatalytic active centers in covalent organic framework isomers via A/K-region positional isomerization of pyrene for H2O2 production

Abstract

The integration of dual active sites for concurrent oxygen reduction (ORR) and water oxidation (WOR) within a single covalent organic framework (COF) remains a fundamental challenge in the artificial photosynthesis of H₂O₂. To address this, we report a positional isomerization strategy that precisely engineers the substitution sites on a pyrene core, constructing four isomeric pyrene-based COFs (A-Py-COF, KA-Py-COF, AK-Py-COF, and K-Py-COF). Structure-activity studies reveal that K-region substitution is pivotal in activating the framework for efficient stepwise two-electron ORR and two-electron WOR. As a result, the optimized K-Py-COF achieves a remarkable photocatalytic H₂O₂ production rate of 468.3 μmol g^–1h⁻¹ in pure water without sacrificial agents, representing a 7.8-fold enhancement over its A-Py-COF analogue. In a biphasic water-benzyl alcohol system, the H₂O₂ production rate of K-Py-COF increases dramatically by 15.3 times, a performance that surpasses most state-of-the-art metal-free COF photocatalysts. By establishing a clear correlation between molecular isomerism and the localization of redox-active sites, this work provides a novel design principle for developing dual-channel COFs toward sustainable H₂O₂ synthesis.