Engineering channel microenvironment and charge dynamics in covalent organic frameworks through linkage-specific povarov cyclization for enhanced photocatalytic hydrogen evolution

Abstract

Covalent organic frameworks (COFs) offer a modular platform for photocatalytic hydrogen evolution (PHE), where linkage topology and channel architecture dictate charge separation and mass transport. However, the role of linkage isomerism in coupling pore microenvironments with photocatalytic function remains unclear. We synthesized COF-PQ and COF-DPPQ via in-situ Povarov cyclization of pyrene-based imine direction distinct intermediates, creating frameworks with identical building blocks but distinct donor-acceptor arrangements and pore microenvironments that underpin their contrasting catalytic behaviors. This structural divergence drives profound functional differences: COF-DPPQ achieves a PHE rate of 37.82 mmol g^–1 h^–1, nearly 100-fold higher than COF-PQ. Mechanistically, COF-DPPQ exhibits lower electron effective mass (0.574 vs. 1.046), stronger donor-acceptor polarization (~0.95 |e| vs. ~0.24 |e|), prolonged carrier lifetimes (37.28 vs. 1.26 ps), and superior proton adsorption and diffusion (2.2-fold capacity; 0.916 × 10^–3 vs. 0.660 × 10^–3 cm² s^–1). These results identify linkage topology as an effective lever to regulate exciton dynamics and mass transport, guiding the design of next-generation COF photocatalysts.