Heterocycle-Linked Covalent Organic Frameworks With Indazole Units for Cooperative H2O2 Photosynthesis and Biomass Valorization.

Developing artificial photosynthesis systems that couple hydrogen peroxide (H2O2) production with organic valorization remains challenging due to rapid carrier recombination. Herein, indazole-linked covalent organic frameworks (COFs) were constructed via Cadogan reductive cyclization of nitro-functionalized imine-linked precursors, which converts labile imine linkages into robust indazole linkages while preserving high crystallinity and enhancing visible-light harvesting ability. Remarkably, in a synergistic system coupling H2O2 production with furfuryl alcohol oxidation, indazole-linked COFs exhibited a nearly 5.6-fold enhancement in photocatalytic performance compared to its imine-linked counterpart. Combined in situ DRIFTS and DFT calculations revealed that the indazole linkage optimizes interfacial reaction kinetics and facilitates substrate adsorption through polarized nitrogen sites. This work establishes heterocyclic linkage engineering as an effective strategy for designing advanced crystalline photocatalysts toward integrated solar energy conversion.