Fused-Heterocycle-Linked Covalent Organic Frameworks With Enhanced Chemical and Photochemical Stability for...

Covalent organic frameworks (COFs) have attracted significant interest for their potential in photocatalytic solar fuel generation. However, their intrinsic stability-particularly the photochemical stability, which influences the durability of their photocatalytic performance-remains a critical challenge. Here, we present the construction of four robust fused-heterocycle thiazole-linked COFs (TZ-COFs 14-17) through a facile one-pot three-component reaction using chrysene-6,12-diamine, aldehydes, and sulfur monomers. The incorporation of thiazole linkages within the fused-ring building blocks imparts exceptional chemical and photochemical stability to these COFs. They demonstrate high stability in strong acid (12 M HCl), strong base (12 M KOH and 1 M MeONa), reducing (1 M NaBH₄), and oxidizing (1 M H₂O₂) agents, along with superior photostability under light degradation tests. Significantly, the in situ formed thiazoles introduce new, robust protonation sites compared to commonly used imine linkages, which improve the hydrophilicity, expand the range of light absorption, and lower the exciton binding energy of the framework. TZ-COF-17 achieves an impressive hydrogen evolution rate of up to 33.27 mmol g^-1 h^-1, surpassing many previously reported COF photocatalysts.