Transformation of Covalent Organic Frameworks from N-Acylhydrazone to Oxadiazole Linkages for Smooth Electron Transfer in Photocatalysis.

Covalent organic frameworks (COFs) are regarded as new platforms for solar-to-chemical energy conversion due to their tailor-made functions and pre-designable structures. Their intrinsic reversibility and the high polarization of organic linkages inevitably result in poor chemical stability and weak optoelectronic properties. Herein, one N-acylhydrazone-linked COF (H-COF) was converted into a stable and π-conjugated oxadiazole-linked COF via post-oxidative cyclization. Both chemical stability and π-electron delocalization throughout the reticular framework are significantly improved, leading to a high hydrogen evolution rate of 2615 μmol g -1  h -1 upon visible light irradiation, which is over four times higher than that of H-COF. This work provides a facile protocol for the fabrication of π-conjugated COFs and the modulation of photophysical properties for photocatalytic application.