Modulating\nQuinoline-Linked Covalent Organic Frameworks\nvia Fluorination for Boosting the Photocatalytic Air Reductive H<sub>2</sub>O<sub>2</sub> Production

The intrinsic reversibility and strong polarization of\nimine linkages\nlimit the application of imine-based covalent organic frameworks (COFs)\nin photocatalysis. Herein, inspired by the aza-Diels–Alder\ncycloaddition reaction, two quinoline-linked fluorinated COFs (termed\nTTB-TTA-Ph-F and TTB-TTA-Ph-3F) are developed based on postsynthetic\nmodification of an imine-linked COF (TTB-TTA). The simultaneous reversibility-to-irreversibility\nbond transformation and fluorination endow the resultant COFs with\nimproved robustness, extended structural conjugation, and intriguing\noptoelectronic properties. The introduced fluorine groups change the\nlocal electronic structures of the COFs and improve charge separation\nand transfer. Benefiting from the rational design on the COF skeleton,\nTTB-TTA-Ph-3F exhibits excellent activity, giving a 3496.9 μmol\ng<sup>–1</sup> h<sup>–1</sup> of photocatalytic H<sub>2</sub>O<sub>2</sub> production rate from water and air after optimizing\nby fluorine modulation.