Covalent Organic Frameworks for Boosting HO Photosynthesis via the Synergy of Multiple Charge Transfer Channels and Polarized Field.

Covalent organic frameworks (COFs) serve as one of the most promising candidates for hydrogen peroxide (HO) photosynthesis, while attaining high-performance COFs remains a formidable challenge due to the insufficient separation of photogenerated charges. Here, through the rational design of bicarbazole-based COFs (Cz-COFs), we showcase the first achievement in piezo-photocatalytic synthesis of HO using COFs. Noteworthily, the ethenyl group-modified Cz-COFs (COF-DH-Eth) demonstrates a record-high yield of HO (9212 μmol g h) from air and pure water through piezo-photocatalysis, which is ca. 2.5 times higher than that of pristine Cz-COFs without ethenyl groups (COF-DH-H) under identical condition and COF-DH-Eth without ultrasonic treatment. The HO production rate originates from the synergistic effect between an ultrasonication-induced polarized electric field and the spatially separated multiple charge transfer channels, which significantly promote the utilization of photogenerated electrons by directional transfer from bicarbazole groups to the ethenyl group-modified benzene rings. Several Cz-COFs and bifluorenylidene-based COFs (COF-BFTB-H) with similar twisted monomers exhibit obvious piezoelectric performance for promoting HO generation, signifying that organic ligands with a twistable structure play a crucial role in creating broken symmetry structures, thereby establishing piezoelectric properties in COFs.