Multifunctional covalent organic frameworks for photocatalytic oxidative hydroxylation of arylboronic acids and fluorescence sensing for Cu2+

Covalent organic frameworks (COFs) with excellent porosity and pre-designable structure have emerged as ideal and promising organic scaffolds for broad applications such as in gas storage, heterogeneous catalysis and fluorescence sensing. Herein, a hydrazone-based COF was synthesized by the condensation of 2,5-bis(2-methoxyethoxy) terephthalohydrazide (BMTH) with 1,3,5-triformylbenzene (TFB) under solvothermal conditions. The resulting COF material (TFB-BMTH) exhibits high crystallinity, excellent porosity with a BET surface area of 632 m2 g−1 and good thermal and chemical stability. The photoactive TFB-BMTH shows significant catalytic activity and recyclability in photocatalytic oxidative hydroxylation of arylboronic acid. The high photocatalytic performance of TFB-BMTH could be attributed to the effective light-harvesting platform with the efficient generation, migration and separation properties of photogenerated charge pairs in such a system. In addition, TFB-BMTH showed significant fluorescence quenching for the sensing of Cu2+. X-ray photoelectron spectroscopy and Fourier transform infrared techniques verified the interaction between Cu2+ and functional units in TFB-BMTH. This work demonstrates the development of multifunctional COFs and makes important contributions to functional exploration in heterogeneous organic transformation and sensing applications.