Designing Local Electron Delocalization in 2D Covalent Organic Frameworks for Enhanced Sunlight-Driven Photocatalytic Activity

Electron delocalization is a versatile method to tune the electronic structure of materials for maximizing their maximizing performances. Herein, TPBD covalent organic frameworks (COFs) with controlled electron-delocalization characteristics (denoted as TPBD-R-COF, R = H, F, CN, and NO2) were synthesized by molecular engineering to systematically investigate the effect of electron delocalization on photocatalytic performance. We found that the photocatalytic performance can be enhanced by modulating local electron delocalization in COFs. The photocatalytic activity of TPBD-CN-COF is more than 12 times greater than that of TPBD-H-COF in oxidative coupling of amines to imines, where the yield of product was increased from 8 to 99%. The experimental results and theoretical calculations revealed that TPBD-CN-COF with the optimal electron-attracting group of −CN shows the highest charge separation efficiency and electron transport rate, while excessive electron delocalization is not better for such properties. Our findings provide a strategy to design and optimize the photocatalytic performance of COF-based catalysts.