Tuning the exciton binding energy of covalent organic frameworks for efficient photocatalysis

Abstract

Owing to the large exciton binding energy (>100 meV) of most organic materials, the process of exciton dissociation into free electrons and holes is seriously hindered, which plays a key role in the photocatalytic system. In this study, a series of chalcogen (S, Se)-substituted mesoporous covalent organic frameworks (COFs) have been synthesized for enhanced photocatalytic organic transformations. Photoelectrochemical measurements indicate that the introduction of semi-metallic Se atom and the enlargement of conjugation degree can not only reduce the exciton binding energy accelerating the charge separation, but also reduce the band gap of COFs. As a result, the COF-NUST-36 with the lowest exciton binding energy (39.5 meV) shows the highest photocatalytic performance for selective oxidation of amines (up to 98% Conv. and 97.5% Sel.). This work provides a feasible method for designing COFs with high photocatalytic activity by adjusting exciton binding energy.