Tailoring Electronic State in Regioisomeric Benzotriazole Covalent Organic Frameworks for Enhanced Photocatalytic Hydrogen Generation.

Photocatalytic hydrogen evolution represents a promising and green technology for solar-to-chemical energy conversion. Recently, covalent organic frameworks (COFs) have become the most competitive platforms in various photocatalysts owing to their customizable structure and function, as well as high orderliness. However, the inefficient utilization of photoinduced charge carriers severely impedes the improvement of the catalytic efficiency of COFs. In this work, two regioisomeric imine-linked COFs, ETTA-N1MBTz COF and ETTA-N2MBTz COF, incorporating N-methyl-benzotriazole moieties with different methyl positions, are constructed using Schiff-base polycondensation. The photoelectric properties, electronic states, and exciton binding energies of both COFs can be easily manipulated through the N-methyl positional isomerization strategy. Importantly, N-2-methyl substituted ETTA-N2MBTz COF shows a superior photocatalytic efficiency with hydrogen evolution rate up to 17,900 μmol g^-1 h^-1 under visible-light irradiation, far outperforming its isomeric ETTA-N1MBTz COF (1360 μmol g^-1 h^-1) under the same conditions. This finding offers an effective strategy for regulating electronic state and charge transfer dynamics in COFs toward efficient solar-energy conversion and storage.