Regulating the Photoisomerization of Covalent Organic Framework for Enhanced Photocatalytic Hydrogen Evolution

• Published in: Chinese journal of chemistry Vol. 42; no. 21; pp. 2621 - 2626
• Main Authors: Huang, Xingye, Guo, Jia
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag GmbH & Co. KGaA 01-11-2024; Wiley Subscription Services, Inc
• Subjects: Charge distribution; Charge separation; Configuration management; Conjugation; Covalent organic framework; Hole distribution; Hydrogen evolution; Hydrogen evolution reaction; Photocatalysis; Photochemicals; Photoisomerization; Quantum efficiency; Water splitting
• ISSN: 1001-604X; 1614-7065
• DOI: 10.1002/cjoc.202400437

Comprehensive Summary
Covalent organic framework (COF) is a desirable platform to tailor electronic properties for improving photocatalytic performances. However, the study on excited‐state configurations that determine photogenerated carrier dynamics has long been neglected. Herein, we concentrate on the molecular design of β‐ketoenamine‐linked COFs to drive their photoisomerization via the excited‐state intra‐molecular proton transfer (ESIPT), which can induce the partial keto‐to‐enol tautomerization and accordingly rearrange the photoinduced charge distribution. We demonstrate that the push‐pull electronic effect of functional side groups attached on the framework linkers is directly correlated with the ESIPT process. The phenylene linkers modified with electron‐withdrawing cyano‐groups reinforce the ESIPT‐induced tautomerization, leading to the in situ partial enolization for extended π‐conjugation and rearranged electron‐hole distribution. In contrast, the electron‐rich linkers limit the photoisomerization of COF and suppress the photoinduced electron accumulation. Thus, the maximum hydrogen evolution rate is achieved by the cyano‐modified COF, reaching as high as 162.72 mmol·g–1·h–1 with an apparent quantum efficiency of 13.44% at 475 nm, which is almost 11.5‐fold higher than those of analogous COFs with electron‐rich linkers. Our work opens up an avenue to control over the excited‐state structure transformation for enhanced photochemical applications.
The molecular engineering on the regulation of the excited‐state configurations for β‐ketoenamine‐linked covalent organic frameworks (COF) has been proposed. Through the chemical modification of COF linkers, it is found that the electron‐withdrawing cyano groups facilitate the ESIPT‐induced photoisomerization of COFs and in turn, benefit the photoinduced electron‐hole separation for the optimum photocatalytic hydrogen evolution rate of as high as 162.72 mmol·g–1·h–1 under visible irradiation.