Designing chemically stable amide-linked covalent organic framework for efficient photocatalytic synthesis of benzimidazole derivatives

Abstract

Visible-light-driven synthesis of benzimidazoles has attracted increasing attention due to its green and sustainable advantages, but the development of efficient and stable photocatalysts remains a major challenge. Covalent organic frameworks (COFs) offer a promising platform, yet traditional imine-linked COFs often suffer from poor chemical stability. In this study, a robust amide-linked COF (Am-COF) was constructed via post-synthetic bond conversion from an imine precursor (Im-COF). The resulting Am-COF retained high crystallinity and exhibited excellent thermal and chemical stability than Im-COF. Am-COF displays excellent photocatalytic activity and reuseability in the green synthesis of benzimidazole derivatives, with yields reaching up to 97 %. This yield is approximately 2 times greater that of Im-COF, demonstrating the superior efficiency of Am-COF. A mechanistic study revealed that the excellent photocatlytic activity of Am-COF is attributed to the enhanced visible-light absorption and more efficient charge separation performance compared with the imine-linked analogue. This work provides a practical strategy to improve COF photocatalysts via amide bond engineering, enabling efficient and recyclable photocatalytic systems for sustainable heterocycle synthesis.