Enaminone-Linked Covalent Organic Frameworks for Boosting Photocatalytic Hydrogen Production

Covalent organic frameworks (COFs), possessing pre-designable structures and tailorable functionalities, are promising candidates for photocatalysis. Nevertheless, the most studied imine-linked COFs (Im-COFs) usually suffer from unsatisfactory stability and photocatalytic performance. To meet this challenge, a series of highly stable enaminone-linked COFs (En-COFs) have been synthesized and afford much improved visible-light-driven hydrogen production activities, ranging from 44 to 1078 times that of isoreticular Im-COFs, with the only difference being the linkages (enaminone vs. imine) in their structures. The enhanced light-harvesting ability, facilitated exciton dissociation and improved chemical stability account for the superior activity. Furthermore, quinoline-linked COFs (Qu-COFs) have been further obtained via the post-modification of Im-COFs. Compared with Im-COFs, the photocatalytic activities of Qu-COFs are significantly improved after modification, but still below those of the corresponding En-COFs (3-107 times). The facile synthesis, excellent activity, and high chemical stability demonstrate that En-COFs are a promising platform for photocatalysis.