Rational Design of Vinylene-Linked Covalent Organic Frameworks for Modulating Photocatalytic H-2 Evolution

Vinylene-linked covalent organic frameworks (COFs) have attracted enormous attention for photocatalytic H-2 evolution from water because of their fully conjugated structures, high chemical stabilities, and enhanced charge-carrier mobilities. In this work, two novel vinylene-linked COFs with tuned cyano contents were successfully synthesized and then employed as photocatalysts for H-2 generation. Notably, the photocatalytic H-2 production rate of the COF with the higher cyano content reached 73 & mu;mol h(-1) under visible light irradiation, which is 2.4 times higher than that with the lower content (30 & mu;mol h(-1)). Both the experimental and computational results demonstrated that the rational design incorporating cyano groups into COF skeletons could precisely tune the corresponding energy levels, expand the visible-light absorption, and improve the photoinduced charge separation. This work not only provides a simple method for modulating the photocatalytic activities of COFs at the molecular level, but also affords interesting insights into the relationship between their structures and photocatalytic performance.