Vinylene-Linked Donor-π-Acceptor Metal-Covalent Organic Framework for Enhanced Photocatalytic CO2 Reduction

Intramolecular charge separation driving force and linkage chemistry between building blocks are critical factors for enhancing the photocatalytic performance of metal-covalent organic framework (MCOF) based photocatalyst. However, robust achieving both simultaneously has yet to be challenging despite ongoing efforts. Here we develop a fully pi-conjugated vinylene-linked multivariate donor-pi-acceptor MCOF (D-pi-A, termed UJN-1) by integrating benzyl cyanides linker with multiple functional building blocks of electron-rich triphenylamine and electron-deficient copper-cyclic trinuclear units (Cu-CTUs) moieties, featuring with strong intramolecular charge separation driving force, extended conjugation degree of skeleton, and abundant active sites. The incorporation of Cu-CTUs acceptor with electron-withdrawing ability and concomitantly giant charge separation driving force can efficiently accelerate the photogenerated electrons transfer from triphenylamine to Cu-CTUs, revealing by experiments and theoretical calculations. Benefiting from the synergistically effect of D-pi-A configuration and vinylene linkage, the highly-efficient charge spatial separation is achieved. Consequently, UJN-1 exhibits an excellent CO formation rate of 114.8 mu mol g-1 in 4 h without any co-catalysts or sacrificial reagents under visible light, outperforming those analogous MCOFs with imine-linked (UJN-2, 28.9 mu mol g-1) and vinylene-linked COF without Cu-CTU active sites (UJN-3, 50.0 mu mol g-1), emphasizing the role of charge separation driving force and linkage chemistry in designing novel COFs-based photocatalyst.