Inducing local charge polarization by constructing isomeric covalent organic frameworks with different orientations of imine bonds for enhancing photocatalytic hydrogen evolution

Abstract

Imine-linked covalent organic frameworks (COFs) have garnered significant attention in photocatalysis due to their ease of synthesis and excellent crystallinity. However, there is still limited research on the influence of imine bond orientation on the processes of exciton dissociation and charge carrier separation in COFs. This study presents the synthesis and characterization of two novel COFs with distinct imine bond orientations. Experimental and theoretical investigations reveal that though the structures of these COFs are similar, their performance in exciton dissociation and electron–hole pair separation varies significantly. The orientation of the imine bond plays a crucial role in inducing local charge polarization and delocalization, thus influencing the efficiency of exciton dissociation and charge separation. Notably, the photocatalytic hydrogen-evolution activity for the COFs with the N-atom orientation in imine bond towards the acceptor is three times higher than that for COFs with the N-atom orientation in imine bond towards the donor. This study provides a clear design strategy for imine-linked COF-based photocatalysts and advances the development of COFs in photocatalysis.