Topology-induced local electric polarization in 2D thiophene-based covalent organic frameworks for boosting photocatalytic H2 evolution

2D Substoichiometric covalent organic frameworks (2D-SSCOFs) are a new kind of porous organic polymers with accurate modifiability, good stability and abundant porosity. However, the strong exciton effects and slow charge transfer in 2D-SSCOFs can severely linker hinder the efficiency of photocatalytic energy conversion. Herein, we report a brand new thiophene-based 2D-SSCOF (PTT-COF) constructed by the Schiff base reaction using thiophene-enriched tri-topic linker and tetra-topic pyrene as structural unit precursors. Interestingly, PTT-COF exhibits a novel topology, high crystallinity, abundant delocalization electrons and weak excitonic effects. Inspired by the unique structural characteristics and photoelectrical performance, PTT-COF is utilized for photocatalytic hydrogen evolution. Experimental and theoretical studies have confirmed that introducing thiophene effectively modulates the topology of the COF, inducing local charge delocalization and redistribution, thus suppressing the excitonic effect and enhancing the photocatalytic performance. In addition, the periodic, uncondensed functional groups allow PTT-COF to be accurately modified by ferrocene carboxaldehyde as organic hole transporting ligands, leading to a further 40% enhancement in hydrogen evolution rate up to 79.610 mmol g–1 h–1. These findings in this work not only offer a brand new 2D-SSCOF with novel topology, but also provide new opportunities and directions for the ration design of 2D-SSCOF for emerging functional applications.