Vinylene-linked donor–acceptor covalent organic polymers with low exciton binding energy for enhanced photocatalytic oxidation of sulfides

Abstract

Photocatalytic organic synthesis is a promising technology for green and sustainable organic conversion. Covalent organic polymers (COPs) as an emerging class of porous organic polymers have attracted more and more attention in photocatalytic organic synthesis. However, the relatively high exciton binding energy (E_b) of COPs significantly restricts the exciton dissociation and charge separation in the photocatalytic process, resulting in low photocatalytic efficiency. In this work, a vinylene-linked conjugated COP (Btt-Bdd) with a donor–acceptor (D–A) structure has been prepared through the Knoevenagel condensation reaction. The introduction of a planar π-skeleton donor and vinylene linkage extends the planar π-conjugation of COPs and significantly reduces the E_b to 39.2 meV and improves the charge separation efficiency. Therefore, fully conjugated Btt-Bdd shows excellent photocatalytic performance towards sulfide oxidation with a high conversion and selectivity. The synergistic effect between the D–A structure and vinylene linkage is proved to be an effective way for reducing E_b and thus improving the photocatalytic performance, which provides a good strategy for designing efficient photocatalysts with low E_b for organic synthesis.