Regulating Donor–Acceptor Interactions within 2-Methylpyridine-Mediated Vinylene-Linked Covalent–Organic Frameworks for Enhanced Photocatalysis

Vinylene-linked covalent–oganic frameworks (COFs), as novel photocatalysts, have garnered considerable attention due to their exceptional stability, remarkable π-electron delocalization, and precisely customizable structures. However, the design of novel monomers for constructing vinylene-linked COFs with tunable electronic structures is still in its early stages and poses a number of challenges. Addressing this, a tritopic monomer was developed by attaching a 3-fold 2-methylpyridine unit to the triphenyl-1,3,5-triazine core. The tritopic monomer was further condensed with tritopic aromatic dialdehydes via a solid-state Knoevenagel polycondensation reaction to form two vinylene-linked 2D COFs (TP-PB and TP-PT COF), which exhibited excellent crystallinity, preeminent stability, and outstanding π-electron delocalization. More importantly, by modulation of the donor–acceptor (D–A) interaction within the COFs, the semiconducting properties of the two COFs could be optimized. Due to the stronger D–A interactions in the TP-PB COF containing 1,3,5-triphenylbenzene unit than the TP-PT COF containing triphenyl-1,3,5-triazine unit, the TP-PB COF exhibited broader visible light absorption, narrower band gap, stronger photocurrent response, and lower charge transfer resistance, which makes the TP-PB COF a more efficient photocatalyst for the photocatalytic selective conversions of organic sulfides to sulfoxides and C-3 thiocyanation of indole derivatives with high catalytic activity and recyclability. This work not only demonstrates the construction of vinylene-linked via 2-methylpyridine Knoevenagel polycondensation but also presents a facile strategy for regulating the semiconducting properties of such COFs by fine-tuning the donor–acceptor (D–A) interactions within the COF matrices.