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 pi-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 pi-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.