Facile construction of olefin-linked covalent organic frameworks for enhanced photocatalytic organic transformation via wall surface engineering

Exploration of fully conjugated covalent organic framework (COF)-based photocatalysts has become valuable research owing to their excellent stability, outstanding semiconducting properties and fascinating properties. However, the design and construction of olefin-linked COF-based photocatalysts are still in an infant stage. Herein, three olefin-linked 2D COFs (F-TBT-COF, TBT-COF and MeO-TBT-COF) with high crystallinity and preeminent stability were designed and synthesized via the Knoevenagel condensation of aryl aldehyde monomers (F-TBT, H-TBT and MeO-TBT) and 2,4,6-trimethyl-1,3,5-triazine (TMT). Significantly, the pore wall surface of these COFs was docked with a single atom or unit to induce distinct inductive and conjugative effects. Then these effects transmitted to the COF's backbone, so that the absorption range, band gap and charge transfer efficiency of the COFs can be regulated via wall surface engineering. The MeO-TBT-COF with a surface methoxy site showed the highest photocatalytic activity and recyclability in the visible-light-driven C-3 thiocyanation reaction of indole derivatives and aerobic transformation of arylboronic acids to phenols. Therefore, we present a facile strategy to design and construct olefin-linked COF based photocatalysts via tuning the groups of the framework's pore wall surface.