Tailoring Vinylene-Linked Triazine Covalent Organic Frameworks for Efficient Photocatalytic Selective Oxidation of Organic Sulfides.

Covalent organic frameworks (COFs) have emerged as a highly promising platform for photocatalytic reactions because their electronic structures can be tailored through the rational selection of linkages and building blocks. Here, by the condensation of 2,4,6-trimethyl-1,3,5-triazine (TMT) with 2,4,6-tris(4-((4-formylphenyl)ethynyl)phenyl)-1,3,5-triazine (TPEPT) and 2,4,6-tris(4'-formyl-biphenyl-4-yl)-1,3,5-triazine (TBPT), respectively, two vinylene-linked triazine COFs, TMT-TPEPT-COF and TMT-TBPT-COF, are rationally designed and constructed. Compared to TMT-TBPT-COF, acetylene insertion enhances the backbone coplanarity of TMT-TPEPT-COF, reducing the dihedral angle from 33.4° to 14.0°. Theoretical calculations reveal a more spatially polarized frontier-orbital distribution in TMT-TPEPT-COF, with the lowest unoccupied molecular orbital preferentially localized on the triazine units. TMT-TPEPT-COF shows a narrower band gap, broader visible-light absorption, faster charge separation and migration than TMT-TBPT-COF. Consequently, TMT-TPEPT-COF exhibits superior activity for the efficient photocatalytic selective oxidation of organic sulfides and the detoxification of a sulfur-mustard gas simulant 2-chloroethyl ethyl sulfide with oxygen. Superoxide is pinpointed as the key reactive oxygen species driving the photocatalytic oxidation. Collectively, this work establishes π-conjugation engineering as a sustainable means to enhance COF electron transfer for solar-driven photocatalytic reactions.