Linkage Engineering of Triazine-Based Covalent Organic Frameworks for Selective Photocatalytic Oxidation of Amines.

Covalent organic frameworks (COFs) have garnered significant attention as versatile photocatalysts due to their tunable structure and activity. In this work, linkage engineering is applied to two triazine-based COFs, yielding TFPT-spc-COF, with a C═C linkage and TFPT-IM-COF, with a C═N linkage. TFPT-spc-COF exhibits better thermal stability and a significantly higher specific surface area than TFPT-IM-COF. More importantly, the C═C linkage in TFPT-spc-COF leads to better optoelectronic properties than the C═N linkage in TFPT-IM-COF, as it promotes efficient charge separation and transfer and π-delocalization, as evidenced by experiments and density functional theory calculations. Consequently, TFPT-spc-COF demonstrates higher activities than TFPT-IM-COF for selective photocatalytic oxidation of amines. Notably, a diverse range of amines achieve high conversions to corresponding imines with high selectivities. Superoxide, generated through photoexcited electron transfer to O, is identified as the predominant reactive oxygen species. This work underscores the pivotal role of linkage engineering in optimizing COFs for selective reactions.