Thiol–Ene Click Chemistry: A General Strategy for Tuning the Properties of Vinylene-Linked Covalent Organic Frameworks

Vinylene-linked Covalent Organic Frameworks (V-2D-COFs) are a class of promising porous organic materials that feature fully π-conjugated structures, high crystallinity, ultrahigh chemical stability, and extraordinary optoelectronic properties. However, the types of reactions and the availability of monomers for synthesizing sp2-c linked COFs are considerably limited by the irreversibility of the C═C bond, and the complete π-conjugated structure restricts their in-depth research in hydrophilicity, membrane materials, and proton conductivity. Postsynthetic modification (PSM), which can avoid these problems by incorporating functional moieties into the predetermined framework, provides an alternative way to construct diverse V-2D-COFs. Herein, we report a general strategy to introduce C–C, C–S–C, and functional groups into sp2-c-COFs via the thiol–ene click reaction. To demonstrate the universality of this approach, we synthesized two sp2-c COFs (COF-CN and COF-1), and subsequently introduced six different types of thiol compounds at their skeletal C═C sites. The quantitative yield was confirmed by X-ray Photoelectron Spectroscopy (XPS) and cross-polarization magic angle spinning 13C NMR spectroscopy. This thiol–ene click modification of vinylene-linked COFs at skeletal C═C sites allows for flexible structural design, providing these COFs with new linkages (C–C and C–S–C) that are otherwise difficult to produce directly. Thus, it facilitates precise modulation of their properties, such as photophysical properties, hydrophilicity, and proton conductivity, promising a diverse range of compelling applications for the future.