Cyano Substituent on the Olefin Linkage: Promoting Rather than Inhibiting the Performance of Covalent Organic Frameworks

Abstract

It is generally believed that the electron-withdrawing cyano group in the olefin linkage would inhibit the stability and π-conjugation of covalent organic frameworks (COFs), which raises concerns about their optoelectronic properties. However, the structure–activity relationship between the structure of olefin linkages and properties of COFs is still inconclusive. In this work, imine-, vinylene-, and acrylonitrile-linked COFs with identical triphenyltriazine building blocks were designed and synthesized. Our work demonstrated that construction of acrylonitrile linkages not only enhanced the chemical stability and photostability but also led to remarkable optoelectronic properties with a record fluorescence quantum yield of 35.37% in the solid state. Further, the acrylonitrile linkage endows TTAN-COF/Pt NPs with superior and durable photocatalytic activity in both the hydrogen evolution reaction (11.94 mmol g^–1 h^–1; BET surface area, 739.28 m² g^–1) and aerobic oxidation reaction. This work demonstrates that the acrylonitrile linkage can significantly enhance the optoelectronic properties and photocatalytic activities of COFs compared with the highly π-conjugated vinylene linkage, providing a valuable reference for the design of optoelectronic functional materials.