2-Pyran-4-Ylidene Malononitrile Based Conjugated Microporous Polymers as Metal-Free Heterogeneous Photocatalysts for Organic Synthesis

Photoactive conjugated microporous polymers (CMPs) as heterogeneous photocatalysts provide a sustainable alternative to classical metal-based semiconductor photosensitizers. However, previously reported CMPs are typically synthesized through metal catalyzed coupling reactions, which bears product separation, but also increases the price of materials. Herein, a new type of sp2 carbon linked DCM-CMPs are successfully designed and synthesized by organic base catalyzed Knoevenagel reaction using 2,6-Dimethyl-4H-pyran-4-ylidene-malononitrile and aromatic polyaldehydes as monomers. The new polymers feature inherent porosity, excellent stability, and fully pi-conjugated skeleton with broad visible-light absorption. They effectively induce the synthesis of benzimidazole compounds under light irradiation, and exhibit wide substrate adaptability with outstanding recyclability. Two new sp2 carbon linked porous polymers are designed and constructed by Knoevenagel reaction. They are found to be excellent metal-free heterogeneous photocatalysts with wide substrate adaptability and outstanding recyclability for the synthesis of benzimidazole compounds under mild conditions. image