Construction of donor-acceptor type conjugated microporous polymers: A fascinating strategy for the development of efficient heterogeneous photocatalysts in organic synthesis

Metal-free, visible-light driven, solid organic photocatalysts provide a more green and environmentally friendly alternative to traditional metal-based photocatalysts. Donor-Acceepor (D-A) dyads possess a feature of easy to adjust the photoelectric properties, and enhance their photocatalytic performances. Here we report a fascinating strategy for screening excellent organic porous photocatalysts through oxidative coupling of single D-A based monomer, which has still an important advantage to ensure uniformity of polymer structure except for the inherent characteristics of D-A polymers. According to this strategy, three D-A typed conjugated microporous polymer (DA-CMP) photocatalysts consisting of alternating electron-rich (carbazole) and electron-deficient (benzene, 4,7-diphenyl-2,1,3-benzothiadiazole or anthraquinone) units have been synthesized, and their porosity and photoelectric properties including adsorption, emission, lifetime, optical bandgaps, energy levels and transient photocurrent response as well as photocatalytic activity, were conveniently tuned by selecting different D-A monomers with tunable electron-deficient moiety. These DA-CMPs were exploited as metal-free photocatalysts in the oxidative C-H functionalization reactions in the presence of visible-light and molecular oxygen. They showed excellent photocatalytic activity, extensive substrate adaptability and outstanding reusability, due to combining some key features like permanent porosity, outstanding stability and optoelectronic properties. In addition, the reaction mechanism for DA-CMP photocatalyzed C-H functionalization reactions under visible-light irradiation was investigated in detail. Moreover, to prove in depth the benefits of the heterogeneous photo catalysis, a continuous flow procedure has been conducted with an excellent yield.