Covalent Organic Frameworks in Photocatalytic Organic Reactions

Covalent organic frameworks (COFs) have become one of the research focuses currently in porous materials due to their excellent photocatalytic activity. Compared with other heterogeneous photocatalysts, COFs possess regular and controllable structures, large specific surface areas, uniform pore channels and good chemical/thermal stability. Additionally, COFs have suitable band structures, adjustable absorption range, and are easy to be functionalized and recovered/reused after the reactions. The advantages above surely endow COFs with potential value in fundamental researches and industrial applications. In recent years, the application of COFs in photocatalysis has gained rapid progress, especially in the field of photocatalytic organic transformations. Theses significant works have greatly promoted the development of COFs. In this review, numerous synthesis strategies for photo-functionalized COFs are briefly introduced, e.g. , "bottom -up" strategy, post modification and combination method. Then, the photocatalytic reaction mechanisms mediated by COFs are condensed into two pathways, i.e. , energy transfer and electron transfer. The latest research progress of COFs as photocatalysts in photocatalytic selective oxidation reaction (oxidation of amines to imines, preparation of sulfoxides through selective oxidation of sulfides, oxidation hydroxylation of arylboronic acids to phenols, and oxidation of N -aryl tetrahydroisoquinoline), reduction reaction (reductive dehalogenation, hydrogenation of nitrobenzene, and hydrogenation of styrene), coupling reaction (C -C cross-dehydrogenative coupling reaction, C-N cross -coupling reaction, and C-S cross -coupling reaction), cyclization reaction, polymerization reaction and asymmetric organic synthesis, etc. , are succinctly outlined and discussed. Finally, the application of COFs in photocatalysis is summarized and prospected.