Covalent organic frameworks and their composites as multifunctional photocatalysts for efficient visible-light induced organic transformations

• This review comprehensively overviews the potential of COFs for photocatalysis and photothermal catalysis. • The synthetic strategies for the COF-based photocatalysts are discussed in detail. • The application scope and corresponding reaction mechanism of COF-based photocatalysts is systematically investigated. • Foreseeable challenges and perspectives for the development of COF-based photocatalysts are proposed. Light-involved catalysis, including photocatalysis and photothermal catalysis, has been considered as one of the most promising alternatives to traditional thermocatalysis for various organic transformation reactions, while the development of highly efficient photocatalysts is the prerequisite and of significant importance in the field of light-mediated catalysis. Covalent organic frameworks (COFs) represent a new class of crystalline molecular solids with periodically ordered skeletons that feature a series of unique properties, such as structural designability and durability, extensive π-electron conjugations, light-harvesting as well as semiconducting characteristics. Benefiting from these outstanding properties, the blooming development of COFs in recent years has brought promising impetus for the realization of visible-light induced organic transformations by photocatalysis or photothermal catalysis. In this review, the up-to-date applications of COFs as versatile platforms for various selective light-initiated organic transformations were comprehensively summarized and discussed. Firstly, the general background and synthetic strategies of COF-based photocatalysts were briefly introduced, followed by the detailed classification and discussion of each type of reactions reported thus far. Finally, the limitations, critical challenges, and future perspectives of COF photocatalysis and photothermal catalysis were provided. It is anticipated that this review can serve as a starting point for the researchers to get in-depth insight into this largely unexplored but promising field and stimulate more intensive research for rational design of more efficient COF-based photocatalysts to achieve more creative visible-light involved photosynthesis.