Visible-light-enabled Transformations Of Small Organic Molecules Catalyzed By Covalent Organic Frameworks

In the past decades,covalent organic frameworks(COFs)have emerged as a new type of porous organic materials with high stability,good crystallinity and periodicity.Many evidences showed that some COFs might be able to be used in heterogeneous photocatalytic chemical transformations for their excellent photoactivity.As heterogeneous photosensitizers,photoactive COFs are easier to be recycled and reused than homogeneous photosensitizers do,and their photoelectric properties can be controlled expediently.However,their applicability in visiblelight-driven organic reactions is still limited,and their photocatalytic mechanism continues to be unclear.Therefore,it is of great importance to develop new methods for photoactive COFs catalyzed organic transformations under visible light irradiation.In this thesis,based on the previous studies of photoactive COFs,including their synthesis,structure and photoactivity,we have developed two new methods for visible-light-driven organic transformations catalyzed by photoactive COFs,the specific results are as follows:A new,practical method for synthesis of diverse 6-substituted-phenanthridines from 2-aryl phenyl isocyanides via visible-light-induced tandem radical addition-cyclization under very mild conditions has been developed.In this method,photoactive COFs were employed as the recyclable heterogeneous photosensitizer.The reaction shows good functional group compatibility and efficiency,the recycling experiments and continuous flow experiments also exhibit the excellent recyclability and practicability of the heterogeneous photosensitizer.The scope of application of covalent organic frameworks in photoinduced reactions has been broadened.Importantly,a new strategy for the construction of compounds containing phenanthridine cores has been provided.A new protocol has been developed for visible light-induced selective oxidation of small organic molecules using covalent organic frameworks as the recyclable heterogeneous photosensitizer,oxygen in air as the green oxidant.A wide range of sulfoxides,amides,quinolones and other heterocyclic compounds were synthesized under very mild reaction conditions,exhibiting high efficiency and excellent functional group tolerance.This approach provides a green,sustainable,operationally simple and low-cost synthetic technology for the construction of potential drugs and diverse biologically active molecules.Additionally,the study on the reaction mechanism and practical applications of this method is still on going.