Design,Synthesis And Photocatalytic Applications Of Covalent Organic Frameworks Based On Multicomponent Reactions

Covalent organic frameworks（COFs）are a class of crystalline organic porous polymers formed by covalent bonding of light elements,exhibiting the features of high crystallinity,high porosity,high specific surface area,and structural and functional diversities.In recent years,the strategy of preparing COF materials based on one-pot multicomponent reactions has gradually received more and more attention and application.COFs with more complex structures and functions can be synthesized by one-pot multicomponent reactions,which has the advantages of convenient operation,high efficiency,structural diversity and strong sustainability.Recently,a new strategy for the synthesis of COFs driven by natural sunlight has been reported.Stable covalent bonds can be formed between the building blocks by the irradiation of the visible light to realize the successful green synthesis of COFs.However,visible light-driven synthesis of COFs based on multicomponent reactions has not been reported.Therefore,the employment of photocatalytic multicomponent reactions to construct stable COFs probably will open up a feasible and green route to access the COFs with different functionalities.The Petasis reaction is a common multicomponent reaction for the synthesis of substituted amines,which can construct various types of complex structures.If Petasis reaction is used to construct COF materials,the diversity of COFs will be greatly improved.Based on the above understanding,this study for the first time realized a multicomponent Petasis reaction driven by visible light to construct a series of structurally stable COFs,and realized an efficient and stable oxidative hydroxylation reaction of arylboronic acids under visible light.At the same time,this study also used iodine-catalyzed multicomponent oxidative cyclization reaction to synthesize COFs based on thiazole linkage and applied them to photocatalytic sulfide oxidation.In this study,the feasibility of constructing COFs by photocatalytic Petasis multicomponent reaction was successfully explored.At the same time,a new method for the synthesis of COFs based on thiazole connection was broadened,and the multicomponent reaction was realized to construct functional COF materials,which opened up ideas for the design and synthesis of complex COFs.This thesis mainly includes the following three parts:1.We provided a brief overview of MCR-driven COF synthesis,focusing on each type of MCR employed for COF synthesis in chronological sequence,including multicomponent Debus-Radziszewski reaction,Strecker and Povarov reaction,A³ coupling,Groebke-Blackburn-Bienayméreaction and Doebner reaction.Afterwards,we discussed the bonding methods and synthetic methods of COFs that have been reported thus far,and finally we briefly provided an overview of the applications of COFs in the field of photocatalysis,mainly including photocatalytic hydrogen evolution,photocatalytic CO₂ reduction,and photocatalytic organic reactions.2.A series of COFs with excellent crystallinity,high stability and permanent porosity were synthesized for the first time by visible-light-activated multicomponent Petasis reaction under ambient conditions and visible light irradiation,and further characterized by PXRD,FT-IR,TGA,solid-state ¹³C CP/MAS NMR and BET.Meanwhile,the obtained Cy-N₃-COF exhibited excellent photocatalytic activity for the oxidative hydroxylation of arylboronic acids,with superior yields of 99%,and the material still exhibited excellent photocatalytic activity and stability even after five cycles of reactions.The concept of multicomponent photocatalytic polymerization not only enriches the methodology for COF synthesis,but also opens up a new route for the construction of COFs that might be not possible with the existing thermally-driven MCRs for COFs synthesis.3.A series of thiazole-linked COFs were designed and synthesized by the condensation of iodine,2,5-dimethoxyterephthaldehyde,NH₄SCN and 1,3,5-tris（4-aminophenyl）benzene via a C-H functionalization and oxidative annulation.To prove the universality of this approach,another thiazole-linked COFs material was also successfully synthesized.FT-IR,PXRD and solid state ¹³C CP/MAS NMR characterization confirmed that the synthesized COF had the thiazole ring structure.The stability and photophysical properties of COFs were determined by TGA and UV-Vis.The thiazole-linked COF was used for photocatalytic oxidation of sulfide,and the yield can reach up to 92%,showing excellent photocatalytic activity.This approach successfully synthesized COFs based on thiazole linkages using ammonium thiocyanate as sulfur source,successfully expanding the synthetic strategies of thiazolyl-linked COFs.