Green Synthesis And Structural Regulation Of Covalent Organic Framework Materials

Covalent Organic Frameworks?COFs?are constructed using dynamic and reversible covalent chemistry.The COFs are synthesized through light elements?C,H,O,N,B,Si,S,etc.?composed of small organic molecules,which are assembled by dynamic covalent bonding to form 1D,2D or 3D structures crystalline organic porous material with a predictable topology.Because of their predictable pores,better specific surface area and designable frame,they have proud application prospects in many fields,such as gas adsorption and separation,heterogeneous catalysis,electrocatalysis,photocatalysis,organic Fluorescence detection,organic photoelectric and electrochemistry.At present,COFs are synthesized through a few reversible chemical reactions.The usual linkages include boron oxygen linkages,amide linkages,imine linkages,enone amine linkages,triazine linkages,sp2 carbon-carbon double bond linkages,polyaryl ether linkages,and ester linkages.First part:Recently our research group reported a series of new types of COF generated by Michael addition-elimination reactions,which has increased the reaction types of COF.These new types of COF are environmentally synthesized under normal temperature and pressure.This method provides us with a green synthesis of COFs strategy,and this is a sustainable and eco-friendly synthesis method.However,there are only four COFs in this series,and it is necessary to develop and explore the COFs generated by the new Michael addition-elimination reaction.It is with these ideas in mind that we show here two new covalent organic frameworks?JUC-524 and JUC-525?synthesized through Michael addition-elimination reactions.The two COF were successfully synthesized using the environmentally friendly water phase method and the conventional organic solvothermal method.This achievement not only expands the series of COF generated by the new Michael addition-elimination reaction,but also explores the difference between the COFs prepared by these two synthetic methods.Second part:Compared with the two-dimensional covalent organic framework,the three-dimensional covalent organic framework has extremely high theoretical porosity and rich pore structure.But in fact,3D-COF generally have the characteristics of excessive penetration number and breathing effect.How to improve this phenomenon is the key to open up 3D-COF bottleneck.Therefore,we explore how to prepare a non-penetrating three-dimensional COF skeleton and inhibit its breathing effect.We prepare a non-penetrating skeleton by adding methoxy groups to the skeleton,and then gradually suppress the respiration effect by increasing the number of methyl groups on the skeleton.We have successfully prepared a JUC-552covalent organic framework with high specific surface,non-penetrating,and no breathing effect.It is worth noting that COF-JUC-552 has a permanent mesopore of26.5?and a specific surface area of 3023 m² g^-1,which is much higher than the reported COF with the same network.To our knowledge,COF-JUC-552 is the first 3D mesoporous COF with non-interpenetrating dia topology.Third part:Nowadays,more and more researchers are turning their attention to the three-dimensional covalent organic framework,but there are still many fields to be studied in this field.The topologies of the currently synthesized 3D COF are all pre-designed and cannot be changed after preparation and synthesis.However,other crystalline materials,such as molecular sieves and MOFs,which have been studied for topological transformations.Accordingly,the topological transformations of 3D COF drive researchers go to explore and discover.Therefore,based on the flexible and variable structural properties of bicarbazole unit modules,we have prepared and synthesized a three-dimensional covalent organic framework that has the ability of topological transformation.Therefore,based on the flexible and variable structural properties of the bicarbazole unit module,we design tetrakis?4-aminophenyl?methane?TPAM?and 4,4?,4??,4???-?[9,9?-Bicarbazole]-3,3?,6,6?-tetrayl?tetrabenzaldehyde?BCTB-4CHO?as building units to successfully synthesize 3D-BCTB-COF.After a series of characterization,we discovered that 3D-BCTB-COF has the amazing topological transformation ability.The transition from pts topology to dia topology can be achieved through the breathing effect of the framework,which is unprecedented in previous COF research.