A Study On Novel Strategies For Constructing 2D Heteropore Covalent Organic Frameworks

Covalent organic frameworks?COFs?possess periodic two dimensional?2D?or three-dimensional?3D?network structures formed by linking organic building blocks with dynamic covalent bonds.COFs have attracted a lot of interest due to their versatile applications in many fields,including gas storage and separation,electrochemistry and energy storage,drug delivery,opto/electronic devices,sensing,proton conduction,ion exchange,environmental governance and catalysis.2D heteropore COFs,as a new branch of the COFs family,bear different kinds of well-ordered and periodically distributed pores in an infinite2D sheet.These materials exhibit ordered hierarchical porosity,which endows them with great potential in fabricating functional materials.The first chapter provides a detailed literature review on COFs,which mainly focuses on the types of covalent bonds used to construct COFs,their synthetic methods and applications,and design principle for different topological structures of COFs.In the second chapter,a multiple-linking-site strategy was developed,which offers precision construction of heteropore COFs containing two kinds of hexagonal pores with different shapes and sizes.This strategy was developed by designing a building block in which double linking sites are introduced at each branch of a C₃-symmetric skeleton,the most widely used scaffold to construct COFs with homogeneous porosity.This design provides a general way to precisely construct heteropore COFs without formation of isomers.Furthermore,the as-prepared heteropore COFs have hollow-spherical morphology,which has rarely been observed for COFs,and an uncommon staggered AB stacking was observed for the layers of the 2D heteropore COFs.In the third chapter,we describe a new approach to produce COFs bearing three different kinds of pores.The design is fulfilled by the combination of vertex-truncation with multiple-linking-site strategy.On the basis of this design,a“V”-shaped building block carrying two aldehyde groups on the end of each branch has been synthesized.Condensation of it with 1,4-diaminobenzene or benzidine leads to the formation of two triple-pore COFs,TP-COF-DAB and TP-COF-BZ,respectively.The topological structures of the triple-pore COFs have been confirmed by PXRD studies,synchrotron small-angle X-ray scattering?SAXS?experiments,theoretical simulations,and pore size distribution analyses.Furthermore,for the first time,an in situ COF-to-COF transformation has also been achieved by heating TP-COF-BZ with 1,4-diaminobenzene under solvothermal condition,which leads to the formation of TP-COF-DAB via in situ replacing the benzidine linkers in TP-COF-BZ with1,4-diaminobenzene linkers.In the fourth chapter,we report two novel 2D heteropore COFs which bears two kinds of hexagonal micropores with different shapes and sizes.They have been constructed by the condensation of monomers with C_2v-and D_3h-symmetry,and their structures been confirmed by PXRD studies,synchrotron SAXS experiments,theoretical simulations and pore size distribution analyses.In the fifth chapter,a hexaazatriphenylene?HAT?derivative?compound 1?that bears four n-octyl chains and two thienyl groups was designed and synthesized.Further light-induced oxidation coupling reaction led to thienyl-fused compound 2.Their photophysical and electrochemical properties and self-assembly behavior have been investigated by UV/Vis,fluorescence,and ¹H NMR spectroscopies,cyclic voltammetry?CV?,scanning electron microscopy?SEM?,and powder X-ray diffraction?PXRD?.Although the difference in compounds 1 and 2 only lie in one single bond that connects the two thienyl segments,they displayed remarkably different properties,revealing an interesting structure-property relationship.