| As a rising star in the field of organic porous materials,due to their tunable structure and functional design,covalent organic frameworks（COFs）are widely explored in gas separation and storage,catalysis,energy storage,sensor and so on.Since the first case of COFs was reported in 2005,researchers have made considerable progress in preparation and design of COFs after years of struggle.However,as a burgeoning class of polymers,the mission of COFs is to perform its function in specific fields and create wealth and value for the world.And scientists have begun to focus on the functions and applications of COFs in the suitable fields.Whereas the inherent insoluble and infusible properties of COFs make it difficult to be directly processed and utilized,researchers try to functionalize them with specific functions at the same time as their preparation and investigate their potential applications.In this context,it is particularly necessary to develop functionalization methods for COFs.It is well known that COFs are a class of crystalline materials with specific spatial structures in which organic units are linked by covalent bonds.The designable composition and spatial structure of COFs are the keys to realize functionalization.Among them,the organic units and linkages are the main sites for functionalization;their spatial structures can be designed and utilized as well.Based on this,this thesis focuses on the functionalization of COFs from four aspects:bottom-up synthesis based on functional monomers,post-synthetic modification,exploration of functional linkage and pre-design of spatial structure.In particular,the detailed studies are presented as follows:1.Bottom-up synthesis based on functional monomers.As a class of ligands with special photophysical and photochemical properties,Salphens has been well investigated in catalysis,sensors,carriers and so on.In the second chapter,three“two-in-one”monomers with different metallosalphen moieties were synthesized,which are named as M-Salphen（M=Ni,Cu,Zn）.Self-polycondensation of these K-shaped monomers facilely afforded three new metallosalphen-based COFs（M-Salphen-COF）with unprecedented topology that does not exist in the database of Topos Pro.Regarding to their outstanding stabilities,broad visible absorption and the densely and uniformly distributed metallosalphens in the skeletons,the photocatalytic bromination performance of the three COFs were further investigated.Among them,Ni-Salphen-COF exhibited the highest performance on both conversion（>99%）and selectivity（>90%）.2.Functionalization based on post-synthetic modification.Sulfonic group has been widely used in the construction of proton-conducting materials,which can not only act as a proton donor but also promote the formation of hydrogen-bonding networks for proton transport.In the third chapter,we designed and synthesized two ultrastable imine COFs annulated with cyclic ether moieties.Amide-linked and sulfonated frameworks were synthesized from imine-linked precursors via sequentially engineering to oxidize into amide linkages and to anchor sulfonic acid groups onto pore walls.The resulting sulfonated COFs exhibited a moderate proton conductivity.In order to further improve the utilization of channels and improve the proton conductivity of the material.Hybrid materials were prepared by introducing sulfonated polyetheretherketone（SPEEK）into the channels of sulfonated COFs.After systematic testing and analysis,the prepared hybrid material can achieve a proton conductivity of 6.22×10-3 S cm-1 at 98%RH and 90℃.3.Exploration of functional linkage.As an important part of COFs,functional linkages can endow COFs with additional tailored properties besides the building units,which thereby further diversify COFs with desired functions.In the fourth chapter,we developed a new arylamine linkage for the construction of COFs.Two new arylamine-linked COFs（AAm-TPB and AAm-Py）were prepared by condensing DMSS with corresponding multitopic amines（TPB-NH2 and Py-NH2）.Compared with the imine-linked COF counterparts,the two arylamine-linked COFs exhibited much improved conjugation and narrower optical bandgaps.Bearing the excellent electrochemical activity of arylamine linkages,the supercapacitor performance of AAm-TPB was systematically investigated with three-electrode and two-electrode systems,respectively.Remarkably,AAm-TPB electrode exhibits a high capacitance of 271 F g-1 with a three-electrode setup at a discharge rate of 1 A g-1.4.Functionalization realized by pre-design of spatial structure.Different from three-dimensional COFs,two-dimensional COFs possess well-defined one-dimensional open channels,which make them excellent candidates for efficient molecular separation.In the fifth chapter,we designed and synthesized a“two-in-one”monomer with a letter“H”shape.Self-polymerization of the monomer afforded a special COF（H-Asym-COF）with“Brick-Wall”topology.After a series of tests and calculations,it is proved that H-Asym-COF possess a distance（d）between two layers about 1 nm,which indicates that the interlayerπ-πinteraction is so weak that H-Asym-COF could be easily exfoliated into 2D nanosheets.The H-Asym-COF membrane with a thickness of 9μm was prepared by vacuum filtration method.And the performance of the COF membrane in terms of dye separation were systematically studied,in which H-Asym-COF membrane exhibit efficient dye molecules rejection（R>97%）and maintain excellent stability. |
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