Construction And Properties Of New Functional Covalent Organic Frameworks

Covalent organic frameworks?COFs?materials are a new kind of porous crystalline polymers synthesized from organic monomers with covalent bonds as commections.COFs have periodic network structures,orderly and adjustable pore environments,good chemical and thermal stability,and excellent functional modifiability.These properties make COFs stand out among many organic porous polymers and have good performance in the fields of gas adsorption,storage and separation,drug release,organic catalysis,detection,analysis and sensing,photoelectric devices and energy storage,etc.In order to further expand the application of COFs,the construction of new functional COFs has been emerging as an important research content in this field.This thesis mainly focuses on the construction and properties of new functional COFs and carries out the following parts of literature research and experimental exploration.In Chapter 1,the background and recent advance of COFs are introduced,which mainly focus on the structural design,functionalization strategies and practical applications.In Chapter 2,a series of new crown ether-functionalized two-dimensional COFs?CE-COFs?have been designed and synthesized by the"Pre-designing"strategy.Through a series of characterizations and tests,we characterized the structural properties and tested the adsorption performance of CE-COFs on Li⁺,Na⁺and K⁺.CE-COFs were used as phase-transfer catalysts in the iodination reaction between n-bromooctane and KI under the solid-liquid-solid?SLS?system.Various important nucleophilic substitution reactions,such as esterification,etherification,and aryl fluorination of halogenated hydrocarbons were also confirmed to be catalyzed by18C6-COF.This is the first example in which COFs were applied as phase-transfer catalyst.In Chapter 3,a new 18-crown-6 functionalized 18C6-COF2 with more stable and hydrophilic structure has been synthesized based on the results in Chapter 2.Compared with the hydrophobic counterpart 18C6-COF1,comparison in many aspects was performed to investigate their differences in structure,ion adsorption,chemical and thermal stability.By using the esterification reaction of benzoic acid and n-bromobutane as a model reaction,the phase-transfer catalytic performance of18C6-COF2 were in-depth studied under liquid-liquid-solid?LLS?system.In this chapter,a stable crown ether functionalized COF was successfully constructed and the detailed investigations on the effect of the hydrophilicity of the COFs backbone on the ion adsorption performance were performed,which was confirmed to further affects the phase-transfer catalytic activity.In Chapter 4,a unique photochromic molecule,dimethyldihydrofluorene,was selected as the C₂ symmetrical dialdehyde monomer to react with Td symmetrical tetraamine monomer.And a new type of dimethyldihydrofluorene functionalized three-dimensional COF?3D-DHP-COF?was successfully constructed by amine condensation reaction.Through PXRD and MS structural simulation analysis,it was found that 3D-DHP-COF has a unique 9-layer interpenetrated three-dimensional structure.Unfortunately,mainly due to the remarkable decrease of the photochromic efficiency in the powder sample,the resultant COF did not show significant solid photochromic properties.