Construction And Properties Of Metal-organic Frameworks Based On Viologen Derivative Ligands

As a class of porous crystalline materials,metal-organic frameworks（MOFs）possess periodic framework structures formed by self-assembly of inorganic metal ions/clusters（known as secondary building units,SBUs）and organic ligands.The diversity of SBUs and organic ligands contributes the most intriguing property with designable and tailorable to MOFs.Compared to traditional microporous and mesoporous materials,such as zeolites,mesoporous Si O₂ and activated carbon,MOFs with diverse structures and compositions possess uniform pore sizes/environments and very high surface areas.So far,more than 20,000 MOFs with different compositions,crystal structures,and morphologies have been synthesized,which show potential applications in gas adsorption/separation,energy storage/conversion,catalysis,luminescence,sensing,biological medicine,liquid purification,magnetic,proton conduction,etc.Photochromism refers to the color change upon photo-irradiation,which often has characteristics of visible and reversible color change.The photochromic materials exhibit promising potential applications in the fields of switches,memory,decoration,display,photometry,and so on.Generally,inorganic photochromic materials have considerable thermal stability,high strength and diverse coordination chemistry,while organic photochromic materials are varied and easy to modify or process.Different from them,as one of inorganic-organic hybrid materials,MOFs can preserve or even improve the respective features of the inorganic and organic components;meanwhile,they may produce new properties originating from the synergistic effect between them.Thus,by taking advantage of inorganic and organic components,the easy controllable and decorated property of MOFs,design and synthesis of photochromic MOFs will help to enrich the diversity of chromic materials and expand the application fields of MOF materials.In this thesis,we designed and synthesized two bipyridinium derivative organic ligand,and constructed a series of photochromic and/or thermolchromic MOFs under solvothermal conditions.Their photochromic behaviors and properties of fluorescence,detection,liquid phase adsorption and separation have been studied.Furthermore,the influence of framework structure of MOFs on the properties has been investigated in order to establish the relationship between structure and properties.This work will help to provide abundant scope to search for novel multifunctional MOF materials with fascinating photochromic property.The main results are as follows:1.Two 4,4’-bipyridinium derivative linkers,1-（3,5-dicarboxyphenyl）-4,4’-bipyri dinium bromide（[H₂ipbp]·Br）and 1,1’-（3,5-dicarboxyphenyl）-4,4’-bipyridinium chlorine（[H₄L]·Cl₂）have been successfully designed and synthesized using Zincke reactions.Both of them are photo-sensitive,which will endow photochr omic property to MOFs constructed based on them.On the other hand,they are zwitterionic,which may contribute to construct MOFs with cationic framework that can be used to adsorb and separate of liquid-phase to removal harmful anion based on ion exchange and charge matching.2.Two new photochromic and/or thermochromic Zn-MOFs have been successfully synthesized by adjustment of the coordination modes between the organic linker and metal ions through varying the solvents based on[H₂ipbp]·Br.[Zn（ipbp）（H₂O）]·NO₃·H₂O（1）possesses a three dimensional（3D） interpenetrated cationic framework,and[Zn（ipbp）（H₂O）₂]·NO₃·H₂O（2）is a 2D layered cationic network.Their different structures result in their distinct chromic behaviours.1 and 2 can have a wide range of light responses,varying form visible to UV light.However,1 is photochromic and highly photosensitive and thermochromic with a low thermal-response temperature,while 2 is only photochromic.In addition,they also exhibit photo-modulated photoluminescent properties.3.Threenew photochromic MOFs,[Eu（ipbp）₂（H₂O）₃]Br·6H₂O（3）,[Cd₂（ipbp）₂（NO₃）₂]·2DMF（4）and[Cd（ipbp）Br]·1.75H₂O（5）,have been successfully synthesized by using[H₂ipbp]·Br ligand in solvothermal system. Compound 3 not only exhibits photochromic properties in response to both UV and visible light,but also displays unique hydrochromism under the stimulus of dehydration accompanied by generation of viologen radicals.Furthermore,it also shows promising luminescent sensing ability for highly sensitive and selective detection of toxic Cr₂O₇^2-and Cr O₄^2-anions.4 and 5 show distinct photochromic behaviors,as well as similar photomodulated photoluminescence properties.In addition,4 shows vapochromism with selective response to diethylamine（DEA） vapor,which can monitor DEA vapor with different concentrations and the vapochromic sample can be reused after being washed with methanol.4.By choosing[H₄L]·Cl₂ as zwitterionic ligand,Cu（NO₃）₂ as source of metal, respectively,one new 3D MOF with cationic skeleton,[Cu₂L（H₂O）₂]·（NO₃）₂·5.5H₂O（6）has been successfully synthesized under solvothermal conditions.It can be used for liquid-phase adsorption and separation by ion exchange.Compound 6 shows interesting selective adsorption ability for anionic dyes due to charge matching,which can be successfully employed in chromatographic column to efficiently separate mixed dyes of Fluorescein Sodium and Methylene Blue.Furthermore,it also has good removal capacity of Cr₂O₇^2-ions due to ion exchange.