Synthesis And Properties Of Novel Photofunctional Metal-Organic Framework Materials

Metal-Organic Frameworks?MOFs?are the two-dimensional?2D?or three-dimensional?3D?complex network structures which are formed by coordination self-assembly processes of metal ions/clusters and organic bridging ligands.As a novel class of organic-inorganic hybrid porous materials,the diverse choices of metal ions and organic ligands endow the diversity and modification of MOF structures.The structural diversity of MOFs endows them many functional properties so that MOFs show excellent performance and great application potential in chemical sensing,gas adsorption,molecular magnetic,drug delivery,heterogeneous catalysis,proton conductivity and many other research fields.After nearly two decades of development,MOFs have become a research hotspot in the field of materials.Among all the MOFs that have been reported,luminescent metal-organic frameworks?LMOFs?have attracted extensive attentions due to their special photoresponse properties.It is estimated that the number of reported LMOF structures accounts for about 10%of the total MOFs.However,the synthesis and efficient construction of LMOFs are still challenging.In this thesis,we have designed and synthesized three kinds of photoresponsive organic ligands with rigid or flexible characteristics.Employing these ligands to react with different transition metal ions or alkaline earth metal ions,we have successfully constructed five kinds of novel MOF structures.These MOF structures were analyzed by single crystal X-ray diffraction,powder X-ray diffraction,infrared spectrum,thermogravimetry analysis.Their luminescent and magnetic properties were also studied systematically.The work in this thesis includes the following aspects:?1?Synthesis,structure and properties of Metal-Organic Frameworks with semi-rigid bifunctional ligand.A semi-rigid bifunctional organic bridging ligand5-??1-methyl-1H-tetrazol-5-yl?thio?isophthalic acid?H₂mttia?was synthesized by C-S bonds cross-coupling reaction.The structure of H₂mttia contains both polycarboxylic acid moieties and tetrazole moieties,which make the ligand have abundant coordination sites.In addition,the flexible thioether functional group between the benzene ring and the substituted tetrazole heterocycle in the bridging ligand molecule affords the flexible and tunable coordination modes of the ligand.Two novel MOFs[Cd?mttia??H₂O?]_n?1?and[Cu?mttia?]_n?2?were synthesized under hydrothermal reaction conditions.The structural analysis indicates that compound 1 has a dinuclear Cd?II?building unit and the overall crystal structure shows a 2D framework with a binodal?3,6?-connected net.Compound 2also has a dinuclear Cu?II?secondary building unit,and the overall crystal structure displays a 3D architecture.The ligand H₂mttia displays completely different coordination modes in the structures of compounds 1-2,which demonstrates the coordination flexibility of flexible ligands in the formation of MOFs.The fluorescence measurement shows that compound 1 has fluorescence emission properties based on the ligand emission,while the variable-temperature magnetic susceptibility measurement of compound 2 indicates a strong antiferromagnetic superexchange between the Cu²⁺ions.?2?Construction of amino-modified magnesium metal-organic framework and its fluorescence sensing properties.Based on Suzuki coupling reaction,we designed and synthesized an amino-decorated bridging ligand 4,4'-?4-aminopyridin-3,5-diyl?dibenzoic acid?H₂APDA?,and employed it to react with Mg²⁺ions under solvothermal reaction condition to fabricate a novel alkaline earth LMOF namely[Mg₂?APDA?₂?H₂O?₃]·5DMA·5H₂O?Mg-APDA?.Mg-APDA is a three-dimensional?3D?host framework with one-dimensional?1D?hexagonal channels with the pore diameter of about 8.0?and the porosity of 62.8%.More importantly,these microporous channels are decorated with Lewis-base amino sites and uncoordinated oxygen atoms,which facilitate the Mg-APDA to anchor and recognize various analytes.Fluorescence detection experiments show that Mg-APDA has multiresponsive fluorescence sensing performance,which could detect Fe?III?ions,pesticides?2,6-dichloro-4-nitroaniline?DCN??,and antibiotics?nitrofurazone?NZF?,nitrofurantoin?NFT??with high selectivity and sensitivity.The high effective dection for Fe?III?ions of Mg-APDA may be attributed to the effective energy transfer process between the host framework and the guest analytes,while the high quenching efficiency for NZF,NFT and DCN may be ascribed to a combined effect from photoinduced electron transfer and resonance energy transfer.The amino group is an electron-donating group in organic luminescent materials.The introduction of amino group could increase the electron cloud density of Mg-APDA,which facilitates the electron-transfer or energy-transfer processes and then results in higher selectivity and sensitivity for luminescent detection.Therefore,the amino functional modification of LMOFs has certain significance for the construction of high-efficiency fluorescence sensors.?3?Construction of carbazole functionalized cadmium metal-organic framework and its fluorescence sensing properties.By the coupling recation,we designed and synthesizedacarbazole-functionalizedpolycarboxylicacidligand4,4'-?9-?4'-carboxy-[1,1'-biphenyl]-4-yl?-9H-indazole-3,6-diyl?-dibenzoic acid?H₃CBCD?,and employed it to react with Cd²⁺ions under solvothermal reaction condition to construct a carbazole-functionalized cadmium luminescent metal-organic framework namely Cd₃?CBCD?₂?DMA?₄?H₂O?₂]·10DMA?Cd-CBCD?.Cd-CBCD is a three-dimensional?3D?supramolecular framework based on two-dimensional?2D?layer structures through???stacking interactions.The introduction of carbazole building block into the backbone structure of the ligand makes Cd-CBCD exhibit intense blue-light emission characteristic.Fluorescence sensing experiments show that Cd-CBCD can be used for efficiently detection of various organic pollutants including pesticides?DCN?,antibiotics?NZF,NFT?and nitroaromatic compounds?4-nitroaniline?4-NA??in the form of fluorescence quenching with low detection limits,excellent anti-interference abilities and good recycling performance.The analysis of fluorescence quenching mechanism indicates that the electron transfer mechanism plays a dominant role in the detection of antibiotics,while the high quenching efficiencies of DCN and 4-NA could be attributed to the combined effect of photoinduced electron transfer and resonance energy transfer.Cd-CBCD represents the first carbazole-functionalized LMOF as a multifunctional chemical sensor for the detection of pesticides,antibiotics and nitroaromatic compounds.?4?Construction of carbazole functionalized MOF?dye composite and its high efficiency white light emission performance.A LMOF structure?Zn-CBCD?with strong blue light emission properties was constructed by solvothermal reaction of carbazole-derived ligand H₃CBCD with Zn²⁺ions.The structural analysis shows that Zn-CBCD is a three-dimensional?3D?framework based on the[Zn₄O?COO^–?₆?H₂O?₂]secondary building unit.With the large channels in the framework,Zn-CBCD can effectively encapsulate the fluorescent dyes rhodamine 6G?R6G?and acridine yellow?Acf?.Due to the efficient energy transfer between the Zn-CBCD host framework and the guest dye molecules,the MOF?dye composite exhibits dual-emitting characteristics including the framework fluorescence emission and fluorescent dye emission.After immersing Zn-CBCD in a mixed DMA solution with R6G and Acf,these two fluorescent dyes were encapsulated in the host framework simultaneously.By adjusting the relative encapsulation content of the two fluorescent dyes in the framework structure,the obtained Zn-CBCD?Acf/R6G composite exhibits excellent white light emission performance.The chromaticity coordinates of Zn-CBCD?Acf/R6G composite are?0.332,0.331?at excitation light with a wavelength of 365 nm,which is very close to the ideal white light chromaticity coordinate value?0.333,0.333?.