Structures And Photoelectromagnetic Properties Of Rare-earth Metal Organic Frameworks Constructed With Aromatic Carboxylic Acid Ligands Containing Benzothiadiazole Primitive

Since rare earth ions(RE^III)have a unique 4f electronic configuration,many rare earth metal-organic frameworks（RE-MOFs）with rich structures and excellent properties have been synthesized when combined with organic ligands.RE-MOFs are attracting more and more attention because of their excellent properties in the field of photoelectromagnetism,especially in the field of luminescence.In this thesis,an organic carboxylate ligand 4’,4’’’-（benzo[c][1,2,5]thiadiazole-4,7-diyl）bis（（[1,1’-biphenyl]-3,5-dicarboxylic acid））（H₄BTDBA）with excellent luminescence properties was designed and synthesized.The structures of H₄BTDBA and the intermediate products were characterized by X-ray single crystal diffraction,nuclear magnetic resonance hydrogen spectroscopy and infrared spectroscopy,and the fluorescence properties of H₄BTDBA were also investigated.A series of RE-MOFs with novel structures were synthesized by solvothermal method using H₄BTDBA as the main ligand bridging RE^III.The structures of RE-MOFs were characterized by means of X-ray single crystal diffraction,X-ray powder diffraction,thermogravimetric analysis and infrared spectroscopy,and the photoelectromagnetic properties of some RE-MOFs were studied in detail.The main contents are as follows:1.Considering the excellent luminescence performance of benzothiadiazole group and the multi-phenylene ring system with rigidπ-conjugated structure,a tetracarboxylic acid organic ligand H₄BTDBA containing BTD group and multiple phenyl rings was designed and synthesized.Fluorescence study showed that the H₄BTDBA ligand has almost complete quenching effect on Fe³⁺and folic acid with good selectivity,and can be used as a fluorescent sensor toward Fe³⁺and folic acid.2.Five isostructural 3D RE-MOFs based on RE^III(Sm³⁺,Eu³⁺,Gd³⁺,Tb³⁺and Dy³⁺)were synthesized by a mixed-ligand strategy using H₄BTDBA as the main ligand and lactic acid as the auxiliary ligand.The porosity of RE-MOFs 1-5 increased sequentially due to the lanthanide shrinkage effect.Fluorescence tests showed that RE-MOF 2 had good fluorescence enhancement naked-eye recognition of arginine and lysine,and the detection limits were 0.023and 0.077μM,respectively.Importantly,the low cytotoxicity of RE-MOF 2 enables the detection of arginine and lysine in living cells and can be used as a potential amino acid biosensor.RE-MOF 4 has good sensitivity for benzaldehyde and salicylaldehyde with good bifunctional sensing properties,which is the first example of a Tb^III-MOF that achieves fluorescence enhancement and blue shift for salicylaldehyde.Proton conductivity tests were performed on RE-MOFs 2-5,where RE-MOF 5 was able to reach 7.38×10^-5 S·cm^-1（98%RH,55°C）with a proton conductivity process can be considered as transport mechanism.In addition,RE-MOF 5 exhibits field-induced slow relaxation behavior.3.Five isostructural RE-MOFs 6-10(RE=Sm³⁺,Eu³⁺,Gd³⁺,Tb³⁺and Dy³⁺)were constructed using H₄BTDBA as the main ligand and formic acid as the auxiliary ligand.Structural analysis showed that all of them were chain-based three-dimensional structures.The fluorescence tests showed that RE-MOF 7 has a good fluorescence quenching effect on folic acid with a detection limit of 0.02 m M,and the recognition mechanism may be competition absorption leading to fluorescence quenching.The naked-eye recognition of RE-MOF 7 toward Al³⁺can be achieved with a detection limit of 0.05μM,and has great interference resistance and high sensitivity.Due to the presence of free dimethylamine and water molecules in the pore channel,proton conductivity studies were performed on RE-MOFs 7-10.The conductivity of RE-MOF 10 is the largest among RE-MOFs 7-10,reaching 9.66×10^-3 S·cm^-1（98%RH,60℃）,and proton conductivity process can be considered as transport mechanism.The magnetic study shows that the-ΔS_m,max of RE-MOF 8 reaches 16.13 J kg^-1 K^-1,which is a potential cryogenic magnetorefrigerant materials.