Synthesis And Fluorescence Properties Of Water Stable Metal-Organic Frameworks Based On N/O-Containing Ligands

Metal-organic frameworks?MOFs?,constructed by organic ligands and metal ions,have emerged as a new type of organic-inorganic hybrid materials,which were widely used in the fields of gas adsorption,fluorescence,catalysis,electrochemistry,drug delivery and etc.Currently,the destruction of surrounding environment,including heavy metal water pollution and pesticide pollution,is harmful to human health and sustainable development of the environment.From the perspective of fluorescent probe,the fluorescence recognition of MOFs for ions and organic small molecules was investigated.In this work,based on the reaction of 4-?4-carboxylphenyl?-2,6-di?4-imidazol-1-yl?phenyl)pyridine)?HCIP?,3,5-di?2',4'-dicar-boxylphenyl?benzoic acid?H₅DDB?with transition metal salts and rare earth metal salts,eight metal-organic frameworks have been synthesized under solvothermal conditions.The structure and properties of the eight complexes were analyzed and characterized by X-ray single crystal diffraction,X-ray powder diffraction,elemental analysis,IR spectroscopy,thermogravimetric analysis,UV-Vis absorption spectroscopy,and fluorescence spectra.The application of MOFs-based fluorescent probe for some inorganic ions,organic molecules,and pesticide molecular were emphatically researched.At the same time,the fluorescence responsive mechanisms for different analytes were discussed in detail.The main research contents are as follows:1.Two novel metal-organic frameworks 1-2 possessing novel structures were synthesized based on the ligands of HCIP,namely,{[Cd?CIP?₂?H₂O?₂]_n·2.5H₂O}?1?;[Ag?CIP^-?]?2?.Both of the complexes have good water stability.Complex 1 exhibits a 1D chain structure,and a 3D supramolecular framework was further formed by H-bonds and and?-stacking interactions.Luminescence tests show that complex 1 displays excellent sensitivity and selectivity to detect Fe³⁺?CrO₄^2-/Cr₂O₇^2-and nitroaromatic explosives.Complex 2 is a 2D+2D?2D 3-fold parallel interpenetrated network.The luminescent results show that complex 2 is a multiresponsive fluorescent probe for Fe³⁺?CrO₄^2-/Cr₂O₇^2-and pesticide2,6-Dich-4-NA?DCN?.More importantly,complex 2 can sensitively and selectively detect DCN with high sensitively(K_sv=5.2×10⁴ M^-1)and low detection limit?1.7×10^-77 M?.The fluorescence sensing mechanisms of complex 1-2 for different analytes were studied by X-ray powder diffraction,IR spectrum,UV-visible absorption spectroscopy and fluorescence lifetime.Based on the high sensitivity and selectivity for different analytes,complex 1 and 2can be as multifunctional fluorescent probes in practical applications.2.Six novel metal-organic frameworks 3-8 were synthesized based on the ligands of H₅DDB,DPE?1,2-di?4-pyriGdl?ethylene?)and bimpy?3,5-bis?1-imidazolyl?pyridine?),namely,[Zn₃?DDB??DPE?]·H₂O?3?;[Cd₂?DDB??bimpy?]·2H₂O?4?;H₃[Cd₄?DDB?₂?DME??H₂O?₃]Cl?5?;[Ln₃?HDDB??DDB??H₂O?₆]·H₂O(Ln=Eu³⁺?6?,Tb³⁺?7?,Gd³⁺?8?).The single-crystal X-ray diffraction analysis suggests that complex 3 is a 3D porous network with six-nuclear clusters,which exhibits good water stability,acid and alkali stability.Luminescence tests suggest that complex 3 exhibits high sensitively and selectively for Fe???,Cr?III?,Cr???,Mn???and pesticide DCN with low detection limit.In addition,complex 3can be used to sense DCN in real samples such as carrot,grape and nectarine extracts.Moreover,even in the presence of surfactant sodium dodecyl sulfate?SDS?,the detection ability for DCN is almost unchanged.Complex 4 shows a 2D structure with binuclear secondary structural unit,which reveals a fluorescence turn-off behaviour towards nitrofuran/nitroimidazole antibiotics and pesticide DCN.Furthermore,the fluorescence of complex 4 can be quenched by Fe³⁺ions.However,the fluorescence intensity of Fe³⁺@4fluorescence-silent system was recovered?turn-on?by adding ascorbic acid?AA?to Fe³⁺@4system.The strong anti-interference ability and good circulation ability prove that complex 3and 4 can be used as fluorescence probe for above analytes.The single-crystal X-ray diffraction analysis suggests that complex 5 is a 2D layered structure,and complexes 6-8 are three 3D porous lanthanide metal-organic frameworks with heteroisomorphic structures.Solid state fluorescence properties of complexes 5-8 were further studied,which indicates the excellent fluorescence properties of complexes 5-8.