The Construction,fluorescent Properties And Host-guest Chemistry Studies Of Ln-MOFs Based On Multipyridine Carboxylate Ligands

Metal-organic frameworks?MOFs?as a class of attractive functional materials,have been extensively studied in recently decades for applications in gas storage,catalysis,separation,sensing and so on.Meanwhile,MOFs are very promising for manufacturing multi-functional materials as light-emitting sensors,because both metal ions and ligands can provide light-emitting platforms,on which certain guest molecules loaded on MOFs can also emit or induce luminescence.Since the compounds containing Ln³⁺ions have unique optical advantages,including large Stokes shifts,wide luminous ranges cover from visible to near infrared region,and high color purity.Ln-MOFs are considered to be promising luminescent probes in prospective and multicolor tunable luminescent materials.In this thesis,two functional multipyridine carboxylate ligands were selected and used to construct series of Ln-MOFs with Ln³⁺ions through self-assembly approach.Or lanthanide cation ions were incorporated into the MOFs network through weak interaction by guest chemistry.We want to obtain novel structures and multifunctional sensing materials based on excellent optical performance,and further explore the corresponding sensing quenching mechanisms.The main research contents of this thesis include the three segments listed as following:1.Series of isostructural Ln-MOFs,formulated as[Ln?tcptpy??H₂O?₂·2H₂O]_n{Ln³⁺=Sm³⁺?1?,Eu³⁺?2?,Gd³⁺?3?,Tb³⁺?4?,Dy³⁺?5?;H₃tcptpy=4-?2,4,6-tricarboxyl phenyl?-4,2':6',4''-terpyridine}have been synthesized under mild hydrothermal conditions and characterized.Structures were established by single crystal X-ray diffraction.All the compounds feature 2D layer with?4,4?-connected topologies.By virtue of the isostructural frameworks,a binary co-doped Tb_0.89Eu_0.11tcptpy for self-calibrating ratiometric temperature sensor is achieved,which shows a good linear response to the temperature range of 305-340 K,with a maximum relative sensitivity?S_m?of 8.41%·K^-1at 340 K.Moreover,Tb-MOF?4?exhibits excellent applications as luminescent sensors for the detection of nitrobenzene?NB?and Fe³⁺cation with high selectivity and sensitivity based on luminescence quenching approach.The possible mechanisms of fluorescence quenching effect were further investigated.2.Same as the preparation procedure of compounds 1-5,we only change the reaction ratio of 4-?2,4,6-tricarboxyphenyl?-4,2':6',4''-terpyridine?H₃tcptpy?ligand and lanthanide nitrate.A series of isomorphic three-dimensional Ln-MOFs,[Ln₂?tcptpy??btca??H₂O?₅]_n(Ln³⁺=Sm³⁺?6?,Gd³⁺?7?and Tb³⁺?8?)were synthesized.Interestingly,it was observed that a new ligand benzene-1,2,3,5-tetracarboxylic acid?H₄btca?was generated via the in-situ reaction,which serves as the second organic linker in the framework to construct MOFs based on mixed ligands.Structural analysis shows that the binuclear{Sm₂O₁₈}units are connected into a 1D double-stranded array by the carboxyl oxygen of the adjacent tcptpy^3-and btca^4-ligands,and the adjacent ligands are further connected to form a 3D framework with1D elliptical channels.The photoluminescence of Sm-MOF?6?and Tb-MOF?8?were also studied.Sm-MOF?6?showed both ligands and Sm³⁺ion dual emission centers due to ligands weak sensitization effect.Tb-MOF?8?exhibits emission originated from characteristic f-f transition of Tb³⁺ion.3.The ligand 2-?[2,2':6',2'-terpyridine]-4'-yl?benzene-1,3,5-tricarboxylic acid?H₃L?was employed with Ag NO₃to prepare Ag-MOF with a 3D supramolecular pore structure.Systematically characterization indicates the structure was stabilized by?-?interaction,and the chemical formula is[Ag?H₂L?·H₂O]_n?9?.9 shows high selectivity and very low detection of limit?DOL?for antibiotic nitrofurazone?NFZ?and furazolidone?FZD?due to its excellent luminescence properties.By means of guest chemistry,Ln³⁺ions were introduced into the Ag-MOF channels to obtain a series of and Yb³⁺?16?),which have shown excellent optical properties emitted in the visible and near infrared regions.Among them,colour of Sm³⁺@Ag-MOF changes depend on the excitation wavelength,showing obvious photochromic behaviour.