Fluorescent Sensors Based On Metal-organic Frameworks: The Designed Synthesis And Applications

Metal-organic frameworks（MOFs）,as a new class of porous materials,are constructed from metal ions/clusters and organic ligands.MOFs,with the superiorities of inherent crystallinity,definite structure,tunable channels,and multiple functionalizations,have shown promising potential for numerous applications,such as gas adsorption and separation,biomedicine,catalysis,proton conductivity,magnetism,luminescence,and other fields.Recently,luminescent MOFs（LMOFs）have bloomed out as MOF-based fluorescent sensors for the detection,mainly focused on the following aspects:ion sensing,trace water（humidity）sensing,volatile organic compounds sensing,explosive sensing,biomolecule sensing,and temperature sensing.In this thesis,based on amino-functionalized tricarboxylic ligand 2-amino-1,3,5-benzenetricarboxylic acid（H₃（NH₂BTC））and pyridyl dicarboxylic ligand 4’-（3,5-dicarboxyphenyl）-4,2’:6’,4”-terpyridine（H₂DCTP）,novel MOFs were synthesized with transition metal ion Zn²⁺and rare-earth ion Ln³⁺,respectively.And strategies of metal ion exchange and Eu³⁺/Tb³⁺co-doping were also used to constructed LMOFs materials.We also explored the fluorescence sensing properties of the synthesized LMOFs.The main research work is as follows:1.A porous metal-organic framework Zn(NH₂BTC^3-)（Me₂NH₂⁺）·（DMF）_1.5（labled as ZnMOF）was synthesized under solvothermal reactions based on designedly using an amino-functionated triphthalic acid（H₃（NH₂BTC））ligand and a d¹⁰ transition metal Zn²⁺ion.Compound ZnMOF exhibits a 3D framework with 1D metal chains,irregular cages,amino groups,and carboxyl oxygen vacancy sites.Its luminescent properties demonstrate that ZnMOF as a dual-functional luminescent sensor realizes the selective detection for the phenylmethanol molecules on the basis of fluorescence“turn-on”mechanism and effectively sensitizing the visible emitting of the Tb³⁺cation based on"antenna effect".More importantly,Tb³⁺functionalized ZnMOF(Tb³⁺@ZnMOF)can also be used for the detection of phenylmethanol,which shows higher sensitivity and detection limit than ZnMOF.To the best of our knowledge,this is the first MOF-based ratiometric fluorescent sensor to sensing phenylmethanol molecules.2.A series of isostructural 3D lanthanide metal-organic frameworks Ln（NH₂BTC）（H₂O）·（H₂O）（DMF）₂（Ln=La,Sm,Eu,Tb,Gd,and Yb,et al.）with one-dimensional channels were constructed with H₃（NH₂BTC）linker and lanthanide ions.Among them,a porous Eu（NH₂BTC）（labeled as MOF 1）with unexpected non-luminescence was obtained by coordination of H₃（NH₂BTC）ligand and Eu³⁺.It exhibits selective fluorescence recovery for sensing dipicolinic acid（DPA）with high selectivity,the biomarker of bacillus anthrax,even in the presence of various interfering amino acids and aromatic molecules.Moreover,a new europium-based MOF（labeled as MOF 2）with evident channel changes was obtained through the single-crystal to single-crystal phase transition in DPA ethanol solution.The SC-SC transition from MOF 1 to MOF 2 signifies the coordination interaction for DPA as“antenna”molecule transferring energy to Eu³⁺ions and emits characteristic red fluorescence.To date,it is the first MOF-based chemosensor for the detection of DPA molecules based on a light recovery mechanism along with SC-SC transition.3.A series of lanthanide metal-organic frameworks Ln（DCTP）（NO₃）（DMF）（labeled as Ln（DCTP））with the same structure were synthesized under solvothermal reactions based on pyridyl dicarboxylic ligand H₂DCTP and lanthanide ions Ln³⁺.These compounds exhibit isomorphic 2D layered network with the coordinated NO₃^-anions and DMF molecules distributed between the layers.Tb（DCTP）and Eu（DCTP）show characteristic green and red missions of the corresponding Ln³⁺ions,respectively.By adjusting the co-doping ratio of Eu³⁺and Tb³⁺into the well-defined host framework,a series of binary mixed-LnMOFs Eu_xTb_1-x（DCTP）（Compounds 1-8）were obtained,showing tunable luminescence emissions including red-light,orange-light,yellow-light and green-light emitting.Besides,the temperature-dependent luminescence properties of Eu_0.022Tb_0.978（DCTP）（Compound 3）and Eu_0.0199Tb_0.9801（DCTP）（Compound 6）have been investigated systematically,which demonstrated that both of them have potential to quantitatively detect temperature as a luminescent thermometer over a wide range from77-318 K.In this paper,a comprehensive study was made on the controllable synthesis and properties of LMOFs,especially in the application of fluorescent sensors,laying a foundation for the further design and synthesis of MOFs and their application research.