Study Of Syntheses, Structures,and Fluorescence Sensors Of Coordination Polymers Based On Pyridyl-containing Polycarboxylic Acid Ligands

In this paper,3-（3,4-dicarboxyphenyl）-6-carboxypyridine（H₃dpcp）was utilized as a ligand to synthesize six zero-dimensional to three-dimensional coordination polymers by the solvothermal methods.Infrared spectrum,elemental analysis,thermogravimetry,UV-Vis spectrum,and X-ray single crystal diffraction were used to characterize the structures and properties of the corresponding coordination polymers,the main research contents of this thesis are focused on the different analytes of fluorescence response.In addition,a coordination polymer with one-dimensional dinuclear chain structure,[Zn（tbda）]_n（Zn-1）was synthesized by using the ligand of4-（2,2’,6’,2’’-tripyridine）-4’-1,2-phthalic acid（H₂tbda）,and its properties of fluorescent probe for different analytes were explored in detail.The main research contents of this paper are as follows:1.The fluorescent sensing properties of some cations,anions,and nitroaromatic compounds were investigated by Zn-1.The experimental results show that Zn-1 has high selectivity and recycle-ability for the detection of Cr（III）,Cr（VI）and TNP.And Zn-1 has good pH stability as a fluorescent probe in aqueous solutions.The mechanism of Zn-1 for selective detection of Cr³⁺was demonstrated by IR,X-ray powder diffraction（PXRD）,X-ray photoelectron spectroscopy（XPS）,and X-ray energy dispersive spectroscopy（EDX）.In addition,the fluorescence quenching mechanisms for Cr（VI）and TNP has been explained by UV-Visible absorption spectroscopy.2.Two isomorphic three-dimensional structures of coordination polymers,namely,[Cd（Hdpcp）]_n（1）and[Zn（Hdpcp）]_n（2）,were synthesized by H₃dpcp ligand,and then three-dimensional supramolecular structures of 1 and 2 are formed throughπ...πinteractions.Both coordination polymers have good thermal stability and pH stability in aqueous solutions.The results of fluorescent detection display that Fe³⁺and TNP can quench the luminescence of 1.It is worth noting that 2 can recognize PO₄^3-ion by fluorescence enhancement,and can visually identify PO₄^3-by naked eye;In addition,2 can also be used to detect TNP by fluorescence quenching.The investigations displayed that higher sensitivity and recyclability of 1 and 2 may be used as potential fluorescent probes for the detection of above analytes.3.A three-dimensional compound,namely,{[Zn（H₂dpcp）₂（H₂O）₂]?H₂O}_n（3）has been synthesized,which further extends to a three-dimensional supramolecular structure throughπ...πinteractions,and 3 has good pH stability in aqueous solutions.The fluorescent measurements show that 3 can be used as a fluorescent probe for PO₄^3-,Fe³⁺and TNP.The addition of PO₄^3-ion to the suspension of 3 turns limpid,indicating that compound 3 can visually identify PO₄^3-ion.The mechanism of fluorescence enhancement of compound 3 for PO₄^3-ion was elucidated through comparative analyses of IR,UV-Visible absorption spectroscopy,PXRD,fluorescence lifetime of 3 and PO₄^3-@3.The absorption competition of UV-Visible absorption spectra demonstrates the quenching effect of TNP and Fe³⁺.4.Three isomorphic three-dimensional rare earth coordination polymers,namely,[Ln（dpcp）（H₂O）]_n（Ln=Eu（4）,Tb（5）,Dy（6））were synthesized.The measurements exhibit that both 4 and 5 can detect tryptophan by fluorescence quenching,and its quenching mechanism has been explained by UV-Visible absorption spectroscopy.In addition,PO₄^3-ion has a quenching effect on 4,while Ca²⁺ion can enhance the fluorescence of 5.PXRD results reveal that the addition of PO₄^3-ion may lead to the collapse of the framework of 4,and consequently results in the fluorescence quenching.The IR,PXRD,EDX,UV-Visible absorption spectroscopy and fluorescence lifetimes of compound 5 and Ca²⁺@5 were explored,the results illustrate that the addition of Ca²⁺makes the energy transfer of ligand-to-metal center more efficient,leading to enhanced fluorescence.