Synthesis And Recognition Performance Of Coordination Polymers Based On4,4’-methylenebis(3-hydroxy-2-naphthalenecarboxylic)Acid

Coordination Polymers are a type of organic-inorganic hybrid supramolecular compound with highly ordered structures and thermal stability characteristics. Compared with traditional optical materials, the polymer with the adjust pore structure and big specific surface can accommodate and adsorb the small molecules, and surface active sites can also interact with certain small molecules. So they show great applications in the fields of sensing and molecular recognition. On the other hand, the detection of nitro compounds for national security and environmental pollution is important. Currently, most of detection techniques require expensive and bulky spectroscopy instruments. Therefore, a series of luminescent coordination polymers based on4,4’-methylenebis(3-hydroxy-2-naphthalenecarboxylic) acid were synthesized. Meanwhile, their crystal structure, luminescence properties and the nitro compounds recognition based on fluorescence sensing were studied fully. The main experiment points are as follows:(1) Synthesis of three-dimensional and cadmium(II) coordination polymers and recognition performance.A three-dimensional structure{[Cd2(PAM)2(dpe)2(H2O)2]·0.5(dpe)}n (1) was hydrothermally synthesized from organic conjugated ligand (H2PAM). Their structures were characterized by X-ray diffraction (XRD), infrared (IR), and the thermal stability was researched by TGA. The fluorescence intensity of compound1decreased significantly after dropping TNP. What’s more, the selective recognition of TNP was still able to achieve in presence of the competing molecule. The fluorescence spectra of1and the UV spectra of the nitro compound proved the possible energy transfer process. DFT calculated frontier molecular orbital values, predicted photo induced electron transfer (PET) process between electron-rich coordination polymers and electron-deficient nitro compounds, resulting in quenching of fluorescent compounds.(2) Organic amine assisted-control the synthesis of coordination polymers and recognition performance. Three different Zn(Ⅱ)compounds2-4were hydrothermally synthesized based on ethylenediamine (en),1,3-propanediamine (PDA) and triethylenetetramine (TETA) assisted-control. Compound2[Zn(Pam)(en)]n showed two-dimensional layers structure, while3[Zn2(Pam)2(1,3-PDA)2] possessed dinuclear ring structure and compound4[Zn(Pam)(TETA)] was dendrutic structure. Their luminescence properties were compared by calculating the fluorescence quantum yield. Compound2-4showed a different degree of fluorescence quenching after dropping TNP. The fluorescence emission spectrum of compound2-4and the UV absorption spectra of the nitro compounds proved possible energy transfer process.(3) Synthesis of rare earth ytterbium Yb(III) coordination polymers and recognition performance. Two isomeric compounds [Yb(Pam)(2,2-bipy)(H2O]n5and6were hydrothermally synthesized at various ratios of reactants. Compound5showed one-dimensional chain structure based on the ring units, and compound6is two-dimensional layers. The fluorescence quantum yield of compound5and6illustrated the impact of the structure on the luminescence properties. The fluorescence intensity of compounds5and6quenched significantly after TNP dropwise. The overlaps between UV spectrum of the nitro compound and the fluorescence emission spectra of compound5-6may prove the energy transfer process.