Preparation And Properties Of Fluorescent Coordination Polymers Based On Pyridine Derivative Ligand

Coordination polymers,a crystalline porous coordination network of organic linkers and metal cluster nodes,have received much attention in recent years for applications in selective adsorption,single-atom catalysts,photocatalysis,biomedicine,fluorescence and magnetism.Among these,ligand polymer fluorescent materials are widely used as luminescent sensors for the detection of various contaminants,such as metal cations,anions,nitroaromatic explosives,and antibiotics.At present,the effective construction of coordination polymers and the structural modulation of their fluorescence properties remain a difficult task.Therefore,this thesis designs new nitrogen heterocyclic ligands,prepares zinc or cadmium coordination polymers,investigates the modulation of organic ligand fluorescence by central ions,etc.and applies the coordination polymers to fluorescent probes.Details of the research are as follows.1.Three new azetidinium primary ligands were designed and synthesized:2-（6-（1H-benzo[d]imidazol-2-yl）pyridin-2-yl）-1-（pyridin-4-ylmethyl）-1H-benzo[d]imidazole（4pybbp）,2-（6-（1H-benzo[d]imidazol-2-yl）pyridin-2-yl）-1-（pyridin-3-ylmethyl）-1H-benzo[d]imidazole（3pybbp）and 2,5-bis（4-（pyridin-4-yl）phenyl）thiazolo[5,4-d]thiazole（4bppyttz）with Zn（II）/Cd（II）as the metal element and selected organic dibasic acids（H₂oa）:terephthalic acid（H₂bdc）,isophthalic acid（H₂ipa）,trans-butenedioic acid（H₂fum）,butanedioic acid（H₂sca）,glutaric acid（H₂gta）,1,8-naphthoic acid（H₂ndc）and 4,4’-oxydibenzoic acid（H₂oba）as co-ligands,adjusting the amount ratio of metal to ligand and selecting different ratios of mixed solvents,the following twelve coordination polymers were constructed by solvothermal method.{[M（4pybbp）（oa）]·sol}_n（1:M=Zn,oa=fum;2:M=Zn,oa=sca;3:M=Zn,oa=gta,sol=H₂O;4:M=Zn,oa=bdc;5:M=Cd,oa=ipa;6:M=Cd,oa=bdc）,{[M（3pybbp）（oa）]·sol}_n（7:M=Cd,oa=bdc,sol=DMF;8:M=Zn,oa=bdc）,{[Zn_x（4bppyttz）（oa）_x]·sol}_n（9:oa=ndc,x=2,sol=1.5DMF;10:oa=ndc,x=2,sol=CH₃OH;11:oa=oba,x=2;12:oa=oba,x=3）。Structural analysis shows that 1-4,6-8 are one-dimensional coordination polymers,5 is a two-dimensional coordination polymer and 9-12 is a three-dimensional coordination polymer.The zinc ions in the coordination polymers form three coordination geometries:a six-coordinated octahedron（1-2,11-12）,a five-coordinated triangular bipyramid（3-4）and a five-coordinated tetragonal cone（8-10）;the cadmium ions form two coordination geometries:a seven-coordinated pentagonal bipyramid（5）and a five-coordinated tetragonal cone（6-7）.The smaller spatial site resistance of the cadmium ions allows the constructed complexes to form higher dimensional skeletal structures more readily.In the coordination polymers the 4pybbp ligand adopts theμ₁-（k¹N,N’,N’’）,μ₂-（k¹N,N’,N’’:k¹N’’’）coordination modes,the 3pybbp ligand adopts theμ₁-（k¹N,N’,N’’）coordination mode and the 4bppyttz ligand adopts theμ₂-（k¹N:k¹N’）coordination mode.The ligands based on theμ₂ ligand have a more complex and high-dimensional structure.The modulation of the ligand polymer structure was achieved through the design of the primary ligand,the selection of metal ions with different radii and the choice of co-ligands.2.Studies on the fluorescence properties of the solids show that the fluorescence peaks of the coordination polymers are significantly blue-shifted and enhanced,which can be attributed to the coordination of ligands and metal ions.On the one hand,the coordination of the ligand with the central ion fixes the backbone structure and reduces the thermal vibrations within the molecule,resulting in enhanced solid fluorescence of the complex;on the other hand,the blue shift of the fluorescence peak is due to the increase in theπ*-πorbital energy level difference of the ligand as a result of coordination.The average bond length between the central atom and the ligand N atom can be used to determine the strength of the interaction between the ligand and the metal central ion.The stronger the ligand effect,the greater the blue shift,indicating that the strength of the ligand effect can judge the degree of blue shift.3.A study of the solid fluorescence properties of the thiazole and thiazole pyridine ligand polymers under non-homogeneous conditions showed that ligand polymers 9-12 exhibited a fluorescence-enhanced recognition response to Al³⁺,Cd²⁺and Re O₄^-plasma in aqueous solution,respectively,with detection limits ranging from 0.0078 to 0.0269μM.This specific fluorescence response was hypothesised to be related to the pore environment in the ligand polymer by experiments such as IR and PXRD and DFT theoretical calculations.The recyclability investigation showed that the ligand polymers used in the experiments could be reused more than four times,indicating that the ligand polymer solid fluorescent materials constructed from pyridine derivatives are capable of detecting some contaminant ions with high sensitivity and can be used as potential fluorescent sensors for the detection of contaminant ions in water bodies.In summary,twelve structurally novel pyridine derivatives ligand polymers were successfully constructed through the design of ligands,the selection of synthesis conditions and co-ligands,and the adjustment of metal-ligand ratios.The further modulation of the ligand fluorescence was achieved through the introduction of central ions and modulation of the ligand polymer structure,and the prepared ligand polymers were applied to fluorescence recognition and fluorescent probes.