Synthesis And Sensing Study Of Rare Earth Luminescent Materials With Flexible N-heterocarboxylic Acid Ligands

Metal coordination polymers are constructed by bridging or chelating metal ions or clusterswith organic ligands.They are a new generation of crystalline porous compounds.Because of their extremely high surface area,significant physical and chemical stability,and adjustable pores,they have become a promising functional material.In recent years,it has received widespread attention and is commonly used for research in fields such as catalysis,luminescence,anti-counterfeiting,sensing,biological imaging,and magnetism.Compared with transition metal coordination polymers,lanthanide metal coordination polymers have outstanding luminescence characteristics,especially Tb（III）and Eu（III）coordination polymer,which have sharp emission spectral bands,long luminescence life,large Stokes shift,high quantum yield and other characteristics,making them have excellent optical,electrical and magnetic properties.Pyridine carboxylic acid ligands have the advantages of rich N and O coordination sites,high light absorption coefficient,etc.When coordinating with metal ions,they can anchor metal ions by chelating or bridging coordination modes,which is conducive to the formation of novel metal organic coordination polymer with diverse coordination structures.In this thesis,a new type of pyridine carboxylic acid ligand was designed and synthesized with flexible diethylene glycol as the linking group and 2,6-pyridine dicarboxylic acid as the chelating terminal group.Through the reaction with rare earth metals,a novel coordination polymer was obtained,and its luminescent properties were further studied.Based on its high-water stability and excellent rare earth characteristic luminescence,its luminescence response performance to anions and cations,nitroaromatic hydrocarbons,and amino acids in water was further explored.In addition,in order to further enhance its application value,improve its portability and recycling performance,metal coordination polymer was doped in polyvinyl alcohol（PVA）to prepare composite films.The content of this paper is divided into the following four parts:1.The research status of rare earth coordination polymer and their luminescent films,and the purpose and significance of this paper are reviewed.2.Using chelidamic acid as the starting material for the reaction,a double branched ligand H₄L with a flexible chain diethylene glycol as the connecting center and a chelating group 2,6-pyridine dicarboxylic acid as the terminal group was synthesized.The ligand H₄L was reacted with Eu（NO₃）₃·6H₂O and Tb（NO₃）₃·6H₂O,respectively,and an Eu/Tb metal coordination polymer([Eu₂L₃]^6–/[Tb₂L₃]^6–)was obtain by solvothermal reactions.The metal coordination polymers were characterized by PXRD and infrared spectroscopy.The result analysis shows that[Eu₂L₃]^6–and[Tb₂L₃]^6–are isomorphic,and they may be composed of six ligands that coordinate with six metal ions and form a six-membered ring structure,and the other ligands are chelated and connected by the metal at the apex of the hexagon,making them a honeycomb like 2D rare earth coordination polymer.The luminescent properties of[Eu₂L₃]^6–and[Tb₂L₃]^6–were studied.The ligand H₄L showed complete sensitization to Tb³⁺and Eu³⁺,and the metal coordination polymers exhibited stable fluorescence emission at p H from 3 to 11,demonstrating p H stability.In addition,[Eu₂L₃]^6–and[Tb₂L₃]^6–have a certain degree of water solubility,and multifunctional detection of Co²⁺,Cu²⁺,Mn O₄^–,4-NT,and tryptophan in aqueous media.They are promising luminescent sensors for detecting Co²⁺,Cu²⁺,Mn O₄^–,4-NT,and tryptophan in water.3.In order to improve the convenience and recycling of[Tb₂L₃]^6–in detecting small molecules in water,[Tb₂L₃]^6–was doped in glutaraldehyde crosslinked PVA films([Tb₂L₃]^6–@PVA-GD)PVA thin film material with rare earth luminescence is prepared.A series of PVA films were prepared by cross-linking with different concentrations of glutaraldehyde and doping with different amounts of rare earth complexes.PVA films with good transparency,certain water resistance,and good fluorescence intensity were selected based on their water absorption,film transparency,and fluorescence intensity.The luminescence response performance of the system for detecting anions and cations,nitroaromatic hydrocarbons,and amino acids in water was studied.Studies have shown that[Tb₂L₃]^6–doped PVA films have excellent detection capabilities for Co²⁺,Cu²⁺,Mn O₄^–,4-NT and tryptophan,and can maximize the recovery of their fluorescence intensity under ethanol washing,with a high recovery ability.Mechanism studies have shown that the detection of Cu²⁺ions is caused by skeleton collapse,while the detection of Co²⁺ions is caused by the interaction with the complex.Characterization by infrared,PXRD,DFT calculations,etc.has demonstrated that the fluorescence quenching of Mn O₄^-,4-NT,and tryptophan is due to the combined effects of energy competition absorption,PET effect,and the interaction between guest molecules and the skeleton.4.Summary and prospect:In this paper,flexible link chain 2-bromoethyl ether is used to connect poly carboxylic acid groups,and lanthanide coordination polymer is formed with rare earth metals,as well as composite film materials doped with lanthanide coordination polymer are studied for luminescence sensing.The research results of this paper have certain theoretical guidance and potential application value for the design and synthesis of lanthanide light-emitting coordination polymer and composite film materials doped with lanthanide coordination polymer as sensors in aqueous media.