Research On Electrochemiluminescence Sensing Of Lanthanide Metal Coordination Polymer

Electrochemiluminescence（ECL）is a kind of luminescence phenomenon that occurs when the electroactive substance（luminophore）on the electrode surface conducts an electrochemical reaction（redox reaction）under a certain voltage,and the electrode surface generates electron transfer to produce unstable high-energy excited state substances,or the luminophore reacts with other substances in the system to form a excited state,and returns to the ground state.ECL is a combination of chemiluminescence and electrochemistry,which not only has the characteristics of high sensitivity and wide dynamic range of traditional chemiluminescence,but also has the advantages of simple and stable electrochemical methods,low background signals,and good controllability.In the construction process of ECL sensors,luminophores play an important role.How to improve the efficiency of luminophores and even explore new efficient species has always been the focus of research.Coordination polymers are inorganic organic hybrid polymers formed by metal ions and organic ligands through coordination bonds,which form one-dimensional,two-dimensional or three-dimensional infinite extended structures in space.Metal organic frameworks（MOFs）belong to one of coordination polymer.MOFs have attracted great attention in the field of ECL because of their large specific surface area,adjustable pore structure,rich active site,and diverse functional groups.Most of the reported ECL materials of MOFs are based on bipyridine ruthenium and its derivatives as the basic luminophore,but bipyridine ruthenium is expensive,with large steric hindrance and limited solid load.Therefore,it is of great significance to select non ruthenium metals to design and synthesize coordination polymer emitters with superior ECL performance.Lanthanide metal ions(Ln³⁺),as a new generation of luminescent materials,have unique optical properties such as long luminescence lifetime and large Stokes shift.However,due to the f→f transition hindrance within the configuration,the absorption coefficient of Ln³⁺is low,making ECL emission more difficult.There are still few studies directly using Ln³⁺as ECL luminophores.In order to enhance the ECL intensity of Ln³⁺,researchers often introduce transition metal ions into the system to regulate the coordination ratio for luminescence enhancement,or introduce organic ligands with"antenna effect"to form coordination polymer with them.For example,the synthesis of terbium organic gel（TOGs）and lanthanide orthophosphate（Eu PO₄）nanowires has improved the ECL intensity of Ln³⁺,but its luminous efficiency still needs to be further improved when applied to ECL sensing.Mainly because a single ligand usually cannot fully participate in the coordination of lanthanide metal ions,causing water molecules in the solvent to participate in the coordination.The introduction of a second ligand will partially or completely replace coordinated water molecules,reducing or even completely avoiding the energy loss caused by water molecules participating in coordination,and enhancing the ECL intensity of Ln³⁺.Therefore,it is of great significance to screen suitable organic ligands and synthesize coordination polymer with Ln³⁺through coordination reaction to expand the application of Ln³⁺in ECL sensing.In view of this,this study selected lanthanide metal,transition metal ions and organic ligands,or lanthanide metal ions and multiple organic ligands to synthesize different lanthanide metal coordination polymer with strong and stable ECL behavior through solvothermal method,which enhanced ECL luminous intensity,and constructed highly sensitive ECL sensors using them as luminophores,realizing effective detection of tetracycline and protocatechuic acid in food.It provides a feasible path for the super luminescence of highly efficient lanthanide metal coordination polymer.The main research content is as follows:1.Research on electrochemiluminescence sensing of binuclear monoligand metal coordination polymerHow to improve the ECL intensity of Ln³⁺and achieve ECL emission of Ln³⁺has been the focus of research.in recent years.In this work,a series of binuclear coordination polymer（Tb-Zn-CPs）with different molar ratios of lanthanide and transition metal ions were successfully synthesized by solvothermal method using Tb（NO₃）₃,Zn（NO₃）₂and[1,1′:4′,1′′-terphenyl]-3,3′′,5,5′′-tetracarboxylic acid（H₄TPTC）as reactants.The morphologies and ECL performances of Tb-Zn-CPs varied with different molar ratios of terbium and zinc ions（Tb:Zn）.The flower-like Tb-Zn-CP（9:3）possessed the highest ECL intensity due to the ligand"antenna effect"and the sensitization of Zn²⁺.An ECL sensor for the detection of tetracycline（TC）was constructed utilizing Tb-Zn-CP（9:3）as a novel ECL luminophore and potassium persulfate（K₂S₂O₈）as a coreactant.In this sensing system,as the TC concentration increases,the ECL intensity gradually decreases,and there is a good linear relationship between the ECL intensity and the logarithm of TC concentration.The proposed sensor achieved sensitive detection of TC in the range of 5.0 fmol·L^-1to 3.0 mmol·L^-1with a low limit of detection of 1.6 fmol·L^-1（S/N=3）.The sensor was used in the TC recovery experiment in dairy products,with a recovery rate range of 95.6%～104.0%,and has high sensitivity and selectivity for precise detection.In conclusion,this work provides an effective strategy for improving ECL intensity of lanthanide metal ions,opens up a new path for developing ruthenium free luminophores with high intensity,and expands the application of multi-core coordination polymer in ECL sensing.2.Research on electrochemiluminescence sensing of lanthanide metal double ligand coordination polymerIn order to further improve the ECL intensity of Ln³⁺,overcome the influence of water molecules in solvents,and realize its ECL sensing applications,four kinds of lanthanide metal double ligand coordination polymers（D-Ln-CPs）were synthesized by solvothermal method using dual organic ligands 1,3,5-benzenetricarboxylic acid（H₃BTC）,1,10-phenanthroline（1,10-phen）and Ln（NO₃）₃as reactants,respectively named D-Sm-CP,D-Eu-CP,D-Tb-CP and D-Dy-CP.Among them,in the presence of coreactant K₂S₂O₈,rod-shaped D-Tb-CP exhibits the most excellent ECL performance.This is because the first ligand（H₃BTC）can transfer energy to Tb³⁺through the"antenna effect",while the second ligand（1,10-phen）exerts the"ligand metal charge transfer（LMCT）effect",greatly enhancing the ECL intensity of D-Tb-CP.A sensitive ECL sensor based on the D-Tb-CP/K₂S₂O₈system was constructed using the target analyte protocatechuic acid（PCA）as a quencher for the determination of PCA in vegetables.In this sensing system,the ECL intensity decreases with the increase of PCA concentration,and there is a good linear negative correlation between ECL intensity and the logarithm of PCA concentration.The sensor signal response range is 10 pmol·L^-1-10mmol·L^-1with a limit of detection of 9.9 pmol·L^-1（S/N=3）.At the same time,the sensor also has good selectivity and stability.In summary,this work provides a new ECL strategy for PCA detection and provides more opportunities for constructing highly sensitive ECL sensors.