Construction And Luminescent Detection Performance Of Rare Earth Coordination Polymers With Ligands Containing Nitrogen Hetero Ring And Carboxyl Group

As a typical class of luminescent materials,rare earth coordination polymers have been widely applied in the fields of lighting materials and luminescent detection due to the advantages of narrowband emission,long luminescent lifetime and high quantum yield.Recently,more and more attentions were taken to environmental pollution and human health,so the detections of various toxic pollutants and biomarkers are urgently needed.For the demands of various substances detection,function-oriented strategy was adopted in this work to design structures with different functional groups,dimensions as well as charged properties via solvothermal processes and 19 rare earth coordination polymers were respectively synthesized by five nitrogen hetero ring aromatic carboxylic acid organic ligands and Ln³⁺ions.The structures of rare earth coordination polymers were analyzed by various characterization techniques(single crystal X-ray diffraction etc.).The density functional theory calculations were utilized to investigate the"antenna effect"process of rare earth coordination polymers.Additionally,based on several detection strategies,emission spectra were adopted to explore the applied value of above rare earth coordination polymers in luminescent detection fields.Aiming at the lacking electrons character of metal ions,2,5-bis(3,5-dicarboxylphenyl)-1,3,4-oxadiazole(H₄bdo)ligand,which contains several N,O atoms and carboxyls was adopted to synthesize a carboxyl functionalized coordination polymer{[Eu(Hbdo)(CH₃OH)(H₂O)₂]·(H₂O)_0.5}_n(1).Three carboxyls of ligand coordinates with Eu³⁺while the last carboxyl remains in channel.The ligand not only contributes to 3D structure,but also sensitizes Eu³⁺emission.Additionally,the oxadiazole ring of ligand is rich in O and N atoms,which together with the uncoordinated carboxyl serve as detection sites for metal ions.Based on the interaction between reserved sites and Fe³⁺,Sn⁴⁺ions as well as the excitation light absorption ability of Fe³⁺,1 realizes quantitative detection towards the Sn⁴⁺and Fe³⁺in water and the limits of detection(LOD)are 291 n M and 254 n M,respectively.5-(3,4-dicarboxylphenoxy)nicotic acid(H₃dpon)ligand was adopted together with Ln³⁺ions(Ln=Nd,Sm,Eu,Gd,Tb,Dy)to synthesize six 2D coordination polymers{[Ln(dpon)(H₂O)₂]·H₂O}_n(2?7).To meet the specific detection demands of formol molecule and VO₄^3-ion,the lanthanide shrinkage effect is utilized to dope Eu³⁺,Tb³⁺and Gd³⁺into above system and further synthesize coordination polymer with three emission centers.The luminescent intensities of three emission centers were balanced via the adjustment of Ln³⁺ratio and excitation wavelength.A white emission material Eu_0.059Tb_0.051Gd_0.89-dpon is achieved with CIE coordinate of(0.33,0.33).Based on the open metal ions sites and three emission centers,Eu_0.059Tb_0.051Gd_0.89-dpon shows specific luminescent response towards formol molecule and VO₄^3-ion,and thus realizes quantitative detection.The LODs towards formol and VO₄^3-are 0.0193 vol%and 420 n M,respectively.To meet the detection demands of antibiotic molecules,5-(2,4-dicarboxylphenyl)nicotic acid(H₃dpn)ligand was adopted together with Ln³⁺ions(Ln=Nd,Sm,Eu,Gd,Tb,Dy)to synthesize six 3D coordination polymers{[Ln(dpn)(DMF)₂]·DMF·H₂O}_n(8?13).Among them,coordination polymer 12can detect chloramphenicol and tetracycline molecules via the photoinduced electron transfer,F(?)rster resonance energy transfer and competitive excitation light absorption processes.To overcome the low detection sensitivity of antibiotic molecules,a heteroepitaxial strategy is introduced to grow ZIF-8 porous frame uniformly on the surface of 12.Benefitting from the pre-concentration effect of outer ZIF-8 framework towards antibiotic molecules,the prepared ZIF-8-on-12heterostructure realizes high sensitivity detection towards tetracycline and chloramphenicol with LODs of 5.6 n M and 37.6 n M,respectively.To meet the structural demands of luminescent adjustment and L-cysteine detection,2,2'-bipyridine-6,6'-dicarboxylic acid(H₂bpda)ligand was adopted to coordinate Ln³⁺ions(Ln=Eu,Tb)and form anionic secondary building unit[Ln(bpda)₂]^-.It is found that bridging K⁺can expand Ln³⁺distances(0.815?1.324nm),which limit the energy transfer between Ln³⁺in two 3D anionic bimetallic coordination polymers{[Ln₂K(bpda)₄(C₂H₅OH)]·H₃O·x H₂O}_n(14,15)and make the luminescent color of the material more precise and controllable.Moreover,an indirect detection strategy was designed based on the strong affinity between L-cysteine and metal ions.Anionic 14 framework was utilized to load quenching metal ions(Fe³⁺and Cu²⁺)and obtain two probes(Fe³⁺@14 and Cu²⁺@14)for indirect L-cysteine detection.An“on-off-on”luminescent mode is constructed to achieve indirect L-cysteine turn-on detection and the LOD of two probes are 149n M and 301 n M,respectively.To meet the demands of indirect L-ascorbic acid detection,the coordination sites were further reduced and the 2-(pyridine-2-yl)-1H-benzimidazole-5-carboxylic acid(Hpbmc)ligand was adopted together with Ln³⁺ions(Ln=Eu,Gd,Tb,Dy)to synthesize four 3D cationic coordination polymers{[Ln_0.5(pbmc)]·(solv)_x}_n(16?19)(Ln=Eu,Gd,Tb,Dy).To improve the crystal material practicality,in situ self-assembled strategy was proposed to prepare the polyacrylonitrile-16 membrane PEM.The obtained PEM material not only ensures the uniformity of 16 distribution,but also overcomes the poor recyclability of crystal materials in solutions and simplifies detection operations.By loading the quenching anion MnO₄^-into the cationic framework,an indirect interaction between coordination polymer and L-ascorbic acid is constructed and thus the L-ascorbic acid can be indirectly detected by the recovery degree of PEM emission intensity with the LOD of 48 n M.