Construction Of Hexanuclear Lanthanide-Organic Frameworks And Their Fluorescence Sensing Applications

Lanthanide metal-organic frameworks(Ln-MOFs)are newly emerged organic-inorganic hybrid porous crystalline materials over the past two decades.Due to their unique luminescent characteristics,abundant luminous centers and variable designability,they have shown broad application prospects in the fields of fluorescence sensing,bio-imaging,white light emission,and display illumination.However,due to the weak bonding orientations and various coordination modes of lanthanide ions.the structure of Ln-MOFs is less predictable and the controlled preparation is still difficult.In view of the above problems,this dissertation proposes a metal cluster-based construction strategy to design and synthesize isomorphic hexanuclear Ln-MOFs.By introducing functional sites into frameworks,extending pore structures or regulating electronic energy levels,we have achieved the highly sensitive detection of neurological disease biomarker glutamate,reducing coenzymes NADP,oxygen and physiological temperature,trace water in organic solvents as well as trinitrophenol.Besides,the patterning of Ln-MOFs for fluorescent anti-counterfeit were realized by inkj et printing and stamping,and a portable optical fiber(?)MOFs fluorescence detection platform was built by the integration of Ln-MOFs and hydrogel optical fiber.Both of them would provide some new ideas for the device application of fluorescent Ln-MOFs probes.Utilizing 2-fluorobenzoic acid as a hexanuclear-directing agent,a class of porous Ln-MOFs Ln(BDC-OH)were synthesized by solvothermal reaction of lanthanide salts and hydroxyl-containing H2BDC-OH.Ln(BDC-OH)is a three-dimensional framework formed by the connection of hexanuclear[Ln6(?3-OH)8(O2C-)12]with the surrounding twelve H2BDC-OH.The framework contains two types of cages,e.g.,tetrahedral and octahedral cages with the radius of 3.4 A and 4.9 A,respectively.The BET area of Eu(BDC-OH)is 767.8 m2·g-1.When the luminescence of the ligand is used as the detection signal and the lanthanide luminescence acts as the internal reference,Ln(BDC-OH)(Ln?Eu,Tb)suspensions can realize the internal calibrated and colorimetric detection of the neuropathy biomarker Glu.The probe has good anti-interference,reproducibility and biocompatibility,and its working range covers the normal physiological concentration range of Glu.Based on the luminescence of ligands and lanthanide ions,a one-to-two decoder logic gate was designed for the monitoring of Glu concentration and the prevention of neurological diseases.Based on biphenyl dicarboxylic acid linear ligands H2BPDC-xN(x=0,1,2),three isomorphous hexanuclear Ln-MOFs Ln(BPDC-xN)(Ln =Eu/Tb,x?0,1,2)were synthesized by the cluster-based construction strategy.The increase of the size of the cages reduces the stability of the frameworks,so that the NADP molecules can effectively destroy the framework of Ln(BPDC-xN)(x = 0,1,2)and interrupt the sensitization of ligands to lanthanide ions,thus realizing the selective detection of NADP.The introduction of nitrogen functional sites into frameworks can attract and drive NADP molecules to accumlulate around the probes.which improves the detection sensitivity significantly.The limit of detection of these three Ln-MOFs are 1.36 ?M,0.84?M and 0.43 ?M,respectively.Ln(BPDC-xN)(x=0,1,2)have high selectivity for NADP detection.The main substances in cell and the analog NAD have little interference.The cluster-based construction strategy is also beneficial for the regulation of energy levels and energy transfer processes in Ln-MOFs.Hexanuclear Ln-MOFs Eu(1,4-NDC)with back energy transfer was prepared by choosing 1,4-H2NDC with lower triplet energy level as the organic ligand.Because of the appropriate back energy transfer efficiency from Eu3+ions to ligands,Eu(1,4-NDC)achieves fast and efficient oxygen sensing with fluorescence quenching constant KSV=13.3 bar-1,LOD=0.02 1%,and fluorescence response and recovery time of 10 s and 70 s,respectively.Furthermore,the Eu3+/Gd3+ co-doped strategy was used to improve the back energy transfer efficiency,and a highly sensitive physiological temperature sensor was obtained.The Eu3+ luminescence generated from the Eu3+/Gd3+ co-doped EuxGdi-x(1,4-NDC)(x=0.0005,0.001,0.003,0.01)are more sensitive to temperature than Eu(1,4-NDC).There is another temperature-insensitive luminescent center as reference,allowing for detecting physiological temperature in single-emission,dual-emission,and colorimetric modes.The maximum relative sensitivity of EuxGd1-x(1,4-NDC)(x =0.0005,0.001,0.003,0.01)are within the physiological temperature range.The relative sensitivity at single-emission and dual-emission modes are above 4.00%?-1 and 3.00%?-1 over the whole physiological temperature range,respectively,indicating an excellent fluorescent thermometer.Based on the organic ligand H2BDC-NH2 with hydrogen bonding and fluorescence response to water molecules,the hexanuclear Ln-MOFs Ln(BDC-NH2)were synthesized successfully.Ln(BDC-NH2)(Ln = Eu,Tb)have a suitable solubility product in water,which can realize the self-calibrated and colorimetric detection of trace water in various organic solvents.The limit of detection in THF are as low as 0.002 vol%and 0.001 vol%,respectively.Furthermore,Eu(BDC-NH2)was prepared into fluorescent anti-counterfeiting patterns by stamping and inkjet printing,and the fluorescent anti-counterfeiting patterns can be read out by water/vapor treatment.In view of the electron-deficient property of PA,the electron-rnch anthracene was immobilized into Eu(1,4-NDC)for PA sensing.Based on the synergistic effect of photo-induced electron transfer and self-absorption,Eu(1,4-NDC)shows excellent detection performances towards PA with Ksv=3.22 × 104 M-1 and LOD=37.6 ppb.Furthermore,we built an optical fiber(?)Eu(1,4-NDC)fluorescence sensor by integrating Eu(1,4-NDC)within hydrogel optical fiber.The resulted Eu(1,4-NDC)integrated hydrogel optical fiber fluorescence sensor has a higher Ksv(6.13 × 104 M-1)for PA sensing.It has been successfully applied to the detection of PA in real water samples,which might provide some guidance for the device application of luminescent MOFs probes.