Construction And Performance Study Of Dual-Emission Metal-Organic Frameworks (MOFs) Ratio Fluorescent Probes

Metal-organic framework（MOFs）,as a new type of porous material with ultra-high specific surface area and adjustable structure,has been widely used in the field of fluorescence sensing.However,most of the MOFs currently used for detection are"Turn-on"or"Turn-off"fluorescent probes with only a single fluorescence emission center,which are easily interfered by environmental factors.Therefore,it is of great significance to construct a MOFs-based ratio fluorescence sensing system with multiple fluorescence emission centers.In this paper,two single ligand MOFs ratio fluorescence sensors with dual fluorescence emission centers（Zn-MOF-Th and Zn-MOF-An-Py）were synthesized by using covalent single bond or ionic bond to introduce organic luminescent molecules to the ligand skeleton of MOFs,aiming at the shortcomings of uncertainty and repeatability in the composition of the supported,mixed metal and mixed ligand MOFs proportional fluorescence probes.Zn-MOF-Th and Zn-MOF-An-Py were used to detect metallic ions in water.The main research contents are as follows.（1）Two kinds of Zn-based MOFs（Zn-MOF-Th and Zn-MOF-An-Py）functionalized by organic luminescence molecules were designed and synthesized.The single crystal diffraction analysis results show that Zn-MOF-Th has one-dimensional pore structure,and the functional thiophene molecules are arranged in parallel in the pore of MOFs.Zn-MOF-An-Py is isomorphic to Zn-MOF-Th.The results of optical properties tests show that both Zn-MOF-Th and Zn-MOF-An-Py have dual luminescence centers.The fluorescence emission peaks of the former are at360 nm and 440 nm at the excitation of 290 nm.Under the 270 nm excitation,fluorescence emission peaks of the latte are at 359 nm,383 nm and 401 nm.（2）The ratio fluorescence sensing of Al³⁺,Cr³⁺and Cd²⁺in water can be realized by Zn-MOF-Th.Within a certain range,as the concentration of metal ions increases,the peak ratio of the probe at the two fluorescence emission centers shows a good linear relationship with the concentration of metal ions.The linear concentration ranges and detection limits（LODs）of Al³⁺,Cr³⁺and Cd²⁺were 1～100μM and 0.68μM,2～200μM and 0.64μM,1～40μM and 0.66μM,respectively.The Zn-MOF-An-Py fluorescence sensor can realize the ratio fluorescence sensing of Cr³⁺and Cu²⁺in water.The linear concentration ranges and detection limits（LODs）of Cr³⁺and Cu²⁺are 3～80μM and 1.01μM,1～80μM and 0.32μM,respectively.The results of PXRD,FT-IR and UV-vis confirm that the detection mechanism of the probe systems can be attributed to the interaction between organic luminescent molecules and metal ions,and the framework of MOFs probes does not collapse before and after detection.The high recovery rate and low standard deviation in real water confirmed the reliability and practicability of Zn-MOF-Th proportional fluorescence probe.