Application Of Metal-Organic Frames With Excited Intramolecular Proton Transfer Activity In Fluorescence Sensing And Imaging

Luminescent metal-organic frameworks(LMOFs)are a new type of inorganic-organic hybrid luminescent materials that have emerged in the past decade.Since the organic ligands and metal ions contained therein could provide good luminescence performance,at the same time,the charge transfer between the metal and the organic ligand can further enhance the luminescent material of the material,this new type of material is widely used.It is considered to be a relatively promising luminescent material.Among them,LMOFs with excited state intramolecular proton transfer(ESIPT)activity began to receive widespread attention.ESIPT usually refers to a type of photochemical process of light-induced enol-ketone tautomerization.After ESIPT occurs,the electronic structure and photophysical properties of matter will change significantly.In this paper,the 2,5-dihydroxyterephthalic acid(DHT)linker is used as the active unit of ESIPT to synthesize porous MOFs-Mg(DHT),and its application is studied.The details are as follows:(1)The LMOFs-Mg(DHT)constructed based on the organic ligand 2,5-dihydroxyterephthalic acid(H₂DHT)with ESIPT activity shows excellent solvent-dependent multicolor emission behavior.Based on this feature,Mg(DHT)can quickly detect trace water in various organic solvents,and has the characteristics of fluorescence enhancement and emission peak shift.This feature can be applied to the test strip to visually detect water content.More importantly,the strong combination between Al³⁺and free hydroxyl groups in the LMOF can enhance the fluorescence intensity of LMOFs,so that Al³⁺ions in the water medium can be detected.At the same time,a solid agarose hydrogel sensing platform can be created,and its fluorescence color change can be detected by mobile phone software for visual detection of Al³⁺.The LMOF fluorescent probe has high sensitivity,high selectivity,fast response and good reversibility,and can be used for Al³⁺fluorescence sensing in complex systems.(2)Due to the reducibility of the ligand phenolic hydroxyl group in the light-emitting metal organic framework Mg(DHT),it can be oxidized by highly reactive oxygen species(such as ClO^-and·OH)into a quinone structure,resulting in fluorescence quenching,which can be used for ClO^-and·OH specific detection.After adding the reducing substance ascorbic acid(AA),its reducibility causes the quinone structure to change back to the phenol structure,and the fluorescence is restored accordingly,realizing the reversible recycling of the probe.The detection limits of this fluorescent probe for ClO^-and·OH were 0.182?M and 0.219?M,respectively.Finally,we successfully realized the detection and imaging of the endogenous and endogenous ClO^-and·OH in cancer cells using a fluorescent confocal microscope.(3)Based on the encapsulation ability of MOFs on guest molecules,the dye methyl green(MG)and the luminescent metal organic framework(Mg(DHT))are integrated through simple electrostatic interaction,and a composite fluorescent probe MG@Mg(DHT)is obtained.Due to the inner filter effect between the two,the ketone-related fluorescence of Mg(DHT)is weakened,and sulfite can undergo a specific Michael addition reaction with MG,effectively blocking the inner filter effect between MG and MOFs,So that the ketone-related fluorescence of Mg(DHT)can be restored,and then the selective detection of SO₃^2-is realized.The fluorescent probe has good sensitivity,the detection limit is 0.583?M,and the reaction is relatively rapid(<2 min).Experiments show that the fluorescent probe has high biocompatibility and mitochondrial targeting,and can be successfully applied to the fluorescence imaging of SO₃^2-in the mitochondria of living cells.