Synthesis And Spectral Properties Of Metal Cation Fluorescent Probes Based On Schiff Base Frameworks

Schiff base is a kind of compound which contains the characteristic group of imine in the structure formed by the reaction of compounds with carbonyl groups（-C=O）and primary amine groups（-NH₂）under certain conditions.Because it has-C=N-structure,it is easy to rotate freely,so it often shows weak or no fluorescence.And the N atom in its structure has a lone pair of electrons,creating an electron-rich chemical environment.It is because of the isomerization of-C=N-and a lone pair of electrons on N atom,which can participate in coordination with metal ions,and has good light stability and strong fluorescence in the visible light range.Moreover,Schiff base compounds are widely used in drug research,biomedicine,and antibacterial disinfection and so on.In addition,by changing the linkage groups of the side chain,it can have different spectral properties,such as introducing hydroxyl group,methyl group,which can provide lone pair electrons,and make it have color or fluorescence response to specific metal ions,so as to achieve the recognition effect of specific metal cations.First,the thesis outlines the development of Schiff compounds as fluorescent probes.Next,the experimental parts are described,using the existing benzopyran-2-one and4-methyl-7-hydroxybenzopyran-2-one in the laboratory as the raw materials and salicylaldehyde derivatives are designed to synthesize four fluorescent probes that can be used to identify metal ions.Because the above-mentioned derivatives all contain functional groups such as phenolic hydroxyl group and methoxy group which can provide lone pair of electrons,it is easy to coordinate with specific transition metal ions,resulting in changes in fluorescence properties.The ability and mechanism of each probe to recognize metal ions is further explored.The main contents are as follows:1.Two Schiff-typed fluorescent probes based on the coumarin:5-(（（（7-hydroxy-4-methyl-2-oxo-2H-benzopyran-8-yl）methylene）amino）isophthalic-acid（probe 1）,6-(（（2-hydroxy-3-m-thoxy-benzylidene）amino）-2H-benzopyran-2-one（probe 2）.Probe 1 can recognizes zinc ions in fluorescence.Only when zinc ions are added,the fluorescence of mixed solution is significantly enhanced and a strong yellow fluorescence is emitted.Probe 2 can recognize two different ions in two different solvent system.It can fluorescently recognize aluminum ions in the ethanol system.Only when aluminum ions are added,the fluorescence is significantly enhanced,also a strong yellow fluorescence is emitted.For anions,cyanide is recognized in UV-vis/fluorescence of the DMSO system.In two different systems can recognize two ions with different emission wavelengths.2.Two Schiff-typed fluorescent probes based on salicylaldehyde derivatives,4-（（5-chloro-2-hydroxybenzylidene）amino）-N-（pyrimidin-2-yl）benzenesulfonamides（probe3）,2,4-dibromo-6-[（2-hydroxybenzylidene）-hydrazino]-phenol（probe 4）.First,the solvent effect test of probe 3 was performed,and it was found that there was no fluorescence response in a pure organic system and the fluorescence was significantly enhanced in aqueous system,the proportion of organic solvent and water were changed at the same concentration.It is found that the greater the proportion of water,the stronger the fluorescence,which proves its AIE（aggregation-induced fluorescence enhancement）effect.And the fluorescence was significantly quenched only after the addition of Cu²⁺.Probe 4 can recognize zinc ions in fluorescence,and the fluorescence is significantly enhanced only after the zinc ions are added,emitting chartreuse fluorescence.3.Through UV titration,fluorescence titration,NMR titration,Job curves and other methods to determine its recognition mechanism,and did EDTA reversibility experiments to determine its reusability,through testing the simulated water samples,to prove the potential value of its application.