Synthesis And Selectivity To Metal Ion Of New Schiff Base As Fluorescent Probe

The analysis and detection of metal ions are currently important because of its implications in suchfields: chemistry, biology, medicine and environment. With the rapid development of fluorescent andcolorimetric chemosensors, there are lots of advantages for fluorescence chemosensors such as highselectivity, sensitivity, simplicity and without resorting to any expensive instruments, which drew more andmore attention of people in resent years and was successfully applied in the detection of many metal ions inaqueous solution. This work was used fluorescent1,8-naphthalene anhydride, anthracene,2-pyridinecarboxalddhyde and4-aminoantipyrine to synthesis Schiff base as fluorescent probe, and theinvestigations of its selectivity towards metal ions in aqueous solution.1.4-Br-1,8-naphthalimide fluorophore contains an electron-donating group conjugated to anelectron-withdrawing group. The change of electron-donating character could induce a shift in fluorescenceexcitation by light. A Schiff base4DVN based on naphthalimide and vanillin was designed and synthesized.The influence of pH and solvents on the absorption and fluorescent emission spectra was firstlyinvestigated. The result shows that the solution of4DVN took on different color in pH8-12. And the probeexhibits high selectivity to Ag⁺over other metal ions in aqueous media on fluorescent spectra. The methodof Job’s plot confirmed the1:2complex between Ag⁺and probe, and the mechanism was proposed. It wasconsidered that the lone pair electrons of imine can combine with Ag⁺ion when the solution of Ag⁺wasadded. As a result, the fluorescence emission quenched at540nm, and a new emission was observed at682nm.2. A new Schiff base P1composed with9-anthraldehyde and4-aminoantipyrine was synthesized andcharacterized as a fluorescent probe. P1shows high selectivity for Fe³⁺in aqueous solution, and the othermetal ions have no effect on the sensitivity to Fe³⁺. In the presence of Fe³⁺, the fluorescent intensity has adramatic enhancement over other examined metal ions in aqueous solution. A good linear relationship wasobserved in the range of1.0×10^-6molL^-1-2.0×10^-5molL^-1, with a detection limit of2.1×10-7molL-1. Themethod of Job’s plot indicated the formation of1:1complex between probe and Fe³⁺, and the possiblebinding mode of the system was also proposed. 3. Based on the fluorescent receptor of2-pyridinecarboxalddhyde, a Schiff base P2containing4-aminoantipyrine was synthesized and characterized by IR,¹H NMR and MS. The coordination withmetal ion was studied by fluorescent emission, and the result shows that P2exhibits high sensitivitytowards Al³⁺over other metal ions in aqueous solution without the influence of other ions. The linearrelationship between the fluorescent intensity and the concentration of Al³⁺was from4.0×10^-6molL^-1to1.6×10^-5molL^-1, and the regression equation is I=18.7692C+107.1538. Based on the results, thedetection limit was3.2×10^-7molL^-1.