Studies On Fluorescent Probes Of Metal Ions Based On Schiff Bases Derivatives

Compounds derivatived from Schiff base have excellent spectrum characteristics, and they always have high selectivity to different metal ions. In this paper, we designed and synthesized a series of compounds derivatived from Schiff base, and investigated their application as metal ion fluorescent probes. The main studies as follows:In chapter 1, this chapter introduces the background of this work, describes the definition and structure of fluorescent chemosensors, and illuminates its design principles. This chapter also introduces the development and application of rhodamine and Schiff base derivatives.In chapter 2, four Schiff base derivatives containing acylhydrazone (L1, L2, L3 and L4) were synthesized, and their spectroscopic behaviors were studied. The coordination modes of the complexes were investigated, the difference between L1, L2, L3 and L4 is the position of-OH group in molecules. We switch the selectivity of Schiff bases to different metal ions by changing the position of-OH group in molecules. Schiff base L1 has high selectivity to Zn2+ and Mg2+ ions in ethanol-water and DMF-water (9:1, v/v) mixtures, respectively. Imine L2 is also a good fluorescent probe for Zn2+ in ethanol-water (9:1, v/v) media. The selectivity mechanism of L1 and L2 to metal ions is based on a combinational effect of proton transfer (ESPT), C=N isomerization and chelation-enhanced fluorescence (CHEF). The coordination mode between L1 and Zn2+ or Mg2+ ions is 2:1 or 1:1, and the stoichiometry between L2 and Zn2+ isalso 2:1.In chapter 3, we synthesized a series of bis Schiff bases derivated from o-phthalaldehyde (OPA), in which L5 has high selectivity to Zn2+ ion. Indicator L5 showed highly selectivity to Zn2+ in various solvents. We speculated the coordination mechanism between L5 and Zn2+ ion according to spectrum data and mass spectrometry, and discussed the coordination mechanism. In chapter 4, the synthesis and investigation of a novel Schiff-based fluorescent probe (L11) for detection of Al3+are described. The structure of the L11 was determined by X-ray and other spectroscopic data. We studied the UV absorption and fluorescence emission spectral properties of the probe in 99:1 HEPES-ethanol solution, and carried out cell staining tests. The fluorescent spectra changes and microscopy images show that indicator L11 has highly selective for Al3+ not only in abiotic system but also in living cells.In chapter 5, two Schiff based fluorescent probes (L12 and L13) for the detection of Zn2+ ion were described. The response of Zn2+ ion to the absorption and fluorescence spectrum of probes was investigated. Both of the probes were found to show good selectivity to Zn2+ ion. The spectra changes of L12 and L13 upon the addition of Zn2+ ion may be attributed to the formation of complex between probes and Zn2+ ion.In chapter 6, a new fluorescent sensor, Schiff base L17, which contains rhodamine framework has been designed and synthesized based on OFF-ON fluorescent chemosensors mechanism. UV/Vis spectroscopy indicates that L17 is a good chromogenic chemosensor for Cu2+ in 1:99 (v/v) ethanol-water media. Fluorescence spectral data reveals that L17 is an excellent fluorescent chemosensor for Hg2+ in ethanol aqueous (1:1, v/v) solution. Mechanisms for the high selectivity of L17 to Cu2+ and Hg2+ are discussed. The change of absorbance upon the addition of Cu2+ ion is caused.by ring opening reaction of L17, which is due to the coordination of L17 and Cu2+; the change of fluorescence upon the addition of Hg2+ maybe caused by Hg2+-promoted hydrolysis reaction. The spectroscopic behavior of L17 in living cells was investigated. The results showed that L17 can be used for the detection of Cu2 and Hg2+ not only in environment but also in biological systems. This is important to environmental monitoring and biomedical research.