Design,Synthesis And Performance Study Of Ionic Fluorescent Probes From Benzothiazole

Benzothiazole compounds have fluorescence emission at long wavelength and high quantum yield.Their structural heteroatoms can coordinate with metal ions.Because of this,they have a potential application for the fluorescence imaging of metal cation.Schiff bases are a class of stable imines,synthesized by the reaction of active carbonyls with primary amines,and able to chelate with transition metal ions.Therefore,Schiff bases could be used to detect heavy metal ions.In addition,Schiff base compounds have good biological activity and photochemical properties.The excellent properties of benzothiazole and Schiff base have aroused great attention of researchers.In this thesis,three kinds of fluorescent probes for detecting metal ions were designed and synthesized by coupling them and modifying their structures.The research work is summarized as follows:Chapter 1:this chapter started from the summary on the role and detriment of transition metal ions in the environment and human daily life.Then the structure and response mechanism of fluorescent probes were classified and summarized.Finally,the detailed studies on the fluorescence probes of Cu²⁺and Zn²⁺as well as the detection were described.Chapter 2:A new"turn-off"Schiff base fluorescent probe（9H-fluoren-9-yl）methyl-2-（3-（benzothiazol-2-yl）-2-hydroxybenzylidene）hydrazine-1-carboxylate（L₁）was synthesized from 2-hydroxy-5-methylbenzaldehyde by Duff reaction and condensation reaction.In Tris-HCl buffer（20.0 mmol,pH=7.40）,L₁ coordinated with Cu²⁺,resulting in a apparent decrease of fluorescence intensity at 590 nm.Based on this phenomenon,L₁ can be used for selective recognition and detection of Cu²⁺,with a detection limit of 2.88×10^-6M.Job’s plot analysis and high-resolution mass spectrum indicated the binding mode of L₁to Cu²⁺as 1:1 with the binding constant 2.78×10⁴ M^-1.The possible binding site of L₁ to Cu²⁺was further studied by infrared data.Also,probe L₁ has good biocompatibility and cell membrane permeability,which can achieve the fluorescence imaging of copper ions in He La cells,so it has potential application in biomedical field.Chapter 3:A new Schiff base fluorescent probe 2,2’-bis（2-benzothialol-2-yl-1-hydroxyl-5-methyl）benziminodiethylamine（L₂）was designed and synthesized by Duff reaction and condensation reaction.Its structure was confirmed by ¹H NMR,¹³C NMR and MS.In the presence of Zn²⁺in Et OH:Tris-HCl=3:2（V/V,20.0 mmol,pH=7.40）solvent,the fluorescence intensity at 480 nm was significantly increased,and the fluorescence color changed from yellow to blue.Based on the changes,it can be used to selectively recognize Zn²⁺with a detection limit of 6.04×10^-8 M.Job’s plot analysis and high resolution mass spectrum indicated the binding mode of probe L₂ to Zn²⁺as 1:1 and the binding constant as1.44×10⁵ M^-1.In addition,the probe L₂ can specifically recognize Zn²⁺in He La cells,which offered some evidence that the probe L₂ could have a certain practical application.Therefore,this study provides a new fluorescent organic small molecule probe for the detection of Zn²⁺.Chapter 4:This chapter described the synthesis of a new Schiff base fluorescent probe2-（2’-（2’’-benzothiazolyl）hydrainyl）allylidene-3-（4-fluorophenyl）-1-isopropyl-indol（L₃）with 2-hydrazinobenzothiazole as the strating material through one-step condensation reaction.The structure was confirmed by MS,¹³C NMR and ¹H NMR.In the presence of Zn²⁺in DMF,the fluorescence intensity at 580 nm was significantly increased,and the detection limit was 2.24×10^-8 M.Both Job’s plot analysis and high-resolution mass spectrum indicated that the probe L₃ coordinated with Zn²⁺at a ratio of 1:1 with a binding constant of 1.07×10⁵ M^-1.L₃ is expected to be developed as a molecular probe for the quantitative determination of Zn²⁺at very low concentration.Chapter 5:The chapter recap the results of this study and the shortcomings.The future work is also proposed.