Synthesis And Recognition Properties Of Schiff Bases Fluorescent Probes

Objective:To explore the preparation of simple and highly selective recognition of transition metal ions Schiff base small molecule fluorescent probes,and applied to the actual sample transition metal ion content determination.Methods:A novel Schiff base fluorescent probe L₁ was prepared by substitution and condensation reacctions using 4-bromo-1,8-naphthalimide,hydrazine hydrate,4-（2-aminoethyl）-morpholine and salicylaldehyde;4-tert-butyl-2,6-dicarboxyphenol and nicotinic acid hydrazide were used as raw materials obtained by one-step condensation of fluorescent probe L₂.The structures and compositions of L₁ and L₂were characterized by ¹H NMR,¹³C NMR,FT-IR,HR-MS and other analytical techniques.Fluorescence spectrophotometry and UV-Vis spectrophotometry were used to study the recognition performances of such two probes to common metal ion and anion in laboratory,¹H NMR titration,HR-MS and EDTA titration experiments confirmed its recognition mechanism.Results:Two novel Schiff-base fluorescent probes were successfully synthesized,the common laboratory identification of anion and cation performance studies have shown that:（1）L₁ can selectively recognize Cu²⁺by fluorescence quenching in a mixed solvent of anhydrous ethanol and Tris-HCl（1/1,v/v,pH=7.4）,and can be observed under the naked eye with 365nm UV lamp possessing fluorescence quenching behavior.The detection limit of Cu²⁺was 0.047μmol/L₁,There is a good linear relationship between the concentration of Cu²⁺and the fluorescence intensity of probe L₁ in the concentration range of（2.0-9.0μmol/L）.The average labeled amount of Cu²⁺for the fluorescent probe was 106.5%,which could be applied to the determination of Cu²⁺in real water sample.（2）L₂ selectively recognizes Ca²⁺,Zn²⁺,Cu²⁺and Co²⁺in a mixed solvent of absolute ethanol and Tris-HCl（9/1,v/v,pH=7.4）.Among them,Ca²⁺combined with L₂ could be observed with naked eye under365nm UV lamp,which meant that it had the special response to fluorescence spectrum.In addition,the detection limits of L₂ for Ca²⁺,Zn²⁺,Cu²⁺and Co²⁺were1.43×10^-7 mol/L,1.12×10^-5 mol/L,3.56×10^-77 mol/L and 3.39×10^-77 mol/L respectively.The concentration range of Ca²⁺in the range of 2-9μmol/L showed a good linear relationship with fluorescence intensity,the absorbance of Zn²⁺,Cu²⁺,and Co²⁺in the concentration range of 0-14μmol/L,6-18μmol/L,and 2-12μmol/L showed a good linear relationship.With regard to the average labeled amount of each ion in the drug,they were Ca²⁺（98.2%）、Zn²⁺（87.0%）、Cu²⁺（94.1%）and Co²⁺（96.0%）respectively,The recoveries of water samples were Ca²⁺（98.9%、94.2%、97.1%）,Zn²⁺（98.1%、101.9%、98.1%）,Cu²⁺（93.8%、91.6%、93.8%）and Co²⁺（91.9%、98.2%、101.0%）,respectively.Conclusion:Preparation of two new Schiff base fluorescent probes can detect and quantify Cu²⁺,Ca²⁺,Zn²⁺and Co²⁺at low detection limit,Among them,the sensor L₂has the function of multi-function recognition of various ions.