Synthesis And Properties Of Coumarin Schiff Base Fluorescent Probes For Metal Ions

Metal ions have great important effects on the metabolic activities of plants and animals and the environment.Some metal ions play positive roles to the cells of the organism activities and they are beneficial to certain organisms.However,others maybe play damage roles and they are harmful to other organisms.Additional,some metal ions in a reasonable range of concentration have promoting effects.If it is below or beyond the corresponding safety concentration range,they would threat to the living activity of the organism.It is necessary that metal ions are detected and monitored in the environment and their living environment.Application of fluorescence molecular probe to detecting metal ions,anions,protein is more relatively mature than other technologies,such as chromatography,spectroscopy,titration,voltammetry,potential technology.The reason is its characteristics of high selectivity,high sensitivity,simple operation.Coumarin-derived fluorescent probes have been mainly used in fluorescent recognition of metal ions owning to their low cost,easy syntheses,low toxicity and simple operation.With benzo-?-pyrone structure,coumarin is easy to modify and heterocyclic carbonyl carbon can participate in the coordination of metal ions.Within the scope of the visible light coumarin has good light stability,strong fluorescence,and large Stokes shift.Therefore,coumarin-derived fluorescent probes are widely used.They have been used for detection of DNA and RNA,enzyme amine,amino acid,protein,anionic and metal ions.In general,the Schiff base,due to the C=N bind free rotation,often presents weak or no fluorescence.Coumarin Schiff base probe containing oxygen or nitrogen donor element can be combined with metal ions and as a fluorescent unit.Based on 7-diethylaminocoumarin,five novel coumarin schiff base compounds have been designed and synthesized showed specific selectivity for some metal ions,respectively.A novel coumarin schiff base fluorescence probe for Zn²⁺,L1 showed good selectivity and strong anti-jamming capability for Zn²⁺,and the complexation of L1 with Zn²⁺ is 1:2 mole ratio.Fluorescent probe L2,which 5-bromothiophene-2-carbohydrazide reacted with 7-Diethylaminocoumarin-3-aldehyde,was designed and synthesized.In acetonitrile solution,after addition of nickel and cobalt ions,the fluorescence intensity of L2 decreased significantly,and L2 showed 2:1 complex formation with nickel and cobalt ions respectively.7-Diethylaminocoumarin-3-carbohydrazide reacted with 4-diethylaminosalicylaldehyde to obtain a Schiff base fluorescent probe L3.In acetonitrile solution,L3 showed good selectivity for Hg2+,and the probe L3 formed a 2:1 complex with Hg2+.7-Diethylaminocoumarin-3-carbohydrazide reacted with 7-Diethylaminocoumarin-3-aldehyde and 2-pyrrolecarbaldehyde probes to obtain a Schiff base fluorescent probe L4 and L5,which showed highly selective fluorescence enhanced for Cu²⁺,both of them formed a 1:2 complex with Cu²⁺ respectively in acetonitrile.