Syntheses And Spectroscopic Properties Of Schiff Bases Organic Compounds

Acting as bioactive substances,metal ions and anions play various vital roles in many biological and environmental processes whereas their abnormal concentration will be very much dangerous towards ecosystem.Therefore,the development of simple and selective methods for the detection of metal ions and anions has attracted considerable amount of attention.The conventional methods require expensive,sophisticated instruments and time consuming procedures.Hence,fluorescent probes are widely used and studied because of their high sensitivity,selectivity,versatility and relatively simple handling.In this paper we have synthesized four Schiff based fluorescent probes,which were characterized by ¹H NMR,¹³C NMR and ESI-mass.1.A novel Schiff-base probe F1 was synthesized in high yield through one-step reaction between cinnamaldehyde and diaminomaleonitrile,which can act as a fluorescent probe for detecting Cu²⁺and PO₄^3-in solvent of DMSO/H₂O（7:3,v/v）and DMSO/H₂O（9:1,v/v）respectively.This probe exhibited a highly sensitive and selective response towards Cu²⁺and PO₄^3-relative to other anions and metal ions.Upon the addition of Cu²⁺and PO₄^3-to the solution of F1 in DMSO,the dramatic naked eye detectable color changes were observed from yellow to red and light green with detection limits of 72.17 nmol/L and 96.53 nmol/L,respectively.In addition,F1 shows fluorescence?turn-on?response in presence of Cu²⁺or PO₄^3-,without the interference of background ions.2.The new Schiff-base fluorescent probe F2 for the selective detection of Cu²⁺has been synthesized by a simple one-step reaction of 1,3,3-trimethyl-2-（formylmethylene）indoline and diaminomaleonitrile.The probe F2 exhibited strong fluorescence enhancement with a large Stokes shift（146 nm）upon addition of Cu²⁺and showed an excellent selectivity in the presence of competitive ions.The detection limits was found to be 6.18×10^-8 mol/L.The 1:1binding mode of F2 with Cu²⁺was supported by the Job?s plot,¹H NMR and ESI-mass analysis.Moreover,F2 also had the ability to quantify Cu²⁺in actual water samples.3.Compound3-[（2,5-dihydroxy-phenyl）-imino]-4-cyano-1H-pyrazole（F3）was synthesized and used for sensing Hg²⁺and Fe³⁺.In a mixed solution of DMSO and water,the probe F3 displayed a highly selective detection of both Hg²⁺and Fe³⁺ions with low detection limit～10^-8 molL^-1.The probe F3 showed a brilliant blue fluorescence under ultraviolet light upon the addition of Hg²⁺and Fe³⁺.Moreover,F3 can distinguish Hg²⁺and Fe³⁺in the presence of other ions such as Co²⁺,Cu²⁺and without obvious interference.Therefore,the probe F3 can simultaneously detect Hg²⁺and Fe³⁺in same solvent systems as a colorimetric chemosensor.4.A new rhodamine B-derived Schiff base F4 was synthesized and its sensing behavior toward various metal ions was investigated by UV–vis and fluorescence spectroscopic techniques.The probe F4 exhibited fluorescence turn-on response to Fe³⁺,Cr³⁺,Al³⁺,Ga³⁺and Hg²⁺in aqueous solution of MeOH with particular selectivity and sensitivity.Upon addition of metal ions,the solution of F4 shows significant enhanced absorbance and fluorescence for Fe³⁺,Cr³⁺,Al³⁺,Ga³⁺and Hg²⁺which accompanied by color change from light yellow to red.The detection limits of probe F4 for Fe³⁺,Cr³⁺,Al³⁺,Ga³⁺and Hg²⁺were 6.31×10^-99 mol/L,1.81×10^-88 mol/L,4.51×10^-99 mol/L,7.81×10^-99 mol/L,2.06×10^-77 mol/L,respectively.It can be seen that the detection limits of these metal ions basically reach the nanomolar level,with high sensitivity and trace substance detection.