| With the rapid development of chemosensors, the study on fluorescent probes has become one of the hottest research fields including chemistry, biology, medical science, and environment, and drew more and more attention of people in recent years. The analysis and detection of metal ions are important for its implications in such fields:chemistry, biology, medicine and environment. There are lots of advantages for fluorescence chemosensors such as high selectivity, sensitivity, simplicity and without resorting to any expensive instruments, which was successfully applied in the detection of many metal ions in aqueous solution. Using the relationship between the fluorescence property and the ions concentration, fluorescent probes is fit for the heavy metal detection in real time or in situ for its characteristics of convenience, shortcut, high sensitivity and selectivity. Based on the principle of C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT), six compounds L1-L6were designed and synthesized. By using UV-vis and fluorescence spectrometry methods, we studied their selectively recognition for the metal ions.A new carbazole-based Schiff-base fluorescent chemosensor (L1) was designed, synthesized by condensation reaction between2-amino-4-nitrophenol and3-formyl-9H-hexylcarbazole, which can selectively recognized Fe3+and Cu2+ions over a number of other metal ions. Compound L1could detect Fe3+and Cu2+by UV-Vis and fluorescence spectrometry method. The stoichiometry ratio of L1-Fe3+and L1-Cu2+determined by the method of Job’s plot are2:1and1:1, respectively. Moreover, the detection limits were calculated to be4.23×10-6mol/L for Fe3+ion and5.67×10-6mol/L for Cu2+ion. In the presence of Fe3+/Cu2+ions, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of compound L1. At the same time, the interactions of compounds L1with other ions were also investigated and no obvious changes of UV-vis absorption and fluorescence were observed. Thus a new kind of chemosensor with high sensitivity and selectivity for Fe3+/Cu2+detection was introduced.The compound L2was synthesized by condensation of4-amino antipyrine with3-formyl-9H-hexylcarbazole. When it bonds Cr3+and Cu2+ions, the color of L2in CH3CN solution alters from colorless to yellow and light yellow, respectively. L2can be used as colorimetric probe for Cr3+and Cu2+ions recognization by simple visual inspection. Addition of Cr3+/Cu2+ions to solution, the UV-vis absorption band occur obvious blue shift. The Ka of L1-Cr3+and L1-Cu2+are2.20×104M-1and1.75×104M-1, respectively. The stoichiometry ratio of L1-Cr3+and L1-Cu2+calculated by the Job’s plot method are2:1and1:1, respectively. The calculated detection limits are2.86×10-6M for Cr3+ion and2.75×10-6M for Cu2+ion.L3and L4were designed by introduced thiophene to the carbazole group. Compound L3was synthesized by condensation of2-amino-4-nitro phenol with3-thienyl-hexylcarbazole. Addition of Fe3+ion to L3solution, there is a new UV-vis absorbance band at313nm and the solution color changes from yellowish green to colorless. So L3can be used as colorimetric probe for Fe3+ion recognization observed by unaided eye. The Kais4.21×104M-1and the detection limit is6.16×10-7M. The experiment results show that the intensity of fluorescence peak enhanced13-fold and11-fold with addition of Fe3+/Cr3+ions, respectively. Thus L3could be used as fluorescence probe for detection of Fe3+/Cr3+ions. The Ka of L3-Fe3+and L3-Cr3+are4.67×104M-1and5.97×104M-1, respectively. Both the stoichiometry ratio of L3-Fe3+and L3-Cr3+are2:1. The detection limits are calculated to be3.74×10-6M for Fe3+ion and2.56x10-6M for Cr3+ion. L4was a Schiff base without-OH group comparing with L3. It could not selectively detect metal ions by UV-Vis and fluorescence spectroscopy method. The results show that the phenolic hydroxy is one important bond site of compound for binding to metal ions.The L5and L6were synthesized by introducing salicylaldehyde to the carbazole group and L5had no-NO2group on salicylaldehyde comparing with L6. In CH3CN solution, L5could selectively recognize for Fe3+ion. Addition of Fe3+ion, a new UV-vis absorbance peak located at432nm. The calculated detection limit is9.21×10-7M and the stoichiometry ratio of L5-Fe+is1:1. In the mixed solvent of acetonitrile and water (volume ratio=3:1), the fluorescence intensity enhancement is observed for reaction of L5and Fe3+/Cr3+ion. The detection limits are8.16×10-7M for Fe3+ion and1.15×10-6M for Cr3+ion. The stoichiometry ratio and the Ka of L5-Fe3+/L5-Cr3+are1:1/2:1and4.67x104M-1/5.97×104M-1, respectively. By fluorescence spectrometry studies, we found L6could be used as a ratio fluorescent probe for Cu2+/Cr3+ions detection in CH3CN solution. The Ka of L6-Cu2+and L6-Cr3+are1.53x106M-1and5.37×105M-1, respectively. Both the stoichiometry ratio of L6-Cu2+and L6-Cr3+are2:1. Moreover, the reaction of L6bonding to Cu2+/Cr3+ions is reversible and the detection limits are2.01x10-7M for Cu2+ion and2.440×10-7M for Cr3+ion. |
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