A highly selective and sensitive thiophene substituted 1,3,4-oxadiazole based turn-off fluorescence chemosensor for Fe2+ and turn on fluorescence chemosensor for Ni2+ and Cu2+ detection

In the present work, a newly synthesized thiophene substituted 1,3,4-oxadiazole derivative namely 2-(-4-(thiophene-3-yl)phenyl)-5-(5-(thiophene-3-yl)thiophene-2-yl)-1,3,4-oxadiazole [TTO] is characterized as chemosensor for detecting Fe2+, Ni2+ and Cu2+ metal ions through absorption and fluorescence studies. We found that, on changing media chemosensor shows different behavior with Fe2+, Ni2+ and Cu2+ metal ions. In ethanol-water (1/1,v/v, pH 7.2) medium on varying concentration of Fe2+, chemosensor shows turn off fluorescence, whereas Ni2+ and Cu2+ metal ions induced a strong turn on fluorescence respectively in methanol-water (1/1,v/v, pH 7.2) and acetonitrile-water (1/1,v/v, pH 7.2) media. The competitive metal ion experimental results revealed that chemosensor is highly selective for recognizing Fe2+, Ni2+ and Cu2+ ions without the interference of other metal ions (Pb2+, Ca2+, Mg2+, Co2+, Zn2+, Na+, and Mn2+). The detection limit of chemosensor for all targeted metal ions is in the range of 0.5-3 mu M. The detection capacity for targeted metal ion studies shows less than 6.5 min indicating highly sensitive nature of the TTO. Job's plot indicates that, the binding stoichiometry between chemosensor TTO and targeted metal ions is 1:1 for Fe2+, Ni2+ and Cu2+ metal ions respectively. Further, linear variation in the fluorescence intensity of the chemosensor with different concentrations of the metal ions suggests the possibility of quantitative measurement of the targeted metal ions. Hence, our experimental findings very strongly suggest that, TTO can be used as chemosensor for detecting Fe2+, Ni2+ and Cu2+ metal ions in future.