Novel nitro substituted formazan derivatives: Selective ratiometric and colorimetric chemosensors for fluoride anion sensing detectable by the naked eye
Novel two formazan derivatives FNB and FDNB were synthesized from their corresponding phenylhydrazone and characterized by various spectroscopic methods. The sensing ability of these formazan sensors towards different anions was determined in THF by colorimetric UV-vis spectroscopy method. FNB had an efficient colorimetric sensing ability for fluoride anion by changing colour from red to green then blue with a Δλ shift of ca. 138 nm, whilst FDNB act as a colorimetric sensor with change colour from yellow to red with a Δλ shift of ca. 95 nm, which recognition by naked eye. Considerably, the detection limit of sensor FNB were found to be 0.051 ppm (under the WHO determined level) in the presence of F− anion. Moreover, the binding forms of F− with sensors were examined by 1H NMR experiments. These results indicated that sensors FNB and FDNB containing nitro groups and hydrazo unit (–NH) hydrogen bond donating exhibited the high sensitivity and selectivity toward fluoride, which has biologically important.