Novel nitro-substituted formazan derivatives: selective ratiometric and colorimetric chemosensors for fluoride anion sensing detectable by the naked eye

Abstract

Two novel formazan derivatives,FNBandFDNB, were synthesized from the corresponding phenylhydrazones and characterized by various spectroscopic methods. The sensing ability of these formazan sensors towards different anions was determined in THF by a colorimetric UV-vis spectroscopy method.FNBhad an efficient colorimetric sensing ability for fluoride anions by changing colour from red to green then blue with a ??shift ofca.138 nm, whilstFDNBacted as a colorimetric sensor by changing colour from yellow to red with a ??shift ofca.95 nm, which could be recognised by the naked eye. The detection limit of sensorFNBwas found to be 0.051 ppm (under the WHO permitted level) in the presence of F?anions. Moreover, the binding forms of F?with the sensors were examined by1H NMR experiments. These results indicated that sensorsFNBandFDNB, containing nitro groups and hydrazo unit (-NH) hydrogen bond donation, exhibited high sensitivity and selectivity toward fluoride, which has biological importance. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020.