Naphthalene-based Azo-azomethine Chemosensor: Naked Eye Detection of Fluoride in Semi-aqueous Media

A new azo-azomethine chemosensor containing active phenolic sites, H2L, has been designed and synthesized for rapid detection of inorganic fluoride over the other anions, such as Clˉ, Brˉ, Iˉ, AcOˉ, H2PO4ˉ, NO3ˉ, N3ˉ in DMSO/water (90/10) media. The 1H NMR titration revealed that the colorimetric response was considered to be the direct consequence of hydrogen-bond formation between phenolic groups of the receptor and fluoride ion followed by deprotonation. The anions recognition ability of H2L was also evaluated using UV-Vis spectroscopy. Importantly, H2L can detect inorganic fluoride even at 2.04×10-6 M level, which is lower than the World Health Organization (WHO) permissible level. Interestingly, H2L was used for qualitative detection of fluoride anion in commercially available mouthwash and toothpaste.