Bisthiocarbohydrazones as Colorimetric and “Turn on” Fluorescent Chemosensors for Selective Recognition of Fluoride

Abstract

Bisthiocarbohydrazone derivatives of two heterocyclic ketones were designed and synthesized to selectively sense fluoride ion from a biologically competing solvent dimethylsulfoxide (DMSO). The selective recognition of fluoride is clearly visible to the naked eye with a distinct color change. The recognition mechanism has been investigated by UV–visible, fluorescence spectroscopy, and 1H NMR titration experiments. From the Benesi–Hidebrand equation and Job's plot, it was inferred that both compounds bind to fluoride with a 1:1 stoichiometry. 1H NMR titration data indicates deprotonation of the NH protons by fluoride as a prominent step in the recognition.