Synthesis of a new colorimetric receptor based on calix[4]pyrrole binding oxime for selective recognition of fluoride ions

A colorimetric anion sensor -meso-heptaethylcalix[4]pyrrole-meso-3-aminophenyl-p-nitrobenzaldoxime was synthesised and characterised by various spectroscopic techniques. Anion-binding studies were carried out using UV-vis, and H-1 NMR titrations, revealing that the receptor exhibits selective recognition towards F- over other anions. The selectivity for F- among the halides is attributed mainly to the hydrogen bond interaction of the receptor with F-. Receptor showed colour change from colourless to yellow in the presence of tetrabutylammonium fluoride with 1:2 stoichiometry. Cyclic voltammetry studies, carried out in CH3CN, provided evidence of an anion-dependent electrochemical response with F- ion. This response was particularly dramatic in the case of receptor after the addition of approximate to 1equiv. of F- ion.