Coumarin based azo dyes as anion sensors: A spectrophotometric study

Abstract

Two 4-hydroxy coumarin based dyes (1 and 2) have been synthesized and their anion detection ability has been studied, for detection of fluoride and acetate ions selectively through the naked eye. On addition of 4 equivalents of fluoride and acetate to the CH₃CN solution of the receptors 1 and 2, colour changes from light yellow to light red while the similar addition of other anions like dihydrogen phosphate, chloride, bromide and iodide does not show any significant change in colour under identical experimental conditions. The corresponding UV-vis data show a blue shift of the band of receptor 1 and a red shift of the band of receptor 2 for both fluoride and acetate ions. In fluorescence studies, both the receptors show quenching in the presence of fluoride and acetate ions. Stoichiometry of anionic interaction has been determined from ¹H-NMR titrations and Job’s plot. Theoretical studies using density functional theory and time dependent density functional theory have been explored. Detection of fluoride in aqueous medium by paper strips is also reported.