Aminophenol based colorimetric chemosensor for naked-eye detection of biologically important fluoride and acetate ions in organo-aqueous medium: Effective and simple anion sensors

Three new novel colorimetric receptors (R1-R3) based on aminophenol have been designed and synthesized by simple Schiff base reaction and their anion sensing properties were examined, characterized by common spectroscopic techniques such as FT-IR, UV–visible, 1HNMR,13CNMR, ESI–MS and fluorescence. Receptors R1 and R2 bearing −OH group at ortho and para position acting as anion binding sites with NO2 moiety as an optical signaling unit. Receptors R1 and R2 elevated selective and sensitive ability towards F− and AcO− ions over the other competing anions in DMSO as well as in CH3CN. Receptors R1 and R2 showed high capability of sensing acetate and fluoride ions present in the form of sodium salts such as NaAcO and NaF in an aqueous medium. The color of both the receptors R1 and R2 solution changes from pale green to blue and pale yellow to peach color with the addition of sodium salts of acetate (NaAcO) and fluoride (NaF) with a bathochromic shift of 168 nm and 165 nm in the UV–vis absorption spectra of receptor R1 and 103 nm and 100 nm in case of receptor R2 due to ICT transition between the electron rich −OH and electron deficient NO2 moiety. Moreover, receptors R1-R2 showed noteworthy fluorescence enhancement, response towards F− and AcO− ion in DMSO. Compared to receptor R2, R1 shows a huge red shift towards F− and AcO− ions in organo-aqueous medium due to the presence of −OH proton at ortho position which effectively bind with both the anions. The binding constant and stoichiometry of the receptors-anions complex was calculated by using Benesi-Hildebrand (B–H) plot. The anion binding properties of receptor R1 via ICT mechanism was enlightened by UV–vis titration, 1HNMR studies.