Highly selective fluorogenic anion chemosensors: naked-eye detection of F− and AcO− ions in natural water using a test strip

Abstract

Two new chemosensors S1 and S2 were synthesized and their chromogenic and fluorogenic behavior towards various biologically important anions in a competing solvent DMSO was investigated. Both the sensors portrayed a substantial color change upon addition of F⁻ and AcO⁻ ions and no significant change was observed on addition of other anions such as Cl⁻, Br⁻, I⁻, ClO₄⁻ and HSO₄⁻. The binding constant showed that both F⁻ and AcO⁻ anions bind to the sensors in an equal proportion, in which S2 was found to be superior and showed a better binding ability than S1. Job's plots indicated that both sensors formed a (1 : 1) complex (sensor : anion) with F⁻ and AcO⁻ anions. Remarkable fluorescence “turn on” emission behavior was observed with both the sensors when treated with F⁻ and AcO⁻ anions respectively. ¹H NMR titration experiments indicated that both S1 and S2 formed a strong hydrogen bond not only with the phenolic-OH but also with the amide-NH of the triazole. We have also demonstrated an easy-to-prepare test strip of S2 to detect F⁻ and AcO⁻ anions even in aqueous medium at a lower limit of about 10 ppm, indicating the potential real-life application of detecting F⁻ and AcO⁻ anions in a natural aqueous environment simply through naked-eye observation.