Selective optical detection of HSO4 - via hydrolysis of a simple Schiff Base

A very simple Schiff Base derived from 1-Naphthylamine and 4-(Trifluoromethy) benzaldehyde (L) was prepared as a selective colorimetric and turn-on fluorescent sensor for hydrogen sulfate. In the CH3CN:H2O (3:2, v/v) solvent system, L shows a highly selective colorimetric response to HSO4 (-) ions by changing its color from yellow to colorless immediately. In addition, the weakly fluorescent receptor L shows a highly selective enhancement of fluorescence intensity at 425 nm for HSO4 (-) upon excitation at 320 nm. The recognition process is proven to be hardly influenced by the other tested competitive anions. The sensing is suggested to involve a hydrolysis process promoted by HSO4 (-) which has been further supported by UV-Vis, H-1 NMR and HRMS spectroscopic studies. Applicability of L to detect HSO4 (-) in tap water has been demonstrated. An easy-to-prepare test strip of L has also been made for the naked-eye detection of HSO4 (-) in real samples.