A ratiometric chemodosimeter for highly selective naked-eye and fluorogenic detection of cyanide

Abstract

A simple indole-based chemosensor (1) with a very low molecular weight of 207 g mol−1 has been synthesized for the highly reactive and selective detection of CN− in aqueous media, even in the presence of other anions, such as F−, Cl−, Br−, AcO−, S2−, SCN−, NO2−, NO3−, CO3−, BzO−, H2PO4−, and HSO4−. The sensor achieves rapid detection of cyanide anion in 2 min, and the pseudo-first-order rate constant is estimated as 1.576 min−1. The colorimetric and ratiometric fluorescent response of the sensor to CN− is attributable to the addition of CN− to the electron-deficient dicyanovinyl group of 1, which prevents intramolecular charge transfer. The sensing mechanism is supported by density functional theory and time-dependent density functional theory calculations. Moreover, sensor 1 exhibits both high accuracy in determining the concentration of CN− in real samples and 1-based test strips can conveniently detect CN− without any additional equipment. The detection limit of the sensor 1 (1.1 μM) for cyanide is lower than the maximum permissible level of CN− (1.9 μM) in drinking water.