Rational design and application of a fluorogenic chemodosimeter for selective detection of cyanide in an aqueous...

A new quinone-benzothiazole imine based chemodosimeter (R) was rationally designed, synthesized and characterized using NMR and mass spectral techniques. The receptor colorimetrically senses cyanide in aq. HEPES buffer: DMF (2:8 v/v) solution with an instantaneous colour change from yellow to bluish green. An enhancement of fluorescence intensity at 429 nm with excimer formation is also observed after addition of cyanide to the receptor, which is accompanied with a colour change from yellow to blue under UV lamp. Nucleophilic addition of cyanide to imine C-atom inhibits intra-molecular charge transfer (ICT) transition, which is responsible for the excimer formation. This chemical reaction is confirmed by ¹H NMR titration. The receptor binds with two equivalents of cyanide with a binding constant of 5.55 × 10⁴ M^-1. The limit of detection (LOD) of cyanide by the receptor is found to be as low as 69 nM, which is much lower than the acceptable limit of cyanide in drinking water as set by the WHO (1.9 μM). Electrochemical studies support the termination of ICT transition upon addition of cyanide ion. Theoretical studies substantiate experimental findings and excimer formation. The receptor fluorometrically detects cyanide present in tap water and food materials such as cassava flour, almond and potato.