Structure-reactivity correlation in selective colorimetric detection of cyanide in solid, organic and aqueous phases using quinone based chemodosimeters

Quinone based colorimetric chemodosimeters, which could instantly detect CN − in solid, organic and aqueous phases with selectivity and sensitivity are described. The results of UV-Vis, fluorescence, 1 H and 13 C NMR spectroscopy, electrochemical studies and product analysis confirmed that the mechanism of sensing is through nucleophilic addition of CN − to the C&z.dbd;C bond of the indole ring. DFT calculations were conducted to rationalize the sensing mechanism of these sensors. Though the sensors show a different color change with F − in organic medium via H-bond formation, they are highly selective towards CN − as shown in the relay experiment as well as when they are added together. A novel attempt is made to explain the effect of substituents on the sensing behavior by carrying out "Structure-Reactivity Correlation" using Hammett's substituent constants ( σ p ). The five new colorimetric chemodosimeters sense cyanide selectively and sensitively in aqueous and organic media via a nucleophilic addition mechanism exhibiting quantitative structure-reactivity correlation.