Spectral and Theoretical Studies on Selective and Sensitive Dual-Channel Detection of Cyanide Via Modulation of ICT...

The escalating trend of industrial cyanide consumption emphasises the critical need for reliable cyanide sensors to ensure the safety of human health and the ecosystem. Thereby, a highly selective and sensitive chemodosimeter (R) was designed, synthesised and characterised as a cyanide sensor. Notably, the non-fluorescent, bright blue-coloured solution of R faded to colourless and then fluoresced bright blue upon interaction with CN^-. The UV-Vis and fluorescence spectral titration profiles confirmed the strong binding affinity of R towards CN^- (10⁴ M^- 1), and the Job's plot revealed the 1:1 binding mode of R + CN^- adduct formation. Mechanistic insights collected from ^IH and ^I3C NMR and mass spectral findings revealed that the interacting CN^- underwent nucleophilic addition at the electropositive carbon atom of the activated olefinic bond, disrupting the conjugation within R. Moreover, the theoretical findings evidenced the interplay of electrons in manipulating the colour and fluorescence emission of R, and highlighted that nucleophilic addition of CN^- terminated the ICT process within R and increased the energy gap between the ground and excited states, thus explaining the changes in the optical properties of R in the presence of CN^-. Further, the lowest limit of detection of R was calculated to be 0.38 µM, which is 5 times lower than the WHO publicised allowable limit of CN^- in drinking water and 52.6 times lower than the lethal level of CN^- estimated in fire victims, highlighting its practical applicability. Since the receptor R selectively distinguishes CN^- without the interference of other competing anions with a very high sensitivity, it was successfully employed as a portable test kit suitable for the on-site detection of CN^-.