Multi-Spectroscopic and TD-DFT Studies on Chromogenic and Fluorogenic Detection of Cyanide in an Aqueous Solution

Different spectroscopic techniques and Density Functional Theory (DFT)/Time-Dependent Density Functional Theory (TDDFT) calculations have been employed to investigate the dual channel CN^- detection behaviour of the developed chemo-dosimeter (AK3). The CN^- with AK3 reaction triggered a colour change from pale yellow to colourless and enhanced fluorescence. UV-Vis, fluorescence, ¹H & ¹³C NMR and mass techniques coupled with theoretical calculations (Mulliken charges, dihedral angles) revealed that the CN^- sensing process mechanism involves deprotonation of the N-H group followed by nucleophilic addition reaction. Detailed TD-DFT calculations showed that the relaxation of excited electrons from LUMO and to two different ground states is responsible for the weak/moderate fluorescence of AK3. Nucleophilic addition of CN^- to the C-atom of the CH = CH bridge terminated the π-conjugation between donor and acceptor regions, reduced the coplanarity, decreased the ICT transition and consequently enhanced the fluorescence of the probe. The practical utility of the probe was demonstrated by detecting cyanide in food materials and determining CN^- in environmental water samples.