Solvatochromism of an ICT-based Colourimetric Probe and its Utility to Sense Cyanide in Aqueous Solution and to Estimate it in Food Materials.

The high malignancy of CN^- to cause critical health problems and even death in trace concentrations and its potential presence in food, water and environment underscore the essence of CN^- detection. This paper outlines the synthesis of a novel intramolecular charge transfer (ICT) based colourimetric probe, PPL2, for the selective detection of cyanide ions in an aqueous solution. The different colours and spectral bands of PPL2 in different solvents reinforce its solvatochromism behaviour and ICT characteristics. The PPL2 exclusively changes its colour from yellow to colourless upon binding with CN^-, credited to deprotonation followed by nucleophilic addition, as accredited by ¹H and ¹³C-NMR and LC-MS spectral studies. The DFT/TD-DFT calculations attested the proposed sensing mechanism and authenticated the signalling mechanism of ICT modulation. The DFT/TD-DFT analysis portrayed the disruption of the ICT process of PPL2 upon cyanide binding. This probe targeted CN^- over other anions with a detection limit of 0.2 µM, eclipsing the WHO's guidelines for cyanide in drinking water. The practical applicability of PPL2 was illustrated through the successful estimation of cyanide in five different food samples, highlighting the probe's potential for food safety monitoring.