ICT / PET Modulated Chromogenic/Fluorogenic Detection of Cyanide Ions: A Spectroscopic and Theoretical Study

The prevalence use of cyanide and its pernicious risks to human health accentuates the prominence of cyanide detection. Concerning this, we have developed a probe VDP4 by coupling a donor (8-hydroxyquinoline-2-carbaldehyde) and an acceptor (2-(1H-benzimidazole-2-yl)acetonitrile) by Knoevenagel condensation reaction for the exclusive detection of cyanide in an aqueous solution. The VDP4 responded to CN^- by changing its color to yellow and switching on its fluorescence following contact with cyanide. ¹H-NMR, ¹³C-NMR, LC-MS, FT-IR, and DFT studies provide an attestation for the signaling mechanism for cyanide detection is the deprotonation of the -OH group combined with nucleophilic addition of cyanide at the electron-deficient vinylic carbon atom of VDP4. A very low colourimetric (86 nM) and fluorometric (44 nM) detection limit highlighted its practicability, and Job studies ratified the 1:1 binding interaction. The DFT/TDDFT studies uncovered that colour changes of VDP4 with CN- were caused by ICT variations, and PET modulations were responsible for fluorescent alterations. The spatial ICT was a key factor for the deep yellow coloration of the VDP4 in the presence of CN^-. The energy level diagram of frontier molecular orbitals unveiled that Photoinduced electron transfer from the benzimidazole part to the 8-hydroxy quinoline part was liable for the frail emission of VDP4 which occluded in the presence of CN^- thereby turning on the fluorescence of the fluorophore. The real-time analysis results advocated that VDP4 was the optimum choice for the qualitative and quantitative estimation of CN^- in food samples.