A triphenylamine scaffold for fluorogenic sensing of noxious cyanide via the ICT mechanism and its bioimaging application†

A novel triphenylamine benzimidazole based fluorogenic chemosensor named (2E,2′E)-3,3′-((phenylazanediyl)bis(4,1-phenylene))bis(2-(1H-benzo[d]imidazol-2-yl)acrylonitrile) (PBIA) has been successfully generated and characterized by varoius spectroscopic techniques. Among various screened anions, only cyanide (CN⁻) showed a distinct fluorogenic property towards PBIA. Hence, the optical properties of PBIA were investigated in the presence of cyanide (CN⁻) by means of UV-vis spectrophotometry and fluorescence spectroscopy in DMSO, where we observed that, upon treatment with CN⁻ to the probe solution, the orange fluorescence of the ligand showed a blue shift and the orange fluorescence changed to greenish-yellow under an UV lamp. The hypsochromic shift in fluorescence maxima upon the addition of cyanide was attributed to nucleophilic addition of cyanide to PBIA inhibiting the electron flow within the molecule and disrupting the ICT process. The interaction behind the sensing of cyanide was investigated by ¹H-NMR titration, a mass spectroscopic study and DFT calculations, which supported the mechanism. The limit of detection (LOD) was calculated and found to be in the order of 10⁻⁸ (M). PBIA showed an immediate response in the spectral pattern (<20 s) towards its target cyanide ion, and the effectiveness of the chemosensor was also examined in the presence of competing anions. Furthermore, the practical efficacy of the PBIA was established by a dipstick experiment along with cyanide detection in various natural water resources. Human breast cancer cells MDA-MB 231 were made susceptible to CN⁻ sensing in a biological system.