Sensing of cyanide ion by tweaking the proton transfer

The highly efficient sensing of cyanide ion was attained using a chemosensor, 2-(4'-diethylamino-2'-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP) by tuning its excited state intramolecular proton transfer to intermolecular proton transfer. Cyanide ion turns the weak blue emission of the chemosensor to bright cyan luminescence. The fluorescence is enhanced by 16 times in the presence of cyanide ion. The detection limit of CN^- ion by DHP is 0.02 μM in acetonitrile. It is reversible, and the reusability was also tested for several cycles. A molecular logic gate was also constructed. The chemosensing was further tweaked by the medium. In addition, DHP has been practically applied for cyanide detection using paper strips, different water samples and sensing and imaging of cyanide ion in MDA-MB 231 breast cancer cells. To substantiate the mechanism of sensing ¹H-NMR titration, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were employed. The transition state structures and visualization of non-covalent interactions (NCI) from reduced density gradient (RDG) and scatter plots support the proposed mechanism.