Pyrene-Hydrazone-π···Hole Coupled Turn-on Fluorescent and Naked- Eye Colorimetric Sensor for Cyanide: Role of Homogeneous π-Hole Dispersion in Anion Selectivity.

A pyrene based probe associated with π···hole - hydrazone as one of the recognizing elements is synthesized and its turn in to a selective colorimetric and turn-on fluorescent sensor, (L3) for cyanide anion. This chemo sensor show high selectivity towards cyanide anion through photo electron transfer (PET) mechanism. The binding strength and sensitivity of the chemo sensor L3 towards cyanide are found to be 2.0 X 104, and 4.44 x 10-4 respectively. We have compared this high selectivity of the receptor towards cyanide, with our previously reported receptors L1 and L2. The detailed UV-Vis, Emission, 1H-NMR, IR spectroscopic and Molecular Electrostatic Potential (MEP) studies reveals that the homogeneous π···hole dispersion in the aromatic ring governing the selectivity of the receptor towards cyanide anion. Such a positive π···hole homogeneous dispersion is missing in the case of sensor L2, instead we have polarized π···hole dispersion towards 2nd and 4th position of di-nitrophenyl chromophoric unit in L2.