A turn-off fluorescence sensor for cyanide detection which in turn inhibit 2-way ESIPT investigated by experimental and theoretical study

Abstract

A ligand based on 3-((quinoline-7-yl) methyeleneamino) phenazine-2-ol) (HAPQA) has been designed and synthesized for the selective detection of cyanide ions. The ligand HAPQA exhibits excited-state intramolecular proton transfer (ESIPT) with a long wavelength emission fluorescent (575nm) which gradually quenches with the addition of cyanide ions. The photophysical properties of the probe as well as its selectivity towards CN− ions are explored using UV–visible, emission spectroscopy and time-resolved fluorescence spectroscopic studies. The ligand exhibits strong H-bonding-mediated inhibition of 2-way excited-state intramolecular proton transfer (ESIPT) in HAPQA selectively with cyanide ions over all other ions. The deep orange colour fluorescence of the ligand in acetonirile turns into bright green coloured solution in presence of cyanide ions with a detection limit of 0.60μM. DFT calculations has been done to study the ground and excited state energy optimized structure and proposed mechanism which is in harmony with the experimental findings and the ESIPT process observed in ligand HAPQA. Thus, the receptor can be used as a Colorimetric and fluorescent sensor for the determination of CN− ion.