Rationally designed dual channel reversible probe for cyanide recognition in aqueous medium with solid-state sensing abilities

Abstract

A novel chromogenic azo-azomethine chemosensor, namely 2-((E)-(2-(benzo[d]thiazol-2-yl) hydrazineylidene)methyl)-4-((E)-phenyldiazenyl)phenol (referred to as L), was rationally designed and synthesized. The molecular structure of L was established using various spectroscopic and spectrometry techniques including NMR, FT-IR and mass. The spectral profile including absorption and fluorescence were recorded in solvents of varying polarity. The sensor responsiveness towards different anions was evaluated visually and established using UV–vis spectroscopy and NMR studies. A binary solution of DMSO/H2O (6:4, v:v) was used for anion recognition studies. A color change from colorless to yellow was noticed upon addition of CN– ion to the probe (L) solution. The developed probe was found to be very sensitive towards CN– ion with a detection limit of 21 nM. Benesi-Hildebrand plot revealed a binding constant of 1.2*103 M-2and the binding stoichiometry of 1:2 was confirmed using Job’s plot. 1H NMR studies were utilised to ascertain the recognition mechanism which revealed the CN– ion assisted deprotonation of N-H and O-H group of L. The recognition mechanism established using NMR technique has been supported theoretically by DFT based studies. Additionally, cost-effective paper strips coated with L has been proved to be a convenient tool for detecting CN– ion in aqueous solutions. The reversibility and reusability of the developed probe was also investigated in both solution as well as solid state using trifluoroacetic acid (TFA) without any loss of the sensitivity of the developed probe. Moreover, the developed probe recognises cyanide ion in environmental samples with around 100 % recovery. The practical application of the Logic gate response of L was confirmed by paper strip experiment.