Electroanalytical and spectral investigation of organic receptors as colorimetric and absorption ratiometric anion chemosensor

<p>Colorimetric receptors <b>R1</b> and <b>R2</b> have been designed and synthesized by Schiff base condensation and characterised by standard spectroscopic techniques. Anion binding ability of the receptors have been investigated quantitatively through optical, electrochemical and <sup>1</sup>HNMR titration studies. UV-vis spectra of receptor <b>R1</b> and <b>R2</b> exhibited a significant red shift for F<sup>−</sup> and AcO<sup>−</sup> ions with a visual color response. Receptor <b>R1</b> exhibited selective response towards AcO<sup>−</sup> ion in the presence of HEPES buffer media. Incremental color change of receptor <b>R2</b> with the higher equivalence of AcO<sup>−</sup> ions clearly represent the ratiometric response. Cyclic voltammetric studies of <b>R1</b> and <b>R2</b> exhibits shift in oxidation and reduction peak with successive addition of AcO<sup>−</sup> ions indicating the anion induced oxidation of -NH and reduction of the keto group and nitro species. Electrooptical and <sup>1</sup>H NMR titration studies of <b>R2</b> collectively reflects the anion induced change of chromophore from C=N to N=N indicative of azo-hydrazone tautomeric signaling in the presence of AcO<sup>−</sup> ions. Lower detection limit of 2.1 and 0.41 ppm achieved with sodium salt of AcO<sup>−</sup> ion with <b>R1</b> and <b>R2</b> reflects their utility as colorimetric chemosensor.</p>