A dual colorimetric chemosensor for Hg(ii) and cyanide ions in aqueous media based on a nitrobenzoxadiazole (NBD)–antipyrine conjugate with INHIBIT logic gate behaviour

Abstract

In this work, we have synthesized nitrobenzoxadiazole–antipyrine conjugate 1 from chloro substituted nitrobenzoxadiazole (NBD) with 4-aminoantipyrine by an elegant method which provides good yield and it is characterized by various spectroscopic techniques. The sensing ability of compound 1 is analyzed with the addition of different metal ions and anions in an aqueous methanol medium. It shows rapid colorimetric response for Hg²⁺ and CN⁻ ions over a wide range of competitive metal ions and anions. On addition of Hg²⁺/CN⁻ ions, 1 shows a distinct color change from pale yellow to pink and orange red, respectively, thus permitting chemosensor 1 to be used for ‘naked eye’ detection of Hg²⁺ and CN⁻ ions. The change in spectral features and color of 1 with the addition of Hg²⁺ and CN⁻ ions is mainly due to the formation of a charge-transfer complex (1₂–Hg²⁺) and cyanide ion induced deprotonation of 1. The interaction between the Hg²⁺/CN⁻ ion and 1 is characterized by mass spectrometry and ¹H-NMR spectral titrations. In addition, sensor 1 is reversible and reusable and it can be developed as an INHIBIT type logic gate. Compound 1 detects Hg²⁺ and CN⁻ ions upto 2.57 × 10⁻⁸ M and 1.67 × 10⁻⁷ M, respectively. Further, compound 1 pre-coated test strips detect Hg²⁺ and CN⁻ ions and they provide a simple and convenient method for determination of Hg²⁺/CN⁻ ions.