Two isoniazid-based chemosensors for the detection of cyanide ions in solution: an experimental and computational study

Colorimetric chemosensors L₁ and L₂, based on isoniazid hydrazones, have been designed for the highly sensitive and selective recognition of CN⁻ ion. Competing experiments were conducted with various other anions such as F⁻, Cl⁻, Br⁻, I⁻, SCN⁻, ClO₃⁻, ClO₄⁻, NO₃⁻, H₂PO₄⁻, SO₃²⁻, and HSO₄⁻ in an acetonitrile solution. In the UV–Vis spectra, a bathochromic shift in the absorption bands of both hydrazones was observed following the addition of cyanide. These spectral changes were accompanied by a color transition from transparent to orange for L₁ and from pale yellow to peach for L₂, which is attributed to the deprotonation of the chemosensors. The detection limits for cyanide ions were determined to be 0.36 µM for L₁ and 2.79 µM for L₂ using the 3σ rule. Quantum chemical calculations were employed to optimize the structure of the chemosensors, compute their UV–Vis spectra, and confirm the proposed detection mechanism for CN⁻ ions.