Spectrophotometric and RGB performances of a new tetraphenylcyclopenta-derived Schiff base for the quantification of cyanide ions

Abstract

In this communication, a new cyanide (CN⁻) ion selective chromogenic receptor (L) was developed by reacting 2,4-dinitrophenylhydrazine with 2,3,4,5-tetraphenylcyclopenta-2,4-dienone. The sensing ability of receptor L was studied with different anions such as F⁻, Cl⁻, Br⁻, I⁻, OH⁻, CN⁻, SO₄²⁻, PO₄³⁻, CH₃COO⁻ and NO₃⁻ by a visual test, UV-Vis spectrometry and a smartphone-based RGB tool in THF : H₂O (6 : 4, v/v) media. The receptor L showed a strong absorption band at 412 nm due to the presence of donor and acceptor units that result in an intense ligand-to-ligand charge transfer (LLCT). Upon interaction with CN⁻, the L showed a selective colour change from yellow to blue along with the formation of a new UV-Vis band at 615 nm. The absorption spectral studies indicate the formation of a complex between the L and CN⁻ with an estimated association constant of 8.9 × 10³ M⁻¹ and binding stoichiometry between them is 1 : 1. The binding interaction of L with CN⁻ was examined using ¹H NMR and density functional theory (DFT) calculations. The sensitivity of L is recognized by the limit of detection (LOD) and it is 1 × 10⁻⁷ M which is lower than that in WHO guidelines (0.02 ppm) for drinking water. The colorimetric change of L has been well integrated with a smartphone RGB color value to make it an analytical signal for real-time analysis of CN⁻ with the detection limit down to 3.98 × 10⁻⁶ M. The L detects CN⁻ without any interference from other tested anions over a wide pH range 3–10. During measurements of absorbance and RGB values, all tested solutions were adjusted to pH 7.5. Besides, L was applied for the analysis of CN⁻ content present in various edible samples using spectrophotometry, test paper strips and an RGB colour tool.