Visually detecting cyanide ion in aqueous solution sensitively and selectively using a merocyanine salt with the help of a smartphone

Abstract

Naked eye visual detection of cyanide ion (CN−) was explored in an aqueous-organic medium (1:1) by using a merocyanine (MC) based probe. The structure validation of the probe was accomplished using spectroscopic techniques. Evaluation of the probe in Tris buffer at pH 7.6 revealed yellow color as a result of its interaction with cyanide ion, which was originally pink in color. Inspection of UV–vis data revealed reduced intensities of absorption bands at 390 nm and 525 nm on adding cyanide ions in probe solution. An abrupt color change visible with the unaided eyes due to the interaction of the probe with cyanide ion proved advantageous in the development of a digital colorimetry-based analytical protocol for evaluation of CN− ions existence in solution. A change in chemical shift of protons in the 1H NMR spectrum implied interaction between the hydroxyl group proton of the probe and CN− ion that results in the displacement of the p-toluenesulfonate group by incoming CN− ion. Dynamic light scattering (DLS) studies also affirmed the aggregation of the probe and in its mixture with CN− ion. The calculation of parameters using density functional theory (DFT) with M06–2X functional further signaled the formation of a complex through the H-bond. Excitation parameters calculated using CAM-B3LYP studies also furnished results in support of experimental data.