Colorimetric and fluorescent probe based on coumarin/ thiophene derivative for sequential detection of mercury(II) and cyanide ions in an aqueous medium

Abstract

A novel colorimetric and fluorescent coumarin hydrazone probe L was prepared by condensing 7-(diethylamino)-coumarin–3-carbaldehyde and (thiophen-2-ylmethyl) hydrazine. Absorbance and emission titrations show that probe L detects Hg2+ rather than other interfering cations. The colorimetric change from yellow to red and the decrease in fluorescence intensity after the addition of Hg2+ cations to probe L are perfectly visible to the naked eye. It could be related to intramolecular charge transfer and d-d transitions of the metal cations. The binding stoichiometry of the probe L to the Hg2+ cation was found to be 1:1, which was confirmed by Job plot and mass spectrum analysis. The resulting complex L.Hg2+ is preferentially fluorescent and presents a distinct blueshift in its absorbance spectrum only with CN− anions, which is caused by the release of the probe L and the production of the Hg(CN)2 complex. The LOD of Hg2+ and CN− were found to be 5.15 nM and 0.208 µM respectively. Therefore, probe L can be employed to detect and quantify Hg2+ and CN− in real solutions.