A light controlled, reversible, sensitive and highly selective colorimetric sensor for mercuric ions in water

Abstract

A merocyanine dye as a p-toluenesulfonate salt was synthesized and characterized using spectroscopic techniques. The structure established through single-crystal X-ray crystallography revealed the presence of an extensive H-bond network of dye molecules linked through water molecule and p-toluenesulfonate group. The crystal explorer program was used to estimate the contribution of different intermolecular interactions in the network of molecular chains. The addition of mercuric ions led to the disruption of the molecular chains through complex formation between mercuric ions and the merocyanine form, which produced a change in color visible to the naked eye. The molecule displayed no change in color upon addition of other metal ions. The change in color was used for the detection of mercuric ions. The interaction between the dye molecule and the mercuric ion was further investigated using UV–Visible, DLS and 1H NMR spectroscopy. The interaction between the merocyanine dye and the mercuric ions can be reversibly disrupted by UV light (365 nm). The interaction between mercuric ions and the merocyanine dye was further investigated using density functional theory to corroborate the experimental data. TD-DFT studies indicated a increase in the HOMO-LUMO gap upon addition of mercuric ions.