Experimental and theoretical studies for sequential detection of copper(II) and cysteine by a colorimetric chemosensor

A simple and selective colorimetric chemosensor 1 was reported for the sequential detection of Cu²⁺ and cysteine (Cys) in aqueous solution. The presence of Cu²⁺ led to a distinct naked-eye color change from colorless to yellow, which was explained by ICT and LMCT with theoretical calculations. The receptor enabled analysis of Cu²⁺ ions with a sensitivity limit of 0.48 μM, which is far below the WHO acceptable limit (31.5 μM) in drinking water. Importantly, chemosensor 1 could be used to detect and quantify Cu²⁺ in water samples, and the binding of the receptor 1 and Cu²⁺ was also chemically reversible with EDTA. Additionally, the resulting 1-Cu²⁺ complex sensed cysteine with the absorption change via an UV-visible or a naked-eye color change.