Sequential detection of Cu²⁺ and anions (CN^- and S^2-) by a colorimetric chemosensor in aqueous solution

A new highly selective colorimetric chemosensor 1 was developed for the sequential detection of Cu²⁺ and anions (CN^- and S^2-). Sensor 1 exhibited an obvious color change from yellow to orange in the presence of Cu²⁺ in an aqueous solution. The detection limit (13.2 μM) of 1 for Cu²⁺ is much lower than the WHO guideline (31.5 μM). In addition, the resulting 1-Cu²⁺ complex can be further used to detect cyanide and sulfide through color changes from orange to yellow and pink, respectively. The sensing mechanism of Cu²⁺ by 1 was proposed to be the decrease in internal charge transfer (ICT) band, based on the experimental results and theoretical calculations, and those of CN^- and S^2- by 1 were proposed to be a copper complex affinity toward anions (CN^- and S^2-).