A colorimetric sensor for the sequential detection of Cu²⁺ and CN^- in fully aqueous media: Practical performance of Cu²⁺

A new highly selective colorimetric chemosensor 1 (E)-9-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol was designed and synthesized for the sequential detection of Cu²⁺ and CN^-. This sensor 1 exhibited an obvious color change from yellow to orange in the presence of Cu²⁺ in a fully aqueous solution. The detection limit (0.9 μM) of 1 for Cu²⁺ is far lower than the WHO limit (31.5 μM) for drinking water. In addition, the resulting Cu²⁺-2·1 complex can be further used to detect toxic cyanide through a color change from orange to yellow, indicating the recovery of 1 from Cu²⁺-2·1. Importantly, chemosensor 1 could be used to detect and quantify Cu²⁺ in water samples, and a colorimetric test strip of 1 for the detection of Cu²⁺ could be useful for all practical purposes.