A colorimetric chemosensor based on a Schiff base for highly selective sensing of cyanide in aqueous solution: The influence of solvents

A new highly selective colorimetric chemosensor 1 (E)-9-(((2-hydroxy-5-nitrophenyl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol for CN^- was developed. Receptor 1 showed exclusive response toward cyanide by a color change in aqueous solution. However, in aprotic solvents and methanol, the unique selectivity of 1 for CN^- disappeared, and its nonselective color change was observed for other anions. This phenomenon could be possibly explained by the combination of the basicity and the hydrogen bonding ability of the anions. Moreover, 1 could be used as a practical, visible colorimetric test kit in an aqueous environment.