A colorimetric and fluorescent sensor for sequential detection of copper ion and cyanide

A simple cation sensor 1 ((E)-9-((2-hydroxynaphthalen-1-ylimino)methyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-8-ol) bearing both a julolidine moiety and a naphthol moiety was designed and synthesized as a colorimetric sensor for Cu2+. In methanol solution of 1, the presence of Cu2+ led to a distinct naked-eye color change from yellow to purple. The proposed sensing mechanism might be attributed to the decrease in internal charge transfer band. Moreover, the resulting 1-Cu2+ complex sensed cyanide in a fluorometric way via fluorescent changes. These results demonstrate a novel type of the sequential recognition of Cu2+ and CN− using two different sensing methods, color change, and fluorescence.