A rhodamine-based chromogenic and fluorescent chemosensor for copper ion in aqueous media

A rhodamine-based chemosensor for copper ion, 1-(rhodamine B)lactam-thiosemicarbazide (I), was designed and synthesized. Compound I is a colorless, non-fluorescent compound and was synthesized via the one-step reaction of rhodamine B hydrazide with KSCN in acidic medium. Upon mixing Cu2+ in acetonitrile–water (30:70, v/v) solution, the spirolactam ring of I was opened, which resulted in the dramatic increases in both fluorescence and absorbance of the mixing solution. Based on this mechanism, a chromo- and fluorogenic chemosensor for Cu2+ was developed. The fluorescence and absorbance signal are linear with Cu2+ concentration in the range 0.2–4.0 μmol L−1 and 0.5–10 μmol L−1, respectively.