Fluorescence quenching of a rhodamine derivative: Selectively sensing Cu2+ in acidic aqueous media

A new rhodamine derivative (RhB-Im) was synthesized as an “on-off” chemosensor for Cu2+ in an acidic aqueous solution. RhB-Im exhibited chemically reversible and highly selective and sensitive fluorescence response toward Cu2+ in aqueous acetate-buffer/DMF solution (pH 3.6) over other competitive metal ions. Upon addition of Cu2+, RhB-Im displayed remarkable fluorescence quenching accompanied by a clear color change from pink to red. Based on the analysis of Stern–Volmer plots, a static quenching mode was proposed to be primarily responsible for the fluorescence quenching event when the concentration of Cu2+ was low, but, the energy- and electron-transfer processes cannot be ruled out.