A Turn‐On Fluorescent Rhodamine‐acyl Hydrazide for Selective Detection of Cu 2+ Ions

We present a rhodamine‐based probe that can detect Cu 2+ ions via Cu 2+ ‐promoted hydrolysis in aqueous solutions. In solution, the probe is non‐fluorescent and colorless, but gives a strong fluorescence at 586 nm and shows a color change to pink on the addition of Cu 2+ ions. We demonstrate that the rhodamine‐based probe undergoes Cu 2+ ‐promoted hydrolysis with a moderate reaction time (within 3 min) and provides a fluorescence off–on change, even in the presence of other competitive metal ions. The rhodamine‐based probe shows a linear correlation between increasing fluorescence at 586 nm and the Cu 2+ concentration, and can detect Cu 2+ at nanomolar levels (10 nM ) in CH 3 CN : H 2 O (v/v, 90:10).