A highly Selective Fluorescent Chemosensor for Zn²⁺ Based on the Rhodamine Derivative Incorporating Coumarin Group

A coumarin-appended rhodamine derivative was prepared by reacting rhodamine hydrazide and coumarin-3-carboxylic acid, which fluorescence sensing behavior toward Zn²⁺ against other metal ions was investigated in CH₃CN. Significantly, the rodamine-coumarin derivative exhibited highly selective and sensitive recognition toward Zn²⁺ with a limit of detection (LOD) down to 10^-9 M. Upon addition of Zn²⁺, remarkable fluorescent intensities enhanced and also clear color changed from colorless to pink. The Job's plot indicated the formation of 1:1 complex between the rhodamine-coumarin derivative and Zn²⁺. The presence of common coexisting alkali, alkaline earth, and transition metal ions showed small or no interference with the detection of Zn²⁺. The conjugate dye could be used for "naked-eye" detection of Zn²⁺.