Coumarin modified rhodamine derivative: Fluorescent chemosensor selectively recognizing Al3+ and Ca2+

A fluorescent probe with a coumarin moiety bound to rhodamine 6G hydrazide(1) was synthesized. Its sensing behavior toward various metal ions was investigated with fluorescence methods. Compound 1 displays different fluorescence emission responses to Al3+ and Ca2+ at the same excitation wavelength in the visible light region, while no changes occur after the addition of other metal ions. The binding ratios of the complexs of 1-Al3+ and 1-Ca2+ are both 2:1 according to the Job plot and high resolution mass spectrometer(HRMS) experiments. Moreover, emission spectrum of 1-Ca2+ complex and absorption spectrum of the rhodamine dyes overlap largely. When Al3+ was added to the 1-Ca2+ system, calcium in complex 1-Ca2+ can be displaced by Al3+, resulting in the output of another ratiometric sensing signal, which demonstrates that the 1-Ca2+ complex can be served as a new and effective fluorescence resonance energy transfer(FRET) donor for rhodamine derivatives.