A new fluorescent ionophore for alkaline earth metal ions, 4′-(9-fluorenecarboxamido)benzo-15-crown-5 (3), was synthesized; its photochemical behavior was investigated using UV, fluorescence, 1H NMR, and 13C NMR spectrometry. In the absence of a metal ion, the fluorene moiety showed weak fluorescence emission (fluorescence “Off” state). However, complexation with metal ions greatly enhanced the fluorescence intensity (fluorescence “On” state).
