Dynamic mechanism of metal-ion-sensitive fluorescence of phenylimidazoanthraquinone with azacrown (PIAQ-AC) was investigated by time-resolved fluorescence and absorption spectra upon excitation with a femtosecond laser. PIAQ-AC showed marked fluorescence quenching, while the fluorescence intensity was greatly enhanced upon binding of either calcium or barium ions. The transient absorption of PIAQ-AC ascribed to the excited singlet decayed with a lifetime of 5.8 ps in the absence of calcium ions;. The lifetime of the excited singlet increased to 200 ps upon binding of calcium ions to the azacrown, Tnt transient absorption spectrum of the phenylimidazoanthraquinone anion radical was observed in the absence of metal ions. These results clearly indicate that the fluorescence was switched on and off by an intramolecular electron-transfer mechanism controlled with metal ions.