Abstract: The diad composed of fluorescein and 2-methyl-anthraquinone(FL-AQ) has been synthesized and its photophysical properties have been examined by absorption, fluorescence spectroscopy and fluorescence lifetime. The charge-separated state formed by photo-induced intramolecular electron transfer has been detected by nanosecond transient absorption spectroscopy for the first time. When FL is excited in solution, the photo-induced electron transter from FL to AQ proceeds efficiently. The rate constant and the efficiency of intramolecular electron transfer are 3.95×10⁹s^-1 and 95% respectively. Its charge-separated state lifetime is too short to detect obviously by transient absorption spectroscopy. Adding of nanometer-size TiO₂ colloids to FL-AQ ethanol solution can prolong the lifetime of charge-separated state, so its transient absorption signal is recorded significantly. The decay lifetime of FL^+· at 480 nm is 11.1 μs. The decay lifetime of AQ^-· at 560 nm is 8.93 μs.

Key words: Fluorescein-anthraquinone-methyl ester, Photo-induced electron transfer, Nanosecond transient absorption spectroscopy, Titania nanometer colloids(TiO₂)