Photochemical behavior of 2-(4-ethylamino-2-hydroxyphenyl)-4-(4-ethylaminophenyl)-squaraine (SQ) in TiO2 system was probed by UV-vis, fluorescence quenching, and nanosecond time-correlated single-photon counting. There was strong interaction between SQ and TiO2 colloidal particles with an apparent association constant of 2.275×10^3mol^-^1 . dm^3 obtained by the fluorescence quenching data. The fluorescence emission of SQ dye could be quenched by TiO2 colloid with an efficiency of 97%. The mechanism of photoinduced interface electron transfer for the fluoorescence quenching was proposed upon the spectral characters, potential discrepancy and the variation of the fluorescence lifetime. The rate constant for the electron injection process was 1.97×10^8 s^-^1 determined from the measurements of fluorescence lifetimes.

Key words: TITANIUM OXIDE, ULTRAMICRON, SURFACES ADSORPTION