Photoinduced Electron Transfer from the Excited J-Aggregate State of a Thiacarbocyanine Dye to TiO 2 Colloids

Abstract

The photophysical properties of the J-aggregate of 3,3′-di(3-sulfopropyl)-4,5,4′,5′-dibenzo-9-phenyl-thiacarbocyanine triethyl-ammonium salt in the absence and presence of TiO 2 colloids have been studied using UV–visible absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and ESR spectroscopy. The fluorescence emission of the J-aggregate decreases with increasing concentration of TiO 2 colloids. The average fluorescence lifetime of the J-aggregate in the presence of TiO 2 colloids is shorter than that in the absence of TiO 2 colloids. A strong photoinduced ESR signal has been observed during illumination by light with λ=633 nm in the presence of TiO 2 and the ESR signal can be attributed to the J-aggregate radical cation. From the above results, it is concluded that photoinduced electron transfer from the excited singlet state of the J-aggregate to the conduction band of TiO 2 takes place and the electron transfer rate is about 1.5×10 8 s −1.