Dynamics of Semiconductor-to-Dye Electron Transfer for Anthracene Dyes Bound to Different Sized TiO2 Particles

IGNACIO MARTINI; JOSE´ H. HODAK; GREGORY V. HARTLAND

JOURNAL OF PHYSICAL CHEMISTRY B

Año: 1999 vol. 103 p. 9104 - 9111

1089-5647

The photosensitization of different sized TiO2 nanoparticles by anthracenecarboxylic acid dye molecules hasbeen studied using transient absorption spectroscopy. These experiments primarily yield information aboutthe semiconductor-to-dye electron transfer reaction. Our measurements show that for TiO2 particles in the 4to 40 nm size range, the rate of this reaction does not depend on the particles’ size. The results were analyzedusing a model where the electrons are assumed to be evenly distributed over the surface of the particle. Toreproduce our experimental results with this analysis, the scaling parameter that describes the distancedependence of the semiconductor-to-dye electron transfer reaction must be > 180 nm. We do not considerthis to be physically reasonable. An alternative explanation is that the injected electrons are in localized trapsites that are spatially close to the dye radical cation, i.e., they are not randomly distributed over the particlesurface. The observation of single exponential decays in the transient absorption data implies that these trapsites have a narrow energy distribution.