Ultrafast Electron Injection from the S₂ State of Carotenoids into TiO₂ Nanoparticles

Dye molecules attached to TiO₂ nanoparticles have been of a great interest in the applications including dye-sensitized solar cells. In this paper, TiO₂ nanoparticle sensitized with a natural photosynthetic dye, 8′-apo-β-caroten-8′-oic acid (ACOA) was investigated by femtosecond transient absorption spectroscopy. Ultrafast excited state dynamics of ACOA and electron injection and recombination dynamics between dye molecules and TiO₂ nanoparticles were compared by changing the excitation wavelength between 403 and 480 nm. Ultrafast electron injection into TiO₂ nanoparticles with quantum yields of 0.33 was observed for both excitation wavelengths.