Electron injection from a chlorophyll derivative (methyl 3-carboxy-3-devinylpyropheophorobide a, abbreviated as PPB a) to TiO2 nanoparticle took place in approximate to 30 fs following the decay of an excimer that was generated immediately after excitation to the Q,. state (681 nm). Then, electron transfer from carotenoids (Cars) to PPB a(.+) took place in approximate to 200-240 ps. The latter observation supports the electron-transfer mechanism proposed in a previous investigation, in which Cars were added as redox spacers to the PPB a-sensitized TiO2 solar cells to enhance their performance (X.-F. Wang, J. Xiang, P. Wang, Y. Koyama, S. Yanagida, Y. Wada, K. Hamada, S. Sasaki, H. Tamiaki, Chem. Phys. Lett. 408 (2005) 409). (c) 2005 Elsevier B.V. All rights reserved.