Generation of carotenoid radical cation in the vicinity of a chlorophyll derivative bound to titanium oxide, upon excitation of the chlorophyll derivative to the Qy state, as identified by time-resolved absorption spectroscopy

Electron injection from a chlorophyll derivative (methyl 3-carboxy-3-devinylpyropheophorobide a, abbreviated as PPB a) to TiO2 nanoparticle took place in ≈30 fs following the decay of an excimer that was generated immediately after excitation to the Qy state (681 nm). Then, electron transfer from carotenoids (Cars) to PPB a+ took place in ≈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).