Comment on “Measurement of Ultrafast Photoinduced Electron Transfer from Chemically Anchored Ru−Dye Molecules into Empty Electronic States in a Colloidal Anatase TiO2 Film”

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Electron transfer from the excited electronic singlet state of chemisorbed ruthenium(II) cis-di(isothiocyanato)bis(2,2‘-bipyridyl-4,4‘-dicarboxylate) into empty electronic states in a colloidal anatase TiO2 film was measured as a transient absorption signal of the injected hot electrons with a rise time <25 fs. Optical absorption of the anchored dye molecules led to the excited singlet state of the dye with a small admixture of charge transfer states. The electron transfer reaction reported here did not involve redistribution of vibrational excitation energy and was thus completely different from the well-known Marcus−Levich−Jortner−Gerischer type of electron transfer in the case of weak electronic interaction. It was also not a direct optical charge transfer transition from the donor to the acceptor level but rather an electron transfer reaction with an ultrashort but finite reaction time.