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Photoinduced Electron Transfer in Langmuir-Blodgett Monolayers of Double-Linked Phthalocyanine-Fullerene Dyads

Year: 2008

Journal: J. Phys. Chem. C, 2008, 112 (26), pp 9896–9902, 20111221

Authors: Heli Lehtivuori, Tatu Kumpulainen, Alexander Efimov, Helge Lemmetyinen, Aiko Kira, Hiroshi Imahori and Nikolai V. Tkachenko

Organizations: Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 541, 33101 Tampere, Finland, and Department of Molecular Engineering, Graduate School of Engineering, and Institute for Integrated Cell-Material Sciences, Kyoto University, Kyotodiagaku-katsura, Nishikyo-ku, Kyoto 615-8510, Japan

Photoinduced electron transfer (ET) in films of the double-linked free-base phthalocyanine−fullerene dyads (Pc−C60) was studied in solid Langmuir−Blodgett (LB) films using femtosecond pump−probe and microsecond flash-photolysis methods. Excitation of the phthalocyanine (Pc) moiety of the dyad results in a rapid (0.8 ps) intramolecular ET from phthalocyanine to fullerene. The formed charge separated (CS) state relaxes in 35 ps, yielding an intermolecular CS state, which relaxes to the ground state in the microsecond time domain. The surface organization of the Pc−C60 dyad monolayers was studied by atomic force microscopy for both pure Pc−C60 films and Pc−C60 mixed films with matrix molecules, octadecylamine (ODA). This study together with the estimations done based on surface pressure−mean molecular area isotherms reveals that the dyads tend to aggregate rather than form a homogeneous mixture with the ODA molecules. This enforces intermolecular interactions and leads to the formation of a long-lived intermolecular CS state.