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Uniquely Shaped Double-Decker BuckyferrocenesDistinct Electron Donor−Acceptor Interactions

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posted on 03.12.2008, 00:00 by Renata Marczak, Mateusz Wielopolski, S. Shankara Gayathri, Dirk M. Guldi, Yutaka Matsuo, Keiko Matsuo, Kazukuni Tahara, Eiichi Nakamura
Quantum chemical calculations and various photophysical techniques, ranging from steady-state absorption and steady-state as well as time-resolved fluorescence to femtosecond pump-probe experiments, were employed to examine ground- and excited-state interactions in a set of novel double-decker buckyferrocenes (i.e., Fe2(C60Me10)Cp2): C2v and D5d isomers. When compared to the individual reference systems, the intimate fullerene/ferrocene contacts reflect appreciable ground-state interactions, namely, substantial redistribution of charge density between the two electron donors (i.e., ferrocenes) and the electron acceptor (i.e., fullerene). Furthermore, an intervalence charge-transfer transition (i.e., ferrocene−ferrocenium interaction) was established, but only in the C2v isomer. The first insight into the electron donor−acceptor interactions came from inspecting the fullerene-centered fluorescence. Relative to the reference compounds that contain no ferrocene, which exhibit quantum yields of up to 0.1, and knowing that the fluorescence of the investigated double-decker type conjugates is quenched to 10−3, transient absorption measurements prove unequivocally the rapid formation of the radical ion-pair states as the dominant products of excited-state deactivation in the double-decker buckyferrocenes. Despite these products having much higher lying radical ion-pair states relative to the corresponding single-decker buckyferrocene, their lifetimes, which vary between 12 and 39 ps, are slightly shorter.

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