p-Phenyleneethynylene Molecular Wires: Influence of Structure on Photoinduced Electron-Transfer Properties

Authors

  • Mateusz Wielopolski,

    1. Department of Chemistry and Pharmacy, Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen (Germany), Fax: (+49) 913-185-28307
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  • Carmen Atienza Dr.,

    1. Department of Chemistry and Pharmacy, Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen (Germany), Fax: (+49) 913-185-28307
    2. Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid (Spain), Fax: (+34) 91-394-4103
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  • Timothy Clark Prof. Dr.,

    1. Computer-Chemie-Centrum, Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Naegelsbachstrasse 25, 91052 Erlangen (Germany)
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  • Dirk M. Guldi Prof. Dr.,

    1. Department of Chemistry and Pharmacy, Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen (Germany), Fax: (+49) 913-185-28307
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  • Nazario Martín Prof. Dr.

    1. Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid (Spain), Fax: (+34) 91-394-4103
    2. Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), 28049 Madrid (Spain)
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Abstract

A series of donor–acceptor arrays (exTTF–oPPE–C60) containing π-conjugated oligo(phenyleneethynylene) wires (oPPE) of different length between π-extended tetrathiafulvalene (exTTF) as electron donor and fullerene (C60) as electron acceptor has been prepared by following a convergent synthesis. The key reaction in these approaches is the bromo–iodo selectivity of the Hagihara–Sonogashira reaction and the deprotecting of acetylenes with different silyl groups to afford the corresponding donor–acceptor conjugates in moderate yields. The electronic interactions between the three electroactive species were determined by using UV-visible spectroscopy and cyclic voltammetry. Our studies clearly confirm that, although the C60 units are connected to the exTTF donor through π-conjugated oPPE frameworks, no significant electronic interactions are observed in the ground state. Theoretical calculations predict how a simple exchange from C[DOUBLE BOND]C double bonds (i.e., oligo(p-phenylenevinylene) to C[TRIPLE BOND]C triple bonds (i.e., oPPE) in the electron donor–acceptor conjugates considerably alters long-range electron transfer. Photoexcitation of exTTF–oPPE–C60 leads to the following features: a transient photoproduct with maxima at 660 and 1000 nm, which are unambiguously attributed to the photolytically generated radical-ion-pair state, [exTTF.+–oPPE–C60.−]. Both charge-separation and charge-recombination processes give rise to a molecular-wire behaviour of the oPPE moiety with an attenuation factor (β) of (0.2±0.05) Å−1.

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