The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene-Based Copolymers

Authors

  • Horst Scheiber,

    1. Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)
    2. Christian Doppler Laboratory Advanced Functional Materials Institute of Nanostructured Materials and Photonics, Joanneum Research Franz-Pichler-Strasse 30, 8160 Weiz (Austria)
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  • Michael Graf,

    1. Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)
    2. Christian Doppler Laboratory Advanced Functional Materials Institute of Nanostructured Materials and Photonics, Joanneum Research Franz-Pichler-Strasse 30, 8160 Weiz (Austria)
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  • Harald Plank,

    1. Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)
    2. Christian Doppler Laboratory Advanced Functional Materials Institute of Nanostructured Materials and Photonics, Joanneum Research Franz-Pichler-Strasse 30, 8160 Weiz (Austria)
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  • Egbert Zojer,

    1. Institute of Solid State Physics Graz University of Technology Petersgasse 16, 8010 Graz (Austria)
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  • Christian Slugovc,

    1. Institute for Chemistry and Technology of Organic Materials Graz University of Technology Stremayrgasse 16, 8010 Graz (Austria)
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  • Stefan Kappaun,

    1. NanoTecCenter Weiz Forschungsgesellschaft mbH Franz-Pichler-Straße 32, 8160 Weiz (Austria)
    2. Institute for Chemistry and Technology of Organic Materials Graz University of Technology Stremayrgasse 16, 8010 Graz (Austria)
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  • Frank Galbrecht,

    1. Macromolecular Chemistry Group Bergische Universität Wuppertal Gauss-Str. 20, 42097 Wuppertal (Germany)
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  • Ullrich Scherf,

    1. Macromolecular Chemistry Group Bergische Universität Wuppertal Gauss-Str. 20, 42097 Wuppertal (Germany)
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  • Emil J. W. List

    Corresponding author
    1. Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)
    2. Christian Doppler Laboratory Advanced Functional Materials Institute of Nanostructured Materials and Photonics, Joanneum Research Franz-Pichler-Strasse 30, 8160 Weiz (Austria)
    3. NanoTecCenter Weiz Forschungsgesellschaft mbH Franz-Pichler-Straße 32, 8160 Weiz (Austria)
    • Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria).
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  • The CDL-AFM gratefully acknowledges the continuous support of AT&S AG.

Abstract

The influence of UV irradiation in inert atmosphere on the emission spectrum of fluorenone containing poly[9,9-bis(2-ethyl)hexylfluorene] (PF2/6) has been investigated by means of optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of green emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross-linking of the films. FTIR measurements show no reduction of the C=O stretching mode upon irradiation, and, moreover, the degree of cross-linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer onto the ketonic defect sites. The found results enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000 cd m−2 at 7 V) two-color OLEDs.

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