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The Role of Keto Defect Sites for the Emission Properties of Polyfluorene-Type Materials

Published online by Cambridge University Press:  11 February 2011

Emil J.W. List ,
Roland Guentner ,
Patricia Scanducci de Freitas  and
Ullrich Scherf
Emil J.W. List
Affiliation:
Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria & Institute of Nanostructured Materials and Photonics, Franz-Pichler-Strasse 30, A-8160 Weiz, Austria.
Roland Guentner
Affiliation:
Department of Chemistry, BUGH Wuppertal, Gauss-Str. 20 D-42097 Wuppertal, Germany.
Patricia Scanducci de Freitas
Affiliation:
Department of Chemistry, BUGH Wuppertal, Gauss-Str. 20 D-42097 Wuppertal, Germany.
Ullrich Scherf
Affiliation:
Department of Chemistry, BUGH Wuppertal, Gauss-Str. 20 D-42097 Wuppertal, Germany.
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Abstract

In this paper we have identified a dominant degradation mechanism of blue light emitting polyfluorene (PF) type polymers, which turns the desired blue emission colour of these polymers into an undesired blue-green emission. As shown low energy emission band at 2.2–2.3 eV can be identified as the emission from exciton and/or charge trapping keto defect sites (9-fluorenone sites), which in fact can be regarded as emission of a guest (defect) accidentally incorporated into the π-conjugated PF backbone. We present spectroscopic evidence for the formation of keto defect sites in 9-monoalkylated polyfluorenes (PF-a) which are identified as the source of the strong low energy emission band. Furthermore we show that the keto defects can be generated directly during polymer synthesis as show for the PF-a or can be formed as main channel of an (photo- or electro-) oxidative degradation process as show for the 9-bisalkylated PF.

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References

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