Exciton–Exciton Annihilation in Mixed-Phase Polyfluorene Films

Authors

  • Paul E. Shaw,

    1. Organic Semiconductor Centre, SUPA School of Physics and Astronomy University of St. Andrews North Haugh, St. Andrews, KY16 9SS (UK)
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  • Arvydas Ruseckas,

    1. Organic Semiconductor Centre, SUPA School of Physics and Astronomy University of St. Andrews North Haugh, St. Andrews, KY16 9SS (UK)
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  • Jeffrey Peet,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106-9510 (USA)
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  • Guillermo C. Bazan,

    1. Center for Polymers and Organic Solids Department of Chemistry and Biochemistry University of California Santa Barbara, CA 93106-9510 (USA)
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  • Ifor D. W. Samuel

    Corresponding author
    1. Organic Semiconductor Centre, SUPA School of Physics and Astronomy University of St. Andrews North Haugh, St. Andrews, KY16 9SS (UK)
    • Organic Semiconductor Centre, SUPA School of Physics and Astronomy University of St. Andrews North Haugh, St. Andrews, KY16 9SS (UK)
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Abstract

Singlet–singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of β-phase chains using time-resolved fluorescence. On a timescale of >15 ps after excitation, the results are fitted well by a time-independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time-dependent annihilation rate is observed during the first 15 ps in the glassy phase and in the β-phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low-energy sites. The annihilation rate in the mixed-phase films increases with increasing fraction of β-phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersedβ-phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line-dipole approximation for an exciton wavefunction extending over 2.5 nm. The results indicate that glassy andβ-phase chromophores are intimately mixed rather than clustered or phase-separated.

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