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How single conjugated polymer molecules respond to electric fields

Nature Materials volume 5, pages 141–146 (2006)Cite this article

Abstract

Conjugated polymers find applications in a range of devices such as light-emitting diodes, field-effect transistors and solar cells. The elementary electronic response of these semiconductors to electric fields is understood in terms of nanoscale perturbations of charge density. We demonstrate a general breaking of spatial charge symmetry by considering the linear Stark effect in the emission of single chromophores on individual chains. Spectral shifts of several nanometres occur due to effective dipoles exceeding 10 D. Although the electric field does not ionize the exciton, some molecules exhibit field-induced intensity modulations. This quenching illustrates the equivalence of charge symmetry breaking and polaron-pair or charge-transfer-state formation, and provides a microscopic picture of permanent charging, which leads to doping and exciton dissociation in actual devices. In addition to using this tuneable emission in single-photon electro-optic modulators, hysteresis in the Stark shift suggests a route to designing nanoscale memory elements such as molecular switches.

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Figure 1: Electric-field modulation of the fluorescence spectrum of a single chromophore on an MEH-PPV polymer molecule at 5 K.
Figure 2: Electric-field modulation of MEH-PPV single-molecule emission.
Figure 3: Effect of the plane of polarization of the incident and emitted radiation relative to the field vector on the electric-field response of two different materials.
Figure 4: Linear and hysteretic field response of the emission of single-polymer molecules.
Figure 5: Field modulation of the single-molecule emission intensity due to charge-induced exciton quenching.

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Acknowledgements

The authors are grateful to W. Stadler, C. Holopirek and A. Helfrich for technical assistance as well as to the Deutsche Forschungsgemeinschaft for financial support through the Sonderforschungsbereich 486 and the Gottfried Wilhelm Leibniz award.

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Authors and Affiliations

  1. Physics Department and Center for NanoScience, Photonics and Optoelectronics Group, Ludwig-Maximilians-Universität, Amalienstrasse 54, 80799, Munich, Germany

    Florian Schindler, John M. Lupton, Josef Müller & Jochen Feldmann

  2. Chemistry Department and IfP, Macromolecular Chemistry Group, Bergische Universität Wuppertal, Gauss-Strasse 20, 42097, Wuppertal, Germany

    Ullrich Scherf

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  1. Florian Schindler
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Correspondence to John M. Lupton.

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Schindler, F., Lupton, J., Müller, J. et al. How single conjugated polymer molecules respond to electric fields. Nature Mater 5, 141–146 (2006). https://doi.org/10.1038/nmat1549

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