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Strongly exchange-coupled triplet pairs in an organic semiconductor

Nature Physics volume 13, pages 176–181 (2017)Cite this article

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Abstract

From biological complexes to devices based on organic semiconductors, spin interactions play a key role in the function of molecular systems. For instance, triplet-pair reactions impact operation of organic light-emitting diodes as well as photovoltaic devices. Conventional models for triplet pairs assume they interact only weakly. Here, using electron spin resonance, we observe long-lived, strongly interacting triplet pairs in an organic semiconductor, generated via singlet fission. Using coherent spin manipulation of these two-triplet states, we identify exchange-coupled (spin-2) quintet complexes coexisting with weakly coupled (spin-1) triplets. We measure strongly coupled pairs with a lifetime approaching 3 μs and a spin coherence time approaching 1 μs, at 10 K. Our results pave the way for the utilization of high-spin systems in organic semiconductors.

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Figure 1: Temperature-dependent formation of exchange-coupled triplet pairs.
Figure 2: Strongly and weakly coupled pairs formed by singlet fission in TIPS-tetracene thin-film samples.
Figure 3: Rabi oscillations of weakly and strongly interacting triplets.
Figure 4: Lifetime and coherence of strongly and weakly coupled triplet pairs.
Figure 5: Quintet formation through time-dependent exchange interaction.

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Acknowledgements

L.R.W. thanks the Gates-Cambridge Trust and Winton Programme for the Physics of Sustainability. This work was supported by the Freie Universität Berlin within the Excellence Initiative of the German Research Foundation. We also acknowledge support from the Engineering and Physical Sciences Research Council Grants No. EP/G060738/1. We thank A. D. Chepelianskii for helpful input.

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Authors and Affiliations

  1. Cavendish Laboratory, J.J. Thomson Avenue, University of Cambridge, Cambridge CB3 OHE, UK

    Leah R. Weiss, Sam L. Bayliss, Richard H. Friend, Akshay Rao & Neil C. Greenham

  2. Berlin Joint EPR Lab, Fachbereich Physik, Freie Universität Berlin, D-14195 Berlin, Germany

    Felix Kraffert, Robert Bittl & Jan Behrends

  3. Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA

    Karl J. Thorley & John E. Anthony

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Contributions

L.R.W. and S.L.B. analysed the data. F.K., J.B., L.R.W. and S.L.B. carried out the experiments. K.J.T. and J.E.A. provided the materials. All authors discussed the results. L.R.W. and S.L.B. wrote the manuscript with input from all authors.

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Correspondence to John E. Anthony, Neil C. Greenham or Jan Behrends.

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Weiss, L., Bayliss, S., Kraffert, F. et al. Strongly exchange-coupled triplet pairs in an organic semiconductor. Nature Phys 13, 176–181 (2017). https://doi.org/10.1038/nphys3908

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