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Quintet multiexciton dynamics in singlet fission

Nature Physics volume 13, pages 182–188 (2017)Cite this article

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Abstract

Singlet fission, in which two triplet excitons are generated from a single absorbed photon, is a key third-generation solar cell concept. Conservation of angular momentum requires that singlet fission populates correlated multiexciton states, which can subsequently dissociate to generate free triplets. However, little is known about electronic and spin correlations in these systems since, due to its typically short lifetime, the multiexciton state is challenging to isolate and study. Here, we use bridged pentacene dimers, which undergo intramolecular singlet fission while isolated in solution and in solid matrices, as a unimolecular model system that can trap long-lived multiexciton states. We combine transient absorption and time-resolved electron spin resonance spectroscopies to show that spin correlations in the multiexciton state persist for hundreds of nanoseconds. Furthermore, we confirm long-standing predictions that singlet fission produces triplet pair states of quintet character. We compare two different pentacene–bridge–pentacene chromophores, systematically tuning the coupling between the pentacenes to understand how differences in molecular structure affect the population and dissociation of multiexciton quintet states.

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Figure 1: Molecular structure and Jablonski diagram of the singlet fission system.
Figure 2: Identifying singlet fission dynamics via transient absorption.
Figure 3: Identifying quintet and triplet spin states via time-resolved electron spin resonance.
Figure 4: Nutation of the (TT) pair and dissociated triplet transitions in BP3.
Figure 5: Singlet fission generates weakly coupled triplets in BP2.
Figure 6: Temperature-dependent dissociation kinetics.

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Acknowledgements

This work was supported by the Australian Research Council (DP160103008 and LE130100146). M.J.Y.T. acknowledges receipt of an ARENA Fellowship and a Travel Award from the CASS Foundation. M.J.Y.T. thanks J. Behrends, R. Bittl and the Berlin Joint EPR Lab (BeJEL) for useful discussions. D.R.M. acknowledges an ARC Future Fellowship (FT130100214). L.M.C. acknowledges support from the Office of Naval Research Young Investigator Program (Award N00014-15-1-2532) and Cottrell Scholar Award. S.N.S. thanks the NSF for GRFP (DGE 11-44155). This research used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. We thank J. Guse for technical assistance.

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Authors and Affiliations

  1. School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia

    Murad J. Y. Tayebjee

  2. Department of Chemistry, Columbia University, New York, New York 10027, USA

    Samuel N. Sanders, Elango Kumarasamy & Luis M. Campos

  3. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA

    Matthew Y. Sfeir

  4. School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia

    Dane R. McCamey

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Contributions

Experiments were designed and performed by M.J.Y.T., S.N.S., M.Y.S. and D.R.M. Materials were designed and synthesized by S.N.S., E.K. and L.M.C. Data were analysed by M.J.Y.T., S.N.S., M.Y.S. and D.R.M., and all authors contributed to the discussion. M.J.Y.T., S.N.S., M.Y.S. and D.R.M. wrote the manuscript, with contributions from all authors.

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Correspondence to Murad J. Y. Tayebjee or Dane R. McCamey.

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Tayebjee, M., Sanders, S., Kumarasamy, E. et al. Quintet multiexciton dynamics in singlet fission. Nature Phys 13, 182–188 (2017). https://doi.org/10.1038/nphys3909

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