Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission

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Singlet exciton fission (SF), the conversion of one spin-singlet exciton (S1) into two spin-triplet excitons (T1), could provide a means to overcome the Shockley–Queisser limit in photovoltaics. SF as measured by the decay of S1 has been shown to occur efficiently and independently of temperature, even when the energy of S1 is as much as 200 meV less than that of 2T1. Here we study films of triisopropylsilyltetracene using transient optical spectroscopy and show that the triplet pair state (TT), which has been proposed to mediate singlet fission, forms on ultrafast timescales (in 300 fs) and that its formation is mediated by the strong coupling of electronic and vibrational degrees of freedom. This is followed by a slower loss of singlet character as the excitation evolves to become only TT. We observe the TT to be thermally dissociated on 10–100 ns timescales to form free triplets. This provides a model for ‘temperature-independent’ efficient TT formation and thermally activated TT separation.

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The authors thank the Winton Programme for the Physics of Sustainability and the Engineering and Physical Sciences Research Council for funding. R.H.F. thanks the Miller Institute for Basic Research and the Heising–Simons Foundation at the University of California Berkeley for support. The authors thank T. Arnold (Diamond Light Source), J. Novak, D. Harkin and J. Rozboril for support during the beamtime at beamline I07 and the Diamond Light Source for financial support. The computational work was supported by the Scientific Discovery through Advanced Computing program funded by the US Department of Energy, Office of Science, Advanced Scientific Computing Research, Basic Energy Sciences.

Author information


  1. Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK

    • Hannah L. Stern
    • , Alexandre Cheminal
    • , Katharina Broch
    • , Sam L. Bayliss
    • , Maxim Tabachnyk
    • , Neil Greenham
    • , Andrew J. Musser
    • , Akshay Rao
    •  & Richard H. Friend
  2. Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley 94720, USA

    • Shane R. Yost
    •  & Martin Head-Gordon
  3. Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley 94720, USA

    • Shane R. Yost
    •  & Martin Head-Gordon
  4. MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand

    • Kai Chen
    •  & Justin M. Hodgkiss
  5. School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140, New Zealand

    • Kai Chen
    •  & Justin M. Hodgkiss
  6. University of Kentucky, Lexington 40506, USA

    • Karl Thorley
    •  & John Anthony
  7. Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK

    • Andrew J. Musser


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H.L.S. and A.C. carried out experiments, interpreted the data and wrote the manuscript. S.R.Y. and M.H.-G. ran the calculations, interpreted data and wrote the manuscript. N.G. and S.L.B. interpreted data. K.B., M.T., K.C. and J.M.H. performed experiments. K.T. and J.A. designed and synthesized the materials. A.R., A.J.M. and R.H.F. interpreted the data and wrote the manuscript. All of the authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Akshay Rao or Richard H. Friend.

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