Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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


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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: TIPS-tetracene energies and structure.
Figure 2: Ultrafast TT formation.
Figure 3: Vibrationally coherent TT formation.
Figure 4: Thermally activated TT separation.
Figure 5: Thermally activated TT emission.
Figure 6: The role of the TT state in endothermic SF.


  1. 1

    Smith, M. B. & Michl, J. Singlet fission. Chem. Rev. 110, 6891–6936 (2010).

    CAS  Article  Google Scholar 

  2. 2

    Pope, M. & Swenberg, C. Electronic Processes in Organic Crystals and Polymers (Oxford Univ. Press, 1999).

    Google Scholar 

  3. 3

    Hanna, M. C. & Nozik, A. J. Solar conversion efficiency of photovoltaic and photoelectrolysis cells with carrier multiplication absorbers. J. Appl. Phys. 100, 074510 (2006).

    Article  Google Scholar 

  4. 4

    Merrifield, R. E. Magnetic effects on triplet exciton interactions. Pure Appl. Chem. 27, 481–498 (1971).

    CAS  Article  Google Scholar 

  5. 5

    Wilson, M. W. B. et al. Ultrafast dynamics of exciton fission in polycrystalline pentacene. J. Am. Chem. Soc. 133, 11830–11833 (2011).

    CAS  Article  Google Scholar 

  6. 6

    Burdett, J. J., Gosztola, D. & Bardeen, C. J. The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: kinetic evidence for a dark intermediate state and implications for singlet fission. J. Chem. Phys. 135, 214508 (2011).

    Article  Google Scholar 

  7. 7

    Eaton, S. W. et al. Singlet exciton fission in polycrystalline thin films of a slip-stacked perylenediimide. J. Am. Chem. Soc. 135, 14701–14712 (2013).

    CAS  Article  Google Scholar 

  8. 8

    Swenberg, C. E. & Stacy, W. T. Bimolecular radiationless transitions in crystalline tetracene. Chem. Phys. Lett. 2, 327–328 (1968).

    CAS  Article  Google Scholar 

  9. 9

    Merrifield, R. E. Theory of magnetic field effects on the mutual annihilation of triplet excitons. J. Chem. Phys. 48, 4318–4319 (1968).

    CAS  Article  Google Scholar 

  10. 10

    Piland, G. B. & Bardeen, C. J. How morphology affects singlet fission in crystalline tetracene. J. Phys. Chem. Lett. 6, 1841–1846 (2015).

    CAS  Article  Google Scholar 

  11. 11

    Burdett, J. J., Muller, A. M., Gosztola, D. & Bardeen, C. J. Excited state dynamics in solid and monomeric tetracene: the roles of superradiance and exciton fission. J. Chem. Phys. 133, 144506 (2010).

    Article  Google Scholar 

  12. 12

    Wilson, M. W. B. et al. Temperature-independent singlet exciton fission in tetracene. J. Am. Chem. Soc. 135, 16680–16688 (2013).

    CAS  Article  Google Scholar 

  13. 13

    Yost, S. R. et al. A transferable model for singlet-fission kinetics. Nat. Chem. 6, 492–497 (2014).

    CAS  Article  Google Scholar 

  14. 14

    Odom, S. A., Parkin, S. R. & Anthony, J. E. Tetracene derivatives as potential red emitters for organic LEDs. Org. Lett. 5, 4245–4248 (2003).

    CAS  Article  Google Scholar 

  15. 15

    Stern, H. L. et al. Identification of a triplet pair intermediate in singlet exciton fission in solution. Proc. Natl Acad. Sci. USA 112, 7656–7661 (2015).

    CAS  Article  Google Scholar 

  16. 16

    Liebel, M. & Kukura, P. Broad-band impulsive vibrational spectroscopy of excited electronic states in the time domain. J. Phys. Chem. Lett. 4, 1358–1364 (2013).

    CAS  Article  Google Scholar 

  17. 17

    Rafiq, S. & Scholes, G. D. Slow intramolecular vibrational relaxation leads to long-lived excited-state wavepackets. J. Phys. Chem. A 120, 6792−6799 (2016).

    CAS  Article  Google Scholar 

  18. 18

    Berkelbach, T. C., Hybertson, S. & Reichman, R. Microscopic theory of singlet exciton fission. I. General formulation. J. Chem. Phys. 138, 114102 (2013).

    Article  Google Scholar 

  19. 19

    Fuemmeler, E. G. et al. A direct mechanism of ultrafast intramolecular singlet fission in pentacene dimers. ACS Cent. Sci. 2, 316–324 (2016).

    CAS  Article  Google Scholar 

  20. 20

    Bakulin, A. A. et al. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy. Nat. Chem. 8, 16–23 (2016).

    CAS  Article  Google Scholar 

  21. 21

    Musser, A. J. et al. Evidence for conical intersection dynamics mediating ultrafast singlet exciton fission. Nat. Phys. 11, 352–357 (2014).

    Article  Google Scholar 

  22. 22

    Monahan, N. R. et al. Dynamics of the triplet-pair state reveals the likely coexistence of coherent and incoherent singlet fission in crystalline hexacene. Nat. Chem. 9, 341–346 (2016).

    Article  Google Scholar 

  23. 23

    Liebel, M., Schnedermann, C. & Kukura, P. Vibrationally coherent crossing and coupling of electronic states during internal conversion in β-carotene. Phys. Rev. Lett. 112, 198302 (2014).

    CAS  Article  Google Scholar 

  24. 24

    Tiwari, V., Peters, W. K. & Jonas, D. M. Electronic resonance with anticorrelated pigment vibrations drives photosynthetic energy transfer outside the adiabatic framework. Proc. Natl Acad. Sci. USA 110, 1203–1208 (2013).

    CAS  Article  Google Scholar 

  25. 25

    Casanova, D. Electronic structure study of singlet fission in tetracene derivatives. J. Chem. Theory Comput. 10, 324–334 (2014).

    CAS  Article  Google Scholar 

  26. 26

    Chan, W. L., Ligges, M. & Zhu, X. Y. The energy barrier in singlet fission can be overcome through coherent coupling and entropic gain. Nat. Chem. 4, 840–845 (2012).

    CAS  Article  Google Scholar 

  27. 27

    Arias, D. H., Ryerson, J. L., Cook, J. D., Damauer, N. H. & Johnson, J. C. Polymorphism influences singlet fission rates in tetracene thin films. Chem. Sci. 7, 1185–1191 (2016).

    CAS  Article  Google Scholar 

  28. 28

    Miyata, K. et al. Coherent singlet fission activated by symmetry breaking. Nat. Chem. (in the press).

  29. 29

    Chang, T.-C. & Dlott, D. D. Picosecond vibrational cooling in mixed molecular crystals studied with a new coherent Raman scattering technique. Chem. Phys. Lett. 147, 18–24 (1988).

    CAS  Article  Google Scholar 

  30. 30

    Gelinas, S. et al. Binding energy of charge-transfer excitons localized at polymeric semiconductor heterojunctions. J. Phys. Chem. 115, 7114–7119 (2011).

    CAS  Google Scholar 

  31. 31

    Pensack, R. D. et al. Observation of two triplet-pair intermediates in singlet exciton fission. J. Phys. Chem. Lett. 7, 2370–2375 (2016).

    CAS  Article  Google Scholar 

  32. 32

    Yost, S. R., Hontz, E., Yeganeh, S. & Van Voorhis, T. Observation of two triplet-pair intermediates in singlet exciton fission. J. Phys. Chem. C 116, 17369–17377 (2012).

    CAS  Article  Google Scholar 

  33. 33

    Burdett, J. J. & Bardeen, C. J. Quantum beats in crystalline tetracene delayed fluorescence due to triplet pair coherences produced by direct singlet fission. J. Am. Chem. Soc. 134, 8597–8607 (2012).

    CAS  Article  Google Scholar 

  34. 34

    Keong Yong, C. et al. The entangled triplet pair state in acene and heteroacene materials. Nat. Commun. 8, 15953 (2017).

    Article  Google Scholar 

  35. 35

    Thorsmølle, V. et al. Morphology effectively controls singlet-triplet exciton relaxation and charge transport in organic semiconductors. Phys. Rev. Lett. 102, 017401 (2009).

    Article  Google Scholar 

  36. 36

    Kolomeisky, A. B., Feng, X. & Krylov, A. I. A simple kinetic model for singlet fission: a role of electronic and entropic contributions to macroscopic rates. J. Phys. Chem. 118, 5188–5195 (2014).

    CAS  Google Scholar 

  37. 37

    Odom, S., Parkin, S. R. & Anthony, J. E. Tetracene derivatives as potential red emitters for organic LEDs. Org. Lett. 5, 4245–4248 (2003).

    CAS  Article  Google Scholar 

  38. 38

    Chen, K., Gallaher, J. K., Barker, A. J. & Hodgkiss, J. M. Transient grating photoluminescence spectroscopy: an ultrafast method of gating broadband spectra. J. Phys. Chem. Lett. 5, 1732–1737 (2014).

    CAS  Article  Google Scholar 

  39. 39

    Rao, A. et al. Exciton fission and charge generation via triplet excitons in pentacene/C60 bilayers. J. Am. Chem. Soc. 132, 12698–12703 (2010).

    CAS  Article  Google Scholar 

Download references


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




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.

Corresponding authors

Correspondence to Akshay Rao or Richard H. Friend.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 10779 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Stern, H., Cheminal, A., Yost, S. et al. Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission. Nature Chem 9, 1205–1212 (2017).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing