Skip to main content

Thank you for visiting nature.com. 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.

Spatial separation of triplet excitons drives endothermic singlet fission

Abstract

Molecules that undergo singlet fission, converting singlet excitons into pairs of triplet excitons, have potential as photovoltaic materials. The possible advantages of endothermic singlet fission (enhanced use of photon energy and larger triplet energies for coupling with common absorbers) motivated us to assess the role of exciton delocalization in the activation of this process. Here we report the synthesis of a series of linear perylene oligomers that undergo endothermic singlet fission and have endothermicities in the range 5–10 kBT at room temperature in solution. We study these compounds using transient spectroscopy and modelling to unravel the singlet and triplet dynamics. We show that the minimal number of coupled chromophores needed to undergo endothermic singlet fission is three, which provides sufficient statistical space for triplet excitons to separate and avoid annihilation—and a subsequent fast return to the singlet state. Our data additionally suggest that torsional motion of chromophores about the molecular axis following triplet-pair separation contributes to the increase in entropy, thus lengthening the triplet lifetime in longer oligomers.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Absorption and emission spectra of dilute THF solutions of each oligomer compound.
Fig. 2: Femtosecond transient absorption spectra of dilute THF solutions of the oligomer compounds.
Fig. 3: Spectral overlap of the triplet features from transient absorption in dilute THF solution.
Fig. 4: Concentration kinetics of singlet and triplet species as derived from transient absorption datasets for 3-OPP and 4-OPP solutions.
Fig. 5: Kinetic model of endothermic SF.
Fig. 6: Spectra associated with femtosecond to nanosecond evolution from 1-OPP to 4-OPP in dilute THF solution.

Data availability

The datasets generated and analysed during the current study are available from the corresponding author on reasonable request.

References

  1. 1.

    Schrauben, J. N. et al. Photocurrent enhanced by singlet fission in a dye-sensitized solar cell. ACS Appl. Mater. Interfaces 7, 2286–2293 (2015).

    CAS  PubMed  Article  Google Scholar 

  2. 2.

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

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  3. 3.

    Smith, M. B. & Michl, J. Recent advances in singlet fission. Annu. Rev. Phys. Chem. 64, 361–386 (2013).

    CAS  PubMed  Article  Google Scholar 

  4. 4.

    Tayebjee, M. J. Y., Mahboubi Soufiani, A. & Conibeer, G. J. Semi-empirical limiting efficiency of singlet-fission-capable polyacene/inorganic hybrid solar cells. J. Phys. Chem. C 118, 2298–2305 (2014).

    CAS  Article  Google Scholar 

  5. 5.

    Kunzmann, A. et al. Singlet fission for photovoltaics with 130% injection efficiency. Angew. Chem. Int. Ed. 57, 10742–10747 (2018).

    CAS  Article  Google Scholar 

  6. 6.

    Congreve, D. N. et al. External quantum efficiency above 100% in a singlet-exciton-fission-based organic photovoltaic cell. Science 340, 334–337 (2013).

    CAS  PubMed  Article  Google Scholar 

  7. 7.

    Tayebjee, M. J. Y., Gray-Weale, A. A. & Schmidt, T. W. Thermodynamic limit of exciton fission solar cell efficiency. J. Phys. Chem. Lett. 3, 2749–2754 (2012).

    CAS  Article  Google Scholar 

  8. 8.

    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  CAS  Google Scholar 

  9. 9.

    Jadhav, P. J., Mohanty, A., Sussman, J., Lee, J. & Baldo, M. A. Singlet exciton fission in nanostructured organic solar cells. Nano Lett. 11, 1495–1498 (2011).

    CAS  PubMed  Article  Google Scholar 

  10. 10.

    Futscher, M. H., Rao, A. & Ehrler, B. The potential of singlet fission photon multipliers as an alternative to silicon-based tandem solar cells. ACS Energy Lett. 3, 2587–2592 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  11. 11.

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

    CAS  PubMed  Article  Google Scholar 

  12. 12.

    Marciniak, H., Pugliesi, I., Nickel, B. & Lochbrunner, S. Ultrafast singlet and triplet dynamics in microcrystalline pentacene films. Phys. Rev. B 79, 235318 (2009).

    Article  CAS  Google Scholar 

  13. 13.

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

    CAS  PubMed  Article  Google Scholar 

  14. 14.

    Rao, A., Wilson, M. W. B., Albert-Seifried, S., Di Pietro, R. & Friend, R. H. Photophysics of pentacene thin films: the role of exciton fission and heating effects. Phys. Rev. B 84, 195411 (2011).

    Article  CAS  Google Scholar 

  15. 15.

    Hwang, D. K. et al. Solvent and polymer matrix effects on TIPS-pentacene/polymer blend organic field-effect transistors. J. Mater. Chem. 22, 5531–5537 (2012).

    CAS  Article  Google Scholar 

  16. 16.

    Grieco, C. et al. Dynamic exchange during triplet transport in nanocrystalline TIPS-pentacene films. J. Am. Chem. Soc. 138, 16069–16080 (2016).

    CAS  PubMed  Article  Google Scholar 

  17. 17.

    Tayebjee, M. J. Y. et al. Morphological evolution and singlet fission in aqueous suspensions of TIPS-pentacene nanoparticles. J. Phys. Chem. C 120, 157–165 (2016).

    CAS  Article  Google Scholar 

  18. 18.

    Lee, S., Hwang, D., Jung, S. I. & Kim, D. Electron transfer from triplet state of TIPS-pentacene generated by singlet fission processes to CH3NH3PbI3 perovskite. J. Phys. Chem. Lett. 8, 884–888 (2017).

    CAS  PubMed  Article  Google Scholar 

  19. 19.

    Pace, N. A. et al. Dynamics of singlet fission and electron injection in self-assembled acene monolayers on titanium dioxide. Chem. Sci. 9, 3004–3013 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  20. 20.

    Lukman, S. et al. Tuneable singlet exciton fission and triplet–triplet annihilation in an orthogonal pentacene dimer. Adv. Funct. Mater. 25, 5452–5461 (2015).

    CAS  Article  Google Scholar 

  21. 21.

    Zirzlmeier, J. et al. Singlet fission in pentacene dimers. Proc. Natl Acad. Sci. USA 112, 5325–5330 (2015).

    CAS  PubMed  Article  Google Scholar 

  22. 22.

    Sakuma, T. et al. Long-lived triplet excited states of bent-shaped pentacene dimers by intramolecular singlet fission. J. Phys. Chem. A 120, 1867–1875 (2016).

    CAS  PubMed  Article  Google Scholar 

  23. 23.

    Zirzlmeier, J. et al. Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers. Nanoscale 8, 10113–10123 (2016).

    CAS  PubMed  Article  Google Scholar 

  24. 24.

    Hetzer, C., Guldi Dirk, M. & Tykwinski Rik, R. Pentacene dimers as a critical tool for the investigation of intramolecular singlet fission. Chem. Eur. J. 0, 8245–8257 (2018).

    CAS  Article  Google Scholar 

  25. 25.

    Sanders, S. N. et al. Quantitative intramolecular singlet fission in bipentacenes. J. Am. Chem. Soc. 137, 8965–8972 (2015).

    CAS  PubMed  Article  Google Scholar 

  26. 26.

    Sanders, S. N. et al. Singlet fission in polypentacene. Chem. 1, 505–511 (2016).

    CAS  Article  Google Scholar 

  27. 27.

    Kumarasamy, E. et al. Tuning singlet fission in π–bridge–π chromophores. J. Am. Chem. Soc. 139, 12488–12494 (2017).

    CAS  PubMed  Article  Google Scholar 

  28. 28.

    Tayebjee, M. J. Y. et al. Quintet multiexciton dynamics in singlet fission. Nat. Phys. 13, 182–188 (2017).

    CAS  Article  Google Scholar 

  29. 29.

    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).

    PubMed  Article  CAS  Google Scholar 

  30. 30.

    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  PubMed  Article  PubMed Central  Google Scholar 

  31. 31.

    Burdett, J. J. & Bardeen, C. J. The dynamics of singlet fission in crystalline tetracene and covalent analogs. Acc. Chem. Res. 46, 1312–1320 (2013).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  32. 32.

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

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  33. 33.

    Tayebjee, M. J. Y., Clady, R. G. C. R. & Schmidt, T. W. The exciton dynamics in tetracene thin films. Phys. Chem. Chem. Phys. 15, 14797–14805 (2013).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  34. 34.

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

    CAS  PubMed  Article  Google Scholar 

  35. 35.

    Kim, H. Y., Bjorklund, T. G., Lim, S. H. & Bardeen, C. J. Spectroscopic and photocatalytic properties of organic tetracene nanoparticles in aqueous solution. Langmuir 19, 3941–3946 (2003).

    CAS  Article  Google Scholar 

  36. 36.

    Korovina, N. V. et al. Singlet fission in a covalently linked cofacial alkynyltetracene dimer. J. Am. Chem. Soc. 138, 617–627 (2016).

    CAS  PubMed  Article  Google Scholar 

  37. 37.

    Korovina, N. V. et al. Linker-dependent singlet fission in tetracene dimers. J. Am. Chem. Soc. 140, 10179–10190 (2018).

    CAS  PubMed  Article  Google Scholar 

  38. 38.

    Pun Andrew, B. et al. Triplet harvesting from intramolecular singlet sission in polytetracene. Adv. Mater. 29, 1701416 (2017).

    Article  CAS  Google Scholar 

  39. 39.

    Gilligan, A. T., Miller, E. G., Sammakia, T. & Damrauer, N. H. Using structurally well-defined norbornyl-bridged acene dimers to map a mechanistic landscape for correlated triplet formation in singlet fission. J. Am. Chem. Soc. 141, 5961–5971 (2019).

    CAS  PubMed  Article  Google Scholar 

  40. 40.

    Müller, A. M., Avlasevich, Y. S., Müllen, K. & Bardeen, C. J. Evidence for exciton fission and fusion in a covalently linked tetracene dimer. Chem. Phys. Lett. 421, 518–522 (2006).

    Article  CAS  Google Scholar 

  41. 41.

    Müller, A. M., Avlasevich, Y. S., Schoeller, W. W., Müllen, K. & Bardeen, C. J. Exciton fission and fusion in bis(tetracene) molecules with different covalent linker structures. J. Am. Chem. Soc. 129, 14240–14250 (2007).

    PubMed  Article  CAS  Google Scholar 

  42. 42.

    Cook, J. D., Carey, T. J. & Damrauer, N. H. Solution-phase singlet fission in a structurally well-defined norbornyl-bridged tetracene dimer. J. Phys. Chem. A 120, 4473–4481 (2016).

    CAS  PubMed  Article  Google Scholar 

  43. 43.

    Carey, T. J., Snyder, J. L., Miller, E. G., Sammakia, T. & Damrauer, N. H. Synthesis of geometrically well-defined covalent acene dimers for mechanistic exploration of singlet fission. J. Org. Chem. 82, 4866–4874 (2017).

    CAS  PubMed  Article  Google Scholar 

  44. 44.

    Cook, J. D., Carey, T. J., Arias, D. H., Johnson, J. C. & Damrauer, N. H. Solvent-controlled branching of localized versus delocalized singlet exciton states and equilibration with charge transfer in a structurally well-defined tetracene dimer. J. Phys. Chem. A 121, 9229–9242 (2017).

    CAS  PubMed  Article  Google Scholar 

  45. 45.

    Matsui, Y. et al. Exergonic intramolecular singlet fission of an adamantane-linked tetracene dyad via twin quintet multiexcitons. J. Phys. Chem. C 31, 18813-18823 (2019).

  46. 46.

    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).

    PubMed  Article  CAS  Google Scholar 

  47. 47.

    Dover, C. B. et al. Endothermic singlet fission is hindered by excimer formation. Nat. Chem. 10, 305–310 (2018).

    CAS  PubMed  Article  Google Scholar 

  48. 48.

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

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  49. 49.

    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  PubMed  Article  Google Scholar 

  50. 50.

    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. C 118, 5188–5195 (2014).

    CAS  Article  Google Scholar 

  51. 51.

    Wang, X. et al. Intramolecular singlet fission in a face-to-face stacked tetracene trimer. Phys. Chem. Chem. Phys. 20, 6330–6336 (2018).

    CAS  PubMed  Article  Google Scholar 

  52. 52.

    Liu, H. et al. Singlet exciton fission in a linear tetracene tetramer. J. Mater. Chem. C 6, 3245–3253 (2018).

    CAS  Article  Google Scholar 

  53. 53.

    Liu, H. et al. A covalently linked tetracene trimer: synthesis and singlet exciton fission property. Org. Lett. 19, 580–583 (2017).

    PubMed  Article  CAS  Google Scholar 

  54. 54.

    Albrecht, W., Michel-Beyerle, M. & Yakhot, V. Exciton fission in excimer forming crystal. dynamics of an excimer build-up in α-perylene. Chem. Phys. 35, 193–200 (1978).

    CAS  Article  Google Scholar 

  55. 55.

    Pensack, R. D., Ashmore, R. J., Paoletta, A. L. & Scholes, G. D. The nature of excimer formation in crystalline pyrene nanoparticles. J. Phys. Chem. C 122, 21004–21017 (2018).

    CAS  Article  Google Scholar 

  56. 56.

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

    CAS  PubMed  Article  Google Scholar 

  57. 57.

    Breen, I. et al. Triplet separation drives singlet fission after femtosecond correlated triplet pair production in rubrene. J. Am. Chem. Soc. 139, 11745–11751 (2017).

    CAS  PubMed  Article  Google Scholar 

  58. 58.

    Micozzi, A. et al. Use of the Pd-promoted extended one-pot (EOP) synthetic protocol for the modular construction of poly-(arylene ethynylene) co-polymers [–Ar‒C≡C‒Ar′‒C≡C‒]n, opto- and electro-responsive materials for advanced technology. Adv. Synth. Catal. 347, 143–160 (2005).

    CAS  Article  Google Scholar 

  59. 59.

    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  PubMed  Article  Google Scholar 

  60. 60.

    Johnson, J. C. et al. Toward designed singlet fission: solution photophysics of two indirectly coupled covalent dimers of 1,3-diphenylisobenzofuran. J. Phys. Chem. B 117, 4680–4695 (2013).

    CAS  PubMed  Article  Google Scholar 

  61. 61.

    Arias, D. H. et al. Thermally-limited exciton delocalization in superradiant molecular aggregates. J. Phys. Chem. B 117, 4553–4559 (2013).

    CAS  PubMed  Article  Google Scholar 

  62. 62.

    Ji, E., Parthasarathy, A., Corbitt, T. S., Schanze, K. S. & Whitten, D. G. Antibacterial activity of conjugated polyelectrolytes with variable chain lengths. Langmuir 27, 10763–10769 (2011).

    CAS  PubMed  Article  Google Scholar 

  63. 63.

    Zhao, X., Jiang, H. & Schanze, K. S. Polymer chain length dependence of amplified fluorescence quenching in conjugated polyelectrolytes. Macromolecules 41, 3422–3428 (2008).

    CAS  Article  Google Scholar 

  64. 64.

    Park, K. H., Kim, W., Yang, J. & Kim, D. Excited-state structural relaxation and exciton delocalization dynamics in linear and cyclic π-conjugated oligothiophenes. Chem. Soc. Rev. 47, 4279–4294 (2018).

    CAS  PubMed  Article  Google Scholar 

  65. 65.

    Wong, K. S., Wang, H. & Lanzani, G. Ultrafast excited-state planarization of the hexamethylsexithiophene oligomer studied by femtosecond time-resolved photoluminescence. Chem. Phys. Lett. 288, 59–64 (1998).

    CAS  Article  Google Scholar 

  66. 66.

    Dykstra, T. E. et al. Conformational disorder and ultrafast exciton relaxation in PPV-family conjugated polymers. J. Phys. Chem. B 113, 656–667 (2009).

    CAS  PubMed  Article  Google Scholar 

  67. 67.

    Umeyama, T. et al. Synthesis and photophysical and photovoltaic properties of porphyrin–furan and –thiophene alternating copolymers. J. Phys. Chem. C 113, 10798–10806 (2009).

    CAS  Article  Google Scholar 

  68. 68.

    Fujitsuka, M., Cho, D. W., Iwamoto, T., Yamago, S. & Majima, T. Size-dependent fluorescence properties of [n]cycloparaphenylenes (n = 8–13), hoop-shaped π-conjugated molecules. Phys. Chem. Chem. Phys. 14, 14585–14588 (2012).

    CAS  PubMed  Article  Google Scholar 

  69. 69.

    Basel, B. S. et al. Unified model for singlet fission within a non-conjugated covalent pentacene dimer. Nat. Commun. 8, 15171 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  70. 70.

    Chen, M. et al. Quintet–triplet mixing determines the fate of the multiexciton state produced by singlet fission in a terrylenediimide dimer at room temperature. Proc. Natl Acad. Sci. USA 116, 8178–8183 (2019).

    CAS  PubMed  Article  Google Scholar 

  71. 71.

    Winters, M. U. et al. Photophysics of a butadiyne-linked porphyrin dimer: influence of conformational flexibility in the ground and first singlet excited state. J. Phys. Chem. C 111, 7192–7199 (2007).

    CAS  Article  Google Scholar 

  72. 72.

    Peeks, M. D., Neuhaus, P. & Anderson, H. L. Experimental and computational evaluation of the barrier to torsional rotation in a butadiyne-linked porphyrin dimer. Phys. Chem. Chem. Phys. 18, 5264–5274 (2016).

    CAS  PubMed  Article  Google Scholar 

  73. 73.

    Pace, N. A. et al. Controlling long-lived triplet generation from intramolecular singlet fission in the solid state. J. Phys. Chem. Lett. 8, 6086–6091 (2017).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

Download references

Acknowledgements

This work was authored by Alliance for Sustainable Energy, the manager and operator of the National Renewable Energy Laboratory for the US Department of Energy (DOE) under contract no. DE-AC36-08GO28308. The views expressed in the Article do not necessarily represent the views of the US Department of Energy nor the US Government. Funding was provided by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. N.V.K. acknowledges the Laboratory Directed Research and Development programme at NREL for a Director’s Postdoctoral Fellowship. The matrix-assisted laser desorption/ionization mass spectrometry–Fourier transform mass spectrometry data were collected by L. Laurens at the NREL spin-resonance facility. We thank G. Dukovic, K. Vrouwenvelder and O. M. Pearce for access to the time-correlated single photon counting apparatus. Gel permeation chromatography data were provided by W. Braunecker.

Author information

Affiliations

Authors

Contributions

N.V.K. synthesized samples, performed steady-state and time-resolved spectroscopic studies, and contributed to experimental design. C.H.C. performed electronic structure calculations. J.C.J. contributed to overall experimental design and supervised the project. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Justin C. Johnson.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Synthesis and characterization of compounds, additional spectroscopic characterization, computational details, Supplementary Figs.1–31 and Tables 1–17.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Korovina, N.V., Chang, C.H. & Johnson, J.C. Spatial separation of triplet excitons drives endothermic singlet fission. Nat. Chem. 12, 391–398 (2020). https://doi.org/10.1038/s41557-020-0422-7

Download citation

Further reading

Search

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