Organic light emitters exhibiting very fast reverse intersystem crossing

Abstract

Reverse intersystem crossing (RISC), originally considered forbidden in purely organic materials, has recently become possible by minimizing the energy gap between the lowest excited singlet state (S1) and lowest triplet state (T1) in thermally activated delayed fluorescence systems. However, direct spin-inversion from T1 to S1 is still inefficient when both states are of the same charge transfer (CT) nature (that is, 3CT and 1CT, respectively). Intervention of locally excited triplet states (3LE) between 3CT and 1CT is expected to trigger fast spin-flipping. Here, we report the systematic design of ideal thermally activated delayed fluorescence molecules with near-degenerate 1CT, 3CT and 3LE states by controlling the distance between the donor and acceptor segments in a molecule with tilted intersegment angles. This system realizes very fast RISC with a rate constant (kRISC) of 1.2 × 107 s−1, resulting in organic light-emitting diodes with excellent performance, particularly at high brightness.

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: Conceptual molecular design.
Fig. 2: Molecular structure of TpAT-tFFO and its frontier molecular orbitals.
Fig. 3: Photoluminescence characteristics.
Fig. 4: Electroluminescence device characteristics of TpAT-tFFO-based OLEDs with doping concentration of 25 vol% with and without an out-coupling sheet.
Fig. 5: Electroluminescence device characteristics of a TpAT-tFFO-based TAF-OLED.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

References

  1. 1.

    Baldo, M. A., Lamansky, S., Burrows, P. E., Thompson, M. E. & Forrest, S. R. Very high-efficiency green organic light-emitting devices based on electrophosphorescence. Appl. Phys. Lett. 75, 4–6 (1999).

    ADS  Google Scholar 

  2. 2.

    Sasabe, H. & Kido, J. Recent progress in phosphorescent organic light-emitting devices. Eur. J. Org. Chem. 2013, 7653–7663 (2013).

    Google Scholar 

  3. 3.

    Uoyama, H., Goushi, K., Shizu, K., Nomura, H. & Adachi, C. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 492, 234–238 (2012).

    ADS  Google Scholar 

  4. 4.

    Onoue, Y., Hiraki, K. & Nishikawa, Y. Interactions of solid supports and fluorescent substances in thermally activated delayed fluorescence. Anal. Sci. 3, 509–513 (1987).

    Google Scholar 

  5. 5.

    Yang, Z. et al. Recent advances in organic thermally activated delayed fluorescence materials. Chem. Soc. Rev. 46, 915–1016 (2017).

    Google Scholar 

  6. 6.

    Wong, M. Y. & Zysman-Colman, E. Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Adv. Mater. 29, 1605444 (2017).

    Google Scholar 

  7. 7.

    Huang, T., Jiang, W. & Duan, L. Recent progress in solution processable TADF materials for organic light-emitting diodes. J. Mater. Chem. C 6, 5577–5596 (2018).

    Google Scholar 

  8. 8.

    Endo, A. et al. Thermally activated delayed fluorescence from Sn4+-porphyrin complexes and their application to organic light emitting diodes—a novel mechanism for electroluminescence. Adv. Mater. 21, 4802–4806 (2009).

    Google Scholar 

  9. 9.

    Zhu, Z.-Q., Fleetham, T., Turner, E. & Li, J. Harvesting all electrogenerated excitons through metal assisted delayed fluorescent materials. Adv. Mater. 27, 2533–2537 (2015).

    Google Scholar 

  10. 10.

    Yersin, H., Czerwieniec, R., Shafikov, M. Z. & Suleymanova, A. F. TADF material design: photophysical background and case studies focusing on CuI and AgI complexes. ChemPhysChem 18, 3508–3535 (2017).

    Google Scholar 

  11. 11.

    Di, D. et al. High-performance light-emitting diodes based on carbene-metal-amides. Science 356, 159–163 (2017).

    ADS  Google Scholar 

  12. 12.

    To, W.-P. et al. Highly luminescent pincer gold(III) aryl emitters: thermally activated delayed fluorescence and solution-processed OLEDs. Angew. Chem. Int. Ed. 56, 14036–14041 (2017).

    Google Scholar 

  13. 13.

    Hamze, R. et al. Eliminating nonradiative decay in Cu(I) emitters: >99% quantum efficiency and microsecond lifetime. Science 363, 601–606 (2019).

    ADS  Google Scholar 

  14. 14.

    Kaji, H. et al. Purely organic electroluminescent material realizing 100% conversion from electricity to light. Nat. Commun. 6, 8476 (2015).

    ADS  Google Scholar 

  15. 15.

    Lin, T.-A. et al. Sky-blue organic light emitting diode with 37% external quantum efficiency using thermally activated delayed fluorescence from spiroacridine-triazine hybrid. Adv. Mater. 28, 6976–6983 (2016).

    ADS  Google Scholar 

  16. 16.

    El-Sayed, M. A. Spin–orbit coupling and the radiationless processes in nitrogen heterocyclics. J. Chem. Phys. 38, 2834–2838 (1963).

    ADS  Google Scholar 

  17. 17.

    Marian, C. M. Mechanism of the triplet-to-singlet upconversion in the assistant dopant ACRXTN. J. Phys. Chem. C 120, 3715–3721 (2016).

    Google Scholar 

  18. 18.

    Dias, F. B. et al. The role of local triplet excited states and D-A relative orientation in thermally activated delayed fluorescence: photophysics and devices. Adv. Sci. 3, 1600080 (2016).

    Google Scholar 

  19. 19.

    Gibson, J., Monkman, A. P. & Penfold, T. J. The importance of vibronic coupling for efficient reverse intersystem crossing in thermally activated delayed fluorescence molecules. ChemPhysChem 17, 2956–2961 (2016).

    Google Scholar 

  20. 20.

    Etherington, M. K., Gibson, J., Higginbotham, H. F., Penfold, T. J. & Monkman, A. P. Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence. Nat. Commun. 7, 13680 (2016).

    ADS  Google Scholar 

  21. 21.

    Lyskov, I. & Marian, C. M. Climbing up the ladder: intermediate triplet states promote the reverse intersystem crossing in the efficient TADF emitter ACRSA. J. Phys. Chem. C 121, 21145–21153 (2017).

    Google Scholar 

  22. 22.

    Hosokai, T. et al. Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states. Sci. Adv. 3, e1603282 (2017).

    ADS  Google Scholar 

  23. 23.

    Samanta, P. K., Kim, D., Coropceanu, V. & Brédas, J.-L. Up-conversion intersystem crossing rates in organic emitters for thermally activated delayed fluorescence: impact of the nature of singlet vs triplet excited states. J. Am. Chem. Soc. 139, 4042–4051 (2017).

    Google Scholar 

  24. 24.

    Noda, H., Nakanotani, H. & Adachi, C. Excited state engineering for efficient reverse intersystem crossing. Sci. Adv. 4, eaao6910 (2018).

    ADS  Google Scholar 

  25. 25.

    Kawasumi, K. et al. Thermally activated delayed fluorescence materials based on homoconjugation effect of donor-acceptor triptycenes. J. Am. Chem. Soc. 137, 11908–11911 (2015).

    Google Scholar 

  26. 26.

    Shao, S. et al. Blue thermally activated delayed fluorescence polymers with nonconjugated backbone and through-space charge transfer effect. J. Am. Chem. Soc. 139, 17739–17742 (2017).

    Google Scholar 

  27. 27.

    Tsujimoto, H. et al. Thermally activated delayed fluorescence and aggregation induced emission with through-space charge transfer. J. Am. Chem. Soc. 139, 4894–4900 (2017).

    Google Scholar 

  28. 28.

    Frisch, M. J. et al. Gaussian 16 revision B.01 (Gaussian Inc., 2016).

  29. 29.

    Sun, H., Zhong, C. & Brédas, J.-L. Reliable prediction with tuned range-separated functionals of the singlet-triplet gap in organic emitters for thermally activated delayed fluorescence. J. Chem. Theory Comput. 11, 3851–3858 (2015).

    Google Scholar 

  30. 30.

    te Velde, G. et al. Chemistry with ADF. J. Comput. Chem. 22, 931–967 (2001).

    Google Scholar 

  31. 31.

    Akinaga, Y. & Ten-no, S. Range-separation by the Yukawa potential in long-range corrected density functional theory with Gaussian-type basis functions. Chem. Phys. Lett. 462, 348–351 (2008).

    ADS  Google Scholar 

  32. 32.

    Tsai, W.-L. et al. A versatile thermally activated delayed fluorescence emitter for both highly efficient doped and non-doped organic light emitting devices. Chem. Commun. 51, 13662–13665 (2015).

    Google Scholar 

  33. 33.

    Wada, Y., Kubo, S. & Kaji, H. Adamantyl substitution strategy for realizing solution-processable thermally stable deep-blue thermally activated delayed fluorescence materials. Adv. Mater. 30, 1705641 (2018).

    Google Scholar 

  34. 34.

    Olivier, Y. et al. Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence. Phys. Rev. Mater. 1, 075602 (2017).

    Google Scholar 

  35. 35.

    Seo, J.-A. et al. Improved efficiency and stable lifetime in blue phosphorescent organic light-emitting diodes using a stable exciton blocking layer. Dyes Pigm. 123, 254–256 (2015).

    Google Scholar 

  36. 36.

    Nakanotani, H. et al. High-efficiency organic light-emitting diodes with fluorescent emitters. Nat. Commun. 5, 4016 (2014).

    ADS  Google Scholar 

  37. 37.

    Lee, I. H., Song, W., Lee, J. Y. & Hwang, S.-H. High efficiency blue fluorescent organic light-emitting diodes using a conventional blue fluorescent emitter. J. Mater. Chem. C 3, 8834–8838 (2015).

    Google Scholar 

  38. 38.

    Song, W., Lee, I. & Lee, J. Y. Host engineering for high quantum efficiency blue and white fluorescent organic light-emitting diodes. Adv. Mater. 27, 4358–4363 (2015).

    Google Scholar 

  39. 39.

    Han, S. H. & Lee, J. Y. Spatial separation of sensitizer and fluorescent emitter for high quantum efficiency in hyperfluorescent organic light-emitting diodes. J. Mater. Chem. C 6, 1504–1508 (2018).

    Google Scholar 

  40. 40.

    Jeon, S. K., Park, H.-J. & Lee, J. Y. Highly efficient soluble blue delayed fluorescent and hyperfluorescent organic light-emitting diodes by host engineering. ACS Appl. Mater. Interfaces 10, 5700–5705 (2018).

    Google Scholar 

  41. 41.

    Goushi, K., Yoshida, K., Sato, K. & Adachi, C. Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion. Nat. Photon. 6, 253–258 (2012).

    ADS  Google Scholar 

Download references

Acknowledgements

This work was supported by JSPS KAKENHI grant numbers 17H01231 (to H.K.) and 17J09631 (to Y.Wada). Computation time was provided by the Super Computer System, Institute for Chemical Research, Kyoto University. NMR measurements were supported by the international Joint Usage/Research Centre (iJURC) at the Institute for Chemical Research, Kyoto University, Japan. We thank A. Jackson for editing a draft of this manuscript.

Author information

Affiliations

Authors

Contributions

Y.Wada led the theoretical calculations, did the data curation, formal analysis, investigation, validation and visualization, and wrote the original draft of the manuscript, as well as supporting the conceptualization. H.N. led the synthesis, and supported the data curation, investigation and writing of the original draft, as well as the conceptualization. S.M. equally contributed to the data curation and validated the TAF system. Y.Wakisaka supported the conceptualization and formal analysis. H.K. proposed the original concept of the tFFO design, did the formal analysis, theoretical analysis of rate constants, visualization, the writing of the original draft, and supervised the project.

Corresponding author

Correspondence to Hironori Kaji.

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

Supplementary text (material synthesis and characterization, theoretical calculations, thermal and photophysical properties), scheme 1, 1H and 13C NMR data, Figs. 1–7 and Tables 1–7.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Wada, Y., Nakagawa, H., Matsumoto, S. et al. Organic light emitters exhibiting very fast reverse intersystem crossing. Nat. Photonics 14, 643–649 (2020). https://doi.org/10.1038/s41566-020-0667-0

Download citation

Further reading

Search

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