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Highly efficient luminescence from space-confined charge-transfer emitters

Abstract

Charge-transfer (CT) complexes, formed by electron transfer from a donor to an acceptor, play a crucial role in organic semiconductors. Excited-state CT complexes, termed exciplexes, harness both singlet and triplet excitons for light emission, and are thus useful for organic light-emitting diodes (OLEDs). However, present exciplex emitters often suffer from low photoluminescence quantum efficiencies (PLQEs), due to limited control over the relative orientation, electronic coupling and non-radiative recombination channels of the donor and acceptor subunits. Here, we use a rigid linker to control the spacing and relative orientation of the donor and acceptor subunits, as demonstrated with a series of intramolecular exciplex emitters based on 10-phenyl-9,10-dihydroacridine and 2,4,6-triphenyl-1,3,5-triazine. Sky-blue OLEDs employing one of these emitters achieve an external quantum efficiency (EQE) of 27.4% at 67 cd m−2 with only minor efficiency roll-off (EQE = 24.4%) at a higher luminous intensity of 1,000 cd m−2. As a control experiment, devices using chemically and structurally related but less rigid emitters reach substantially lower EQEs. These design rules are transferrable to other donor/acceptor combinations, which will allow further tuning of emission colour and other key optoelectronic properties.

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Fig. 1: Molecular structures and spectra of the space-confined charge-transfer TADF emitters.
Fig. 2: Quantum-chemical calculations.
Fig. 3: OLED device performance.
Fig. 4: Photophysical characterization of DM-B, DM-Bm, DM-G, DM-X and DM-Z.

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Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request. Source data for Figs. 1c, 3 and 4 are provided with the paper. The crystallographic coordinates for the molecular structure in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers of 1879795 (DM-B), 1907767 (DM-Bm), 1879719 (DM-G) and 1907768 (DM-X). The crystallographic data for the materials are also available in the Supplementary Data. Source data are provided with this paper.

References

  1. Leonhardt, H. & Weller, A. Elektronenübertragungsreaktionen des angeregten Perylens. Ber. Bunsenges. Phys. Chem. 67, 791–795 (1963).

    CAS  Google Scholar 

  2. Beens, H., Knibbe, H., Weller, A., H., L. & A., W. Dipolar nature of molecular complexes formed in the excited state. J. Chem. Phys. 47, 1183–1184 (1967).

    CAS  Google Scholar 

  3. Potashnik, R., Goldschmidt, C. R., Ottolenghi, M. & Weller, A. Absorption spectra of exciplexes. J. Chem. Phys. 55, 5344–5348 (1971).

    CAS  Google Scholar 

  4. 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).

    CAS  Google Scholar 

  5. Lin, T. C. et al. Probe exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes. Nat. Commun. 9, 3111 (2018).

    Google Scholar 

  6. Hirata, S. et al. Highly efficient blue electroluminescence based on thermally activated delayed fluorescence. Nat. Mater. 14, 330–336 (2015).

    CAS  Google Scholar 

  7. Cui, L. S. et al. Controlling singlet–triplet energy splitting for deep-blue thermally activated delayed fluorescence emitters. Angew. Chem. Int. Ed. Engl. 56, 1571–1575 (2017).

    CAS  Google Scholar 

  8. Nakagawa, T., Ku, S. Y., Wong, K. T. & Adachi, C. Electroluminescence based on thermally activated delayed fluorescence generated by a spirobifluorene donor-acceptor structure. Chem. Commun. 48, 9580–9582 (2012).

    CAS  Google Scholar 

  9. 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).

    CAS  Google Scholar 

  10. Cui, L. S. et al. Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts. Nat. Commun. 8, 2250 (2017).

    Google Scholar 

  11. Liu, Y., Li, C., Ren, Z., Yan, S. & Bryce, M. R. All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Nat. Rev. Mater. 3, 18020 (2018).

    CAS  Google Scholar 

  12. Ahn, D. H. et al. Highly efficient blue thermally activated delayed fluorescence emitters based on symmetrical and rigid oxygen-bridged boron acceptors. Nat. Photon. 13, 540–546 (2019).

    CAS  Google Scholar 

  13. Kondo, Y. et al. Narrowband deep-blue organic light-emitting diode featuring an organoboron-based emitter. Nat. Photon. 13, 678–682 (2019).

    CAS  Google Scholar 

  14. Zhang, Q. et al. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nat. Photon. 8, 326–332 (2014).

    CAS  Google Scholar 

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

    CAS  Google Scholar 

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

    CAS  Google Scholar 

  17. Cui, L. S., Kim, J. U., Nomura, H., Nakanotani, H. & Adachi, C. Benzimidazobenzothiazole-based bipolar hosts to harvest nearly all of the excitons from blue delayed fluorescence and phosphorescent organic light-emitting diodes. Angew. Chem. Int. Ed. Engl. 55, 6864–6868 (2016).

    CAS  Google Scholar 

  18. Ly, K. T. et al. Near-infrared organic light-emitting diodes with very high external quantum efficiency and radiance. Nat. Photon. 11, 63–68 (2017).

    Google Scholar 

  19. 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 

  20. Cox, G. S., Turro, N. J., Yang, N. C. C. & Chen, M. J. Intramolecular exciplex emission from aqueous β-cyclodextrin solutions. J. Am. Chem. Soc. 106, 422–424 (1984).

    CAS  Google Scholar 

  21. Itoh, M., Mimura, T., Usui, H. & Okamoto, T. Intramolecular exciplex and charge transfer complex formations in (9,10-dicyanoanthracene)-(trimethylene)-(naphthalene) systems. J. Am. Chem. Soc. 95, 4388–4392 (1973).

    CAS  Google Scholar 

  22. Geng, Y. et al. Donor–σ–acceptor motifs: thermally activated delayed fluorescence emitters with dual upconversion. Angew. Chem. Int. Ed. Engl. 56, 16536–16540 (2017).

    CAS  Google Scholar 

  23. 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).

    CAS  Google Scholar 

  24. 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).

    CAS  Google Scholar 

  25. Shi, Y. Z. et al. Intermolecular charge-transfer transition emitter showing thermally activated delayed fluorescence for efficient non-doped OLEDs. Angew. Chem. Int. Ed. Engl. 57, 9480–9484 (2018).

    CAS  Google Scholar 

  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).

    CAS  Google Scholar 

  27. Spuling, E., Sharma, N., Samuel, I. D. W., Zysman-Colman, E. & Bräse, S. (Deep) blue through-space conjugated TADF emitters based on [2.2]paracyclophanes. Chem. Commun. 54, 9278–9281 (2018).

    CAS  Google Scholar 

  28. Turro N. J., Scaiano J. C. & Ramamurthy V. Modern Molecular Photochemistry of Organic Molecules (University Science Books, 2010).

  29. Nakanotani, H., Furukawa, T., Morimoto, K. & Adachi, C. Long-range coupling of electron–hole pairs in spatially separated organic donor-acceptor layers. Sci. Adv. 2, e1501470 (2016).

    Google Scholar 

  30. Inoue, M. et al. Effect of reverse intersystem crossing rate to suppress efficiency roll-off in organic light-emitting diodes with thermally activated delayed fluorescence emitters. Chem. Phys. Lett. 644, 62–67 (2016).

    CAS  Google Scholar 

  31. Sicard, L. J. et al. C1-linked spirobifluorene dimers: pure hydrocarbon hosts for high-performance blue phosphorescent oleds. Angew. Chem. Int. Ed. Engl. 58, 3848–3853 (2019).

    CAS  Google Scholar 

  32. Benedict, L. X. et al. Microscopic determination of the interlayer binding energy in graphite. Chem. Phys. Lett. 286, 490–496 (1998).

    CAS  Google Scholar 

  33. Kulkarni, A. P. & Jenekhe, S. A. Blue-green, orange, and white organic light-emitting diodes based on exciplex electroluminescence of an oligoquinoline acceptor and different hole-transport materials. J. Phys. Chem. C. 112, 5174–5184 (2008).

    CAS  Google Scholar 

  34. Reichardt, C. Solvatochromic dyes as solvent polarity indicators. Chem. Rev. 94, 2319–2358 (1994).

    CAS  Google Scholar 

  35. Hussain, A., Yuan, H., Li, W. & Zhang, J. Theoretical investigations of the realization of sky-blue to blue TADF materials via CH/N and H/CN substitution at the diphenylsulphone acceptor. J. Mater. Chem. C. 7, 6685–6691 (2019).

    CAS  Google Scholar 

  36. Yersin, H et al. Highly Efficient OLEDs: Materials Based on Thermally Activated Delayed Fluorescence (Wiley, 2019).

  37. 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).

    CAS  Google Scholar 

  38. Sun, H. et al. Impact of dielectric constant on the singlet–triplet gap in thermally activated delayed fluorescence materials. J. Phys. Chem. Lett. 8, 2393–2398 (2017).

    CAS  Google Scholar 

  39. Bertho, S. et al. Improved thermal stability of bulk heterojunctions based on side-chain functionalized poly(3-alkylthiophene) copolymers and PCBM. Sol. Energy Mater. Sol. Cells 110, 69–76 (2013).

    CAS  Google Scholar 

  40. Kim, H. S., Park, S. R. & Suh, M. C. Concentration quenching behavior of thermally activated delayed fluorescence in a solid film. J. Phys. Chem. C. 121, 13986–13997 (2017).

    CAS  Google Scholar 

  41. Nasu, K. et al. A highly luminescent spiro-anthracenone-based organic light-emitting diode exhibiting thermally activated delayed fluorescence. Chem. Commun. 49, 10385–10387 (2013).

    CAS  Google Scholar 

  42. Méhes, G., Nomura, H., Zhang, Q., Nakagawa, T. & Adachi, C. Enhanced electroluminescence efficiency in a spiro-acridine derivative through thermally activated delayed fluorescence. Angew. Chem. Int. Ed. Engl. 51, 11311–11315 (2012).

    Google Scholar 

  43. Gómez-Bombarelli, R. et al. Design of efficient molecular organic light-emitting diodes by a high-throughput virtual screening and experimental approach. Nat. Mater. 15, 1120–1127 (2016).

    Google Scholar 

  44. Grimme, S., Ehrlich, S. & Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 32, 1456–1465 (2011).

    CAS  Google Scholar 

  45. Sun, H. & Autschbach, J. Electronic energy gaps for π-conjugated oligomers and polymers calculated with density functional theory. J. Chem. Theory Comput. 10, 1035–1047 (2014).

    CAS  Google Scholar 

  46. Lu, T. & Chen, F. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 33, 580–592 (2012).

    Google Scholar 

Download references

Acknowledgements

X.T., H.-C.L., Y.-K.Q., Z.-Q.J. and L.-S.L acknowledge financial support from the National Natural Science Foundation of China (grant nos. 51773141, 61961160731 and 51873139), the National Key R&D Programme of China (no. 2016YFB0400700). L.-S.C., A.J.G. and R.H.F. acknowledge the Engineering and Physical Sciences Research Council (EPSRC) for funding (EP/M01083X/1 and EP/M005143/1). F.A. acknowledges financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 670405). This project is also funded by the Natural Science Foundation of Jiangsu Province of China (BK20181442), Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Priority Academic Programme Development of Jiangsu Higher Education Institutions (PAPD) and the ‘111’ Project.

Author information

Authors and Affiliations

Authors

Contributions

The project was conceived and designed by L.-S.C. and Z.-Q.J. X.T. carried out the device characterizations under the supervision of L.-S.L. H.-C.L. synthesized the compounds under the supervision of Z.-Q.J. A.J.G. conducted the transient absorption experiments and analysed the results. F.A. participated in the discussion and edited the manuscript. Y.-K.Q. conducted the crystal structure measurements and analysed the results. C.Z. performed the computational experiments. S.T.E.J. assisted with the temperature-dependent transient photoluminescence measurements. L.-S.L. and R.H.F. supervised the work. X.T., L.-S.C. and Z.-Q.J. analysed all data and wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Lin-Song Cui, Zuo-Quan Jiang, Richard H. Friend or Liang-Sheng Liao.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–33, note and Tables 1–10.

Supplementary Data 1

Crystallographic data of DM-B.

Supplementary Data 2

Crystallographic data of DM-Bm.

Supplementary Data 3

Crystallographic data of DM-G.

Supplementary Data 4

Crystallographic data of DM-X.

Source data

Source Data Fig. 1

Absorption, photoluminescence and phosphorescence data to generate Fig. 1c.

Source Data Fig. 3

Device performance data to generate Fig. 3.

Source Data Fig. 4

Transient PL and transient absorption data to generate Fig. 4.

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Tang, X., Cui, LS., Li, HC. et al. Highly efficient luminescence from space-confined charge-transfer emitters. Nat. Mater. 19, 1332–1338 (2020). https://doi.org/10.1038/s41563-020-0710-z

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