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Critical role of intermediate electronic states for spin-flip processes in charge-transfer-type organic molecules with multiple donors and acceptors

Abstract

Spin-flip in purely organic molecular systems is often described as a forbidden process; however, it is commonly observed and utilized to harvest triplet excitons in a wide variety of organic material-based applications. Although the initial and final electronic states of spin-flip between the lowest singlet and lowest triplet excited state are self-evident, the exact process and the role of intermediate states through which spin-flip occurs are still far from being comprehensively determined. Here, via experimental photo-physical investigations in solution combined with first-principles quantum-mechanical calculations, we show that efficient spin-flip in multiple donor–acceptor charge-transfer-type organic molecular systems involves the critical role of an intermediate triplet excited state that corresponds to a partial molecular structure of the system. Our proposed mechanism unifies the understanding of the intersystem crossing mechanism in a wide variety of charge-transfer-type molecular systems, opening the way to greater control over spin-flip rates.

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Fig. 1: Temperature dependence of spin-flip processes in CzCN derivatives in solution.
Fig. 2: Spin-flip process through an intermediate higher-lying triplet excited state of 4CzIPN.
Fig. 3: Theoretical description of the excited states of 4CzIPN.
Fig. 4: Illustration of the intermediate state for the spin-flip process in other donor–acceptor-type molecules.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

References

  1. 1.

    Lamola, A. A. & Hammond, G. S. Mechanisms of photochemical reactions in solution. XXXIII. Intersystem crossing efficiencies. J. Chem. Phys. 43, 2129–2135 (1965).

    CAS  Article  Google Scholar 

  2. 2.

    Baldo, M. A. et al. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 395, 151–154 (1998).

    CAS  Article  Google Scholar 

  3. 3.

    Reineke, S. et al. White organic light-emitting diodes with fluorescent tube efficiency. Nature 459, 234–238 (2009).

    CAS  Article  Google Scholar 

  4. 4.

    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  Article  Google Scholar 

  5. 5.

    Hirata., S. Recent advances in materials with room-temperature phosphorescence: photophysics for triplet exciton stabilization. Adv. Opt. Mater. 5, 1700116 (2017).

    Article  Google Scholar 

  6. 6.

    Zhao, Q., Huang, C. & Li, F. Phosphorescent heavy-metal complexes for bioimaging. Chem. Soc. Rev. 40, 2508–2524 (2011).

    CAS  Article  Google Scholar 

  7. 7.

    Xiong, X. et al. Thermally activated delayed fluorescence of fluorescein derivative for time-resolved and confocal fluorescence imaging. J. Am. Chem. Soc. 136, 9590–9597 (2014).

    CAS  Article  Google Scholar 

  8. 8.

    Maeda, K. et al. Chemical compass model of avian magnetoreception. Nature 453, 387–390 (2008).

    CAS  Article  Google Scholar 

  9. 9.

    Baluschev, S. et al. Up-conversion fluorescence: noncoherent excitation by sunlight. Phys. Rev. Lett. 97, 143903 (2006).

    CAS  Article  Google Scholar 

  10. 10.

    Castano, P., Mroz, P. & Hamblim, M. R. Photodynamic therapy and anti-tumourimmunity. Nat. Rev. Cancer 6, 535–545 (2006).

    CAS  Article  Google Scholar 

  11. 11.

    Baldo, M. A. & O’Brien, D. F. Excitonic singlet-triplet ratio in a semiconducting organic thin film. Phys. Rev. B 60, 14422 (1999).

    CAS  Article  Google Scholar 

  12. 12.

    Turro, N. J., Ramamurthy, V. & Scaiano, J. C. in Principle of Molecular Photochemistry: An Introduction Ch. 3, 113–118 (University Science Books, 2009).

  13. 13.

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

    Article  Google Scholar 

  14. 14.

    El-Sayed, M. A. The radiationless processes involving change of multiplicity in the diazenes. J. Chem. Phys. 36, 573–574 (1962).

    CAS  Article  Google Scholar 

  15. 15.

    Chen, X. K., Zhang, S. F., Fan, J. X. & Ren, A. M. Nature of highly efficient thermally activated delayed fluorescence in organic light-emitting diode emitters: nonadiabatic effect between excited states. J. Phys. Chem. C 119, 9728–9733 (2015).

    CAS  Article  Google Scholar 

  16. 16.

    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).

    CAS  Article  Google Scholar 

  17. 17.

    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).

    Article  Google Scholar 

  18. 18.

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

    CAS  Article  Google Scholar 

  19. 19.

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

    Article  Google Scholar 

  20. 20.

    Gibson, J. & Penfold, T. J. Nonadiabatic coupling reduces the activation energy in thermally activated delayed fluorescence. Phys. Chem. Chem. Phys. 19, 8248–8434 (2017).

    Google Scholar 

  21. 21.

    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).

    CAS  Article  Google Scholar 

  22. 22.

    Hayashi, H. & Nagakura, S. The E.S.R. and phosphorescence spectra of some dicyanobenzene complexes with methyl-substituted benzenes. Mol. Phys. 19, 45–53 (1970).

    CAS  Article  Google Scholar 

  23. 23.

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

    Article  Google Scholar 

  24. 24.

    Kobayashi, T. et al. Contributions of a higher triplet excited state to the emission properties of a thermally activated delayed-fluorescence emitter. Phys. Rev. Appl. 7, 034002 (2017).

    Article  Google Scholar 

  25. 25.

    Evans, E. W. et al. Vibrationally assisted intersystem crossing in benchmark thermally activated delayed fluorescence molecules. J. Phys. Chem. Lett. 9, 4053–4058 (2018).

    CAS  Article  Google Scholar 

  26. 26.

    Cho, Y. J., Jeon, S. K. & Lee, J. Y. Molecular engineering of high efficiency and long lifetime blue thermally activated delayed fluorescent emitters for vacuum and solution processed organic light-emitting diodes. Adv. Opt. Mater. 4, 688–693 (2016).

    CAS  Article  Google Scholar 

  27. 27.

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

    Article  Google Scholar 

  28. 28.

    Yanai, N. & Kimizuka, N. New triplet sensitization routes for photon upconversion: thermally activated delayed fluorescence molecules, inorganic nanocrystals, and singlet-to-triplet absorption. Acc. Chem. Res. 10, 2487–2495 (2017).

    Article  Google Scholar 

  29. 29.

    Penfold, T. J., Gindensperger, E., Daniel, C. & Marian, C. M. Spin-vibronic mechanism for intersystem crossing. Chem. Rev. 118, 6975–7025 (2018).

    CAS  Article  Google Scholar 

  30. 30.

    Mopsik, F. I. Dielectric properties of slightly polar organic liquids as a function of pressure, volume, and temperature. J. Chem. Phys. 50, 2559–2569 (1969).

    CAS  Article  Google Scholar 

  31. 31.

    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).

    CAS  Article  Google Scholar 

  32. 32.

    Körzdörfer, T. & Brédas, J. L. Organic electronic materials: recent advances in the dft description of the ground and excited states using tuned range-separated hybrid functionals. Acc. Chem. Res. 47, 3284–3291 (2014).

    Article  Google Scholar 

  33. 33.

    Yamamoto, M., Tsuji, Y. & Tuchida, A. Near-infrared charge resonance band of intramolecular carbazole dimer radical cations studied by nanosecond laser photolysis. Chem. Phys. Lett. 154, 559–562 (1989).

    CAS  Article  Google Scholar 

  34. 34.

    Kaafarani, B. R. et al. Mixed-valence cations of di(carbazol-9-yl) biphenyl, tetrahydropyrene, and pyrene derivatives. J. Phys. Chem. C 120, 3156–3166 (2016).

    CAS  Article  Google Scholar 

  35. 35.

    Lawetz, V., Orlandi, G. & Siebrand, W. Theory of intersystem crossing in aromatic hydrocarbons. J. Chem. Phys. 56, 4058–4072 (1972).

    CAS  Article  Google Scholar 

  36. 36.

    Robinson, G. W. & Frosch, R. P. Electronic excitation transfer and relaxation. J. Chem. Phys. 38, 1187–1203 (1963).

    CAS  Article  Google Scholar 

  37. 37.

    Nan, G., Yang, X., Wang, L., Shuai, Z. & Zhao, Y. Nuclear tunneling effects of charge transport in rubrene, tetracene, and pentacene. Phys. Rev. B 79, 115203–115211 (2009).

    Article  Google Scholar 

  38. 38.

    Bowen, E. J. & Sahu, J. The effect of temperature on fluorescence of solutions. J. Phys. Chem. 63, 4–7 (1959).

    CAS  Article  Google Scholar 

  39. 39.

    Bennett, R. G. & McCartin, P. J. Radiationless deactivation of the fluorescent state of substituted anthracenes. J. Chem. Phys. 44, 1966 (1969).

    Google Scholar 

  40. 40.

    Katoh, R., Suzuki, K., Furube, A., Kotani, M. & Tokumaru, K. Fluorescence quantum yield of aromatic hydrocarbon crystals. J. Phys. Chem. C 113, 2961–2965 (2009).

    CAS  Article  Google Scholar 

  41. 41.

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

    CAS  Article  Google Scholar 

  42. 42.

    Cho, Y. J., Yook, K. S. & Lee, J. Y. Cool and warm hybrid white organic light-emitting diode with blue delayed fluorescent emitter both as blue emitter and triplet host. Sci. Rep. 5, 7859 (2015).

    CAS  Article  Google Scholar 

  43. 43.

    Lee, Y. H. et al. Rigidity-induced delayed fluorescence by ortho donor-appended triarylboron compounds: record-high efficiency in pure blue fluorescent organic light-emitting diodes. ACS Appl. Mater. Interfaces 9, 24035–24042 (2017).

    CAS  Article  Google Scholar 

  44. 44.

    Masui, K., Nakanotani, H. & Adachi, C. Analysis of exciton annihilation in high-efficiency sky-blue organic light-emitting diodes with thermally activated delayed fluorescence. Org. Electron. 14, 2721–2726 (2013).

    CAS  Article  Google Scholar 

  45. 45.

    Yoshihara, T., Murai, M., Tamaki, Y., Furube, A. & Katoh, R. Trace analysis by transient absorption spectroscopy: estimation of the solubility of C60 in polar solvents. Chem. Phys. Lett. 394, 161–164 (2004).

    CAS  Article  Google Scholar 

  46. 46.

    Martin, R. L. Natural transition orbitals. J. Chem. Phys. 118, 4775–4777 (2003).

    CAS  Article  Google Scholar 

  47. 47.

    M. J. Frisch et al. Gaussian 09 (Gaussian, Inc., 2009).

  48. 48.

    Gao, X., Bai, S., Fazzi, D., Niehaus, T. & Barbatti, M. Evaluation of spin-orbit couplings with linear-response time-dependent density functional methods. J. Chem. Theory Comput. 13, 515–524 (2017).

    CAS  Article  Google Scholar 

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Acknowledgements

This work was supported in part by the Japan Science and Technology Agency, ERATO, Adachi Molecular Exciton Engineering Project, under JST ERATO grant no. JPMJER1305, and the Japan Society for the Promotion of Science KAKENHI (grant nos. JP17J04907, JP18H02047 and JP18H03902). Work at the Georgia Institute of Technology is supported by the Department of Energy (no. DE-EE0008205). X.-K.C. and J.-L.B. are also grateful to Kyulux for generous support of their TADF activities.

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The project was conceived and designed by H. Nakanotani and H. Noda. H. Noda, M.M. and N.N. synthesized the organic compounds used in this study. H. Noda, Y.K. and M.M. prepared the samples and measured their properties. T.H. performed the TAS measurements. X.-K.C. carried out the quantum-chemical calculations under the supervision of J.-L.B. H. Nakanotani, H. Noda and X.-K.C. analysed all data. C.A. supervised the project. All authors contributed to writing the paper and critically commented on the project. H. Noda and X.-K.C. contributed equally to this work.

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Correspondence to Hajime Nakanotani or Jean-Luc Brédas or Chihaya Adachi.

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Supplementary Methods, Supplementary Table 1, Supplementary Figs. 1–14 and Supplementary refs. 1–4.

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Noda, H., Chen, XK., Nakanotani, H. et al. Critical role of intermediate electronic states for spin-flip processes in charge-transfer-type organic molecules with multiple donors and acceptors. Nat. Mater. 18, 1084–1090 (2019). https://doi.org/10.1038/s41563-019-0465-6

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