Carbazole isomers induce ultralong organic phosphorescence


Commercial carbazole has been widely used to synthesize organic functional materials that have led to recent breakthroughs in ultralong organic phosphorescence1, thermally activated delayed fluorescence2,3, organic luminescent radicals4 and organic semiconductor lasers5. However, the impact of low-concentration isomeric impurities present within commercial batches on the properties of the synthesized molecules requires further analysis. Here, we have synthesized highly pure carbazole and observed that its fluorescence is blueshifted by 54 nm with respect to commercial samples and its room-temperature ultralong phosphorescence almost disappears6. We discover that such differences are due to the presence of a carbazole isomeric impurity in commercial carbazole sources, with concentrations <0.5 mol%. Ten representative carbazole derivatives synthesized from the highly pure carbazole failed to show the ultralong phosphorescence reported in the literature1,7,8,9,10,11,12,13,14,15. However, the phosphorescence was recovered by adding 0.1 mol% isomers, which act as charge traps. Investigating the role of the isomers may therefore provide alternative insights into the mechanisms behind ultralong organic phosphorescence1,6,7,8,9,10,11,12,13,14,15,16,17,18.

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Fig. 1: Paradox of the ultralong phosphorescence of carbazole.
Fig. 2: Impurity effect on carbazole derivatives.
Fig. 3: Emission characteristics with different isomer doping concentrations.
Fig. 4: Transient absorption, photoluminescence and ultralong phosphorescence mechanism.

Data availability

The data that support the findings of this study are available from C.C. and L.B. upon reasonable request. The X-ray crystallographic data for the structures reported here have been deposited at the Cambridge Crystallographic Data Centre (CCDC) under deposition numbers CCDC 1953802–1953811 and 2019581–2019589. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre at Source data are provided with this paper.


  1. 1.

    An, Z. et al. Stabilizing triplet excited states for ultralong organic phosphorescence. Nat. Mater. 14, 685–690 (2015).

    CAS  Article  Google Scholar 

  2. 2.

    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 

  3. 3.

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

    CAS  Article  Google Scholar 

  4. 4.

    Ai, X. et al. Efficient radical-based light-emitting diodes with doublet emission. Nature 563, 536–540 (2018).

    CAS  Article  Google Scholar 

  5. 5.

    Sandanayaka, A. S. D. et al. Indication of current-injection lasing from an organic semiconductor. Appl. Phys. Express 12, 061010 (2019).

    CAS  Article  Google Scholar 

  6. 6.

    Bilen, C. S., Harrison, N. & Morantz, D. J. Unusual room temperature afterglow in some crystalline organic compounds. Nature 271, 235–237 (1978).

    CAS  Article  Google Scholar 

  7. 7.

    Cai, S. et al. Visible-light-excited ultralong organic phosphorescence by manipulating intermolecular interactions. Adv. Mater. 29, 1701244 (2017).

    Article  Google Scholar 

  8. 8.

    Xie, Y. et al. How the molecular packing affects the room temperature phosphorescence in pure organic compounds: ingenious molecular design, detailed crystal analysis, and rational theoretical calculations. Adv. Mater. 29, 1606829 (2017).

    Article  Google Scholar 

  9. 9.

    Xiong, Y. et al. Designing efficient and ultralong pure organic room-temperature phosphorescent materials by structural isomerism. Angew. Chem. Int. Ed. 57, 7997–8001 (2018).

    CAS  Article  Google Scholar 

  10. 10.

    Zhang, T. et al. Pure organic persistent room-temperature phosphorescence at both crystalline and amorphous states. ChemPhysChem 19, 2389–2396 (2018).

    CAS  Article  Google Scholar 

  11. 11.

    Gong, Y. et al. Achieving persistent room temperature phosphorescence and remarkable mechanochromism from pure organic luminogens. Adv. Mater. 27, 6195–6201 (2015).

    CAS  Article  Google Scholar 

  12. 12.

    Yang, Z. et al. Intermolecular electronic coupling of organic units for efficient persistent room-temperature phosphorescence. Angew. Chem. Int. Ed. 55, 2181–2185 (2016).

    CAS  Article  Google Scholar 

  13. 13.

    Fateminia, S. M. A. et al. Organic nanocrystals with bright red persistent room-temperature phosphorescence for biological applications. Angew. Chem. Int. Ed. 56, 12160–12164 (2017).

    CAS  Article  Google Scholar 

  14. 14.

    Kenry, Chen,C. & Liu, B. Enhancing the performance of pure organic room-temperature phosphorescent luminophores. Nat. Commun. 10, 2111 (2019).

    CAS  Article  Google Scholar 

  15. 15.

    Xue, P. et al. Correction: Bright persistent luminescence from pure organic molecules through a moderate intermolecular heavy atom effect. Chem. Sci. 8, 6691–6691 (2017).

    CAS  Article  Google Scholar 

  16. 16.

    Gu, L. et al. Dynamic ultralong organic phosphorescence by photoactivation. Angew. Chem. Int. Ed. 57, 8425–8431 (2018).

    CAS  Article  Google Scholar 

  17. 17.

    Zhao, W. et al. Boosting the efficiency of organic persistent room-temperature phosphorescence by intramolecular triplet-triplet energy transfer. Nat. Commun. 10, 1595 (2019).

    Article  Google Scholar 

  18. 18.

    Mao, Z. et al. Two-photon-excited ultralong organic room temperature phosphorescence by dual-channel triplet harvesting. Chem. Sci. 10, 7352–7357 (2019).

    CAS  Article  Google Scholar 

  19. 19.

    Li, Y., Gecevicius, M. & Qiu, J. Long persistent phosphors—from fundamentals to applications. Chem. Soc. Rev. 45, 2090–2136 (2016).

    CAS  Article  Google Scholar 

  20. 20.

    Kabe, R. & Adachi, C. Organic long persistent luminescence. Nature 550, 384–387 (2017).

    CAS  Article  Google Scholar 

  21. 21.

    Lastusaari, M. et al. The Bologna Stone: history’s first persistent luminescent material. Eur. J. Miner. 24, 885–890 (2012).

    CAS  Article  Google Scholar 

  22. 22.

    Matsuzawa, T., Aoki, Y., Takeuchi, N. & Murayama, Y. A new long phosphorescent phosphor with high brightness, SrAl2O4:Eu2+,Dy3+. J. Electrochem. Soc. 143, 2670–2673 (1996).

    CAS  Article  Google Scholar 

  23. 23.

    Clapp, D. B. The phosphorescence of tetraphenylmethane and certain related substances. J. Am. Chem. Soc. 61, 523–524 (1939).

    CAS  Article  Google Scholar 

  24. 24.

    Graebe, C. & Glaser, C. Ber. Dtsch. Chem. Ges. 5, 12 (1872).

    Google Scholar 

  25. 25.

    Feng, H. et al. Tuning molecular emission of organic emitters from fluorescence to phosphorescence through push-pull electronic effects. Nat. Commun. 11, 2617 (2020).

    CAS  Article  Google Scholar 

  26. 26.

    Chen, C. et al. Intramolecular charge transfer controls switching between room temperature phosphorescence and thermally activated delayed fluorescence. Angew. Chem. Int. Ed. 57, 16407–16411 (2018).

    CAS  Article  Google Scholar 

  27. 27.

    Noda, 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).

    CAS  Article  Google Scholar 

  28. 28.

    Bolton, O., Lee, K., Kim, H.-J., Lin, K. Y. & Kim, J. Activating efficient phosphorescence from purely organic materials by crystal design. Nat. Chem. 3, 205–210 (2011).

    CAS  Article  Google Scholar 

  29. 29.

    Ullah, E., McNulty, J. & Robertson, A. Highly chemoselective mono-Suzuki arylation reactions on all three dichlorobenzene isomers and applications development. Eur. J. Org. Chem. 2012, 2127–2131 (2012).

    CAS  Article  Google Scholar 

  30. 30.

    Yang, L., Zhang, Y., Zou, X., Lu, H. & Li, G. Visible-light-promoted intramolecular C–H amination in aqueous solution: synthesis of carbazole. Green. Chem. 20, 1362–1366 (2018).

    CAS  Article  Google Scholar 

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This study was supported by the Singapore National Research Foundation (NRF) Competitive Research Program (R279-000-483-281), the NRF Investigatorship (R279-000-444-281) and the National University of Singapore (R279-000-482-133).

Author information




C.C. and B.L. designed the experiments. C.C. optimized the HPLC and grew crystals. C.C., Z.C., Z.Y., Z.M. and Z.Y. contributed to the optical characterizations. C.C. and K.C.C. synthesized all compounds. A.S.B. and C.C. solved the crystal structures. C.C. and B.L. discussed the results and drafted the manuscript. B.L. supervised the project. All authors contributed to the proofreading of the manuscript.

Corresponding author

Correspondence to Bin Liu.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary methods, Scheme 1, Figs. 1–37 and Tables 1–11.

Source data

Source Data Fig. 1

HPLC spectra of TCI-Cz.

Source Data Fig. 2

HPLC spectra monitored at the onset absorption of 346 nm for Cz and 354 nm for CPhCz.

Source Data Fig. 3

Emission characteristics with different isomer doping concentrations.

Source Data Fig. 4

Transient absorption and photoluminescence.

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Chen, C., Chi, Z., Chong, K.C. et al. Carbazole isomers induce ultralong organic phosphorescence. Nat. Mater. (2020).

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