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.

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.

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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.

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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 or Zuo-Quan Jiang or Richard H. Friend or Liang-Sheng Liao.

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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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