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Entropy-driven charge-transfer complexation yields thermally activated delayed fluorescence and highly efficient OLEDs

Nature Chemistry volume 16, pages 98–106 (2024)Cite this article

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Abstract

Exciplex-forming systems that display thermally activated delayed fluorescence are widely used for fabricating organic light-emitting diodes. However, their further development can be hindered through a lack of structural and thermodynamic characterization. Here we report the generation of inclusion complexes between a cage-like, macrocyclic, electron-accepting host (A) and various N-methyl-indolocarbazole-based electron-donating guests (D), which exhibit exciplex-like thermally activated delayed fluorescence via a through-space electron-transfer process. The D/A cocrystals are fully resolved by X-ray analyses, and UV–visible titration data show their formation to be an endothermic and entropy-driven process. Moreover, their emission can be fine-tuned through the molecular orbitals of the donor. Organic light-emitting diodes were fabricated using one of the D/A systems, and the maximum external quantum efficiency measured was 15.2%. An external quantum efficiency of 10.3% was maintained under a luminance of 1,000 cd m–2. The results show the potential of adopting inclusion complexation to better understand the relationships between the structure, formation thermodynamics and properties of exciplexes.

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Fig. 1: Chemical structures, synthetic route and X-ray crystal structures.
Fig. 2: Thermodynamics of the complexation between TrMe and Trz-cage.
Fig. 3: TADF properties and the various rate constants of TrMe@Trz-cage.
Fig. 4: Transition properties of TrMe@Trz-cage and emission properties of the various complexes.
Fig. 5: OLED device performances based on TrMe@Trz-cage as an emitter.

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Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2245430 (Trz-cage), CCDC 2245433 (TrMe@Trz-cage), CCDC 2245431 (ICzMeCN@Trz-cage), CCDC 2245434 (ICzMe@Trz-cage) and CCDC 2245432 (ICzMeOMe@Trz-cage). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures. All data are available in this Article and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

C.-Y.L. thanks C.-W. Chiu, M.-T. Hsu, Y.-H. Chang, L.-M. Chen, Y.-S. Chen and K.-H. Kuo for their discussions on variable-temperature NMR and photophysical data. We are grateful to the National Centre for High-Performance Computing (NCHC) of Taiwan for valuable computer time and facilities. We acknowledge the Instrumentation Centre, National Taiwan University for the use of their facilities. We thank S.-J. Huang of the Instrumentation Centre for assistance with the 600 MHz solid-state NMR experiments. We thank H.-C. Tseng of the Instrumentation Centre for assistance with the variable-temperature NMR and one-dimensional selective TOCSY experiments. We also thank the mass spectrometry technical research services from the NTU Consortia of Key Technologies for the assistance with matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy and electrospray ionization time-of-flight mass spectroscopy. We acknowledge Y.-Y. Yang of the Instrumentation Centre for the assistance in the scanning electron microscope analyses. K.-T.W. thanks the National Science and Technology Council (grant nos NSTC-110-2113-M-002-008-MY3 and NSTC-111-2113-M-002-026), and P.-T.C. thanks the National Science and Technology Council (grant no. NSTC-111-2639-M-002-005-ASP) for gracious support.

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Author notes

  1. These authors contributed equally: Chun-Yen Lin, Chao-Hsien Hsu, Chieh-Ming Hung.

Authors and Affiliations

  1. Department of Chemistry, National Taiwan University, Taipei, Taiwan

    Chun-Yen Lin, Chao-Hsien Hsu, Chieh-Ming Hung, Chi-Chi Wu, Yi-Hung Liu, Emily Hsue-Chi Shi, Tse-Hung Lin, Yuan-Cheng Hu, Ken-Tsung Wong & Pi-Tai Chou

  2. Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan

    Wen-Yi Hung

  3. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

    Ken-Tsung Wong

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Contributions

C.-Y.L., Y.-C.H. and K.-T.W. designed and executed the synthesis and characterization of all studied compounds and grew the corresponding cocrystals. Y.-H.L. resolved all the single-crystal structures. C.-H.H., C.-C.W., E.H.-C.S. and P.-T.C. conducted optical measurements and theoretical derivations. C.-M.H., T.-H.L. and W.-Y.H. executed OLED fabrications and analysed the data. C.-Y.L., C.-H.H., C.-M.H., C.-C.W., W.-Y.H., K.-T.W. and P.-T.C. cowrote the paper. All authors discussed the results and contributed to the paper.

Corresponding authors

Correspondence to Ken-Tsung Wong or Pi-Tai Chou.

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The authors declare no competing interests.

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Peer review information

Nature Chemistry thanks Chihaya Adachi, Hironori Kaji, Marc Little and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–37, Tables 1–12 and details of synthetic procedures, crystallographic analysis, spectroscopy data, computation analysis and OLED device characterization.

Supplementary Data 1

Crystal structure of Trz-cage; CCDC 2245430.

Supplementary Data 2

Crystal structure of TrMe@Trz-cage; CCDC 2245433.

Supplementary Data 3

Crystal structure of ICzMeCN@Trz-cage; CCDC 2245431.

Supplementary Data 4

Crystal structure of ICzMe@Trz-cage; CCDC 2245434.

Supplementary Data 5

Crystal structure of ICzMeOMe@Trz-cage; CCDC 2245432.

Source data

Source Data Fig. 2

Steady-state absorption and photoluminescence spectra, Benesi–Hildebrand plot, and van’t Hoff plot.

Source Data Fig. 3

Time-correlated single-photon counting emission spectra.

Source Data Fig. 4

Absorption and emission spectra.

Source Data Fig. 5

EL spectra, current and luminance versus voltage curves, and EQE and power efficiency versus current density curves.

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Lin, CY., Hsu, CH., Hung, CM. et al. Entropy-driven charge-transfer complexation yields thermally activated delayed fluorescence and highly efficient OLEDs. Nat. Chem. 16, 98–106 (2024). https://doi.org/10.1038/s41557-023-01357-0

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