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Asymmetrical‐Dendronized TADF Emitters for Efficient Non‐doped Solution‐Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes

Li, Chensen; Harrison, Alastair K.; Liu, Yuchao; Zhao, Zhennan; Zeng, Cheng; Dias, Fernando B.; Ren, Zhongjie; Yan, Shouke; Bryce, Martin R.

Asymmetrical‐Dendronized TADF Emitters for Efficient Non‐doped Solution‐Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes Thumbnail


Authors

Chensen Li

Alastair K. Harrison

Yuchao Liu

Zhennan Zhao

Cheng Zeng

Zhongjie Ren

Shouke Yan



Abstract

Two asymmetric “half-dendronized” and “half-dendronized-half-encapsulated” TADF emitters eliminate degenerate excited states, assuring a solely thermal equilibrium route for an effective spin-flip process. AEE properties can minimize the exciton quenching. The isolated encapsulating tricarbazole unit protects the TADF unit, reducing nonradiative decay. Non-doped OLEDs with a remarkably high EQEmax of 24.0 % and low roll-off are achieved. The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully-conjugated or fully-nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half-dendronized” and “half-dendronized-half-encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge-transfer state, assuring a solely thermal equilibrium route for an effective spin-flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non-doped solution-processed devices reach a high external quantum efficiency (EQEmax) of 24.0 % (65.9 cd A−1, 59.2 lm W−1) with CIE coordinates of (0.24, 0.45) with a low efficiency roll-off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m−2.

Citation

Li, C., Harrison, A. K., Liu, Y., Zhao, Z., Zeng, C., Dias, F. B., …Bryce, M. R. (2022). Asymmetrical‐Dendronized TADF Emitters for Efficient Non‐doped Solution‐Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes. Angewandte Chemie International Edition, 61(19), Article e202115140. https://doi.org/10.1002/anie.202115140

Journal Article Type Article
Acceptance Date Dec 6, 2021
Online Publication Date Jan 20, 2022
Publication Date May 2, 2022
Deposit Date Feb 9, 2022
Publicly Available Date Feb 10, 2022
Journal Angewandte Chemie International Edition
Print ISSN 1433-7851
Electronic ISSN 1521-3773
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 61
Issue 19
Article Number e202115140
DOI https://doi.org/10.1002/anie.202115140

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.





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