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Fine‐Tuning the Photophysics of Donor‐Acceptor (D‐A 3 ) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation

L. dos Santos, Paloma; de Sa Pereira, Daniel; Eng, Julien; Ward, Jonathan S.; Bryce, Martin R.; Penfold, Thomas J.; Monkman, Andrew P.

Fine‐Tuning the Photophysics of Donor‐Acceptor (D‐A 3 ) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation Thumbnail


Authors

Daniel de Sa Pereira

Julien Eng

Jonathan S. Ward

Thomas J. Penfold



Abstract

Here two D–A3 regioisomers, comprising three dibenzothiophene-S,S-dioxide acceptor units attached to a central triazatruxene core, are studied. Both molecules show thermally activated delayed fluorescence (TADF), however, the efficiency of the TADF mechanism is strongly affected by the D–A substitution position. The meta- substituted emitter (1 b) shows a slightly higher-lying singlet charge transfer state and a lower-lying triplet state than that observed in the para- substituted emitter (1 a), resulting in a larger singlet–triplet splitting (ΔEST) of 0.28 eV compared to only 0.01 eV found in 1 a. As expected, this ΔEST difference strongly impacts the reverse intersystem crossing (rISC) rates and the para- isomer 1 a exhibits a much faster delayed fluorescence emission. Calculations show that the triplet energy difference between the two isomers is due to steric hindrance variances along the donor–acceptor rotation axis in these molecules: as 1 b is less restricted, rotation of its acceptor unit leads to a lower T1 energy, further away from the region of high density of states (the region where larger vibronic coupling is found, favouring rISC). Therefore, our results show how the substitution pattern has a marked effect on triplet state energies and character, verifying the key structural designs for highly efficient TADF materials.

Citation

L. dos Santos, P., de Sa Pereira, D., Eng, J., Ward, J. S., Bryce, M. R., Penfold, T. J., & Monkman, A. P. (2023). Fine‐Tuning the Photophysics of Donor‐Acceptor (D‐A 3 ) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation. ChemPhotoChem, 7(2), Article e202200248. https://doi.org/10.1002/cptc.202200248

Journal Article Type Article
Acceptance Date Oct 14, 2022
Online Publication Date Dec 15, 2022
Publication Date 2023-02
Deposit Date Jan 9, 2023
Publicly Available Date Mar 29, 2023
Journal ChemPhotoChem
Print ISSN 2367-0932
Electronic ISSN 2367-0932
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 7
Issue 2
Article Number e202200248
DOI https://doi.org/10.1002/cptc.202200248
Public URL https://durham-repository.worktribe.com/output/1183930

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

Copyright Statement
© 2022 The Authors. ChemPhotoChem published by Wiley-VCH GmbH

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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