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Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D’-A TADF Emitters

Woon, Kai Lin; Yi, Chih-Lun; Pan, Kuan-Chung; Etherington, Marc K.; Wu, Chung-Chih; Wong, Ken-Tsung; Monkman, Andrew P.

Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D’-A TADF Emitters Thumbnail


Authors

Kai Lin Woon

Chih-Lun Yi

Kuan-Chung Pan

Marc K. Etherington

Chung-Chih Wu

Ken-Tsung Wong



Abstract

Understanding the excited-state dynamics and conformational relaxation in thermallyactivated delayed fluorescence (TADF) molecules, including conformations that potentially support intramolecular through-space charge transfer, can open new avenues for TADF molecular design as well as elucidate complex photophysical pathways in structurally complex molecules. Emissive molecules comprising a donor (triphenylamine, TPA) and an acceptor (triphenyltriazine, TRZ) bridged by a second donor (9,9 dimethyl-9-10- dihydroacridin, DMAC or phenoxazine, PXZ) are synthesized and characterized. In solution, the flexibility of the sp3-hybridized carbon atom in DMAC of DMAC-TPA-TRZ, compared to the rigid PXZ, allows significant conformational reorganisation giving rise to multiple charge-transfer excited states. As a result of such reorganization, the TRZ and TPA moieties become co-facially aligned, driven by strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge transfer dimer state, in stark contrast to the case of PXZTPA- TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ CT state. The low energy TPA-TRZ dimer, is found to have a high energy dimer local triplet state, which quenches delayed emission because the resultant singlet CT local triplet energy gap is too large to mediate efficient reverse intersystem crossing. However, organic light emitting diodes using PXZ-TPA-TRZ as an emitting dopant resulted in EQE as high as 22%, more than 2 times higher than that of DMAC-TPA-TRZ-based device showing the impact that such intramolecular reorganization and donor acceptor dimerization has on TADF performance.

Citation

Woon, K. L., Yi, C., Pan, K., Etherington, M. K., Wu, C., Wong, K., & Monkman, A. P. (2019). Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D-D’-A TADF Emitters. Journal of Physical Chemistry C, 123(19), 12400-12410. https://doi.org/10.1021/acs.jpcc.9b01900

Journal Article Type Article
Acceptance Date Apr 17, 2019
Online Publication Date Apr 17, 2019
Publication Date May 17, 2019
Deposit Date May 1, 2019
Publicly Available Date May 21, 2019
Journal Journal of Physical Chemistry C
Print ISSN 1932-7447
Electronic ISSN 1932-7455
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 123
Issue 19
Pages 12400-12410
DOI https://doi.org/10.1021/acs.jpcc.9b01900
Public URL https://durham-repository.worktribe.com/output/1302827

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

Copyright Statement
This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.






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