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Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters

Understanding the excited-state dynamics and conformational relaxation in thermally activated 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 comp...

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Main Authors: Woon, Kai Lin, Yi, Chih-Lun, Pan, Kuan-Chung, Etherington, Marc K., Wu, Chung-Chih, Wong, Ken-Tsung, Monkman, Andrew P.
Format: Article
Published: American Chemical Society 2019
Subjects:
Q Science (General)
QC Physics
Online Access:http://eprints.um.edu.my/23147/
https://doi.org/10.1021/acs.jpcc.9b01900
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spelling my.um.eprints.231472019-11-28T08:55:59Z http://eprints.um.edu.my/23147/ 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. Q Science (General) QC Physics Understanding the excited-state dynamics and conformational relaxation in thermally activated 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 reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ-TPA-TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ charge transfer (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 external quantum efficiency as high as 22%, more than two times higher than that of DMAC-TPA-TRZ-based device, showing the impact that such intramolecular reorganization and donor-acceptor dimerization have on TADF performance. © 2019 American Chemical Society. American Chemical Society 2019 Article PeerReviewed Woon, Kai Lin and Yi, Chih-Lun and Pan, Kuan-Chung and Etherington, Marc K. and Wu, Chung-Chih and Wong, Ken-Tsung and Monkman, Andrew P. (2019) Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters. The Journal of Physical Chemistry C, 123 (19). pp. 12400-12410. ISSN 1932-7447 https://doi.org/10.1021/acs.jpcc.9b01900 doi:10.1021/acs.jpcc.9b01900
institution Universiti Malaya
building UM Library
collection Institutional Repository
continent Asia
country Malaysia
content_provider Universiti Malaya
content_source UM Research Repository
url_provider http://eprints.um.edu.my/
topic Q Science (General)
QC Physics
spellingShingle Q Science (General)
QC Physics
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
description Understanding the excited-state dynamics and conformational relaxation in thermally activated 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 reorganization, giving rise to multiple charge-transfer excited states. As a result of such a reorganization, the TRZ and TPA moieties become cofacially aligned, driven by a strong dipole-dipole attraction between the TPA and TRZ units, forming a weakly charge-transfer dimer state, in stark contrast to the case of PXZ-TPA-TRZ where the rigid PXZ bridge only supports a single PXZ-TRZ charge transfer (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 external quantum efficiency as high as 22%, more than two times higher than that of DMAC-TPA-TRZ-based device, showing the impact that such intramolecular reorganization and donor-acceptor dimerization have on TADF performance. © 2019 American Chemical Society.
format Article
author Woon, Kai Lin
Yi, Chih-Lun
Pan, Kuan-Chung
Etherington, Marc K.
Wu, Chung-Chih
Wong, Ken-Tsung
Monkman, Andrew P.
author_facet Woon, Kai Lin
Yi, Chih-Lun
Pan, Kuan-Chung
Etherington, Marc K.
Wu, Chung-Chih
Wong, Ken-Tsung
Monkman, Andrew P.
author_sort Woon, Kai Lin
title Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters
title_short Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters
title_full Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters
title_fullStr Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters
title_full_unstemmed Intramolecular Dimerization Quenching of Delayed Emission in Asymmetric D–D′–A TADF Emitters
title_sort intramolecular dimerization quenching of delayed emission in asymmetric d–d′–a tadf emitters
publisher American Chemical Society
publishDate 2019
url http://eprints.um.edu.my/23147/
https://doi.org/10.1021/acs.jpcc.9b01900
_version_ 1651867406521335808
score 13.211869

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