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Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors

Alexander J. Gillett, Claire Tonnelé, Giacomo Londi, Gaetano Ricci, Manon Catherin, Darcy M. L. Unson, David Casanova, Frédéric Castet, Yoann Olivier, Weimin M. Chen, Elena Zaborova, Emrys Evans, Bluebell H. Drummond, Patrick J. Conaghan, Lin-Song Cui, Neil C. Greenham, Yuttapoom Puttisong, Frédéric Fages, David Beljonne, Richard H. Friend

Nature Communications, Volume: 12, Issue: 1, Start page: 6640

Swansea University Author: Emrys Evans

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Abstract

Engineering a low singlet-triplet energy gap (ΔEST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a stron...

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Published in: Nature Communications
ISSN: 2041-1723
Published: Springer Science and Business Media LLC 2021
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In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 &#x3BC;s), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of &#x2265;1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. 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spelling 2021-12-07T10:34:01.6738149 v2 58730 2021-11-22 Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors 538e217307dac24c9642ef1b03b41485 Emrys Evans Emrys Evans true false 2021-11-22 CHEM Engineering a low singlet-triplet energy gap (ΔEST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 × 105 cm−1) and a relatively large ΔEST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 μs), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of ≥1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low ΔEST in organic DF emitters. Journal Article Nature Communications 12 1 6640 Springer Science and Business Media LLC 2041-1723 17 11 2021 2021-11-17 10.1038/s41467-021-26689-8 COLLEGE NANME Chemistry COLLEGE CODE CHEM Swansea University EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council) Grant: 670405 Identifier: doi https://doi.org/10.13039/100010663 RCUK | Engineering and Physical Sciences Research Council (EPSRC) Grant: EP/M01083X/1 Grant: EP/M005143/1 Identifier: doi https://doi.org/10.13039/501100000266 Simons Foundation Grant: 601946 Identifier: doi https://doi.org/10.13039/100000893 2021-12-07T10:34:01.6738149 2021-11-22T10:40:01.2812332 College of Science Chemistry Alexander J. Gillett 1 Claire Tonnelé 2 Giacomo Londi 3 Gaetano Ricci 4 Manon Catherin 5 Darcy M. L. Unson 6 David Casanova 7 Frédéric Castet 8 Yoann Olivier 9 Weimin M. Chen 10 Elena Zaborova 11 Emrys Evans 12 Bluebell H. Drummond 13 Patrick J. Conaghan 14 Lin-Song Cui 15 Neil C. Greenham 16 Yuttapoom Puttisong 17 Frédéric Fages 18 David Beljonne 19 Richard H. Friend 20 58730__21617__237e0d63e3f7487eb6dc2eb8f8968c7e.pdf 58730.pdf 2021-11-22T10:43:25.0921404 Output 1378333 application/pdf Version of Record true Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. true eng http://creativecommons.org/licenses/by/4.0/
title Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
spellingShingle Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
Emrys Evans
title_short Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
title_full Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
title_fullStr Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
title_full_unstemmed Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
title_sort Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
author_id_str_mv 538e217307dac24c9642ef1b03b41485
author_id_fullname_str_mv 538e217307dac24c9642ef1b03b41485_***_Emrys Evans
author Emrys Evans
author2 Alexander J. Gillett
Claire Tonnelé
Giacomo Londi
Gaetano Ricci
Manon Catherin
Darcy M. L. Unson
David Casanova
Frédéric Castet
Yoann Olivier
Weimin M. Chen
Elena Zaborova
Emrys Evans
Bluebell H. Drummond
Patrick J. Conaghan
Lin-Song Cui
Neil C. Greenham
Yuttapoom Puttisong
Frédéric Fages
David Beljonne
Richard H. Friend
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description Engineering a low singlet-triplet energy gap (ΔEST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 × 105 cm−1) and a relatively large ΔEST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 μs), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a ~24 ns timescale and have an average electron-hole separation of ≥1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low ΔEST in organic DF emitters.
published_date 2021-11-17T04:15:35Z
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