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Dielectric control of reverse intersystem crossing in thermally activated delayed fluorescence emitters

Alexander J. Gillett Orcid Logo, Anton Pershin Orcid Logo, Raj Pandya, Sascha Feldmann Orcid Logo, Alexander J. Sneyd Orcid Logo, Antonios M. Alvertis, Emrys Evans Orcid Logo, Tudor H. Thomas, Lin-Song Cui Orcid Logo, Bluebell H. Drummond Orcid Logo, Gregory D. Scholes Orcid Logo, Yoann Olivier, Akshay Rao Orcid Logo, Richard H. Friend Orcid Logo, David Beljonne Orcid Logo

Nature Materials, Volume: 21, Issue: 10, Pages: 1150 - 1157

Swansea University Author: Emrys Evans Orcid Logo

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Abstract

Thermally activated delayed fluorescence enables organic semiconductors with charge transfer-type excitons to convert dark triplet states into bright singlets via reverse intersystem crossing. However, thus far, the contribution from the dielectric environment has received insufficient attention. He...

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Published in: Nature Materials
ISSN: 1476-1122 1476-4660
Published: Springer Science and Business Media LLC 2022
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URI: https://cronfa.swan.ac.uk/Record/cronfa60976
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Abstract: Thermally activated delayed fluorescence enables organic semiconductors with charge transfer-type excitons to convert dark triplet states into bright singlets via reverse intersystem crossing. However, thus far, the contribution from the dielectric environment has received insufficient attention. Here we study the role of the dielectric environment in a range of thermally activated delayed fluorescence materials with varying changes in dipole moment upon optical excitation. In dipolar emitters, we observe how environmental reorganization after excitation triggers the full charge transfer exciton formation, minimizing the singlet–triplet energy gap, with the emergence of two (reactant-inactive) modes acting as a vibrational fingerprint of the charge transfer product. In contrast, the dielectric environment plays a smaller role in less dipolar materials. The analysis of energy–time trajectories and their free-energy functions reveals that the dielectric environment substantially reduces the activation energy for reverse intersystem crossing in dipolar thermally activated delayed fluorescence emitters, increasing the reverse intersystem crossing rate by three orders of magnitude versus the isolated molecule.
Keywords: Atomistic models, Molecular dynamics, Organic LEDs, Optical spectroscopy
College: Faculty of Science and Engineering
Funders: A.J.G. and R.H.F. acknowledge support from the Simons Foundation (grant no. 601946) and the Engineering and Physical Sciences Research Council (EPSRC) (EP/M01083X/1 and EP/M005143/1). This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (R.H.F., grant agreement no. 670405; A.R., grant agreement no. 758826). A.R. thanks the Winton Programme for the Physics of Sustainability for funding. A.P., Y.O. and D.B. were supported by the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska Curie Grant agreement 748042 (MILORD project). R.P. acknowledges financial support from an EPSRC Doctoral Prize Fellowship. A.J.S. acknowledges the Royal Society Te Apārangi and the Cambridge Commonwealth European and International Trust for their financial support. Y.O. acknowledges funding by the FNRS under grant no. F.4534.21 (MIS-IMAGINE). L.-S.C. acknowledges funding from the University of Science and Technology of China (USTC) Research Funds of the Double First-Class Initiative and the National Natural Science Foundation of China (grant no. 52103242).
Issue: 10
Start Page: 1150
End Page: 1157