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Dielectric control of reverse intersystem crossing in thermally activated delayed fluorescence emitters
Alexander J. Gillett , Anton Pershin , Raj Pandya, Sascha Feldmann , Alexander J. Sneyd , Antonios M. Alvertis, Emrys Evans , Tudor H. Thomas, Lin-Song Cui , Bluebell H. Drummond , Gregory D. Scholes , Yoann Olivier, Akshay Rao , Richard H. Friend , David Beljonne
Nature Materials, Volume: 21, Issue: 10, Pages: 1150 - 1157
Swansea University Author: Emrys Evans
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DOI (Published version): 10.1038/s41563-022-01321-2
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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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.
Atomistic models, Molecular dynamics, Organic LEDs, Optical spectroscopy
Faculty of Science and Engineering
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).