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Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Bluebell H. Drummond, Naoya Aizawa, Yadong Zhang, William K. Myers, Yao Xiong, Matthew W. Cooper, Stephen Barlow, Qinying Gu, Leah R. Weiss, Alexander J. Gillett, Dan Credgington, Yong-Jin Pu, Seth R. Marder, Emrys Evans

Nature Communications, Volume: 12, Issue: 1

Swansea University Author: Emrys Evans

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Abstract

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic state...

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Published in: Nature Communications
ISSN: 2041-1723
Published: Springer Science and Business Media LLC 2021
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa57410
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Abstract: Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.
College: College of Science
Funders: Engineering and Physical Sciences Research Council
Issue: 1