Perdeuterated Conjugated Polymers for Ultralow-Frequency Magnetic Resonance of OLEDs |
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Authors: | Sebastian Milster Tobias Grünbaum Dr Sebastian Bange Simon Kurrmann Hermann Kraus Dr Dani M Stoltzfus Dr Anna E Leung Dr Tamim A Darwish Prof Paul L Burn Prof Dr Christoph Boehme Prof Dr John M Lupton |
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Institution: | 1. Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany;2. Centre for Organic Photonics & Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland, 4072 Australia;3. National Deuteration Facility, Australian Nuclear Science and Technology Organization (ANSTO), Locked Bag 2001, Kirrawee DC, NSW, 2232 Australia;4. Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, UT, 84112 USA |
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Abstract: | The formation of excitons in OLEDs is spin dependent and can be controlled by electron-paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin- Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π-conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero-field feature and local hyperfine fields. The zero-field peak results from a quasistatic magnetic-field effect of the RF radiation for periods comparable to the carrier-pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero-field peak, we suggest that this result may constitute a fundamental low-field limit of magnetic resonance in carrier-pair-based systems. OLEDs offer an alternative solid-state platform to investigate the radical-pair mechanism of magnetic-field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments. |
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Keywords: | conjugated polymers deuteration isotopes magnetic resonance organic light-emitting diodes |
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