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Isotope Effect in the Magneto-Optoelectronic Response of Organic Light-Emitting Diodes Based on Donor-Acceptor Exciplexes

Journal
ADV MATER
Date
2020.10.29
Abstract

We have studied the isotope effect in the magneto-electroluminescence (MEL) and pulsed electrically-detected magnetic resonance of organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) from donor-acceptor exciplexes that are either protonated (H) or deuterated (D). We found that at ambient temperature, the exchange of H to D has no effect on the spin-dependent current and MEL responses in the devices. However, at cryogenic temperatures, where the reverse intersystem crossing (RISC) from triplet to singlet exciplex diminishes, a pronounced isotope effect is observed. These results show that the RISC process is not governed by the hyperfine interaction as thought previously, but proceeds through spin-mixing in the triplet exciplex. Our observations are corroborated by electrically detected transient spin nutation experiments that show relatively long dephasing time at ambient temperature, and interpreted in the context of a model that involves exchange and hyperfine interactions in the spin triplet exciplex. These findings deepen our understanding of the RISC process in TADF materials.

Reference
Advanced Materials, 32(48) 2004421(1-8), 2020
DOI
http://dx.doi.org/DOI:10.1002/adma.202004421