Mechanism of Intersystem Crossing of Thermally Activated Delayed Fluorescence Molecules
- 26 March 2015
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry A
- Vol. 119 (14), 3415-3418
- https://doi.org/10.1021/acs.jpca.5b02253
Abstract
The spin sublevel dynamics of the excited triplet state in thermally activated delayed fluorescence (TADF) molecules have not been investigated for high-intensity organic light-emitting diode materials. Understanding the mechanism for intersystem crossing (ISC) is thus important for designing novel TADF materials. We report the first study on the ISC dynamics of the lowest excited triplet state from the lowest excited singlet state with charge-transfer (CT) character of TADF molecules with different external quantum efficiencies (EQEs) using time-resolved electron paramagnetic resonance methods. Analysis of the observed spin polarization indicates a strong correlation of the EQE with the population rate due to ISC induced by hyperfine coupling with the magnetic nuclei. It is concluded that molecules with high EQE have an extremely small energy gap between the 1CT and 3CT states, which allows an additional ISC channel due to the hyperfine interactions.Keywords
Funding Information
- Ministry of Education, Culture, Sports, Science, and Technology (2610088)
- Core Research for Evolutional Science and Technology, Japan Science and Technology Agency
- Network Joint Research Center for Materials and Devices
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