| Summary: | Host–guest systems are crucial for achieving high efficiency in most organic light-emitting diode (OLED) devices. However, charge recombination in such systems is poorly understood due to complicated molecular environment, making the rational design of host–guest systems difficult. In this article, we present a computational study of a phosphorescent OLED with 2,8-bis(triphenylsilyl)dibenzofuran (BTDF) as the host and fac-tris(2-phenylpyridine) iridium (fac-Ir(ppy)₃) as the guest, using a combined quantum mechanics/molecular mechanics (QM/MM) scheme. A new reaction coordinate is introduced to measure the electrostatic interactions between the host and guest molecules. Ionization potentials and electron affinities of the host show broader distributions as the host–guest interaction increases. On the basis of these distributions, we describe a molecular picture of charge recombination on the guest and find a direct charge trapping route for this system. Our results suggest several strategies for the design of more efficient host and guest combinations.
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