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Issue 48, 2014
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Correlating the transition dipole moment orientation of phosphorescent emitter molecules in OLEDs with basic material properties

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Abstract

The orientation of the emissive dipole moment of seven iridium-based phosphorescent emitter molecules commonly used in organic light-emitting diodes (OLEDs) is investigated. The orientation of Ir(ppy)3, Ir(ppy)2(acac), Ir(chpy)3, Ir(dhfpy)2(acac), Ir(BT)2(acac), Ir(MDQ)2(acac), and Ir(piq)3 is determined by measuring the angle dependent spectral radiant intensity of the transverse magnetic polarized emission from p–i–n OLEDs comprising these emitters. The experimental data are compared to the intensity calculated by a multilayer simulation method that includes the anisotropy factor describing the average dipole orientation. Surprisingly, among these molecules, Ir(ppy)3 is the only emitter showing an isotropically distributed transition dipole moment. In order to correlate our results with basic molecular properties, the permanent dipole moment and the size of the molecules are calculated by density functional theory (DFT). The dipole–dipole potential obtained for Ir(ppy)3 is more than 2.5 times larger than those for all other emitter molecules investigated here, indicating that this parameter is correlated with the transition dipole moment orientation.

Graphical abstract: Correlating the transition dipole moment orientation of phosphorescent emitter molecules in OLEDs with basic material properties

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Publication details

The article was received on 13 May 2014, accepted on 16 Oct 2014 and first published on 17 Oct 2014


Article type: Paper
DOI: 10.1039/C4TC00997E
Citation: J. Mater. Chem. C, 2014,2, 10298-10304
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    Correlating the transition dipole moment orientation of phosphorescent emitter molecules in OLEDs with basic material properties

    A. Graf, P. Liehm, C. Murawski, S. Hofmann, K. Leo and M. C. Gather, J. Mater. Chem. C, 2014, 2, 10298
    DOI: 10.1039/C4TC00997E

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