Abstract
The efficiency of an organic light-emitting diode (OLED) depends on the microscopic orientation of transition dipole moments of the molecular emitters. The most effective materials used for light generation have 3-fold symmetry, which prohibits a priori determination of dipole orientation due to the degeneracy of the fundamental transition. Single molecule spectroscopy reveals that the model ...
Abstract
The efficiency of an organic light-emitting diode (OLED) depends on the microscopic orientation of transition dipole moments of the molecular emitters. The most effective materials used for light generation have 3-fold symmetry, which prohibits a priori determination of dipole orientation due to the degeneracy of the fundamental transition. Single molecule spectroscopy reveals that the model triplet emitter tris(1-phenylisoquinoline)iridium(III) (Ir(piq)(3)) does not behave as a linear dipole, radiating with lower polarization anisotropy than expected Spontaneous symmetry breaking occurs in the excited state, leading to a random selection of one of the three ligands to form a charge transfer state with the metal. This nondeterministic localization is revealed in switching of the degree of linear polarization of phosphorescence. Polarization scrambling likely raises out coupling efficiency and should be taken into account when deriving molecular orientation of the guest emitter within the OLED host from ensemble angular emission profiles.
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