Polarized phosphorescent organic light-emitting devices adopting mesogenic host–guest systems

We report successful realization of workable polarized phosphorescent organic light-emitting devices (OLEDs) by combining a recently developed mesogenic phosphorescent Pt(II) complex and a mesogenic oligofluorene host to form the corresponding mesogenic host–guest emitting system. In the host–guest film, the mesogenic Pt(II) complex tends to aggregate and self-assemble into the columnar stacking arrangement, exhibiting metal–metal-to-ligand charge transfer (MMLCT) emission of the Pt(II) complex. Both the host molecules and guest aggregates in the host–guest films were successfully aligned by using the rubbed conducting polymer as the alignment layer. With such aligned host–guest films, polarized red-emitting OLEDs were successfully implemented, showing an EL polarization ratio of ∼2, a maximal brightness exceeding 2000 cd/m2, and a cd/A efficiency up to 2.4 cd/A. Due to the particular alignment mechanism of guest aggregates and the unique MMLCT emission mechanism, the polarized OLED exhibiting stronger electroluminescence perpendicular to the rubbing direction than along the rubbing direction.