Controllably tunable phenanthroimidazole–carbazole hybrid bipolar host materials for efficient green electrophosphorescent devices

Abstract

A series of phenanthroimidazole–carbazole (1 : 2) hybrids as bipolar host materials have been designed and synthesized through facile typical Ullmann reactions. These compounds with rigid configurations exhibit excellent thermal and morphological stabilities with high glass transition temperatures (T_g) (143–282 °C). Their photoelectronic properties, energy levels, charge transport mobility, and film morphologies can be controllably tuned through judicious engineering of the linkage modes between the two carbazole groups and the 2,5-diphenyl-1,3,4-phenanthroimidazole (para and meta). The promising physical properties of these new compounds make them suitable for use as hosts doped with Ir-based phosphor for realizing highly efficient phosphorescent organic light emitting diodes (PhOLEDs). A green device hosted by compound PhBIDmpCP shows a maximum current efficiency of 74.3 cd A⁻¹ and a maximum power efficiency of 74.4 lm W⁻¹ (corresponding EQE_max = 20.2%).