Carbazole-based materials for guest-host electroluminescent systems

The invention is directed to guest-host emissive systems suitable for use with organic light emitting devices. In one aspect, the host material comprises a compound having a carbazole core with an electron-donating species bonded to the nitrogen, and aromatic amine groups or carbazole groups bonded to one or more of the carbon atoms. In another aspect, the host material comprises a compound having a single-atom or single-ring core bonded to one or more carbazole moieties, which may themselves be substituted with electron-donating groups. The disclosed host materials have a large band gap potential and high-energy triplet excited states to permit short-wavelength phosphorescent emission by an associated guest material.