High-Tg carbazole derivatives as blue-emitting hole-transporting materials for electroluminescent devices

A series of dicarbazolyl derivatives bridged by various aromatic spacers and decorated with peripheral diarylamines were synthesized using Ullmann and Pd-catalyzed-C-N, coupling procedures. These derivatives emit blue light in solution. In general, they possess high glass-transition temperatures (T-g > 125 degreesC) which vary with the bridging segment and methyl susbtitution on the peripheral amine. Double-layer organic light-emitting devices wers successfully fabricated using these molecules as hole-transporting and emitting materials. Devices of the configuration ITO/HTL/TPBI/Mg:Ag (ITO: indium tin oxide; HTL: hole-transporting layer; TPBI: 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene) display blue emission from the HTL layer. The EL spectra of these devices appear slightly distorted due to the exciplex formation at the interfaces. However, for the devices of the configuration ITO/HTL/Alq(3)/Mg:Ag (Alq(3) = tris(8-hydroxyquinoline)aluminum) a bright green light from the Alq(3) was observed. This clearly demonstrates the facile hole-transporting property of the materials described here.