Quinoxalines incorporating triarylamines: Dipolar electroluminescent materials with tunable emission characteristics

Dipolar compounds (abbreviated as QuPy) featuring quinoxaline acceptors and diarylamine or triarylamine donors were prepared via palladium-catalyzed C-N or C-C bond formation in good yields. They possess high thermal stability with a high decomposition temperature (T-d > 400 degrees C) and exhibit no crystalline character. The emission colors of the materials vary from green to orange red and are dependent on the nature of the electron-withdrawing segments and solvents. Two types of double-layer organic light-emitting diodes (OLEDs) were constructed using these dipolar compounds as hole-transporting/emitting layers and TPBI or Alq(3) as an electron-transporting layer: (I) ITO/QuPy/Alq(3)/Mg:Ag and (II) ITO/QuPy/TPBI/Mg:Ag (TPBI = 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzen; Alq(3) = 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene). The recombination zone in most of those devices were confined in the quinoxaline layers, The green to orange colors in these devices correspond well with the film PL of the material used. The relation between the energy levels of the compounds and the performance of the light-emitting diode are discussed.