Light-emitting carbazole derivatives for electroluminescent materials

Abstract

Amorphous carbazole derivatives containing peripheral diarylamines at the 3- and 6-positions and an ethyl or aryl substituent at the 9-position of the carbazole moiety have been synthesized. These new carbazole compounds (carbs) possess high glass transition temperatures (T g : 120- 194 degree(s)C) and high thermal decomposition temperatures (T d >450 degree(s)C). The compounds are weakly to moderately luminescent with the emission wavelength ranging from green to blue. Two types of light-emitting diodes (LED) were constructed from carb:(I)ITO/carb/TPBI/Mg:Ag and (II)ITO/carb/Alq 3 /Mg:Ag, where TPBI and Alq 3 are 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene and tris(8- hydroxyquinoline) aluminum, respectively. In type I devices the carb functions as the hole-transporting as well as emitting material. In type II devices either carb and/or Alq 3 is the light emitting material. Several green light-emitting devices exhibit exceptional maximum brightness and the physical performance is superior to those of typical green-light-emitting devices of the structure ITO/diamine/Alq 3 /Mg:Ag. Relation between the LUMO of the carb and the performance of the light-emitting diode is discussed.