Organic electroluminescent derivatives containing dibenzothiophene and diarylamine segments

A new series of 2,8-disubstituted dibenzothiophenes have been successfully synthesized via palladium-catalyzed C-N or C-C bond formation using 2,8-dibromodibenzothiophene and diarylamines as starting materials. These new dibenzothiophene derivatives are amorphous with a glass transition temperature ranging from 86 to 190 degrees C. Furthermore, they are fluorescent in the blue to bluish green region. Two types of light-emitting diodes ( LED) were constructed from these compounds, ( I) ITO/Cpd/TPBI/LiF/Al and (II) ITO/Cpd/Alq3/LiF/Al, where TPBI and Alq(3) are 1,3,5-tris(N-phenylbenzimidazol-2-yl) benzene and tris(8-hydroxyquinolinato) aluminium, respectively. In type I devices, the compounds function as the hole-transporting and emitting material. In type II devices, emission from Alq3 is observed. Several type I devices emit pure blue light, and most of the devices II have very promising performance. The relation between the energy levels of the materials and the performance of the light-emitting diodes is discussed.