Structure and electronic properties of triphenylamine-substituted indolo[3,2-b]carbazole derivatives as hole-transporting materials for organic light-emitting diodes

Two new triphenylamine-substituted indolo[3,2-b]carbazole compounds, 2,8-bis(4-diphenylaminophenyl)-5,11-di-n-octylindolo[3,2- b]carbazole (1) and 6,12-bis(4-diphenylaminophenyl)-5,11-di-n-octylindolo[3,2- b]carbazole (2), have been designed and synthesized. The theoretical and experimental studies show that the different substituted-positions of triphenylamine groups have great effect on the optical and electrochemical properties. EL devices with the configuration of ITO/1(or 2)/Alq3/Mg:Ag/Ag show green emission. The activating voltages (recorded at 1 cd/m2) are 4.1 and 3.7 V, respectively. The maximal luminance efficiencies are 0.738 and 1.464 lm/W, respectively. The difference of EL performances indicates 6,12-disubstituted indolo[3,2-b]carbazole compound possessing better hole-injecting and transporting performance than that of the 2,8-disubstituted compound.