Diphenylaminocarbazoles by 1,8-functionalization of carbazole: Materials and application to phosphorescent organic light-emitting diodes

A series of novel carbazole-based materials, DPACz1, DPACz2 and DPACz3 having diphenylamino moieties at 1- and 8-positions of carbazole have been synthesized and characterized for the first time. The introduction of diphenylamino substituents at 1- or 1,8-positions of carbazole resulted into increase of the band-gap compared with the previously reported 3,6- or 2,7-substituted ones. The HOMO levels increased from DPACz1 to DPACz2 with the addition of one additional diplienylamino unit, and further increased in case of DPACz3, a dimer of DPACz1 having a benzidine moiety. The materials have high triplet energy levels of 2.68, 2.60 and 2.45 eV, respectively. Based on suitable HOMO levels and high triplet energies, the newly synthesized diphenylaminocabazoles were investigated for their potential as solution-processable host materials for green phosphorescent OLEDs with the device configuration, [ITO/PEDOT:PSS/Emitting layer/TPBi/CsF/Al]. All the devices emitted typical green light with high luminance and had low turn-on voltages along with good luminous efficiencies which were further improved by adjusting charge balance using PBD, as a co-host. The basic characteristics and the preliminary OLED results showed the usefulness of our new materials, and this kind of 1-/1,8-substitution of carbazole would open a new way of materials design. (C) 2015 Elsevier Ltd. All rights reserved.