Adamantane-based wide-bandgap host material: blue electrophosphorescence with high efficiency and very high brightness.

An adamantane-based host material, namely, 4-{3-[4-(9H-carbazol-9-yl)phenyl]adamantan-1-yl}benzonitrile (CzCN-Ad), was prepared by linking an electron-donating carbazole unit and an electron-accepting benzonitrile moiety through an adamantane bridge. In this approach, two functional groups were attached to tetrahedral points of adamantane to construct an "sp(3)" topological configuration. This design strategy endows the host material with a high triplet energy of 3.03 eV due to the disruption of intramolecular charge transfer. Although CzCN-Ad has a low molecular weight, the rigid nonconjugated adamantane bridge results in a glass transition temperature of 89 °C. These features make CzCN-Ad suitable for fabricating blue phosphorescent organic light-emitting diodes (PhOLEDs). The devices based on sky-blue phosphor bis[(4,6-difluorophenyl)pyridinato-N,C(2')](picolinato)iridium(III) (FIrpic) achieved a high maximum external quantum efficiency (EQE) of 24.1%, which is among the best results for blue PhOLEDs ever reported. Furthermore, blue PhOLEDs with bis(2,4-difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III) (FIr6) as dopant exhibited a maximum EQE of 14.2% and a maximum luminance of 34 262 cd m(-2). To the best of our knowledge, this is the highest luminance ever reported for FIr6-based PhOLEDs.