Simple bipolar hosts with high glass transition temperatures based on 1,8-disubstituted carbazole for efficient blue and green electrophosphorescent devices with "ideal" turn-on voltage.

Two hybrids based on 1,8-disubstituted carbazole, 1,8-OXDCz and 1,8-mBICz, have been designed and synthesized through a facile process. The incorporation of oxadiazole or N-phenylbenzimidazole moieties at the 1,8-positions of carbazole greatly improves its morphological stability, giving glass transition temperatures (T(g)) as high as 138 and 154 °C, respectively. Blue phosphorescent organic light-emitting devices (PhOLEDs) with 1,8-mBICz exhibit almost the same performance as a similarly structured device based on the mCP host, and green PhOLEDs employing the new host material 1,8-OXDCz exhibit an ideal turn-on voltage (2.5 V at 1.58 cd m(-2)), a maximum current efficiency (η(c,max)) of 73.9 cd A(-1), and a power efficiency (η(p,max)) of 89.7 lm W(-1). These results are among the best performances of [Ir(ppy)(3)]-based devices with simple device configurations.