Benzobisoxazole-based electron transporting materials with high T sub(g) and ambipolar property: high efficiency deep-red phosphorescent OLEDs

Two new benzobisoxazole-based compounds, namely, 4,8-bis(3,5-di(pyridin-3-yl)phenyl)-2,6-dimethylbenzo[1,2-d: 4,5-d']bis(oxazole) (3Py-DBBO) and 4,8-bis(4-yl-triphenylphosphine oxide)-2,6-dimethylbenzo[1,2-d:4,5-d']bis(oxazole) (TPO-DBBO), were synthesized and characterized. The steric effect of the orthohydrogens on the phenyl ring at 4,8-positions of benzobisoxazole resulted in out-of-plane twisting, and consequently a decrease of the intermolecular pi - pi interaction. The two new compounds showed excellent thermal stabilities with high glass-transition temperatures (T sub(g)) of 248 degree C for 3Py-DBBO and 142 degree C for TPO-DBBO. The two compounds exhibited ambipolar transport properties, with both electron and hole mobilities of 10 super(-6)-10 super(-5) cm super(2) V super(-1) s super(-1). Using the compounds as electron-transport materials, the deep-red phosphorescent organic light-emitting devices achieved a maximum external quantum efficiency up to 19.3%.