Simple oxadiazole derivatives as deep blue fluorescent emitter and bipolar host for organic light-emitting diodes

To obtain highly efficient and stable electroluminescence, a bipolar molecule of 2, 5-bis(4'-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1, 3, 4-oxadiazole (Oxd-bCz) is designed and synthesized. By incorporating electron-donating and electron-withdrawing moieties into a single molecule endows the compound bipolar characteristic and obtains high performance OLED. Oxd-bCz emits purple-blue fluorescence with emission peak at 431 nm in dilute dichloromethane. The blue OLED with Oxd-bCz as emitter exhibited high performances of a low turn-on voltage of 3.6 V and a maximum external quantum efficiency of 5.6% with excellent color saturation (CIEy ∼0.07). With a triplet energy of 2.39eV, Oxd-bCz can be utilized as host for Ir (ppy)3-guested green OLED with a low turn-on voltage of 2.8 V, current efficiency of 29 cd/A and an EQE value of 8.17%.