By conjugating carbazole moiety to the different positions of the rigid skeleton 1,2-diphenyl-1Hphenanthro [9,10-d]imidazole, a series of hybrid bipolar phosphorescent hosts was synthesized, and their photophysical properties were investigated. The introduction of a rigid phenanthroimidazole moiety greatly improves their morphological stability, with high decomposition temperatures (T d ) and high glass transition temperatures (T g ) in the range of 394−417 and 113−243 °C, respectively. The highly efficient green and orange phosphorescent organic light-emitting diodes (PhOLEDs) have been achieved by employing these compounds as the phosphorescent hosts. For the device of ITO/MoO 3 (10 nm)/NPB (80 nm)/TCTA (5 nm)/mPhBINCP:9 wt % Ir(ppy) 3 (20 nm)/TmPyPB (45 nm)/LiF (1 nm)/Al (100 nm), a maximum luminous efficiency (η c,max ) of 77.6 cd/A, maximum power efficiency (η p,max ) of 80.3 lm/W, and maximum external quantum efficiency (η EQE,max ) of 21% were obtained. Furthermore, these hosts are also applicable for the orange phosphorescent emitter (fbi) 2 Ir(acac), a yellow PhOLEDs with pPhBICP as host, for which a performance of η c,max of 57.2 cd/A, η EQE,max of 19.3%, and η p,max of 59.8 lm/W was achieved. These results demonstrated that the phenanthroimidazole unit is an excellent electron-transporting group for constructing the bipolar phosphorescent host.

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A novel electron-transporting moiety, 1,2,4-thiadiazole, was first introduced to construct bipolar host molecules for phosphorescent organic light-emitting diodes (PhOLEDs). By incorporating 1,2,4-thiadiazole with typical hole-transporting carbazole moieties, a series of thiadiazole/carbazole hybrids, o -CzTHZ, m -CzTHZ, and p -CzTHZ, were synthesized. All the hybrids exhibit very high glass transition temperatures (T g ≥ 167 °C) and show good thermal and morphological stability in films. Moreover, these host materials possess good bipolar charge transporting properties; electron and hole mobilities of these bipolar thiadiazole/carbazole hybrids can be tuned by simply adjusting the linkage modes between thiadiazole and carbazole moieties. The maximum external quantum efficiencies (η EQE, max) in the green PhOLEDs with o -CzTHZ, m -CzTHZ, and p -CzTHZ as the hosts reached 26.1%, 24.0%, and 22.9%, respectively, and their EQE were still over 20% even at the high luminance of 10,000 cd/m2. This study demonstrates that 1,2,4-thiadiazole should be an excellent electron-transporting unit for bipolar phosphorescent hosts.