Phosphorescent OLEDs assembled using Os(II) phosphors and a bipolar host material consisting of both carbazole and dibenzophosphole oxide

We report on the synthesis of a new series of Os(II) complexes (1-3) functionalized with 2-pyridyl (or 2-isoquinolyl) pyrazole chelates, together with a new diphosphine, 1,2-bis(phospholano)benzene chelate (pp2b). The resulting Os(II) complexes are fully characterized and their structural versus spectroscopic properties have been comprehended by absorption/emission together with computational approaches. The inherent electron richness, restricted rotational barrier and good steric hindrance of pp2b lead to the production of both orange and red phosphorescence with high quantum efficiency. For exploring these Os(II) based OLEDs, we also synthesized a bipolar material 5-[4-(carbazo-9-yl)phenyl] dibenzophosphole-5-oxide (CzPhO), possessing both carbazole donor and dibenzophosphole oxide acceptor. Successful fabrication of OLEDs using complexes 1 and 3 as the dopant and either 4,4′-N,N′-dicarbazolebiphenyl (CBP) or CzPhO as host is reported. For comparison, the CBP and CzPhO devices with 1 as the emitter showed peak efficiencies EQE of 10.9%, η_L of 21.7 cd A^-1, and η_p of 11.9 lm W^-1, and EQE of 14.3%, η_L of 34.8 cd A^-1, and η_p of 45.2 lm W^-1, respectively.