Phenoxazines having various electron acceptor or donor fragments as new host materials for green phosphorescent OLEDs

We report on the synthesis and characterization of a new series of phenoxazine-based compounds as potential host materials of phosphorescent OLEDs. The derivatives are thermally stable materials as it was demonstrated by thermogravimetric analysis. Electron photoemission spectra of thin layers of the materials show ionization potentials in the range of 5.24-5.56 eV. Some of the developed materials formed homogenous amorphous layers with high glass transition temperatures and were used as hosts for bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III), Ir(ppy)(2)(acac), guest in green phosphorescent organic light-emitting diodes. Results indicated that a device with 3-[bis(9-ethylcarbazol-3-yl)methyl)-10-hexylphenoxazine host exhibited superior performance with external quantum efficiency exceeding 5.9%, maximum current efficiency of 18.3 cd/A, maximum brightness of 5366 cd/m(2) and low turn on voltage of 3.1 V.