Phenanthro[9,10-d]imidazole based new host materials for efficient red phosphorescent OLEDs

We report on the synthesis and characterization of a new series of bipolar phenanthro[9,10-d]imidazole based compounds. The derivatives are highly thermally stable materials as demonstrated by thermogravimetric analysis. Electron photoemission spectra of thin layers of the materials show ionization potentials in the range of 5.1-5.4 eV. Spectroscopic properties of the phenanthro[9,10-d]imidazole based derivatives were determined by absorption and photoluminescence measurements. All the developed materials were used as hosts in red phosphorescent organic light-emitting diodes and their properties were compared with commercially available host materials. Results indicate that a device with 2-[4-(N,N-diphenylamino)pheny1]-1-phenylphenanthro[9,10-d]imidazole exhibited superior performance with peak efficiency of 15.9% (21.5 cd/A and 29.91 m/W) and very low turn on voltage of 2.8 V. Efficiency of the device is about 35-67% higher than those of devices containing commercial host materials. (C) 2016 Elsevier Ltd. All rights reserved.