The Unusual Electrochemical and Photophysical Behavior of 2,2‘-Bis(1,3,4-oxadiazol-2-yl)biphenyls, Effective Electron Transport Hosts for Phosphorescent Organic Light Emitting Diodes

The fluorescence and phosphorescence of 2,2‘-bis(5-phenyl-1,3,4-oxadiazol-2-yl)biphenyl shows good spectral matching with the absorption spectra of the MLCT1 and MLCT3 transitions of Ir(ppy)3. The red-shift of the 0−0 band in the phosphorescence at 77 K is due to the intramolecular π−π interactions between the oxadiazole side chains. Maximum brightness of 43 000 cd/m2 with an efficiency of 26 cd/A at 200 cd/m2 was achieved when BOBP was used as the host material for Ir(ppy)3 in the PHOLED study.