Oxadiazole-containing material with intense blue phosphorescence emission for organic light-emitting diodes

2-(2-hydroxyphenyl)-5-phenyl-1, 3, 4-oxadiazole (HOXD), characteristic of excited state intramolecular proton-transfer (ESIPT), was synthesized and found to emit strong blue phosphorescence in the solid state at room temperature and at low temperature (77 K). The photoluminescent spectrum measurement in solution showed that there are two kinds of emission: fluorescence originated from the singlet state and phosphorescence derived from the triplet state in HOXD formed by ESIPT. For the photoluminescent spectrum in the solid state, only phosphorescence emission with the lifetime of 66 μs was observed. Multiple-layer light-emitting diodes with the configuration of $\mathrm{ITO/NPB/}{HOXD}/{\mathrm{BCP/Alq}}_3/\mathrm{Mg:Ag}$ were fabricated using HOXD as emitter and the maximum brightness of $\text{656\hspace{0.17em}}{\mathrm{cd/m}}^2$ and the luminous efficiency of 0.14 lm/W was obtained.