Synthesis and Properties of a Novel Bipolar Host Material Based on 1,2,4-Oxadiazole for Green Phosphorescent OLEDs

A novel bipolar green phosphorescence host material, 3,5-bis (4-(9H-phenol-thiazine-9-yl) phenyl)-1,2,4-oxadiazole (PPOXD), was designed and synthesized, and its structure was characterized by means of 1H NMR and 13C NMR. The photophysical properties of PPOXD were studied by ultraviolet-visble (UV-Vis) absorption, fluorescence, phosphorescent spectroscopies at 77 K and cyclic voltammetry (CV) and density functional theory (DFT). The results show that the maximum absorption wavelength is located in about 210、247、270 and 307 nm, and the photofluorescence emission peaks in 378 and 448 nm in CH2Cl2 solution. Its phosphorescence emission peaks were observed at 504 and 535 nm, and suitable triplet energy ( 2.46 eV) for PPOXD was achieved, which could meet the basic requirement of green host material for the green emitter Ir (ppy)3 (2.40 eV). Cyclic voltammetry exhibits that HOMO and LUMO level of PPOXD is located in-5.25 and-2.32eV respectively. TGA and DSC results reveal that PPOXD has good thermal stability, the decomposition temperature and glass transition temperature are 275 and 170 °C, respectively. Therefore, PPOXD is a potential green phosphorescence host material with bipolar feature.