Synthesis And Properties Of Triazole Derivatives As Bipolar Host Materials For Blue Phosphorescent Organic Light-emitting Diodes

Organic light-emitting diodes (OLEDs), are regarded as the mainstream technology in flat panel displays field due to its great advantage compared with conventional one like CRT and LCD. The unique superiorities as low driving voltage, low-power, high-contrast, active luminescence, thin and light body suggest that it has been outstanding in the FDP. Organic electrophosphorescent devices can be used to circumvent the limitation in quantum efficiency of organic electroluminescent devices due to the spin-forbidden of triplet exciton transition, so that it will have a wider application prospect. So far, the study of blue PHOLEDs is laggard due to the lack of high-performance host materials so that have restricted the development of OLED. Bipolar hosr materials have become worldwide research focus because of its more balanced carrier transmission capabilities and more appropriate energy level which can increase the OLED’s efficiency drastically.Carbazole has received a lot of attention as host materials due to its excellent hole transporting ability in the areas of the photo electronic materials. Triazole is proved to be one of good N-type semiconductor materials with great potential. So in this paper, the two kinds of materials are chosen to build the bipolar host molecules as part of hole transporting unit and electron transporting unit respectively. According to the triplet energy has to be much higher than2.65eV for a host material used in blue PHOLEDs, using the saturated N-single bond, the meta position of benzene, and steric hindrance effect for isolating method can weaken the molecular conjugation effectively to enhance the triplet energy of molecules. In this paper, seven molecules have been synthesized by this way, and their molecular structures were confirmed by1H NMR and MS. Meanwhile, their photophysical properties, electrochemical properties and thermal properties had been researched by UV-Vis absorption and photoluminescence spectrum, low-temperature phosphorescence spectrum, cyclic voltammetry and density functional theory, thermogravimetric analysis and differential scanning calorimetry respectively. the triplet energy of the target compounds are between2.65eV and2.76eV, the thermal decomposition temperature and glass transition temperature are much higher than355℃and110℃. All of results support the idea of molecular design.In this paper, six of designed bipolar molecules were chosen to prepare blue PHOLED respectively as the host materials with FIrpic as the emitting guest material using vacuum evaporation technique to examine the electroluminescent properties of these materials. The turn on voltage is2.9V and the maximum brightness is about22450cd m-2, corresponding to a maximum current efficiency and power efficiency are36.3cd A-1and28.5lm W-1respectively when mCPTz as the host material; The turn on voltage is3.4V and the maximum brightness is about19580cd m-2, corresponding to a maximum current efficiency and power efficiency are37.2cd A-1and29.2lm W-1respectively when CzoTz as the host material, obtained two ideal perpformance. The results indicate that these materials are hopeful to be applied in the OLED fields.