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

Organic light-emitting diodes (OLEDs) have been one of the research focuses in science and industry due to their great application prospects in flat-panel displays and white-light emitting. In the past decades, OLEDs had achieved remarkable results. Compared with traditional display technology, the advantages of OLEDs are low cost, fast response, high luminescence, wide view angle, low driving voltage, flexible substrates and so on. Phosphorescent Organic Light-emitting Diodes (PHOLEDs) is more promising than Fluorescent Organic Light-emitting Diodes, because it can realize nearly100%internal quantum efficiency of electroluminescence. Compared with red and green PHOLEDs, the development of blue PHOLEDs is laggard. One of the most important reasons is that the host materials used in blue PHOLEDs is rare. So researching and developing new blue phosphorescent host materials is of great significance.Carbazole and their derivatives have received more attention as host materials due to their excellent hole transporting ability and high triplet energy. In this paper, the nine target molecules that we designed and synthesized all have carbazole. The triplet energy must be higher than2.70eV for a host material used in blue PHOLEDs. so the conjugacy of molecules can’t be too strong. We chose Durene, tetra-phenyl silane and tirs-duryl borane as steric hindrance to decouple the phenyl carbazoles to enhance the triplet energy of molecules. The structures of target molecules were confirmed by1H NMR and MALDI-TOF-MS. Their photophysical properties, electrochemical properties and thermal stability properties had been researched by UV-Vis absorption and photo luminescence spectrum, cyclic voltammetry and thermogravimetric Analysis respectively. The triplet energy of DCz and DTCz were3.06eV and3.05eV respectively, which were measured from the highest energy peak of phosphorescence spectra at77K.We also used DCz and DTCz as host materials respectively to prepare FIrpic-based blue Phosphorescent Organic Light-emitting Diodes by vacuum deposition. The turn on voltage is4.3V, corresponding to a maximum current efficiency and power efficiency are26.2cd/A and14.8lm/W respectively with CIE coordinates (0.20,0.46) when DCz as the host material; The turn on voltage is6.5V. corresponding to a maximum current efficiency and power efficiency are18.0cd/A and8.0lm/W respectively, CIE coordinates (0.19,0.43) when DTCz as the host material. The results indicate that triplet energy is efficiently confined on FIrpic molecules, resulting in the high efficiency.