Synthesis And Properties Characterization Of Phosphorescent Dopants And Host Materials In Phosphorescent Organic Light-Emitting Devices

The thesis mainly described the design and synthesis of a series of carbazole derivatives with high triplet energy as host materials and a series of Ir-complex featuring pinene-2-phenylpyridine ligands as phosphorescent dopants in Phosphorescent Organic Light-Emitting Devices (PHOLED). Their photophysical properties and energy level structures were intensively investigated.The main results of the thesis are summarized as follows:(1) A new series of carbazole derivatives as host materials have been designed and synthesized. Their triplet energy is 0.1-0.3eV higher than that of CBP, and the other typical blue phosphorescent dopants. They can be employed in blue PHOLED as host materials. The results of PHOLED fabricated using these derivatives as the host materials indicated that the properties of them are equal to or better than those of CBP.(2) The new series of Ir-complexes(Ir(RO-pppy)3)featuring pinene group and various alkoxy side chains have been designed and synthesized. The results of the photophysical properties indicated that the complex with long side chains could reduce the interaction between molecules. The Ir(C16H33O-pppy)3-based devices exhibit better EL performance, the maximum luminance efficiency, 19.9 cd/A (7.8 lm/W) at 9.1V, was obtained with doping concentration of 3.4wt.-%, and the maximum luminance of the devices was 15700 cd/m2 at 8.4V.(3) A new family of cyclometalated Ir-complexes, FpIrpic, FpIr(acac) and FpIrN4 ,featuring 2-phenyl-pinenepyridine ligands have been synthesized. Their main emitting peaks are located at 469nm, 479nm and 460nm, respectively. Their phosphorescence quantum yields were 0.68, 0.52 and 0.064, respectively. The results indicated that they are novel blue phosphorescent dopants. (4) Two host materials, C1PBD and C5PBD, with ambipolar carrier transport properties have been synthesized and investigated. The results indicated that their HOMO and LUMO energy levels match well with those of blue/green Ir-complex dopants developed by us. Their triplet energy is 2.68eV, which indicates that they can be employed as blue/green host materials in PHOLED.(5) The energy transfer mechanism of host-guest system composed of each of 5 the novel blue host materials (using CBP as a reference) and FIrpic have been investigated. The results indicated that there were relatively poor energy transfer efficiencies between CBP or o-CBP and FIrpic. The results of the excitation spectroscopy proved the existence of the energy transfer in the system. Transit photoluminescence decays indicated the triplet-triplet energy transfer from FIrpic back to CBP, which is the possible reason for the poor energy transfer efficiency.