| Organic light-emitting diodes have attracted considerable interest owing to their potential applications in large-area full-color flat-panel displays. Since the breakthrough in the electroluminescence by Kodak in 1987, much progress has been made in the electroluminescence for science research and practical application. The promising technologies are continuously developed and the novel materials are endlessly designed, synthesized and improved in order to fulfill the requirements of this application. Because the materials differ from one another by their structure but also by the mechanism involved in the electroluminescence produced (fluorescence versus phosphorescence), it has become an important task that various properties of organic materials are measured and estimated. Thereinto, it is of the significance that the energy level structure of organic materials is characterized for design and synthesis of the materials, improving and perfecting properties of devices and designing the multilayers high-efficiency and long-life devices.In this work, we focus on the energy level structure and the effect of molecular structure on the properties of several series of organic materials, including a series of oxadiazole derivatives, phenanthroline derivatives and corresponding Re(I) complexes system, the donor and acceptor system consisted of carbazole group and pyrene group, by the electrochemical methods and quantum theory calculation methods.The effect of the changes of side chain substituents on the energy level structure of this series of oxadiazole derivatives has been studied by cyclic voltammetry (CV), spectroscopy and quantum chemical calculation. It is indicated that the frontier molecular orbitals of oxadiazole derivatives OXD-X, OXD-An, OXD-Bn, OXD-Cn are perturbed, and the distribution of energy level orbitals is changed and the results are improvement of the electron transport abilities. The adjusting range of LUMO is from -2.63eV to -2.96eV, while that of HOMO from -6.35eV to -5.80eV, by introducing different side chain substituents. At the same time, the properties of this series of oxadiazole derivatives are also improved in the thermal stabilities, the optic properties and the electrochemical behavior.It has been investigated in the effect of the position changes of the symmetrical alkoxy subsituents on the energy level structure of this series of oxadiazole derivatives. With the position changes of the symmetrical alkoxy subsituents from tail-end benzene group to central benzene group, the HOMO level of 0XD-1E, 0XD-3En, 0XD-2Fn increases and energy band gap (Eg~opt) reduces by increasing the electron abilities. It is shown that HOMO level changes from -6.20eV to -5.75eV, while Eg~opt changes from 3.31eV to 2.97eV. Similarly, the correspondingproperties of this kind of oxadiazole derivatives markedly change. Moreover, the electron transport properties of this kind of oxadiazole derivatives are investigated by preparation of the blend device. The results indicate that the properties of the doped device are improved, and the maximal efficiency obtain 1.1 cd/A, and enhance an order magnitude, comparing with undoped device.Furthermore, we study on the effect of alkyl substituents on the properties of new oxadiazole derivatives DOXD-3, DOXD-7, D0XD-T3, D0XD-T7, it is shown that the thermal stabilities, the optic properties and the electrochemical behavior are adjusted by introducing alkyl substituents.It has been investigated not only in the effect of the different substituents on the energy level structure and the correlative properties of ligand, but also in the effect of the different ligand or different substituents on the same ligand on the energy level structure and correlative properties of phenanthroline derivatives and corresponding Re(I) complexes system. It is indicated that both HOMO level and LUMO level of Re(I) complexes increase with introduction of carbazole substituents, while the HOMO level of ligand increases and the LUMO level reduces. Similarly, both HOMO level and LUMO level of Re(I) complexes increase with introduction of pyrrolo-pyridine subsituents, while the HOMO level of ligand increases and the LUMO level reduces. Moreover, on contrast of corresponding ligand, the LUMO level of Re(I) complexes evidently reduces, and the HOMO level slightly changes, and it is due to the interaction of Re(I) ion and ligand unit.The light emission of the phenanthroline derivatives can contribute to the carbazole-to-phenanthroline or pyrrolo-pyridine substituent-to-phenanthroline charge transfer transition, while that of Re(I) complexes should attribute to the substituents-to-phenanthroline and metal ion Re(I)-to-ligand charge transfer transition in the solution. It is indicated that two light-emitting peaks come forth in the solution. The electrochemical behavior of the ligand is ascribed to the oxadition of substituents and the reduction of phenanthroline unit, while that of Re(I) complexes come from the oxadition of metal ion Re(I) and the reduction of ligand unit, so it is consistent with the theoretical calculation results.The blue pyrene derivatives including the donor unit and acceptor unit, L-Z-l, L-Z-2 and L-Z-3, are investigated. It is shown that L-Z-l, L-Z-2 and L-Z-3 are high effective blue materials with good thermal stabilities, and the different intramolecular charge transfer abilities have been appeared owing to the difference of molecular structure. Moreover, L-Z-l, L-Z-2 and L-Z-3 reveal the good electrochemical behavior by CV measurement. Namely, L-Z-l, L-Z-2 and L-Z-3 undergo a reversible oxadition reaction and a reversible reduction reaction.We selected L-Z-3 as an example to investigate the electroluminescent properties of these pyrene derivatives. The properties of the doped device are improved by the different doped rate, the design of device and thermal process. The results show that L-Z-3 is the blue light emission with maximal efficiency (1.9cd.A) at 10V, when the doped rate is 3:2 in the device including the thermal-processed emission layer.
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