Synthesis And Electroluminescence Characteristics Of Aluminum And Gallium Complexes Containing 8-Hydroxyquinoline Ligand

Organic electroluminescent (EL) materials are the substances that give out lights when excited by electric field. Organic light-emitting diodes (OLED) is one of the most promising candidates for the next generation display technologies. Especially, OLEDs also have great potential for backlights in flat-panel displays and general solid state lighting application. Along with the implementation of further architectural refinements, the enhancement of the electroluminescence efficiency passes obviously through the synthesis of the new molecules possessing very dedicated capacities. For instance and good quantum yield, high charge mobility are generally required to achieve good device output. Considering low efficiency is resulted from the fact that electron-transporting materials exhibit poorer mobility than hole-transporting ones, we designed a series of emissive materials having the required charge transporting properties, and investigated their optical and electrical properties by steady and transient state measurement.1. An aluminum complex, bis(8-hydroxyquinoline) acetylacetone aluminum (Alq2A) was synthesized, which has luminescence in solution, powder and solid state at room temperature. Its fluorescence quantum yields was determined to be 6.75 times that of Alq3. Analysis of the electronic structure of Alq2A calculated by quantum chemical simulation revealed that the fluorescent emission of Alq2A originates from ligand-centeredπ-π* transition. The Al (Ⅲ) centers play an important role in enhancing the fluorescent emission of the ligands.2. Tris(acetylacetone) aluminum (Alacac), as a byproduct in the third chapter, was obtained and investigated. Its crystalline structure was determined from X-ray diffraction data on single crystals. It was discovered firstly that the complex has intense fluorescence and good fluorescence life.3. The transport properties of charge carrier in bilayer organic light-emitting diodes were studied by transient electroluminescence. The electron mobility of Alq2A with different purity was found to be obviously dependent on its purity, i.e. higher purity led to higher electron mobility. The measurement of electron mobility of Alq3 indicated that the electron mobility of Alq2A is higher than that of Alq3.4. The Electroluminescence performance of Alq2A-based OLED was investigated by steady-state current-voltage characteristics, and the electronic transport properties was proved furtherly by qualitative experiment. The emission of the Alq2A-based device peaks at 513 nm, similar to that of Alq3. Alq2A device has an approximately 75% higher current efficiency and 165% higher power efficiency than Alq3 structure. Alq2A complex shows a higher EL efficiency in steady-state EL studies, which is considered to be derived from: 1) improved electron mobility; 2) high fluorescene efficiency; and 3) good film-forming.5. An 8-hydroxyquinoline complex, GaMq2Cl, was synthesized and purified by vacuum sublimation. Experimental results show that the complex was a thermally stable material, with decomposition temperature being 348℃. Its powder emitted intensive blue fluorescence with peak wavelength of 471nm under UV irradiation. GaMq2Cl-based device was fabricated, which emitted blue-greenish fluorescence with peak wavelength of 502nm.The major results of this thesis were summarized as follows:(1) The introduction of the second ligand acetylacetone has great effect on fluorescence quantum efficiency and electron transport property of aluminum complex containing 8-hydroxyquinoline. Organic electro- luminescence materials with balanced electron/hole injection and good carrier-transporting property and good photoluminescence can improve the performance of the fabricated OLEDs. (2) Tris(acetylacetone) aluminum synthesized in given conditions has intense fluorescence and good fluorescence lifetime, indicating that molecular structure is not the only-factor affecting fluorescence property.(3) The forming ability of mixed ligand complexes containing acetylacetone and 8-hydroxyquinoline differs in center ions Al and Ga, Corresponding Ga complex were not sythesized in the same conditions as for Al complex, indicating that acetylacetone and 8-hydroxyquinoline ligands can not dissolve in inner boundary in the presence of Ga ions.