【作者】 王华；

【导师】 许并社；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2007， 博士

【摘要】 自1987年美国的C.W.Tang首次报道采用三（8-羟基喹啉）铝（Alq₃）制作有机电致发光器件（OLED：Organic Light-emitting Device）以来，众多的新型有机电致发光材料（OELM：Organic Electroluminescence Material）被成功合成来满足改善OLED器件性能的要求。在众多的OELM中，由于8-羟基喹啉金属配合物（Mq_n）的各项性能优于其它类型的OELM，到目前为止只有Mq_n能作为一种技术成熟的OELM被广泛应用在各种OLED中。有关Mq_n的性能以及应用方面的研究已经成熟，然而Mq_n研究中仍然存在以下问题：Mq_n的合成方法与提纯方法的研究不足，不能满足其商业化大规模生产的要求，不利于OLED生产成本的降低；Mq_n的发光机理的研究相对比较薄弱，尤其是分子空间结构与材料性能之间的关系还需要大量的研究工作。以上两个问题制约了Mq_n的发展。本文针对Mq_n的研究现状开展研究，以Alq₃、二（8-羟基喹啉）锌（Znq₂）、8-羟基喹啉锂（Liq）为主要研究对象，对其合成、改性及材料性能进行了大量的实验研究与理论分析，从而揭示出Mq_n的分子空间结构与材料性能之间的关系，主要结果如下：1、探索研究了Alq₃、Znq₂和Liq的最佳的合成方法与提纯方法，优化各项工艺参数，从而满足提高合成产物产率和纯度的要求。本文设计并采用全新的真空提纯装置提纯Mq_n，大大提高了提纯效率，降低了提纯过程中产物的损失。该研究工作有助于降低合成Mq_n的生产成本，提高其合成效率，从而推动Mq_n商业化生产发展。2、首次采用真空加热与化学提纯相结合的方法制备了能实现蓝光发射的Alq₃，即δ-Alq₃，通过对δ-Alq₃和α-Alq₃的分子空间结构与各项性能进行分析与讨论，认为α-Alq₃在真空加热生成δ-Alq₃的过程中，分子结构与分子堆叠方式发生变化，分子之间的π-π相互作用增强；在光致发光光谱中，δ-Alq₃的最大发射峰较α-Alq₃发生蓝移，δ-Alq₃具有明显的蓝色荧光效果；固态中δ-Alq₃的荧光发射来自相邻分子的喹啉环间π→π^*电子跃迁，而α-Alq₃的荧光发射主要来自分子内定域在酚环的最高占据轨道（HOMO：the Highest Occupied Molecular Orbit）与定域在吡啶环的最低未占轨道（LUMO：the Lowest Unoccupied Molecular Orbit）之间的π→π^*电子跃迁；δ-Alq₃在真空热蒸发成膜的过程中会转变为α-Alq₃，因而当δ-Alq₃在OLED中作为发光层时电致发光光谱与α-Alq₃基本一致，发绿光；δ-Alq₃的成膜性优于α-Alq₃，导致其各项电致发光性能优于α-Alq₃。3、采用重结晶与真空加热相结合的方法制备了（Znq₂）₄和Znq₂，通过对（Znq₂）₄和Znq₂的分子空间结构与性能进行分析与讨论，发现（Znq₂）₄是由四个Znq₂通过Z-O-Zn键桥连接构成的，其分子平面结构的刚性程度大大强于Znq₂；（Znq₂）₄的荧光量子效率高于Znq₂，成膜性优于Znq₂；（Znq₂）₄相邻分子之间具有较强的π-π相互作用，而Znq₂相邻分子之间的π-π相互作用较弱，（Znq₂）₄的电子传输性能优于Znq₂，当（Znq₂）₄在OLED中作为发光层时，其各项性能参数优于Znq₂；（Znq₂）₄的荧光发射主要来自（Znq₂）₄分子中喹啉环间的π→π^*的电子跃迁和喹啉环内HOMO与LUMO之间的π→π^*电子跃迁，而Znq₂的荧光发射来自喹啉环内HOMO与LUMO之间的π→π^*电子跃迁，因而在电致发光光谱中（Znq₂）₄的光谱宽度比Znq₂宽。4、制备了（Liq·Naq）₂，通过对（Liq·Naq）₂和Liq的分子空间结构与性能进行分析与讨论，发现（Liq·Naq）₂是通过两个Na-O-Na键桥将两个Liq和两个Naq连接构成的，其分子平面结构的刚性程度强于Liq，空间位阻大于Liq，分子之间的距离大于Liq，分子极性远远小于Liq；（Liq·Naq）₂的荧光寿命长于Liq，荧光量子效率高于Liq，成膜性优于Liq；（Liq·Naq）₂的禁带宽度比Liq大，光致发光光谱中（Liq·Naq）₂的最大发射峰较Liq发生蓝移；当（Liq·Naq）₂在OLED中作为发光层时，激发二聚体与激基复合物的生成几率远远小于Liq，发的光比Liq更蓝，电流效率大于Liq；（Liq·Naq）₂超薄膜中有Na离子的存在，与Liq超薄膜相比，当其在OLED中作为电子注入层时，具有更大的电流密度，更高的发光强度，更低的阈值电压和更高的电流效率5、对上述Alq₃、Znq₂和Liq的分子空间结构与材料性能之间的关系进行了归纳总结，认为Mq_n的分子空间结构主要在分子平面结构的刚性程度，相邻分子之间的相互作用，分子堆叠的方式和分子之间的距离这四个方面影响其性能。根据这样的理论，能够根据对Mq_n材料性能不同的要求，采用不同的方法对Mq_n的分子空间结构进行相应改造，从而实现分子水平上Mq_n的改性，为Mq_n的改性研究开辟新的道路。更多还原

【Abstract】 Since C.W.Tang fabricated the first organic light-emitting device （OLED） using tris（8-hydroxyquinoline）aluminum （Alq₃） in 1987, plenty of novel organic electroluminescence materials （OELMs） have been synthesized to improve the performance of OLED. Among them, 8-hydroxyquinoline metal complex （Mq_n） is widely used in all kinds of OLEDs as a kind of well-developed OELM, for its superior performance over other kinds of OELMs. Though, the performance and application of Mqn had been extensively investigated, there still exist problems to be solved, such as the effective and low-cost synthesis and purification for commercialization, and the well-established light-emitting mechanism of Mq_n, especially the relationship between molecular spatial structure and material performance of Mq_n. In this paper, Alq₃, bis（8-hydroxyquioline）zinc （Znq₂） and 8-hydroxyquioline lithium （Liq） were main research objects. In order to elucidate the relationship between molecular spatial structure and material performance of Mqn, the synthesis, performance modification and material performance of above Mq_n molecules were studied experimentally and theoretically. The main research conclusions are as follows:1. The synthesis and purification of Alq₃, Znq₂ and Liq wereoptimized to satisfy the requirement for high yield and high purity of product. A novel vacuum evaporation equipment for Mq_n purification was designed, which can increase purification efficiency and reduce product loss. This work may be helpful for preparing Mq_n with low cost and high yield, and consequently for promoting the development of commercialization of Mq_n.2. For the first time, blue-light-emittingδ-Alq₃ was synthesized by vacuum heating and chemical purification. The analysis of molecular spatial structure and the characterization of material performance ofδ-Alq₃ andα-Alq₃ revealed that the molecular structure and molecule packing mode ofα-Alq₃ can change when converted toδ-Alq₃ by vacuum heating, resulting in strengthening intermolecularπ-πinteraction. In photoluminescence （PL） spectra, the maximum emission peak ofα-Alq₃ blue-shifts relative toα-Alq₃, andδ-Alq₃ possesses blue fluorescence effect. In solid state, the fluorescence emission ofδ-Alq₃ is attributed to the intermolecularπ-π^* electron transition, while the fluorescence emission ofα-Alq₃ is attributed to theπ→π^* electron transition between the Highest Occupied Molecular Orbit （HOMO） located in phenol ring and the Lowest Unoccupied Molecular Orbit （LUMO） located in pyridine ring of 8-hydroxyquinoline. Becauseδ-Alq₃ can convert toα-Alq₃ again during the film preparation by vacuum evaporation, the electroluminescence （EL） spectra ofδ-Alq₃ is nearly identical with that ofα-Alq₃ whenδ-Alq₃ is used as light emitting layer in OLED. Compared withα-Alq₃, better film formability ofδ-Alq₃ induces better electroluminescent performance.3. （Znq₂）₄ and Znq₂ were synthesized by recrystallization and vacuum heating. The analysis of molecular spatial structure and the characterization of material performance of （Znq₂）₄ and Znq₂ indicated that four Znq₂ were connected by Zn-O-Zn bond bridges to form （Znq₂）₄, which can strengthen the rigidity of planar molecular structure of Znq₂. Compared with Znq₂, （Znq₂）₄ exhibits higher fluorescence quantum efficiency and better film formability. The intermolecularπ-πinteraction between adjacent （Znq₂）₄ molecules is stronger than that between adjacent Znq₂ molecules, so the electron transporting performance of （Znq₂）₄ is better than Znq₂. When used as light emitting layer in OLED, （Znq₂）₄ gives much better electroluminescent performance than Znq₂. In （Znq₂）₄ molecule, the fluorescence emission is not only attributed to theπ→πelectron transition between HOMO and LUMO of hydroxyquinoline ring, but also attributed to theπ→πelectron transition between adjacent hydroxyquinoline rings. However, the fluorescence emission of Znq₂ is attributed toπ→π^* electron transition between HOMO and LUMO of hydroxyquinoline ring. Therefore, the EL spectra of （Znq₂）₄ is wider than that of Znq₂.4. （Liq·Naq）₂ was synthesized. The analysis of molecular spatial structure and the characterization of material performance of （Liq-Naq）₂ and Liq showed that two Liq molecules and two Naq molecules were connected by Na-O-Na bond bridges to form （Liq·Naq）₂. Compared with Liq, （Liq·Naq）₂ exhibits stronger rigidity in planar molecular structure, larger steric hindrance and intermolecular distance, and much smaller molecular polarity, thus resulting in much longer fluorescence lifetime, much higher fluorescence quantum efficiency, wider energy bandgap and better film formability. When used as light-emitting layer in OLED, （Liq·Naq）₂ shows lower formation probability of excited dimmer and exciplex formation than Liq, thus emits bluer light with higher current efficiency than Liq. When （Liq·Naq）₂ ultrathin film is used as electron injection layer in OLED, it exhibits higher current density, higher luminance, lower turn-on voltage and higher current efficiency than Liq ultrathin film for the existence of sodium ions in （Liq·Naq）₂ ultrathin film.5. The summarization the relationship between molecular spatial structure and material performance of Alq₃, （Znq₂） and Liq, lead the conclusion that the molecular spatial structure of Mq_n affects its material performance in such aspects as the rigidity of planar molecular structure, intermolecular interaction, molecule stacking mode and intermolecular distance. On the base of this theory, the performance of different Mq_n molecules can be modified at molecular level by changing their molecular spatial structure in response to different requirement for material performance. This would open a new route for the research on Mqn performance modification.更多还原