利用碘化銅催化碳-氧鍵耦合反應於樹枝狀氮-苯基咔唑衍生物之合成、性質探討及其在電致磷光發光二極體上的應用

Utilizing Copper Iodide Catalyzed C-O Coupling Reactions in the Synthesis of Dendritic N-Phenylcarbazole derivatives, Their Physical Properties and Applications in Electrophosphorescent Light Emitting Devices

李中傑(Chung-Chieh Lee)

指導教授 ： 梁文傑

國立臺灣大學/理學院/化學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.01812

摘要

在本論文中，我們合成了一系列樹枝狀氧鏈氮-苯基咔唑衍生物。藉由紫外光吸收光譜、光致放光光譜等光物理測量，與循環伏安法、差式脈衝伏安法等電化學量測，對此系列之化合物性質進行詳細探討。在電化學的測量中，我們發現此樹枝狀氧鏈氮-苯基咔唑化合物，具有由內(核心)向外逐漸提高的氧化電位梯度。在光物理性質的探討中，發現以氧原子為鏈結，會打斷各苯基咔唑單元間之共軛，使得此系列化合物具有較高的最高佔有軌域(HOMO)與三重態能量。因此，進一步將其應用於電致磷光元件之主體材料，發現有良好的元件特性。最大電流效率可達24.7 cd/A 。值得一提的是，在此最大電流效率時之亮度高達 484 cd/m2。
另一方面，我們也合成了樹枝狀氧鏈氮-苯基咔唑的銥錯合物，對其光物理與電化學性質進行探討，並將其應用於電致磷光元件之客體發光材料。結果發現，不同代數的銥錯合物(Ir-G1 and Ir-G2)，擁有相近的最大電流效率。其中第二代銥錯合物(Ir-G2)最大電流效率可達14.3 cd/A，在此最大電流效率時之亮度高達 981 cd/m2。

關鍵字

咔唑 ； 碳-氧鍵耦合 ； 磷光 ； 發光二極體

並列摘要

A series of novel oxygen-linked N-phenyl-carbazole (NPC) dendritic wedges (3-5) and triphenylamine-centered dendrimers (CBD-G0 to G2) have been synthesized and extensively studied. The aryl-oxygen-aryl (Ar-O-Ar) linkages were established on 3,6-positions of carbazole and 4-position of N-phenyl group. The analyses of UV-Vis spectra revealed that the Ar-O-Ar linkage would break down the π conjugation and make NPC units manifest their individual absorption peaks. The photoluminescent properties were characterized by steady-state luminescence spectroscopy both at room temperature and 77K in THF. The low-temperature fluorescence decay time was determined by time-resolved fluorescence spectroscopy at 77K. The results suggested that the energy transfer from the carbazole wedges to the triphenylamine core operates so that the luminescence mainly arises from the core unit and exhibits much shorter lifetime. However, quenching of the emission from carbazole wedges by the TPA core might become less effective as the generation grows up to CBD-G2. From the measurements of the oxidation potentials of the NPC derivatives, the mesomeric electron-donating effect of the oxygen atom and inductive electron-withdrawing effect of the carbazole unit were revealed. The potential gradient could be established on those triphenylamine-centered dendrimers (CBD-G1 and CBD-G2) such that the outer layer is electron-poor and the inner layer is electron-rich. Overall, with this novel Ar-O-Ar linkage, the NPC dendrimers demonstrated intriguing physical properties. It is worth to mention that the HOMO level of the NPC dendrimers could be obtained as high as -5.14 eV and triplet energy level could be kept above 2.8 eV. Therefore, these NPC dendrimers with good thermal stability and compatibility of solution processing are potential host materials for blue triplet emitters. The FIrpic based electrophosphorescent devices were fabricated and maximum luminous efficiency could be achieved up to 24.7 cd/A at 484 cd/m2.
In addition, two dendritic iridium complexes (Ir-G1 and Ir-G2), which are linked with NPC dendritic wedges, are synthesized. The photophysical and electrochemical properties have been extensively studied. The devices utilized these complexes as triplet emitters were fabricated. In conclusion, Ir-G2 devices do not show superior performance over Ir-G1 devices. Both of them show similar current efficiency. This coincided with previous results in PVK+ETMs devices. The maximum current efficiency of 13.3 cd/A at 411 cd/m2 could be obtained by Ir-G1 in CBD-G2 host. The maximum current efficiency of 14.3 cd/A at 981 cd/m2 could be achieved by Ir-G2 in CBD-G2 host. It is noteworthy Ir-G2 provides better color stability than FIrPic and Ir-G1.
The dendritic effects on turn-on voltages could be found in PVK based devices. Ir-G2 doped device exhibits the higher charge injection barrier and turn-on voltage than FIrPic doped device, which is not observed in Ir-G1 doped device. In CBD-G2 based devices, such dendritic effects on turn-on voltages might be leveled off.

並列關鍵字

carbazole ； C-O coupling ； phosphorescence ； OLED

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