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
| Autor: | Chung-Chieh Lee, 李中傑 |
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| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 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. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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