Synthesis, Properties, and Applications of Pure-hydrocarbon and Bipolar Host Materials For Electrophosphorescent Devices

本論文總共分為兩部分，在第一部分我們設計出一系列以茚芴為主並具有適合三重態能階的純碳氫主體材料，可將其應用於綠光和紅光電致磷光元件。在設計概念上，我們引入芳香環和環旋芴基於茚芴中，藉由這些立體障礙基團可以減少分子間作用力使聚集和活化雙體的情形有效減少，不僅可減少在元件上放光不純的行為，也可使熱性質和成膜性上升。另外在InDSF中，我們可以發現苯環和芴基間的距離為3.29 Å，已足以產生分子內的π-π作用力。以InDSF做為主體材料應用在綠光元件時外量子效率可達到17.6%，而InF3tt及ITS做為主體材料在紅光元件效率上可分別達到19.2% 及17.3%。在論文第一部份中將深入探討這三個純碳氫材料的物理性質、晶體結構和元件效能。在第二部分中我們將缺電子的benzimidazole和推電子的indolocarbazole結合，利用Donor-Acceptor的概念合成出TICCBI及TICNBI這兩個雙極性材料。Indolocarbazole本身具有良好的電洞傳輸能力，且其剛硬的結構使螢光有高量子效率，而benzimidazole可做為立體障礙基團使分子間減少堆疊，也同時提升了熱穩定性。過去常使用Fischer indolization進行indolocarbazole的合成，但常常會有產物難以純化及反應時間過長的問題，所以我們改用indole、甲醛和triethoxymethane進行脫水環化的反應，這個方法不僅可以節省反應時間，也可有非常高的產率。而TICNBI及TICCBI做為主體材料應用在磷光元件上表現相當好，尤其TICNBI在紅光和綠光元件上分別具有22%及16.2%的外部放光效率。There are two parts of this thesis. In the first part, we designed and synthesized a series of pure hydrocarbon host materials which exhibit suitable triplet energy levels for green and red phosphorescent OLED. In the molecular design, we combine aromatic rings and fluorenes to the indenofluorene core through spiro-linkage. By means of increasing steric hindrance in indenofluorene, we can prevent intermolecular interaction such as π-aggregates and excimer formation which may cause an additional emission band and a decrease in electroluminescence; therefore, thermal and morphological stability can be enhanced. The distance between phenyl and fluorene in InDSF is 3.29 Å, suggesting sufficient intramolecular π-π interaction. Devices incorporating with InDSF, InF3-tt, and ITS doped with Os or Ir complexes emitters as host materials showed the maximum EL quantum efficiency of 17.6%, 19.2% and 17.3% for electrophosphorescence, respectively. In this thesis, we will report the physical properties, X-ray structures, and device characteristics.In the second part, we synthesized the bipolar host materials combining electron-withdrawing benzimidazole and electron-donating indolocarbazole. Instead of using Fischer indolization which would lead to a mixture of products, we unitized condensation reaction of indole, formaldehyde, and triethoxymethane. This new synthetic route was not only time-saving but also with high yield for indolocarbazole. High performance of PhOLEDs have been reached with TICCBI and TICNBI as host materials. Among the devices, TICNBI-based device shows the maximum EL quantum efficiency of 22% and 16.2% for red and green electrophosphorescence, respectively