三咔唑與苯并咪唑雙極材料之合成、性質探討以及在磷光有機發光二極體之應用

Abstract

近年來，有機發光二極體元件中雙極主體(bipolar host) 發光層系統的研究正蓬勃發展，而提升電子與電洞在發光層的結合率是首要課題。因此在材料分子的設計上，期盼主體分子結構能夠整合電子與電洞傳導基團，使材料同時具備電子及電洞傳導特性。本篇論文利用三咔唑(Tricarbazole，3cbz)基團修飾在苯并咪唑(Benzimidazole)之C1-苯環及N1-苯環合成兩系列化合物。其中，在此雙偶極(bipolar)系統中，三咔唑(Tricarbazole，3cbz)具有高三重態能階之外，也具備傳電洞特性，而苯并咪唑(Benzimidazole)基團，則具備良好的電子注入特性。在分子設計上，使用碳-氮鍵結，能有更佳的電子雲正交分布效果，維持高三重態能階。我們也針對化合物的熱性質、光物理性質及電化學性質進行討論，結果顯示兩系列化合物均具有高玻璃轉換溫度(Tg＞175 °C)和出色的三重態能階(Et＞2.83 eV)。此外，也透過X-Ray單晶繞射進行晶體結構排列研究與探討。以三咔唑苯并咪唑化合物作為主發光體材料，摻混FIrpic應用在藍色磷光有機發光二極體元件製作。在元件初步優化後，測量結果顯示，化合物4-3cbzBIZ其在電荷密度為20 mA/cm2時驅動電壓為7.14 V、最大亮度為15220 cd/m2、電流效率為57.26 cd/A以及外部量子產率高達27.73 %。

Charge recombination efficiency of holes and electrons in an emitting layer of OLED is a critical factor that strongly determines the performance of the device. Therefore, integration of appropriate hole- and electron-transporting units in one molecule to form an ambipolar host becomes an important topic to study. In the present thesis, two series of ambipolar compounds based on tricarbazole (3cbz) substituted benzimidazole have been synthesized, in which the tricarbazole is C1- or N1-linked to the benzimidazole unit at different location. Tricarbazole is a well-known good hole-transporting moiety while the benzimidazole unit plays an important role in electron transporting materials. In this ambipolar system, perhaps due to the steric hindrance reasons, the hole-transporting tricarbazole (3cbz) and electron-transporting benzimidazole are expected to be orthogonally linked to each other so that their triplet energy can stay high in most of the molecules. Furthermore, their thermal properties, photophysical properties, and electrochemical properties have been carefully evaluated. Our results show that all of these compounds display not only a high glass transition temperature (Tg＞175 °C), but also a high triplet energy level (Et＞2.83 eV). We have utilized these molecules as the host materials for FIrpic-doped blue PhOLED devices. The compound 4-3cbzBIZ exhibits excellent performances with the turn on voltage of 7.14 V, a maximum luminance of 15220 cd/m2, a maximum current efficiency of 57.26 cd/A, and a maximum external quantum efficiency of 27.73 % after optimizing.