以嘧啶、吡啶及三嗪為主體之電子傳輸層材料設計、合成與元件應用

Abstract

近年來，具熱激活化延遲螢光 (Thermally Activated Delayed fluorescence, TADF) 分子慢慢受到矚目，因其不需使用到昂貴的稀有金屬又對環境友善，所以比磷光分子更受到大家關注。然而，傳統的TADF分子是運用分子內的電荷轉移來達到放光的效果，所以在分子設計上相對困難。在近期，科學家發展出了以物理性混摻的方式創造出激發錯合物以達到放光的效果，因其電子予體和電子受體可以分開設計，所以使合成步驟大大的簡化。另外，激發錯合物具有很小的單重態和三重態能量差，一樣具有熱激活化螢光的現象。 在本論文中主要設計與合成一系列具有良好的電子注入能力的電子傳輸材料，並與適當的電子予體搭配運用於激發錯合體上。並將新的激發錯合體當作放光層或者主層材料。透過光物理分析及元件應用，探討分子結構、特性與元件的效能之間的關係。第一部分和第二部分分別為以嘧啶和吡啶為核心，並在2,4,6取代的苯環間位上引入強拉電子基團 (包括吡啶、嘧啶、氰基、吡唑與磷氧官能基) 去減少分子間的π共軛，合成出一系列的星狀電子傳輸型材料。並透過引入缺電子性的基團，使得這些材料展現出良好的電子注入能力與電子傳輸性質。 而第三部分為保留原有的嘧啶為中心，在2號位置分別引入苯環和吡啶，並且從原本的星狀分子變成線狀分子，希望藉由提高水平方向的躍遷偶極，進而提高整體元件的出光率，使元件效率可以提高。 第四部份為以1,3,5-三嗪為核心，並且只在2號取代的苯環的兩個間位上引入強拉電子基團，探討分別引入氯原子和氰基之後的差別，另外，分別引入不同的拉電子性基團，藉由拉電子性基團去提升整體的電子傳輸效率。此四個部分的電子傳輸材料分別選用適當的電洞傳輸層進行搭配，探討形成激發錯合物的效率並將其運用在發光層或主層材料上。

In recent years, Thermal Activated Delayed fluorescence, TADF materials have attracted the scientist’s attention gradually. It is environmental-friendly and no need to use rarely-heavy metal. That’s why we’re more focusing on the TADF materials than the phosphorescent emitters. The synthetic process of traditional TADF is difficult because it emit light by intramolecular charge transfer. Recently, scientist developed a new way to emit the light with exciplex, which is made by mixing electron donor and acceptor. This synthetic process is more simple than traditional one since the electron donor and acceptor can be designed and synthesized separately. On the other hand, the exciplex contain small energy gap between the singlet state and the triplet state, so it also shows the phenomenon of Thermal Activated Delayed Fluorescence. The main purpose of this thesis are designing and synthesizing a series of electron transporting materials with good injection ability. We chose the appropriate electron donor to produce the exciplex and serve as emitting layer and host materials. We probed the device efficiency between the molecular structure and molecular character via photo-physical analysis and application of device. In the first and second chapter, we synthesized a series of star shape electron transporting materials. These materials are comprised of pyrimidine and pyridine as the building block respectively, and combined different electron-withdrawing groups such as pyrimidine, pyridine, benzonitrile, pyrazole and the phosphine oxide at meta-position to break their π conjugation. By introducing the electron-withdrawing groups, these materials displayed excellent electron injection and transporting capability. In the third chapter, we kept the pyrimidine as core and introduced benzene and pyridine at the 2 position, and also change the shape from star to linear. We expect that raised the horizontal dipole would lead to increase light out-coupling of device, thus enhancing the efficiency of device. In the last chapter, we selected the 2,4,6-triphenyl-1,3,5-triazine as core structure and then introduced different electron-withdrawing groups at meta-meta position on one of the benzene. In the first section, we compared the different properties between introducting of chloride and cyano. In the second section, we introduced different electron-withdrawing groups to improve the electron-transporting mobility. For these four chapters we selected appropriate hole-transporting materials to arrange in pairs with the electron-transporting materials. We discussed the performance of forming exciplex, then applied it on emitting layer and host materials.