新型熱延遲螢光分子和雙極性主體材料的設計、合成與其在有機發光二極體之應用

Abstract

近年來，有機發光二極體(Organic Light-Emitting Diodes，OLEDs)廣泛的應用在照明和顯示螢幕上，目前學術上對於能夠有效利用100%激子又可避免使用貴重過渡金屬的熱激活化延遲螢光 (Thermal Activated Delayed Fluorescent, TADF)材料作為發光材料的OLEDs有顯著的研究興趣。TADF 發光材料的單重態 (S1) 和三重態 (T1) 之間的能階差 (ΔEST) 很小，使其可以獲取電致激發過程中所生成的三重態激子經由反向系統間跨越 (RISC)回到單重態放出延遲螢光，進而達到100%的激子利用率。 在本論文中，我們設計與合成一系列具有小的單重態及三重態能階差的分子，應用於第三代有機發光二極體的發光層中作為放光體以及雙極性(D-A)主體材料。透過光物理分析及元件應用，探討分子結構、特性與元件效能之間的關係。各章節內容簡要如下：第一部分，主要概括有機電致發光元件的簡介、發光原理與機制；第二章，開發十個新型態雙極性分子作為TADF發光材料潛力的研究以及探討，其中兩個修改已知具有TADF特性的咔唑-鄰苯二甲腈衍生物作為發光材料4CzIPN-1-CF3和2CzTPN，並且搭配主客體系統以及混合式主體系統開發出綠光以及藍光TADF-OLED元件。另外具有六員環電子予體的NPAc和NPAb也同樣具有TADF性質，期許後續置作成OLED元件能有不錯表現。其餘六個D-A分子雖不具TADF行為，能然可以做為OLED元件中主體材料使用；第三章，探討不同鍵結型態的D-A分子作為TADF OLED的主體材料的性質以及光物理分析，在電子予體引入咔唑或二苯胺與電子受體二氮雜萘合成出具有鄰、間和對位的D-A分子探討其鍵結型態對光物理特性以及搭配TADF發光材料之影響，同時搭配已知的TADF發光材料作為OLED元件的表現探討；第四章，介紹一系列具有較高水平偶極比率(horizontal dipole ratio)的長形分子作為TADF放光材料，比較以苯環、吡啶及嘧啶作為D-A之間的架橋對於TADF放光行為以及對水平偶極比率的影響。

The molecules with small singlet and triplet energy gap (ΔEST) and thermal activated delayed fluorescence (TADF) character are the mainstream of current OLEDs development due to their potential of utilizing 100% exciton. The molecular design strategies are in aim to separate distribution of HOMO and LUMO in order to reduce the exchange energy. In first part of this dissertation, we generally introduce the basic principle and development of organic light-emitting diodes (OLEDs). Second, we design and synthesis ten bipolar molecules, among them, two CzPN type TADF emitters according to literature, the external quantum efficiency (EQE) of CzPN-based TADF-OLED with proper device fabrication could reach 21.6%. Furthermore, we introduce exciplex-based host material to improve the efficiency and reduce the efficiency roll-off. Another two bipolar molecules consisted of electron-withdrawing triphenyltiazene/NP as acceptor and commonly used electron-donating dimethylacridine/mesitylazaborine derivatives as donor were synthesized and evaluated their TADF potential by transient photoluminescence. According to the TRPL analysis, NPAc and NPAb seems to have TADF feature. Although the other six molecules exhibit no TADF behavior, they still can be employed as bipolar host materials in OLEDs. Third, a series of bipolar host materials composed of electron-transporting naphthyridine (NP) and phenylene bridge with ortho- ,meta-, and para-substituted hole-transporting carbazole (Cz)/diphenylamine (Da) were synthesized and characterized. By adjusting the linkage topology, the physical properties are subtly tuned. The characteristics of devices employing these new bipolar hosts with green TADF emitter 4CzIPN employed as emitter were investigated under the same device structure. The last part, we design six sticklike molecules to enhance the horizontal dipole moment ratio and devices out coupling factor.