- 學位論文
有機熱激活化延遲螢光材料之設計、合成與元件應用
Design, Synthesis and Device Application of Organic TADF Materials
摘要
近年來，熱激活化延遲螢光 (Thermal Activated Delayed Fluorescent, TADF) 材料比磷光材料更受矚目，因為不需要使用到昂貴的重金屬元素，且同時可以獲取電致激發過程中所生成的單態和三重態激子。由於TADF材料的單態 (S1) 和三重態 (T1) 之間的能階差 (ΔEST) 很小，三重態激子能夠有效地經反向系統間跨越 (RISC) 上轉換成為單態激子而放出延遲螢光。因此，有機發光二極體使用TADF作為放光體也具有與磷光材料一樣實現100%內部量子效率的潛力。 在本論文中，主要設計與合成一系列具有小的單態及三重態能階差的TADF分子，並應用於第三代有機發光二極體的發光層中作為放光體。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：第一章，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，論述如何透過分子結構的微調設計出藍光TADF分子，並且搭配新穎的混合式主體系統創造出藍光TADF有機發光二極體的元件；第三章，探討D-A類型的TADF分子中，在電子予體的鄰位引入具有立體障礙的苯基對於分子構型及與電子受體之間的影響，進而反應出不同的熱激活化延遲螢光的行為；第四章，引入非共軛系統的架橋去連接電子予體和電子受軆以分離最高佔據的分子軌域 (HOMO) 和最低未佔據的分子軌域 (LUMO) ，設計出具有透過空間電荷轉移性質的TADF分子，及其應用在有機發光二極體的元件；第五章，介紹一系列以吡啶及嘧啶作為D-A類型之間的架橋去增強拉電子能力，進而提升分子內電荷轉移的行為。這些分子展現明顯的TADF特徵，由於他們單態與三重態之間的能階差很小，最終達到高效率的有機發光二極體元件。
並列摘要
In recent years, thermally activated delayed fluorescence (TADF) materials have been gaining more attentions than the phosphorescent emitters because all-organic low-cost materials can also harvest both the electro-generated singlet and triplet excitons. The triplet excitons can up-convert into emissive singlet excitions through effective reverse intersystem crossing (RISC) process due to a small energy gap (∆EST) between the singlet state (S1) and triplet state (T1). Thus, similar as the phosphorescent materials, OLED employing TADF emitters also possess the ability to achieve 100% internal quantum efficiency. The main attribute in this dissertation are design and synthesis of the series TADF molecules with a small energy gap between singlet state and triplet state as emitting materials for third-generation OLEDs. Their photophysical properties and device applications were fully studied to explore the relationship between molecular structures, characteristics and device performances. The essence of each chapters are briefly introduced as follows. The first chapter provides an overview of organic electroluminescent device, the emission principle and mechanism of OLEDs. The second chapter focuses on the structure manipulation to design the newly TADF emitters. These new molecules are then introduced to the novel co-host system rendering blue TADF based devices. The third chapter explores the D-A type TADF molecules with a phenyl group introduced at the ortho position of donor, which is used to probe the effects of the congested aryl substitution on the molecular conformation and electronic coupling toward the acceptor core, as well as TADF behavior. The fourth chapter illuminates the concept of designing molecules with through-space charge transfer characteristic by introducing non-conjugated moiety as a bridge to connect the electron donor and acceptor. The non-conjugated D-A molecules would lead to small overlap of HOMO and LUMO and result in a small ∆EST. The through-space charge transfer TADF emitter can be further applied in OLED devices with better performance. The fifth chapter introduces a series of TADF molecules by applying pyridine and pyrimidine as π-bridge to increase electron-withdrawing ability, furthermore, enhance intramolecular charge transfer behavior. These molecules exhibit significant TADF character due to their small ∆EST. Finally, high efficiency TADF OLEDs are achieved by pyridine and pyrimidine based TADF molecules as emitters.