有機大環分子於熱激活化延遲螢光材料之設計、合成 與元件應用

Abstract

近年來，有機發光材料發展蓬勃，目前已發展至第三代熱激活化延遲螢光材料(Thermally activated delayed fluorescence, TADF)。第二代磷光材料利用有機金屬錯合物放出磷光，但由於銥及鉑金屬的稀有性極高，使同樣具備回收三重態激子且擁有100% 之內部量子效率的純有機TADF成為替代方案。TADF材料主要分為兩種，一種是單分子TADF，透過分子的設計使單態/三重態能階縮小，並以熱活化的方式有效利用三重態激子；另一種是將電子予體和電子受體進行物理性混摻，並藉由分子間電荷轉移生成激發錯合物。雖然激發活化錯合物具備設計合成方便和能階調控等優勢，但相較於單分子的TADF分子，其放光效率會受限於電子予體和電子受體之介面作用，因此發展高效率的TADF系統仍需做進一步的研究與探討。 本論文中主要合成有機大環結構，作為TADF發光材料上的應用。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，概括有機電致發光元件之發光原理與運作機制；第二章則是論述如何透過分子結構的設計，提升單分子TADF的放光效率，其中又分成三小節 (1)以分子c-MeNS探討D-A分子在大環結構中對TADF的性質影響。(2)透過含二苯胺之大環電子予體，並以具備較高LUMO與較高T1能階之BO-MR作為電子受體，設計且合成出兩個具備極小ΔEST與極高PLQY表現的深藍光TADF放光材料，c-NN-BOtBu和c-NN-BOtBu-Tol。(3)以大環架構設計出具有透過空間電荷轉移性質的TADF放光材料；第三章則是設計與合成相似結構之大環電子予體c-NN、c-ON和電子受體c-SS，並根據其結果分為兩部份 (1)大環D/A在共晶上的研究以及激發錯合物的初測，結果表明以相同結構之大環D/A在高效激發錯合物的生成策略上仍顯不足。 (2)以大環電子予體搭配PO-T2T於激發活化錯合物的應用及後續元件性質探討。

In recent years, the development of organic light-emitting materials has been flourishing. Thermally activated delayed fluorescence (TADF) materials have been gaining more attentions than the phosphorescent emitters because TADF materials are of numerous advantages such as, all-organic, low-cost, and could harvest both the electro-generated singlet and triplet excitons to achieve 100% internal quantum efficiency. The TADF materials can be mainly classified into two categories. The first is intramolecular charge-transfer type TADF, which is using molecular design strategy to reduce the energy gap between singlet and triplet states and thus the triplet excitons can up-convert to emissive singlet state through effective reverse intersystem crossing (RISC) process. The second is intermolecular charge-transfer type TADF which involves the physical blending of selective electron donors and acceptors, forming exciplex TADF emission when either donors or acceptors are excited. Although exciplex is of several advantages such as simplified syntheric procedures and high energy level tunability, their emission efficiencies are largely affected by the contact interface between the electron donor and acceptor. Therefore, developing highly efficient TADF systems still requires further research and investigation. This study primarily focuses on synthesizing organic macrocyclic structures and their application as TADF emitter. Their photophysical properties and device applications were 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 enhancing the emissive efficiency of intramolecular charge-transfer type TADF through molecular structure design. It is divided into three subsections: (1) Investigating the influence of macrocyclic structures on the development of D-A molecules, c-MeNS, as TADF emitters. (2) Designing and synthesizing two deep-blue TADF emitters, c-NN-BOtBu and c-NN-BOtBu-Tol. These emitters are incorporated with diphenylamine-based macrocyclic donors and acceptor with high LUMO and high T1 energy level (BO-MR). Both of them exhibit a small ΔEST and high PLQY. (3) Using macrocyclic structures to design TADF emitter with spatial charge transfer properties. The third chapter, similar macrocyclic structure are designed and synthesized, where c-NN and c-ON is electron donor and c-SS is electron acceptor. This chapter is divided into two parts: (1) Studying the co-crystallization behavior of macrocyclic D/A systems and initial measurements of exciplex formation. The results show that the limitations in achieving efficient exciplex formation using similar macrocyclic D/A structures. (2) Investigating the application of exciplex, which is using macrocyclic electron donor to combinate with electron acceptor PO-T2T.