低單態及三重態能階差材料之設計、合成、鑑定與其有機發光二極體上之應用

Designs, Syntheses, Characterizations and Application of Small Singlet and Triplet Energy Gap Materials for Organic Light Emitting Diodes

李書瑋(Shu-Wei Li)

指導教授 ： 汪根欉

國立臺灣大學/理學院/化學研究所/博士(2018年)

https://doi.org/10.6342/NTU201800793

摘要

具有低單態及三重態能階差的有機材料，因其具有使用100%激子的潛力，近年來已經成為有機發光二極體(OLEDs)的主流。目前，主要有兩種方法設計具低單態及三重態能階差的有機材料，熱激活化延遲螢光(Thermal Activated Delayed Fluorescence, TADF)以及激發錯合物(Exciplex)。兩種皆利用分離分子中最高佔據分子軌域 (HOMO)及最低未佔分子軌域 (LUMO)來降低單態及三重態能階差。成功的分子設計再搭配適當的元件材層搭配，可使整體元件外部效率超過30%，因此成為近期OLED研究領域中的熱門題目。
在本論文中，藉由設計及合成一系列具有低單態及三重態能階差的有機芳香材料，並依照其特性應用於二代(PhOLEDs)或三代(TADF OLEDs)有機發光二極體的發光層中作為主體或客體材料。除了藉由光物理分析，了解分子的特性外，亦透過元件應用系統性的了解分子結構與元件效能之間的關係。各章節內容簡要如下：第一章簡述OLEDs的歷史、放光原理及機制；第二章介紹利用分子內激發錯合物的理念，設計PhOLEDs的主體材料並推測其放光機制；第三章論述兩個簡易合成且具有TADF特性的分子作為TADF OLEDs的主體材料，並進一步剖析如何透過分子拓樸影響其光物理特性，以達到高效率之TADF OLEDs；第四章介紹一系列以二甲基吖啶作為電子予體再與不同雜環之電子受體所共同組合之TADF放光材料，並藉由搭配適當的元件材層，達到高效率的TADF OLEDs元件表現；第五章以第四章的分子為雛形，引入更多電子聚集的吩噻嗪作為電子予體，設計出放光波段位於橘紅光的分子，此外，更利用吩噻嗪在基態同時具有兩種不同構型的特性，設計出具有TADF特性的單分子白光；第六章闡述藉由引用雙單鍵架橋的結構分離分子的HOMO及LUMO，藉由發展TADF以外之放光機制，設計及合成出具有短延遲螢光的藍光分子，期望藉此降低元件的延遲放光行為。

關鍵字

有機發光二極體

並列摘要

The molecules with small singlet and triplet energy gap (∆EST) are the mainstream of current OLEDs development due to their potential of utilizing 100% excitons. Nowadays, there are two main routes to design small ∆EST organic materials, Thermal Activated Delayed Fluorescence (TADF) and exciplex. Both strategies are in aim to separate distribution of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in order to further reduce ∆EST. The external quantum efficiency (EQE) can be reached above 30% by combination of adequate molecules with proper device’s fabrication. Therefore, it has been attractive to both academia and industries.
In this dissertation, we have designed and synthesized series of small singlet and triplet energy gap pure-organic aromatic molecules and introduced them into Phosphorescence OLEDs (PhOLEDs) and TADF OLEDs as either host or guest materials. The photophysical properties of molecules and the relationship between molecular structure and device’s performances were fully studied. The essence of every chapters are briefly introduced as follows. The 1st chapter provides an overview for the history, principle and emission mechanism of OLEDs. The 2nd chapter introduces a new type guest materials for PhOLEDs by using the strategy of intramolecular exciplex. The 3rd chapter describes two facile synthesized molecules with TADF character as host materials in TADF OLEDs. Moreover, the relationship between molecular topology and their photophysical properties was investigated to elucidate high efficiency TADF OLEDs. The 4th chapter introduces a series of TADF emitters by using dimethylacridine as donor moiety and combination with various heteroaromatic as acceptor moiety. The extremely high efficiency TADF OLEDs can be achieved by introducing these material as emitter with proper device fabrication. The 5th chapter depicts the orange-red emissive TADF molecules, which change their donor moiety from dimethylacridine to phenothiazine to increase its electron-donating ability from the molecules in chapter 4. In addition, by using two conformers of phenothiazine, the single white light emission molecule was achieved. The 6th chapter illuminates short delay lifetime blue emitting materials beyond TADF mechanism by using two-bridged connection to separate the HOMO and LUMO. The short delay lifetime of emitters can further reduce the afterimage of devices.

並列關鍵字

Organic light emitting diodes

參考文獻

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