喹喔啉/二苯基笏及順式二苯乙烯/笏之雙重鄰位混成系統在光電材料上的應用

Doubly Ortho-Linked Quinoxaline/Diphenylfluorene and cis-Stilbene/Fluorene Hybrids for Optoelectronic Applications

魏屹(Wei Yi)

指導教授 ： 陳建添

國立臺灣師範大學/理學院/化學系/博士(2008年)

摘要

有機電激發光二極體技術在近20年來蓬勃發展，對於多功能性的偶極與雙極型材料的追尋更是近幾年來的熱門研究重點。
本實驗室過去已先後發展出喹喔啉/三芳香胺與喹喔啉/二苯基笏之雙重鄰位混成系統，並成功地將它們拿來作為偶極型有機電激發光二極體材料使用。在本論文中，我們先藉由改變原先分子的設計概念，將三芳香胺片段與喹喔啉基板在不同位置上進行組裝後得到具有雙重偶極性的高效能黃光材料，也因此只要透過系統化的合成方式，再與適當片段進行最後的組裝之後便能調整喹喔啉/二苯基笏雙重鄰位混成體的發光，使其成為藍、綠、黃、紅等各種重要顏色的材料；除此之外，以類似分子結構作為配子的金屬銥鉗合物也成功地被合成，並被預期會是效率良好的紅光磷光性材料。
另一方面由於極易產生光異構化現象的因素，導致不同的二苯乙烯衍生物分子雖然早已被報導具有相當高的螢光量子產率，但卻鮮少被應用來作為有機電激發光二極體材料，但在新的分子設計概念下，其構形將可藉由旋環笏片段加以被固定—如此一來在順式二苯乙烯/笏之雙重鄰位混成系統當中將可避免上述現象的發生。在分別與不同電子施體和受體的片段進行組裝之後，我們先是成功地發展出高效率的非摻雜型藍光發光材料，其外部螢光量子產率皆介於5.19-8.74 %之間，這一類偶極型材料同時也具備電洞的傳輸功能；接著相同的基板結構也被應用於其他客體摻雜物與主體材料的設計上，都已有初步的結果。
最後在關於電激發光機制的探討當中，我們藉由脈衝輻射技術來對實驗室已發展的偶極型材料分子進行系統性之研究，並發現它們的脈衝輻射實驗結果與其有機電激發光二極體元件的效能表現之間可以找出關聯—首先，這些分子的電荷傳輸能力與其瞬時吸收光譜的半生期呈現正向的關聯性，因此除了對其電荷移動率直接進行測量之外，脈衝輻射技術則提供了另外一個方法來對偶極型與雙極型材料分子必須具備的電荷傳輸能力加以檢驗；除此之外，在脈衝輻射實驗中所觀察到的瞬時放射光譜結果同樣可以用來對材料分子在元件中的電激發光行為進行評估與分析，它們的瞬時放射光譜與相對應的發光強度分別與其在元件中的電激發光光譜與外部螢光量子產率展現出絕對的正相關性；而在經過整理之後，上述偶極型材料分子在元件中的電激發光機制也已利用脈衝輻射實驗予以確認，在其電子與電洞再結合的過程當中，根據分子去定域化能力的不同而產生了不同形式的分子交互作用，也導致其電激發光機制略有不同。
總結以上的研究成果，希望它們提供了一個更明確的方向，有助於大家進行關於偶極與雙極型材料分子之設計與研究。

關鍵字

有激電機發光二極體 ； 脈衝輻射 ； 偶極 ； 雙極

並列摘要

The development of organic light-emitting diodes (OLEDs) has been investigated because of its widel use in flat-panel display technology in the past two decades. Of all the fluorescent materials, dipolar molecule with charge transporting function in the device was focused in recent years. Moreover, the further bipolar material for single-layered device was newly reported.
The applicaions of “quinoxlaine/triphenylamine hydrids” was first reported in our lab in 2005. Furthermore, dipolar “quinoxaline/diphenylfluorene hybrids” as efficiently fluorescence chameleons in OLEDs was then developed by us, too. Based on the concepts, extended molecular design of combining triarylamine units with quinoxaline/ diphenylfluorene backbone leads to yellow-emitting material with comparable electorluminance (EL) efficiencies and makes them become color tuneable in full range. Beside these fluorescent materials, Ir-complexes by using quinoxaline/diphenylfluorene or pyrazine/diphenylfluorene hybrids as cyclomatalating ligands were also investigated as red phosphorescent materials and their devices performance will be examined.
On the other hand, the excellent fluorescent quantum yields of stilbene derivatives have been reported but rarely used in OLEDs because of their easy photo-isomerization in nature. One may come up with a new molecule design by linking cis-stilbene moiety with fluorene damper to prevent such undesired behavior. The highly efficient, blue-emitting fluorescence materials were first realized. Moreover, the electron donor/acceptor fragments were combined with the central cis-stilbene core for further applicated to host and dopant materials. On the other hand, some key elements for advanced molecule design of bipolar materials may be consolidated.
Finally, those materials developed by ourselves were investigated by using pulse radiolysis (PR) technique. Some relations were shown between their PR results and the features of OLEDs displays after complete examinations. First of all, the experiments for transient absorption studies were carried out. The charge transporting behaviors of one given molecule are used to be measured by its charge mobilities, however, the transient absorption half-lives may provide us another approach to judge these behaviors for dipolar/bipolar molecules. On the other hand, the transient emission profiles for such molecules and their related intensities are also comparable to their EL profiles and efficiencies, respectively. Based on these observations, they are possible to be predicted in advance.
Moreover, the EL mechanism after charge recombinations for above materials in OLEDs could be understood by PR studies, too. In the former “quinoxaline/diphenylfluorene hybrids” system, the electron donating properties were effected by the substituents at C5 and C8 positions of each quinoxaline moiety and the processes were then proposed to be different even though these molecules have similar structures. On the other hand, it is supposed to be the same at the later “cis-stilbene/fluorine hybrids” system.
In conclusions, we would like to gain some insights to the molecule design for dipoar/bipolar materials in OLEDs. Moreover, it is suggested the use of PR technique in predicting parts of their features in OLEDs in the near future.

並列關鍵字

OLED ； Pulse Radiolysis ； dipolar ； bipolar

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(48) (a) 由於材料在真空與溶液狀態中所測的之HOMO能階值仍有些許不同，因此本論文中所有材料之HOMO能階值係經由與文獻報導中NPB在真空與二氯甲烷溶液中利用循環伏安分析實驗所測得的氧化電位值交互比對後而決定。 (b) Zhang, Q.; Chen, J.; Cheng, Y.; Wang, L.; Ma, D.; Jing X.; Wang, F. J. Mater. Chem., 2004, 14, 895.