新型綠光摻雜物的合成及其在有機電激發光上的應用

Abstract

Coumarin-6是著名的綠光雷射染料，也是最早使用在有機電激發光(OLED)元件上之綠色摻雜物(dopant)之一，其最大放射波峰位置在510 nm。在顯示器應用上，若分子的放射波峰能再偏向紅位移，會更趨近於理想綠光。為了改善其發光顏色及量子效率，文獻中曾提及的方法之一便是在coumarin環第七個碳的位置上以julolidine環化取代。此類型的coumarin卻因立體障礙不足導致分子間的聚集（aggregate），在長波長位置容易形成波肩（shoulder）現象，改善此波肩現象方法之一便是增加分子間的立體障礙，並利用立體障礙來降低因濃度效應所引起的自我驟熄現象。 本論文第一部份是針對如何增加立體障礙的主題，設計並試著去合成此一分子，10-(3,3-Dimethyl-3H-2-indolyl)-1,1,7,7-tetra- methyl-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrido- [3,2,1-ij]quinolin-11-one，然而關鍵的中間產物，Ethyl 2-(3,3- dimethyl-3H-2-indolyl)acetate，因為互變異構性的因素，傾向較穩定的結構，Ethyl 2-(3,3-dimethyl-2,3-dihydro-1H-2-indolyl- idenyl)acetate，經我們嘗試不同的反應條件，依然無法依循原設計的路徑環化，所以在考慮關鍵的中間物性質後，在此論文中我們建議了另一條合成路徑。 本論文第二部份的構想是利用在藍光多分子PF8的兩端以末端接蓋(end capping)的方式，設計與合成功能性綠光摻雜物(C-545TPhBr)，並研究其能量轉移的效果。為了保持多分子原有光色，我們設計摻雜物的構型來截斷主鏈多分子與摻雜物間的共軛連續性，卻因為摻雜物上原本設計用來截斷連續共軛的苯環會旋轉消耗能量，致使螢光強度下降許多，而未能得到預期的效果。如何設計與合成立體障礙來防止苯環的旋轉，應該是本計畫未來研究的目標。

Coumarin-6 is one of the well-known green laser dyes which has a fluorescence emission peaked around 510 nm. For display application, it is desirable to have a green emission slightly shifted to the red. This can be achieved by substituting a julolidyl moiety at the C-7 position of coumarin ring. But, most of these emissions tend to shift further to the red at high concentration due to molecular aggregation. One of the ways to alleviate this concentration broadening effect is to increase the steric bulkiness of the dye. Part I of the thesis deals with the design and attempted synthesis toward one such sterically bulky molecule, 10-(3,3-dimethyl-3H-2-indol- yl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrid-o[3,2,1-ij]quinolin-11-one. In the synthesis of the target compound, the intermediate, ethyl 2-(3,3-dimethyl-2,3-dihydro-1H-2-indolylidenyl)acet- ate, was tautomerized to the more stable form, ethyl 2-(3,3-dimethyl-2,3- dihydro-1H-2-indolylidenyl)acetate. Although tried with many different conditions, it did not lead to the compound as expected. This result led us to propose another synthetic scheme which might circumvent the tautomerism problem. Part II of the thesis is focused on the design and synthesis of a new functionalized green fluorescent coumarin (C-545TPhBr), for the purpose of end capping the PF8 blue fluorescent polymer to study its energy transfer. In order to maintain the emissive characteristics of the host polymer, the conjugation between the dopant molecule and the polymer has to be disrupted. Unfortunately, free rotation of the phenyl group on the designed molecule led to a much reduced fluorescence emission. Introduction of substituent to prevent free rotation of the phenyl group is proposal for enhancing the fluorescence quantum efficiency of this new dopant.