對位苯系高分子之結構與光電行為的關係以及單一共軛高分子鏈的構形之研究

Studies of poly(para-phenylene)s on their structures and properties relationships and of characterization on conformation of single conjugated polymer chain

蕭安恩(An-En Hsiao)

指導教授 ： 陳壽安 博士

國立清華大學/工學院/化學工程學系/碩士(2007年)

摘要

本論文包含兩部分。第ㄧ部分為改善Yamamoto聚合方法以得高分子量之聚對位苯系高分子與探討其結構和光電行為。聚對位苯系高分子應用於發光二極體及光電池元件中,具有深藍色螢光性質。目前合成聚對位苯系高分子,主要有Suzuki polycondensation 和 Yamamoto polycondensation。 Suzuki聚合方式雖然比Yamamoto聚合方法得到較高分子量,不過所需單體(指硼酸酯結構)合成麻煩。為了改善Yamamoto聚合方法,本研究首先探討兩種聚對位苯系高分子之單體:含碘結構單體1,4-diiodo-2,5-bis(octyloxy)benzene與含溴結構單體1,4-dibromo-2,5-bis(octyloxy)benzene,進行Yamamoto聚合反應。含碘結構單體無法有效聚合, 所得分子量皆小於5,000 daltons。而含溴結構單體隨著濃度增加,對於分子量有明顯上升的趨勢。當濃度提升至0.3M時,反應時有高分子析出,得到最高分子量五萬五已是極限。為了解決在高的反應濃度,使高分子析出之問題,將Yamamoto反應溶劑改成四氫呋喃(THF),利用其對於Ni觸媒與高分子皆有好的溶解性, 能有效提升聚合反應性。在濃度為0.28 M時,得到最高分子量約十七萬,且所得分子量分布指數(polydispersity index，簡稱PDI)皆可小於2.5。
利用上述的聚合條件,我們合成出三種高分子量之聚對位苯系高分子:側鏈含烷氧基之雙取代聚對位苯系高分子(DR8O-PPP),單取代聚對位苯系高分子(mR8O-PPP),以及側鏈含Carbazole基團之雙取代聚對位苯系高分子(Cz-PPP)。我們以光譜分析(UV-Vis、PL、CV,以及XRD)來探討其結構與物性之關係。在XRD光譜中,在2θ約3.42度,DR8O-PPP比其他兩種高分子有一個明顯的特徵峰, 表示DR8O-PPP結晶程度較其他兩種高; mR8O-PPP並沒有明顯的特徵峰,表示高分子結晶程度小,而Cz-PPP完全沒有特徵峰,即為amorphous狀態。且DR8O-PPP與mR8O-PPP在固態薄膜下,其PL光譜與溶液態相比,皆有明顯紅移現象, DR8O-PPP紅移44 nm, mR8O-PPP紅移12 nm, Cz-PPP則與溶液態相同為399 nm。測其改變不同濃度下之PLE光譜可知, 高濃度下在長波長處的強度有增強的趨勢, 此為集聚體(aggregates)造成PL光譜紅移。可知聚對位苯系高分子,其側鏈引入長碳鏈,使分子側鏈間排列規則,共軛鏈段增長。
三種高分子摻雜8 wt%綠光銥金屬錯合物,從AFM之相位圖(phase imgae)可知,將carbazole導入高分子側鏈(Cz-PPP),可增加與綠光銥金屬錯合物的化學相容性。
在摻雜8 wt%綠光銥金屬錯合物之元件結構
( ITO/PEDOT(AI 4083)/Polymer+ 8 wt% Ir-G /CsF/Ca/Al ),由於DR8O-PPP在薄膜態易結晶,元件燒壞性最高; mR8O-PPP與Ir-G化學相容性最差,所得EL光譜仍來自於主鏈; Cz-PPP成膜性好,且與Ir-G化學相容性好,所得元件亮度與效率最高,最大亮度為3882 cd/m2(24.8 V , 107.6 mA/cm2),最大效率14.31 cd/A (13.6 V, 0.85 mA/cm2),EL光譜不隨操作電壓而變。在元件結構加入電洞阻礙層(hole-blocking layer) TPBI, mR8O-PPP與DR8O-PPP不管在亮度與效率皆有顯著的提升,表示TPBI能有效將電洞擋在發光層,增加與電子的再結合。雖然陰極加入TPBI對於Cz-PPP元件並沒有顯著的提升效能,卻能在低電流密度下得到高的元件效率, mR8O-PPP更是明顯。
第二部分是鑑定單一共軛高分子鏈之構形。把單分子的兩端用電極連接似乎是很簡單的目標,而想要實現卻是不容易。近幾年來已有人嘗試了許多種方法企圖把單分子與金屬電極相連結以量測單分子的導電性。我們先以化學還原法先合成出以正丁硫醇為保護基的金奈米粒子,以TEM與UV/VIS確認粒徑約2.6 nm;再合成出末端含硫醇基的poly(9,9-dioctylfluorene)s (SH-PFO),利用動態交換使兩者反應,將金奈米粒子接在SH-PFO兩端。以tapping mode AFM找尋SH-PFO單分子鏈成對金粒子,我們找尋到成對金粒子,其高度與金粒子的粒徑相吻合, 且成對金粒子間之距離分佈(30-130 nm)落在用凝膠滲透層析儀 (Gel permeation chromatography,GPC)所得分子量分佈之全伸展鏈長分佈(6-143 nm)之間,證實了單分子鏈製作方法的正確性。

關鍵字

聚對位苯 ； 發光二極體 ； 單分子鏈 ； Yamamoto 聚合

並列摘要

My study includes two following parts. The first is to improve Yamamoto polycondensation to yield high molecular weight poly(para-phenylene)s (PPPs) and to characterize their properties. PPPs are one of the most important classes of conjugated polymers and have been the subject of extensive research, particularly as active materials for use in light-emitting diodes (LEDs) and solar cell. These materials have been particular interest as potential blue emitters in such devices. The two main polycondensation methods used are the Suzuki polycondensation of aryl halides with arylboronic acids and the Yamamoto polymerisation of aryl dihalides using nickel(0) reagents.
Generally speaking, the Suzuki method yield higher molecular weight than the Yamamoto procedure, but is synthetically more demanding (refer to arylboronic acids). To improve Yamamoto method, Using THF as reaction solvent to substitute for DMF and toluene used in common Yamamoto polycondensation, the reaction reactivity can be increased resulting from good solubility for both Ni catalysts and polymers. We can obtain high-molecular weight PPP as Suzuki polycondensation did.
Then we synthesize three high-molecular weight PPP derivatives: mono-substituted alkoxyl group (mR8O-PPP), di-substituted alkoxyl group (dR8O-PPP), and Cz capping on the ends of alkoxyl group (Cz-PPP), and to study their structure-property relationships. The incorporation of long alkyl-chain substitute on side chain can pack in order in thin film as cast from THF and thus increase conjugation; Cz on the ends of alkoxyl group for Cz-PPP can destroy the order pack in thin film and thus reduces conjugation.
While doping with 8 wt% Ir-G complex, Cz-PPP has less phase separation because the Cz on the ends of alkoxyl group exhibits excellent chemical compatibility with guest material. The device (ITO/PEDOT/Polymer : dopant /CsF/Ca/Al) based on this material exhibits stable green emission (spectrum remains unchanged upon successive operation) and luminous efficiency of 14.31 cd/A (13.6 V, 0.85 mA/cm2), and the highest luminance of 3882 cd/m2 (24.8 V , 107.6 mA/cm2). And we can obtain better balance of carrier by inserting TPBI as hole-blocking layer.
The second is to determine the conformation of single conjugated polymer chain. A technique for grafting a polymer to a solid metal or semiconductor surface is essential for the development of such applications. This is because the chemical and electrical connectivity between a polymer terminus and an electrode surface may have an important influence on effective electron or photon signal transportation. A high density polymer grafted on a surface is commonly called a polymer brush, and such polymers have been well investigated such as surface modification. In contrast, a low-density grafted polymer is useful for observing nanostructures and physical properties at a single polymer chain level. As a methodology for polymer grafting, we use two-phase (water-toluene) reduction of AuCl4- by sodium borohydride in the presence of an alkanethiol, the gold particles of average 2.6 nm diameters bearing a surface of thiol have been prepared and characterized by TEM and UV-Vis absorption. Then we synthesized end-functionalized PFO bearing thiolacetate (SH-PFO). Furthermore, with the chemisorption of thiolacetate modified polymer on a gold particle surface, we visualized the polymer connection onto particle surfaces by AFM and clearly observed dumbbells-type nanohybrids that consisted of the polymer bridging between two Au nanoparticles.

並列關鍵字

poly(para-phenylene)s (PPPs) ； PLED ； single chain ； Yamamoto polycondensation

參考文獻

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