行政院國家科學委員會專題研究計畫 期中進度報告
含有多立面倍半矽氧烷寡聚體或樹枝狀側鏈之發光高分子
之合成與研究(1/2)
計畫類別： 個別型計畫
計畫編號： NSC94-2216-E-009-017-
執行期間： 94 年 08 月 01 日至 95 年 07 月 31 日
執行單位： 國立交通大學材料科學與工程學系(所)
計畫主持人： 韋光華
計畫參與人員： 周嘉宏、許碩麟、張耀德
報告類型： 精簡報告
處理方式： 本計畫可公開查詢
中 華 民 國 95 年 5 月 22 日
行政院國家科學委員會補助專題研究計畫
□ 成 果 報 告
□期中進度報告
√
含有多立面倍半矽氧烷寡聚體或樹枝狀側鏈之發光高分子之合成與
研究(I) (II)
計畫類別：□ 個別型計畫 □ 整合型計畫
計畫編號：NSC 94－2216－E－009－017－
執行期間： 94 年 8 月 1 日至 95 年 7 月 31 日
√
計畫主持人：韋光華
共同主持人：
計畫參與人員： 周嘉宏 許碩麟 張耀德
成果報告類型(依經費核定清單規定繳交)：□精簡報告 □完整報告
√
本成果報告包括以下應繳交之附件：
□赴國外出差或研習心得報告一份
□赴大陸地區出差或研習心得報告一份
□出席國際學術會議心得報告及發表之論文各一份
□國際合作研究計畫國外研究報告書一份
處理方式：除產學合作研究計畫、提升產業技術及人才培育研究計畫、
I
含有多立面倍半矽氧烷寡聚體或樹枝狀側鏈之發光高分子之合成與研究(I) (II)
研究計畫中英文摘要
中文摘要:
本案之分子設計藉由引入(1)高立體障礙結構及高熱穩定性之 POSS 孔洞材料及(2)樹
枝狀側鏈，避免分子間堆疊所導致的自我驟息現象。利用不同功能的共軛基團引入，可開
發不同需求藍色發光材料或紅光系材料。不但可有效地提昇螢光及電激發光效率至原來之
兩倍至三倍，同時也增強原本材料在製程元件後的穩定度及電性。
關鍵字: 多立面倍半矽氧烷寡聚體; 發光高分子; 高分子發光二極體
Synthesis and Characterization of Luminescent Polyphenyl vinylene Incorporating
Side-Chain-Tethered Polyhedral Oligomeric Silsesquioxane or dendritic structure Units
英文摘要:
We have synthesized, using the Gilch polymerization method, a new series of
high-brightness, soluble copolymers (POSS-PPV-co-MEHPPV) of poly(p-phenylenevinylene)
(PPV) containing side-chain-tethered polyhedral oligomeric silsesquioxane (POSS) pendent units
and poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV). This particular
molecular architecture of POSS-PPV-co-MEHPPV copolymers possesses not only a larger
quantum yield (0.85 vs. 0.19) but also higher degradation and glass transition temperatures
relative to those of pure MEHPPV. The maximum brightness of a double-layered-configured
light emitting diode (ITO/PEDOT/emissive polymer/Ca/Al) incorporating a copolymer of
MEHPPV and 10 mol% PPV-POSS was five times as large as that of a similar light emitting
diode incorporating pure MEHPPV (2196 vs. 473 cd/m
2). Moreover, we have also synthesized
a thermally stable and high molecular weight fluorescent poly-(phenylenevinylene) (PPV)
incorporating side-chain-tethered dendritic phenyl groups (DENPPV) through Gilch route; this
DENPPV has a low abundance of tolane-bisbenzyl defects. Intramolecular energy transfer from
the dendritic phenyl side group to the PPV backbone was evidenced from UV-vis and
photoluminescence spectra of the DENPPV polymer and its model compound. Copolymers of
DENPPV with 2-methoxy-5-(2-ethylhexyloxy) -1,4-phenylenevinylene (MEHPPV) display
excellent photoluminescence both in solution and in the solid state; the highest quantum yield we
observed was 82%. The electroluminescence of the copolymer MEHPPV/DENPPV (molar ratio:
25/75) was 70% higher than that of MEHPPV (0.12 lm/W vs. 0.07).
Keywords:
POSS, Light-Emitting Polymer, PLED
計畫名稱: 含有多立面倍半矽氧烷寡聚體(POSS)於側鏈之發光高分
子之合成與研究
第一章 研究計畫內容
1. 研究計畫之背景及目的
1-1. 多面體倍半矽氧烷寡聚物(POSS):
多面體倍半矽氧烷寡聚物/高分子奈米複合材料屬於金屬氧化物分子簇/高
分子奈米複合材料的一種，自從
1993 年加拿大Air Force Research 實驗室將多面
體倍半矽氧烷寡聚物(polyhedral oligomeric silsesquioxane (POSS))引入高分子中
獲得突出之性質後，該倍半矽氧烷寡聚物受到多方的注意，並且由Hybrid Plastics
公司將其量產，最早是在以溶膠-凝膠(sol-gel)法合成多孔性材料(zeolites)時被發
現的【1】，多面體倍半矽氧烷寡聚物的化學結構是介於二氧化矽(SiO
2)和矽氧烷
(R
2-SiO)之間，其化學結構式通常以(RSiO1.5)
n表示，圖一為其立體結構圖。多面
體倍半矽氧烷寡聚物為單一分子結晶體、結構相當對稱、分子大小約為
0.7 nm
至
2 nm之間且對許多有機溶劑有良好的溶解度，是一種很適合用來製備有機-無
機奈米複合材料的無機金屬氧化物寡聚物。其中以(RSiO1.5)
8這一系列多面體倍
半矽氧烷寡聚物最常被用來與高分子結合刑成多面體倍半矽氧烷寡聚物/高分子
奈米複合材料(POSS/polymer nanocomposites)。(以下將稱(RSiO1.5)
8這一系列多
面體倍半矽氧烷寡聚物為POSS。)
n=6
O Si O Si O Si O O Si R R R O Si R O O Si O R Si R R R O Si O O Si O Si O Si Si O O O Si O Si O O O R R R R R Si R O Si O Si Si O O Si R R R O Si R O Si O R O Si O Si O O Si O O O O R R R Rn=8
n=10
圖一. 多面體倍半矽氧烷寡聚物(RSiO1.5)
n的立體結構圖
1圖二為
POSS 的化學立體結構圖，POSS 為一大小約為 1.5 nm 的六面體結晶
體 (rhombohedral crystal structure) 【2】
，其由一結構剛硬的六面體二氧化矽為中
心及
8 個有機取代基接在矽上所組成。其結構上的有機取代基可分為兩大類，一
為沒有反應性的有機取代基，可以增加
POSS 的溶解度及與高分子的相容性；一
為單一或多個具反應性取代基，可與高分子刑成共價鍵連結。
O Si O Si O Si Si O Si O Si O O Si O Si O O O O R X R R R R R R具反應性單或多官能基
可與高分子結合或或與
高分子單體進行聚合反
應
非反應型取代基可以
增加 POSS 分子的溶解
度或與高分子的相容
性。
POSS 分子大小約 1.5
nm，(Si-Si = 0.5 nm,
R-R = 1.5 nm)。
POSS 的立體
結構明確是分
子級的高分子
補強材。
圖二. 多面體倍半矽氧烷寡聚物(RSiO1.5)
8(POSS)的立體結構圖
反應式一為
POSS 的合成方法，反應式二為最常用來合成具不同官能基 POSS 的
方法(如圖三)。
SiR R R O Si O O Si O Si O Si Si O O O Si O Si O O O R R R R R R R OH Si O OH Si O Si O Si Si O O O Si O Si OH O O R R R R R R-Si-(OR')3+
Base, H2O(1)
(2)
Si OH R Si X Si O RO Si O Si O Si Si O Si O Si O O Si O Si O O O O R X R R R R R R
Si-O
1.5八面體核心
V = 0.082 nm
3R
R
V = 1.685 nm
3整個POSS的體積為 1.767 nm
3圖四. POSS 的結構與體積關係圖
另外，POSS 為一微孔性材料(micoporous materials)，其孔洞是存在於其結構
中的六面體二氧化矽，孔洞大小約為
0.3-0.4nm【1】，(圖四) 。由於 POSS 分子
為奈米級顆粒,並且與高分子之間相容性甚好，可以均勻地分散於高分子材料
中，形成奈米級複合材料，達到良好補強效果。
1-2. POSS/高分子奈米複合材料的發展:
POSS分子自 1993 年來，以不同方式被引入高分子中來補強其熱性質及機械
性質，其中具單反應官能基的POSS (R
7R’Si
8O
12)已經以單體的方式引入線性高分
子中，其包括methacrylates【3】
、styrenics【4,10】
、norbornenes【5-6】和urethanes
【7】等。另外，具多反應官能基的POSS分子以分子起始劑或交聯劑形成星狀或
網狀結構高分子奈米複合材料【8-9】【11-12】。
POSS 分子除了加入高分子中當補強材外，另外可以用來合成其它功能性材
料，如催化材料、孔洞性材料、發光材料與透氣膜材料。如此適用多功能應用乃
因為
POSS 分子的高表面積、可控制的結構及多變化的官能基。雖然 POSS/高分
子奈米複合材料的應用性受到大家注意但所有研究仍在初步研究階段，仍需更多
及更深入研究來發研究及開發更多的
POSS/高分子奈米複合材料。
31-3. POSS/高分子光電複合材料
相較於無機半導體發光二極體需要高真空、高溫之製程環境，高分子發光二
極體具有製程簡便、易大面積化及可製作撓曲形狀元件的優勢，亦是工業上極具
發展潛力的材料。多立面倍半矽氧烷寡聚體(POSS) 本身屬多孔洞無機材料，耐
熱性及熱穩定性優異，導入高分子(如:聚亞醯胺(PI))中可降低材料本身的介電係
數(dielectric constant)，大幅提升材料的應用價值。本實驗室已合成出一系列之
PF-POSS 高分子(如圖五、圖六)，已發表並將刊登於 Macromolecules 期刊【13】。
除此之外，近期來已有探討
POSS 與應用於光電材料的文獻，主要可分為
三類:
1. 將 POSS 官能基鍵結於高分子尾端(end-capped) 【14】: 將 POSS 鍵結於
PF(polyfluorene) 及 MEHPPV 的尾端，提高元件整體的光電性質。
2. 星狀結構(Star-like)之 poss【15】: 以 POSS 為中心，與 PF(polyfluorene)結合
成星狀結構(Star-like)。可提高材料的熱穩定度、元件的光電性質、EL 光色純
度。
3. 側鏈(side chain) 鍵結 POSS 結構: 相較於其他兩種方式 POSS 於高分子中的
含量(Starlike 3.8%， end-capped 1.2%)，側鏈(side chain) 鍵結 POSS 的方法
提供了較大的變化性。由於其鍵結端位於高分子側鏈，一方面可藉由合成含
POSS 之單體與其他單體聚合，藉以控制 POSS 在高分子中的含量，可測試
出最有效的比例; 另外由於導入此巨大官能基於側鏈上，也可以防止高分子
堆疊(aggregation)所造成的自我驟息(self-quench)，提高元件整體的發光效益。
我們在設計整個分子結構將考量合成簡易性即可溶性，第一年將藉由化學合
成法嘗試導入
POSS 於一般常見高量子效率之發光高分子，如 Polyfluorene,
polyphenylvinylene……dendritic 等，製程元件並量測其光電性質。第二年計畫將
著重於
polymer 的改質(合成樹枝狀 PPV)、元件製程的改良與 morphology 的研究。
Br Br Br Br O Br Br NH2 H2N Br Br NH HN Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R Cl 1 2 3 4 Where R= (i) (ii) (iii)
圖五. 本實驗室合成出之 POSS 單體
Br Br B B O O O O + Aliquate 336, K2CO3 5 6 Pd (PPh3)4(i) phenylboronic acid
4 NH HN Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R R R R + (ii) bromobenzene Where R= m n
圖六. 本實驗室合成出之 PFO-POSS copolymer
51-4. 結果與討論:
首先我們先合成含有
POSS 的側鏈分子，利用 Gilch 途徑共聚合時趨向於形
成交替型共聚物。而其合成方法如下(b)：
Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R Cl Si O Si Si O Si O O Si OH Si O Si O OH O O OH O R R R R R R R i Cl-POSS Cl-POSS OH ii + O Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R (1) (2) R= 2 1 iii O Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R Br Br O CH2Br BrH2C Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R O BrH2C H3CO CH2Br O H3CO O Si O Si Si O Si O O Si O Si Si O Si O O O O O O R R R R R R R tBOK AIBN + 1-n n Polymerization製程出以多立面倍半矽氧烷寡聚體(POSS)/Conducting polymer 奈米複合材
料為發光層之
LED 元件。初期希望可控制半導體奈米量子點的 particle size 與表
面官能基的置換，並將合成出之高分子完成物性、結構鑑定與基本光學性質的量
測。接下來已完成
POSS/ 高分子奈米複材的製作與製程條件的測試，在製作的
過程中尋找改進的方法，進一步探討不同濃度配比與
particle size 對物理及光學
性質的影響，最後以適當比例條件製成元件後，量測量子效率及
EL 元件性質；
Table 1. Optical Properties of the POSS-PPV-co-MEHPPV Nanocomposites.
λ
max(UV, nm)
λ
max(PL, nm)
aQ.Y
solution
bfilm
solution
bfilm film
cMEHPPV
499
517
553 (592)
591 (634)
0.19
POSS-PPV1-co-MEHPPV
499
512
552 (591)
588 (633)
0.43
POSS-PPV3-co-MEHPPV
498
512
552 (591)
586 (632)
0.62
POSS-PPV5-co-MEHPPV
497
511
552 (591)
585 (631)
0.84
POSS-PPV10-co-MEHPPV
494
505
551 (590)
584 (631)
0.87
a
The data in parentheses are the wavelengths of the shoulders and subpeaks.
bThe absorption and emission were measured in THF.
c
PL quantum yield estimated relative to a sample of Rhodamine 6G (Φ
FL
= 0.95).
在量子產率的測量上，亦是利用已知在
Rhodamine 6G 作為標準品，
POSS-PPV10-co-MEHPPV 結構最高可達 0.87。此外放射半波高寬也相當的窄
（小於
100 nm），這對光色上的純度有很佳的助益。
電性方面的特性，對於製程雙層結構之LED元件(ITO/PEDOT:PSS/polymer
/Ca/Al)，分析如下:
1. 固態PL (圖一): 導入POSS 的 PPV高分子，熱性質明顯提升。
2. 元件EL (圖二): 原材料MEHPPV 之EL 放光 為橘紅光 (590 nm) ，經由導入
POSS後，半高寬(FWHM)明顯驟減，自110 nm降低至75 nm(抑制excimer生
成)，提高原本光色純度。
3. I-V and L-V curve(圖三及圖四): 導入POSS 的 PPV高分子，元件可乘載的電
流值明顯提升，因此在亮度部分增強為原來的四倍(2196 vs. 473 cd/m
2)。
550 600 650 700 750 800 (b)POSS10-PPV-co-MEHPPV (a) MEHPPVIn
te
nsity (
a.u
.)
Wavelength (nm)
RT after 2h anneal at 150oC 500 550 600 650 700 750 Intensity (a.u.) Wavelength (nm) PPV-POSS-5% PPV-POSS-10% MEHPPV (圖二) 7 (圖一)(圖四) 0 1 2 3 4 5 6 7 8 9 10 11 0 200 400 600 800 1000 1200 1400 1600 1800 C urrent d en sity (m A /c m 2 ) Voltage (V) MEHPPV PPV-POSS-1% PPV-POSS-3% PPV-POSS-5% PPV-POSS-10% (圖三) 0 2 4 6 8 10 12 14 16 500 1000 1500 2000 Luminanc e (c d/m 2 ) Voltage (V) MEHPPV PPV-POSS-1% PPV-POSS-3% PPV-POSS-5% PPV-POSS-10%
對現有的平面顯示器而言，在大尺寸領域裡，因電漿激發顯示技術的發展，
促使電漿顯示器在商品化上大步邁進，但在製作良率和價格上仍然有待克服。在
中小尺寸中，最成熟且廣泛應用的是液晶顯示器，但產品受限於畫質、應答速度
和對溫度的穩定性。對於有機電激發光顯示技術而言，小分子系統在中小尺寸較
占優勢，已有許多商業化產品，高分子系統雖然進展較慢，商業化產品較少，然
而一旦在材料與噴墨列印量產技術上有所突破，必能在大尺寸與可撓曲的顯示器
上大放異彩。本計畫之特色在於導入
POSS 於高分子材料，以提高此種奈米複合
材料製成之發光二極體元件的電激發光效率。由於使用同一種材料製作，製程較
容易，運用此改質方法結合之高分子奈米複合材料，可得到一均勻密度的薄膜，
提高發光高分子之發光效率、元件效率並提升其耐熱度及使用壽命。
2.參考文獻:
1. C. Zhang, F. Babonneau, C. Bonhomme, R. M. Laine, C. L. Soles, H. A. Hristov,
A. F. Yee, J. Am. Chem. Soc. 1998, 120, 8380.
2. L. Zheng, A. J. Waddon, R. J. Farris, E. B. Coughlin, Macromolecules 2002, 35,
2375.
3. F.Gao, B. M. Culbertson, Y. Tong, S. R. Schricker, Polym. Prepr. 2001, 41, 580.
4. A. Romo-Uribe, P. T. Mather, T. S. Haddad, J. D. Lichtenhan, J. Polym. Sci., Part
B: Polym. Phys. 1998, 36, 1857.
5. P. T.Mather, H. G. Jeon, A. Romo-Uribe, T. S. Haddad, J. D. Lichtenhan,
Macromolecules 1999, 32, 1194.
6. R. K. Bharadwaj, R. J. Berry, B. L. Farmer, Polymer 2000, 41, 7209.
7. B. X. Fu, B. S. Hsiao, H. White, M. Rafailovich, P. T. Mather, H. G. Jeon, S.
Phillips, J. D. Lichtenhan, J. J. Schwab, Polym. Int. 2000, 49,437.
8. J. Choi, J. Harcup, A. F. Yee, Q. Zhu, R. M. Laine, J. Am. Chem. Soc. 2001, 123,
11420.
9. R. Tamaki, Y. Tanaka, M. Z. Asuncion, J. Choi, R. M. Laine, J. Am. Chem. Soc.
2001, 123, 12416.
10. T. S. Haddad, J. D. Lichtenhan, Macromolecules 1996, 29, 7302.
11. C. Zhang, R. M. Laine, J. Am. Chem. Soc. 2000 122, 6979.
12. R. M. Laine, J. Choi, I. Lee, Adv. Mater. 2001, 13, 800.
13. Chou, C. H.; Hsu, S. L.; Dinakaran, K. ; Chiu, M. Y.; Wei, K. H. Macromolecules
2004, accepted.
14. Xiao, S.; Nguyen, M.; Gong, X.; Cao, Y.; Wu, H.; Moses, D.; Heeger, A. J. Adv.
Funct. Mater. 2003, 13, 25.
15. Lin, W. J.; Chen, W. C.; Wu, W. C.; Niu, Y. H.; Jen, A. K. Y. Macromolecules
2004, 37, 2335.
3.
計畫成果自評
3-1.第一年度預期工作項目及進度：
年度 94 年度
94 ~ 95 年度
季別
第 一 季
第 二 季
第 三 季
第 四 季
工作項目
七
月
八
月
九
月
十
月
十
一
月
十
二
月
一
月
二
月
三
月
四
月
五
月
六
月
參考資料之蒐集與研
讀、化學藥品之購得、
儀器與製作流程之熟
悉
多立面倍半矽氧烷寡
聚體(POSS) 之合成
高分子單體的合成
高分子材料的合成、分
子量的控制與結構的
鑑定
量測不同濃度配比對
物理及光學性質的影
響(熱性質研究)
量測固態薄膜光學性
質/改變參數並製成元
件比較
量子效率及
EL 元件性
質之量測
報告之撰寫
預定累積進度
30 %
50 %
80 %
100 %
1. Kannaiyan Dinakaran, Shu-Min Hsiao, Chia-Hung Chou, So-Lin Shu and
Kung-Hwa Wei* “Synthesis and characterization of an efficiently fluorescent
polyphenylenevinylene possessing pendant dendritic phenyl groups”
Macromolecules 2005, 38(25), 10429.
2. Chia-Hung Chou, So-Lin Hsu, Siao-Wei Yeh, Hsu-Shen Wang, Kung-Hwa Wei
“Enhanced Luminance and Thermal Properties of Polyphenylenevinylene
Copolymer Presenting Side-Chain-Tethered Silsesquioxane Units”
Macromolecules 2005, 38(22), 9117.
研究中，製程出以多立面倍半矽氧烷寡聚體(POSS)/Conducting polymer 奈米
複合材料為發光層之
LED 元件。初期希望可控制半導體奈米量子點的 particle
size 與表面官能基的置換，並將合成出之高分子完成物性、結構鑑定與基本光學
性質的量測。接下來希望能完成
POSS/高分子奈米複材的製作與製程條件的測
試，在製作的過程中尋找改進的方法，再進一步探討不同濃度配比與
particle size
對物理及光學性質的影響，最後以適當比例條件製成元件後，量測量子效率及
EL 元件性質。
3-3. 下一年度計畫執行:
由於本計劃屬有機無機之高分子奈米複合材料之光電性質探討，整體來說，對
於參與研究生之訓練較具多元性，其中囊括:複合材料結構設計、有機無機材料
製備合成技術、化學結構鑑定、材料性質量測鑑定(表面微結構、熱性質及光電
性質)、元件製程及量測技術……等。導入無機材之技術若能充分利用，即可應
用在多種類之高分子發光材料上;如此一來，不僅保有高分子容易大面積化、製
程容易、成本較低等優點，結合易製備、光電特性佳的奈米複材，除了對於
PLED
往後在材料選擇及結構設計上，有許多可以發展空間外; 也期望研究能實際應用
於產業界，在未來能結合現有之顯示技術而達到全彩化及大面積、高品質、低成
本的顯示器，提高國內顯示科技研發之技術。在明年的計畫部分，期望能進一步
利用化學鍵結合奈米粒子於高分子中並提升高分子之光電性質。
11可供推廣之研發成果資料表
□ 可申請專利 □ 可技術移轉
日期：95 年 5 月 15 日
國科會補助計畫
計畫名稱： 含有多立面倍半矽氧烷寡聚體或樹枝狀側鏈之發光高
分子之合成與研究
計畫主持人：
韋光華
計畫編號：
NSC 94－2216－E－009－017－
學門領域： 工程處
技術/創作名稱
側鏈含有多立面倍半矽氧烷寡聚體之發光高分子材料
發明人/創作人
韋光華
技術說明
中文：大部份的電激發光高分子，由於天生有著豐富的
π 電子，因
此電洞注入特性和傳輸電洞的能力遠比電子注入特性和傳輸電子
的能力來的有效率。因此，為了增加元件的效率，合成高效率的電
子傳輸高分子是必要的。聚奎林高分子（Polyquinoline）及其衍生
物是最近發表可以應用在二極體上的電子傳輸層的高分子，因為它
們有高熱穩定性、高抗氧化能力、優異的機械性質和良好的成膜能
力。然而，卻有一個缺點---溶解度不好。 氟（Fluorene）的衍
生物由於包含一剛性且共平面的雙苯環結構，所以表現出特殊的物
理和化學性質，再加上在氟上
C9 的位置接上不同的取代基可以增
加溶解度且不會明顯的增加高分子骨幹間的立體作用力。且氟的高
量子效率和優良的熱穩定度，與氟共聚合的高分子變成了最吸引人
的藍光發光材料。然而，無論是
PPV 或者是 PF 系列元件在製成
薄膜時，由於材料累積濃度過高造成分子堆疊，甚至於產生
excimer，嚴重影響了光色以及降低了發光效率;此外，PF 系列由於
C9 位置容易產生氧化現象(keto defect)，也會改變元件原有的發光
光色。
為了改善這些缺點，選擇導入
POSS 於高分子材料期望以考量
製程簡單與成本低廉的條件之下能對於高分子的性質做一些改
英文：We have synthesized, using the Gilch polymerization method, a
new series of high-brightness, soluble copolymers
(POSS-PPV-co-MEHPPV) of poly(p-phenylenevinylene) (PPV)
containing side-chain-tethered polyhedral oligomeric silsesquioxane
(POSS) pendent units and
poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene)
(MEHPPV). This particular molecular architecture of
POSS-PPV-co-MEHPPV copolymers possesses not only a larger
quantum yield (0.85 vs. 0.19) but also higher degradation and glass
transition temperatures relative to those of pure MEHPPV. The
maximum brightness of a double-layered-configured light emitting
diode (ITO/PEDOT/emissive polymer/Ca/Al) incorporating a
copolymer of MEHPPV and 10 mol% PPV-POSS was five times as
large as that of a similar light emitting diode incorporating pure
MEHPPV (2196 vs. 473 cd/m
2).
可利用之產業
及
可開發之產品
1. 光電產業; OLED/PLED 相關。
2. 產率高，步驟簡單的優勢。在元件效能表現上，發光效率可達
0.87，光電效率也隨之提升。全新核心結構，可依此無限延伸，開
發其他新型有機半導體材料及其應用產品; 如此一來，不僅保有高
分子容易大面積化、製程容易、成本較低等優點，結合易製備、光
電特性佳的奈米複材，除了對於
PLED 往後在材料選擇及結構設計
上，有許多可以發展空間外; 也期望研究能實際應用於產業界，在
未來能結合現有之顯示技術而達到全彩化及大面積、高品質、低成
本的顯示器，提高國內顯示科技研發之技術。
技術特點
本案之技術中心在於結合高熱穩定性之
POSS 與發光高分子，
提高此種奈米複合材料製成之發光二極體元件的電激發光效率。藉
由改變
POSS 導入的單體濃度，可控制不同的成分比﹔由於使用同
一種材料製作，製程較容易，運用此方法結合之奈米複合材料，可
得到一均勻密度的有機薄膜，並提升原本
EL 之強度。
推廣及運用的價值
對現有的平面顯示器而言，在大尺寸領域裡，因電漿激發顯示
技術的發展，促使電漿顯示器在商品化上大步邁進，但在製作良率
和價格上仍然有待克服。在中小尺寸中，最成熟且廣泛應用的是液
晶顯示器，但產品受限於畫質、應答速度和對溫度的穩定性。對於
有機電激發光顯示技術而言，小分子系統在中小尺寸較占優勢，已
有許多商業化產品，高分子系統雖然進展較慢，商業化產品較少，
然而一旦在材料與噴墨列印量產技術上有所突破，必能在大尺寸與
可撓曲的顯示器上大放異彩。本申請案之特色在於導入POSS於高
13分子材料，以提高此種奈米複合材料製成之發光二極體元件的電激
發光效率。由於使用同一種材料製作，製程較容易，運用此改質方
法結合之高分子奈米複合材料，可得到一均勻密度的薄膜，提高發
光高分子之發光效率、元件效率並提升其耐熱度及使用壽命。
※
1.每項研發成果請填寫一式二份，一份隨成果報告送繳本會，一份送
貴單位研發成果推廣單位（如技術移轉中心）
。
※ 2.本項研發成果若尚未申請專利，請勿揭露可申請專利之主要內容。
※
3.本表若不敷使用，請自行影印使用。
附錄:
1. Kannaiyan Dinakaran, Shu-Min Hsiao, Chia-Hung Chou, So-Lin Shu and
Kung-Hwa Wei* “Synthesis and characterization of an efficiently fluorescent
polyphenylenevinylene possessing pendant dendritic phenyl groups”
Macromolecules 2005, 38(25), 10429.
2. Chia-Hung Chou, So-Lin Hsu, Siao-Wei Yeh, Hsu-Shen Wang, Kung-Hwa Wei
“Enhanced Luminance and Thermal Properties of Polyphenylenevinylene
Copolymer Presenting Side-Chain-Tethered Silsesquioxane Units”
Synthesis and Characterization of an Efficiently Fluorescent
Poly(phenylenevinylene) Possessing Pendant Dendritic Phenyl Groups
K. Dinakaran, Shu-Min Hsiao, Chia-Hung Chou, So-Lin Shu, and Kung-Hwa Wei*
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30049, R.O.C.
Received February 4, 2005; Revised Manuscript Received August 10, 2005
ABSTRACT: We have synthesized a thermally stable and high molecular weight fluorescent poly-(phenylenevinylene) (PPV) incorporating side-chain-tethered dendritic phenyl groups (DENPPV) through Gilch route; this DENPPV has a low abundance of tolane-bisbenzyl defects. Intramolecular energy transfer from the dendritic phenyl side group to the PPV backbone was evidenced from UV-vis and photolumi-nescence spectra of the DENPPV polymer and its model compound. Copolymers of DENPPV with 2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEHPPV) display excellent photoluminescence both in solution and in the solid state; the highest quantum yield we observed was 82%. The electroluminescence of the copolymer MEHPPV/DENPPV (molar ratio: 25/75) was 70% higher than that of MEHPPV (0.12 lm/W vs 0.07).
Introduction
Electroluminescence devices based on organic thin films are of great interest because of their potential applications as large-area light-emitting displays that require a low driving voltage and have good
process-ability and a fast response time.1Although many
poly-(phenylenevinylene) (PPV) derivatives have been syn-thesized and applied in light-emitting diode (LED) applications, very few display high photoluminescence
efficiencies.2 There are a number of reasons for these
low photoluminescence efficiencies: (a) Conjugated
backbones tend to stack cofacially with one another as a result of favorable interchain π-π interactions, which leads to a self-quenching of excitons. (b) An imbalance of hole/electron injection and transport occurs in the emission layer in devices because most emissive
poly-mers conduct holes in preference to electrons.3 (c)
Trapping of excitons by defect sites in the polymer backbone causes nonradiative decay. These structural defects in the polymer not only reduce the photolumi-nescence quantum yield but also are responsible for the
short operational lifetimes of LED devices.4
Various techniques have been proposed to improve the efficiency of PPVs, either by modifying their chemical structure with bulky side groups or by using a copo-lymerization approach to incorporate conjugated phe-nylenevinylene segments among nonconjugated
spac-ers.5For example, soluble PPV derivative with bulky
alkoxy side groups, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) has been
de-veloped.6-9More recently, various bulky substituents,
such as alkoxy, alkylsilyl, phenyl, and fluorenyl groups, have been substituted at the 2- or 2,5-positions of the PPV backbone to suppress the aggregation, caused by intermolecular interactions, that quench the formation
of excimers.9,10Three new soluble PPV derivatives have
been obtained through use of the Horner-Witting-Emmons (HWE) reaction; these materials in the solid state display a photoluminescence quantum yields of
61%,10d which is higher than that of MEHPPV. One
weak feature of PPV derivatives that have flexible side chains is that they are sensitive to a combination of air
and light.11In contrast, phenyl-substituted PPVs have
higher resistance to photooxidation than do other
substituted PPVs.12LEDs having longer lifetimes can
be fabricated from a single phenyl group substituted PPVs that contain few head-to-head (HH) and
tail-to-tail (TT) couplings,13,14 such couplings referred to as
tolane-bis(benzyl) (TBB) defects. It has also been demonstrated that polymers presenting fourth-genera-tion dendrimers have a diminished amount of intermo-lecular π-stacking and, consequently aggregate
forma-tion is inhibited.15The photonic effects observed by the
dendronization of polymers have been explored in recent
years.16 We have already demonstrated that higher
luminescence efficiencies exist for polyfluorenes pos-sessing side-chain tethered polyhedral oligomeric
sils-esquioxane (POSS).17aMoreover, Frechet-type
dendrim-ers, a benzyl alcohol dendrimer, have been shown to
have high photoluminescence.17b In contrast to the
Frechet-type dendrimers, Mullen-type dendrimers,18,19
which are polyphenylene dendrimers, are both shape-persistent and chemically stable. Therefore, their π-stack-ing is precluded at lower dendritic generations than it is for the Frechet type. Their three-dimensional shield-ing ability has been demonstrated by usshield-ing perylene
dyes as core units.18The Mullen type dendrimers do not
interfere with the charge transport or emission proper-ties of the polyfluorene. Dendrimer substitution has been performed to hinder excimer formation and exciton migration to oxidized ketonic sites, which thereby
increases the color stability of the devices.19 In the
present study, we have employed the dendritic phenyl (Mullen-type) PPV, which offers the following advan-tages: (i) It permits spatial control of the polymer chain and shields it from interchain excimer formation; (ii) it is a fully conjugated PPV; (iii) it provides a very low abundance of TBB defects as a result of electronic (the stronger acidity of the bromomethyl moiety at the ortho position of the highly conjugated dendritic phenyl group) and steric effect of the substituent; (iv) its rigid aromatic structure provides higher stability to thermal oxidation; (v) its excitation energy is transferred to the polymer
* Corresponding author. E-mail: [email protected]. Tele-phone: 886-35-731871. Fax: 886-35-724727.
10429
Macromolecules 2005, 38, 10429-10435
10.1021/ma050252q CCC: $30.25 © 2005 American Chemical Society Published on Web 11/12/2005
backbone, which leads to enhanced device performance and quantum efficiency. The preparation of this polymer is also a part of our effort to a production of fully conjugated PPVs possessing bulky pendants. To deter-mine the minimal steric requirements necessary to prevent of aggregation and to enhance the solubility in organic solvents, we also prepared copolymers with MEHPPV. In this paper, we report the synthesis of a new PPV derivative containing dendritic phenyl groups on its side chains (DENPPV) as an example of highly thermally stable, and TBB defect-free phenyl-substi-tuted PPV; in addition, we describe the performance of these polymers as emissive layers in LEDs.
Experimental Section
Materials and Characterization. Bromoxylene, n-butyl-lithium, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, tetraphenylcyclopentadienone, and 4-bromophenylacetylene were purchased from Aldrich and were used as received. All other solvents were distilled before use.1H and13C nuclear magnetic resonance (NMR) spectra were obtained using a Bruker DRX 300 MHz spectrometer. Mass spectra were obtained on a JEOL JMS-SX 102A spectrometer. Fourier transform infrared (FTIR) spectra were acquired using a Nicolet 360 FT-IR spectrometer. Gel permeation chromato-graphic analyses were performed on a Waters 410 differential refractometer and a Waters 600 controller (Waters Styragel Column). All GPC analyses of polymers were performed in THF solutions at a flow rate of 1 mL/min at 40 °C; the samples were calibrated using polystyrene standards. Thermogravi-metric analyses (TGA) and differential scanning calorimetry (DSC) measurements were performed under a nitrogen atmo-sphere at heating rates of 20 and 10 °C/min, respectively, using Du Pont TGA-2950 and TA-2000 instruments, respectively. UV-vis absorption and photoluminescence (PL) spectra were recorded on an HP 8453 spectrophotometer and a Hitachi F-4500 luminescence spectrometer, respectively. Before inves-tigating the thermal stability of the synthesized polymers, their polymer films were annealed in air at 200 °C for 2 h.
Synthesis of 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)xylene. n-Butyllithium (1.6 M in hexane, 17.0 mL, 27.09 mmol) was added, by syringe, to a solution of bromoxylene (5.0 g, 28.7 mmol) in THF (100 mL) at -78 °C. The mixture was stirred at -78 °C, warmed to -10 °C for 15 min, and cooled again at -78 °C for 15 min 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (15.0 g, 80.9 mmol) was added rapidly to the solution, and the resulting mixture was warmed to room temperature and stirred for 24 h. The mixture was poured into water and extracted with ethyl acetate. The organic extracts were washed with brine and dried over magnesium sulfate. The solvent was removed by rotary evaporation and the residue was purified by column chromatography (silica gel, hexane, Rf0.12) to provide 4.63 g (74%) of the title product. 1H NMR (300 MHz, CDCl3): δ 7.54 (s, 1H), 7.06 (dd, 2H, J ) 7.6 Hz), 2.41 (s, 3H), 2.22 (s, 3H), 1.19-1.37 (m, 12H). HRMS: calcd for C14H21O2B, 232.1634; found, 232.1636.
Synthesis of 2,3,4,5-Tetraphenyl-4′-bromophenyl (DEN-Br). A mixture of tetraphenylcyclopentadienone and 4-bro-mophenylacetylene was refluxed in xylene at 135 °C under
Synthesis of 2′-(2,3,4,5-Tetraphenyl-4′-phenyl)-1,4′′ -dimethylbenzene (D-CH3). Suzuki Coupling Reaction.
Carefully purified DENBr, (1.0 g 1.84 mmol), 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)xylene (0.43 g 1.84 mmol), and (PPh3)4Pd0(1 mol %) were dissolved in a mixture of toluene and 2 M aqueous K2CO3(1.5:1). The solution was placed under a nitrogen atmosphere and heated under reflux with vigorous stirring for 48 h. The mixture was poured into water and extracted with ethyl acetate. The organic extracts were washed with brine and then dried (MgSO4). The solvent was removed by rotary evaporation and the residue was purified by column chromatography (silica gel; 2% ethyl acetate in hexane, Rf0.3)
to provide 650 mg (65%) of the title product. 1H NMR (300 MHz, CDCl3) δ: 7.64 (s, 1H), 7.25 (s, 1H), 7.10-7.18 (m, 10H), 7.02-7.09 (m, 2H), 6.81-6.90 (m, 14H), 2.33 (s, 3H), 2.16 (s, 3H).13C NMR (300 Hz CDCl3) δ:142.08, 142.07, 142.06, 141.73, 141.12, 140.94, 140.70, 140.38, 140.33, 140.21, 140.12, 139.71, 139.61, 135.43, 132.53, 131.95, 131.89, 131.85, 131.67, 131.27, 130.75, 130.56, 130.33, 128.74, 128.16, 127.93, 127.43, 127.25, 126.97, 126.59, 125.93, 125.67, 21.38, 20.23. Anal. Calcd For C44CH34: C, 93.91; H, 6.09. Found: C, 93.91; H, 6.01. HRMS: calcd for C44H34, 562.2661; found, 562.2662.
Synthesis of 2-(2,3,4,5-Tetraphenyl-4′ -phenyl)-1,4-di-bromomethylbenzene (D-CH2Br). A mixture of D-CH3, (1.0
g, 1.77 mmol) NBS (0.63 g, 3.55 mmol), and AIBN (0.04 g) was heated under reflux in carbon tetrachloride under nitrogen for 5 days. The reaction mixture was filtered to remove succin-imide, the solvent was evaporated, and the residue was purified by column chromatography. 1H NMR (500 MHz, CDCl3), δ: 7.62 (s, 1H), 7.46 (d, J ) 7.92 Hz, 1H), 7.34 (d, J ) 7.70 Hz, 1H) 7.24-7.15 (m, 10H), 6.94-6.88 (m, 15H), 4.46 (s, 2H), 4.35 (s, 2H). 13C NMR (500 MHz, CDCl3), δ: 142.27, 141.79, 141.66, 141.24, 140.87, 140.25, 139.91, 139.86, 139.51, 139.40, 137.96, 137.36, 135.50, 131.57, 131.52, 131.47, 131.21, 130.83, 129.95, 128.48, 128.15, 127.60, 126.99, 126.93, 126.65, 126.29, 125.74, 125.63, 125.38, 32.72, 31.44. Anal. Calcd for C44H32Br2: C, 73.34; H, 4.48. Found: C, 73.05; H, 4.41. HRMS: calcd for C44H32Br2, 720.0871; found, 720.0848.
General Procedure for the Synthesis of Copolymers. A 1 M solution of potassium tert-butoxide in THF was added to a solution of the monomer D-CH2Br in dry THF at room temperature, and then the mixture was stirred for 4 h. Addition of the THF solution to methanol precipitated the polymer, which was collected, washed with methanol, and stirred with a mixture of methanol and water (1/1) for 1 h. The polymer was again collected, stirred with a mixture of methanol and water (1/1) for 1 h, filtered, washed with methanol, and dried at 60 °C for 24 h.
Device Fabrication and Testing. The electroluminescent (EL) devices were fabricated on an ITO-coated glass substrate that was precleaned and then treated with oxygen plasma before use. A layer of poly(ethylene dioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS, Baytron P from Bayer Co.; ca. 40 nm thick) was formed by spin-coating from its aqueous solution (1.3 wt %). The EL layer was spin-coated at 1500 rpm from the corresponding toluene solution (15 mg mL-1) on top of the vacuum-dried PEDOT:PSS layer. The nominal thickness of the EL layer was 65 nm. Using a base pressure below 1× 10-6Torr. a layer of Ca (30 nm) was vacuum deposited as the cathode and a thick layer of Al was deposited subsequently
of tetrakis(triphenylphosphine)palladium(0) as catalyst, gave the dendritic phenyl-substituted xylene derivative. The dendritic phenyl-substituted dibromo monomer
(D-CH2Br) was synthesized by bromination of 2′
-(2,3,4,5-tetraphenyl-4′-phenyl)-1,4′′-dimethylbenzene with NBS,
using AIBN as the radical initiator. The polymers were prepared according to Scheme 2.
The copolymers were prepared using comonomer feed
ratios of D-CH2Br and
2-methoxy-5-(2-ethyl)hexyloxy-1,4-bis(bromomethyl)benzene of 100:00, 88:12, 75:25, 63: 37, 50:50, 25:75, and 0:100; we name the corresponding
copolymers DENPPV, 88DENPPV, 75DENPPV, 63DENPPV, 50DENPPV, 25DENPPV, and MEH-PPV, respectively. Figure 1 displays the FTIR spectra of DENPPV and MEHPPV. The absorption bands that
appear at 1581-1596 cm-1, are characteristic of CdC
bonds. The absorption bands at 3056 and 961 cm-1are
due to stretching modes for the vinylene CdC bond and C-H out-of-plane bending, respectively, of the trans
configuration. The1H NMR and13C H NMR spectra of
DENPPV have been presented as Supporting Informa-tion. The aromatic and vinyl protons appear within the range of 7.60-6.84 ppm. PPVs containing TBB defect (head-to-head (H-H) or tail to tail (T-T) couplings, that
are formed as the result of a side reactions4,20 are
responsible for the CH2-CH2 groups that present the
peaks at 2.5-2.9 ppm. We did not observe peaks for
H-H couplings in the1H NMR spectrum of the obtained
polymer. It is clear that this side reaction is suppressed because of (i) the electronic effect arising from the stronger acidity of the bromomethyl moiety at the ortho position of the dendritic phenyl group and (ii) the steric effect of the substituting dendritic phenyl group. We
Scheme 1. Synthesis of Dendritic Phenyl Bromide
Scheme 2. Synthesis of DEN PPV and Copolymers
measured the molecular mass and polydispersity index (PDI) of each copolymer by GPC using THF as the eluent; the results are presented in Table 1. We deter-mined the weight-average molecular weights of the
polymers to be in the range (1.6-3) × 105 with
poly-dispersities ranges from 1.1 to 2.1. The DENPPV polymer exhibits limited solubility in THF and in DMF, and it has very low solubility when its molecular weight
reaches above 3× 105. The glass transition temperature
(Tg) of DENPPV occurs at 243 °C, which is much higher than that of MEHPPV, that can extended device
longevity.21,22 TGA of the DENPPV copolymers
dis-played that their 5% weight losses occurred between 502 and 336 °C. These thermal stabilities and glass transi-tion temperatures are higher than those of other phe-nylated PPVs reported previously. The higher glass transition and thermal stability are due to the restricted polymer chain mobility and resistant to thermal oxida-tion imparted by the rigid dendritic phenyl group.
reduction (Ered) and oxidation (Eox) potentials for
DEN-PPV were 1.63 and 1.13, respectively. The highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energies were estimated electrochemically to be -5.43 and -2.77 eV, respectively, with a band gap of 2.66 eV. Figure 2b presents the energy level diagram of DENPPV and MEHPPV. The LUMO of DENPPV is higher than that of MEHPPV, while the HOMO of DENPPV is lower than that of MEHPPV. From Figure 2, parts a and b, we conclude that intramolecular energy transfer can occur effectively from the phenylated dendrimer units to the polymer backbone.
The UV and PL spectra of the polymers in THF solution are presented in Figure 3. The absorption peak maximum of each polymer appears between 423 and 485 nm. The polymer solutions display intense blue-green emissions (peak maxima at 492-551 nm), which are blue-shifted as the concentration of the dendritic phenyl monomer in the copolymer increased. The DENPPV polymer displays an emission maximum at 492 nm and
Figure 1. IR spectra of DENPPV and MEHPPV. Table 1. Molecular Weights and Thermal Properties of
DENPPV and Copolymers
mol wtc polymer Mn Mw PDIa Tg(°C)b TGA 5 wt % loss temp (°C) DENPPV 100 000 280 000 2.1 243 502 88DENPPV 120 000 173 000 1.5 226 468 75DENPPV 110 600 136 000 1.1 208 448 63DENPPV 98 000 188 000 1.9 198 427 50DENPPV 78 000 110 000 1.5 186 398 25DENPPV 95 000 238 000 2.0 145 389
aPDI ) Polydispersity index.bT
g) Glass transition
temper-ature.cMolecular weights were calculated with relative to
poly-styrene standard.
Figure 2. (a) UV and PL spectra of the DENPPV and a
dendritic phenyl model compound and (b) energy level diagram of DENPPV and MEHPPV.26
Figure 4 presents the excitation spectra of the poly-mers in solution; they indicate that the well-resolved small peak at 300 nm is due to the substituent dendritic phenyl group, which also confirms that energy transfer occurs from the side chain to the polymer backbone. We observe from Figure 4 that the excitation spectra are the same as the UV-vis spectra; this finding indicates the high purity of the emitting chromophores.
The thin film PL spectra was observed to be similar to those of the solutions, e.g., DENPPV undergoes no significant red shift in the film. In contrast, the MEH-PPV, lacking dendron substituents exhibits a marked red shift in its solid state from its solution state absorption and emission spectra (551 vs 582 nm), which we believe can be attributed to interactions, such as π-π stacking, between the chromophores. These spectra also suggest that the aggregation and migration of the chromophores are reduced in the dendrimers and indi-cate that even the first-generation dendrimers can effectively suppress π-π stacking among polymer chains. Table 2 presents the quantum yields of polymers in the solid state and in solution, and their photoluminescence data. The decadic molar extinction coefficient () was determined in THF using eq 1:
where OD is the optical density, c is the concentration of the polymer in solution, and l is the optical path length of the sample. We determined the fluorescent chromophore concentration (M) in the thin film using eq 2:
where L is the thickness of the film.
DENPPV displays a quantum yield of 0.67 in THF, calculated with reference to coumarin 6; this quantum yield is for about 2-fold higher than that of the well-established MEHPPV, in the solid state it is 0.65. The copolymer 75DENPPV displays a higher quantum yield (0.82) in the solid state than that of DENPPV, which
can be explained by quantum confinement.24The higher
quantum yields of copolymers 88DENPPV and 75 DENPPV in their solid state than that of solution can be explained as being due to the steric effect of dendritic phenyls where the PPV backbone forces the pendant dendritic phenyl ring to point away (one up and one down) from the conjugated plane. Such a three-sional structure prevents PPV stacking in any
dimen-sion, providing higher quantum yields.10d
We fabricated double-layer LED devices having the configuration ITO/poly(3,4-ethylenedioxythiophene)
(PE-Figure 3. UV and PL spectra of DENPPV and copolymers.
Figure 4. Excitation spectra of the copolymers in THF
solution.
)OD/cl (dm3mol-1cm-1) (1)
Table 2. Absorption and Photoluminescence Data of DENPPV and Copolymers
polymer (M-1 cm-1)a ODb L (nm)c M (mol/cm3)d ηs e ηtf f DENPPV 72 900 0.241 47 65 5.04 0.67 0.65 88DENPPV 11 920 0.0855 45 3.09 0.66 0.68 75DENPPV 60 070 0.0862 52 2.75 0.55 0.82 63DENPPV 21 506 0.167 58 65 2.07 0.47 0.41 50DENPPV 52 185 0.169 08 60 5.33 0.50 0.42 25DENPPV 92 065 0.4284 45 1.33 0.33 0.30 MEHPPV 99 274 0.140 78 85 1.48 0.30 0.27
a )Decadic molar extinction coefficient (dm3mol-1cm-1).bOD
) Absorbance or optical density in the solid state.cL ) Thickness
of the thin film.dM ) Fluorescent chromophore concentration in
the film of each composite.eηtf ) Thin-film quantum yield
estimated by using coumarin 6 dispersed in PMMA film at a concentration <10-3M.25 fηs) Solution quantum yield estimated
by using coumarin 6 in THF as the reference.
Figure 5. UV and PL spectra of DENPPV and copolymer
thin films.
M ) OD/L (mol/cm3) (2)
DOT):poly(styrene sulfonic acid) (PSS)/DENPPV/Ca/Al. The EL spectrum of the DENPPV device was similar to its PL spectrum in that it displays an intense signal having a peak maximum at 499 nm (Figure 6.). The copolymer MEHPPV/DENPPV at a molar ratio of 25/ 75 exhibits an even more intense signal at 547 nm. Figure 7 presents the variations of the current density and brightness of the EL devices prepared from MEH-PPV and 75DENMEH-PPV. The electroluminescence of copolymer 75DENPPV displays highest efficiency (0.12 lm/W), it is 70% higher than that of MEHPPV (0.07 lm/W) measured under similar conditions. All of these polymers shows better electroluminescence efficiency
(ηEL) providing that a minimization of the self-quenching
has occurred by attaching the bulky dendrons on the
transfer that occurs from the dendritic phenyl groups to the PPV backbone. The PL quantum yield of DEN-PPV (67%) is among the highest values reported for fully conjugated PPV. The copolymer DENPPV/ME-HPPV molar ratio of 75/25 exhibited increased values
of ηELand ηPL that may make them useful as active
layers in devices such as LEDs and photovoltaic diodes.
Supporting Information Available: 1H NMR and13C NMR spectra of DENPPV and the monomer. This material is available free of charge via the Internet at http://pubs.ac-s.org.
Acknowledgment. The authors thank the National Science Council, Taiwan, for financial support through NSC 92-2120-M-009-009.
References and Notes
(1) (a) Yang, Z.; Karasz, F. E.; Geise, H. J. Macromolecules 1993,
26, 6570. (b) Strukelj, M.; Papadimitrakopoulos, F.; Miller,
T. M. Science 1995, 267, 1969. (c) Grem, G.; Leditzky, G.; Ullrich, B.; Leising, G. Adv. Mater. 1992, 4, 3621. (d) Berggren, M.; Ingana¨s, O.; Gustafsson, G.; Carberg, J. C.; Rasmusson, J.; Anderson, M. R.; Hjertberg, T.; Wennerstron, O. Nature 1994, 372, 444.
(2) (a) Greenham, N. C.; Samuel, I. D. W.; Hayes, G. R.; Phillips, R. T.; Kessener, Y. A. R. R.; Moratti, S. C.; Holmes, A. B.; Friend, R. H. Chem. Phys. Lett. 1995, 241, 89. (b) Samuel, I. D. W.; Rumbles, G.; Collison, C. J.; Crystall, B.; Moratti, S. C.; Holmes, A. B. Synth. Met. 1996, 76, 15. (c) Gettinger, C. L.; Heeger, A. J.; Drake, J. M.; Pine, D. J. J. Chem. Phys.
1994, 101, 1673. (d) Hwang, D.-H.; Kim, S. T.; Li, X. C.;
Chuah, B. S.; Demello, J. C.; Friend, R. H.; Moratti, S. C.; Holmes, A. B. Polym. Prepr. 1997, 38, 319.
(3) (a) Bao, Z.; Peng, Z.; Galvin, M. E.; Chandross, E. A. Chem.
Mater. 1998, 10, 1201. (b) Chung, S. J.; Kwon, K. Y.; Lee, S.
W.; Jin, J. I.; Lee, C. H.; Lee, C. E.; Park, Y. Adv. Mater.
1998, 10, 1112. (c) Chen, Z. K.; Meng, H.; Lai, Y. H.; Huang,
W. Macromolecules 1999, 32, 4351. (d) Greenham, A. C.; Morrati, S. C.; Bradley, D. D. C.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature (London) 1993, 365, 628.
(4) Becker, H.; Spreitzer, H.; Kreuder, W.; Kluge, E.; Schenk, H.; Parker, I.; Cao, Y. Adv. Mater. 2000, 12, 42.
(5) Sokolik, I.; Yang, Z.; Karasz, F. E.; Morton, D. C. J. Appl.
Phys. 1993, 74, 3584. (b) Yang, Z.; Karasz, F. E.; Geise, H. J. Macromolecules 1993, 26, 6570. (c) Pasco, S. T.; Lahti, P. M.;
Karasz, F. E. Macromolecules 1999, 32, 6933. (d) Mikroyan-nidis, J. A. Chem. Mater. 2003, 15, 1865.
(6) Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavetter, F.; Colaneri, N.; Heeger, A. J. Nature 1992, 357, 477.
(7) Aratani, S.; Zhang, C.; Pakbaz, K.; Hoger, S.; Wudl, F.; Heeger, A. J. J. Elec. Mater. 1993, 22, 745.
(8) Yang, Y.; Heeger, A. J. Appl. Phys. Lett. 1994, 64, 1245. (9) Braun, D.; Heeger, A. J. Appl. Phys. Lett. 1991, 58, 1982. (10) (a) Chu, H. Y.; Hwang, D.-H.; Do, L.-M.; Chang, J.-H.; Shim,
H.-K.; Holmes, A. B.; Zyung, T. Synth. Met. 1999, 101, 216. (b) Hsieh, B. R.; Yu, Y.; Forsythe, E. W.; Schaaf, G. M.; Feld, W. A. J. Am. Chem. Soc. 1998, 120, 231. (c) Lee, S. H.; Jang, B.-B.; Tsutsui, T. Chem. Lett. 2000, 1184. (d) Peng, Z.; Zhang,
Figure 6. EL spectra of DENPPV and copolymers.
Figure 7. Plots of current density vs voltage and
lumines-cence vs voltage of the devices prepared from 75DENPPV and
MEHPPV.
(17) Chou, C.-H.; Hsu, S. L.; Dinakaran, K.; Chiu, M. Y.; Wei, K. H. Macromolecules 2005, 35, 745. (b) Chou, H.; Shu, C.-F. Macromolecules 2002, 35, 9673.
(18) Qu, J.; Zhang, J.; Grimsdale, A. C.; Mu1len, K.; Jaiser, F.; Yang, X.; Neher, D. Macromolecules 2004, 37, 8297. (19) Pogantsch, A.; Wenzel, F. P.; List, E. J. W.; Leising, G.;
Grimsdale, A. C.; Mullen, K. Adv. Mater. 2002, 14, 1061. (20) Becker, H.; Spreitzer, H.; Ibrom, K.; Kreuder, W.
Macromol-ecules 1999, 32, 4925.
(21) Dogariu, A.; Gupta, R.; Heeger, A. J.; Wang, H. Synth. Met.
1999, 100, 95.
(22) Shin, D. C.; Ahn, J. H.; Kim, Y. H.; Kwon, S. K. J. Polym.
Sci., Part A: Polym. Chem. 2000, 38, 3086.
(23) Chen, S. H.; Su, A. C.; Chou, H. L.; Peng, K. Y.; Chen, S. A.
Macromolecules 2004, 37, 167.
(24) Johansson, D. M.; Srdanov, G.; Yu, G.; Theander, M.; Inganas, O.; Andersson, M. R. Macromolecules 2000, 33, 2525. (25) Swanson, S. A.; Wallraff, G. M.; Chen, J. P.; Zhang, W.;
Bozano, L. D.; Carter, K. R.; Salem, J. R.; Villa, R.; Scott, J. C. Chem. Mater. 2003, 15, 2305.
(26) Jin, S. H.; Jang, M. S.; Suh, H. S.; Cho, H. N.; Lee, J. H.; Gal, Y. S. Chem. Mater. 2002, 14, 643.
MA050252Q
Enhanced Luminance and Thermal Properties of
Poly(phenylenevinylene) Copolymer Presenting Side-Chain-Tethered
Silsesquioxane Units
Chia-Hung Chou, So-Lin Hsu, Siao-Wei Yeh, Hsu-Shen Wang, and Kung-Hwa Wei*
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30049, R.O.C.
Received May 24, 2005; Revised Manuscript Received August 17, 2005
ABSTRACT: We have synthesized, using the Gilch polymerization method, a new series of high-brightness, soluble copolymers (POSS-PPV-co-MEHPPV) of poly(p-phenylenevinylene) (PPV) containing side-chain-tethered polyhedral oligomeric silsesquioxane (POSS) pendent units and poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV). This particular molecular architecture of POSS-PPV-co-MEHPPV copolymers possesses not only a larger quantum yield (0.85 vs 0.19) but also higher degradation and glass transition temperatures relative to those of pure MEHPPV. The maximum brightness of a double-layered-configured light-emitting diode (ITO/PEDOT/emissive polymer/Ca/Al) incorporating a copolymer of MEHPPV and 10 mol % PPV-POSS was 5 times as large as that of a similar light-emitting diode incorporating pure MEHPPV (2196 vs 473 cd/m2).
Introduction
Emissive media based on electroluminescent (EL) polymers are currently under development for a number of display applications,1-4including large-area flat-panel
displays that can be driven at low voltage. Polymer light-emitting diodes (PLEDs) are very promising can-didates for the development of low-cost, multicolored, large-area flat-panel displays because their molecular structures are readily modified and because they can be handled using a range of wet processing
tech-niques.5,6 A number of issues remain to be resolved,
however, before commercialization of these devices can occur. The formation of excimers resulting from the aggregation of their molecular chains in the solid state, and rather short operating lifetimes, owing to their low thermal stabilities. Several attempts have been made to reduce the formation of aggregates of polymer chains in the solid state. One such approach is the introduction of bulky organic units into the side chains of the polymer. This tactic has been used, for example, in the case of poly(p-phenylenevinylene) (PPV)-based alternat-ing copolymers containalternat-ing conjugated
phenylenevi-nylene segments and nonconjugated spacers;7-9 these
bulky side groups disrupt the packing of the polymer chains, which results in the formation of amorphous PPVs displaying reduced aggregation. Another approach to improving the efficiency of the devices is to blend hole-transporting and electron-hole-transporting materials to
balance the injected charges.10-12aWhen such a device
is operated for a long time, however, this method can
pendent groups as the side chains of the conjugated polymers.
The chemistry of polyhedral oligomeric silsesquioxane (POSS) covalently bonded to organic polymers has been developed recently. One set of members of the polyhe-dral oligomeric silsesquioxane family are octamers having the general formula (RSiO1.5)8; they consist of a
rigid, cubic silica core having a nanopore diameter of
ca. 0.3-0.4 nm.15The incorporation of (RSiO
1.5)8 into
some polymers leads to an enhancement of their
ther-mal stability and mechanical properties.16-18
The first study in which POSS and conjugate poly-mers were combined involved tethering POSS to the chain ends of
poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV)19and the luminescent
polymer poly(9,9′-dioctylfluorene) (PFO). The enhanced
electroluminescence of these nanostructured polymers was attributed to POSS, imparting a reduction in the
degree of either aggregation or excimer formation.13The
approach of tethering POSS at the ends of a polymer’s chain, however, limits the number of POSS units that can be attached. In a previous study, we synthesized a series of side-chain-tethered POSS derivatives of
poly-imide as a method of lowering its dielectric constant.20
More recently, side-chain-tethered PF-POSS copoly-mers have been synthesized; they display a stronger and
purer blue electroluminescence.21a In this paper, we
report a new series of asymmetric PPV derivatives presenting POSS units in their side chains. We
synthe-9117
copolymers has not yet been described. We believe that developing POSS/poly(p-phenylenevinylene) copolymers having well-defined architectures will allow its lumi-nescence properties to be tailored more precisely through modifications of its molecular structure.
Experimental Section
Chlorobenzylcyclopentyl-POSS19awas synthesized according to literature procedures. THF was distilled under nitrogen from sodium benzophenone ketyl; other solvents were dried using standard procedures. All other reagents were used as received from commercial sources, unless otherwise stated.
Chlorobenzylcyclopentyl-POSS. 1H NMR (300 MHz,
CDCl3): δ 7.64 (d, J ) 8.1 Hz, 2H), 7.37 (d, J ) 8.1 Hz, 2H), 4.57 (s, 2H), 2.26-1.21 (m, 56H), 1.16-0.81 ppm (m, 7H).29Si NMR (600 MHz, THF): -67.8, -68.2, -79.6 ppm.
Synthesis of POSS-CH3(1). 2,5-Dimethylphenol (238 mg,
1.95 mmol) was stirred with K2CO3(4.58 g, 33.18 mmol) and KI (1.57 g, 9.48 mmol) in DMF (30 mL) and THF (15 mL) at room temperature for 1 h. A small amount of Cl-POSS (2.0 g, 1.95 mmol) was added, and then the whole mixture was heated at 70 °C for 3 h. The reaction mixture was then slowly poured into water (300 mL) and extracted with chloroform (3× 50 mL). The combined extracts were dried (MgSO4), the solvents were evaporated, and the residue was purified by column chromatography (hexane/chloroform, 1:10) to afford 1 (1.86 g, 81%).1H NMR (300 MHz, CDCl3): δ 7.70 (d, J ) 8.1 Hz, 2H),
7.51-7.31 (b, 3H), 7.03 (d, J ) 6.9 Hz, 1H), 6.67 (s, 1H), 5.09 (s, 2H), 2.37 (s, 3H), 2.32 (s, 3H), 2.27-1.21 (m, 56H), 1.17-0.81 ppm (m, 7H).
Synthesis of POSS-CH2Br (2). A mixture of POSS-CH3 (1; 600 mg, 0.510 mmol), NBS (198.6 mg, 1.02 mmol), and AIBN (8.0 mg) was heated under reflux in carbon tetrachloride under nitrogen for 3 h. The reaction mixture was filtered to remove succinimide, the solvent was evaporated, and the residue was purified by column chromatography (hexane/ chloroform, 1:10).1H NMR (300 MHz, CDCl3) δ: 7.73 (d, J ) 8.1 Hz, 2H), 7.59 (d, J ) 6.9 Hz, 1H), 7.38 (d, J ) 8.1 Hz, 2H), 7.09 (d, J ) 6.9 Hz, 1H), 7.01 (s, 1H), 5.18 (s, 2H), 4.73 (s, 2H), 4.57 (s, 2H), 2.26-1.21 (m, 56H), 1.16-0.81 ppm (m, 7H). Anal. Calcd for C50H76Br2O13Si8 (%): C, 47.30; H, 6.03. Found: C, 47.18; H, 6.09.
General Procedure for the Synthesis of Copolymers POSS-PPV-co-MEHPPV. A solution of potassium tert-butoxide (1 M in THF) was added to a solution of the monomer in dry THF, and then the mixture was stirred for 4 h. End-group capping was performed by heating the solution under reflux for 1 h in the presence of tetrabutylbenzyl bromide. Addition of the THF solution to methanol precipitated the polymer, which was collected, washed with methanol, and stirred in a mixture of methanol and water (1:1) for 1 h. The polymer was collected, washed with methanol, filtered, and dried at 50 °C for 24 h. After cooling, the polymer was recovered by precipitating it into a mixture of methanol and acetone (4:1). The crude polymer was collected, purified twice
Scheme 1.a Synthesis of POSS-PPV-co-MEHPPV Copolymers
aReagents and conditions: i, trichloro[4-(chloromethyl)phenyl]silane, HNEt
3Cl; ii, K2CO3, DMF/THF; iii, N-bromosuccinimide
(NBS)/AIBN/CCl4; iv, tert-BuOK/THF.
by reprecipitation from THF into methanol, and subsequently dried under vacuum at 50 °C for 24 h. The1H and13C NMR spectra of MEHPPV and PPV-POSS appear to be identical because of the low content of POSS in the latter polymer.
Characterization. 1H, 13C, and 29Si nuclear magnetic resonance (NMR) spectra of the compounds were obtained using a Bruker DRX 300 MHz spectrometer. Mass spectra of the samples were obtained on a JEOL JMS-SX 102A spec-trometer. Fourier transform infrared (FTIR) spectra of the synthesized materials were acquired using a Nicolet 360 FT-IR spectrometer. Gel permeation chromatographic analyses were performed on a Waters 410 differential refractometer and a Waters 600 controller (Waters styragel column). All GPC analyses of polymers in THF solutions were performed at a flow rate of 1 mL/min at 40 °C; the samples were calibrated using polystyrene standards. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measure-ments were performed under a nitrogen atmosphere at heating rates of 20 and 10 °C/min, respectively, using Du Pont TGA-2950 and TA-2000 instruments, respectively. UV-vis absorp-tion and photoluminescence (PL) spectra were recorded on a HP 8453 spectrophotometer and a Hitachi F-4500 lumines-cence spectrometer, respectively. Before investigating the thermal stability of the synthesized polymers, their polymer films were annealed in air at 200 °C for 2 h.
Device Fabrication and Testing. The electroluminescent (EL) devices were fabricated on an ITO-coated glass substrate that was precleaned and then treated with oxygen plasma before use. A layer of poly(ethylenedioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS, Baytron P from Bayer Co.; ca. 40 nm thick) was formed by spin-coating it from an aqueous solution (1.3 wt %). The EL layer was spin-coated, at 1500 rpm from the corresponding toluene solution (15 mg mL-1), on top of the vacuum-dried PEDOT:PSS layer. The nominal thickness of the EL layer was 65 nm. Using a base pressure below 1× 10-6Torr, a layer of Ca (35 nm) was vacuum-deposited as the cathode, and a thick layer of Al was deposited subsequently as the protecting layer. The current-voltage characteristics were measured using a Hewlett-Packard 4155B semiconductor parameter analyzer. The power of the EL emission was measured using a Newport 2835-C multifunction optical meter. The brightness was calculated using the forward output power and the EL spectra of the devices; a Lambertian distribution of the EL emission was assumed.
Results and Discussion
Figure 1 displays the 1H NMR spectra of Cl-POSS,
POSS-CH3(1), and POSS-CH2Br (2). The CH2peak of the tethered bulky POSS enhanced the thermal stability
Table 1. Physical Properties of the POSS-PPV-co-MEHPPV Copolymers
Tg(°C) Tda(°C) Mn Mw PDI yield (%) MEHPPV 71 370 61 000 111 000 1.82 78 POSS-PPV1-co-MEHPPV 90 381 55 000 107 000 1.95 66 POSS-PPV3-co-MEHPPV 96 395 52 000 98 000 1.88 64 POSS-PPV5-co-MEHPPV b 417 48 000 91 000 1.90 69 POSS-PPV10-co-MEHPPV b 453 39 000 73 000 1.87 60
aTemperature at which 5% weight loss occurred, based on the initial weight.bThe glass transition disappeared because of the steric
hindrance imposed on the main molecular chains by the POSS units.
Figure 1. 1H NMR spectra of (a) Cl-POSS, (b) POSS-CH 3,
and (c) POSS-CH2Br.
Figure 2. FTIR spectra of (a) MEHPPV, (b)
POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-POSS-PPV1-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, and (e) POSS-PPV10-co-MEHPPV.
peak maxima of MEHPPV occurred at 499 and 553 nm, respectively; these values are close to those reported in
the literature.19 We observed no aggregation band in
these spectra because THF is a good solvent for MEH-PPV. The absortion and emission peaks for MEHPPV and POSS-PPV-co-MEHPPV are almost identical. For
each polymer, the absorption peak maximum in solution (THF) is located between 499 and 494 nm, with a slight blue shift caused by the presence of POSS; the PL maxima occur at similar wavelengths for all of the polymers. Figure 3A presents the normalized absorption and PL emission spectra of the MEHPPV-POSS co-Table 2. Optical Properties of the POSS-PPV-co-MEHPPV Nanocomposites
λmax(UV, nm) λmax(PL, nm)a QY
solutionb film solutionb film filmc
MEHPPV 499 517 553 (592) 591 (634) 0.19
POSS-PPV1-co-MEHPPV 499 512 552 (591) 588 (633) 0.43
POSS-PPV3-co-MEHPPV 498 512 552 (591) 586 (632) 0.62
POSS-PPV5-co-MEHPPV 497 511 552 (591) 585 (631) 0.84
POSS-PPV10-co-MEHPPV 494 505 551 (590) 584 (631) 0.87
aThe data in parentheses are the wavelengths of the shoulders and subpeaks.bThe absorption and emission were measured in THF. cPL quantum yield estimated relative to a sample of Rhodamine 6G (Φ
r) 0.95).23-25
Figure 3. (A) UV-vis absorption and PL spectra of (a) MEHPPV, (b) POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, and (e) POSS-PPV10-co-MEHPPV recorded in the solid state. (B) Normalized (relative to their maximum wavelengths) PL spectra of (a) MEHPPV and (b) POSS-PPV10-co-MEHPPV annealed at room temperature and 150 °C in the solid state. (C) X-ray diffraction spectra of (a) MEHPPV, (b) POSS-PPV1-co-MEHPPV, (c) POSS-PPV3-co-MEHPPV, (d) POSS-PPV5-co-MEHPPV, (e) POSS-PPV10-co-MEHPPV, and (f) Cl-POSS. (D) Deconvoluted X-ray diffraction spectra of (a) MEHPPV and (b) POSS-PPV10-co-MEHPPV.
