1.高熱穩定性之二維非線性光學聚亞醯胺研究2.高倍頻轉換效率之全共軛型式非線性光學高分子研究

Investigation of Thermal stability and High Second Harmonic Generation Efficiency Nonlinear Optical Polymers

蔡協致(Hsieh-Chih Tsai)

指導教授 ： 薛敬和

國立清華大學/工學院/化學工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00495

摘要

有機非線性光學(non-linear optical,NLO)材料的主要應用於數據儲存及光電通訊技術等方面，高分子NLO材料需於高溫下進行極化(poling) ，使發色團之偶極矩順向排列，然而材料於高溫使用下,其分子鍵會因應力鬆弛(relaxation)而導致順向性變差,從而喪失其非線性光學性質。另外倍頻轉換效率提升，亦是目前研究主軸，轉換效率提升能大幅降低光電調制器之驅動電壓降至一個伏特以下，從而擴大NLO高分子材料之應用範圍。故本研究第一部份針對NLO高分子穩定性方面做探討，藉由二維結構發色團於高玻璃轉移溫度(Tg)的聚亞醯胺高分子，以期達到穩定材料的配向偶極之方法。第二部份針對NLO高分子中之發色團共軛延伸做探討，不同已往，利用Yamamoto聚縮合反應於主鏈上設計全共軛形式，發色團共軛區域於主鏈共軛共享，藉由聚合方式延伸發色團共軛長度。第三部份高倍頻轉換效率之NLO高分子，早期共軛長度延伸主要設計於推拉電子基兩端，此延伸長度會受限於有效共軛長度，利用分子設計將推拉電子基軸向與延伸方式垂直，大幅提高其非線性光學係數。
高溫穩定型含二維咔唑發色團之NLO聚亞醯胺
主要以「熱穩定性之非線性光學高分子」為研究主軸，而非線性光學材料選擇上利用咔唑之等電位特性，可在3，6位置上引入強拉電子基之磺醯基之結構，形成二維結構之含磺醯基咔唑發色團，此二維結構雖會導致非線性光學係數d33之降低但可預期整個結構之穩定性卻也相對的提高，對高分子方面則以高玻璃轉移溫度之聚亞醯胺為主，除了高溫穩定優點之外，聚亞醯胺還有幾項特點，高機械強度，化學穩定性，低介電常數等增加了其在光電材料方面的應用。研究結果，本系列Λ型聚亞醯胺材料經過電場排列後具有高的非線性光學係數，其d33值可達17.2 pm/V。此二維非線性光學聚亞醯胺，於非線性光學之熱穩定性實驗觀察下，有效轉移溫度(Effective Transition Temperature)T0高達240℃，另外，本材料同時具有穩定配向偶極之材料特性，儘管經過配向後之材料的操作溫度在100℃條件下，其SH訊號仍能在長時間的熱處理過程其SH穩定性僅衰退2％。其主要原因除了二維發色團之特殊分子結構所造成之影響外，直接將此二維發色團埋入高分子主鏈結構中對其自由體積的降低亦是一重要之因素。藉由發色團旋轉體積的提升以及高分子本身自由體積的減小使其配向偶極即使在100℃時仍能保持相當程度的穩定性。
側鏈型全共軛式NLO高分子
本研究主旨在探討發色團嵌入於主鏈全共軛結構，並藉由主鏈共軛延伸來延長發色團共軛長度，探討其對非線性光學之提升作用。以poly(N-vinylcarbazole)(PVK)與poly(2,7-carbazole) (PCz)進行硝基化反應，合成出相近的硝基比率之非線性光學高分子(PVKNO2與PCzNO2)。熱性質測量(TGA、DSC)均顯示具主鏈剛硬特性之PCzNO2有較高的熱穩定性。在極化過程中，PCzNO2有較高的有效二次諧波(SH)數值，因此證明發色團嵌入於主鏈的全共軛結構對於非線性光學係數確實有增強的功用。另外，本研究以單一發色團利用Yamamoto聚合方法，成功的合成出具2,7-咔唑之非線性光學高分子(PCzCCSO2)與(PCzCCNO2)，其達到近100％發色團對單一高分子比。在溶解度方面，即使具有高度的發色團含量仍易溶於THF、DMF、DMSO以及NMP等溶劑。在熱性質方面，藉由主鏈上延伸剛硬的stilbene結構，以提升高分子間的嵌合效應以及分子旋轉所需的自由體積，測得其玻璃轉移溫度為140℃。在非線性光學方面，因具高度發色團含量與主鏈共軛結構等優勢，故在雷射波長為1064nm下，研究成果顯示PCzCCNO2顯示出優異的倍頻非線性光學係數d33值為45.6pm/V、d31=10.2 pm/V。在時間穩定性上，於85℃下經過200小時，仍維持原來的76％數值。
高效率主鏈型全共軛式NLO高分子
主鏈型全共軛式NLO高分子材料的研究上，利用2-(2,6-Diphenethyl- pyran-4- ylidene)-malononitrile分別進行Yamamoto聚縮合及Suzuki 偶合成功合成出一系列具主鏈共軛結構之非線性光學高分子P1、P2、P3。三個高分子之Td/Tg分別為276℃/125.6℃(P1)、329.5℃/118.2℃(P2)及301.7℃/135.6℃(P3)。此主練全共軛形式NLO形成類似3維結構中空圓球狀，配向過程中，能有效降低發色團所產生中心對稱排列，再利用溶媒色移法，觀察出這類發色團具備極佳一次分子過極化率(β)，此型態共軛延升方式，異於傳統，一般β值增加雖會隨著共軛長度增加，但能仍限於有效共軛長度，此方式設計能大幅降低NLO發色團之限制，故經過極化後，此一系列主鏈全共軛NLO高分子展現最佳的二次非線性光學係數155.2-192.2 pm/V之間。利用Suzuki 偶合聚合反應增加高分子聚合度，使其分子量增加，故P2與P3經過極化後擁有較佳非線光學係數。而材料之熱穩定性測試，在動態熱穩定性測試結果P1亦展現最佳的穩定性(P1、P2、P3之T0分別為100.4℃、86.4℃及81.3℃)，可歸咎於其較高玻璃轉移溫度以及具備較剛硬芳香族鏈段所構成，而在85℃下P1於85℃下經過200小時，仍維持原來的79％數值。

關鍵字

非線性光學 ； 高熱穩定性 ； 高倍頻轉換效率 ； 聚亞醯胺 ； 共軛高分子

並列摘要

Abstract
Second-order nonlinear optical(NLO) materials have attracted interest because of their potential application in optoelectronic technology. Organic polymer system have emerged in recent years as a new class of promising because they offer the flexibility, both molecular and bulk levels, to optimized the nonlinearity and other required properties for device application. However, some crucial issue such as thermal stability, temporal stability of dipole orientation and high frequency doubling efficiency are important challenge to materials scientists. In this work, a series of NLO polymer architecture have been designed. Thermal stability, temporal stability and frequency doubling efficiency made a leap in these NLO polymers designed.
Highly thermal stability of Two dimensional nonlinear optical polyimide
A new NLO-active lambda-shape main-chain polyimide containing the two-dimensional carbazole chromophore has been synthesis. This polyimide overcomes some drawbacks of head-to-tail type main-chain NLO polymers. It can be dissolved in many aprotic solvents and the thin film easily aligned under corona poling process to generate large d33 (17.2 pm/V) value. This polyimide exhibits high thermal and temporal stability. it can endure as high as 240 oC in a transient time and maintain large SH signal at 100 oC for a long time. This is due to the fact that embedding the two-dimensional chromophores onto a fully aromatic polyimide backbone effectively hinders randomization of the oriented dipole at high temperature.
Fully conjugated side chain nonlinear optical polymer
Most NLO organic materials are based on an aromatic π-electron system asymmetrically end-capped with electron-donating and electron-accepting electrons. Structural relationships indicate that β increases with π-conjugating length or the use of stronger electron-donating or electron-accepting moieties. Therefore, increasing conjugation length has been the usual method of modeling NLO materials. A new strategy for the self-polymerization of chromophores is investigated to develop a 2,7-carbazole-based nonlinear optical (NLO) conjugated polymer with an increasing conjugation length of chromophores. Elongation the conjugation path length in chromophores is established engineering guidelines to enhance optical nonlinearity. Compared with traditional synthesis of NLO polymer, the chromophores should be well designed at a limited conjugation spacer then incorporated into polymer matrix. Furthermore, this study marks the first research of integrating the π-electrons of chromophores and conjugated polymer. Integrating the π-electron of chromophores into the conjugated polymer provides more opportunity for simultaneously optimizing macroscopic nonlinear optical activity and temporal stability, than are associated with general NLO polymers. In an NLO conjugated polymer system, the rigid aromatic main chain may provide a high Tg, effectively suppressing the relaxation of the NLO chromophores-polymer system. Additionally the conjugated polymer parts increase the nonlinear optical coefficient. This kind of NLO polymers exhibit more potential in Electro-optic devices.
Highly efficiency fully conjugated main chain nonlinear optical polymer
Recent progress in developing highly efficient nonlinear optical polymers for high-performance electro-optic (EO) devices has been published. Our efforts are focused on conjugation extension on perpendicular the dipole moment of chromophore. To realize the different extention system of macro-chromophores, we observed the first hyperpolarizabilities of these macro-chromophores by solvatochromism method. The result showed that first hyperpolarizabilities would increase via extension of conjugation length without disrupted by effective conjugation length. Moreover, these integrating π-electron of chromophores into the conjugated polymer main chain system form three dimensional hollow annularity structures. Spatial isolation from the three dimensional structures decreases chromophore-chromophore electrostatic interaction As result, these fully conjugated main chain nonlinear optical polymer exhibit the excellent nonlinear optical properties may attribute the high efficiency first hyperpolarizabilities in microscopic level and site-isolation of macro-chromophores in macroscopic level.

並列關鍵字

Nonlinear optical ； Thermal stability ； High SH efficiency ； polyimide ； conjugated polyumer