側鏈液晶聚乙炔之合成及光電性質研究

Abstract

本研究主要目的在於探討聚乙炔衍生物之合成及其在光電方面的應用。聚乙炔衍生物大致上可分為單取代及雙取代兩大類，由於結構上的差異使兩者不管在合成條件或光電性質上均具有明顯的差別，因此本論文將分成兩部份加以探討，第一部份為單取代聚乙炔衍生物之合成及光電性質研究，第二部份則為雙取代聚乙炔衍生物之合成及光電性質研究。 在單體設計方面，均於炔基上導入具反式環己烷之液晶基，但為了討論聚合物主鏈對材料熱性質及光激發光和電激發光效應的影響，於乙炔基旁之連接基團分別使用了氫原子、苯基及長碳鏈烷基。另一方面，為了探討聚合物側鏈大小對於材料光電性質的影響，於液晶基之末端基及側取代基也有所變化。 在第一部份中總共合成了18個聚乙炔衍生物，依結構的不同可分為聚苯基乙炔( polyphenylacetylene，PPA )衍生物及聚烷基乙炔( polyalkylacetylene )衍生物兩類。聚合反應以rhodium complex及metathesis catalyst為催化劑，其中rhodium complex適用於具有較大立體障礙的PPA衍生物( 1P ~ 6P )之合成並可得到主鏈共軛雙鍵主要為順式之產物，而含VIB族過渡金屬之metathesis催化劑則適用於起始聚烷基乙炔衍生物( 7P ~ 18P )之合成，且其主鏈結構均為反式。所合成聚合物具有良好的熱穩定性，但PPA系列因結構太過剛硬而不具任何液晶相。於光電性質方面，聚烷基乙炔系列具有光激發光效果，且其放射光波長約為500 nm，屬於藍綠光材料，唯其強度甚低，雖經摻混入聚甲基丙烯酸酯後因減低了interchain interaction作用而可提昇其光激發光強度，但仍無法順利的量測到製做為元件後之電激發光譜圖。PPA系列則因具有過高的結晶度且發光團直接與極性官能基相連接，使得生成的exciton易被quench住而不具光激發光效果。 在第二部份中則合成了6個雙取代之乙炔單體，與第一部份不同，此具極性基團的雙取代乙炔液晶單體19M ~ 24M並無法以任何催化劑起始其聚合反應，經改以使用本實驗室以往合成過之無極性官能基tolane衍生物，乃順利以含VB族過渡金屬之metathesis催化劑合成出具有聚雙苯基乙炔( polydiphenylacetylene )主鏈結構之聚合物25P ~ 28P。此類聚合物熱穩定性佳但亦因主鏈過於剛硬而不具液晶相，然而其光激發光強度較第一部份所合成之單取代聚乙炔改善許多，可高達近2000倍。經製做為雙層二極體元件( ITO/PEDOT/ polymer/Al )後，可於520 ~ 550 nm間測得單一放射峰，為藍綠光或黃光材料，但其發光效率並不高，僅為3.82×10-3 lm/W。在元件性質的改良方面，我們在做為發光層之高分子薄膜中摻混入poly(vinylcarbazole) ( PVK )，所得元件的電激發光放射波長及發光效率並無太大變化，但其驅動電壓可由原本的10 V大幅降低至6.5 V，推論這是由於PVK具有電洞傳輸的作用。

The goal of this research is to study the polymerization and application of polyacetylene ( PA ) derivatives. Based on different substituents, two kinds of PA derivatives were synthesized in this study. The first part of this study will focus on the synthesis and electro-optical properties of mono-substituted PA derivatives. The second part of this study will focus on the synthesis and electro-optical properties of di-substituted PA derivatives. In the first part, four series of mono-substituted polyacetylenes containing trans-4-n-alkylcyclohexanoate side groups were synthesized by using [Rh(nbd)Cl]2, MoCl5, and WCl6 as catalysts. Polymers 1P ~ 6P, which contain no flexible spacer, show no mesomorphic properties due to the rigid polyphenylacetylene backbone. Polymers 7P ~ 18P, which contain three or four methylene units in their spacers, exhibit both smectic and nematic phases. X-ray diffraction diagrams reveal that the liquid crystalline polyacetylenes display an interdigitated bilayer structure for the smectic phases. Polymers 7P ~ 18P emitted a green photoluminescence ( PL ) at about 500 nm. The PL intensity increased dramatically when a polyacetylene was blended with poly(methyl methacrylate). In the second part, two series of di-substituted acetylene monomers were synthesized and polymerized. Monomers 19M ~ 24M which containing polar ester group in their tolane or phenylalkylacetylene core, were unable to be polymerized by Ta- or Nb-based catalyst. Monomers 25M ~ 28M which containing no polar ester or ether group in their tolane core, were polymerized by Ta- and Nb-based catalyst. The obtained polymers 25P ~ 28P exhibit no mesomorphic property due to their rigid polydiphenylacetylene backbone, too. The PL and electroluminescence (EL) properties of the four polymers made as double-layer device ITO/PEDOT/ polymer/Al have been comprehensively studied. They emit green or yellow PL and EL at about 520 ~ 550 nm. When they were blended with poly(vinylcarbazole) and used as the emission layer, the driving voltage of LED device decreased from 10 V to 6.5 V. however, their EL intensities were kept at about a same value.