L-丙氨酸誘導之手性單股螺旋降冰片烯高分子

Abstract

本篇論文的主旨在設計及合成出懸掛手性丙氨酸和蒽發色團之單股螺旋降冰片烯高分子，並利用圓二色光譜、紫外可見光吸收及螢光光譜等光物理方法研究高分子的螺旋性以及發色團之間相互作用的變化。 氫鍵在對於降冰片烯高分子形成螺旋結構上占有重要的地位。在蒽發色團與降冰片烯高分子骨架間引入具有二醯胺基團的手性丙氨酸連接基團，如此可以調整發色團之間的位向而有利於激發子偶合，同時手性中心的引入也可誘導高分子及所懸掛之發色團產生螺旋排列。單一醯胺連接基團並不足以有效調整懸掛發色團之間的位向，因此這類高分子不具有裂分的CD訊號。在此我們利用在蒽發色團與4-胺基苯醯胺基團區域的激發子偶合來瞭解降冰片烯高分子的螺旋性。 加入不同量的(R)-及(S)-鏡像單體所造成具有鏡像超越值的共聚合所得到的無規共聚物，由於雙氫鍵網路將懸掛基團間的位向緊密固定，手性中心的甲基便較容易影響每一單體單元的螺旋方向。高分子中每當手性中心由(R)變(S)或由(S)變(R)，螺旋結構也跟著反轉，而導致CD訊號之抵消。所以並不具有單一螺旋的結構，即不遵循Majority rule。

The purpose of this thesis is to design and synthesis single-stranded helical polynorbornenes (PNBs) appended with chiral alanine and anthracene chromophores and further use photophysical methods to study the helicity of these polymers and interactions between pendant Hydrogen bonding plays an important role for the helical structure of these polymers. Bisamidic linkers are essential to ensure the bisignate CD curves for these polymers. Single amidic linkage may be not strong enough to hold the pendants in proper orientation, and therefore polymers with with such linkers are CD inactive. Exciton coupling method at the absorptions for the anthracene and 4-aminobenzamide chromophores is used to depict the helicity of the polymers. Because hydrogen bond networks bring the pending adjacent groups into a fixed orientation, the chiral center would induce the right-handed or left-handed helical direction of every monomeric unit. Therefore the random copolymer from the copolymerization of a mixture of (R)- and (S)-enantiomeric monomers with a enantiomeric excess cannot produce PNBs with a single-handed helical conformation. This helical PNB system does not follow Majority rule.