香蕉型液晶之合成及自組裝研究

Abstract

本研究成功的合成了對稱結構之KBC7、BC7、BC11、DBC7、BC7RR、BC7SS以及不對稱化合物BC7R、BC7S、TBC6、B6-PEG。其中化合物KBC7為向列型液晶，DBC7化合物具藍光發光現象，但是由於結構過於平面，於是並未顯現液晶相，但在分子自組裝以及光電特性相關研究上仍然有很大的發展空間。TBC6分子則由於tolane結構過於平面且較剛硬，以致於不易誘導液晶相產生。親水性分子B6-PEG為黏稠狀流體，於室溫下的自組裝製程中，無法得到預期的結果。化合物BC7和BC11分別為B2及B1香蕉型液晶相，我們成功的利用BC7及BC11排列出螺旋的結構，證實三級結構下香蕉型分子的排列並且推測出其可能的機制。化合物BC7R以及BC7S皆具有B1香蕉型液晶相。根據BC7及BC11的結果，我們進一步的將光學活性中心引進香蕉型分子，BC7R及BC7S化合物中。由分子自組裝的結論，我們可以得知引進光學活性官能基至香蕉型分子末端基時，由於光學活性中心的立體障礙由分子層面進而轉移到分子堆疊上使結構扭轉成螺旋管狀。BC7R化合物自組裝為右旋扭轉，BC7S化合物為左旋扭轉。我們利用光學活性官能基的引入成功的有方向性的控制香蕉型液晶的螺旋扭轉方向。本研究係首度證實香蕉型液晶分子可以在溶液中自組裝形成具有螺旋結構狀之超分子結構。

We have designed and synthesized several banana shaped liquid crystalline (LC) compounds, namely KBC7, BC7, BC11, DBC7, BC7RR,and BC7SS, and asymmetric LC compounds BC7R, BC7S, TBC6,and B6-PEG. The compound KBC7 exhibits nematic phase. DBC7 shows no mesomorphic behavior, however it exhibits photoluminescence behavior. The self-assembly of BC7 from molecular to macroscopic level, in particular the morphology of hierarchical superstructure, has been studied to examine the mechanisms of chirality from achiral banana-shaped LC molecules at different self-assembling levels. Various hierarchical superstructures including flat-elongated lamellar crystal, left- and right-handed helical ribbons, and tubular texture were observed when BC7 molecules were self-assembled in THF/H2O solution. Furthermore, a new variety of bent-core LC molecules with chiral entity, BC7R and BC7S, has been synthesized. The formation of hierarchical superstructures with helical sense can be found via the self-assembly of the BC7R and BC7S. The results indicate that the controlled helicity of the helical architectures can be successfully achieved by introducing the chirality from molecular level. Here we demonstrate the first example of a banana-shaped liquid crystal to form a hierachical superstructure with helical sence via self-assembly of molexules in solution.