| 摘要: | 本篇論文主要分成兩個系列，在系列一中，成功合成出以苯環為中心硬核且含 pyrazole及isoxazole 之不對稱異雜環衍生化合物2a-1c。本實驗藉由引入雜環系統、改變分子軟硬端比、改變位相、引入氫氧基來觀察以上因素對化合物液晶行為的影響。改變碳數可以得到2a、1a，呈現SmA或SmC相，氧烷鏈碳數較短時澄清點溫度較高，液晶相範圍也較廣，推測是碳數增加熱擾動增加使得液晶相較難以形成；改變雜環可以得到2a、2b，呈現SmA或SmC相，具有pyrazole的分子2b因為具有NH的氫鍵所以澄清點溫度較高，液晶相範圍也較廣；改變位向可以得到2a、2c、1a、1c，Meta位相的2c、1c皆為結晶相，Para位相的2a-1a則具有液晶相，表示當分子是Para位相時較為直線，容易誘導出層列行液晶相；改變氫氧基位置得到1a、1b、Ia。從結果可得知化合物皆為桿狀液晶，且為層列型液晶SmA或SmC，透過培養1a與Ia之單晶結構，討論1a與Ⅰa的單晶作用力與排列情況，並發現1a因為有較強的分子間氫鍵以及較小的二面角，導致1a分子澄清點較高，液晶相較廣。
在系列二中成功合成出以苯環為中心硬核且含有兩個且含 pyrazole及isoxazole 之對稱異雜環衍生化合物3a-3c’，本實驗藉由引入雜環系統、改變分子軟硬端比、改變位相、引入氫氧基來觀察以上因素對化合物液晶行為的影響。改變軟硬端比可以得到3a、3b，氧烷鏈碳數較短時澄清點溫度較高，液晶相範圍也較廣；改變雜環可以得到3a、IIIa，具有pyrazole的IIIa澄清點溫度較高，液晶相範圍也較廣，推測是具有NH的氫鍵使分子間作用力增加；改變位向可以得到3b-b’、3a-a’， 間位化合物3a’不具液晶相，推測是分子彎曲使其不易形成桿狀液晶，而3b’卻有具有SmA相，表示置入氫氧基後分子形狀可能趨於桿狀，變成較線型的分子；改變氫氧基位置得到3b、IIIa，發現置入氫氧基的3b的OH的氫鍵使分子間作用力增加，使其誘導出溫度範圍更廣的液晶相，澄清點溫度較高。
;Nowadays liquid-crystalline compounds containing five-membered heterocycles are the subject of much investigation. These heterocyclic structures generally incorporated of such electronegative atoms (O or N atom), often resulting in a reduced symmetry for the overall molecules or/and a stronger polar induction. Both pyrazole and isoxazole are in fact aromatic rings and have good planarity which makes molecules easier to stack together, thus inducing better molecular interaction such as π-πinteractions and possibly H-bonds. In this work, a few new series of asymmetrical structures derived from pyrazoles and isoxazoles was synthesized and their mesomorphic properties were also investigated.
In the first series, for new series of unsymmetric isoxazoles and pyrazoles compounds 2a-1c was synthesized and characterized by 1H NMR, 13C NMR, Mass spectrometry and Elementary anaylysis. Single crystals of mesogenic compounds 1a (n = 8) were obtained, and their single crystal and molecular structures were resolved. Intermolecular and intramolecular Hbonds was observed in crystal lattices. All their precursors 2ab were mesogenic, giving SmA or/ and SmC phases, however, other compounds 2c were not mesogenic. Shape effect and Hbonds inherent in the core might be attributed to the formation of the mesophases. On the other hand, bisheterocyclic compounds 1ab were mesogenic, exhibiting SmC or SmA phases, and other compounds 1c were not mesogenic. H-bonding and shape effect were attributed to the formation of the mesophases observed in such bisheterocyclic compounds. Compound Ia withiout hydroxyl group exhibits lower clearing temperature and shorter range of mesogen phase because of the larger dihedral angels 16.15 and weaker intermolecular interactions.
In the second series, a system of twin mesogens containing pyrazoles and isoxazoles was synthesized and characterized by 1H NMR, 13C NMR, Mass spectrometry and Elementary anaylysis. Meta-substituted benzene 3a’ and 3c’ were not mesogen because the bent shape. On other hand, para-
substituted benzene 3a and 3b were mesogen because the linear shape tends to induce the calimatic liquid crystal. Interestingly, higher clearing temperature and better mesogenic performance were observe in 3b than IIIa because of stronger hydrogen bonding in 3b. |
