| 摘要: | 本篇論文主要在介紹具有雜環之結構液晶。所有化合物經由1H-NMR、13C-NMR與元素分析以鑑定其結構及純度，液晶相性質則是利用偏光顯微鏡(POM)來觀測相種類及熱微差掃描分析儀 (DSC) 測量相變化時之溫度與熱焓值，最後以變溫粉末X光繞射儀 (XRD) 確認相的種類，並運用單晶結構之討論，來解釋化合物的排列及其作用力。
在第一部分中，成功合成出兩系列具有pyrazole 和 isoxazole的雙雜環衍生物化合物1a-b。透過X-ray分析鑑定出化合物2a (n = 8) 的單晶結構，而它的晶系為triclinic空間群則為P-1，其a = 7.0511 (2), b = 7.6303 (2) and c = 21.2143 (5) Å, Z = 2。從單晶結果可以得知化合物長度約為24.9 Å，且分子形狀呈現些許的彎曲，分子彼此利用氫鍵形成dimer，因此有利於液晶相的生成。如預期的，所有化合物皆出現了N, SmA, N/SmC或SmA/SmC的桿狀形液晶相。由於雙雜環結構具有更高的dipole及分子間作用力，因此代號1的化合物皆比代號2的化合物有更高的澄清點及更廣的液晶相範圍。
在第二部分中，成功合成出兩系列具有pyrazole雜環的化合物3a-b。這些帶有pyrazole雜環的衍生物，是利用它的前驅物4a-b上的α,βdiketones官能基合環而成的。透過X-ray分析鑑定出化合物4b (n = 6) 的單晶結構，而他的晶系為triclinic空間群則為P-1，其a = 4.7804 (2), b = 16.5849 (8) and c = 19.9328 (10) Å, Z = 2。化合物3a出現了層列型液晶相SmA/SmC，但化合物3b則是結晶相，兩者之間的差異在於化合物3a能夠利用五元雜環使其平面性較佳且分子較為線性，有利於液晶相的生成。因此我們將在內文中討論分子形狀及其液晶相的關聯性。;In this thesis, we report the synthesis, characterization and mesomorphic properties of four novel series of new mesogenic derivates based on heterocyclic structures. All compounds were characterized by 1H, 13C-NMR spectroscopy and elemental analysis. The phase behavior of these mesogenic compounds was characterized and studied by differential scanning calorimeter (DSC) and polarization optical microscope.
In the first part, two new series of mesogenic bis-heterocyclic derivatives containing pyrazoles and isoxazoles 1a-b were reported. One single crystallographic structure of mesogenic 2a (n = 8) was determined by X-ray analysis, and it crystallizes in a triclinic space group P-1, with a = 7.0511(2), b = 7.6303(2) and c = 21.2143(5) Å, and Z = 2. The crystal was considered as slightly bent-shaped molecule with a molecular length of ca. ~24.9Å. A dimeric correlated structure induced by H-bonds was observed in the crystal lattice, which was favorable to the formation of mesophases. All compounds 1-2 exhibited N, SmA, N/SmC or SmA/SmC phases, as expected for linear-shaped molecules. All compounds 1 have higher clearing temperatures and wider ranges of mesophases than those of their precursors 2, which might be attributed to have higher dipoles polarized by two heterocyclic rings in 2.
In the second part, two new series of isomeric bis-pyrazoles 3a-b are prepared, characterized, and their mesomorphic properties investigated. These pyrazoyl derivatives were obtained from the condensation of α,β-diketones 4a-b with hydrazine monohydrate in refluxing THF. One single crystallographic structure of mesogenic 4b (n = 6) was determined by X-ray analysis, and it crystallizes in a triclinic space group P-1, with a = 4.7804(2), b = 16.5849(8) and c = 19.9328(10) Å, and Z = 2. Derivatives 3a exhibited smectic A/C mesophases, in contrast, derivatives 3b were all nonmesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation and the coplanarity of the five rings over than in 3a. The correlation between the molecular structures and the mesomorphic properties is discussed. |
