| 摘要: | 本篇論文主要分成兩個系列，在系列一中，我們成功合成出以thiophene為中心硬核且含 pyrazoles及1,3,4-oxa(thia)diazoles 之不對稱三雜環衍生化合物1a-1f，並且藉由引入OH基團或增加側鏈基的數目，來觀察對液晶行為表現的影響。從結果可得知，化合物1a-1d出現了N/SmC, SmC, SmA或SmA/SmC的桿狀型液晶相，化合物1a與1b結構中均含有oxadiazole 雜環且多了一個OH基團，提供更多氫鍵作用力使得分子排列更為規則，因此與1a相比有較高的澄清點以及較廣的液晶相範圍；然而化合物1c與1d結構中含有thiadiazole雜環，可使整體分子結構更為線性且後者多了一個OH基團，提供更多氫鍵作用力讓分子排列更有秩序性，使得1d在四者中澄清點較高，而其中以 1d (n = 8) 液晶範圍最廣。之後藉由增加側鏈基的數目合成出化合物1e-1f，從結果可得知1e與1f配合偏光紋理圖以及X-ray粉末繞射儀的鑑定判斷其為Colh液晶相，並將粉末繞射所得到的數據做理論計算模擬出化合物1e-1f在液晶相中的堆疊情形。
在系列二中成功合成出以pyridine為中心硬核且含有兩個1,3,4-oxadiazoles之對稱雙雜環衍生化合物2a-2d，並藉由改變不同位向的pyridine與側鏈基數目，探討對液晶相範圍的影響。從結果可得知2a-2d均為盤狀型液晶，且2c與2d液晶範圍相較於2a與2b寬廣，推測原因為para位之2c與2d在液晶相時的排列更有利於堆疊，其中又以2c (n = 12)液晶相範圍最廣。接著透過偏光紋理圖及X-ray粉末繞射鑑定出2a-2d均為Colh液晶相，並將粉末繞射所得到的數據做理論計算模擬出化合物2a-2d在液晶相中的堆疊情形。最後對化合物的光學性質做探討，可觀察到化合物2c與2d之最大吸收峰比化合物2a與2b來得紅位移，因此可以得知化合物2c與2d的平面性比2a與2b來得更好。
;Nowadays more and more liquid-crystalline compounds containing five-membered heterocycles are the subject of much investigation. These heterocyclic structures generally incorporated of such electronegative atoms (S, O or N atom) often resulted in a reduced symmetry for the overall molecules or/and a stronger polar induction. Heterocyclic compounds, such as pyrazoles or 1,3,4-oxadiazoles are often considered as electron acceptors. In contrast, thiophene is multi-electron heterocycle ring and has better planarity, and it is also considered as an electron donor. Incorporation of a polar hydroxyl group might greatly impact its thermal and mesomorphic behavior.
In the first part, six new series of asymmetry structures based on thiophene as core 1a-f containing terminal pyrazoles and 1,3,4-oxa(/thia)diazoles. Compared with compounds 1a and 1c, compounds 1b and 1d have an extra hydroxyl group substitutes to the 1,3,4-oxa(/thia)diazoles. All compounds 1a-f were characterized by 1H and 13C-NMR spectroscopy. The phase behaviors of these mesogenic compounds were characterized and studied by polarized optical microscope (POM) and differential scanning calorimeter (DSC). All compounds 1a-d exhibited smectic mesophases except 1a (n = 8) which has a short nematic mesophase, and all compounds 1e-f exhibited columnar phases, which were confirmed by powder XRD diffractometer. Ncell and Rar value equal to 5.48, 5.66 and 22.71, 23.73 Å within a slice of 9.0 Å thick were obtained for derivatives 1e-f (n = 8), indicating that a more disc-like structure constructed by two molecules lying side-by-side were correlated in Colh phases.
In the second part, four new series of isomeric bis-1,3,4-oxadiazole 2a-d were prepared, characterized, and their mesomorphic properties investigated. All compounds exhibited columnar phases, which were confirmed by powder XRD diffractometer. Ncell and Rar value equal to 6.65, 5.47 and 24.74, 22.52 Å within a slice of 9.0 Å thick were obtained for derivatives 2a, 2c (n = 8), indicating that a more disc-like structure constructed by two molecules lying side-by-side were correlated in Colh phases. In contrast, Ncell and Rar value equal to 4.04, 4.33 and 18.82, 19.48 Å within a slice of 9.0 Å thick were obtained for derivatives 2b, 2d (n = 8), indicating that two molecules were correlated within columns in Colh phases. The UV-vis absorption spectra of all compounds 2a-d (n = 8) show maximum absorption peaks at 320-353 nm, indicating that 2c-d have more coplanarity than 2a-b, and the PL spectra of all compounds 2a-d (n = 8) show blue emission with maxima of the emission peaks at 438-518 nm. |
