| dc.description.abstract | 在系列一中成功合成出以1,3,4-oxadiazole或1,3,4-thiadiazole為中心硬核且含有兩個isoxazoles之對稱三雜環衍生化合物1b3c，藉由改變中心雜環與側鏈基數目，來觀察對液晶行為表現的影響。從結果可得知，化合物1b擁有N/SmC的桿狀型液晶相，與實驗室慧珊學姊之化合物Ia相互比較，Ia與1b具有相同的液晶相產生，且化合物1b之液晶相溫度範圍比Ia廣，推測原因為1,3,4-thiadiazole之exocyclic angle比1,3,4-oxadiazole的大，分子形狀較呈線性，有利於桿狀液晶的行成；總側鏈基數目為4之化合物2ab，縱使縮短長碳鏈之碳數改變分子長度，仍因其分子結構類似於板狀，並無出現液晶性質；總側鏈基數目增加至6之化合物3ab經由偏光紋理圖與powder X-ray diffraction實驗結果判定為Colh盤狀液晶，並將粉末繞射所得到的數據做理論計算模擬出化合物3ab在液晶相中的堆疊情形，此外，我們發現化合物3b之液晶相範圍比3a廣，推測原因為將中心雜環上的氧原子替換成硫原子後增加了分子的dipole moment，使得3b分子有較大的極化現象，分子與分子間之吸引力增加有利於分子堆疊，盤狀液晶相溫度範圍增加。
第二系列成功以substituted tetraketonates 2ac為配位基，與boron difluoride (BF2)形成錯合物1ac，其中化合物1a和1b並無液晶相產生，而化合物1c (n = 8, 10, 12) 因達適合的軟端硬核比例，經由偏光紋理圖與powder X-ray diffraction實驗結果判定為Colh盤狀液晶，另外從培養出的化合物1a (n = 14)單晶探討分子之排列情形與作用力多寡。化合物1ac ( n = 8) 以UV可見光光譜、螢光光譜探討該分子的光學性質，從結果可得知增加推電子的烷氧基數目，使得最大放光波長紅移，即 max = 538 (1a) < 641 (1b) < 708 nm (1c)。化合物1c為目前第一個含雙BF2結構之盤狀液晶。
系列三以substituted 2-(2’-hydroxyphenyl)benzoxazole 2ab為配位基與boron difluoride (BF2)形成錯合物1ab，其中化合物1a (n = 6, 8, 12, 16)皆為單向型SmC相液晶，化合物1a (n = 1)和1b皆因軟鏈比例太少和排列情形不同於具有液晶性質之化合物而無液晶的性質出現，從培養出的化合物1a (n = 8)單晶探討分子之排列情形與作用力多寡，並藉由化合物1a (n = 8)之單晶排列與1a (n = 12)之XRD實驗結果可推論1a (n = 12)分子在液晶相時符合SmC相的傾斜排列。化合物1a與2a (all n = 8, 12, 16)以UV可見光光譜、螢光光譜探討光學性質，由結果可知改變烷氧鏈碳數長短對最大吸收波長與最大放光波長不造成影響，化合物2a受激發後發微微的藍光、化合物1a則發很亮的紫光，另外化合物2a 受excited state intramolecular proton transfer (ESIPT) effect影響，其Stokes shift大於化合物1a。 | zh_TW |
| dc.description.abstract |
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 or lowering symmetry for the overall molecules or/and a stronger polar induction. Quite a few examples, including pyrazoles, isoxazole, 1,3,4-oxaziazoles, and others have been prepared and investigated in our group. Most of them formed smectic phases whereas, only a few of them exhibited columnar phases.
In the first part, six new series of symmetry structures based on oxadiazole or thiadiazole as core 1a-3b containing isoxazoles and different numbers of terminal alkyl chains. Compared with compounds Ia, made by Hui-Shan Chen, compounds 1b have substituted oxygen with sulfur to increase temperature range of calamitic phases. Compounds 2a and 2b did not exhibit liquid crystal behaviour because of their catenar stuctures. Increasing the number of terminal alkyl chains, compounds 3a and 3b exhibit columnar mesogen behaviour. Compounds 3b have more wider temperature range of mesogenic phases than those of compounds 3a, which is attributed to the substitution of oxygen with sulfur to increase the dipole moments and packing of molecules. A value of Ncell = 3.82 and 4.04 within a column slice of 9.0 Å thick was obtained for compound 3a and 3b, respectively, indicating that two molecules were correlated within columns in Colh phases.
Complexes or adducts containing boron difluoride (BF2) have been paid much attention during the past years. Many known boron difluoride complexes, widely investigated as fluorescent materials showed potential applications in many areas; such as biological imaging, molecular probes, electroluminescent devices, photosensitizers and others. However, only a few examples were reported among mesogenic applications.
In the second part, three new series of bis(boron difluoride) complexes 1ac derived from substituted tetraketonates 2ac were reported, and their mesomorphic and optical properties were also investigated. The single crystal of nonmesogenic diboron complex 1a (n = 14) was obtained, and its single crystal and molecular structures were resolved. Results appeared that bis(BF2) complexes 1ab were nonmesogenic and 1c (n = 8, 10, 12) exhibited enantiotropic columnar mesophases. A value of Ncell = 2.702.86 within a column slice of 9.0 Å thick was obtained for compound 1c, indicating that a single discshaped molecule was stacked within columns in Colh phases. Bis(BF2) complexes 1ac (n = 8) possess a pronounced yellowred emission in solution at room temperature. The luminescent emission showed a strong dependence with structural moiety incorporated with a max = 538 (1a) < 641 (1b) < 708 nm (1c). To our best knowledge, this is the first example of columnar bis(BF2) complexes.
In the third part, two new series of mono(boron difluoride) complexes 1ab derived from substituted 2-(2’-hydroxyphenyl)benzoxazole 2ab were reported, and their mesomorphic and optical properties were also investigated. The single crystal of mesogenic boron complex 1a (n = 8) was obtained, and its single crystal and molecular structures were resolved. Results appeared that mono(BF2) complexes 1a (n = 6, 8, 12, 16) exhibited monotropic smectic C phases, however, 1a (n = 1) and 1b were not mesogenic. Ligand 2a (n = 8, 12, 16) and mono(BF2) complex 1a (n = 8, 12, 16) possess a pronounced blue and violet emission in solution at room temperature, respectively. Because of excited state intramolecular proton transfer (ESIPT) effect, ligand 2a exhibited a larger Stokes shift than complex 1a. | en_US |