| 摘要: | 本論文第一章節主要以triphenylamine與苯胺為中心單元，合成出簡單且對稱性較低的星形盤形液晶分子。在分子架構上均利用黑克反應(Heck reaction)將苯乙烯與中心單元連結，藉此延伸π電子的共振；因此，此部分的分子均具有強螢光的特性。在液晶行為方面，無論中心單元為triphenylamine或苯胺，其外圍烷氧鏈數目需九條以上而碳數為6，8，12及14時才有液晶相生成，其液晶相結構經X-ray繞射實驗證明為六角形柱狀液晶相(columnar hexagonal phase)。在摻混實驗中，AN-ST-A與TNF比例為1/4時有最穩定的液晶相生成，而此混合物的固態吸收光譜在長波長範圍亦有明顯的電荷轉移吸收峰，此結果顯示AN-ST-A因與TNF發生電荷轉移作用力導致其分子間作用力增強而生成六角形柱狀液晶相。
以1,4-di-(4-hydroxy-stryryl)-2,5-bis-(2-hydroxy-ethoxy)benzene (HOB-ST) 為中心單元的X型發光液晶分子，利用與取代基不同計量比進行DCC酯化反應，可獲得四取代(1,4-及2,5-位置)和雙取代(1,4-位置)之化合物；在低溫、鹼性環境下，利用acyl chloride與HOB-ST進行酯化反應則可獲得2,5-位置雙取代之化合物。在液晶行為上，除了2,5-位置雙取代之化合物為非液晶質外，其餘化合物均可觀察到液晶相，顯然的取代基接在分子主軸兩側是較不利於液晶相的生成。此部分化合物末端烷氧鏈碳數均為12個碳，當每一取代基末端烷氧鏈數由1條增加至3條時，其液晶相種類則由條型液晶轉變成盤型液晶；然而增加取代基的苯環數時，除因分子間π-π堆疊作用力增強而導致其澄清點溫度明顯提高外，對液晶相種類則無影響。在分子構型上，枝架末端為單條烷氧鏈之四取代化合物，因2,5-位置上柔軟的亞乙基及立體障礙較小的緣故，使得其取代基往分子主軸方向靠攏，導致其構型近似條型分子因而觀察到條形向列相。
第三章以二甲氧基苯與4-乙烯基吡啶進行雙取代反應(黑克反應)合成出一系列染料分子。依兩個甲氧基的相對位置-鄰位、間位及對位，分為I、II及III系列；再以其官能基的變化-甲氧基、羥基及吡啶基甲基化，細分為a、b及c共九個染料分子。當染料分子上的甲氧基轉變成羥基時(I-a→I-b、II-a→II-b、III-a→III-b)，其吸收與螢光光譜均有些許的紅位移，但變化量則介於5到30nm之間，而兩者在不同極性溶劑下的光譜變化則更輕微，僅有數個nm左右，顯示其對溶劑極性的變化並不敏感。然而吡啶基甲基化後的染料分子(I-c、II-c、III-c)，其光譜的變化明顯劇烈許多，其中以II-c染料分子的變化最大(最大吸收波長紅位移130nm而螢光波長位移了將近100nm之多)。這是因為吡啶基甲基化後成為一個強拉電子基使得分子共振效能變強所致。在溶劑顯色效應方面則也是染料II-c最為明顯(Δλ = 4196㎝-1)，其次是I-c分子(Δλ = 3871㎝-1)而III-c分子相對的較不明顯(Δλ = 2117㎝-1)。以線性溶劑溶合能量關係式(Linear Solvation Energy Relationships，LSER’S)計算三個染料分子對溶劑極性/極化能力之指數時發現，不考慮參數的係數之正負值情形下，由計算結果可以看出在中性條件下，染料II-c分子具有最大的溶劑效應靈敏度及較大的解離能力，此與光譜所得的數據結果相符。
Star-shaped discogens consisted of triphenylamine and 2,4,6-trisubstituent aniline as the central core with different styryl-based side arms, and having 3 and 9 peripheral chains were synthesized. Columnar phases, uniaxially negative, were observed for compounds consisted of 9 peripheral chains (longer than 6 carbon units), but not with 3 peripheral chains. Hexagonal packing of columns was observed from the results of X-ray diffraction. However, the diameter of the column is less than the molecular dimension indicating the interdigitations of peripheral chains of the neighboring columns. Compound AN-ST-A, mixing with TNF (1/4) could induce columnar mesophase due to the intermolecular charge transfer interaction.
X-shaped mesogens consisted of 1,4-di-(4-hydroxy-stryryl)-2,5-bis-(2-hydroxy-ethoxy)benzene as the central core with different side arms, and having 2, 4, 6 and 12 peripheral chains were synthesized and each of peripheral chains has 12 carbon units. The compounds having 2 and 4 peripheral chains exhibit rod-like mesophases (N, SA and SC phases) and the others exhibit disc-like mesophases. Increasing the benzoate unit in side arms did not change the mesophase behaviors but increase the clearing temperature.
New merocyanine dyes were synthesized basing on 4-vinylpyridine coupling with various dihydroxybenzene by Heck reaction : 1,2-di-(N-methylpyridinium-4-ylviny)-4,5-dihydroxybenzene (I-c), 1,3-di-1,3-di-(N-methyl N-methylpyridinium-4-ylviny)-4,6-dihydroxybenzene (II-c) and 1,4-di-(N-methylpyridinium- 4-ylviny)-2,5-dihydroxybenzene ( III-c ). Solvatochromism behaviors of these dyes in various solvents were studied by UV-vis absorption and fluorescence spectroscopy. These stocky shifts resulted from the degree of solvation between dyes and solvents, including ICT (intramolecular charge transfer) from proton transfer or electron transfer. Molecule II-c exhibited the largest negative solvatochromism (Δλ = 4196 cm-1 from DMF to H2O) and can be used to be proton sensor or probe. |
