1,4-雙三唑偶氮苯為橋聯之雙芳杯衍生物之合成、自組裝與順反異構化熱力學研究

Abstract

從文獻中可知，凝膠因子通常含有長碳鏈來增加分子間的凡得瓦作用力，而本實驗室曾發表過不含長碳鏈，以異咢唑取代的雙芳杯化合物，在特定的條件下形成膠體。此外，依據本實驗室蘇培湄學姐之論文，利用相同之雙芳杯化合物以偶氮苯作為橋聯，能夠合成出具有光刺激應答之膠體。故本文中主要探討芳杯上三級丁基形成之凡得瓦作用力、及芳杯下緣氫鍵作用力對於形成膠體所造成之影響力。 本文成功利用點擊化學之方式，合成出分別在芳杯上緣及下緣以偶氮苯為橋聯之雙芳杯化合物。經過一系列膠體性質測試，我們發現下緣雙芳杯化合物45及上緣雙芳杯化合物46分別在苯及正丁醇中會形成膠體。對照實驗室合成之化合物，我們可以證實，三級丁基所提供之凡得瓦作用力對於形成膠體具有很大之影響力。接著，我們藉由掃描式與穿透式電子顯微鏡來探討其自組裝的形貌，並運用變溫NMR、紫外可見光吸收光譜、粉末X-ray繞射儀、紅外光譜儀來推測自組裝的模型。 偶氮苯可藉由照光及調控溫度而具有順反異構化之特性，目前已經有許多文獻討論影響順反異構化速率之因素，在本文中主要以一系列偶氮苯為橋聯之巨環分子 (Macrocycles) 進行機制之探討。由實驗結果我們推論有以下兩種可能：(一) 我們將化合物分為兩系列，分別是化合物53、50、45及48為甲氧基系列及化合物46、49甲基系列，我們可以發現，此兩系列間之活化能，皆隨著分子量增加而有些微上升之趨勢，因此我們認為可能有rotation之機制；(二) 我們推測此處可能受電子效應影響，偶氮苯對位皆為拉電子的三唑分子，會致使活化能下降，而三唑環旁的基團可能引發電子誘導效應，進而影響其推拉電子能力，導致其活化能間之差異，故可能為inversion之機制，但目前仍有此兩種推測仍有許多討論空間，且需借助更多對照化合物及理論計算以釐清其反應機制。

Gelator molecules usually contain long alkyl chains to increase the van der Waals interaction among them. However, we have previously reported a serendipitous discovery that isoxazole bridged biscalix[4]arene without any long alkyl chains forms gel in certain conditions. Besides, in our previously group reseach thesis of Ms. Su, we introduced azobenzene to synthesize azobenzene bridged biscalix[4]arene derivatives which can be used to form photo responsive organogelators. In this thesis, we synthesize the lower and the upper-rim azobenzene bridged biscalix[4]arenes without tert-butyl group by the click reaction to study the function of the tert-butyl and the hydroxyl group of calix[4]arene in forming gels. According to the results, we find compound 45 only in benzene and compound 46 only in n-butanol can form gel. It means van der Waals interactions among the tert-butyl groups play an important role in forming gels. The variable-temperature 1H-NMR, variable-temperature absorption spectra, PXRD, SEM, TEM, and IR spectroscopy are used to gain our understanding of possible packing models of compound 45 and 46. Furthermore, we study the thermally induced cis-trans isomerization of a series of azobenzene-bridged macrocycles. On the basis of the literatures, two mechanisms—rotation and inversion, have been proposed as possible pathways for azobenzene thermal isomerization. We suspect that the activation energies will be affected by the macrocycles at the para position. According to the results, we propose two possible viewpoints. First, the results shows the energy barrier of these compounds slightly increase as the molecular weights increase. It means the rotation mechanism may happen. In other word, the size of substitutes will influence on the isomerization of azobenzene derivatives. Second, we study about the electronic effect of the substituents. We find the activation energies become smaller as the electron-withdrawing effect increases. The results indicate the inversion mechanism works in this place. Hence, electronic effect plays a crucial role on the energy barrier of the thermally induced cis-trans isomerization of the azobenzene. The mechanisms of these azobenzene-bridged macrocycles still remain to be discussed further, and the computational calculations is worthy of studying.