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Title: | 設計並合成具有推電子基-架橋-拉電子基之分子架構並將其應用於熱致變色、價態間電荷轉移機制與分
子開關研究 Design and Syntheses of Donor-Bridge-Acceptor Molecular Frameworks in the Applications of Thermochromism, Intervalence Charge Transfer, and Molecular Switch |
Authors: | Chao-Che Chang 張肇哲 |
Advisor: | 陳昭岑(Chao-Tsen Chen) |
Keyword: | 熱致變色,光致變色,自由基陽離子,分子開關, thermochromism,photochromism,radical cation,molecular switch, |
Publication Year : | 2012 |
Degree: | 博士 |
Abstract: | 本文的研究目的是設計並合成具有推電子基-架橋-拉電子基的分子系統,並分為三個部分探討熱致變色現象、價態間電荷轉移機制以及作為分子開關之研究。在第一部分的研究是發展具有可逆性之熱致變色分子,如圖(1)所示,藉由改變不同的共軛架橋官能基,探討化合物在質子化後的熱致變色行為。由吸收光譜和螢光光譜的結果顯示,質子化後產生紅位移現象,並且螢光產生了驟息現象。在乙腈溶液中可藉由升溫回復至中性狀態,而在二氯甲烷溶液中,則是需要降低溫度使其回復至中性狀態。氫核磁共振光譜得知,質子化的位置在苯並噻唑的氮原子上,並由變溫實驗可得知氫訊號可隨溫度升高而回復至原本的中性狀態。當架橋分子的芳香性越差,中性狀態和質子化狀態之間的反應焓差異也較小,因此具有較佳之熱致變色特性,並且擁有較好的可逆性。
第二部分的研究是以銅二價金屬離子作為氧化劑將苯胺衍生物氧化形成自由基陽離子,如圖2所示,以芴作為連接苯胺基的架橋分子發現到當其中一個苯胺被氧化形成自由基陽離子時,會產生價態間電荷轉移的現象,因此在吸收光譜中會在近紅外光區有吸收峰的生成。由電子自旋共振光譜實驗得知,自由基陽離子的形成可藉由量測未成對電子訊號證明其存在。除了芴之外,引入不同的架橋分子對於電荷轉移現象也有明顯的影響。 具有光致變色特性的二噻吩乙烯除了可經由照光進行結構之間的轉換,氧化還原的方式也可達到同樣的目的,原因在於經由所產生自由基陽離子可驅使開環或合環反應的進行。在本文的研究中在二噻吩乙烯引入二甲苯胺基並修飾不同的推拉電子基集團,如圖3所示,以銅二價金屬離子作為氧化劑可將苯胺進行氧化形成自由基陽離子,在合環狀態在形成自由基陽離子後可進一步做開環反應形成開環狀態的自由基陽離子。除此之外,由光譜電化學實驗可得到同樣的實驗結果,並藉由還原電位回到原本的中性狀態,電子自旋共振光譜說明開環反應的過程中有自由基陽離子的生成。 The research is focused on the design and synthesis of donor-bridge-acceptor systems in the application of thermochromism, intervalence charge transfer, and molecular switches. In the first part of the study is the development of donor-bridge-acceptor systems as reversible thermochromic applications. As shown in Figure 1, different π-conjugation bridged fragments explore the thermochromic properties in the protonated form. From UV-vis and fluorescence spectra, these molecules show the red shift and the fluorescence quenching after protonation. In acetonitrile solution, the protonated forms can return to the corresponding neutral forms by heating. In dichloromethane solution, it has to reduce the temperature back to its neutral forms. Variable temperature 1H NMR spectroscopy demonstrates that protons of benzothiazole and bridged fragments can restore to the original neutral form at high temperatures in acetonitrile solution. When the aromaticity of bridges is worse, the enthalpy different between the neutral form and the protonated form is smaller, and therefore it can be better thermochromic properties, and has a good reversibility. The second part of the study develops Cu(ClO4)2 as an oxidant to oxidize arylamine derivatives to corresponding radical cation. As shown in Figure 2, fluorene as a bridged fragment connecting two arylamines demonstrates that intervalence charge transfer will take place when one of arylamine is oxidized to form radical cation. Therefore, the absorption spectra will observe absorption band in the near infrared region. Moreover, electron spin resonance experiments can measure the signal of unpaired electron to prove the formation of arylaminium radical cation. In addition to fluorene, the introduction of different bridged fragments also can offer more electron coupling information for charge transfer phenomenon. Photochromic properties of dithienylethene can change its structures reversibly by stimuli like as light and redox. It is because that the generation of radical cation can drive the ring-opening or ring-closing reactions. In this study, we introduce the ditolylamine and different functional groups on dithienylethene (Figure 3). Cu(ClO4)2 as the oxidant can oxidize DTEs derivatives to form corresponding radical cation. In the ring-closed form of DTEs derivatives, arylaminium radical cations can trigger ring-opening reaction and form corresponding ring-opened form. In addition, spectroelectrochemical experiments demonstrate the same results, and the reduction potential can return to the original neutral form. Electron spin resonance spectroscopy shows ring-opening reaction in the process of radical cation generation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/66485 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 化學系 |
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