以五苯荑-吲哚衍生物為主體之分子煞車合成與性質研究

Abstract

本論文主要是合成與探討分子煞車系統IMe 與IAn，以五苯荑為轉子，吲哚 衍生物為分子煞車器，煞車器與轉子間以可進行順反式異構化之雙鍵連結，以期 應用於光電控制之分子機械元件設計。利用變溫1H 和13C NMR 圖譜、DFT 理論 計算，探討轉子於煞車前與煞車後之轉動動能與動力學參數。當化合物於順式結 構時（cis-IMe ，cis-IAn），煞車器與轉子間由於立體障礙因素，使轉子之單鍵 旋轉速率較慢（煞車開啓），而當化合物於反式結構時（trans-IMe，trans-IAn） 煞車器與轉子間則因無明顯立體障礙，使轉子有較快的旋轉速率（煞車關閉）， 轉子於煞車開啓與關閉狀態間旋轉速率差可達108 倍。 此分子煞車系統之控制，則是利用煞車器與轉子間連接之雙鍵，在二氯甲烷 溶劑中之順反異構化進行煞車轉換。以反式化合物（trans-IMe，trans-IAn）為起 始物，利用大於370 奈米波長為激發光源，當達到光反應穩定狀態時，反式異構 物轉換為順式異構物之效率可達90％以上，此乃由於化合物於反式結構時於370 奈米波長之吸收度較大，因此可有效率被激發至激發態，進而進行異構化反應。 同樣，順式異構物可經由激發290 奈米波長，轉換回反式異構物，當達到光反應 穩定狀態時，兩者比例約為55:45 （順式：反式），由於吸收光譜之重疊性，使 得順式異構物利用光為能源時，轉換為反式異構物之效率較差。另一方面，若使 用電化學氧化方式，將順式異構物經由陽離子自由基中間體，轉換為反式異構物 之單次轉換效率則可達72%，但由於化合物對於電化學實驗之低穩定性， 使其無 法成為一理想光電轉換之分子煞車系統。

We designed pentiptycene-indole-derived molecular brakes IMe and IAn for the purpose of achieving both high switching efficiency and efficient brake performance. Rotational rate and kinetic parameters were deduced form variable-temperature 1H and 13C NMR simulation and DFT calculation. The rotational rate could reach 108 -folded difference between brake on and brake off states. We compared 2 different energy input, light and electric energy, for isomerization switch of the compounds. For photoisomerization switch, the efficiency could reach > 90% from trans isomers to corresponding cis isomers when the compound was irradiated with > 370 nm light. The high switching efficiency was because of the larger absorbance for trans isomers at the wavelength. However, the photoisomerization switching efficiency was only 45% for cis isomers to corresponding trans isomers for their overlapping absorption spectra. On the other hand, the electrochemical isomerization switch could reach 72% efficiency from cis-IMe to thermodynamically stable trans-IMe through a cation radical intermediate. However, because of the instability of indole moiety upon electric pulse, the pentiptycene-indole-derived molecular brakes are not ideal systems with electric energy input.