五苯荑-烯酮-苯乙烯架構之分子雙剎車系統

Abstract

本論文探討了五苯荑衍生之分子雙剎車系統：化合物1的分子設計、合成及其性質研究。我們以五苯荑分子作為轉輪，於其中心苯環的兩端分別引入烯酮與苯乙烯等兩個基團作為剎車；透過雙鍵的異構化，化合物1共可形成四個順反異構物，其中五苯荑各受不同程度的立體阻礙，如此我們期望它能展出現四階段的轉速。 透過變溫碳譜的模擬結果，我們得知化合物 (E,trans)-1在室溫下的轉速約為8500 轉/秒，化合物 (E,cis)-1約為80 轉/秒，化合物 (Z,trans)-1約為50 轉/秒，而化合物 (Z,cis)-1因訊號過於混雜，無法做光譜模擬，但這也暗示著此時五苯荑的旋轉幾乎是停止的。 透過在不同波長下四個異構物的分佈比例，我們得知E→Z的轉換在吸光範圍內都有很好的效率，反之Z→E的轉換則幾乎不會進行；在260 nm下可進行(E,trans)-1 → (Z,cis)-1與 (E,cis)-1 → (Z,cis)-1的轉換；在290 nm下可進行(E,trans)-1 → (Z,trans)-1與 (E,cis)-1 → (Z,trans)-1的轉換。然而，當以Z位向的化合物為起始時，其在260 nm與290 nm下之cis/trans的轉換效率不佳，可能是有其它去活化路徑競爭掉了雙鍵異構化的途徑。對於Z→E的轉換，我們期望透過電化學的方式，使其經過自由基陰離子中間體來進行異構化，然而操控的條件目前仍在找尋中。

Abstract In this thesis, we report the design, synthesis and performance of a brand-new molecular double brake system (1), which consists of a pentiptycene rotor, a styrene brake and an enone brake. Isomerization of double bonds would cause four isomers, corresponding to four distinct mechanical sates. Due to different extent of steric hindrance among the rotor and the two brake units in each state, compound 1 is expected to perform rotary motions of four stages. Simulation for the 13C NMR spectra under various temperatures reveals rotation kinetics in each state. Under room temperature, (E,trans)-1 has the rotation rate of 8500 s-1, (E,cis)-1 of 80 s-1, and (Z,trans)-1 of 80 s-1. Data for (Z,cis)-1 are not available due to mixed and broadened NMR signals; however it suggests that the rotation of pentiptycene is nearly stopped in this state. Distribution among four isomers under various irradiating wavelengths shows that E→Z conversion is highly efficient within the absorption range, while Z→E conversion almost doesn’t occur. Irradiating either of the E isomers leads to larger portion of (Z,cis)-1 under 260 nm, while more (Z,trans)-1 is obtained under 290 nm. Cis/trans conversion under 260 nm and 290 nm is inefficient for both Z isomers; other deactivating pathway may preclude their isomerization. As far as the conversion of Z→E is considered, we would like to apply electrochemical inputs, under which isomerization occurs via a radical anion intermediate. However, the operation strategy is still under study.