本篇研究方向為透過全新設計的雙喹啉骨架分子天平，利用低溫核磁共振觀測構型平衡，藉此精確量化多環芳香烴間的堆疊作用力，並且進一步揭露此微弱作用力與結構之間的關聯。 我們利用經典的Friedländer縮合反應建構出具有灣區取代的雙喹啉骨架，並且以鈴木偶聯反應 (Suzuki coupling reaction) 及 布赫瓦爾德-哈特維希偶聯反應 (Buchwald-Hartwig coupling reaction) 進行芳香基團的延伸。接著，利用低溫NMR實驗中所得的構型比例帶入標準吉布斯自由能變化 (Standard Gibbs free energy change) 及吉布斯自由能變化 (Gibbs free energy change) 公式中，即可計算出不同構型間的能量差異。 藉由此分子天平，我們首次觀測到以堆疊構型為主的結果，這在既有文獻中尚未被報導，並且也觀察到隨著多環芳香烴面積增加，堆疊構型比例會顯著上升的結果；另外，我們也發現了多環芳香烴的幾何形狀，也會影響著堆疊作用力的強度。 ;This study focuses on the development of a newly designed molecular balance featuring a diquinoline scaffold, which enables the precise quantification of stacking interactions between polycyclic aromatic hydrocarbons (PAHs) through the observation of conformational equilibria via low-temperature nuclear magnetic resonance (NMR) spectroscopy. Furthermore, this system allows us to explore the subtle relationship between these weak non-covalent interactions and molecular structure.
The diquinoline scaffold bearing bay-region substituents was synthesized via a classic Friedländer condensation reaction, followed by the extension of aromatic substituents through Suzuki coupling and Buchwald–Hartwig coupling reactions. The conformer ratios obtained from low-temperature NMR experiments were then applied to the equations for standard Gibbs free energy change and Gibbs free energy change to calculate the energy differences between the conformers.
Using this molecular balance, we observed for the first time a predominant preference for the stacked conformation — a result not previously reported in the literature. Moreover, we found that the proportion of stacked conformers significantly increases with the surface area of the PAHs. In addition, we discovered that the geometric shape of the PAHs also influences the strength of the stacking interactions.
