Sun Hui, Zhao Yunfeng, Huang Zhaowei, Wang Yue, Li Fei
State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, People's Republic of China.
J Phys Chem A. 2008 Nov 13;112(45):11382-90. doi: 10.1021/jp804846n. Epub 2008 Oct 15.
The pi-stacking structures and self-association thermodynamics of N, N'-di(n-alkyl) quinacridone derivatives (n-alkyl QAs) with various substituents on the side aromatic rings and different length of n-alkyl chains are investigated in organic solvents by (1)H NMR spectroscopy. The stacking geometries are built based on both the magnitudes and directions of peak shifts with concentration and solvent polarity. The intermolecular interaction between nitrogen atoms and oxygen atoms dominates the general geometrical preferences of the stacking in which the molecules are face-to-face arranged in a parallel and an antiparallel fashion, respectively. The stacking structures are little affected by the length of the n-alkyl chains but are regulated in an allowed range by the size and properties of the substituents. The association processes of all the n-alkyl QAs are enthalpically favorable at 298 K, while the relative stability of these n-alkyl QAs assemblies is governed mainly by the entropy of the association processes. The introduction of larger substituents and longer n-alkyl chains disfavors the association of the n-alkyl QAs, while the binding of the halogen atoms on the side aromatic rings is favorable to the association. The relative strength of the stacking interaction for the substituted n-alkyl QAs has not obvious correlation with the electron-donating or electron-withdrawing nature of the substituents, while it is well associated to the dispersion energy and repulsive exchange energy. The different entropy-enthalpy compensation of the halogen-substituted n-alkyl QAs from others may suggest different association mechanism for the two types of n-alkyl QAs.
通过¹H NMR光谱研究了在有机溶剂中，侧芳环上具有各种取代基且正烷基链长度不同的N,N'-二（正烷基）喹吖啶酮衍生物（正烷基QA）的π-堆积结构和自缔合热力学。基于峰位移随浓度和溶剂极性的大小和方向构建堆积几何结构。氮原子和氧原子之间的分子间相互作用主导了堆积的一般几何偏好，其中分子分别以平行和反平行方式面对面排列。堆积结构几乎不受正烷基链长度的影响，但受取代基的大小和性质在允许范围内调节。所有正烷基QA的缔合过程在298 K时在焓上是有利的，而这些正烷基QA聚集体的相对稳定性主要由缔合过程的熵决定。引入较大的取代基和较长的正烷基链不利于正烷基QA的缔合，而侧芳环上卤素原子的结合有利于缔合。取代正烷基QA的堆积相互作用的相对强度与取代基的供电子或吸电子性质没有明显相关性，而与色散能和排斥交换能密切相关。卤素取代的正烷基QA与其他正烷基QA不同的熵焓补偿可能表明这两种正烷基QA有不同的缔合机制。
