Matsushita Takeshi, Koseki Shiro
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan.
J Phys Chem B. 2005 Jul 21;109(28):13493-8. doi: 10.1021/jp050959e.
The structures and intermolecular interaction energies of 10 dimers, included in the mesogenic core structures of typical liquid crystalline (LC) compounds, are obtained at the MP2/6-31G(d) level of theory. It is proved that the dispersion energy significantly contributes to the total interaction energy of these dimers. Even when bulky substituents are introduced into the core part, the interaction energy is still large. It is also revealed that when a long intermolecular distance is provided by a high steric repulsion originating from the linkage of two phenyl groups, the dispersion energy is significantly small. However, in this range of intermolecular distances, the electrostatic energy caused by a strong quadrupole-quadrupole attractive interaction plays a dominant role, and as a result, a rather stable dimer is formed. In all 10 dimers, the dispersion, electrostatic, and exchange-repulsion energies strongly depend on the geometrical orientation of the molecules. The calculated interaction energies of these dimers are also compared with the corresponding experimentally measured viscosities. The results suggest an explicit linear relationship between the interaction energies and viscosities.
在MP2/6 - 31G(d)理论水平下，获得了典型液晶（LC）化合物介晶核心结构中包含的10个二聚体的结构和分子间相互作用能。结果表明，色散能对这些二聚体的总相互作用能有显著贡献。即使在核心部分引入庞大的取代基，相互作用能仍然很大。研究还发现，当两个苯基连接产生的高空间排斥作用导致分子间距离较长时，色散能显著减小。然而，在这个分子间距离范围内，由强四极 - 四极吸引相互作用引起的静电能起主导作用，从而形成相当稳定的二聚体。在所有10个二聚体中，色散、静电和交换排斥能强烈依赖于分子的几何取向。还将这些二聚体计算得到的相互作用能与相应的实验测量粘度进行了比较。结果表明相互作用能与粘度之间存在明确的线性关系。
