Calucci Lucia, Forte Claudia, Csorba Katalin Fodor, Mennucci Benedetta, Pizzanelli Silvia
Istituto per i Processi Chimico Fisici, CNR, Area della Ricerca di Pisa, via G. Moruzzi 1, Pisa, Italy.
J Phys Chem B. 2007 Jan 11;111(1):53-61. doi: 10.1021/jp066025n.
ClPbis11BB and Pbis11BB, two banana-shaped mesogens differing by a chlorine substituent on the central phenyl ring, show a nematic and a B2 phase, respectively. To obtain information on the structural features responsible for their different mesomorphic behavior, a study of the preferred conformations of these mesogens has been performed by NMR spectroscopy in two nematic media (Phase IV and ZLI1167), which should mimic the environment of the molecules in their own mesophases, avoiding problems of sample alignment by a magnetic field. To this aim, 2H NMR experiments have been performed on selectively deuterated isotopomers of ClPbis11BB and Pbis11BB and of two parent molecules, ClPbisB and PbisB, assumed as models in previous theoretical and experimental conformational studies. We found that only a limited number of conformations is compatible with experimental data, often very different from those inferred from theoretical calculations in vacuo, indicating a strong influence of the liquid crystalline environment on molecular conformation. No significant differences between chlorinated and non-chlorinated molecules were found, this suggesting that chlorine does not change the molecular conformational equilibrium, as previously proposed.
ClPbis11BB和Pbis11BB是两种香蕉形介晶，它们在中心苯环上有一个氯取代基的差异，分别呈现向列相和B2相。为了获得有关导致它们不同介晶行为的结构特征的信息，通过核磁共振光谱在两种向列相介质（IV相和ZLI1167）中对这些介晶的优选构象进行了研究，这两种介质应模拟分子在其自身中间相中的环境，避免磁场导致的样品取向问题。为此，对ClPbis11BB和Pbis11BB以及两种母体分子ClPbisB和PbisB的选择性氘代同位素异构体进行了2H NMR实验，这两种母体分子在先前的理论和实验构象研究中被用作模型。我们发现只有有限数量的构象与实验数据相符，这些构象通常与真空理论计算推断的构象非常不同，这表明液晶环境对分子构象有很强的影响。在氯化和非氯化分子之间未发现显著差异，这表明氯不会像先前提出的那样改变分子构象平衡。
