Department of Chemistry, University of York, York, YO10 5DD, UK.
Chemistry. 2019 Nov 13;25(63):14454-14459. doi: 10.1002/chem.201903677. Epub 2019 Oct 17.
The N phase phases possess a local helical structure with a pitch length of a few nanometers and is typically exhibited by materials consisting of two rigid mesogenic units linked by a flexible oligomethylene spacer of odd parity, giving a bent shape. We report the synthesis and characterisation of two novel dimeric liquid crystals, and perform a computational study on 10 cyanobiphenyl dimers with varying linking groups, generating a large library of conformers for each compound; this allows us to present molecular bend angles as probability weighted averages of many conformers, rather than use a single conformer. We validate conformer libraries by comparison of interproton distances with those obtained from solution-based 1D H NOESY NMR, finding good agreement between experiment and computational work. Conversely, we find that using any single conformer fails to reproduce experimental interproton distances. We find the use of a single conformer significantly overestimates the molecular bend angle while also ignoring flexibility; in addition, we show that the average bend angle and flexibility are both linked to the relative stability of the N phase.
N 相具有局部螺旋结构，螺距长度为几个纳米，通常由由两个刚性介晶单元通过奇数奇偶性的柔性低聚亚甲基间隔物连接而成的材料表现出来，呈现弯曲形状。我们报告了两种新型二聚液晶的合成和表征，并对具有不同连接基团的 10 个氰基联苯二聚体进行了计算研究，为每个化合物生成了大量构象库；这使我们能够将分子弯曲角度表示为许多构象的概率加权平均值，而不是使用单个构象。我们通过与基于溶液的 1D H NOESY NMR 获得的质子间距离进行比较来验证构象库，发现实验和计算工作之间有很好的一致性。相反，我们发现使用单个构象无法重现实验质子间距离。我们发现使用单个构象会严重高估分子弯曲角度，同时忽略了灵活性；此外，我们还表明，平均弯曲角度和灵活性都与 N 相的相对稳定性有关。
