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首页> 外文期刊>Physical chemistry chemical physics: PCCP >A solid-state NMR investigation of the odd-even effect in a series of liquid-crystal dimers
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A solid-state NMR investigation of the odd-even effect in a series of liquid-crystal dimers

机译：固态NMR研究一系列液晶二聚体中的奇偶效应

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The origin of the odd-even effect in the solid-nematic phase transition temperatures for a series of molecules is investigated by a variety of solid-state NMR experiments and powder XRD. The molecules consist of a flexible alkyl chain -(CH2)(n-), with identical aromatic mesogenic groups at either end. It is found that the alkyl chain in the molecules exists in a range of different conformations in the solid state. The different conformations are in exchange with each other at room temperature and above. Molecules with n odd show a greater range of conformations at any given temperature than those with n even. The conformational distributions in the nematic phases is investigated by quenching samples from the nematic phase to low temperature. It is found that the range of conformations available to the alkyl chains in the nematic phase is similar to that in the solid state at room temperature. The molecular packing in the solid state is investigated by powder XRD and by studying the molecular dynamics of both the alkyl chains and the mesogenic groups by solid-state NMR. It is concluded that compounds with n odd have significantly different packing from those with n even. This in turn accounts for the different range of alkyl chain conformations seen in the n odd and n even compounds, and at least in part explains the odd-even effect in the solid - nematic phase transition temperatures seen along the series of molecules. [References: 30]
机译：通过各种固态NMR实验和粉末XRD研究了一系列分子在固态向列相转变温度中奇偶效应的起源。分子由柔性烷基链-（CH2）（n-）组成，在两端均具有相同的芳香族介晶基团。发现分子中的烷基链以固态存在一系列不同的构象。在室温及更高温度下，不同的构象相互交换。具有n个奇数的分子在任何给定温度下的构象范围都比具有n个偶数的分子更大。通过将样品从向列相骤冷至低温，研究了向列相的构象分布。发现向列相中烷基链可用的构象范围类似于室温下固态的构象范围。通过粉末XRD研究固态中的分子堆积，并通过固态NMR研究烷基链和介晶基团的分子动力学。结论是，n奇数的化合物与n奇数的化合物具有明显不同的堆积。这又解释了在n个奇数和n个偶数化合物中看到的烷基链构象的不同范围，并且至少部分解释了沿一系列分子看到的固-向列相转变温度中的奇偶效应。 [参考：30]

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