含亚胺和胆甾烯基不对称液晶二聚体的合成及介晶性

报道含亚胺和胆甾烯基不对称液晶二聚体化合物XC₆H₄N＝CHC₆H₄OC₁₀H₂₀COOCh* [X＝OC_nH_2n＋1, (n＝1～12,14), F, Cl, Br, CH₃] (1a～1q)的合成及液晶性. 目标化合物通过600 MHz ¹H NMR和元素分析进行了结构表征. 其介晶性通过偏光显微镜(POM)和差示扫描量热计(DSC)进行了研究. 结果显示: 所有化合物都具有胆甾相(N*). 对于烷氧基系列(X＝OC_nH_2n＋1), 有部分化合物还呈现了近晶A相(S_A), 且随着末端烷氧链长度的增加, 化合物的清亮点呈现缓慢下降的趋势, 而化合物从胆甾相到各向同性液体转变的熵变(ΔS_N*→I)则呈现奇-偶效应. 同时我们对比研究了取代基X对胆甾相稳定性的影响, 发现取代基X对胆甾相的稳定性高低顺序为: MeO＞Cl＞Br＞Me＞F. 这些结果证实了末端取代基的改变对化合物的相转变温度以及介晶性质有显著的影响.

Synthesis and Mesomorphism of Unsymmetrical Liquid Crystalline Dimers with Imine and Cholesteryl Moieties

series of unsymmetrical liquid crystal dimers containing imine and cholesteryl moieties interconnected by 11-oxyundecanoyl were reported, which have the structure of XC₆H₄N＝CHC₆H₄OC₁₀H₂₀- COOCh* [X＝OC_nH_2n＋1 (n＝1～12, 14), F, Cl, Br, CH₃]. The target compounds were characterized with 600 MHz ¹H NMR and elemental analysis. Their mesomorphic properties were studied with polarizing optical microscopy and differential scanning calorimetry. The results showed that all of these dimesogens exhibited a cholesteric phase. For these dimesogens containing terminal alkoxy chain (X＝OC_nH_2n＋1), some also showed the smectic A phase. And it was discovered that, as the length of terminal alkoxy chain increased, the clearing points of these dimesogens decrease slowly, but the entropy change (ΔS＝ΔH/T) of these dimesogens from the cholesteric phase to isotropic liquid had an obvious odd-even effect. At the same time, the influences of the terminal substituent group X on the stability of the cholesteric phase were studied and it was discovered that the sequence of stability was: MeO＞Cl＞Br＞Me＞F. The results confirmed that the change of the terminal substituent group has a remarkable influence on the phase transition temperatures as well as the mesomorphic behavior.