Liquid crystalline macrocycles containing phenylpyrimidine units
Liquid crystalline macrocycles containing phenylpyrimidine units
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DOI：
10.1039/b210271d
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发表时间：
2003-01-01
影响因子：
--
通讯作者：
Tschierske, C
中科院分区：
文献类型：
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作者：
Neumann, B;Hegmann, T;Tschierske, C
在高稀释条件下，通过大环化反应合成了几种不同的大环液晶，它们由两个棒状的2-苯基嘧啶或5-苯基嘧啶单元通过聚醚或烷基链在两端连接而成。刚性核的性质对形成的液晶相具有强烈的影响。所有的2-苯基嘧啶paracyclophanes显示的α-相，而对于一系列的5-苯基嘧啶衍生物的近晶A-相专门形成。这种行为与传统的棒状苯基嘧啶液晶有关，但中间相在大环中是强烈稳定的。聚醚链与烷基链的交换导致显著的中间相稳定化，而增加间隔基长度降低了中间相稳定性。预组织的calamitic核心和化学上不同的分子部分的微观偏析进行了讨论，作为观察到的分子结构对这些化合物的中间相行为的影响的原因。
Several different macrocyclic liquid crystals consisting of two calamitic 2-phenylpyrimidine or 5-phenylpyrimidine units connected at both ends by polyether or alkyl chains have been synthesised by macrocyclisation reactions under high dilution conditions. The nature of the rigid core has a strong impact on the liquid crystalline phases formed. All 2-phenylpyrimidine paracyclophanes show nematic phases, whereas for the series of the 5-phenylpyrimidine derivatives smectic A-phases are exclusively formed. This behaviour is related to conventional calamitic phenylpyrimidine liquid crystals, but the mesophases are strongly stabilised in the macrocycles. An exchange of polyether chains by alkyl chains leads to significant mesophase stabilisation, whereas increasing the spacer length reduces mesophase stability. Pre-organization of the calamitic cores and micro-segregation of chemically distinct molecular parts are discussed as reasons for the observed effects of molecular structure on the mesophase behaviour of these compounds.