Mesogenic properties of two 1,3,4-oxadiazole-based bent-core geometrical isomers
Mesogenic properties of two 1,3,4-oxadiazole-based bent-core geometrical isomers
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DOI：
10.1080/02678292.2012.755226
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发表时间：
2013-03-01
期刊：
影响因子：
2.2
通讯作者：
Goodby, John W.
中科院分区：
文献类型：
--
作者：
Belaissaoui, Abdelhak;Cowling, Stephen J.;Goodby, John W.
两个新的对称恶二唑为基础的双核介晶轴承顺式和反式几何立体异构体尾巴，香叶基氧基和橙花氧基，已被合成和顺反式几何构型的末端链的热分布和介晶行为的影响进行了研究，使用差示扫描量热法和偏光显微镜。具有末端香叶基氧基链的反式-反式立体异构体化合物4g表现出以纹影织构为特征的双相，其含有2-和4-刷状缺陷并且显著地没有近晶中间相。顺式-顺式立体异构体橙花氧基衍生物4 n具有低得多的熔融温度，但不表现出介晶性。为了进一步降低中间相的熔点，在香叶基氧基和橙花基氧基2，5-双（4-羟基苯基）-1，3，4-恶二唑衍生物之间进行了二元混合物研究。介晶性保持高达50%的比例，在香叶基氧基反式-反式立体异构体4g的70%处达到交叉，导致混合物的单变行为。一旦橙花氧基顺式-顺式立体异构体同系物4 n过量，则中间相被完全抑制。
Two new symmetrical oxadiazole-based bent-core mesogens bearing cis and trans geometrical stereoisomer tails, geranyloxy and neryloxy, have been synthesised and the effect of the cis-trans geometric configuration of the terminal chains on the thermal profile and mesomorphic behaviour were investigated using differential scanning calorimetry and polarised optical microscopy. The trans-trans stereoisomer compound 4g with terminal geranyloxy chains exhibited a nematic phase characterised by the schlieren texture, which contained both 2- and 4-brush defects and remarkably no smectic mesophases. The cis-cis stereoisomer neryloxy derivative 4n has a much lower melting temperature but did not exhibit mesomorphism. In an attempt to further lower the melting point of the nematic mesophase, a binary mixture study was carried out between the geranyloxy and neryloxy 2,5-bis(4-hydroxyphenyl)-1,3,4-oxadiazole derivatives. The mesomorphism is retained up to 50% ratio, with a cross-over reached at 70% of the geranyloxy trans-trans stereoisomer 4g, resulting in monotropic behaviour of the mixture. Once neryloxy cis-cis stereoisomer homologue 4n is in excess, the mesophase is completely suppressed.