Intercalated liquid-crystalline phases formed by symmetric dimers with an α,ω-diiminoalkylene spacer
作者:Maja Šepelj、Andreja Lesac、Ute Baumeister、Siegmar Diele、H. Loc Nguyen、Duncan W. Bruce
DOI:10.1039/b612517d
日期:——
Four series of symmetric, dimeric molecules with flexible α,Ï-diiminoalkylene spacers have been synthesised and characterised by polarising optical microscopy, differential scanning calorimetry, and X-ray diffraction. The effects on the mesomorphism of the various alkylene spacer (number of methylene units m = 5 to 8) as well as the terminal alkoxy chain length (n = 4 to 14) on the mesomorphic properties have been studied. The compounds with an even-numbered spacer display, in addition to a nematic phase, various smectic phases whose nature depends on the ratio between the length of the terminal chain and the length of the spacer (n/m). A modulated Smà phase was found for the ratio n/m = 1 to 1.6 and a SmC/crystal G polymorphism emerges at n/m > 1.7. In contrast, all liquid-crystalline dimers with odd-numbered spacers display an intercalated B6 phase regardless of the chain length. The preference for intercalated structures is discussed based on dipolar considerations following electronic structure calculations using a model molecule.
合成并表征了四系列对称的二聚体分子,这些分子具有灵活的α,ω-二氨基烷烃间隔基。通过偏振光学显微镜、差示扫描量热法和X射线衍射技术对其进行了表征。研究了不同烷烃间隔基(亚甲基单元数m=5至8)以及末端烷氧链长度(n=4至14)对其介晶特性的影响。具有偶数间隔基的化合物除了表现出一个向列相外,还展现出各种层状相,其性质取决于末端链的长度与间隔基长度之间的比率(n/m)。在比率n/m=1到1.6时发现了调制的SmA相,而在n/m>1.7时则出现了SmC/晶体G多型性。相反,所有具有奇数间隔基的液晶二聚体无论链长如何均表现出夹层B6相。基于使用模型分子的电子结构计算,讨论了夹层结构偏好的偶极考虑。