Department of Chemistry, Key Laboratory of Medicinal Chemistry for Natural Resources (Ministry of Education), Yunnan University, Kunming, Yunnan 650091, P. R. China.
J Am Chem Soc. 2011 May 25;133(20):7872-81. doi: 10.1021/ja200822z. Epub 2011 May 2.
T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col(hex)/p6mm, Col(rec)/p2gg, Col(squ)/p4gm and Col(squ)/p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col(rec)/c2mm phase made up of rhombic cylinders with the Col(squ)/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col(rec)/p2gg to Col(squ)/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.
已合成并通过偏光显微镜、DSC 和 X 射线散射研究了由联苯刚性核、半氟化侧链、末端两个极性 1,2-二醇基团和连接极性基团与联苯核的柔性烷基间隔物组成的 T 形 bolaamphiphiles。研究了间隔物长度和间隔物位置对液晶相自组装的影响。随着间隔物长度的增加，发现了一系列四种不同的柱状相（Col(hex)/p6mm、Col(rec)/p2gg、Col(squ)/p4gm 和 Col(squ)/p4mm），代表由具有六边形、五边形和正方形横截面的圆柱组成的液晶蜂窝状结构。还表明，在 T 形 bolaamphiphiles 的主链中引入脂肪族间隔物会取代由菱形圆柱组成的 Col(rec)/c2mm 相，而由正方形圆柱组成的 Col(squ)/p4mm 相。它还导致五边形圆柱的 2d 晶格从 Col(rec)/p2gg 增加到 Col(squ)/p4gm 的对称性。首次观察到这两种五边形圆柱结构之间的温度依赖性二阶相变。除了对圆柱形状和相对称性的这些影响外，柔性间隔物单元还导致相转变温度降低，并允许调整圆柱边长以包围更广泛的侧链尺寸。电子密度图表明，这可能涉及牺牲一些氢键。
