The liquid crystalline (LC) properties of two series of non-symmetric dimesogenic compounds consisting of cholesterol and ring-fluorinated azobenzene mesogenic moieties interconnected by ω-oxyalkanoyl spacers of varying length are compared; one series (F-AOC-n) has the octyloxy tail attached to the fluorinated azobenzene mesogen unit while the other (F-AOCF-n) has the perfluoroheptylmethyloxy tail. In general, compounds with the fluorinated alkoxy tail exhibited a mesophase over a much wider temperature range than those with the alkoxy tail. On the other hand, the F-AOC-n series exhibited a greater variety of mesophases: TGB (twisted grain boundary), chiral smectic C (SC*), antiphase smectic A (SÃ), cholesteric (N*) and solid state smectic (SX) phases were observed depending on the length of the central spacer, whereas the F-AOCF-n series favored the formation of only the SA phase with the N* phase completely suppressed. Both series showed an odd-even dependence of the isotropization temperature on the spacer length.
比较了两系列非对称二向色性化合物的液晶性质,这些化合物由
胆甾醇和环
氟化的
偶氮苯介晶基团组成,通过不同长度的ω-氧烷酰间隔基连接;其中一系列(F-AOC-n)在
氟化的
偶氮苯介晶单元上连接了辛氧基尾,而另一系列(F-AOCF-n)则连接了
全氟庚基甲氧基尾。总的来说,具有
氟化烷氧基尾的化合物的液晶相温度范围更广,而具有烷氧基尾的化合物的温度范围较窄。另一方面,F-AOC-n系列表现出更丰富的液晶相:根据中心间隔基的长度,观察到了扭结晶界(TGB)、手性层状C(SC*)、反相层状A(SÃ)、胆甾相(N*)和固态层状(SX)相,而F-AOCF-n系列主要形成层状A(
SA)相,完全抑制了N*相的形成。两系列化合物均显示出间隔基长度的奇偶依赖性,对均质化温度有影响。