Effects of polar end group, flexible spacer length and molecular conformation on properties of the liquid crystal dimers

Two series of symmetric liquid crystal dimers, namely 1F and 3F, have been synthesised by varying the length of the flexible odd spacer. The melting temperatures and clear points of the 3F series are higher than those of the 1F series. The 1F series only exhibits nematic phase, while the 3F series displays both smectic A and nematic phases. As the length of the flexible spacer increases, the dominance of the smectic phase becomes more pronounced. This phenomenon may be attributed to the combined effect by the polar end group CF3 and the long flexible spacer on the molecular conformation.