Liquid crystal tetramers: influence of molecular shape on liquid crystal behaviour

Abstract

The synthesis and characterization of two homologous series of tetramers in which four mesogenic units are linked via three alkyl spacers are reported. Both series contain a hexamethylene central spacer while the length of the two outer spacers, n, is varied from three to 12 methylene units. The two series differ only in the substitution pattern around the inner two mesogenic units. The series in which one mesogenic unit is attached to the central spacer in the 4‐position while the other is connected at the 3‐position is referred to as the n‐p6m‐n series, while in the n‐m6m‐n series both inner units are attached in the 3‐position. All the members of the n‐p6m‐n series exhibited a nematic phase while no liquid crystallinity was observed for the n‐m6m‐n series. The thermal behaviour of this series is compared with that of the n‐p6p‐n series and also with that of the corresponding series containing a pentamethylene central spacer. The trends observed are interpreted in terms of the average molecular shapes of these tetramers.