Mesophasic helical structures with high twisting power in optically active 3-methyladipic acid bis esters

Abstract

A homologous series of novel twin molecules, (R)-3-methyladipic acid bis[4-(5-alkyl-2-pyrimidinyl)phenyl] ester, has been prepared and the physical properties investigated, where the chirality was generated in the system by introducing the chiral centre in the central region of the molecular structure. Heptyl and octyl members of the series show a monotropic cholesteric phase. The chirality-dependent properties of the series of the twin materials were compared with those of analogous ‘monomeric’ materials carrying a chiral centre in the peripheral aliphatic chain. Pitch measurements revealed that the twin materials induce a strong helical structure in both cholesteric and chiral smectic C phases. Furthermore, a chiral twin molecule possessing only one phenyl ring at each core part, i.e.(R)-3-methyladipic acid bis(4-octyloxyphenyl) ester, was prepared. The S*_c pitch of this compound was found to be longer than that for the former series of twin materials. These results allow us to propose a possible model for producing the strong helical structure in the S*_c phases where the chirality had been induced by the twin molecules. In addition, the strong desire for the twin materials to form a helical ordering in smectic phases was also found to induce an unusual smectic phase, in contact studies with an achiral liquid-crystalline material, where a texture similar to that reported for the twist grain boundary (TGB) phases was observed.