Liquid crystal trimers showing stable anticlinic structures in smectic C and I phases

Abstract

A homogeneous series of chiral trimeric compounds, possessing three biphenyl mesogenic cores connected by flexible alkyl spacers, were prepared and the liquid-crystalline properties investigated. The trimers were designed to have chiral moieties at both peripheral ends of the molecular structure and the properties were compared with those of the related dimeric and monomeric systems. Some of the optically active trimers showed stable antiferroelectric smectic C and I phases. The racemic mixture of optical isomers also showed anticlinic versions of the smectic C and I phases, however, synclinic structures were not observed. The optical isomers and the racemic mixture showed quite similar transition temperatures, suggesting that the chirality-induced properties have little effect on the stability of the anticlinic structures. The trimers showed a third-order X-ray diffraction peak indicating the formation of a higher order smectic layer structure, which is considered to stabilize the anticlinic molecular ordering.