Novel non-symmetric chiral twin liquid crystals possessing two identical chiral moieties at both peripheral ends: highly chirality-sensitive phases appeared between smectic and isotropic liquid phases

Abstract

A novel strategy for preparing non-symmetric chiral twin liquid crystals was proposed, where two identical chiral moieties were designed to be located at both peripheral ends and the non-symmetric character was introduced by the non-symmetric central connecting structure. Thus, optically active chiral non-symmetric twin homologues, [4′-(1-methylheptyloxycarbonyl)-1,1′-biphenyl-4-yl] 4″″-[ω-[{4″-(1-methylheptyloxycarbonyl)-1″,1″′-biphenyl-4″′-yl}oxycarbonyl]alkyloxy]benzoate, were prepared, which were found to exhibit the antiferro-, ferri-, and ferroelectric phases. Furthermore, two more phases were observed between the ferroelectric and isotropic liquid phases. The lower-temperature phase was optically isotropic under the polarized light microscopy for both of the homogeneously and pseudo-homeotropically aligned thin samples, whereas the high-temperature phase showed a mosaic texture. Both of these anomalous phases were found to have a layered structure with a smaller layer spacing than the smectic phase. The stability of these phases was quite sensitive to the optical activity. With reduction of the optical purity, these phases disappeared but the Twist Grain Boundary phase was observed. A 1 ∶ 1 mixture of (S,S)- and (R,R)-isomers just showed the smectic A phase instead of these anomalous phases.