Banana-shaped molecules with 4,6-dichlorinated central core: effect of lateral substituents and terminal chains on the formation of antiferroelectric smectic mesophases

Six banana-shaped compounds with a central core based on a 4,6-dichloro-1,3-phenylene group were synthesized by varying the terminal chains (R=OC10H21 or OC11H21) and the lateral substituents (X=H, F or Cl). Their mesophases were characterized by a combination of differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry. Mesomorphic properties of the banana-shaped mesogens with an olefinic group (R=OC11H21) as a terminal chain are sensitive to lateral halogen substituents as much as those of the analogues with a saturated group (R=OC10H21). The compounds with X=F showed an antiferroelectric switchable smectic phase, which has been designated a B-2 phase. The compounds without a lateral halogen substituent only formed a nematic phase, while the compounds with X=Cl did not exhibit a mesophase in the melt.