Effect of Molecular Structure on Smectic Phase Structures in Two Homologues Series of Bent-Shaped Molecules with Asymmetric Central Naphthalene Core

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Two homologous series of achiral banana-shaped liquid crystals with an asymmetric central core based on 1,6- and 1,7-dihydroxynaphthalene and with side wings containing Schiff's based moiety, N(1,7)-n-O-PIMB and N(1,6)-n-O-PIMB (n = 4, 8, 12, and 16) were synthesized. The mesophases and phase structures of all the compounds were studied by means of electrooptic, polarization reversal current, circular dichroism, and X-ray diffraction measurements in order to confirm the relationship between the molecular structures and mesomorphic behaviors. Most of N(1,7)-n-O-PIMB compounds (n = 8, 12, and 16) exhibitedjhe chiral blue phase although the bent angle of central bent core is 60° which is unconventional conformation of banana-shaped molecules. In contrast, N(1,6)-n-O-PIMB showed the typical B1 phase with frustrated layer structure or the B2 phase with the racemic SmC S P A structure in accordance with the length of alkyl terminal chain. These results indicate that the size of the bent core, the position as well as the magnitude of the bend, and the length of alkyl terminal chain play an important role for the emergence of particular banana smectic phases.