Mesomorphic behaviour in bent-shaped molecules with side wings at different positions of a central naphthalene core

Six bent-shaped molecules were prepared with central bent cores based on 2,7-, 1,7-, 1,6-, 1,3-, 1,2- and 2,3-dihydroxynaphthalene groups with side wings containing a Schiff's base moiety and dodecyloxy tail, N(2,7), N(1,7), N(1,6), N(1,3), N(1,2) and N(2,3). All of the compounds form fluid smectic mesophases and their mesomorphic behaviour and properties are discussed in terms of their molecular structure. The compounds are categorized into two groups; in one of them, N(2,7), N(1,6) and N(1,3), the bent cores have a bent angle of 120 degrees between the side wings, whereas in the other, N(1,7), N(1,2) and N(2,3), the bent angle is 60 degrees. The typical banana molecule, N(2,7), in the first group, forms a chiral blue phase that shows two distinguishable domains with opposite optical rotations and circular dichroism. Under an electric field, the chiral blue phase is transformed to strongly birefringent B2 phase which possesses a basically homochiral SmCAPA structure. N(1,3) also forms a chiral blue phase, but, in contrast, N(1,6), where the side wings are asymmetrically substituted, forms a typical antiferroelectric B2 phase with the racemic SmCSPA structure. N(1,2) and N(2,3) of the other group assume a U-like shape to form a conventional SmA phase. Of interest is the fact that N(1,7) forms a chiral blue phase irrespective of having a small bent angle of 60 degrees. This indicates that the distance between side wings as well as the bent angle plays an important role for the formation of banana-shaped smectic phases.