Crown ethers with lateral ortho-terphenyl units: effect of ester groups and sodium salts on the mesomorphic properties

Abstract

Unsymmetrical crown ether derivatives 7 and 12 with one lateral o-terphenyl unit bearing different ester substituents were synthesized starting from methoxymethyl (MOM) protected bromobenzenes 3 and 8 by conversion into the respective borolanes 4 and 9, twofold Suzuki coupling with dibromobenzo[15]crown-5, acidic deprotection and finally esterification either with various alkanoic chlorides or gallic acids. Reaction with NaI provided the complexes [NaI·(7a–g)] and [NaI·(12a–d)], respectively. Uncomplexed crown ethers as well as their complexes [NaI·7a–c] and [NaI·12a–d] are non-mesogenic. In the case of [NaI·(7d–g)], however, the complexation induced a mesophase formation. As exemplarily shown for [NaI·7d], different textures were observed upon cooling, a fan-shaped texture, which is typical for a columnar hexagonal mesophase, and a striped fan-shaped texture, indicating a second mesophase Col_x at low-temperature. From the SAXS diffraction pattern this mesophase was assigned to be columnar rectangular. For [NaI·7g] a different diffraction pattern was found, from which the low-temperature mesophase might be attributed to a soft crystal or a highly ordered columnar mesophase with orthorhombic symmetry.