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

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 center dot(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.