Flying-seed-like liquid crystals. Part 4: a novel series of bulky substituents inducing mesomorphism instead of using long alkyl chains

Abstract

We synthesized a novel series of flying-seed-like derivatives (3a–g) based on phthalocyaninato copper(II) (abbreviated as PcCu) substituted by bulky groups {PhO (a), (o-C₁)PhO (b), (m-C₁)PhO (c), (p-C₁)PhO (d), [m,p-(C₁)₂]PhO (e), [m,m′-(C₁)₂]PhO (f), and [m,p,m′-(C₁)₃]PhO (g)} instead of using long alkyl chains, in order to investigate their mesomorphism. Their phase transition behaviour and the mesophase structures were established using a polarizing optical microscope, a differential scanning calorimeter, a thermogravimetry analyser and a temperature-dependent small angle X-ray diffractometer. It was demonstrated that (PhO)₈PcCu (3a) and [(p-C₁)PhO]₈PcCu (3d) show no mesophase, whereas [(m-C₁)PhO]₈PcCu (3c), {[m,p-(C₁)₂]PhO}₈PcCu (3e), {[m,m′-(C₁)₂]PhO}₈PcCu (3f), and {[m,p,m′-(C₁)₃]PhO}₈PcCu (3g) show various kinds of columnar mesophases of Col_ro(P2₁/a), Col_ro(P2₁/a), Col_ro(C2/m) and Col_tet.o, respectively, while [(o-C₁)PhO]₈PcCu (3b) shows a monotropic Col_ro(P2m) mesophase. Thus, we revealed that mesomorphism could be induced by these novel bulky substituents instead of using long alkyl chains, and that the mesophase structures were greatly affected by the number and position of the methoxy groups. In particular, it is very interesting that the derivatives with methoxy group(s) at the meta position(s), namely, 3c, 3e, 3f and 3g, tend to show enantiotropic mesophase(s), whereas neither the derivative with no methoxy group, 3a, nor the derivative with a methoxy group at the para position, 3d, show a mesophase.