Effects of reducing structural symmetry on mesophase behaviour: the synthesis and characterization of the 2-alkoxy-6-[4-(4-alkoxyphenyl)buta-1,3-diynyl]naphthalenes

Unsymmetrical 2-alkoxy-6-[4-(4-alkoxyphenyl)buta-1,3-diynyl]naphthalenes were synthesized and their mesomorphic properties studied. In addition to an increase the mesophase temperature range of 10°C, the melting temperatures are significantly lower while there is a less pronounced decrease in the clearing temperatures when compared with those of the symmetrical 1,4-bis(6-alkoxy-2-naphthyl)butadiynes. Further reducing the symmetry by introducing the two terminal chains of unequal length shows little effect on the mesogenic properties. Shortening the linker from a butadiynyne unit to an ethyne unit significantly reduces the overall mesophase and nematic temperature ranges but the smectic range markedly increases.