New series of 4-(4′-octyloxybiphenyl-4-yloxymethyl)benzoic acid derivatives with mesogenic properties

Three homologous series of (4'-octyloxybiphenyl-4-yloxymethyl)benzoic acid derivatives were synthesised and studied. The compounds, substituted by n-alkyl esters, reveal strong discrimination of the tilted phases formation upon elongation of the alkyl group. In compounds with 2 methylalkyl chains, tilted phases were exclusively observed with both ferroelectric and antiferroelectric properties. It has been observed that for chiral derivatives an elongation of the chiral chain leads to odd-even effect on the polar properties. Also elongation of non-chiral alkoxy terminal chains affects the polar properties. For short homologues the antiferroelectric phases dominate, while for long homologues only ferroelectric behaviour is observed. The influence of strongly polar lateral groups (Cl, Br, NO2) attached to the biphenyl ring on LC phase properties was also determined. It was detected that monosubstituted compounds have lower mesogenic stability then their disubtituted counterparts. The effect is probably related to restricted rotation around the phenyl-O bond that leads to a more rigid core structure.