Coupling between chirality and odd-even effect of twin materials in smectic liquid-crystalline phases

Novel chiral twin molecules, (S)-2-methylnonanedioic acid bis[4-(5-octyl-2-pyrimidinyl)phenyl] ester (MNB-8-PYP) and (S)-2-methyldecanedioic acid bis[4-(5-octyl-2-pyrimidinyl)phenyl] ester (MDB-8-PYP), have been prepared and the odd-even effect of the chiral spacer on the helical twisting power investigated. Pitch measurements in a mixture with a host material revealed that MDB-8-PYP with an even number of atoms in the spacer induces a stronger helical structure in the cholesteric phase and particularly in the chiral smectic C phase than MNB-8-PYP with an odd-numbered spacer. The marked odd-even effect observed in the S, pitch can be explained by our proposed 'intercalated chirality' model for twisting power in smectic phases induced by a chiral twin molecule.