On the relative propensities of ether and methylene linkages for liquid crystal formation in calamitics

The nematic-isotropic transition temperatures for aromatic calamitic compounds with terminal alkyl chains attached via a methylene group are usually found to be lower than those with an ether link. This difference is generally attributed to the higher anisotropy of the molecular polarizability expected for an ether linkage in comparison with a methylene group. However these two modes of attachment for the chain also differ in their geometry and here we show, using a molecular field theory for flexible molecules, that this also results in higher transition temperatures for nematogens, both monomers and dimers, with the alkyl chains attached through ether rather than methylene linkages.