The Influence of Methyl Groups on the Formation of the Ferroelectric Nematic Phase.

The synthesis and characterization of 12 ferroelectric nematogens based on the RM734 structural template are reported in the form of two series named ECMe and ECMeF. Within both series, the position of the methyl groups present was varied and all 12 of these compounds exhibited the ferroelectric nematic phase. In general, when modifications were made that decreased the shape anisotropy of the molecule, the value of decreased in line with the literature. The behavior of was, however, much more complex, appearing to be directed by the substituents present, and the transition temperatures did not follow a distinct trend as modifications were made. This is particularly apparent when comparing 2ECMe and 3ECMe which both have a terminal methyl group and a lateral methoxy group: the of 3ECMe is 25 °C higher than that of 2ECMe, while their equivalent methoxy-substituted materials have transition temperatures essentially identical to one another. The properties of these materials can be justified, in general, by the model of Madhusudana and are sensitive to the electronic distribution within the compounds.