The effect of thioester linkages on the stability of the ferroelectric nematic phase

The synthesis and characterisation of thirteen sulfur-based liquid crystals are reported, based on the molecular backbone of RM734 and containing thioester linkages. Ten of these materials are new examples of ferroelectric nematogens. Phase transition temperatures are compared for systematic changes to molecular structure including the position and extent of fluorination, and the nature of lateral and terminal substituents. The new materials are compared with their ester-linked counterparts. In line with expected behaviour of the nematic phase, replacement of an ester with a thioester raised T_NI, but N_F phase stability upon making this change proved more variable. These findings remain in line with the general view that the formation of the N_F phase is not solely governed by the magnitude of the molecular dipole moment, but is able to be tuned by the interplay of steric and electronic effects endowed by different molecular fragments.