Nitro and bromo derivatives of a highly fluorinated thiobenzoate

Several compounds derived from monosubstituted thiobenzoates, with substituents in the meta- or para-position, have been prepared; these contain a thioester spacer between a semifluorinated chain and the rigid core unit. The substituent is either a bromo or a nitro group. Their mesomorphic properties were evaluated using polarizing optical microscopy and differential scanning calorimetry. The influence of the different substituents on the phenyl core was considered. No mesomorphic behaviour was seen except for one nitro derivative. The introduction of the nitro group in the para-position of the thiobenzoate core leads to a LC transition on heating. As with previous studies, these results show that substitution at the 4 position on a monophenyl core can lead to liquid crystallinity, whereas substitution in the meta- position does not; this supports the view that meta- substitution is not a necessary condition for obtaining a LC phase.