Laterally Brominated Symmetric Liquid Crystal Trimers with (S)-(-)-2-Methylbutyl-4′-(4″-phenyl)benzoate Exhibiting N* and Blue Phases

The series of eight symmetric trimers, 4,4′-bis[ω-[2-methylbutyl-4′-(4″-phenyl)benzoateoxy]-3-bromo-4-alkyloxybenzylidene]-1,4-phenylenediamines has been synthesized and characterized. Except pentyl and undecyl homologues, the seven-ring chiral trimers exhibit the enantiotropic N* phase. In addition to the N* phase, the odd trimers with heptyl and nonyl spacers also exhibit the blue phase with platelet texture. The nematogenic properties of the trimers are attributed to the presence of two lateral bulky bromine atoms in the central mesogenic core. The suppression of mesophase thermal stability is largely due to the increase in molecular breadth at positions the bromine atoms are attached, which results in weaker overall lateral intermolecular attraction. The thermal properties of the trimers are also compared to those of the earlier reported analogous trimers that do not possess any lateral substituents in the mesogenic cores.