Siloxane -terminated phenylpyrimidine liquid crystal hosts

We report the synthesis and characterization of trisiloxane-terminated liquid crystals with 2-phenylpyrimidine cores that form partially bilayered SmA and SmC phases. Variable temperature measurements of smectic layer spacings by powder X-ray diffraction combined with measurements of optical tilt angles and observations of birefringence changes by polarized optical microscopy reveal that the trisiloxane end-group causes the SmA–SmC transition of these compounds to be more ‘de Vries-like’ when compared to a non-siloxane analogue. One such compound, 2-(4-(11-(1,1,1,3,3,5,5-heptamethyltrisiloxanyl)undecyloxy)phenyl)-5-(1-chlorooctyloxy)pyrimidine (3), is characterized by a maximum layer shrinkage of only 1.6% and may be considered a bona fide de Vries material.