The effect of fluorinated terminal chains on the mesomorphic properties of 4,4′‐disubstituted phenyl benzoates

A variety of 4,4′‐disubstituted phenyl benzoates having a terminal chain containing multifluorine atoms, attached directly to the benzene ring or through an ester group, have been synthesized and their mesomorphic properties determined by hot stage polarizing optical microscopy. These properties were compared to those of the corresponding hydrogenated esters and to other esters containing rigid terminal chains. Usually transition temperatures were higher and mesophase ranges wider than those observed for the parent compounds but no nematic phases were found. Any mesophase seen was usually a smectic A phase sometimes accompanied by a smectic C phase. Crystal E phases were found along with the smectic A phase in alkyl or alkoxy esters having a C9F19CO2 chain on the acid side. A first order smectic A–smectic C transition was observed in the ester with CN on the acid side and O2CC7F15 on the phenol side. A comparison of the effect of a terminal fluorinated chain and a lateral fluorine group on one set of esters is also included.