Synthesis and thermotropic liquid crystal partially fluorinated materials derived from biphenyl incorporating an ester connector

We have developed new molecules which consist of a 4,4'-biphenyl unit linke d at the 4 position to a linear fluorinated chain via a short spacer of est er type. The 4' position of the biphenyl group can be an hydrogen, or a bro mine atom, a methoxy or a cyano group. The mesomorphic properties have been characterized by light microscopy and by differential thermal analysis. Th e influence of the fluorinated chain and the nature of the 4' substituent o n the stability of the mesophases has been investigated. All the compounds showed a very interesting smectic enantiotropic behavior over a wide temper ature range. The increase of the number of fluoromethylene units simultaneo us increase both the melting and the clearing temperatures. The introductio n of methoxy unit lead to a dimorphic behavior and the presence of the brom ine atom dramatically affect the span of the mesophase as compared to the o ther 4' substituents.