Synthesis, mesomorphic behaviour and optical anisotropy of some novel liquid crystals with lateral and terminal fluoro substituents and a 2,6-disubstituted naphthalene core

Abstract

The synthesis, mesomorphic properties and optical anisotropy of a range of diphenylnaphthalenes are detailed. One phenyl ring contains two lateral ortho fluoro substituents, with either a terminal butoxy chain or a pentyl chain; in both cases, the other phenyl ring possesses one, two or three fluoro substituents at the end of the molecule. The synthesis of the materials was effected efficiently using a combination of low-temperature lithiations and Suzuki palladium-catalysed cross-coupling reactions. All six novel compounds exhibit the nematic phase at very high temperature (between 125°C and 245°C), particularly those with fewer lateral fluoro substituents, and all show a smectic A phase. The melting points are rather high, but those compounds with a terminal pentyl chain and more lateral fluoro substituents do have much lower melting points (around 100°C). As expected from naphthalene liquid crystals, the optical anisotropy (measured as extrapolated values at 25°C) is very high (0.27–0.35), particularly for those compounds with a terminal butoxy chain and fewer lateral fluoro substituents.