Laterally fluorinated liquid crystals containing the 2,2'-bithiophene moiety

The synthesis and systematic evaluation of the influence of lateral mono-, di- and tetra-fluorination of the terminal phenyl ring on mesomorphic properties in seven novel series of suitably fluoro-substituted 5-n-alkyl-5'-(4-n-decyloxyphenyl)-2,2'-bithienyls is reported. Compared with their non-fluorinated parent counterparts, lateral fluorination eliminates high order smectic phases and reduces thermal stability, to reveal compounds exhibiting a selection of nematic, smectic A and smectic C phase types. As the number of fluoro-substituents increases from one to two, mesophase thermal stability drops drastically; the disposition of the second fluoro-substituent is important. Across-axis disposition is more detrimental than along-axis. However, complete fluorination does not destroy mesophase formation. Indeed, tetrafluorophenyl compounds are more stable than certain 3,5- and 2,6-difluoro compunds. The extrapolated birefringence for members of a series of 5-n-alkyl-5'-(2,3-difluoro-4-n-decyloxyphenyl)-2,2'-bithienyls is approximately 0.21.