Laterally fluorinated liquid crystals containing the 2,2′‐bithiophene moiety

Abstract

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.