High birefringence nematic liquid crystals containing both thieno[3,2-b]thiophene core and acetylene bond

Abstract

ABSTRACT A new series of thieno[3,2-b]thiophene-based liquid crystals with a – C ≡ C- triple bond were synthesised via Sonogashira cross-coupling and characterised. Thermo analysis show that all of these compounds exhibit a stable nematic phase, which is superior to the thieno[3,2-b]thiophene-phenyl and classical tolane anologues. Improved mesophase may be attributing to the increased aspect ratio of molecules and much lower energy barrier of conformation rotation between the aromatic rings than that of the reference compounds. These newly compounds present higher birefringence (0.40 ~ 0.48) than the reference compounds because of the extended π-conjugated. When doped to the mixture, it is found that these new compounds have the advantage of good solubility, higher birefringence, larger dielectric anisotropy and higher clearing point.