Liquid Crystalline Compounds in the Thiophene Series, Part 7

Compounds with two mesogenic groups without terminal alkyl chains or other groups containing thiophene systems have been prepared from α.ω-bis(5-formyl-2-thienyl)alkanes (series 1) and various phosphonium salts by Wittig-reaction. The chemical structures of the new compounds have been characterized by their elemental analyses, IR and H NMR spectra and MS. The liquid crystalline properties of these compounds were characterized by differential scanning calorimetry (DSC) and polarizing microscopy. Mesogenic cores with one thiophene system and two benzene systems give rise to liquid crystalline phases. These compounds with one vinylene group in each core (series 2 and 3) are mostly monotropic, those with two or three vinylene groups are enantiotropic liquid crystalline. Exchanging one vinylene group by a azomethine group in each core reduces the temperature range of the mesophase or destroys the liquid crystallinity completely. In contrast to E,E-1-(5-butyl-2-thienylvinyl)-4-(styryl)benzene (9) with no mesophase the corresponding all-E-α.ω-bis{5-[4-(4-styryl)styryl]-2-thienyl}alkanes (series 5) show over a wide temperature range with increasing inner chain length more and more high ordered mesophases. all-E-α.ω-Bis{5-[4-(4-phenylbuta-1.3-dienyl)styryl]-2-thienyl}alkanes (series 7) decompose in their mesophases.