LIQUID-CRYSTALLINE COMPOUNDS IN THE THIOPHENE SERIES .9. SYNTHESIS AND CHARACTERIZATION OF LIQUID-CRYSTALLINE VINYLENES WITH 2 MESOGENIC GROUPS CONTAINING EXCLUSIVELY THIOPHENE SYSTEM

The first examples of compounds with two mesogenic groups connected by an alkylene chain and containing mesogenic groups with exclusively two, three or four thiophene rings and one, two or three vinylene groups in each moiety are reported. Only the materials with three or four thiophene rings in each core have nematic phases. For example all-E-1.6-bis{5-[5-(2-thienylvinyl)-2-thienylvinyl]-2-thienyl} hexane shows a monotropic nematic phase while cooling the sample, but E,E-2-(5-butyl-2-thienylvinyl)-5-(thienylvinyl)thiophene has no mesophases. The liquid crystalline behaviour of the various compounds is dependent on the length of the flexible inner chain. Compounds with terminal alkyl groups show nematic phases in a broader temperature range than those without substituents. The temperature range of a mesophase is enhanced by substituting thiophene rings in the described compounds for benzene rings. The thermal behaviour of the compounds has been studied by DSC and polarizing microscopy.