LIQUID-CRYSTALLINE COMPOUNDS IN THE THIOPHENE SERIES .13. SYNTHESIS AND CHARACTERIZATION OF OLIGOMERIC LIQUID-CRYSTALLINE MODEL COMPOUNDS WITH VINYLENE UNITS, THIOPHENE RING-SYSTEMS AND HEXAMETHYLENE CHAINS

'Oligomeric compounds' with three, four or six mesogenic groups in the chain were synthesized by the Wittig reaction from different bis Witt ig salts and various heteroaromatic aldehydes. The mesogenic,groups ar e connected via hexamethylene moieties. All derivatives containing at each terminal position of the chain E-1,2-di-(2-thienyl)ethylene units and one, two or four E,E-2,5-bis(2-thienylvinyl)thiophene units in th e chain show nematic phases while heating and/or cooling the samples ( 2a, 4 and 5). Moreover, the oligomeric compound having the chain from 2a and one terminal formyl group (5) also has a nematic phase. The der ivative with four E-2-(2-thienylvinyl)thiophene units in the chain (3a ) melts without forming a mesophase. Also two 'oligomeric compounds' w ith benzene and thiophene systems in the mesogenic groups were synthes ized. The compounds l)-2-thienyl]hexamethylene}-2-thienylvinyl]benzene (2b) with three mesogenic groups and hienyl]hexamethylene}-2-thienylv inyl]phenyl}hexane (3b) with four mesogenic groups in the chain do not show liquid crystalline phases.