Liquid Crystalline Compounds in the Thiophene Series, Part T Synthesis and Characterization of Yinylenes with Two Mesogenic Groups Each Containing Three Aromatic Systems with Different Connecting Units

Abstract

Gerhard Koßmehl*, Frank Dirk Hoppe Institut für Organische Chemie der Freien Universität Berlin, Takustraße 3, D-14195 Berlin Z. Naturforsch. 48 b, 1807-1820 (1993); received April 9,1993 Liquid Crystalline (LC) Thiophene Compounds, Vinylenes with LC-Phases, Mesogenic Groups Compounds with two mesogenic groups without terminal alkyl chains or other groups con­ taining thiophene systems have been prepared from a.<o-bis(5-formyl-2-thienyI)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 spec­ tra and MS. The liquid crystalline properties of these compounds were characterized by dif­ ferential scanning calorimetry (DSC) and polarizing microscopy. Mesogenic cores with one thiophene system and two benzene systems give rise to liquid crystalline phases. These com­ pounds 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 viny­ lene 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-l-(5-butyl-2-thienylvinyl)-4-(styryl)benzene (9) with no mesophase the corresponding all-E-a.ö>-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-a.a>-Bis{5-[4-(4-phenylbuta-1.3-dienyl)styryl]-2-thienyl}alkanes (series 7) decompose in their mesophases.

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