Novel Nonsymmetric Trimeric Liquid Crystals Exhibiting Glassy Nematic State at Low Temperatures

Series of nonsymmetric 4-ethyl- and 4-fluoroanilinebenzylidene-2′,4′-oxy-bis(4″-halogenoanilinebenzylidene-4″′oxy)alkanes trimers have been synthesized and characterized. Every member in this series possesses either Cl or Br terminal atoms. The molecular structure of these novel trimers is composed of six aromatic rings interconnected via two methylene spacers and three azomethine linking groups. In each molecule, the two identical methylene spacers vary from either C4H8 or C6H12. The trimers exhibit relatively low Tm and Tc (< 160°C). Three of the homologues with ethyl group are glassy nematic liquid crystals with Tg < 15°C. The low transition temperatures are attributed to the branched molecular architecture which leads to steric hindrance and lesser degree of lateral intermolecular attraction. The liquid crystallinity of the intermediary aldehydes is also investigated.