Synthesis and Mesomorphic Properties of Multiynylthiophenes: 2,3,4,5Tetrakis(4-alkoxyphenylethynyl)thiophenes and 2,3,5-Tris(4alkoxyphenylethynyl)thiophenes

The synthesis and characterization of multiynylthiophenes, tetrakis(4-alkoxyphenylethynyl)thiophenes (1) and tris(4alkoxyphenylethynyl)thiophenes (2), are reported, and their structure-mesomorphism relationship is discussed. The tetraynyl series 1 with a trapezoid core do not show any liquid-crystalline properties. With one less peripheral arm, series 2 compounds are of the Y-shape geometry with rigid linear spacers and nematic phases are observed for the octyloxyl, decyloxyl, and dodecyloxyl derivatives. Although the dipole-dipole interactions, desymmetrization, and disparity of the mesogenic cores can be accountable for their corresponding mesomorphic behaviors, the formation of the nematic phases of 2 may be most likely attributed to the shape disparity of these two series of compounds.