Star-like substituted hexaarylbenzenes:: synthesis and mesomorphic properties

A series of hexaarylbenzenes (1-6) with a variety of different aryl arms (i.e. phenyl, biphenylyl, mono-, bi-, and terthienylyl) around a benzene core, decorated with flexible dodecyl chains on the terminal positions, were synthesized. Their mesomorphic behaviors were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XD) techniques. Compounds 1-3, which have a hexaphenylbenzene core, form columnar mesophases. In particular 3, in which the core is composed of hexaphenylbenzene surrounded by thiophene rings, shows a stable columnar mesophase (d-D-h) over a large temperature range compared to its phenyl analogs, hexakis(4-dodecylphenyl-4-yl)benzene (1) and hexakis(4'-dodecylbiphenylyl)benzene (2). Compounds 4-6, hexa(oligo-alpha -thienylyl)benzenes, tend to form less ordered mesophases after annealing for a longer time. Compounds 4 and 5 form discotic nematic mesophases (N-d) at temperatures well below the decomposition temperature.