Room-temperature discotic liquid crystals based on oligothiophenes—attached and fused triazatruxenes

Abstract

A new class of discotic liquid crystals based on oligothiophenes - attached and fused triazatruxenes, were synthesized in high yields. The synthesis was carried out first by microwave-assisted six-fold Stille cross-coupling reactions to yield the hexakis-oligothiophenes - substituted triazatruxenes TAT-T1 and TAT-T2 and followed by successful oxidative cyclodehydrogenation of TAT-T1 to afford the planar TAT-T1-C with an extended core. Their optical properties, electronic properties, thermal behavior and self-assembly were investigated by various techniques. UV-vis absorption and fluorescence spectroscopic measurements demonstrate that TAT-T1-C is a largely delocalized and rigid polycyclic aromatic π-system. All of these disk-like molecules, in particular TAT-T1-C, show a strong π–π interaction in the solid state and exhibit columnar liquid crystalline properties at room temperature with a wide-range mesophase. Elongation of the peripheral oligothiophene arms or expansion of the rigid core size upon cyclization of the neighbouring thiophene moieties gives rise to dramatic increases of both the isotropic temperatures and the mesophase width.