Star-Shaped Discotic Oligomesogens Based on Radial Pentakisphenylethynylbenzene Moieties

Abstract

New monodisperse star-shaped discotic oligomesogens are presented which consist of three flat radial pentaalkyne building blocks connected with a central benzene linking unit via flexible alkyl spacers. Different alkyl substituents were attached to the periphery of the pentayne units in order to modify the molecular dimensions. The thermal properties of the star oligomers in their pure state and of donor-acceptor complexes with 2,4,7-triniti-ofluoren-9-one (TNF) were investigated by polarizing microscopy, differential scanning calorimetry, and X-ray scattering. The pentayne oligomers as well as the binary mixtures with TNF exhibit a nematic-columnar (N-Col) mesophase. On the contrary, the corresponding hydroxy-substituted pentayne monomers display a nematic-discotic (N-D) liquid crystalline phase as pure compounds, and CT interactions with TNF lead to the induction of hexagonal columnar (Col(h)) mesophases. The unexpected phase behavior of the oligomers and of the CT complexes derived there from is mainly the result of the molecular architecture arising from covalent linkage of the flat anisometric moieties.