Surface controlled orientation of a novel star-shaped discotic oligomesogen 

The alignment behaviour of a nematic-columnar phase forming discotic liquid crystal was explored on various substrates. The mesogen employed was a new star-shaped monodisperse oligomesogen characterized by three flat radial pentaalkynylbenzene moieties grafted to a central benzene linking unit via flexible alkyl spacers. It is shown that suitable polyimide orientation layers along with the mesomorphic properties give rise to a tilted alignment of the disc-shaped pentayne cores. The photoluminescence spectra of oriented films were lineary polarized upon isotropic excitation and unambigiously reveal that, beside the tilted alignment of the rigid cores, the molecular directors of the discotic building blocks preferentially are oriented along the rubbing direction of the orientation layer. The three-dimensional ordering is stable even at room temperature due to the glass forming properties of the applied discotic mesogen.