Combination of an Aromatic Core and Aromatic Side Chains Which Constitutes Discotic Liquid Crystal and Organogel Supramolecular Assemblies

This paper reports unique and unusual formations of columnar liquid crystals and organogels by self-assembling discotic molecules, which are composed of an aromatic hexaazatriphenylene (HAT) core and six flexible aromatic side chains. In HAT derivatives <b>3a</b>, with 4‘-(<i>N</i>,<i>N</i>-diphenylamino)biphenyl-4-yl chains, <b>3b</b>, with 4‘-[<i>N</i>-(2-naphthyl)-<i>N</i>-phenylamino]biphenyl-4-yl chains, and <b>3c</b>, with 4‘-phenoxybiphenyl-4-yl chains, the two-dimensional hexagonal packings can be created by their self-assembling in the liquid crystalline phase, which were characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In certain solvents, HAT molecules <b>3a</b>−<b>c</b> can form the viscoelastic fluid organogels, in which one-dimensional aggregates composed of the HAT molecules are self-assembled and entangled into three-dimensional network structures. The organogel structures were analyzed by scanning electron microscopy observation, ¹H NMR, UV−vis, and circular dichroism spectroscopy. In contrast to <b>3a</b>−<b>c</b>, none of the liquid crystalline and organogel phases could be formed from <b>3d</b> and <b>3e</b> with short aromatic side chains including a phenylene spacer, and <b>3f</b> (except a few specific solutions) and <b>3g</b> without terminal diarylamino and phenoxy groups. In <b>3a</b>−<b>c</b>, the aromatic side chains with terminal flexible groups make up soft regions that cooperatively stabilize the liquid crystalline and organogel supramolecular structures together with the hard regions of the hexaazatriphenylene core.