title: Star-shaped oligobenzoates: non-conventional mesogens forming columnar helical mesophases.
abstract: Star-shaped mesogens with a phloroglucinol or a trimesic acid core and oligobenzoate arms with up to five repeating units have been synthesised. These non-conventional mesogens form various columnar mesophases over a broad temperature range. The liquid-crystal phases were characterised by optical microscopy, differential scanning calorimetry, X-ray diffraction, dilatometry and solid-state NMR spectroscopy. In addition to the high-temperature hexagonal columnar phases, the columnar self-assemblies undulate upon cooling and consequently form higher-ordered body-centred orthorhombic columnar 3D structures. A model of E-shaped folded conformers helically displaced along the columns is proposed. Helical preorganisation in the hexagonal phase precedes the transition to the low-temperature phases. Space filling and nano-segregation compete in the self-organisation process, thus aliphatic chains and the polar oligobenzoate scaffold are not perfectly separated in these star-shaped mesogens.
authors.affiliation: Institute of Chemistry, Chemnitz University of Technology, Strasse der Nationen 62, 09111 Chemnitz, Germany. matthias.lehmann@chemie.tu-chemnitz.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Lehmann
authors.forename: Michael
authors.initials: M
authors.lastname: Jahr
authors.forename: Bertrand
authors.initials: B
authors.lastname: Donnio
authors.forename: Robert
authors.initials: R
authors.lastname: Graf
authors.forename: Sibylle
authors.initials: S
authors.lastname: Gemming
authors.forename: Igor
authors.initials: I
authors.lastname: Popov