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Star‐Shaped Oligobenzoates: Non‐conventional Mesogens Forming Columnar Helical Mesophases
Author(s) -
Lehmann Matthias,
Jahr Michael,
Donnio Bertrand,
Graf Robert,
Gemming Sibylle,
Popov Igor
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700922
Subject(s) - materials science , crystallography , orthorhombic crystal system , columnar phase , differential scanning calorimetry , phase (matter) , liquid crystal , trimesic acid , discotic liquid crystal , phase transition , thermotropic crystal , hexagonal phase , mesophase , hexagonal crystal system , crystal structure , chemistry , organic chemistry , molecule , condensed matter physics , thermodynamics , liquid crystalline , physics , optoelectronics
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.