title: Carbohydrate rod conjugates: ternary rod-coil molecules forming complex liquid crystal structures.
abstract: T-shaped polyphilic triblock molecules, consisting of a rodlike p-terphenyl unit, a hydrophilic and flexible laterally attached oligo(oxyethylene) chain terminated by an 1-acylamino-1-deoxy-D-sorbitol unit, and two end-attached lipophilic alkyl chains, have been synthesized by palladium-catalyzed cross-coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, differential scanning calorimetry (DSC), and X-ray scattering. We investigated the mode of self-organization as a function of the length and position of the lateral polar chain and the length of the terminal alkyl chains. Depending on the size of the polar and lipophilic segments, a series of unusual liquid crystalline phases was detected. In three of these phases, the space is divided into three distinct periodic subspaces. In addition to a hexagonal channeled layer phase (ChL(hex)) consisting of layers that are penetrated by polar columns, there are also two honeycomb-like network structures formed by square (Col(squ)/p4mm) or pentagonal cylinders (Col(squ)/p4gm). The cylinder walls consist of the terphenyl units fused by columns of alkyl chains, and the interior contains the polar side chains. In addition, a hexagonal columnar phase was observed in which the polar columns are organized in a continuum of terphenyls and alkyl chains with an organization of the terphenyl cores tangentially around the columns with the long axis perpendicular to the columns. For one compound, a reversal of birefringence was observed, which is explained by a reorientation of the terphenyl cores. The addition of protic solvents induces lamellar phases.
authors.affiliation: Institute of Organic Chemistry, University Halle, Kurt-Mothes-Strasse 2, D-06120 Halle, Germany.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.forename: Ute
authors.initials: U
authors.lastname: Baumeister
authors.forename: Gerhard
authors.initials: G
authors.lastname: Pelzl
authors.forename: Malay Kumar
authors.initials: MK
authors.lastname: Das
authors.forename: Xiangbing
authors.initials: X
authors.lastname: Zeng
authors.forename: Goran
authors.initials: G
authors.lastname: Ungar
authors.forename: Carsten
authors.initials: C
authors.lastname: Tschierske
mesh_terms: D002236:Carbohydrate Conformation; D002241:Carbohydrates / Q000138:chemical synthesis* / Q000737:chemistry*; D003460:Crystallization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D012996:Solutions / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D012996:Solutions