Structural reassignment of the condensation product of the 2-phenylimidazole-4,5-dione benzamidinium salt

It is shown by ¹³C nmr spectroscopy that the thermolysis and dehydration of the 2-phenyl-imidazole-4,5-dione benzamidinium salt ( 1 ) yield 2-cyano-4,6-diphenyl-1,3,5-triazine ( 7 ) and not as postulated previously, 2,5-diphenylimidazo[4,5-d]imidazole ( 3 ) as the reaction product.     

Liquid crystalline bolaamphiphiles with semiperfluorinated lateral chains: competition between layerlike and honeycomb-like organization

Novel bolaamphiphilic triblockmolecules consisting of a rigid biphenyl unit, with a polar 2,3-dihydroxypropyloxy group and a phenolic OH group at opposite ends, as well as a semiperfluorinated chain in a lateral position have been synthesized via palladium catalyzed cross coupling reactions as the key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by polarized light microscopy, DSC and X-ray scattering, and the influence of the length of the lateral chain on the mesomorphic properties was studied. The compound with the shortest chain as well as the long chain derivatives form lamellar mesophases composed of segregated layers of the bolaamphiphilic moieties and sublayers comprising the fluid lateral chains. The layers within the lamellar phases of the short chain compound adopt a positional correlation, leading to a 2D lattice (Col(r)/p2mm), whereas the layers of the lamellar phases of the long chain derivatives are noncorrelated (Lam). Compounds with a medium chain length organize into columnar phases, where the nonpolar lateral chains segregate into columns, which are embedded in networks of regular (Col(h)) or stretched (Col(r)/c2mm) hexagonal cylinder shells consisting of the bolaamphiphilic units. In total, an unusual phase sequence was found, where, with respect to the chain length, columnar mesophases occur between two mesophases with layer organization.     

Correlated layer structures: a novel type of liquid crystalline phase with 2D-lattice

A novel liquid crystalline quaternary five-block molecule is reported which is composed of four incompatible molecular parts, a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a branched semiperfluorinated chain in the lateral 3-position, consisting of a perfluorinated and a lipophilic hydrocarbon wing. The self-organization of this compound was studied by polarized light optical microscopy, differential scanning calorimetry, and X-ray diffraction of aligned samples. These investigations confirm a novel liquid crystalline phase with two-dimensional (2D) lattice (columnar mesophase), which results from the positional correlation of smectic layers. The layer structure results from the segregation of the bolaamphiphilic parts from the side chains. Within the aromatic sublayers the biphenyl cores are arranged parallel to the layer planes, and the hydrogen-bonding networks of the terminal diol groups are segregated from the biphenyl cores, forming separate columns. The correlation between adjacent layers is due to the (partial) segregation of the fluorinated and hydrogenated parts of the lateral chains in the nonpolar sublayers.     

Comparing investigation of the smectic C and A phases of the di-n-alkyl 4,4′-azoxycinnamates (I). Calorimetric investigations

We present calorimetric investigations (DSC) of 9 members of the homologous series of the di-n-alkyl 4-4′-azoxycinnamates. The phase transitions smectic C/A and smectic A/isotropic are characterized by thermodynamic changes which are discussed comparingly. With increasing length of the n-alkyl chains in the series the clearing temperatures are depressed, the S_A regions are diminshed and the character of the phase transitions C/A changes from second order to the direction of first order.     

Liquid crystalline swallow-tailed compounds (II) dielectric relaxation

Dielectric investigations in the kHz-range on swallow-tailed liquid crystals show a strong decrease of the dielectric constant as well as of the dielectric loss parallel to the nematic director with decreasing temperature. In the perpendicular direction no strong anomaly has been observed. By consideration of X-ray data of the S_A phase the dielectric results can be interpreted by the dipole-dipole interaction which is forced by the anisotropy of repulsive forces of the respective molecules.     

The Structure and Unusual Optical Textures of Smectic C2 Phases of New Tail-to-Tail Twins

New tail-to-tail twins with alkyl or perfluorinated spacers were synthesized. The mesomorphic properties were studied by polarizing microscopy and X-ray diffraction measurements. It was found that the smectic C phase is a Sc₂ phase with alternating tilt and an intercalated structure. The alternating tilt gives rise to an unusual schlieren texture which exhibits not only singularities with the strength s = ±1 but also those with s = ±1/2 and s = ±3/2.