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A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films at the air/water interface is presented. Both the end chains (siloxane vs hydrocarbon) and the core (more or less amphiphilic) are varied, to allow an exploration of different possible layer structures at the interface. The characterization includes systematic surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. The properties of these layers are strongly dependent on the individual type of molecule:  the molecules with amphiphilic end chains lie quite flat on the surface, while the molecules with hydrophobic end chains construct multilayer structures. In both cases, the three-dimensional collapse structure is reversible.

Ferroelectric liquid crystalline phases formed by achiral bent-core mesogens have been known for about seven years. However, only few materials have been found to exhibit both conventional nematicsmectic mesophases and “banana” phases, where steric packing of bent mesogens results in ferroelectric properties. In this paper we report some studies of such compounds showing transitions between paraelectric smectic A, smectic C and antiferroelectric smectic CP phases. Structure characterization as well as studies of ordering in mesophases have been performed with the help of a variety of experimental techniques including X-ray diffraction, NMR and dielectric spectroscopy as well as electrooptical measurements.

AbstractBinary systems of 1-heptyl-4-(4-pyridyl)pyridinium bromide with different proton acceptors were investigated. The existence of hydrogen bonded liquid-crystalline associates was proven.

AbstractTerminally alkyl- and alkyloxysubstituted 4,6-dichloro-1,3-phenylene bis[4-(phenyliminomethyl)benzoates] have been synthesized and studied by optical microscopy, differential scanning calorimetry, NMR spectroscopy, X-ray diffraction and dielectric measurements. Surprisingly, nematic and smectic phases are observed, although comparable bisesters of resorcinol and monochlororesorcinol exhibit B phases typical for banana-shaped mesogens. It could be proved by NMR investigations in the liquid crystallinen state that the molecules have a nearly rod-like shape. Dielectric measurements indicate a rotation around the molecular long axis as known from calamitic mesogens, which is clearly distinguished from the behaviour of bent molecules. Obviously, substitution of the central phenyl ring of the bent 1,3-phenylene bis[4(4-n-alkyloxyphenyliminomethyl)benzoates] by two chlorine atomas causes a markedly change of the molecular shape resulting in nearly calamitic mesogens. These results are supported by single crystal structure studies, which allow the precise determination of the molecular structure and packing in the solid state.

Abstract4-Chloro-1,3-phenylene bis[4-(4-n-alkylphenyliminomethyl)benzoates] have been synthesized and the mesophases were investigated by optical microscopy, X-ray diffraction measurements and electrooptical methods. Some derivatives exhibit the electrooptically switchable mesophase B2between 75–125°C, which can be supercooled additionally by about 20 K. This existence range is very useful for further physical measurements.

The diagrams of state of 11 binary systems are presented which form EDA Complexes in the liquid dcrystalline state. The influence of the molecular length and the complex stability on the formation of enhanced smectic A phases have been studied.

Several homologous series of chemically related compounds were synthesized. The influence of the terminal polar group and of the length of the conjugated system on the reentrant phenomenon was studied.

The effect of pressure on phase transitions has been studied for four compounds, viz., di-ethyl-p-azoxybenzoate, 4-nitrophenyl-4'-octyloxybenzoate, 4-n-pentyloxyphenyl-4'-n-decyloxybenzoate and 4-n-heptyloxyphenyl-4'-n-decyloxybenzoate, which exhibit different types of mesophases at atmospheric pressure. The experimental phase diagrams are presented and the dT/dP values of the various transitions as well as the volume change at these transitions are evaluated.

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 Sc2phase 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. Neue terminal verknüpfte Zwillingsverbindungen mit Alkyl‐ oder perfluorierten Spacern wurden synthetisiert. Die mesomorphen Eigenschaften wurden polarisationsmikroskopisch und mit Hilfe der Röntgenbeugung untersucht. Es wurde gefunden, daß die smektische C‐Phase als Sc2‐Phase mit alternierendem Tilt und einer intercalierten Struktur eingestuft werden kann. Der alternierende Tilt bedingt eine ungewöhnliche Schlierentextur, welche nicht nur Singularitäten der Stärke s= ±1, sondern auch solche mit s= ±1/2 und s= ±3/2 zeigt.

A new achiral banana-shaped mesogen is presented which exhibits a nematic phase and an isotropic mesomorphic phase with spontaneous chiral ordering.