In this paper we present selected members of 7 new series of bent-shaped five-ring resorcinol derivatives which are distinguished by substituents at the central core as well as at the outer rings. Depending on the kind and position of the substituents and depending on the length of the terminal chains not only have new mesophases (the C PA phase or three unidentified B 2 -like phases) been identified, but also interesting phase sequences have been observed (B 2 -N; B 2 -SmA; B 2 -SmA-SmC; B 2 -SmA-SmC-N).

Materials with a macroscopic polar order have a variety of useful properties, such as piezo-and pyroelectricity and second-order nonlinear optical activity [1, 2] Especially ferroelectric (FE) and antiferroelectric (AF) liquid crystalline (LC) materials are of great interest, because they can be rapidly switched between different states by means of external electrical fields. [3, 4] These properties makes them useful for numerous applications, such as electrooptic devices, information storage, switchable NLO (nonlinear optic) devices and light modulators, which may be of interest for optical computing and other future technologies. At first, smectic LC phases with tilted arrangements of nonracemic chiral rodlike and disclike molecules have been used for this purpose and for a long time molecular chirality appeared to be essential for obtaining such materials. [3] However, the discovery by Niori et al. that bent-core mesogenic compounds (banana-shaped molecules) without molecular chirality, can also organize in fluid smectic phases with a polar order opened a new area in the field of LC research. [5,6] The polar structure of the smectic layers of such molecules is provided by the dense directed packing of their bent aromatic cores. However, to escape from a macroscopic polar order the bent direction in adjacent layers is antiparallel, so that the layer polarization alternates from layer to layer, which leads to a macroscopic apolar AF structure. [7] In most cases of such mesophases the molecules are additionally tilted relative to the layer normal. [8] Therefore these phases (also known as ™B2∫-phases) can be described as tilted smectic phases (SmC) with a polar order of the molecules (P) within the layers, and an antiparallel polarization in adjacent layers (A), which leads to the notation SmCP A . Because the molecules in adjacent layers can have either a synclinic (molecules in adjacent layers are tilted in the same direction, C S ) or an anticlinic (molecules in adjacent layers are tilted in opposite directions, C A ) interlayer correlation, the four different phase structures shown in Figure 1 may result for such mesophases. [7] Usually, the AF phases represent the ground states, whereas the FE states (SmC S P F and SmC A P F ) can only be achieved after with response times of less than one minute. The average response ratio at 3 ppm NO 2 was 1.16.Individual SnO 2 nanoribbons are small, fast and sensitive devices for detecting ppm-level NO 2 at room temperature under UV light. These nanodevices can be operated under laboratory conditions over many cycles without loss of sensitivity. The advantages of low-temperature, potentially drift-free operation make SnO 2 nanoribbons good candidates for miniaturized, ultrasensitive gas sensors in many applications. Further sensitivity increases should be achievable by using thinner nanoribbons, developing ohmic SnO 2 ± metal contacts and decorating these structures with catalysts. With such innovations, the chemical detection of single molecules on nanowires may soon b...

We report unambiguous experimental evidence for an achiral orthogonal biaxial smectic-A phase which exhibits antiferroelectric switching behavior. The evidence is based on x-ray-diffraction measurements, texture observation, and the results of dielectric and electro-optical measurements.

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