A variety of simple bent-core molecules exhibit smectic liquid crystal phases of planar fluid layers that are spontaneously both polar and chiral in the absence of crystalline order. We found that because of intralayer structural mismatch, such layers are also only marginally stable against spontaneous saddle splay deformation, which is incompatible with long-range order. This results in macroscopically isotropic fluids that possess only short-range orientational and positional order, in which the only macroscopically broken symmetry is chirality--even though the phases are formed from achiral molecules. Their conglomerate domains exhibit optical rotatory powers comparable to the highest ever found for isotropic fluids of chiral molecules.

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...

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...

Depending on the number of dimethylsiloxane units in the spacer connecting two banana-shaped molecules either ferroelectric or antiferroelectric switchable polar smectic C phases have been obtained.

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