Different nematic phases and a switchable SmCP phase formed by homologues of a new class of asymmetric bent-core mesogens

Schröder, Martin; Diele, Siegmar; Pelzl, G.; Dunemann, Ulrike; Kresse, H.; Weißflog, W.

doi:10.1039/b305451a

Cited by 94 publications

(60 citation statements)

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“…Although the N TB phase shows focal-conic textures characteristic of soft systems with one-dimensional periodic ordering, the absence of lamellar x-ray reflections indicates that there is no modulation of the electron density associated with this periodic structure. When cooled to the columnar phase, the XRD pattern shows two peaks, one at q~0.14 Å -1 and one at q~0.15 Å -1 , corresponding to a rectangular columnar structure with lattice parameters a~4.2 nm and b~4.5 nm [13].…”

Section: Experiments and Resultsmentioning

confidence: 99%

“…We provide direct evidence of the chiral, periodic, conical helical structure of UD68, using freeze-fracture transmission electron microscopy (FFTEM), x-ray diffraction (XRD), depolarized transmission light microscopy (DTLM), and electro-optical measurements. UD68 was synthesized by Schröder et al [13], who proposed in the bent-core series in Figure 1a for n < 7 an unusual nematic-to-nematic phase transition, with the molecules in the lower temperature phase stacked in the bend direction, forming bundles of non-defined length as the precursor of the columnar phase. We show that the structural characteristics of this low temperature nematic phase are nearly identical to those found in the N TB phases of the bent molecular dimers.…”

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confidence: 99%

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Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

et al. 2014

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The chiral, heliconical (twist-bend) nematic ground state is reported in an achiral, rigid, bent-core mesogen (UD68). Similar to the nematic twist-bend (N TB ) phase observed in bent molecular dimers, the N TB phase of UD68 forms macroscopic, smectic-like focal-conic textures and exhibits nanoscale, periodic modulation with no associated modulation of the electron density, i.e., without a detectable lamellar x-ray reflection peak. The N TB helical pitch is p TB ~ 14 nm. When an electric field is applied normal to the helix axis, a weak electroclinic effect is observed, revealing 50 µm -scale left-and right-handed domains in a chiral conglomerate.2

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Section: Experiments and Resultsmentioning

confidence: 99%

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Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

et al. 2014

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“…In the X-ray pattern of the lower temperature phase no evidence of a layer structure could be found, although the fan-like texture indicates the existence of a smectic-like phase. Thus the optical and X-ray measurements point to an Nx phase as found for instance for liquid crystalline bent dimers of cyanobiphenyl connected by flexible spacers which has recently been characterized as a nematic phase with a conical twist-bend helical arrangement of the molecules and which has been called nematic twist-bend (NTB) phase [44,[58][59][60][61][62][63][64].…”

Section: Dimers Terminally Cyano Substituted At the Bent-core Mesogenmentioning

confidence: 99%

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

et al. 2014

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Banana-calamitic dimers are a topic in the field of bent-core mesogens. New materials were prepared by chemical variations at the bent-core fragment that is by a cyano group terminally attached to the bent-core fragment, by lateral substitution with a chlorine atom and methyl group, respectively, and by increasing the number of phenyl rings from five to six. The bent-core and the calamitic mesogenic moieties are connected by aliphatic spacers of different length. The materials were investigated by optical microscopy, DSC, X-ray diffraction studies and electro-optical measurements. This way nematic, smectic and various types of polar columnar phases have been characterized. The low temperature phase in a sequence of two nematic phases exhibiting different properties can be classified as a nematic twist-bend phase. Such NTB phases are only formed if a bend exists along the molecular long axes. This prerequisite can be doubly achieved in banana-calamitic dimers: by the intrinsic bend of one of the mesogenic fragments and by an odd-numbered spacer.

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“…This twist makes the bend angle ␣ deviate from the bond angle (i.e., central angle) of the central BUs. There are some compounds incorporating nonaromatic central BUs such as ester [41], amide [42][43][44], tetrahydropyrane [45], and cyclic urine groups [46]. The tetrahydropyrane BU derives from a sugar derivative, 3,4,6-tri-O-acetyl-D-glucal.…”

Section: General Molecular Structure Of Bent-core Lcsmentioning

confidence: 99%

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

Zhang¹

2013

Intelligent Stimuli‐Responsive Materials

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The three classic states of matter are well known and ubiquitous in everyday life: solid, liquid, and gas. Liquid crystals (LCs), an intermediate state between solid crystal and isotropic liquid, constitute a new fascinating class of condensed soft matter uniquely combining both fluidity and long-range order. The fluid-like mobility enables LCs to be switchable under external stimuli, and crystal-like long-range order bestows anisotropic physical properties on LCs. LCs can be divided into two main classes: thermotropic and lyotropic. Thermotropic LCs consist of individual molecules (or ion pairs) and exhibit phase transitions with the change of temperature. In this case, temperature is the fundamental thermodynamic factor determining mesophase formation. Lyotropic LCs are a special type of solution system that can form mesophases as a function of both temperature and concentration of LC molecules. The building block of a lyotropic phase is an aggregate (called a micelle) formed via self-assembly of many molecules (typically on the order of 100). Examples of LCs can be found both in the natural world and in technological applications. Thermotropic LCs find 189 190 ELECTRIC-AND LIGHT-RESPONSIVE BENT-CORE LIQUID CRYSTALS a wide variety of uses in displays, and an important example of lyotropic LCs is cell membranes formed by amphiphilic lipids. Surfactants in water (i.e., soap water) constitute another useful example of lyotropic LCs. Although the majority of LCs are organic molecules, there exist many LC materials incorporating metals into organic anisotropic molecules [1-3]. These organic-inorganic hybrid LC materials are described as metallomesogens and are recently called metallotropic LCs [4] as distinguished from two main LC classes. In fact, metallomesogens can be classified as either thermotropic or lyotropic LCs depending on their composition and conditions. However, it should be noted that metallomesogens offer a material platform to incorporate magnetic, electronic, optical, redox, and catalytic properties common to inorganic materials into LCs.Although thermotropic LCs have been known to scientists for over 100 years since a discovery by the Austrian botanical physiologist Friedrich Reintizer in 1888, it was only in the late 1960s that they began to be used in display applications. Today, they are best known for their exceptionally successful commercial applications in flat panel display products such as TVs, smart phones, computer displays, and digital projectors. Although today's LC display technology is becoming very advanced, LC materials used in display devices possess the simplest nematic (N) phase and their molecules have been variants on simple rod shapes (Fig. 6.1a). Besides nematic phases, LCs can exhibit other phases: smectic (Sm), columnar (Col), and cubic phases, depending on the orientational or positional orders of their molecules. Nematic phases have only long-range orientational order, smectic mesophases exhibit one-dimensional (1D) positional order and form two-dimensional (2D) layered ...

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Different nematic phases and a switchable SmCP phase formed by homologues of a new class of asymmetric bent-core mesogens

Cited by 94 publications

References 20 publications

Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

Banana-calamitic Dimers: Further Variations of the Bent-core Mesogenic Unit

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

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