Laterally Substituted and Swallow‐Tailed Liquid Crystals

Weißflog, W.; Demus, D.; Goodby, John W.; Gray, G. W.; Spieß, Hans Wolfgang; Vill, V.

doi:10.1002/9783527619276.ch8c

Cited by 4 publications

(6 citation statements)

References 129 publications

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“…Yet already for the relatively small methyl group, a significant barrier was predicted. It was proposed that the reduction in conformational flexibility, in combination with the known steric effects described for classical mesogens (which actually constitute the dominating factor), 68,730 curvature (SmA for f V,C < 0.5, Col hex for f V,C ≈ 0.6−0.72, and Cub I for f V,C > 0.72, with f V,C being the volume fraction of the Cterminal chains); (ii) increasing the length of the alkyl chain attached to the "free" imidazolium nitrogen atom (= N-terminal chain) results in the reverse sequence for these compounds (Figure 29); and (iii) the amide-based compounds shows higher melting points and only forms SmA and Col hex phases (Figure 29); the single-chain amide salts have such high melting points that decomposition occurs before a potential mesophase can develop.…”

Section: Chemical Reviewsmentioning

confidence: 99%

“…436 Attachment of relatively large, flexible lateral substituents to a rod-like aromatic system is a common way to suppress smectic phase formation in classical calamitic LCs, and to induce a decrease of the transition temperatures. 68,730 While at first sight long-chain lateral substituents seem to decrease the shape anisotropy and are thus expected to be detrimental for (nematic) mesophase formation, it has been shown for 1,4-bis[4-(n-alkyloxy)benzoyloxy]-2-(n-alkyl)benzenes that the long lateral substituent aligns nearly parallel to the molecular long axis, thus forming an anisometric molecular shape. 809,810 More specifically, that part of the flexible lateral chain exceeding five carbon atoms was proposed to be more or less parallel to the rigid aromatic core.…”

Section: Attachment Of Mesogenic Groupsmentioning

confidence: 99%

Section: Imidazolium-based Ionic Liquid Crystalsmentioning

confidence: 99%

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Ionic Liquid Crystals: Versatile Materials

et al. 2016

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This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

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Section: Chemical Reviewsmentioning

confidence: 99%

Section: Attachment Of Mesogenic Groupsmentioning

confidence: 99%

Section: Imidazolium-based Ionic Liquid Crystalsmentioning

confidence: 99%

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Ionic Liquid Crystals: Versatile Materials

et al. 2016

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“…Such chain length-dependent effective molecule shape in a liquid crystal phase has previously been identified for the case of mesogens with chains of varying length attached laterally to the core. 14 Looking now at Fig. 1 we first note that the clinicity transition takes place deeper in the temperature range of tilted smectic order the longer the meta-substituted alkyloxy chain, favoring SmC at the cost of SmC a .…”

Section: Achiral Hockey-stick Mesogensmentioning

confidence: 88%

On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants

et al. 2009

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A series of achiral hockey stick-shaped mesogens forming tilted smectic liquid crystal phases of synclinic SmC-as well as anticlinic SmC a -type was prepared and characterized. While all homologues exhibit both phases, the balance shifts from anticlinic to synclinic order upon 10 elongation of the terminal chain at the meta (m) position, defining the hockey stick shape. The elongation also leads to an increased kinetic hindrance of the transition between syn-and anticlinic phases and a decreased transition enthalpy. These observations indicate that a well-defined kink (short m-substituted chain) promotes the anticlinic structure while a higher flexibility between kinked and rod-shape (long m-substituted chain) promotes synclinic order. An intermediate chain-15 length homologue was selected as host material for doping with syn-and anticlinic rod-shaped chiral dopants, respectively, at varying concentrations. Opposite of what might be expected the balance between syn-and anticlinic order was not simply dictated by the choice of dopant. Instead both types of tilting order prevailed with roughly the same strength as in the achiral host regardless of which chiral material was added, up to concentrations well beyond normal doping conditions. 20Thus, at least with hockey stick-shaped achiral hosts, syn-as well as anticlinic chiral compounds can be used effectively as chiral dopants without necessarily having an important impact on the clinicity of the resulting mixture. The hockey stick design concept should be useful in producing achiral anticlinic-forming mesogens for low-polarization, long-pitch antiferroelectric liquid crystal mixtures. Finally, we point out that a mixture study like the one carried out here yields a 25 conclusive means of establishing the clinicity of achiral tilted smectics, an endeavour that can sometimes be far from trivial.

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“…[49,50] It seems reasonable to suggest that in case of the decyloxy-substituted analogue 5d, the steric lateral repulsion is compensated for by the elongation of the terminal flexible chain segment.…”

Section: Thermal Propertiesmentioning

confidence: 98%

Coumarin-based emissive liquid crystals

Buchs

Gäbler²,

Janietz

et al. 2014

Liquid Crystals

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Calamitic luminophores are presented based on an elongated aryl-substituted coumarin core. The substitution pattern at terminal and lateral positions were systematically modified. The new compounds exhibit smectic C and/or nematic liquid crystalline phases. The chromophores show fluorescence in the blue spectral region. The benzopyranones are miscible with acrylate-substituted reactive nematic mesogens. Uniaxial orientation of the mixed systems was achieved by surface-assisted alignment on polyimide orientation layers. The film anisotropy was stabilised by subsequent photocrosslinking. The crosslinked oriented films display linear polarised photoluminescence upon isotropic excitation

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Laterally Substituted and Swallow‐Tailed Liquid Crystals

Cited by 4 publications

References 129 publications

Ionic Liquid Crystals: Versatile Materials

Ionic Liquid Crystals: Versatile Materials

On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants

Coumarin-based emissive liquid crystals

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