The Magic 4-Cyanoresocinols - Their Role in the Understanding of Phenomena at the Rod-Banana Cross-Over and Relations to Twist-Bend Phases and Other Newly Emerging LC Phase Types

Tschierske, Carsten

doi:10.1080/02678292.2021.2010142

Cited by 7 publications

(4 citation statements)

References 208 publications

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“…17–19 Orthogonal re-entrant phases following a tilted SmC phase are rare and limited to bent mesogenic dimers and rod-like molecules with permanent chirality. 20,21 Novotná et al found a SmA*–SmC*–SmA* re phase sequence for 9ZBL (Fig. 2a).…”

Section: Introductionmentioning

confidence: 91%

First azulene liquid crystal with de Vries behavior and a SmA re-entrant phase

et al. 2023

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Section: Introductionmentioning

confidence: 91%

First azulene liquid crystal with de Vries behavior and a SmA re-entrant phase

et al. 2023

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“…Given the similarity in structure between the SmC TB phase shown by CB6OIBeOm series and the SmCα* phase, we designate this SmC TB variant as the SmC TB-α phase. Polar bent core molecules had also been reported to show a short pitch heliconical smectic phase designated Sm(CP) hel and this is thought to be associated with the growth of polar order at the anticlinic-synclinic transition in smectic phases with a small tilt angle [98][99][100]. Again, the pitch length was incommensurate with the layer spacing, and typically around three-layer thicknesses.…”

Section: The Twist-bend Smectic Phasesmentioning

confidence: 99%

Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend

et al. 2022

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In this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules containing two mesogenic groups linked through a flexible spacer, and even- and odd-membered dimers differ in terms of their average molecular shapes. The former tend to be linear whereas the latter are bent, and this difference in shape drives very different smectic behaviour. For symmetric dimers, in which the two mesogenic groups are identical, smectic phase formation may be understood in terms of a microphase separation into distinct sublayers consisting of terminal chains, mesogenic units and spacers, and monolayer smectic phases are observed. By contrast, intercalated smectic phases were discovered for nonsymmetric dimers in which the two mesogenic units differ. In these phases, the ratio of the layer spacing to the molecular length is typically around 0.5 indicating that unlike segments of the molecules overlap. The formation of intercalated phases is driven by a favourable interaction between the different liquid crystal groups. If an odd-membered dimer possesses sufficient molecular curvature, then the twist-bend nematic phase may be seen in which spontaneous chirality is observed for a system consisting of achiral molecules. Combining the empirical relationships developed for smectogenic dimers, and more recently for twist-bend nematogenic dimers, we show how dimers were designed to show the new twist-bend, heliconical smectic phases. These have been designated SmCTB phases in which the director is tilted with respect to the layer plane, and the tilt direction describes a helix on passing between layers. We describe three variants of the SmCTB phase, and in each the origin of the symmetry breaking is attributed to the anomalously low-bend elastic constant arising from the bent molecular structures.

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“…Bent-core mesogens with 4-cyanoresorcinol central core are extensively researched for their unconventional polar and chiral mesophases. [34][35][36][37] The terminal cyano-substituted bent-core systems have been reported for the biaxial Smectic A (SmA b ) phase, [38][39][40] nematic phase, [17,33,41,42] and polar orthogonal phases [43] whereas, there are a few reports on nitro-terminated bent-core mesogens. [31,33,42] In addition to the bent angle, [44,45] the terminal or lateral substitutions [46] play a crucial role in bend-splay anisotropy, a significant parameter for electrooptical devices.…”

Section: Introductionmentioning

confidence: 99%

Nematic Phase of Polar Unsymmetrical Bent‐Core Molecules

et al. 2023

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In liquid crystalline systems, the presence of polar groups at lateral or terminal positions is fundamentally and technologically important. Bent-core nematics composed of polar molecules with short rigid cores usually exhibit highly disordered mesomorphism with some ordered clusters that favourably nucleate within. Herein, we have systematically designed and synthesized two new series of highly polar bent-core compounds comprised of two unsymmetrical wings, highly electronegative À CN and À NO 2 groups at one end, and flexible alkyl chains at the other end. All the compounds showed a wide range of nematic phases composed of cybotactic clusters of smectic-type (N cyb ). The birefringent microscopic textures of the nematic phase were accompanied by dark regions. Further, the cybotactic clustering in the nematic phase was characterized via temperature-dependent XRD studies and dielectric spectroscopy. Besides, the birefringence measurements demonstrated the ordering of the molecules in the cybotactic clusters upon lowering the temperature. DFT calculations illustrated the favourable antiparallel arrangement of these polar bent-core molecules as it minimizes the large net dipole moment of the system.

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The Magic 4-Cyanoresocinols - Their Role in the Understanding of Phenomena at the Rod-Banana Cross-Over and Relations to Twist-Bend Phases and Other Newly Emerging LC Phase Types

Cited by 7 publications

References 208 publications

First azulene liquid crystal with de Vries behavior and a SmA re-entrant phase

First azulene liquid crystal with de Vries behavior and a SmA re-entrant phase

Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend

Nematic Phase of Polar Unsymmetrical Bent‐Core Molecules

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