115883-87-9Relevant academic research and scientific papers
Field-induced switching of chirality in undulated ferroelectric and antiferroelectric smCP phases formed by bent-core mesogens
Reddy, Ramaiahgari Amaranatha,Schroeder, Martin W.,Bodyagin, Michael,Kresse, Horst,Diele, Siegmar,Pelzl, Gerhard,Weissflog, Wolfgang
, p. 774 - 778 (2005)
Switching signs: The polar structure of a tilted smectic C phase formed by a homologous series of bent-core mesogens changes from antiferroelectric to ferroelectric with increasing chain length. The polar switching of the banana-shaped molecules occurs by
Controlling the formation of heliconical smectic phases by molecular design of achiral bent-core molecules
Alaasar, Mohamed,Cai, Xiaoqian,Eremin, Alexey,Kurachkina, Marharyta,Lehmann, Anne,Liu, Feng,Nagaraj, Mamatha,Poppe, Marco,Poppe, Silvio,Tamba, Maria-Gabriela,Tschierske, Carsten,Vij, Jagdish K.
supporting information, p. 3316 - 3336 (2020/03/23)
Fluids with spontaneous helical structures formed by achiral low molecular mass molecules is a newly emerging field with great application potential. Here, we explore the chemical mechanisms of the helix formation by systematically modifying the structure of a bent 4-cyanoresorcinol unit functionalized with two different phenyl benzoate based aromatic rods and terminated with two alkyl chains of variable length. The majority of these achiral compounds self-assemble, forming a short-pitch heliconical liquid crystalline phase in broad temperature ranges. In some cases, it occurs without any competing low-temperature phase. We demonstrate that the mirror symmetry broken mesophase occurs at the paraelectric-(anti)ferroelectric transition if the tilt angle of the molecules in the smectic layers is around 18-20° and if this transition coincides with a change of the tilt correlation between the layers. In the close vicinity of this transition, a field-induced heliconical phase develops as well as a new heliconical phase with polarization-randomized structure. These investigations provide a blueprint for the future design of achiral molecules capable of spontaneous mirror symmetry breaking by the formation of heliconical liquid crystalline phases.
Polar Order and Symmetry Breaking at the Boundary between Bent-Core and Rodlike Molecular Forms: When 4-Cyanoresorcinol Meets the Carbosilane End Group
Westphal, Eduard,Gallardo, Hugo,Caramori, Giovanni Finoto,Sebastián, Nerea,Tamba, Maria-Gabriela,Eremin, Alexey,Kawauchi, Susumu,Prehm, Marko,Tschierske, Carsten
supporting information, p. 8181 - 8197 (2016/06/14)
Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment (CN1) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLsPS) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR) and ferroelectric polydomain SmCsPSphases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror-symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1. These investigations contribute to the general understanding of the development of polar order and chirality in soft matter. The power of an ester group: Reversing one COO group in a bent-core mesogen leads to very different dipole moments, gives rise to distinct segregation of the carbosilane end groups from the aliphatic and aromatic segments, and thus modifies the mode of self-assembly, the coherence length of polar order, and the capability of mirror-symmetry breaking. One of the isomers forms a new leaning-type liquid-crystalline (LC) phase in which the tilt coincides with the polar direction, whereas the other forms a ferroelectric LC in which the tilt is perpendicular to the polar direction (see figure).
