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Layer Frustration, Polar Order and Chirality in Liquid Crystalline Phases of Silyl‐Terminated Achiral Bent‐Core Molecules
Author(s) -
Keith Christina,
Amaranatha Reddy Ramaiahgari,
Prehm Marko,
Baumeister Ute,
Kresse Horst,
Chao Jessie Lorenzo,
Hahn Harald,
Lang Heinrich,
Tschierske Carsten
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600876
Subject(s) - ferroelectricity , antiferroelectricity , materials science , frustration , liquid crystal , crystallography , birefringence , chirality (physics) , layer (electronics) , bent molecular geometry , molecule , polar , dielectric , chemical physics , condensed matter physics , optics , chemistry , nanotechnology , organic chemistry , symmetry breaking , optoelectronics , composite material , physics , chiral symmetry breaking , quantum mechanics , astronomy , nambu–jona lasinio model
A novel class of bent‐core molecules with oligo(siloxane) or carbosilane units at both ends was synthesized and the self‐organization of these molecules was investigated by polarizing microscopy, DSC, X‐ray scattering, dielectric and electrooptical methods. Depending on the size of the silicon‐containing segments, smectic and columnar liquid crystalline phases are formed. Most smectic phases are low birefringent and composed of macroscopic domains of opposite handedness (dark conglomerate phases). The switching process in these smectic phases is surface stabilized ferroelectric and, depending on the conditions, two distinct slow relaxation processes to nonpolar structures were observed. It is proposed that the smectic phases are built up by chiral and polar SmC s P F layer stacks which are separated by anticlinic interfaces. If the size of these layer stacks is sufficiently large a coupling to the substrate surfaces takes place and ferroelectric switching is observed. It is also suggested that the sponge‐like layer distortion, occurring in the low birefringent mesophases, is due to an escape from the local polar order within these SmC s P F layer stacks. For compounds with larger silylated units a steric frustration arises, which leads to layer modulation (columnar ribbon phases) and this is associated with a transition from ferroelectric to antiferroelectric switching. All compounds show a switching of the molecules around the long axis which reverses the layer chirality.