Mirror symmetry breaking in liquids and liquid crystals

Abstract

In the recent two decades liquid crystal science has contributed significantly to the understanding of mirror symmetry breaking and spontaneous emergence of chirality in fluids. This account tries to summarise the current state of understanding of mirror symmetry breaking in the liquid and liquid crystalline mesophases, ranging from isotropic liquids, via cubic, columnar and tetragonal SmQ phases of polycatenar compounds, the twist bend nematic phases of bent dimesogens to the heliconical and conglomerate type smectic phases of bent-core mesogens. Especially, the importance of dynamic chirality synchronisation of molecular conformers, cooperativity, helical superstructures, layer chirality, network formation, as well as chiral and achiral surface effects is discussed. At the end the transition from local to absolute symmetry breaking, chirality amplification and the relevance for the emergence of uniform chirality in prebiotic fluids and biosystems are considered. Dynamic Mirror Symmetry Breaking Transiently chiral molecules Cooperativity Super structural chirality Chirality synchronisation in fluids Network connectivity

The Chiral Twist‐Bend Nematic Phase (N*TB)

“…The proposed structures of all final products and their intermediates were characterised by using acombination of 1 Ha nd 13 CNMR, and FTIR spectroscopies. 1 Ha nd 13 CNMR spectra were recorded on either a4 00 MHz Varian Unity INOVA, or a3 00 MHz Bruker Ultrashield NMR spectrometer.I nfrared spectra were recorded on a Thermal Scientific Nicolet IR100 FTIR spectrometer with an ATRd iamond cell. The purities of the final products were verified using C, H, Nm icroanalysis performed by the Micro Analytical Laboratory in the School of Chemistry at the University of Manchester or Sheffield Analytical and Scientific Services Elemental Microanalysis Service at the University of Sheffield.…”

“…The spontaneouse mergence of chirality in systems composed of achiral molecules is of fundamental importance in both physicala nd biological sciences andt hought to play ap ivotal role in the origin of biological homochirality.I nt his context, the study of liquid crystalline systems has greatlye nhanced our understandingo fs ymmetry breaking in fluids. [1] Indeed, the first example of spontaneousc hiral symmetry breaking in af luid with no spatial ordering was provided by the twistbend nematic, N TB ,p hase in which the director forms ac onical helix. [2] The formation of chirality in the N TB phase is spontaneous and, hence, equal numbers of degenerate heliceso fo pposite handedness would be expected.…”

Stereochemical Rules Govern the Soft Self‐Assembly of Achiral Compounds: Understanding the Heliconical Liquid‐Crystalline Phases of Bent‐Core Mesogens

“…Based on stereochemical principles, there is an inherent driving force for helix formation associated with the homochirality of the SmC a P A and SmC s P F phases. Usually it develops as a transversal twist leading to frustrated smectic phases (HNF, DC). The alternative longitudinal twist along the layer normal, reported here, can obviously only develop if the interlayer coupling is sufficiently weak, that is, close to the transition from a de Vries SmA phase to a weakly tilted SmC phase being close to the transition between anticlinic and synclinic tilt.…”

Polar Order, Mirror Symmetry Breaking, and Photoswitching of Chirality and Polarity in Functional Bent‐Core Mesogens

“…We assume that the basis of chirality in the investigated smectic phases is the formation of a heliconical structure with the helix axis parallel to the layer normal, owing to the escape from a growing polarization in the clusters . This might be combined with a synchronization of helical molecular conformations of the transiently chiral 4‐cyanoresorcinol based bent‐core mesogens, allowing a denser packing . A helical modulation of the polar direction, combined with chirality synchronization of the involved molecules was recently indicated in simulations of nematic phases of bent dimesogens for which a polar twist model (N PT ) was proposed as an alternative model of the heliconical low‐temperature nematic phases, known as N x or N TB phases.…”

“…In the smectic phases reported here, the developing chirality can in addition couple through diastereomeric relations with the layer chirality of the SmC s P F clusters, defined by tilt direction and polar direction . With growing polarization and cluster size, the energy gain of this cooperative coupling between transient molecular and superstructural chirality increasingly compensates for unfavorable entropic effects of segregation and reduced conformational diversity . If a uniform tilt direction is stabilized by the surface anchoring of the molecules, then the preferred tilt and chirality of the SmC s P F clusters can become biased over macroscopic areas .…”