Chiral self-sorting and amplification in isotropic liquids of achiral molecules

Supramolecular Chirality of the Two-Component Supramolecular Copolymer Gels: Who Determines the Handedness?

Natural supramolecular systems typically contain a wide variety of chiral molecules. Studying the chiral conflict within different supramolecular assemblies not only can be very helpful for understanding the inherent principles of supramolecular chirality but also can guide the preparation of many functional chiral soft matters. For assemblies containing only structurally similar molecules, supramolecular chirality is determined by enantiomeric excess of molecular building blocks. For supramolecular systems assembled by structurally different chiral molecules, however, the optical activity of the systems and the chiral conflict among different chiral molecules can be very complex. We found rather unexpected results regarding the chiral conflict within two-component supramolecular copolymer gels in this study. The handedness of the chirality of supramolecular copolymer gels, which were formed by the coassembly of bolaamphiphilic L-histidine derivatives and tartaric acids, was found to be dependent on the ordering molecular packing, instead of the preponderance of certain chiral molecules.

Spontaneous Mirror-Symmetry Breaking in Isotropic Liquid Phases of Photoisomerizable Achiral Molecules

Spontaneous mirror-symmetry breaking is of fundamental importance in science as it contributes to the development of chiral superstructures and new materials and has a major impact on the discussion around the emergence of uniform chirality in biological systems. Herein we report chirality synchronization, leading to spontaneous chiral conglomerate formation in isotropic liquids of achiral and photoisomerizable azobenzene-based rod-like molecules. The position of fluorine substituents at the aromatic core is found to have a significant effect on the stability and the temperature range of these chiral liquids. Moreover, these liquid conglomerates occur in a new phase sequence adjacent to a 3D tetragonal mesophase.

Mirror symmetry breaking by mixing of equimolar amounts of two gyroid phase-forming achiral molecules

Mirror symmetry breaking was realised by mixing of two achiral molecules both of which form themselves achiral bicontinuous cubic phases.

A structural model of the chiral “Im3m” cubic phase

Assuming the twisted arrangement of rodlike molecules as the origin of the chirality as in the existing model, a new model of the molecular arrangement in the cubic “Im3m” phase is proposed.

Mirror symmetry breaking in fluorinated bent-core mesogens

New fluorinated bent-core liquid crystals exhibiting helical nano-crystallite phases composed of chiral domains with opposite handedness and polar smcetic phases.

Synchronization of conformational chirality in mixtures of achiral bent-core molecules

SEM images and frequency variation of ε′′ in PDMBC with flat layers, M50 and M20 with respectively weak and strong layer deformation.

Mirror symmetry breaking in cubic phases and isotropic liquids driven by hydrogen bonding

Achiral hydrogen bonded rod-like complexes with four nonequally distributed terminal alkyl chains form a chirality synchronized isotropic liquid conglomerate as well as a conglomerate type chiral cubic phase.

Chiral conglomerates observed for a binary mixture of a nematic liquid crystal trimer and 6OCB

Dark conglomerates of domains with opposite handedness, which are designated as dark conglomerate phases (DC phases), have attracted much attention. After designing an achiral liquid crystal trimer, 4,4′-bis{7-[4-(5-octyloxypyrimidin-2-yl)phenyloxy]heptyloxy}biphenyl (1), which exhibits only a nematic phase, we prepared binary mixtures with some typical rod-like nematic liquid crystals, i.e., 4′-hexyloxy-4-cyanobiphenyl (6OCB), 2-(4-hexyloxyphenyl)-5-pentyloxypyrimidine (PPY), or 4-methyloxyphenyl 4-hexyloxycyclohexanecarboxylate (PCA), and investigated their phase transition behaviour. The binary mixtures containing 55–90 mol% of 6OCB were found to exhibit a nematic phase and a DC phase of chiral domains with opposite handedness. However, neither PPY nor PCA induced such a chiral conglomerate phase in the mixture with trimer 1. We discuss how core–core interactions contribute to produce such a chiral conglomerate phase.

Spontaneous mirror symmetry breaking in a re-entrant isotropic liquid

An achiral double-swallow tailed tetracatenar compound forms a re-entrant isotropic liquid between a bicontinuous cubic phase and a nematic liquid crystalline phase. This isotropic liquid was found to represent a conglomerate of two immiscible chiral liquids. The chirality is retained and eventually becomes uniform at the transition to the cubic I432 phase.

Right handed chiral superstructures from achiral molecules: self-assembly with a twist

The induction and development of chiral supramolecular structures from hierarchical self-assembly of achiral compounds is closely related to the evolution of life and the chiral amplification found in nature. Here we show that the combination of achiral tetraphenylethene (TPE) an AIE-active luminophore bearing four long alkyl chains via amide linkage allows the entire process of induction and control of supramolecular chirality into well-defined uniform right-handed twisted superstructures via solvent composition and polarity, i.e. solvophobic effect. We showed that the degree of twist and the pitch of the ribbons can be controlled to one-handed helical structure via solvophobic effects. The twisted superstructure assembly was visualised by scanning electron microscope (SEM) and transmission electron microscopy (TEM), furthermore, circular dichroism (CD) confirms used to determine controlled right-handed assembly. This controlled assembly of an AIE-active molecule can be of practical value; for example, as templates for helical crystallisation, catalysis and a chiral mechanochromic luminescent superstructure formation.

Controlling Chirality of Entropic Crystals

Colloidal crystal structures with complexity and diversity rivaling atomic and molecular crystals have been predicted and obtained for hard particles by entropy maximization. However, thus far homochiral colloidal crystals, which are candidates for photonic metamaterials, are absent. Using Monte Carlo simulations we show that chiral polyhedra exhibiting weak directional entropic forces self-assemble either an achiral crystal or a chiral crystal with limited control over the crystal handedness. Building blocks with stronger faceting exhibit higher selectivity and assemble a chiral crystal with handedness uniquely determined by the particle chirality. Tuning the strength of directional entropic forces by means of particle rounding or the use of depletants allows for reconfiguration between achiral and homochiral crystals. We rationalize our findings by quantifying the chirality strength of each particle, both from particle geometry and potential of mean force and torque diagrams.

Helical buckling in columnar assemblies of soft discotic mesogens

We investigate the emergence of chiral meso-structures in one-dimensional fluids consisting of stacked discotic particles and demonstrate that helical undulations are generated spontaneously from internal elastic stresses. The stability of these helical conformations arises from an interplay between long-ranged soft repulsions and nanopore confinement which is naturally present in columnar liquid crystals. Using a simple mean-field theory based on microscopic considerations we identify generic scaling expressions for the typical buckling radius and helical pitch as a function of the density and interaction potential of the constituent particles.

Self-sorting behavior of a four-component host–guest system and its incorporation into a linear supramolecular alternating copolymer

Self-sorting behavior of a four-component host–guest system was found, which could be utilized to construct a linear supramolecular alternating copolymer.

The design and investigation of the self-assembly of dimers with two nematic phases

Non-symmetric nematic dimers are designed and investigated by OPM, DSC and XRD; assembly models for the N_x phase are developed.

Twist grain boundary (TGB) states of chiral liquid crystalline bent-core mesogens

Chiral 4-cyanoresorcinol derived bent-core molecules form liquid crystalline phases with helically deformed layers representing TGBA and TGBC-like structures.

Dynamic mirror-symmetry breaking in bicontinuous cubic phases

Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the Im3̄m cubic phase is always chiral, while the Ia3̄d phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the Ia3̄d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3̄m phase. The high twist in the Im3̄m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.