Helical Nano‐crystallite (HNC) Phases: Chirality Synchronization of Achiral Bent‐Core Mesogens in a New Type of Dark Conglomerates

Abstract

Spontaneous generation of macroscopic homochirality in soft matter systems by self-assembly of exclusively achiral molecules under achiral conditions is a challenging task with relevance for fundamental scientific research and technological applications. Dark conglomerate phases (DC phases), being optically isotropic mesophases composed of conglomerates of macroscopic chiral domains and formed by some non-chiral bent-core mesogens, represent such a case. Here we report two new series of non-symmetric bent-core molecules capable of forming a new type of mirror symmetry broken DC phases. In the synthesized molecules, a bent 4-bromoresorcinol core is connected to a phenyl benzoate wing and an azobenzene wing with or without additional peripheral fluorine substitution. The self-assembly was investigated by DSC, polarizing microscopy, electro-optical studies and XRD. Chiral and apparently achiral DC phases were observed besides distinct types of lamellar liquid crystalline phases with different degree of polar order, allowing the investigation of the transition from smectic to DC phases. This indicates a process in which increased packing density at first gives rise to restricted rotation and thus to growing polar order, which then leads to chirality synchronization, layer frustration and nano-scale crystallization. Topological constraints arising from the twisted packing of helical conformers in lamellar crystals is proposed to lead to amorphous solids composed of helical nano-crystallites with short coherence length (HNC phases). This is considered as a third major type of DC phases, distinct from the previously known liquid crystalline sponge phases and the helical nano-filament phases (HNF phases). Guidelines for the molecular design of new materials capable of self-assembly into these three types of DC phases are proposed.

Сhiral and Racemic Fields Concept for Understanding of the Homochirality Origin, Asymmetric Catalysis, Chiral Superstructure Formation from Achiral Molecules, and B-Z DNA Conformational Transition

“…Similar effects were observed in the ongoing formation of other chiral superstructures from achiral molecules [57,[177][178][179][180]. The dependence of chiral nanostructures from various mesophase temperatures of LC (maximal order) suggests that this regularity is of general nature.…”

The Chiral Trimer and a Metastable Chiral Dimer of Achiral Hexafluoroisopropanol: A Multi‐Messenger Study

“…It is not uncommon to find such processes in crystallization, where many analogous interactions in the growing crystal add to a powerful driving force attracting other monomers. Chirality synchronization phenomena involving achiral building blocks on the nanometer scale are less well studied but of particular interest for nucleation phenomena and chiral liquids . Vacuum isolation and low temperatures can amplify the driving force for the adaptive aggregation by removing diluting solvation and entropy influences .…”

The Chiral Trimer and a Metastable Chiral Dimer of Achiral Hexafluoroisopropanol: A Multi‐Messenger Study

“…These interactions must compensate for the reorganization energy,usually by allowing for compact, more strongly bound packings.I ti sn ot uncommon to find such processes in crystallization, [1][2][3][4] where many analogous interactions in the growing crystal add to ap owerful driving force attracting other monomers.C hirality synchronization phenomena involving achiral building blocks on the nanometer scale are less well studied but of particular interest for nucleation phenomena and chiral liquids. [5,6] Va cuum isolation and low temperatures can amplify the driving force for the adaptive aggregation by removing diluting solvation and entropy influences. [7] Fluorous interactions appear to favor such processes.…”