The Solution of the Puzzle of Smectic‐Q: The Phase Structure and the Origin of Spontaneous Chirality

Abstract

The so-called smectic-Q (SmQ) liquid crystal phase was discovered in 1983 in rod-like molecules, but its structure remain unclear in spite of numerous attempts to solve it. Herein, we report what we believe to be the solution: A unique bicontinuous phase that is non-cubic and is made up of orthogonal twisted columns with planar 4-way junctions. While SmQ had only been observed in chiral compounds, we show that this chiral phase forms also in achiral materials through spontaneous symmetry breaking. The results strongly support the idea of a helical substructure of bicontinuous phases and long-range homochirality being sustained by helicity-matching at network junctions. The model also explains the triangular shape of double-gyroid domains growing within a SmQ environment. SmQ-forming materials hold potential for applications such as circularly polarized light emitters that require no alignment or asymmetric synthesis.

Helical Networks of π‐Conjugated Rods – A Robust Design Concept for Bicontinuous Cubic Liquid Crystalline Phases with Achiral Ia3¯d and Chiral I23 Lattice

“…[7,14,17] However, as soon as rod-like segments are included in the molecular structure ( Figure 1c-f), new cubic and also noncubic network phases can be observed. [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65] In most cases, these rods are organized in the networks and on average lie perpendicular to the network segments. [14][15][16][17]66] For these Cub bi phases, beside the Ia3 d phase, a second more complex type of cubic phase with a larger lattice parameter was found.…”

Multi-level chirality in liquid crystals formed by achiral molecules

“…Whether for achiral molecules a helical structure can be multihierarchical is still unclear. Helical arrangements that are self-repeating in 3D have been proposed for cubic or tetragonal phases formed by multiple end-chain molecules 11–15 . Lamellar phases - smectics, with helical structures, were suggested 16–18 and unambiguously proved just for one material 19 .…”

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

“…Thus, this work shows that fundamental stereochemical rules can determine the phase structures and properties of LC systems formed by achiral compounds.T his contributes to the understanding of the complex behavior of bent-core mesogensd epending on the conditions [95] and the observations made with other weakly polar LC systemsa tt he paraelectric-(anti)ferroelectric cross-over,a sf or example, with some hockey-stickm olecules. [96] In addition, it contributes to an improved understandingo fm irror symmetry breakingi no ther soft matter systems, as for example the bicontinuousc ubic and related phases, [12,97,98] the dark conglomerate phases, [25,39,41,42] the heliconical nematic [62][63][64][65][66] and smectic phases, [67] andt he spontaneously chirali sotropic liquids. [9] Further investigations in these directionsm ight lead to as imilar diversity of different heliconical phases as known for the permanently chiral rod-likem olecules.…”