New Spontaneously Chiral 3D Network Structures in Thermotropic Liquid Crystals

Spontaneous mirror symmetry breaking has been discovered recently in bicontinuous cubic phases [1], as well as in a special isotropic melt phase [2] of achiral rod-like mesogens. While the double gyroid Ia-3d phase is always achiral, the triple network cubic, previously given the Im-3m spacegroup, is always chiral. More recently in such compounds another chiral phase was found [3], turning out to be the so-called “SmQ”. This phase has previously been found only in enantiopure chiral compounds, and its structure was unclear. Now we find that it is also bicontinuous, with two isochiral networks of orthogonal twisted columns [3]. We have also re-examined the triple-network phase; due to its now recognised chirality, a new lower-symmetry spacegroup is assigned, resulting in a new structural model, still a triple network. It thus turns out that all known bicontinuous phases formed by transverse-lying rods in networks segments feature induced chirality, which is cancelled only in the racemic double gyroid.

[1] C. Dressel et al. Angew. Chem. Int. Ed., 2014, 53, 13115.
[2] C. Dressel et al. Nat. Chem., 2014, 6, 971.
[3] H. Lu et al. Angew. Chem. Int. Ed., 2018, 57, 2835.