Credit: © 2009 AAAS

The chirality, or handedness, of molecular systems is of significant interest in many areas and the spontaneous formation of chiral crystals, clusters or monolayers have been observed with a variety of chiral and achiral molecules. In particular, achiral bent-core — or 'boomerang'-shaped — molecules organize into layered liquid-crystal phases with chiral domains. The cores of the molecules in each domain are twisted and ordered along one direction. These directions are different for each domain, leading to anisotropic materials.

Now, a team led by Noel Clark from the University of Colorado has observed the spontaneous formation of isotropic yet chiral liquid crystals from such achiral bent-core molecules1. Intralayer 'saddle splay' deformations cause the layers to twist and entangle across large areas, thus propagating the chirality without leading to long-range order. The resulting fluids are highly active optically and dark between crossed polarizers, whereas the anisotropic phases exhibit dark and light domains.

With related achiral, bent-core molecules, Clark and co-workers have observed the formation of helical nanofilaments2. In this case, the competition between the twist of the molecules and their macroscopic ordering in layers leads to twisted, homochiral layers that are helically packed into nanofilaments. These in turn organize into a homochiral liquid-crystal phase, which is nanoporous as the fibres cannot be closely packed.