From Chiral Molecules to Chiral Phases1: Comments on the Chirality of Liquid Crystalline Phases

Abstract

In liquid crystal science the phenomenon of chirality has often played an important role in the context of phase structures or as an origin of symmetry breaking. Fundamental questions about ‘chirality’ in the context of liquid crystal properties have not been widely discussed or taken into account in the development of suitable concepts. For example, the questions of whether or not the spontaneous polarization or the circular dichroism (CD) with a light beam propagating obliquely to the optical axis of the phase is a chirality observation, have never been asked. With the report in 1996 of chiral liquid crystal phases [1], formed from achiral ‘banana-shaped compounds’, a new era of discussion dawned. Many questions are now raised which seem to be trivial, but are also fundamental, e.g. can a commercial CD instrument measure CD of an anisotropic and inhomogeneous phase without artifacts or whether or not a measured CD is an unequivocal proof for the existence of a chiral structure.