Biaxial nematics from their prediction to the materials and the vicious circle of molecular design

Besides the uniaxial nematic phase, omnipresent in liquid crystal (LC) displays, the biaxial nematic phase has been theoretically proposed to exist in which all molecular axes are oriented along individual directors. Although some high molecular mass systems (lyotropic phases, LC-polymers and colloidal LCs) reveal this fascinating phase, the formation of the thermotropic biaxial nematic phase among low molecular mass systems is strongly debated. This article gives a brief review of the methods frequently used to detect biaxiality and the different molecular biaxial systems which are under consideration to assemble in such a biaxial nematic phase. It appears that molecular design is in a vicious circle with respect to the preparation of ideal mesogens which should possess an enantiotropic, true biaxial nematic phase of molecules at ambient temperature and with a sufficiently low viscosity for a possible application in fast switching biaxial LC displays.