Chirality in discotic lyomesophases

Properties of isotropic and columnar cholesteric lyomesophases of triphenyl ene derivatives dissolved in dodecane were investigated by selective reflec tion (SR) and dynamic light scattering (DLS) spectroscopy. The selective re flection measurements reveal a strong dependence of the helical pitch on co ncentration and temperature, which can be explained by competing effects of the molecular twisting power and the intercolumnar steric forces. The DLS measurements reveal a presence of three relaxational type dynamic modes in the pre-transitional region of the isotropic-cholesteric phase transition. Two of these modes exhibit an arrhenius like temperature dependence and doe s no: seem to be directly related with the transition. The third mode shows a critical slowing down near the transition temperature and is presumably related to the translational diffusion of the columnar stacks, which rapidl y increase in their length with decreasing temperature.