Absorption and Fluorescence Measurements in Compensated Cholesteric Mesophases. Part I: Orientation of Chromophores in Liquid Crystal Solvents

A mixture of cholesteric compounds of opposite helical twisting power at a definite temperature T gets nematic properties because the long molecular axes take a parallel arrangement. If the sample is placed between lecithin-treated quartz plates the long axes at T switch by an angle of 90° into a direction normal to the cover surfaces. As the orientation of the cholesteric molecules is transferred to the anisotropic solute molecules this effect has been detected by means of measure­ment of absorptivity and fluorescence efficiency of soluted chromophores. By the method described a possibility opens to determine the direction of optical transitions by a very simple technique.