The orientation axis comparison of order parameters of anthraquinone dyes in a liquid crystal phase

Three different molecule‐fixed coordinate systems have a distinct significance for the calculation of order parameters. Only one of them is suitable to define an orientation axis (x*3) in order to obtain order parameters which can be used for a comparison between systems of different molecules. For the majority of point symmetry groups, these axes x* are fixed by symmetry. The selection of the orientation axis x*3 from the x3 depends on a special quantitative condition. By means of 15 aminoanthraquinones dissolved in the compensated nematic phase of cholesteryl chloride/cholesteryl laurate and in addition some of them in ZLI 1695 (Merck), the consequences of the choice of the reference axis x3 for determining order parameters have been analyzed. By this it has been shown experimentally that order parameters ‐ measured by different methods IR, UV, e. g. ‐ are only comparable if they refer to x*3. For two dyes (4,12) the orientation axis x*3 switches about π/2 depending on the special type of substituents. For the structure ‐ order parameter relation it has been shown that the 15 dyes can be arranged in two series. One series obeys the usual rule of increasing S* with increasing length to width ratio. The second series does not fit in this dependence.