The purple color corresponds to sodium resorufin whereas the yellow color is originating from sodium fluorescein. The crystals functionalized only with sodium fluorescein do not exhibit strong polarized anisotropy, whereas crystals with sodium resorufin show clear polarization-dependent color anisotropy at relatively low concentrations (vide supra, Figure ). The crystals are dark purple when the polarized light is oriented in parallel to the channels showing that the long axis of the dyes are confined along the crystallographic c-axis. Combining these two different properties within a single host crystal resulted in polarization-dependent dichromism.