Dispersion states and orientation of aromatic solutes in monocrystalline matrices of n -heptane

Solid solutions of coronene, perylene, and pyrene in monocrystalline n -heptane have been prepared by slow cooling. The solutes exhibit dichroic absorption, fluorescence, and phosphorescence spectra that make evident an orientation of aromatic molecules in the paraffinic crystal lattice. Molecular aromatic planes are found to be nearly perpendicular to the growth axis, while their largest axis is oriented in the direction of alkane chains. The sites in which the molecules are trapped appear to be similar to the ones obtained with low concentrated quickly frozen solutions. Although aggregates could be present, they are not observed.