Factors affecting the formation in the solid state of the metastable complex between naphthalene and dimethyl-beta-cyclodextrin

An equimolar mixture of naphthalene and amorphous heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DM beta CD) was heated at 70 or 90 degrees C in a sealed container, After heating for 15 min at 90 degrees C, the mixture was crystallized to show an excimer fluorescence of naphthalene, and the fluorescence spectrum changed to a monomer emission by further prolongation of heating time, accompanied by a slight change in its powder X-ray diffractogram. It is suggested that a metastable complex showing the excimer emission of naphthalene was transformed to a stable complex showing the monomer emission. The mixing molar ratio of naphthalene to DM beta CD was also found to affect the transformation temperature of the complex.