Photoluminescence of Pharmaceutical Materials in the Solid State. 4. Fluorescence Studies of Various Solvated and Desolvated Solvatomorphs of Erythromycin A

Abstract

The hydrate, methanolate, ethanolate, and isopropanolate solvatomorphs of erythromycin A have been prepared and characterized as to their crystallographic and solvent content characteristics. Even though erythromycin A does not exhibit fluorescence when in a dissolved state, in the solid state the solvated materials were found to be mildly fluorescent. Differences in fluorescence intensity were noted among the solvatomorphs, which could be roughly correlated with the degree of crystallinity of the materials. Desolvation of the dihydrate phase (known to yield an isomorphic desolvate) led to only minor changes in the excitation and emission spectra, but desolvation of the alchoholate solvatomorphs (known to yield largely amorphous products) caused large decreases in the intensities of the excitation and emission spectra. Since the fluorescence properties of organic solids are critically dependent on the details of the crystal structure and the delocalization of excitation energy, the loss of crystal structure appears to suppress the degree of energy transfer and this in turn affects the fluorescence intensities.