PHOTOCHEMICAL STABILITY OF BIOLOGICALLY ACTIVE COMPOUNDS. IX. CHARACTERIZATION OF THE SPECTROSCOPIC PROPERTIES OF THE 4-AMINOQUINOLINES, CHLOROQUINE AND HYDROXYCHLOROQUINE, AND OF SELECTED METABOLITES BY ABSORPTION, FLUORESCENCE AND PHOSPHORESCENCE MEASUREMENTS

Abstract The spectroscopic properties of the antimalarials chloroquine, hydroxychloroquineand selected metabolites were investigated by absorption, fluorescence and phosphorescence measurements. The antimalarials exhibit both fluorescence and phosphorescence. Fluorescence dominates for the deprotonated forms of the 4-aminoquinolines, while phosphorescence dominates when the compounds are protonated. The phosphorescence lifetimes of the 4-aminoquinolines were measured. Both the protonated and the deprotonated forms have long phosphorescence lifetimes indicating a long-lived triplet state.