Spectroscopic and photophysical studies of the anticancer drug: Camptothecin

Electronic absorption and fluorescence spectra as well as the photophysical properties of 20-(S)-camptothecin were studied in a series of organic solvents and in aqueous solution. The fluorescence quantum yield and lifetime were measured. In contrast to previously reported results, this study has demonstrated that there is a marked increase of fluorescence quantum yield and fluorescence lifetime with an increase in solvent polarity and hydrogen-bonding capacity. The solvent dependence of the fluorescence quantum yield and lifetime are explained. The solvent effects indicate that the S-1 state of CAM is (1) pi,pi*-type with some contribution from a close-lying higher energy (1)n,pi* state. The fluorescence lifetime of the drug was measured in sucrose solutions of varying viscosity and it was observed that the lifetime decreased with an increase in viscosity. The fluorescence quenching of both camptothecin lactone and camptothecin carboxylate in interactions with I- ion in aqueous medium is reported. The fluorescence intensity of both forms are mainly quenched by the dynamic process. The quenching constant of the lactone form is twice as high as that of the carboxylate form.