EXCITED-STATES OF ANTHOCYANINS - THE CHALCONE ISOMERS OF MALVIDIN 3,5-DIGLUCOSIDE

The excited state properties of the chalcone isomers of malvidin 3,5-diglucoside (malvin) in acidic aqueous solution (0 < pH < 4) were investigated using steady-state and time-resolved fluorescence spectroscopy. The two chalcone isomers of malvin were first isolated by high-performance liquid chromatography and then characterized by UV/visible absorption and fluorescence spectroscopy. The results were supported by molecular orbital calculations. The rate constants for photodeprotonation (k(1) = 1 x 10(9) s(-1)) and protonation (k(-1) = 1.3 x 10(10) L mol(-1) s(-1)) were determined, both from the multiexponential fluorescence decays and the fluorescence intensities measured at the emission wavelengths of the neutral and ionized chalcone forms. The results here obtained are relevant for the understanding of the photoreactivity of anthocyanins in acidic medium.