The chemistry and photochemistry of 3′,4′-(methylenedioxy) flavylium was studied by means of UV-Vis spectrophotometry, 1H NMR, stopped flow, and continuous irradiation, in acidic and basic aqueous solutions. Six species were identified: the flavylium cation, AH+; the hemiketal, B; the cis- and the trans-chalcones, Cc and Ct, and their ionized forms. Cc- and Ct-. These species define a multiequilibria network whose kinetics and thermodynamics were completely characterized. The two pairs of chalcones define two coupled photochromic systems, respectively in acidic and basic media, both allowing cycles capable of writing, reading and erasing to be defined.