Chromogenic systems based on 8-(1,3-benzoxazol-2-yl) substituted spirobenzopyrans undergoing ion modulated photochromic rearrangements

Abstract 8-(1,3-Benzoxazol-2-yl) substituted spirobenzopyrans 1A appear as a chromogenic system susceptible of switching between positive and negative photochromism under complexation with metal ions. The thermal and photochemical reactions accompanying metal ion-induced transformation of spiropyrans 1A to the complexes formed by their photoinduced merocyanine isomers 1B were investigated. In the dark, the colorless spiropyrans interact with Mn 2+ , Cd 2+ and Zn 2+ transition metal ions to yield deeply colored 1:1 complexes possessing fluorescence, while Co 2+ , Ni 2+ , Cu 2+ ions prefer to form non-fluorescent complexes with two merocyanines. Under irradiation with visible light solutions of the merocyanine-metal complexes undergo photobleaching. This effect was quantified using photokinetic method.