Acidichromism and ionochromism of two spirooxazines functionalized by a crown ether unit

The mechanism of the photochromic reaction upon addition of HCl is similar for both compounds: the acid species causes the formation of the protonated merocyanin, and a visible absorbance band appears thermally. The two species show a negative photochromism: under visible light irradiation the photobleaching is observed, by returning to the initial structural configuration of spirooxazines. The spectrokinetic experiments pointed out the presence of a dynamic equilibrium between the thermal colouration and the photobleaching reactions. Spectrokinetic parameters such as quantitative absorption spectra and rate constants of the processes have been measured. The interaction between the two spirooxazines and bi- and trivalent ions has been evaluated and compared, observing changes in the absorption spectra. The ions taken into account are cadmium (Cd2+), and iron (Fe+2 and Fe+3). The results show different optical properties for the two spirooxazines as a function of the nature of the ion. Moreover, under UV irradiation, in all cases the formation of a stable compound that absorbs in the visible range is observed.