Degradation of Organic Photochromes: Light-Promoted and Dark Reactions

Degradation processes limit the number of darkening ⇔ bleaching cycles that functional photochromic dyes spirooxazines (SO) and spiropyrans (SP) can sustain. Beside photochemical photooxidation, degradative processes based on dark reactions that include electron-transfer to organic and inorganic acceptor, trapping of free radical species, and reactions with nucleophiles substantially limit the useful lifetime of these dyes. The ability of spiro- and/or merocyanine forms to sensitize formation of Singlet oxygen (1O2) is rather poor and the chemical reactivity of both their closed and open form toward 1O2 sluggish.