Evidence for a photophysical deactivation pathway competing with the photochromic transformation in a cyano-substituted spironaphthoxazine

The photochromic reaction dynamics of 6′-cyano-spiroindolinenaphthoxazine (6′CN-SNO) in solution is followed by femtosecond transient absorption spectroscopy. In addition to the formation of the merocyanine coloured form, we demonstrate the presence of a new metastable species with intense absorption bands in the 400–600 and 650–975 nm spectral regions that was not observed for the non-substituted parent molecule. The formation of this species parallels the photochromic reaction. The existence of this concurrent photophysical process can explain the 50% reduction in the photocoloration quantum yield of this molecule relative to that of the parent molecule.