Thermal and photostability of 5′,7′-dialkoxy-5,6′-dinitro-1,3,3-trimethylspiro(lndolin-2,2′-[2H]chromenes)

Some photochromic indoline spiropyrans have been synthesized and their thermal and photostability examined in films and in solution. Introduction of the NO2 group into the indoline moiety of the molecule stabilizes the spiropyran form in solution and in films, but blocking the NO2 group in the pyran moiety by adjacent alkoxy groups enhances the light stability of the compounds.