Exploring fast fading photochromic lactone-fused naphthopyrans

Abstract A series of lactone-fused naphthopyrans substituted by electron-donating groups were prepared. While the linkage of these groups to the naphthalene part of the photoactive molecule had little effect on the colour observed after UV exposure, the introduction of methoxyphenyl groups at the aromatic sp3 substituents gave uncoloured naphthopyrans that develop intense orange/red colourations under UV/sunlight and return to the uncoloured state, in the dark, in less than 3 min either in solution or in a polymeric film.