Fast blue-switching photochromic lactone-fused naphthopyrans

New colorless lactone-fused naphthopyrans with amino substituents were prepared and their photochromic properties studied in solution and dispersed in an organic polymeric matrix. UV irradiation of these compounds leads to an immediate development of an intense blue color which fades in a few seconds in the dark, unlike the parent unfused naphthopyrans which show a much slower response to the variable UV light intensity. • Synthesis of lactone-fused naphthopyrans substituted with amines • An intense blue color is generated under UV light • The blue coloration fades with t1/2 ∼ 1-5 s • Fully reversible coloration-bleaching cycles • A violet-bluish switching photochromic polymer was produced