Synthesis and characterization of indeno-fused naphthopyrans containing methacryloyl and urethane groups for photochromic contact lenses applications

This study reports the synthesis and photochromic properties of four indeno-naphthopyrans. These compounds contain oxo, hydroxyl, methacryloyl, and urethane groups on the C13 position of indeno-fused naphthopyrans. They are light pink or colorless in solvents, and turn purple after UV irradiation. They reached the maximum optical density efficiently in 60 s in tetrahydrofuran. They also demonstrated high optical density and rapidly faded to half optical density (t_1/2) in 32–152 s. Compounds (8) (3,3-diphenyl-13-methacrylate-indeno[2,1-f]naphtho[1,2-b]pyran) and compound (9) (3,3-diphenyl-13-(2-(methacryloyloxy)ethylcarbamate)-indeno[2,1-f]naphtho[1,2-b]pyran) containing methacryloyl and urethane groups, respectively, exhibited excellent fatigue resistance after cycles of UV. Compounds (8) and (9) containing vinylic groups can polymerize with other vinyl monomers to prepare photochromic contact lenses by photo-initiated polymerization. These lenses are colorless and turn deep purple after UV irradiation. The contact lenses faded to their half optical density in 138–238 s. Although they do not fully return to their original colorless state within 3600 s after UV irradiation is turned off, the residual color is very light. They faded to 30 % of their maximum optical density in 321 to 1791 s. Additional strategies need to be explored to achieve the practical application of the photochromic contact lenses based on compounds (8) and (9).