Joining High Coloration and Fast Color Fading with Photochromic Fused‐Naphthopyrans
Céu M. Sousa, Paulo J. Coelho
Abstract
An easy synthesis of photochromic naphthopyrans with a lactone ring linking the naphthalene core to the pyran double bond is described. UV irradiation (or exposure to sunlight) of these uncolored compounds provide a single photoisomer with an intense orange coloration that returns completely to the initial uncolored state much faster than common naphthopyrans used in commercial photochromic ophthalmic lenses. A polymeric uncolored material doped with one of these lactone‐fused naphthopyrans develops an intense orange coloration (ΔAbs = 0.73) when exposed to the UV light for 30 s, at room temperature, and returns to the uncolored state in just 1 min. The use of these photochromic compounds allows a faster adaptation of the material's coloration to the surrounding UV‐light intensity, without compromising the color intensity, an important feature to create high performance photochromic ophthalmic lenses.