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Control of the Switching Speed of Photochromic Naphthopyrans through Restriction of Double Bond Isomerization

Sousa, Céu M., Berthet, Jerome, Delbaere, Stephanie, Polónia, André, Coelho, Paulo J.
Journal of organic chemistry 2017 v.82 no.23 pp. 12028-12037
ambient temperature, chemical bonding, color, irradiation, isomerization, isomers, nuclear magnetic resonance spectroscopy, organic chemistry, organic compounds, photochemistry, solar radiation, ultraviolet radiation
An efficient synthesis of photochromic fused-naphthopyrans was developed. UV–vis or sunlight irradiation of these uncolored compounds in solution led to the formation of a single colored photoisomer along with an unusual and uncolored bicyclic compound formed through an intramolecular photochemical Diels–Alder reaction. Both species faded thermally in the dark to the initial form. A mechanism for this transformation is proposed based on NMR studies of irradiated solutions. The new fused-naphthopyrans have been incorporated into hybrid organic–inorganic matrices affording light-yellow materials that develop intense red colorations under UV light and return to the initial uncolored state in just a few seconds, in the dark, at room temperature. These results are useful for the development of fast switching materials used in the production of photochromic lenses.