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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.