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

• Published in: Journal of organic chemistry 2017-12, Vol.82 (23), p.12028-12037
• Main Authors: Sousa, Céu M, Berthet, Jerome, Delbaere, Stephanie, Polónia, André, Coelho, Paulo J
• Format: Article
• Language: English
• Subjects: Chemical Sciences; or physical chemistry; Theoretical and
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.7b01669

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.