title: Photochromic fused-naphthopyrans without residual color.
abstract: A series of new photochromic fused-naphthopyrans with an alkyl bridge between the pyran ring and the naphthalenic core was synthesized in several steps from 4-(bromomethyl)benzocoumarin. The presence of the alkyl bridge in these new fused-naphthopyrans prevents the formation of one long-lived photoisomer and therefore has a dramatic effect on their photochromic properties: UV irradiation of common naphthopyrans gives rise to two isomeric colored photoisomers, one of which fades very slowly and is responsible for a persistent residual color. UV excitation of these new uncolored fused-naphthopyrans leads to the formation of only one colored photoisomer that fades completely to the uncolored state in few seconds/minutes following a monoexponential decay law, thus avoiding the problem of the residual coloration typically observed with naphthopyrans.
authors.affiliation: Centro de Química-Vila Real, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal.
authors.forename: Céu M
authors.initials: CM
authors.lastname: Sousa
authors.forename: Jerome
authors.initials: J
authors.lastname: Berthet
authors.forename: Stephanie
authors.initials: S
authors.lastname: Delbaere
authors.forename: Paulo J
authors.initials: PJ
authors.lastname: Coelho
mesh_terms: D003116:Color; D006572:Heterocyclic Compounds, Bridged-Ring / Q000737:chemistry*; D007536:Isomerism; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*; D055668:Photochemical Processes; D011714:Pyrans / Q000737:chemistry*
chemical_list: D006572:Heterocyclic Compounds, Bridged-Ring; D009281:Naphthalenes; D011714:Pyrans