title: Comprehensive photokinetic and NMR study of a biphotochromic supermolecule involving two naphthopyrans linked to a central thiophene unit through acetylenic bonds.
abstract: A photophysical and photochemical study of a biphotochromic compound where two naphthopyran units are linked by an acetylene-thiophene-acetylene bridge has been carried out in toluene. Both fluorescence and intersystem crossing to the triplet manifold were found to compete with the photocoloration process. Two photoproducts (transoid-trans and transoid-cis stereoisomers), absorbing at approximately 480 nm and corresponding to the opening of a single photochromic unit, were detected by spectrophotometric analysis after short irradiation time in diluted solution and identified by 1H-nuclear magnetic resonance (NMR) spectroscopy. After prolonged irradiation at 228 K of highly concentrated solutions (up to 3 x 10(-3) mol dm(-3)), two additional isomers, absorbing at approximately 550 nm, were formed. Their NMR spectra indicate the opening of both photochromic units. An interesting effect of selective vibronic excitation was found, showing that the photoreaction is favored at excited vibronic levels to the detriment of the radiative relaxation.
authors.affiliation: Dipartimento di Chimica, Università di Perugia, Perugia, Italy.
authors.forename: Fausto
authors.initials: F
authors.lastname: Ortica
authors.forename: Corinne
authors.initials: C
authors.lastname: Moustrou
authors.forename: Jérôme
authors.initials: J
authors.lastname: Berthet
authors.forename: Gianna
authors.initials: G
authors.lastname: Favaro
authors.forename: André
authors.initials: A
authors.lastname: Samat
authors.forename: Robert
authors.initials: R
authors.lastname: Guglielmetti
authors.forename: Gaston
authors.initials: G
authors.lastname: Vermeersch
authors.forename: Ugo
authors.initials: U
authors.lastname: Mazzucato
mesh_terms: D000114:Acetylene / Q000737:chemistry; D006576:Heterocyclic Compounds, 4 or More Rings / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010777:Photochemistry / Q000379:methods*; D011714:Pyrans / Q000737:chemistry*; D013057:Spectrum Analysis; D013876:Thiophenes / Q000737:chemistry
chemical_list: D006576:Heterocyclic Compounds, 4 or More Rings; D011714:Pyrans; D013876:Thiophenes; D000114:Acetylene