title: Unexpected halogen substituent effects on the complex thermal relaxation of naphthopyrans after UV irradiation.
abstract: The kinetics of the thermal fading of four halogenated naphthopyrans (NP) have been analyzed using NMR spectroscopy in CD(3)CN. Two photomerocyanines (TT and TC) were detected after UV irradiation. The main relaxation process TC --> NP was coupled with TT/TC isomerization. The activation parameters of the various processes were rationalized by considering electronegativity and polarizability of the halogen substituents and their selective solvation by the electronegative nitrogen of acetonitrile.
authors.affiliation: CNRS UMR 8009, Laboratoire de Physique, Faculté de Pharmacie, Université de Lille 2, Lille, France. sdelbaer@pharma.univ-lille2.fr
authors.forename: Stephanie
authors.initials: S
authors.lastname: Delbaere
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Micheau
authors.forename: Michel
authors.initials: M
authors.lastname: Frigoli
authors.forename: Gaston
authors.initials: G
authors.lastname: Vermeersch