title: Transient absorption studies of the photochromic behavior of 3H-naphtho[2,1-b]pyrans linked to thiophene oligomers via an acetylenic junction.
abstract: The photophysical and photochemical properties of four 3,3-diphenyl-3H-naphtho[2,1- b]pyrans substituted, via an acetylenic junction, to (thiophene) n oligomers (n = 0-3 units) were investigated by transient absorption in the femtosecond to microsecond time domain and by stationary absorption and fluorescence. The decay of the initially produced excited S1(pi pi*) state is found to occur via three competing processes: fluorescence, intersystem crossing, and a ring-opening reaction leading to a colored merocyanine product, with relative yields varying drastically with n. Whereas ultrafast (sub-picosecond) reaction dynamics and high product quantum yield are observed for n = 0 and 1, the reaction is considerably slowed down on going to the n = 2 (105 ps) compound and does not occur for n = 3. A reaction scheme that accounts for this behavior is proposed and the effect of the oligothiophenic chain length on the photoinduced properties is discussed. It is suggested that increasing the chain length from 1 to 3 thiophene units stabilizes the S1(pi pi*) state by pi conjugation and induces an excited-state potential barrier along the reaction pathway.
authors.affiliation: Laboratoire de Spectrochimie Infrarouge et Raman (UMR 8516 du CNRS), Centre d'Etudes et de Recherches Lasers et Applications (FR 2416 du CNRS), Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France. Baptiste.moine@univ-st-etienne.fr
authors.forename: Baptiste
authors.initials: B
authors.lastname: Moine
authors.forename: Julien
authors.initials: J
authors.lastname: Réhault
authors.forename: Stéphane
authors.initials: S
authors.lastname: Aloïse
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Micheau
authors.forename: Corinne
authors.initials: C
authors.lastname: Moustrou
authors.forename: André
authors.initials: A
authors.lastname: Samat
authors.forename: Olivier
authors.initials: O
authors.lastname: Poizat
authors.forename: Guy
authors.initials: G
authors.lastname: Buntinx