title: Comparing a photoinduced pericyclic ring opening and closure: differences in the excited state pathways.
abstract: The photochromicity of fulgimides rests on the existence of open (E) and closed ring (C) isomers. As predicted by the Woodward-Hoffmann rules both isomers can photochemically be interconverted. This interconversion has been studied by femtosecond fluorescence and transient absorption spectroscopy. For either direction (E --> C cyclization and C --> E cycloreversion) a biphasic fluorescence decay on the 0.1-1 ps time scale is observed. The longer time constants of the decays equal the formation times of the photoproducts. The time constants retrieved (0.06 and 0.4 ps for E --> C, 0.09 and 2.4 ps for C --> E) and the associated spectral signatures differ substantially. This indicates that no common excited-state pathway for the two directions exists, as one would infer from a simple Woodward-Hoffmann consideration. These findings support recent quantum dynamic calculations on the excited-state topology of fulgimides.
authors.affiliation: Department für Physik - Munich Center for Integrated Protein Science, Ludwig-Maximilians-Universität, Oettingenstrasse 67, D-80538 München, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Heinz
authors.forename: Stephan
authors.initials: S
authors.lastname: Malkmus
authors.forename: Stefan
authors.initials: S
authors.lastname: Laimgruber
authors.forename: Steffen
authors.initials: S
authors.lastname: Dietrich
authors.forename: Christine
authors.initials: C
authors.lastname: Schulz
authors.forename: Karola
authors.initials: K
authors.lastname: Rück-Braun
authors.forename: Markus
authors.initials: M
authors.lastname: Braun
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Zinth
authors.forename: Peter
authors.initials: P
authors.lastname: Gilch