title: The Paternò-Büchi reaction: importance of triplet states in the excited-state reaction pathway.
abstract: The Paternò-Büchi (PB) reaction between an excited carbonyl compound and an alkene has been widely studied, but so far little is known about the excited-state dynamics of the reaction. In this investigation, we used a compound in which a formyl and a vinyl group are attached to a [2.2]paracyclophane in order to obtain a model system in pre-reactive conformation for the PB reaction. We studied the excited-state dynamics of the isolated molecule in a molecular beam using femtosecond time-resolved photoelectron spectroscopy and ab initio calculations. The results show that inter-system crossing within two picoseconds competes efficiently with the reaction in the singlet manifold. Thus, the PB reaction in this model system takes place in the triplet state on a time scale of nanoseconds. This result stresses the importance of triplet states in the excited-state pathway of the PB reaction involving aromatic carbonyl compounds, even in situations in which the reacting moieties are in immediate vicinity.
authors.affiliation: Department of Chemistry, University of Copenhagen, Copenhagen, Denmark. theis@kiku.dk.
authors.forename: Rasmus Y
authors.initials: RY
authors.lastname: Brogaard
authors.forename: Oliver
authors.initials: O
authors.lastname: Schalk
authors.forename: Andrey E
authors.initials: AE
authors.lastname: Boguslavskiy
authors.forename: Gary D
authors.initials: GD
authors.lastname: Enright
authors.forename: Henning
authors.initials: H
authors.lastname: Hopf
authors.forename: Vitaly
authors.initials: V
authors.lastname: Raev
authors.forename: Eliza
authors.initials: E
authors.lastname: Tarcoveanu
authors.forename: Theis I
authors.initials: TI
authors.lastname: Sølling
authors.forename: Albert
authors.initials: A
authors.lastname: Stolow