title: Mechanistic aspects of ketene formation deduced from femtosecond photolysis of diazocyclohexadienone, o-phenylene thioxocarbonate, and 2-chlorophenol.
abstract: The photochemistry of diazocyclohexadienone (1), o-phenylene thioxocarbonate (2), and 2-chlorophenol (3) in solution was studied using time-resolved UV-vis and IR transient absorption spectroscopies. In these three cases, the same product cyclopentadienyl ketene (5) is formed, and two different mechanistic pathways leading to this product are discussed: (a) rearrangement in the excited state (RIES) and (b) a stepwise route involving the intermediacy of vibrationally excited or relaxed carbene. Femtosecond UV-vis detection allows observation of an absorption band assigned to singlet 2-oxocyclohexa-3,5-dienylidene (4), and this absorption feature decays with an ∼30 ps time constant in hexane and acetonitrile. The excess vibrational energy present in nascent carbenes results in the ultrafast Wolff rearrangement of the hot species. IR detection shows that photoexcited o-phenylene thioxocarbonate (2) and 2-chlorophenol (3) efficiently form the carbene species while diazocyclohexadienone (1) photochemistry proceeds mainly by a concerted process.
authors.affiliation: Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University in Poznan, Umultowska 85, 61-614 Poznan, Poland. gotardb@amu.edu.pl
authors.forename: Gotard
authors.initials: G
authors.lastname: Burdzinski
authors.forename: Jacek
authors.initials: J
authors.lastname: Kubicki
authors.forename: Michel
authors.initials: M
authors.lastname: Sliwa
authors.forename: Julien
authors.initials: J
authors.lastname: Réhault
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Shubham
authors.initials: S
authors.lastname: Vyas
authors.forename: Hoi Ling
authors.initials: HL
authors.lastname: Luk
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Hadad
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Platz