title: Transient UV pump-IR probe investigation of heterocyclic ring-opening dynamics in the solution phase: the role played by nσ* states in the photoinduced reactions of thiophenone and furanone.
abstract: The heterocyclic ring-opening dynamics of thiophenone and furanone dissolved in CH3CN have been probed by ultrafast transient infrared spectroscopy. Following irradiation at 267 nm (thiophenone) or 225 nm (furanone), prompt (τ < 1 ps) ring-opening is confirmed by the appearance of a characteristic antisymmetric ketene stretching feature around 2150 cm(-1). The ring-opened product molecules are formed highly vibrationally excited, and cool subsequently on a ∼6.7 ps timescale. By monitoring the recovery of the parent (S0) bleach, it is found that ∼60% of the initially photoexcited thiophenone molecules reform the parent molecule, in stark contrast with the case in furanone where there is less than 10% parent bleach recovery. Complementary ab initio calculations of potential energy cuts along the S-C([double bond, length as m-dash]O) and O-C([double bond, length as m-dash]O) ring-opening coordinate reveals insights into the reaction mechanism, and the important role played by dissociative (n/π)σ* states in the UV-induced photochemistry of such heterocyclic systems.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, UKBS8 1TS. daniel.murdock@bristol.ac.uk mike.ashfold@bristol.ac.uk.
authors.forename: Daniel
authors.initials: D
authors.lastname: Murdock
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Harris
authors.forename: Joel
authors.initials: J
authors.lastname: Luke
authors.forename: Michael P
authors.initials: MP
authors.lastname: Grubb
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Orr-Ewing
authors.forename: Michael N R
authors.initials: MN
authors.lastname: Ashfold