title: Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.
abstract: Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ΔG°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -ΔG° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-ΔG°) can restore fast rates of electron transfer.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
authors.forename: Matibur
authors.initials: M
authors.lastname: Zamadar
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Cook
authors.forename: Anna
authors.initials: A
authors.lastname: Lewandowska-Andralojc
authors.forename: Richard
authors.initials: R
authors.lastname: Holroyd
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Jin
authors.initials: J
authors.lastname: Bikalis
authors.forename: John R
authors.initials: JR
authors.lastname: Miller
mesh_terms: D000838:Anions / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D005609:Free Radicals; D007700:Kinetics; D015394:Molecular Structure
chemical_list: D000838:Anions; D016227:Benzoquinones; D005609:Free Radicals; C004532:quinone