title: Quinones as Reversible Electron Relays in Artificial Photosynthesis.
abstract: We explore the potential of various hydroquinone/quinone redox couples as electron relays in a homogenous water reduction system between a Re-based photosensitizer and a sacrificial electron donor [tris-(2-carboxyethyl)-phosphine, TCEP]. By using transient IR spectroscopy, flash photolysis as well as stopped-flow techniques covering timescales from picoseconds to 100 ms, we determine quenching rates and cage escape yields, the kinetics of the follow-up chemistry of the semiquinone, the recombination rates, as well as the re-reduction rates by TCEP. The overall quantum yield of hydrogen production is low, and we show that the limiting factors are the small cage escape yields and, more importantly, the slow regeneration rate by TCEP in comparison to the undesired charge recombination with the reduced water reduction catalyst.
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Rodenberg
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Margherita
authors.initials: M
authors.lastname: Orazietti
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Mathias
authors.initials: M
authors.lastname: Mosberger
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Cyril
authors.initials: C
authors.lastname: Bachmann
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Probst
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland.
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
authors.affiliation: Department of Chemistry, University of Zurich, Winterthurerstr. 190, Zurich, 8057, Switzerland. peter.hamm@chem.uzh.ch.
authors.forename: Peter
authors.initials: P
authors.lastname: Hamm
mesh_terms: D004583:Electrons; D010788:Photosynthesis; D011809:Quinones / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011809:Quinones
keywords: artificial photosynthesis; kinetics; quinones; spectroscopy; water splitting