Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium–Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water Jihane Hankache David Hanss Oliver S. Wenger 10.1021/jp300090n.s001 https://acs.figshare.com/articles/journal_contribution/Hydrogen_Bond_Strengthening_upon_Photoinduced_Electron_Transfer_in_Ruthenium_Anthraquinone_Dyads_Interacting_with_Hexafluoroisopropanol_or_Water/2534587 Quinones play a key role as primary electron acceptors in natural photosynthesis, and their reduction is known to be facilitated by hydrogen-bond donors or protonation. In this study, the influence of hydrogen-bond donating solvents on the thermodynamics and kinetics of intramolecular electron transfer between Ru­(bpy)<sub>3</sub><sup>2+</sup> (bpy = 2,2′-bipyridine) and 9,10-anthraquinone redox partners linked together via one up to three <i>p</i>-xylene units was investigated. Addition of relatively small amounts of hexafluoroisopropanol to dichloromethane solutions of these rigid rodlike donor–bridge–acceptor molecules is found to accelerate intramolecular Ru­(bpy)<sub>3</sub><sup>2+</sup>-to-anthraquinone electron transfer substantially because anthraquinone reduction occurs more easily in the presence of the strong hydrogen-bond donor. Similarly, the rates for intramolecular electron transfer are significantly higher in acetonitrile/water mixtures than in dry acetonitrile. In dichloromethane, an increase in the association constant between hexafluoroisopropanol and anthraquinone by more than 1 order of magnitude following quinone reduction points to a significant strengthening of the hydrogen bonds between the hydroxyl group of hexafluoroisopropanol and the anthraquinone carbonyl functions. The photoinduced intramolecular long-range electron transfer process thus appears to be followed by proton motion; hence the overall photoinduced reaction may be considered a variant of stepwise proton-coupled electron transfer (PCET) in which substantial proton density (rather than a full proton) is transferred after the electron transfer has occurred. 2012-04-05 00:00:00 anthraquinone reduction proton motion PCET electron transfer Photoinduced Electron Transfer anthraquinone carbonyl functions electron acceptors hydroxyl group hexafluoroisopropanol electron transfer process dichloromethane solutions quinone reduction points donor hydrogen bonds photoinduced intramolecular intramolecular electron transfer photoinduced reaction proton density 1 order