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