Hydrogen bonding association in the electroreduced intermediates of benzoquinones and naphthoquinones

Ahmed, Safeer; Khan, Athar Yaseen; Qureshi, Rumana; Subhani, M. S.

doi:10.1134/s1023193507070117

Cited by 14 publications

(11 citation statements)

References 35 publications

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“…Gupta and Linschitz demonstrated that hydrogen-bonding to benzoquinone monoanions can be evaluated quantitatively from cyclic voltammetry data. Specifically, it is possible to determine the equilibrium constant ( K eq (AQ – ) ) associated with the chemical reaction of eq from the experimentally observed shifts in AQ reduction potentials (Δ E red ) using the following expression: , ΔE red = n · ( R · T / F ) · ln ( false[ HFIP false] ) + ( R · T / F ) · ln ( K eq ( AQ − ) ) In eq , R is the gas constant, T is the temperature, and F is the Faraday constant. Δ E red is the difference between the electrochemical potentials for AQ reduction at a given HFIP concentration above 0.0 mM and the potential at [HFIP] = 0 mM.…”

Section: Resultsmentioning

confidence: 99%

Section: +mentioning

confidence: 99%

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Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium–Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water

2012

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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)(3)(2+) (bpy = 2,2'-bipyridine) and 9,10-anthraquinone redox partners linked together via one up to three p-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)(3)(2+)-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.

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Section: Resultsmentioning

confidence: 99%

Section: +mentioning

confidence: 99%

Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium–Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water

2012

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“…Prior electrochemical investigations demonstrated that addition of HFIP to CH 2 Cl 2 solutions of various benzoquinones leads to substantial shifts in the reduction potentials of these compounds 9. 12, 13 CV studies of TAA–Os II –AQ in CH 2 Cl 2 show that the wave associated with reduction of the AQ unit shifts positively when the HFIP concentration is increased, whereas all other redox couples remain virtually unaffected (Figure S8 in the Supporting Information). The highest HFIP concentration for which voltammograms of reasonable quality can still be measured is 4 m M (Figure S8 in the Supporting Information),8 and at this point the shift of E (AQ − /AQ) amounts to 150 mV relative to the value in pure CH 2 Cl 2 .…”

Section: Methodsmentioning

confidence: 99%

Large Increase of the Lifetime of a Charge‐Separated State in a Molecular Triad Induced by Hydrogen‐Bonding Solvent

Hankache

Wenger

2012

Chemistry A European J

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“…Gupta and Linschitz demonstrated that based on cyclic voltammetry hydrogen-bonding equilibria such as those from eqs 1a/1b can be evaluated quantitatively in the sense that equilibrium constants (K eq ) can be determined. 30,65 Specifically, based on eq 1b K eq can be obtained from plots of ΔE red versus log([HFIP]), where ΔE red is the difference between the anthraquinone reduction potential at a given HFIP concentration ([HFIP]) and the respective potential in pure CH 2 Cl 2 . 30,65…”

Section: Table 1 Reduction Potentials (In Volts Vsmentioning

confidence: 99%

Hydrogen-Bonding Effects on the Formation and Lifetimes of Charge-Separated States in Molecular Triads

et al. 2012

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Photoinduced electron transfer in two molecular triads comprised of a triarylamine donor, a d(6) metal diimine photosensitizer, and a 9,10-anthraquinone acceptor was investigated with particular focus on the influence of hydrogen-bonding solvents on the electron transfer kinetics. Photoexcitation of the ruthenium(II) and osmium(II) sensitizers of these triads leads to charge-separated states containing an oxidized triarylamine unit and a reduced anthraquinone moiety. The kinetics for formation of these charge-separated states were explored by using femtosecond transient absorption spectroscopy. Strong hydrogen bond donors such as hexafluoroisopropanol or trifluoroethanol cause a thermodynamic and kinetic stabilization of these charge-separated states that is attributed to hydrogen bonding between alcoholic solvent and reduced anthraquinone. In the ruthenium triad this effect leads to a lengthening of the lifetime of the charge-separated state from ~750 ns in dichloromethane to ~3000 ns in hexafluoroisopropanol while in the osmium triad the respective lifetime increases from ~50 to ~2000 ns between the same two solvents. In both triads the lifetime of the charge-separated state correlates with the hydrogen bond donor strength of the solvent but not with the solvent dielectric constant. These findings are relevant in the greater context of solar energy conversion in which one is interested in storing light energy in charge-separated states that are as long-lived as possible. Furthermore they are relevant for understanding proton-coupled electron transfer (PCET) reactivity of electronically excited states at a fundamental level because changes in hydrogen-bonding strength accompanying changes in redox states may be regarded as an attenuated form of PCET.

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Hydrogen bonding association in the electroreduced intermediates of benzoquinones and naphthoquinones

Cited by 14 publications

References 35 publications

Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium–Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water

Hydrogen-Bond Strengthening upon Photoinduced Electron Transfer in Ruthenium–Anthraquinone Dyads Interacting with Hexafluoroisopropanol or Water

Large Increase of the Lifetime of a Charge‐Separated State in a Molecular Triad Induced by Hydrogen‐Bonding Solvent

Hydrogen-Bonding Effects on the Formation and Lifetimes of Charge-Separated States in Molecular Triads

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