Homogeneous electron-transfer reactions of several aromatic anion and cation radicals

Kowert, Bruce A.; Marcoux, Lynn; Bard, Allen J.

doi:10.1021/ja00771a003

Cited by 120 publications

(40 citation statements)

References 2 publications

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“…In contrast, the VT-EPR spectra for R 6þ show the trend that, as the temperature is increased, the linewidth increases. This temperature-dependent line broadening can be used to detect dynamic electron transfer processes (14,38,39) and k ET can be calculated in the fast exchange regime, as suggested by the change in line shapes as the temperature is increased (SI Appendix). An Eyring plot (SI Appendix, Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Marcus-Hush theory is now widely applied to the study of electron transfer in a plethora of organic-based mixed-valence systems in order to understand (i) spatial interactions between redox centers (10)(11)(12); (ii) the use of different solvents and counterions (13)(14)(15); and (iii) how the existence of covalent bridges (16,17) affects the kinetics (k ET ) and thermodynamics (ΔG ‡ ) of electron transfer. In this article, we demonstrate how the switching mechanism present in a molecular shuttle-comprised of a bistable [2]rotaxane (R 6þ ) (Fig.…”

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confidence: 99%

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Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Barnes

Fahrenbach

Dyar

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylenebridged bipyridinium (P-BIPY 2þ ) unit and a cyclobis (paraquatp-phenylene) (CBPQT 4þ ) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT 4þ ring encircles the DNP unit. Reduction of the CBPQT 4þ leads to the CBPQT 2ð•þÞ diradical dication while the P-BIPY 2þ unit is reduced to its P-BIPY •þ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT 2ð•þÞ ring along the dumbbell to surround the P-BIPY •þ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY •þ unit, a property which is absent between these redox centers in the free dumbbell and in the 1∶1 complex formed between the CBPQT 2ð•þÞ ring and the radical cation of methyl-phenylene-viologen (MPV •þ ). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (k ET ¼ 1.33 × 10 7 s −1 ) and activation energy (ΔG ‡ ¼ 1.01 kcal mol −1 ) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus-Hush theory.T he simplest organic intervalence compounds consist (1) of two redox centers (X) which are connected by a covalent bridge (b) wherein the two centers possess oxidation states that range from being equal ( nþ0.5 X − b − X nþ0.5 ) to differing by as much as one unit ( n X − b − X nþ1 ). According to the Robin-Day classification (2), there are three main types of organic compounds, which can be defined by the degree of the electronic coupling element, H, that exists between the two interacting redox centers. Compounds that exhibit low electronic coupling between each X redox center have localized charges and exhibit no intramolecular electron transfer (IET) are classified as Class I systems ( n X − b − X nþ1 , H ¼ 0), whereas those that possess a strong electronic coupling between X redox centers and undergo complete delocalization of charge and fast IET are considered Class III systems ( nþ0.5 X − b − X nþ0.5 , H ≫ 0). In between these two classifications lie Class II systems, where the electronic coupling between X redox centers is moderate, leading to a mixture of charge between each unit as well as a measurable IET event.In the 1960s, Marcus (3-6) developed a theory for electron transfer in bridged transition metal-coordinated complexes by identifying the reorganizational energy, λ, required for solvent polarization and subsequent electron transfer between two metal centers. Shortly thereafter, Hush (7-9) proposed a theoretical method that could be applied to Class II intervalence compounds by focusing on the low-energy intervalence charge transfer (IT) bands in optical abso...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Barnes

Fahrenbach

Dyar

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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show abstract

“…Voltammetric studies of 2-, 3-and 4-cyanopyridine in liquid ammonia showed that 2-and 4-cyanopyridine both give a reversible one-electron reduction to a persistent anion radical whereas the reduction of 3-cyanopyridine proceeds irreversibly in an overall one-electron process with the product postulated to be a dimer [6]. The stability of the anion radical of 4-cyanopyridine has been confirmed in studies with DMF or acetonitrile as solvent [7][8][9][10][11]. In a related system, Carelli et al isolated four dimers from the electrochemical reduction of 3-cyano-1-methylpyridinium iodide in aqueous media.…”

Section: Introductionmentioning

confidence: 86%

Reversible dimerization of anion radicals: Studies of two cyanopyridines

Macı́as-Ruvalcaba

Evans

2011

Journal of Electroanalytical Chemistry

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“…7. Kowert has showed that the self-exchange reaction of phenothiazine was associated with intramolecular reorganization energy (k i ) of 0.32 eV [43]. The k i of the series quenchers was adopted as 0.25 eV [44,45].…”

Section: Correlation Between Values Of K Q and Free Energy Change (Dgmentioning

confidence: 99%

Proton transfer in phenothiazine photochemical oxidation: Laser flash photolysis and fluorescence studies

et al. 2007

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Homogeneous electron-transfer reactions of several aromatic anion and cation radicals

Cited by 120 publications

References 2 publications

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

Reversible dimerization of anion radicals: Studies of two cyanopyridines

Proton transfer in phenothiazine photochemical oxidation: Laser flash photolysis and fluorescence studies

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