ESR and ENDOR investigations of the degenerate electron exchange reactions of various viologens in solution. Solvent dynamical effects

Abstract

The temperature dependences of the rates of the degenerate electron transfer of various viologens (l,l'-di(hydrocarbyl)-4,4'-bipyridinium salts) are measured in seven different solvents by means of electron spin resonance (ESR) line broadening. Rates vary between 1.7.10 s and 1.1 -l0 9 M-~s -~ at room temperature and clearly show a solvent dynamical effect, which is inferred from the dependence of the rate constants on the longitudinal relaxation time of the solvent. Activation energies ranging from 5.3 to 24.4 kJ mol -l are found. For the first time, hyperfine coupling constants are reported for the radical cations of the hydroxyethyl viologen and the amino viologen based on both continuous-wave ESR and electron-nuclear double resonance spectroscopy. Furthermore, the temperature and the solvent dependence of the hyperfine coupling constants of the methyl viologen radical cation are reported.

Spectroelectrochemistry of alternating ambipolar copolymers of 4,4′- and 2,2′-bipyridine isomers and quaterthiophene

“…Their EPR signals are strong ( Fig. 10c and d) featuring complex hyperfine structure, similar to spectra of different viologen radical cation derivatives [82][83][84][85]. Analysis of these counterion-specific hyperfine patterns allowed to elaborate on unpaired spin distribution in radical cations of 1a(PF 6 ) and 1a(OTf).…”

Spatially Constrained Organic Diquat Anolyte for Stable Aqueous Flow Batteries

“…(a) Experimental and simulated first-derivative continuous-wave EPR spectra of electrochemically generated 1 mM 5 +• in 1 M NaCl solution (X-band, 0.1 G modulation at 100 kHz). Due to rapid degenerate electron exchange, , some resonance lines in the wings are selectively broadened and shifted, which was not taken into account in our EPR simulation. Dynamic averaging of the methylene hfcc’s was assumed.…”

Spin-dependent charge transfer at chiral electrodes probed by magnetic resonance

“…43 Grampp et al attributed the broad featureless resonance of MV + to the fast rate of electron exchange due to the comproportionation reaction. 44 In our case, the broadening is due to the field inhomogeneity with respect to the size of the sample and modulation broadening. 45 We recall that these EPR spectra are not acquired in the normal way.…”