Studies on the solution-phase ESR spectra of the C60 monoanion under varying experimental conditions

Abstract

ESR spectroscopic studies on C60−· electrochemically generated from C60 in toluene–acetonitrile solutions (with Bu4NPF6 as the supporting electrolyte) were performed under varying time (0–35 days), temperature (293–133 K), concentration (0.2–1.0 mM), oxygen content, purity and photolytic conditions. It was found that the ESR signals frequently referred to as sharp (ΔHpp ≈ 0.1 mT), that are present in low abundance (∼1–2%) in most samples of C60−· (ΔHpp ≈ 3–6 mT), can exist in several different forms with distinct linewidths and g‐values depending on the temperature, the oxygen content of solution and the time following the generation of C60−·. Only one sharp signal (in addition to the broad signal) was evident immediately after the electrochemical generation of C60−·, but with increasing time (hours–days), in the presence of light and/or in the presence of atmospheric air, other sharp signals appeared, some of which were attributable to the formation of precipitate radicals. Data obtained from a number of experiments suggest that the sharp linewidth signals behave independently of the broad linewidth signal, which reduces the likelihood that the species responsible for the two types of signals (broad and sharp) are in equilibrium, or that the paramagnetic species responsible for the broad signal converts into the species responsible for the sharp signals. Instead, the data are consistent with the sharp linewidth signals originating from an impurity in the original C60 that is converted to a radical species upon reduction of C60, which subsequently undergoes further chemical reactions to form other paramagnetic species. Copyright © 2000 John Wiley & Sons, Ltd.

In Situ ESR/Vis/NIR Spectroelectrochemistry of [60]Fullerene: The Origin of ESR “Spikes” and the Reactivity of Pristine Fullerene Anions

“…À . In experiments with low-purity solvents, exposure to the atmosphere, and long timescales, [20,21] complex chemical reactions of fullerene anions led to a variety of ESR lines.Herein we report on quantitative in situ spectroelectrochemistry of C 60 reduction using different high-purity electrolyte systems and highly purified C 60 to determine the source of the ESR spikes. The main focus is on chemical reactions of [fullerene] nÀ species in solution.…”

“…À . In experiments with low-purity solvents, exposure to the atmosphere, and long timescales, [20,21] complex chemical reactions of fullerene anions led to a variety of ESR lines.…”

“…As the broad and sharp ESR lines are correlated, a decrease of the broad ESR line is linked to an increase of the sharp ESR line. The results with high-purity C 60 and electrolytes exclude the explanation previously reported, [21] that sharp ESR line signals originate from an impurity in C 60 or from low-purity electrolytes.…”

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“…225 The first electron affinities of two [36]fulleride anion isomers are predicted to be 2.3 and 2.4 eV. 226 The origin of the narrow line-width signal routinely observed in the EPR spectra of [60]fullerene 227 has been confirmed to be due to the fullerene dimer oxide C 120 O. 228 The electrochemically generated trianion of [60]fullerene reacts with dichloromethane producing polymethano [60]fullerene derivatives.…”

In situ electrochemical-ATR-FTIR spectroscopic studies on solution phase carboxylate radical anionsElectronic supplementary information (ESI) available: first derivative EPR spectra of radical anions. See http://www.rsc.org/suppdata/p2/b2/b206087f/

“…See http://www.rsc.org/suppdata/p2/b2/ b206087f/ on diffusion control where the IR spectra may represent mixtures of the starting material and product(s), and which can be difficult to interpret if the individual species have overlapping vibrational bands. For this study, a conventional 13 twocompartment bulk electrolysis cell was used to exhaustively generate solutions of reactive radical anions for analysis by FTIR spectroscopy using a commercial 14 ATR diamond composite sensor.…”