Fullerene cyclic voltammetry

One aspect that reflects the electronic configuration of fullerenes relates to the electrochemically induced reduction and oxidation processes in solution. In good agreement with the tlireefold degenerate LUMO, the redox chemistry of [60]fullerene, investigated primarily with cyclic voltammetry and Osteryoung square wave voltammetry, unravels six reversible, one-electron reduction steps with potentials that are equally separated from each other. The separation between any two successive reduction steps is -450 50 mV. The low reduction potential (only -0.44 V versus SCE) of the process, that corresponds to the generation of the rt-radical anion 131,109,110,111 and 1121, deserves special attention. 

Allemand P-M, Koch A, WudI F, Rubin Y, Diederich F, Alvarez M M, Anz S J and Whetten R L 1991 Two different fullerenes have the same cyclic voltammetry J. Am. Chem. Soc. 113 1051-2... 

Electroactive 3-(N-phenylpyrazolyl)fullereno[l,2-r/]isoxazolines have been synthesized by using 1,3-dipolar cycloaddition of pyrazole nitrile oxides, generated in situ, to Cgo at elevated temperature or microwave irradiation. The cyclic voltammetry measurements show a strong donor pyrazole ring, and a better acceptor ability of the fullerene moiety than the parent C60 (538). Treating fullerene Cgo with mesitonitrile oxide in toluene gives fullerene-nitrile oxide adduct, which is supposed to be useful for electrical and optical components (539). 

An enantiopure dimer 149 with a l,l -binaphthyl-bridge was prepared via the bis-tosylhydrazone (see Table 4.4, page 130/131) [122], The electronic properties of these dimers, such as the electronic absorphon spectra and cyclic voltammetry, are indistinguishable from those of other methano-bridged fullerenes. CV-data show clearly that the two CgQ-imits of the binaphthyl-dimer are reduced independently [122],... 

Cyclic silylphosphanes, see Silylphosphanes, phosphorus-rich, cyclic Cyclic sulfur-nitrogen compounds, see Sulfur-nitrogen compounds, cyclic Cyclic trithiolate ligand, 38 8-9 Cyclic voltammetry A. chroococcum Fd 1, 38 130-131 fullerene adducts, 44 19 nickel(ll) macrocyclic complexes, 44 112 Rieske proteins, 47 138, 139 Cyclidenes, as cobalt complex ligands, 44 282-284... 

Fig. 5 (a) Electrochemistry of Cgo fullerene, cyclic voltammetry (top) and differential pulse voltammetry (bottom) (Reprinted with permission from [54]). (b) Schematic representation of HOMO and LUMO orbitals after addition of six electrons (red arrows) to the fullerene... 

The first members of the fullerene family to be discovered were C60 and C7o-The electrochemical properties of these compounds have been well characterized. Both fullerenes show six reversible reductions and one oxidation by cyclic voltammetry.4 5 The reductions are almost equally spaced, with the first reduction occurring at — 1.0 V versus ferrocene/ferrocenium couple. Successive reductions occur approximately 400mV apart (Fig. 8.1). 

An important feature of the rotaxane in Scheme 9.12 is that the translocation of the macrocycle is also achieved by the reduction of the fullerene to its trianion, which is both effected and observed by cyclic voltammetry. In DMSO, the proximity of the macrocycle to the fullerene stabilized substantially the electrogenerated trianion (A i/2 = 46 mV) through n—n interactions. Surprisingly, in THF where the macrocycle is preferentially positioned on the peptide station, a similar behavior was... 

Additionally, substantial effects on the fullerene-centered reduction steps due to cation complexation by the tangential and proximal dibenzo-crown ether were observed by cyclic voltammetry (CV) for ( )-37 [30,55] (Figure 16). The CV was recorded both in the presence of one equivalent of [2.2.2]cryptand and in the presence of ten equivalents of KPF6. The cryptand was added to ensure that the species observed initially was uncomplexed, since peaks corresponding with the Na+ and K+ complexes were observed in the FAB mass spectrum of... 

For OPVn-Ceo and mixtures of OPVn and MP Ceo in solution, Eox and Ered were determined via cyclic voltammetry in dichloromethane (e = 8.93) (Table 1.1). The distances Rcc in the dyads (Table 1.3) were determined by molecular modelling, assuming that the charges are located at the centres of the OPV and fullerene moieties. For intermolecular charge transfer, the value... 

It was in 1990 that Kratschmer et al. [217,218] reported the first macroscopic preparation of in gram quantities by contact-arc vaporization of a graphite rod in a 100 Torr atmosphere of helium, followed by extraction of the resultant soot with toluene. Fullerene ions could also be detected by mass spectrometry in low-pressure hydrocarbon flames [219]. The door was opened by, Kratschmer and co-workers preparative success to extensive studies of the electrochemical behavior of the new materials. Cyclic voltammetry of molecular solutions of Ceo in aprotic electrolytes, e.g., methylene chloride/quatemary ammonium salts, revealed the reversible cathodic formation of anionic species, the radical anion, the dianion, etc. (cf. [220,221]). Finally, an uptake of six electrons in the potential range of 1-3.3 V vs. SHE in MeCN/toluene at — 10°C to form the hexavalent anion was reported by Xie et al. [222]. This was in full accordance with MO calculations. A parametric study of the electroreduction of Cgo in aprotic solvents was performed [223]. No reversible oxidation of C o was possible, not even to the radical cation. However, the stability of di- and trications with special counterions, in the Li/PEO/C 3 MoFf cell, was claimed later [224]. 

More recently, pulse radiolysis started to play a major role in the characterization of photolytically generated (A —D ) radical pairs in a variety of fullerene containing donor-bridge-acceptor dyads (68,69). While the latter evolve from photoinduced intramolecular electron transfer reactions complementary employment of pulse radiolysis allowed to generate the reduced and oxidized entities in separate experiments and to superimpose the features of the two reactive moieties. In this context, it should be noted that conventional methods, such as cyclic voltammetry, due to their unfavorable time resolution, fail to contribute to the radical pair characterization. 

Fullerenes are excellent electron acceptors, since the electron affinity of Cgo is exceptionally large (2.8 eV) and the LUMO is sixfold degenerate. Suggestions have been made to use fullerenes as storage of electrons, and indeed there is some sense in it. It has been possible to fill all six orbitals subsequently at an electrode, using cyclic voltammetry. The surface of the molecule is large, which permits solvent molecules to polarize and neutralize six electrons. 

A similar rotaxane was further synthesized and experiments showed a reverse shuttling behav-ior. 2 This reverse performance was explained by means of n-n interactions that in this case are allowed between the C o and the macrocycle. Indeed, in the previous system, there was an additional amide between the fullerene stopper and the template station, and the solvation of all the amides in DMSO hampered the possibility for the macrocycle to get close to the Cgg. Therefore, this promoted shuttling over the alkyl chain. In the second system, shown in Figure 2.21b, the solvation of the suc-cinamide template released the macrocycle that was attracted by the fullerene via n-n interactions, as demonstrated through cyclic voltammetry experiments. 

Reduction of Fullerenes. In agreement with the existence of low-lying un occupied molecular orbitals described above, fullerenes are mild oxidation agents. Reduction potentials for buckminsterfullerene can be appreciated in the cyclic voltammetry studies illustrated in Fig. 4.39 in which the electrochemical behavior of 50 with the diphylderivative Ph2C6i is compared (vide infra). Interestingly C70 shows a similar electrochemical behavior. 

Lhotak and coworkers [11] produced the mono-nitrated tetramethylcalix[5]arene (4) which had been designed to smdy fullerene complexation using cyclic voltammetry. Although this method was ultimately tmsuccessful, complexes between 4 and Ceo or C70 in solution were proven by mass spectrometry an equimolar mixture of 4, Ceo and C70 in toluene was subjected to mass spectrometry screening using electrospray ionization in the negative mode. The peaks corresponding to the formation of complexes 4 Ceo (jn z= 1351.25534) and 4 C7o... 

Cyclic voltammetry measurements elucidated that in this kind of molecule the carborane behaves as a donor because of its smaller acceptor strength compared with the fullerene. 

The electrochemical properties of all of these bis-adducts have been studied in reasonable detail, using either cyclic voltammetry (CV) or steady-state voltammetry (SSV) at a rotating disk electrode [10]. While many interesting observations have been made about their electrochemical behavior, the most relevant to the present work concerns the cis-2 isomer, 3 [11]. The bis(methano)fullerenes with a cis-2 addition pattern exhibit a chemically irreversible second one-electron reduction, as determined by using CV and SSV on a rotating disk electrode. Of all the isomers studied, the cis-2 is the only one that exhibits such an irreversible second reduction step on the voltammetric time scales. This observation led to the initiation of a project that eventually culminated in the observations that are presented in this chapter. Most of the work reported here was... 

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