Thermal behavior of a mixture of fullerenes and fullerites C60/70

The thermal behavior of a mixture of fullerites C_60/70 was studied by X-ray diffraction and IR and UV spectroscopy. The temperature range in which the molecular and crystal states degrade was determined (825?C875°C in a CO medium). In the C_60/70 mixture, fullerenes decomposed at lower temperatures than in pure C₆₀ and C₇₀; the decomposition temperature depended on the impurity (oxygen and solvent) content.     

Crystal structures of chloroform solvates of fullerenes

The chloroform solvates of C₆₀ and C₇₀ fullerenes and of the C₆₀/C₇₀ mixture were synthesized and investigated by X-ray powder diffraction.     

Polythermal solubility of fullerenes in higher isomeric carboxylic acids

The solubility of individual fullerenes C₆₀ and C₇₀ and a fullerene mixture enriched in higher fullerenes (C₆₀ 38.8, C₇₀ 33.0, C_76–78 5.6, C₈₄ 8.6, C₉₀ 2.6, and C₉₆ 3.3%) in higher isomeric carboxylic acids was studied within the 20–80°C temperature range; the corresponding solubility polytherms are presented.     

Reactions of carbanions of bis(dialkoxyphosphoryl)bromomethane with fullerenes C60 and C70

The reactions of carbanions of bis(dialkoxyphosphoryl)bromomethanes with fullerenes C₆₀ and C₇₀ afforded new bis(dialkoxyphosphoryl)methanofullerenes C₆₀ and C₇₀, respectively, whose structures were established by spectroscopic methods.     

Nonlinear optical properties of solutions of heavy fullerenes in the near-ultraviolet region

Nonlinear optical properties (particularly optical limiting) are determined for solutions of heavy fullerenes C₇₆ + C₇₈ + C₈₄ + C₉₀ + …, in the near-ultraviolet region (λ ≈ 280 ± 7 nm). It is shown that no optical limiting is observed in solutions of light fullerenes (C₆₀ and C₇₀), but found in solutions of water-soluble fullerenol-d (a mixture of oxypolyalcohols of fullerene C₆₀-C₆₀(OH) _n1O _n2, with their sodium salts) based on light fullerenes.     

Polymer Nanocomposites Containing Fullerene C60 Nanofillers

Summary: The effect of fulleroids (fullerene C₆₀, mixture of C₆₀/C₇₀ and fulleroids soot which used for fullerenes production) and carbon fillers (carbon black, graphite) on mechanical properties of polymer nanocomposites based on reactoplasts (epoxy resins) and thermoplasts (polyamide-12) was investigated. The nanocomposites were prepared by in situ polymerization. It was found that additives of these fillers did not influenced on the properties of reactoplasts. Therefore, the tensile modulus and tensile strength of thermoplast based polymer nanocomposites are improved by about 30-40% with loading of 0.02-0.08 fulleroids materials. Best results were obtained for a mixture of C₆₀/C₇₀.     

Towards the selective formation of specific isomers of fullerenes: T - and p-dependence in the yield of various isomers of fullerenes C60–C84

Systematic fractional change in the yield of various isomers of fullerenes was revealed to strongly depend on temperature of a buffer gas. A new kinetic consideration is proposed for understanding the observed temperature- and pressure-dependence of yield of fullerenes. The model consists of three competitive reactions in consideration of plausible behaviors of a precursor, (1) decomposition into smaller fragments, (2) isomerization leading to formation of a stable fullerene cage, and (3) growth into a larger carbon cluster. Arrhenius activation energy of formation of stable fullerenes was determined to be 0.8 eV for both C₆₀ and C₇₀, while a higher energy of 2.0?3.3 eV for seven different isomers of higher fullerenes ranging from C₇₆ to C₈₄. Correlation in the activation energy is noted for a series of higher fullerenes with different sizes, suggesting the existence of a specific precursor in their formation processes.     

Distribution of C60 and C70 fullerenes in the extraction system (C60 + C70)-α-pinene-ethanol-H2O

The distribution of C₆₀ and C₇₀ fullerenes in the extraction system (C₆₀ + C₇₀)-α-pinene-ethanol-H₂O was studied at constant C₆₀ to C₇₀ ratio and variable total fullerene concentration at 25°C. The relationship between the C₆₀ and C₇₀ content in ethanol (I) and α-pinene (II) phases is nonlinear over the entire fullerene concentration range.     

Photoinduced Electron Transfer between N,N, Nr,N' ‐Tetra‐(p‐methylphenyl)‐4, 4‐diamino‐1, 1'‐diphenyl Ether (TPDAE) and Fullerenes (C60/C70) by Laser Flash Photolysis

The photoinduced electron‐transfer reaction of N, N, N', N'‐tetra‐(p‐methylphenyl)‐4,4'‐diamino‐1,1'‐diphenyl ether (TPDAE) and fullerenes (C₆₀/C₇₀) by nanosecond laser flash photolysis occurred in benzonitrile. Transient absorption spectral measurements were carried out during 532 nm laser flash photolysis of a mixture of the fullerenes (C₆₀/C₇₀) and TPDAE. The electron transfer from the TPDAE to excited triplet state of the fullerenes (C₆₀/C₇₀) quantum yields and rate constants of electron transfer from TPDAE to excited triplet state of fullerenes (C₆₀/C₇₀) in benzonitrile have been evaluated by observing the transient absorption bands in the near‐IR region where the excited triplet state, radical anion of fullerenes (C₆₀/C₇₀) and radical cations of TPDAE are expected to appear.     

A model of perealkylation reactions of trifluormethyl derivatives of fullerenes C60 and C70

A computational model for determination of the product composition of perealkylation reactions in mixtures of trifluormethyl derivatives C_60/70(CF₃) _n (n = 0–20) is proposed. Qualification of the model is carried out over a series of experiments on high-temperature annealing of mixtures of trifluormethyl derivatives of fullerenes and pure fullerenes.     

Solubility of fullerenes in n-alkanoic acids C2–C9

The solubility of fullerene C₆₀ and a fullerene mixture [C₆₀ (75%), C₇₀ (24%), C_76–80 (1%)] in linear alkanoic acids (C₂–C₉) was determined at 20°C. The solubilities of C₆₀ and a fullerene mixture in carboxylic acids were examined in relation to the number of carbon atoms in the carboxylic acid.     

Production of carbon soot with a high content of C60 and C70 fullerenes by electric arc

The effect of the parameters of the electric arc (helium pressure, current and voltage, clearance between electrodes) and of the peculiarities of the setup design (arrangement of electrodes, distance between the arc and the cooling surface, temperature of the soot condensation surface) on the yield of fullerenes has been studied. Conditions for producing soot with a C₆₀ and C₇₀ content up to 43% (toluene extract) have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 805–809, May, 1994.The authors are grateful to N. G. Spitsyna and A. V. Dubovitskii for the determination of the content of C₆₀ and C₇₀ fullerenes in the extract.The work was financially supported by the Russian Foundation for Basic Research (Project 93-03-18705).     

Transient Absorption Spectral characterization of Electron Transfer between Fullerenes（C60／C70）and N,N,N’，N’—Tetra（p—methylphenyl）—4,4’—diamino—1,1’—diphenyl Sulphide（TPDAS）

In search of new systems with a photoexcited redox pair which exhibits a strong and stable photoinduced absorption band to understand the photophyscial and photochemical properties of electron transfer between fullernes (C60/C70) and organic donor[N,N,N’，N’-tetra(p-methylphenyl)-4,4’-diamino-1,1’-diphenyl sulphide(TPDAS)],we studied characteristic absorption spectra in the near-IR region obtained from 532nm nanosecond laser flash photolysis of a mixture of the fullerenes (C60/C70) and TPDAS in polar solvents.When fullerenes (C60/C70)were photoexcithed,the rise of the radical anion of fullerenes (C60/C70)with the rapid decay of their excited triplet states were observed in benzonitrile.It can be deduced that the electron transfer reaction does take place from TPDAS to excithed triplet state of rullerens(C60/C70).The rate consants(ket)and quantum yiekls(φet) of this process have been also evaluated.     

Photoinduced electron transfer of fullerenes (C60 and C70) studied by transient absorption measurements in near-IR region

Efficiencies and rates of electron transfer from various electron donors to excited fullerenes (C₆₀ and C₇₀) have been determined by observing the transient absorption bands in the near-IR region, where the anion radicals of fullerenes appear. From the rise of the absorption bands of C₆₀ ⁻⁺ and C₇₀ ⁻⁺ in the near-IR region, electron transfer takes place via the triplet states (^TC₆₀ ^* and ^TC₇₀ ^*) under appropriately low concentrations of electron donors. By analysis of the rise curves C₆₀ ⁻⁺ and C₇₀ ⁻⁺, contribution of the excited singlet states (^SC₆₀ ^* and ^SC₇₀ ^*) in addition to the route of the triplet states (^TC₆₀ ^* and ^TC₇₀ ^*) is confirmed. The quantum yield for electron transfer via the triplet states Φ_ct ^T was evaluated by the ratio of [C₆₀ ⁻⁺]/[^TC₆₀ ^*] (or [C₇₀ ⁻⁺/[^TC₇₀ ^*]). The Φ_ct ^T depends upon the donor-ability, donor concentration, and solvent polarity. The back electron-transfer process, which was evaluated by observing C₆₀ ⁻⁺, also depends upon the solvent polarity.     

Addition of sulfur radicals to fullerenes

The addition of oxygen‐centered radicals to fullerenes has been intensively studied due to their role in cell protection against against hydrogen peroxide induced oxidative damage. However, the analogous reaction of sulfur‐centered radicals has been largely overlooked. Herein, we investigate the addition of S‐centered radicals to C₅₀, C₆₀, C₇₀, and C₁₀₀ fullerenes by means of DFT calculations. The radicals assayed were: S, SH, SCH₃, SCH₂CH₃, SC₆H₅, SCH₂C₆H₅, and the open‐disulfide SCH₂CH₂CH₂CH₂S. Sulfur, the most reactive species, prefers to be attached to a 66‐bond of C₆₀ with a binding energy (E_bind) of 2.4 eV. For the SR radicals the electronic binding energies to C₆₀ are 0.77, 0.74, 0.58, 0.67, and 0.35 eV for SH, SCH₃, SCH₂CH₃, SCH₂C₆H₅, and SC₆H₅, respectively. The reactivity of C₆₀ toward SR radicals can be increased by lithium doping. For Li@C₆₀, the E_bind is increased by 0.65 eV with respect to C₆₀, but only by 0.33 eV for the exohedral doping. Fullerenes act like free radical sponges. Indeed, the C₆₀‐SR E_bind can be duplicated if two radicals are added in ortho or para positions. The enhanced reactivity because of multiple additions is mostly a local effect, although the addition of one radical makes the whole cage more reactive. Therefore, as observed for hydroxylated fullerenes, they should protect cells from oxidative damage. However, the thiolated fullerenes have one advantage, they can be easily attached to gold nanoparticles. For the addition on pentagon junctions smaller fullerenes like C₅₀ are more reactive than C₆₀. Interestingly, C₇₀ is as reactive as C₆₀, even for the addition on the equatorial belt. For larger fullerenes like C₁₀₀, reactivity decreases for the carbon atoms belonging to hexagon junctions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Solubility of light fullerenes in vegetable oils

Polythermal (in the temperature range 0−80°C) solubility of light fullerenes (C₆₀ and C₇₀), and also of fullerene mixtures (65% C₆₀, 34% C₇₀, and 1% C_76–90) in vegetable oils (of unrefined and refined sunflower, corn, olive, linen, apricot, grape, cedar, and walnut) was studied; the corresponding solubility polytherms are given and characterized.     

Quadrupole ion trap mass spectrometry of fullerenes

The fullerenes C₆₀ and C₇₀ can be ionized by desorption from a liquid matrix upon bombardment by Cs⁺ ions of 7 keV kinetic energy. The resulting radical cations, when activated in the ion trap by collisions with Xe target, in the presence of helium, undergo extensive dissociation by loss of multiple C₂ units. Large internal energies are deposited into these molecular ions and the dissociation efficiency is in excess of 60%.     

Separation of C60 and C70 fullerenes on silica modified by polyaromatic and π-acid aromatic compounds

Separation of C₆₀ and C₇₀ fullerenes by HPLC was studied using sorbents synthesized by reaction of perylenedicarboxylic anhydride, dimethoxyviolanthrene, the tetramer of chromotropic acid with formaldehyde (TCA), trinitrobenzoyl chloride, or chlorotrinitrobenzene with γ-aminopropyl silica. These sorbents possess satisfactory chromatographic properties. The sorbent based on TCA is effective for separation of preparative amounts of fullerenes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1544–1546, August, 1997.     

Radical scavenging efficiency of different fullerenes C60-C70 and fullerene soot

This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C₆₀ and C₇₀ in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C₆₀ and C₇₀ and fullerene soot. All fullerenes - C₆₀ of gold grade, C₆₀/C₇₀ (93/7, mix 1), C₆₀/C₇₀ (80 ± 5/20 ± 5, mix 2) and C₇₀ operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C₆₀ and C₇₀ the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k_(333K) = (1.9 ± 0.2) × 10⁸ (C₆₀); (2.3 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 1); (2.7 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 2); (3.0 ± 0.3) × 10⁸ (C₇₀), M⁻¹ s⁻¹. The increasing C₇₀ constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C₆₀−soot] = (2.0 ± 0.1) × 10⁻⁴ mol g⁻¹ and k_inh = (6.5 ± 1.5) × 10³ M⁻¹ s⁻¹ respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.     

Mechanism of selection of perfect fullerenes in arc synthesis

Joint consideration of the gas flow dynamics in an arc chamber for fullerene production and fullerene assembly kinetics shows that the efficient fullerene annealing and the giant prevalence of magic fullerenes C₆₀ and C₇₀ are associated with the gas flow structure generated by the arc in the discharge chamber. Most nascent fullerenes are not immediately removed from the chamber; rather, they are entrained by closed gas flows. Analysis of fullerene annealing makes it possible to optimize fullerene production not only for arc parameters but also for chamber geometry.