Showing papers on "Fullerene published in 1997"

Fullerene nanotubes : c1,000,000 and beyond

Abstract: “Fullerene Nanotubes: C1,000,000 and Beyond”, Boris I. Yakobson and Richard E. Smalley, American Scientist, vol. 85, pp. 324–337, Jul-Aug. 1997. “Carbon Rings and Cages in the Growth of Singled-Walled Carbon Nanotubes”, Ching-Hwa Kiang, Journal of Chemi cal Physics, vol. 113, No. 11, pp. 4763–4766, Sep. 15, 2000. “Growth of a Single Freestanding Multiwall Carbon Nano tube on Each Nonnickel Dot”, Z.F. Ren, Z.P. Huang, D.Z. Wang and J.G. Wen, Applied Physics Letters, vol. 75. No. 8. pp. 1086–1088, Aug. 23, 1999.

Donor‐Linked Fullerenes: Photoinduced electron transfer and its potential application

Abstract: Redox-active fullerenes can be covalently bound to a variety of donors; their photophysical properties have been investigated. Their photochemical processes, including electron transfer and energy transfer, are varied, depending on the donor, linkage between the donor and C 60 , and solvent. Regardless of the solvent and linkage, the charge-separated state is produced efficiently in zinc porphyrin-C 60 systems, showing that C 60 is a good electron acceptor. The most intriguing characteristic of C 60 in electron transfer is that C 60 accelerates photoinduced charge separation and retards charge recombination in the dark. The long-lived charge-transfer state of the C 60 -porphyrin dyad was successfully converted to photocurrent using a self-assembled monolayer technique. These findings will provide a new strategy for the design and synthesis of artificial photosynthethic systems and photoactive materials using C 60 as a building block.

Purification of single-wall carbon nanotubes by microfiltration

Abstract: A purification procedure for single-wall carbon nanotubes (SWNTs) prepared by pulsed laser ablation is discussed, which separates coexisting carbon nanospheres (CNS), metal nanoparticles, polyaromatic carbons, and fullerenes from the SWNT fraction. The process involves the suspension of CNS, metal nanoparticles, and SWNTs in an aqueous solution using a cationic surfactant and the subsequent trapping of SWNTs on a membrane filter. No oxidative treatment is required. Scanning/transmission electron microscopy and Raman scattering were used to evaluate the purification process and the vibrational features of SWNTs. Purity of SWNTs at the final stage sample is in excess of 90% by weight, and no evidence of impurity carbon phases was revealed in the Raman spectrum of the SWNT fraction.

Catalytic Growth of Single-Wall Carbon Nanotubes: An Ab Initio Study

Abstract: We propose a catalytic growth mechanism of single-wall carbon nanotubes based on density functional total energy calculations Our results indicate nanotubes with an “armchair” edge to be energetically favored over “zigzag” nanotubes We also suggest that highly mobile Ni catalyst atoms adsorb at the growing edge of the nanotube, where they catalyze the continuing assembly of hexagons from carbon feedstock diffusing along the nanotube wall In a concerted exchange mechanism, Ni atoms anneal carbon pentagons that would initiate a dome closure of the nanotube [S0031-9007(97)02791-9]

Graphitic nanofibers in electrochemical capacitors

Abstract: Graphitic nanofibers, which include tubular fullerenes (commonly called 'buckytubes'), nanotubes and fibrils, which are fucntionalized by chemical substitution, are used as electrodes in electrochemical capacitors. The graphitic nanofiber based electrode increases the performance of the electrochemical capacitors.

Macrocyclization on the fullerene core: Direct regio‐ and diastereoselective multi‐functionalization of [60]fullerene, and synthesis of fullerene‐dendrimer derivatives

Abstract: The macrocyclization between buckminsterfullerene, C60, and bis-malonate derivatives in double Bingel reaction provides a versatile and simple method for the preparation of covalent bis-adducts of C60 with high regio- and diastereoselectivity. A combination of spectral analysis, stereochemical considerations, and X-ray crystallography (Fig. 2) revealed that out of the possible in-in, in-out, and out-out stereoisomers, the reaction of bis-malonates linked by o-, m-, or p-xylylene tethers afforded only the out-out ones (Scheme 1). In contrast, the use of larger tethers derived from 1,10-phenanthroline also provided a first example, (±)-19 (Scheme 2), of an in-out product. Starting from optically pure bis-malonate derivatives, the new bis-functionalization method permitted the diastereoselective preparation of optically active fullerene derivatives (Schemes 4 and 5) and, ultimately, the enantioselective preparation (enantiomeric excess ee > 97%) of optically active cis-3 bis-adducts whose chirality results exclusively from the addition pattern (Fig. 6). The macrocyclic fixation of a bis-malonate with an optically active, 9,9′-spirobi[9H-fluorene]-derived tether to C60 under generation of 24 and ent-24 with an achiral addition pattern (Scheme 4) was found to induce dramatic changes in the chiroptical properties of the tether chromophore such as strong enhancement and reversal of sign of the Cotton effects in the circular dichroism (CD) spectra (Figs. 4 and 5). By the same method, the functionafized bis-adducts 50 and 51 (Schemes 10 and 11) were prepared as initiator cores for the synthesis of the fullerene dendrimers 62, 63, and 66 (Schemes 12 and 13) by convergent growth. Finally, the new methodology was extended, to the regio- and diastereoselective construction of higher cyclopropanated adducts. Starting from mono-adduct 71, a clipping reaction provided exclusively the all-cis-2 tris-adduct (±)-72 (Scheme 14), whereas the similar reaction of bis-adduct 76 afforded the all-cis-2 tetrakis-adduct 77 (Scheme 15). Electrochemical investigations by steady-state voltammetry (Table 2) in CH2Cl2 (+0.1M Bu4NPF6) showed that all macroeyciic bis(methano)fullerenes underwent multiple reduction steps, and that regioisomerism was not much influencing the redox potentials, All cis-2 bis-adducts gave an instable dianion which decomposed during the electrochemical reduction. In CH2Cl2, the redox potential of the fullerene core in dendrimers 62, 63, and 66 is not affected by differences in size and density of the surrounding poly(ether-amide) dendrons. The all-cis-2 tris- and tetrakis(meihano)fullercnes (±)-72 and 77, respectively, are reduced at more negative potential than previously reported all-e tris- and tetrakis-adducts with methane bridges that are also located along an equatorial belt. This indicates a larger perturbation of the original fullerene π-chromophore and a larger raise in LUMO energy in the former derivatives.

Organic Approaches to Endohedral Metallofullerenes: Cracking Open or Zipping Up Carbon Shells?

Abstract: We have been investigating the synthesis of endohedral metallofullerenes since we successfully opened an orifice on the framework of C60 in the form of a cobalt complex having the metal sitting on top of the opening. A second approach aims at the synthesis of spherically-shaped acetylenic macrocycles, which are expected to rearrange to endohedral metal complexes of fullerenes in a controlled process analogous to the gas-phase coalescence of mono- and polycyclic polyynes during fullerene formation by the graphite evaporation method. Since the potential benefits from obtaining endohedral metal complexes of C60 are enormous, both approaches are being actively pursued in our group.

Isolation and characterisation of C70O

Abstract: C70O has been isolated in ca. 0.5% yield by HPLC separation of the soot extract obtained from a novel arc-discharge reactor for fullerene production. The reactor (DC conditions) can be operated continuously for 24 h, employs a rotating cathode and an anode consisting of continuously-fed strips cut from a carbon sheet. The 13C NMR spectrum of C70O shows that two isomers (1,2-epoxy[70]fullerene and 5,6-epoxy[70]fullerene) are present in a ratio of ca. 43∶57 and all 37 peaks corresponding to each isomer have been identified. These are the first [70]fullerene derivatives in which 5,6-addition is preferred over 1,2-addition, this preference probably deriving from the considerable strain that accompanies bridging with a single atom; the greater curvature across the 1,2-positions compared with the 5,6-positions therefore disfavours the former. Differential polarisabilities of the electrons of the 1,2- and 5,6-bonds, a factor producing a variation in reactivity order according to the attacking reagent (but not considered hitherto in the context of fullerene chemistry) may also be significant. The epoxides are unstable towards EI mass spectrometry, in contrast to epoxides possessing additional addends, and this may reflect the reduced cage strain present in the latter.

Structures of Silicon-Doped Carbon Clusters

Abstract: Gas phase ion mobility measurements have been used to examine the geometries of silicon-doped carbon cluster cations, CnSi+ (n = 3−69). The observed isomers resemble those found for pure carbon clusters: linear chains, monocyclic, bicyclic, and polycyclic rings, graphite sheets, and fullerenes. Generally, the silicon atom substitutes for a carbon atom and has only a minor effect on the structure. The linear chain and monocyclic ring isomers coexist for CnSi+ clusters over a wider range than for pure carbon cluster cations. The results provide the first conclusive experimental evidence that C2n-1Si+ fullerenes with an even number of atoms are closed-cage structures with the silicon atom networked into the cage. For C2nSi+ fullerenes with an odd number of atoms the silicon atom appears to be exohedral.

Two Dimensional Graphite Films on Metals and Their Intercalation

Abstract: Two-dimensional graphite films (2DGF) on solids are wonderful objects, real nature-made two-dimensional crystals. Formation on active metal surface of a 2DGF with extremely high adsorption, chemical and catalytic passivity leads to a number of staggering effects. The review is devoted to 2DGF on metals and their nature, structure, modes of formation and physico chemical properties. A nature of absorption bond between 2DGF and metal substrate is discussed in details. A special attention is paid to intercalation of 2DGF — a process when foreign atoms and even molecules (fullerenes C60 molecules) spontaneously penetrate between graphite film and metal substrate. Modes of intercalation are discussed and a mechanism of it, based on thermal movements of carbon atoms of a graphite layer, proposed earlier, is used for explanation of experimental data. A new, practically important effect-superefficient diffusion of alkaline atoms into transition metal bulk, covered by 2DGF, is reported.

Formation and growth of carbon nanostructures: fullerenes, nanoparticles, nanotubes and cones

Abstract: Various formation models for fullerenes and other carbon nanostructures are reviewed. The formation models considered include fullerene assembling from graphite sheets, 'nautilus' model, assemblage from clusters, 'fullerene road', and carbon cluster annealing. The selection of magic fullerenes and fullerene isomers is discussed. Carbon nanoparticle formation mechanisms are analyzed and their relation to fullerene formation mechanisms is outlined. Molecular dynamics simulation of the possible mechanisms of nanoparticle formation is considered and possible growth nuclei and growth mechanisms for single- and multishell nanotubes and for carbon cones are discussed. Some promising techniques intended for fabrication of carbon-containing nanoobjects were described.

Polycyclic Aromatic Hydrocarbons and Fullerenes as Decomposition Products of Hydrogenated Amorphous Carbon

Abstract: The gaseous products evolved from solid hydrogenated amorphous carbon (HAC) under UV irradiation have been sampled using time of flight (TOF) mass spectrometry. A notable feature is the appearance of an extended sequence of aromatic carbon clusters containing in excess of 30 carbon atoms and including fullerenes such as C50, C60, and C70. Under certain conditions, clusters containing up to several hundred C atoms are detected. The radiation-induced decomposition of HAC is found to occur in a series of stages in which small (<20 atom) molecules including alkanes and unsaturated carbon chain (C=C)nHm radicals with m = 1-4 are the first to be released. There is also evidence in these mass spectra for the ejection of small dehydrogenated polycyclic aromatic hydrocarbon (PAH) molecules. After these lighter molecules have been released, we observe a strong mass peak near 500 amu corresponding to clusters with ~40 C atoms. These clusters, which are protographitic aromatic structures, have been detected in IR spectra of HAC and show absorption and emission features at 3.3, 3.4, and 6.2 μm and other wavelengths characteristic of PAH molecules. These data show that the decomposition of HAC in interstellar shocks may be a source of large PAH and fullerene molecules.

Photoinduced electron transfer from phthalocyanines to fullerenes (C60 and C70)

Abstract: Photoinduced electron transfer between fullerenes (C60 and C70) and phthalocyanines such as tetra-tert-butylphthalocyanine (H2TBPc) and its zinc derivative (ZnTBPc) in solution has been investigated with nanosecond laser photolysis method by observing the transient absorption bands in the visible/near-IR regions. By the predominant excitation of fullerenes with 532 nm laser light, slow rises of the transient absorption bands of phthalocyanine cation radicals and fullerene anion radicals were observed instead of the decays of the excited triplet states of fullerenes (TC60* and TC70*) in polar solvents. Electron-transfer from the phthalocyanines to TC60* or TC70* was confirmed. The quantum yield of the electron transfer via TC70* is higher than that via TC60*; ZnTBPc acts as stronger electron donor than H2TBPc. In nonpolar solvent, energy transfer from TC60* (and TC70*) to the phthalocyanines occurs predominantly as confirmed by the consecutive appearance of the triplet states of the phthalocyanines.

Intercalation of Inorganic Fullerene-like Structures Yields Photosensitive Films and New Tips for Scanning Probe Microscopy

Abstract: Evaporation of metals, like W, Mo, V, and In, in the presence of water vapor and subsequent sulfidization has yielded bulk quantities of nested fullerenes, nanotubes, and structures with negative c...

Bis- through Tetrakis-Adducts of C60 by Reversible Tether-Directed Remote Functionalization and systematic investigation of the changes in fullerene properties as a function of degree, pattern, and nature of functionalization

Abstract: By the tether-directed remote functionalization method, a series of bis- to hexakis-adducts of C60, i.e., 1–7 (Fig. 1), had previously been prepared with high regioselectivity. An efficient method for the removal of the tether-reactive-group conjugate was now developed and its utility demonstrated in the regioselective synthesis of bis- to tetrakis(methano)fullerenes ( = di- to tetracyclopropafullerenes-C60-Ih) 9–11 starting from 4, 5, and 7, respectively (Schemes 2, 4, and 5). This versatile protocol consists of a 1O2 ene reaction with the two cyclohexene rings in the starting materials, reduction of the formed mixture of isomeric allylic hydroperoxides to the corresponding alcohols, acid-promoted elimination of H2O to cyclohexa-1,3-dienes, Diels-Alder addition of dimethyl acetylenedicarboxylate, retro-Diels-Alder addition, and, ultimately, transesterification. In the series 9–11, all methano moieties are attached along an equatorial belt of the fullerene. Starting from C2v-symmetrical tetrakis-adduct 15, transesterification with dodecan-1-ol or octan-1-ol yielded the octaesters 16 and 17, respectively, as noncrystalline fullerene derivatives (Scheme 3). The X-ray crystal structure of a CHCl3 solvate of 11 (Fig. 3) showed that the residual conjugated π-chromophore of the C-sphere is reduced to two tetrabenzopyracylene substructures connected by four biphenyl-type bonds (Fig. 5). In the eight six-membered rings surrounding the two pyracylene (= cyclopent[fg]acenaphthylene) moieties, 6–6 and 6–5 bond-length alteration (0.05 A) was reduced by ca. 0.01 A as compared to the free C60 skeleton (0.06 A) (Fig. 4). The crystal packing (Fig. 6) revealed short contacts between Cl-atoms of the solvent molecule and sp2- and sp3-C-atoms of the C-sphere, as well as short contacts between Cl-atoms and O-atoms of the EtOOC groups attached to the methano moieties of 11. The physical properties and chemical reactivity of compounds 1-11 were comprehensively investigated as a function of degree and pattern of addition and the nature of the addends. Methods applied to this study were UV/VIS (Figs. 7–11), IR, and NMR spectroscopy (Table 2), cyclic (CV) and steady-state (SSV) voltammetry (Table 1), calculations of the energies of the lowest uunoccupied mmolecular orbitals (LUMOs) and electron affinities (Figs. 12 and 13), and evaluation of chemical reactivity in competition experiments. It was found that the properties of the fullerene derivatives were not only affected by the degree and pattern of addition but also, in a remarkable way, by the nature of the addends (methano vs. but-2-ene-1, 4-diyl) anellated to the C-sphere. Attachment of multiple thano moieties along an equatorial belt as in the series 8–11 induces only a small perturbation of the original fullerene π-chromophore. In general, with increasing attenuation of the conjugated fullerene π-chromophore, the optical (HOMO-LUMO) gap in the UV/VIS spectrum is shifted to higher energy, the number of reversible one-electron reductions decreases, and the first reduction potential becomes increasingly negative, the computed LUMO energy increases and the electron affinity decreases, and the reactivity of the fullerene towards nucleophiles and carbenes and as dienophile in cycloadditions decreases.

The Covalent Chemistry of Higher Fullerenes: C70 and Beyond

Abstract: Although higher fullerenes are not yet available in larger amounts, their accessibility, like that of C60, has gradually improved since the early days of fullerence chemistry. Today, many of the soluble larger carben can be purchased either in pure form or as isomeric mixtures. In particular, pure C70 is available in preparative amounts from fullerene soot without the need for tedious separation by high-performance liquid chromatography; this has had a major impact on the progress of the chemistry of this higher fullerene. Over the last years C70 has been functionalized in many ways, and pure derivatives of even the larger, more complex carbon spheres C76, C84, and recently also C78, have been isolated and characterized. From the collected body of data, first general principles of reactivity and selectivity begin to emerge for these fullerenes, which are all less symmetric than C60. Important information is provided by multiple additions to higher fullerenes, in which certain isomers are formed with a remarkable selectivity that exceedes that observed for C60. A particularly attractive aspect is the chirality of certain allotropes and many derivatives. Although the chirality of fullerene derivatives is not restricted to the larger carbon cages, it was sofar mostly explored through their chemistry and can be related to different structural characteristics. A recently proposed system allows simple specification by a single descriptor of the configuration of chiral fullerenes and fullerene derivatives with a chiral functionalization pattern, including highly branched carbon frameworks with a multitude of possible stereogenic centers.

Generation of higher fullerenes in flames

Abstract: The presence of fullerenes up to C116 was observed in condensable material from a benzene/oxygen flame. The flame material was Soxhlet-extracted with toluene for 363 h, fractionationed by means of a silica-based semipreparative HPLC column, and analyzed by HPLC coupled to a mass spectrometer via a heated nebulizer interface using a 2-(1-pyrenyl)ethylsilica stationary phase. UV−vis spectra were measured for C60, C60O, C60·CH4, C70, C70O, C76, C78, C80, C84, a C84 adduct, C86, C88, C90, C92, C94, C96, C98, C100, C102, and C108. Isomers could be discerned for C78, C90, and C94. A calibration using external standards was performed for C60, C70, C76, C78, and C84. For all other species the relative abundances were estimated based on HPLC peak integration results. Electric arc soot was extracted under similar conditions and the quantification of fullerenes compared to the data obtained with flame-generated condensable material. Except for C60 and C76, the abundances were significantly higher in the case of flam...

First-Principles Determination of the Dispersion Interaction between Fullerenes and Their Intermolecular Potential

Abstract: We compute, from first principles, the dispersion interaction between two and three fullerenes, in time-dependent density functional theory. These results, complemented with total energy calculations at small and intermediate distances, lead to a parameter-free determination of the interaction between fullerenes. Agreement with experiment, within $4%$, is found for all quantities, computed via Monte Carlo simulations of fullerite. Inclusion of the three-body term is found to increase by $6%$ the cohesive energy at equilibrium density.

Synthesis of 1,4-Dipolystyryldihydro[60]fullerenes by Using 2,2,6,6-Tetramethyl-1-polystyroxypiperidine as a Radical Source

Abstract: This is the first report of the synthesis of well-defined disubstituted polymer derivatives of C60 by a radical mechanism. Narrow-polydispersity polystyryl adducts with TEMPO (2,2,6,6-tetramethylpi...

Optical Limiting Properties of [60]Fullerene Derivatives

Abstract: Optical limiting properties of methano[60]fullerene and pyrrolidino[60]fullerene derivatives in room-temperature solutions are studied systematically. The results show that the derivatives are very similar to the parent [60]fullerene in optical limiting, despite the fact that the linear absorption and emission properties of the derivatives are very different from those of [60]fullerene. The optical limiting properties of the [60]fullerene derivatives are discussed in the context of nonlinear optical effects due to reverse saturable absorption.

Multi-substituted fullerenes and methods for their preparation and characterization

Abstract: The invention is directed to multiply-substituted fullerene derivatives of novel configurations, and methods for their preparation and use. The methods involve the combinatorial synthesis of a library of fullerene derivatives and comprises the steps of forming a mixture of fullerene derivatives by reacting the Cn fullerene with two or more reactive precursor compounds, and removing the unreacted compounds to yield the fullerene derivatives having the desired activity. Methods for the identification and screening of a combinatorial library of fullerenes by 3He-nuclear magnetic resonance and electrospray mass spectrometry to define members with the optimal desired activity are also provided.

Noble Gas Endohedral Complexes of C60 Buckminsterfullerene

Abstract: Equilibrium geometries and binding energies (corrected for basis set superposition error) of single and multiple noble gas atom complexes of C60 are calculated at DFT and MP2 levels of theory using basis sets including polarization functions. B3LYP and MP2 give similar van der Waals dispersion interactions, predicting repulsive energies for the He and Ne complexes of about 1 kcal/mol, and higher energies for the larger noble gas atom complexes. As expected, C60 is resilient to deformation in all cases studied, with the geometry of the fullerene cage barely affected by the presence of multiple noble gas atoms inside.

Selective Functionalization on [60]Fullerene Governed by Tether Length

Abstract: In order to accomplish the selective synthesis of [60]fullerene bisadducts, the reactions of [60]fullerene with compounds in which two α,α‘-dibromo-o-xylene moieties were connected by an oligomethylene chain (n = 2−5) were investigated. By this method, only two isomers (cis-2- and cis-3-isomers) were selectively obtained when n = 2 and 3, while another isomer (e-isomer) was obtained when n = 5. When n = 4, a complex mixture of bisadducts was formed and has not been separated so far. cis-2-Bisadducts have been, for the first time, selectively obtained in the fullerene chemistry. The structures of bisadducts were determined on the basis of 1H, 13C NMR, IR, UV−vis, and mass spectroscopies. According to the NMR experiments, the symmetries of cis-2-, cis-3-, and e-isomers were concluded to be Cs, C2, and C1, respectively. Chiral cis-3- and e-bisadducts were successfully resolved into the respective enantiomers on a chiral HPLC column, although cis-2-bisadducts only gave a single peak. The UV−vis spectra of cis...

Fullerenes in photoconductive polymers. charge generation and charge transport

Abstract: Fullerenes enhance the photoconductivity of photoconductive polymers. This paper studies the mechansim of enhancement both experimentally and theoretically. The effects of fullerene doping on the spectroscopic, charge generation, and charge transport properties of the polymer are reported. Electrical field effects and magnetic field effects are examined. On the basis of these data a charge generation mechansim involving a singlet of weak charge-transfer complex is proposed for fullerene-doped N-poly(vinylcarbazole). A new theoretical model combining both the Onsager and Marcus theory is developed to quantitatively account for the field-dependent charge generation efficiency in nonpolar medium.

Capped Fullerenes: Stabilization of Water-Soluble Fullerene Monomers As Studied by Flash Photolysis and Pulse Radiolysis

Abstract: Functionalization of C60 with hydrophilic groups promotes the water solubility of the fullerene core which leads in aqueous solution to the irreversible formation of clusters. Capping the surface of water-soluble fullerene derivatives with surfactants (cetyltrimethylammonium chloride or Triton X-100) was found to exclude formation of fullerene clusters and, in turn, to stabilize fullerene monomers. Flash photolytic and pulse radiolytic techniques were employed to generated excited and reduced states of fullerene monomers and fullerene clusters 1−3. Fullerene aggregation was found to have no significant effects on the physicochemical properties related to the generation and lifetime of the excited singlet state. Nanosecond studies of the processes following photoexcitation revealed noticeable differences between monomeric and colloidal derivatives 1−3 for the absorption maximum of the corresponding *T1 → *Tn absorptions. Clustering was found to invoke also remarkable changes for the decay of the fullerene'...