Showing papers on "Fullerene published in 2000"

Carbon Nanofibers: Catalytic Synthesis and Applications

Abstract: Carbon nanofibers (diameter range, 3–100 nm; length range, 0.1–1000 µm) have been known for a long time as a nuisance that often emerges during catalytic conversion of carbon-containing gases. The recent outburst of interest in these graphitic materials originates from their potential for unique applications as well as their chemical similarity to fullerenes and carbon nanotubes. In this review, we focus on the growth of nanofibers using metallic particles as a catalyst to precipitate the graphitic carbon. First, we summarize some of the earlier literature that has contributed greatly to understand the nucleation and growth of carbon nanofibers and nanotubes. Thereafter, we describe in detail recent progress to control the fiber surface structure, texture, and growth into mechanically strong agglomerates. It is argued that carbon nanofibers are unique high-surface-area materials (˜200 m2/g) that can expose exclusively either basal graphite planes or edge planes. Subsequently, we will present the recently ...

Excited-state properties of C(60) fullerene derivatives.

Abstract: This Account reviews our main achievements in the field of excited-state properties of fullerene derivatives. The photosensitizing and electron-acceptor features of some relevant classes of functionalized fullerene materials are highlighted, considering the impact of functionalization on fullerene characteristics. In addition, the unique optimization in terms of redox potentials, water-solubility, and singlet oxygen generation is presented for several novel fullerene-based materials.

Thin films of fullerene-like MoS2 nanoparticles with ultra-low friction and wear

Abstract: The tribological properties of solid lubricants such as graphite and the metal dichalcogenides MX2 (where M is molybdenum or tungsten and X is sulphur or selenium) are of technological interest for reducing wear in circumstances where liquid lubricants are impractical, such as in space technology, ultra-high vacuum or automotive transport. These materials are characterized by weak interatomic interactions (van der Waals forces) between their layered structures, allowing easy, low-strength shearing. Although these materials exhibit excellent friction and wear resistance and extended lifetime in vacuum, their tribological properties remain poor in the presence of humidity or oxygen, thereby limiting their technological applications in the Earth's atmosphere. But using MX2 in the form of isolated inorganic fullerene-like hollow nanoparticles similar to carbon fullerenes and nanotubes can improve its performance. Here we show that thin films of hollow MoS2 nanoparticles, deposited by a localized high-pressure arc discharge method, exhibit ultra-low friction (an order of magnitude lower than for sputtered MoS2 thin films) and wear in nitrogen and 45% humidity. We attribute this 'dry' behaviour in humid environments to the presence of curved S-Mo-S planes that prevent oxidation and preserve the layered structure.

Gas-phase production and photoelectron spectroscopy of the smallest fullerene, C20

Abstract: Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

C66 fullerene encaging a scandium dimer

Abstract: The geometry of carbon cages (fullerenes) is governed by the isolated-pentagon rule (IPR)1,2, which states that the most stable fullerenes are those in which all pentagons are surrounded by five hexagons. Although this rule has been verified experimentally3,4,5, it is impossible for fullerenes in the range C60 to C70 to obey it. Here we describe the production and characterization of an IPR-violating metallofullerene, Sc2@C66, a C66 fullerene encaging a scandium dimer. Our results indicate that encapsulation of the metal dimer significantly stabilizes this otherwise extremely unstable C66 fullerene.

One-dimensional metallofullerene crystal generated inside single-walled carbon nanotubes.

Abstract: Electron microscope imaging for gadolinium metallofullerenes encapsulating in single-wall carbon nanotubes [(Gd@C82)n@SWNTs] identifies the single Gd atom encaged in each. The intermolecular distance between Gd@C82 is extremely regular, regarding the chains of Gd@C82 as novel one-dimensional crystals. Chemical state analysis of Gd atoms suggests evidence for charge transfer from Gd to either a fullerene cage or a nanotube. The slopes of the temperature dependence of electric resistance for the mat-like films of (Gd@C82)n@SWNTs and (C60)n@SWNTs are much steeper than that for empty SWNTs, suggesting the electron scattering due to the electrostatic potential from inside fullerenes playing an important role.

A stable non-classical metallofullerene family

Abstract: In the evolving field of fullerenes, nanotubes and endohedral metallofullerenes, the isolated-pentagon rule (IPR)1 is sacrosanct — exceptions have been predicted2,3, but no bare carbon cages with adjacent pentagons have been characterized. Small organic molecules with metal-stabilized fused five-membered rings (pentalenes) have been created4, however, and here we describe a family of non-classical endohedral metallofullerenes with the general structure AxSc3−xN@C68 (where x = 0–2, A is a rare-earth metal, Sc is scandium and N is nitrogen) that has a non-IPR cage of only 68 carbon atoms containing annelated five-membered rings. This internal ring network is metal-stabilized and is accessible for external organic reaction chemistry.

Fullerenes : chemistry, physics, and technology

Abstract: Electrochemistry of Fullerenes (L Echegoyen, et al) Solubility of the Fullerenes (M Korobov & A Smith) Organic Chemistry of Fullerenes (S Wilson, et al) Structural Inorganic Chemistry of Fullerenes and Fullerene--Like Compounds (A Balch) Photophysical Properties of Pristine Fullerenes, Functionalized Fullerenes, and Fullerene--Containing Donor--Bridge Acceptor Systems (D Guldi & P Kamat) Calculations of Higher Fullerenes and Quasi--Fullerenes (Z Slanina, et al) Polymer Derivatives of Fullerenes (L Chiang & L Wang) Endohedral Metallofullerenes: Production, Separation, and Structural Properties (H Shinohara) Endohedral Metallofullerenes: Theory, Electrochemistry, and Chemical Reactions (S Nagase, et al) Biological Aspects of Fullerenes (S Wilson) Carboxyfullerenes as Neuroprotective Antioxidants (L Dugan, et al) Fullerenes and Fullerene Ions in the Gas Phase (D Bohme, et al) Fullerene--Surface Interactions (A Hamza) Structures of Fullerene--Based Solids ( K Prassides & S Margadonna) Fullerenes Under High Pressure (B Sundqvist) Superconductivity in Fullerenes (V Buntar) Boron Nitride--Containing Nanotubes (N Chopra & A Zettl) Synthesis and Characterization of Materials Incorporated within Carbon Nanotubes (J Sloan & M Green) Synthesis, Structure, and Properties of Carbon Encapsulated Metal Nanoparticles (M McHenry & S Subramoney) Molecular and Solid C 36 (J Grossman, et al) Index

Synthesis, atomic structures and properties of carbon and boron nitride fullerene materials

Abstract: Carbon (C) and boron nitride (BN) fullerene materials (clusters, onions, intercalation, nanopolyhedra, nanotubes and nanocapsules) were synthesized by polymer pyrolysis, chemical reaction, arc-melting and electron-beam irradiation. Atomic structure and formation mechanism were investigated by high-resolution electron microscopy, energy dispersive spectroscopy and electron energy-loss spectroscopy. Fullerene clusters and atomic clouds (atom hopping) were formed on the surface of the C and BN fullerene materials. They provided angular and spherical nanocage structures which consist of four-, five-, six-, and seven-membered ring bonding. Detection possibility of doping atoms in metallofullerene was discussed. Included clusters showed some crystallographic relationship with {001} layers of C and BN fullerene materials, and a structure model was proposed. Photoluminescence and magnetic properties of C and BN nanocapsules were measured, which showed higher energy shift of luminescence and superparamagnetism. The present work indicates that the new C and BN fullerene materials with various atomic structure and properties can be produced by various synthesis methods, and a guideline for designing the C and BN fullerene materials is summarized.

Charge-transfer interactions in face-to-face porphyrin-fullerene systems: solvent-dependent luminescence in the infrared spectral region

Abstract: The cyclophane-type molecular dyads 1 x 2H and 1 x Zn, in which a doubly bridged porphyrin donor adopts a close, tangential orientation relative to the surface of a fullerene acceptor, were prepared by Bingel macrocylization. The porphyrin derivatives 2 x 2H and 2 x Zn with two appended, singly linked C60 moieties were also formed as side products. NMR investigations revealed that the latter compounds strongly prefer conformations with one of the carbon spheres nesting on the porphyrin surface, thereby taking a similar orientation to that of the fullerene moiety in the doubly bridged systems. Cyclic voltammetric measurements showed that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa are only small in all four dyads, despite the close proximity of the donor and acceptor components. The steady-state and time-resolved absorption and luminescence properties of 1 x Zn and 2 x Zn were investigated in toluene solution and it was shown that, upon light excitation, both the porphyrin- and the fullerene-centered excited states are deactivated to a lower-lying CT state, emitting in the IR spectral region (lambda max = 890 and 800 nm at 298 and 77 K, respectively). In the more polar solvent benzonitrile, this CT state is still detected but, owing to its very low energy (below 1.4 eV), is not luminescent and shorter-lived than in toluene. The remarkable observation of similar photophysical behavior of 1 x Zn and 2 x Zn suggests that a tight donor-acceptor distance cannot only be established in doubly bridged cyclophane-type structures but also in singly bridged dyads, by taking advantage of favourable fullerene-porphyrin ground-state interactions.

[60]Fullerene dimers

Abstract: The main types of fullerene dimers synthesized so far, including the early all-carbon fullerene dimers, other new carbon allotropes containing two fullerene units and the specially interesting fullerene dimers bridged through electroactive spacers, are reviewed. The different synthetic strategies employed have been divided into two main types, namely: (i) dimerization of C60 itself or some C60 derivatives and (ii) bifunctional cycloaddition reactions to C60. These new systems are of interest since they can find applications in areas such as artificial photosynthesis, novel molecular electronic devices and in supramolecular chemistry.

Isolation and Crystallographic Characterization of ErSc2N@C80: an Endohedral Fullerene Which Crystallizes with Remarkable Internal Order

Abstract: The ErnSc3-nN@C80 (n = 0−3) family of four endohedral fullerenes has been prepared by vaporization of graphite rods packed with 2% Sc2O3/3% Er2O3/95% graphite powder in a Kratschmer−Huffman fullerene generator under dynamic flow of helium and dinitrogen. ErSc2N@C80 has been isolated in pure form via three stages of high-pressure liquid chromatography and characterized by mass spectrometry. The first structure of a mixed metal endohedral, ErSc2N@C80, has been determined by single-crystal X-ray diffraction at 90 K on ErSc2N@C80·CoII(OEP)·1.5C6H6·0.3CHCl3, which was obtained by diffusion of a solution of ErSc2N@C80 in benzene into a solution of CoII(OEP) (OEP is the dianion of octaethylporphyrin) in chloroform. The structure of ErSc2N@C80 consists of a planar ErSc2N unit surrounded by an icosahedral C80 cage. The nominal Er−N distance is 2.089(9) A and the Sc−N distance is, as expected, shorter, 1.968(6) A. Despite its location within the C80 cage, the ErSc2N unit displays a remarkable degree of order within...

Photoinduced Electron Transfer in Carotenoporphyrin−Fullerene Triads: Temperature and Solvent Effects

Abstract: A carotenoid (C) porphyrin (P) fullerene (C60) molecular triad (C−P−C60) has been synthesized and found to undergo photoinduced electron transfer from the porphyrin first excited singlet state or to the fullerene first excited singlet state to yield C−P•+−C60•-. Electron transfer from the carotenoid then gives a C•+−P−C60•- final charge-separated state. This state is formed with quantum yields up to 0.88 and has a lifetime of up to 1 μs, depending upon the conditions. The various electron transfer rate constants are relatively insensitive to solvent and temperature. The quantum yield of C•+−P−C60•- is relatively constant under conditions ranging from fluid solutions at ambient temperatures to a rigid organic glass at 8 K. In most solvents, recombination of C•+−P−C60•- yields the carotenoid triplet state, rather than the ground state. The results suggest that the energies of the charge-separated states of fullerene-based systems are only about half as sensitive to changes in solvent dielectric constant as ...

Adsorption and Desorption of an O 2 Molecule on Carbon Nanotubes

Abstract: Adsorption and desorption of an oxygen molecule on carbon nanotubes are investigated using density functional calculations. Several precursor states exist at the edge of armchair nanotubes, whereas an exothermic adsorption takes place at the edge of zigzag nanotubes. We also estimate desorption barriers of a CO molecule from nanotubes as well as fullerenes and amorphous phases. Our calculations suggest that carbon nanotubes can survive selectively during the oxidative etching process with a precise control of annealing temperature, in good agreement with experimental results of purification process of carbon nanotubes.

Photoinduced Energy And Electron Transfer In Fullerene-oligothiophene-fullerene Triads

Abstract: A series of fullerene−oligothiophene−fullerene (C60−nT−C60) triads with n = 3, 6, or 9 thiophene units has been synthesized, and their photophysical properties have been studied using photoinduced absorption and fluorescence spectroscopy in solution and in the solid state as thin films. The results are compared to those of mixtures of oligothiophenes (nT) with N-methylfulleropyrrolidine (MP−C60). Photoexcitation of the triads in the film results in an electron-transfer reaction for n = 6 and 9, but not for n = 3. The lifetime of the charge-separated state in the film is on the order of milliseconds. Photoexcitation of the oligothiophene moiety of the C60−nT−C60 triads, dissolved in an apolar solvent, results in a singlet energy-transfer reaction to the fullerene moiety with rates varying between 1012 and 1013 s-1. In more polar solvents, an intramolecular photoinduced charge separation occurs for n = 6 and 9 and, to some extent, for n = 3. The quenching of the MP−C60(S1) fluorescence provides a lower limi...

X-ray crystal structure of an anti-Buckminsterfullerene antibody fab fragment: biomolecular recognition of C(60).

Abstract: We have prepared a monoclonal Buckminsterfullerene specific antibody and report the sequences of its light and heavy chains. We also show, by x-ray crystallographic analysis of the Fab fragment and by model building, that the fullerene binding site is formed by the interface of the antibody light and heavy chains. Shape-complementary clustering of hydrophobic amino acids, several of which participate in putative stacking interactions with fullerene, form the binding site. Moreover, an induced fit mechanism appears to participate in the fullerene binding process. Affinity of the antibody–fullerene complex is 22 nM as measured by competitive binding. These findings should be applicable not only to the use of antibodies to assay and direct potential fullerene-based drug design but could also lead to new methodologies for the production of fullerene derivatives and nanotubes as well.

Fullerenes: An extraterrestrial carbon carrier phase for noble gases

Abstract: In this work, we report on the discovery of naturally occurring fullerenes (C60 to C400) in the Allende and Murchison meteorites and some sediment samples from the 65 million-year-old Cretaceous/Tertiary boundary layer (KTB). Unlike the other pure forms of carbon (diamond and graphite), fullerenes are extractable in an organic solvent (e.g., toluene or 1,2,4-trichlorobenzene). The recognition of this unique property led to the detection and isolation of the higher fullerenes in the Kratschmer/Huffmann arc evaporated graphite soot and in the carbon material in the meteorite and impact deposits. By further exploiting the unique ability of the fullerene cage structure to encapsulate and retain noble gases, we have determined that both the Allende and Murchison fullerenes and the KTB fullerenes contain trapped noble gases with ratios that can only be described as extraterrestrial in origin.

Optical and electronic properties of fullerenes and fullerene-based materials

Abstract: Theoretical studies of photoexcitations in fullerenes ultrafast dynamics of electronic and vibrational excitations in fullerenes photoexcited state and electron transfer properties of fullerenes and related materials optical studies of fullerene triplet states the electronic third order nonlinear optical properties of C60 and C70 films optical limiting and excited-state absorption in fullerene solutions and doped glasses magnetic resonance studies of photoexcited fullerenes electrons and phonons in fullerenes and carbon nanotubes photoconductivity in fullerene thin films and solids optical and electronic properties of polymeric fullerenes electronic properties of fullerene/pi-conjugated polymer composites.

Monolayer Assembly of Zeolite Crystals on Glass with Fullerene as the Covalent Linker

Abstract: Glass plates tethered with 3-aminopropyl groups were prepared and fullerene (C60) was mounted onto the amine groups via NH insertion of the terminal amine moiety into one of the double bonds of fullerene. Cubic zeolite-A crystals covered with 3-aminopropyl groups on the external surface were independently prepared by treating the crystals with (3-aminopropyl)triethoxysilane. The zeolite-A crystals readily assembled in the form of monolayers on the fullerene-tethering glass substrates when they were allowed to contact in boiling toluene. The assembled zeolite-A monolayers remained intact even after sonication for 5 min in toluene. In contrast, the assembly of zeolite crystals does not occur if the tethering of either 3-aminopropyl or fullerene is omitted. Based on the two contrasting results, the monolayer assembly of zeolite crystals on glass is proposed to occur by formation of a large number of propylamine−fullerene−propylamine covalent linkages between each zeolite crystal and the glass substrate. Scan...

Correlation found between the HOMO–LUMO energy separation and the chemical reactivity at the most reactive site for isolated-pentagon isomers of fullerenes

Abstract: For isolated-pentagon isomers of fullerenes with up to 90 carbon atoms, the HOMO–LUMO energy separation is closely associated with the chemical reactivity at the most reactive site of the molecule. To be exact, the T value correlates very well with the minimum bond resonance energy (min BRE). Here, the T value is the HOMO–LUMO energy separation multiplied by the number of carbon atoms, and the min BRE is the minimum bond resonance energy in the molecule. This correlation explicitly shows that an isolated-pentagon fullerene isomer with chemically reactive substructures in general has a small HOMO–LUMO gap energy.