Fullerene Solutions Research Articles

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (IDV) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (EAV) of [60]- and [70]fullerenes in solution. The value of EAV for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.

Thermal relaxation mechanism and role of chemical functionalization in fullerene solutions

Using molecular-dynamics simulations we investigate thermal relaxation of C60 and C84 molecules suspended in octane liquid. Pristine fullerenes exhibit relatively slow relaxation due to weak thermal coupling with the liquid. A comparison of the interfacial transport characteristics obtained from relaxation simulations with those obtained from equilibrium simulations and fluctuation-dissipation theorem analysis demonstrates that the relaxation process involves two main steps: (i) energy flow from high- to low-frequency modes within the fullerene, and (ii) energy flow from low-frequency fullerene modes to the liquid. Functionalization of fullerenes with alkene chains leads to significant reduction of the thermal relaxation time. The relaxation time of functionalized fullerenes becomes independent from the functionalizing chain length beyond approximately 10 carbon segments; this can be understood in terms of thermal conductivity along the chain and heat transfer between the chain and the solvent.

Development of the Soret Forced Rayleigh Scattering Method for Measurement of Mass Diffusion Coefficient (1st Report, Development of the Measurement System and Measurement of the Fullerene in Solution)

Development of the Soret Forced Rayleigh Scattering Method for Measurement of Mass Diffusion Coefficient (1st Report, Development of the Measurement System and Measurement of the Fullerene in Solution)

Complexation of carbon nanorings with fullerenes

To explore the supramolecular properties of the hollow space of carbon nanotubes, the belt-shaped conjugated systems with sizable and deep cavities are intriguing molecules. Recently, we found that the "carbon nanorings", cyclic [6]paraphenyleneacetylene ([6]CPPA), and the related compounds involving two naphthylene rings, form stable inclusion complexes with fullerenes in solution as well as in the solid state. The stability of these complexes correlates well with the van der Waals (VDW) contact between the host and guest. Thus, carbon nanorings having a deep cavity should form considerably stable complexes with fullerenes. In this context, we have designed a new carbon nanoring, cyclic [6](1,4)naphthyleneacetylene. The host forms considerably stable inclusion complexes with fullerenes and can act as the best fluorescence sensor for fullerenes among all the known hosts. The NMR spectra reveal the formation of two major conformational isomers, in which five or six naphthylene rings surround a guest molecule to gain wide contact area. The high affinity between C60 and naphthylene rings similar to an ion-dipolar interaction plays an important role in the novel guest-induced conformation fixation.

Efficient and Scalable Method for [60]Fullerene Separation from a Fullerene Mixture: Selective Complexation of Fullerenes with DBU in the Presence of Water

The acceleration effect of water in the selective complexation of fullerenes with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was investigated. Although selective complexation with DBU is useful for large-scale [60]fullerene separation from a fullerene mixture, the complexation is too slow for practical application at ambient temperature without the addition of water. In the presence of a small amount of water, the complexation accelerated considerably, and a pure [60]fullerene solution was readily obtained by complexation at 20 °C. The procedure was easily scaled up, and 1.3 kg of pure [60]fullerene was obtained from 3.0 kg of the fullerene mixture.

On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C60 solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of IC with increase of scattering angle. The value of IC depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C60 in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C60 by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C60 solutions in good solvents are considered.

Effect of surface temperature on the concentration of C60/C70 molecules in dc arc discharge fullerene generator

Synthesis of C60, C70 and higher fullerenes was carried out at Pakistan Institute of Nuclear Science and Technology (PINSTECH) using dc arc discharge technique. High-performance liquid chromatography (HPLC) and UV–vis spectroscopy are employed to characterize the fullerenes. The toluene extracted fullerene solutions of the raw soot collected from four different regions (A–D) of dc arc discharge fullerene generator were compared with pure C60 toluene solution. Due to poor solubility of C60 in HPLC grade methanol, different fractions of methanol as a mobile phase with toluene were tried. The mobile phase composition of 80:20 methanol:toluene was found an optimal ratio to achieve the best separation factor of 1.246 between C60 and C70 fullerenes. Quantitative concentration is calculated from the HPLC and UV–vis spectra. The molarity of C60 carbon molecules for all the regions is calculated from the HPLC spectra by comparing the spectra of known molar solution of C60. The maximum concentration of C70 is found to be 21% in the region B that is nearer the arc zone and at a higher temperature than other regions. Both the techniques confirm the presence of C60, C70 and higher fullerenes in all the four regions with variation in concentration of C60 and C70. UV–vis spectra of the region C show the additional absorption bands at 285 and 305nm.

Small‐Angle Neutron Scattering and Photon Correlation Spectroscopy Investigation on Buckminsterfullerene Solutions

Small‐Angle Neutron Scattering (SANS) and Photon Correlation Spectroscopy (PCS) findings on Buckminsterfullerene (C60) solutions are presented. The analysis of SANS data allows to characterize the shape and to determine the value of the gyration radius of C60 dissolved in CS2, a solvent capable to guarantee a good contrast for the neutron probe. We obtained information about the conformation of fullerene in solution, and, by means of comparisons with experimental and theoretical data existing in literature, we found a confirmation that the gyration radius R g is independent on concentration. PCS measurements were performed on fullerene/organic solvents (toluene, chloroform and CCl4) solutions. Since the diffusion coefficient is related, through the Stokes‐Einstein relation, to the scatterer hydrodynamic radius, R H , we have obtained information about the conformation of fullerene in solution and about the character of the structural and hydrodynamic interaction.

Optical limiting with higher fullerenes

Optical limiting has been investigated for higher fullerenes and compared with C60. The transmission through an aperture placed after solutions of C76, C78, and C84 in tetrahydronaphthalene was measured using Q-switched laser pulses with a wavelength of 532 nm and a pulse width of 8 ns FWHM. Unlike C60, the transmission for these higher fullerene solutions decreased linearly with increasing optical pulse energy. We attribute the linearized optical limiting response to self-defocusing of the optical beam and the absence of excited-state absorption. The ground state absorption spectra for the higher fullerenes suggest their use for optical limiting in the near infrared, and the C84-tetrahydronaphthalene solution was found to be an optical limiter at 1.064 μm.

Stable aqueous dispersions of C60 fullerene by the use of a block copolymer

Stable aqueous solutions of C60 fullerene have been prepared by the use of a well defined block copolymer, namely poly(styrene-b-ethyleneoxide) (PS-b-PEO). The protocol that has been followed involves, in a first step, the co-dissolution of C60 fullerene and diblock copolymer in toluene, a solvent where formation of micelles with the PEO as the core block is favored. In the second step evaporation of toluene at room temperature takes place. Finally re-dissolution of the formed film in water, with simultaneous inversion of the micellar structure (PS containing C60 as the core), is achieved. The aggregates prepared in this way have been characterized by dynamic light scattering as well as scanning electron microscopy. All the applied techniques have indicated the formation of at least two kinds of aggregates, of different sizes, that enclose fullerenes in their cores. This protocol allows the preparation of micellar aggregates, with biocompatible coronas, containing C60 in 1-20% by weight in respect to the PS component.

Study of the Submerged Electric Arc in Hexane in Presence of C60 Fullerene

The effect of the electric arc between graphite electrodes submerged in n‐hexane solutions of C60 fullerene has been studied by electronic absorption spectroscopy, liquid chromatographic analysis (HPLC‐DAD), and FT‐IR spectroscopy. The experimental results show that C60 does not appear able to inhibit the polyynes' formation at the concentration used. Polyynes are formed in large amounts as usual from the graphite arc, and polycyclic aromatic hydrocarbons have been detected as by‐products. Prolonged arcing causes the disappearance of C60 from the solution. There is experimental evidence that C60 undergoes radical addition reactions during the early stages of arcing.

Morphology of C60 nanotubes fabricated by the liquid–liquid interfacial precipitation method

Single crystalline C60 fullerene nanowhiskers are formed by adding isopropyl alcohol gently to fullerene saturated solutions. The method is called the liquid–liquid interfacial precipitation method. In the present study, observation using transmission electron microscope was made for C60 nanowhiskers with hollow structure, i.e. C60 fullerene nanotubes fabricated by the modification of liquid–liquid interfacial precipitation method using pyridine as solvent. After adding isopropyl alcohol to the C60 solution in the glass bottles, ultrasonic dispersion was applied for 1 min and then the bottles were kept at 10°C. Within 24 h, fibrous solids with the length larger than several millimeters and the diameters ranging from submicrons to 1ΰm were precipitated. For the transmission electron microscope study, the samples were pulverized by the ultrasonic dispersion. Under the transmission electron microscope, tubular morphology was usually observed for the whiskers with the diameters larger than 200 nm and hardly observed for those with the diameters smaller than 200 nm; both the C60 fullerene nanotubes and the fullerene C60 nanowhiskers were in crystalline state. Since partly tubular structures were sometimes observed at the end of the C60 fullerene nanowhiskers, the mechanism for the formation of tubular morphology is suggested to be a dissolution process after the crystal growth. When the samples were kept in the glass bottles for several hours after the pulverization, closing of nanotubes at the ends was observed for relatively smaller nanotubes in diameter. For relatively larger nanotubes in diameter, zigzag thinning of tube wall edges was observed. It is thus expected that subsequent growth or dissolution occurred at the end of the pulverized C60 nanotubes, which may be an effective way to control the shape of tubes. The C60 nanotubes presented here will be useful as adsorbents, catalysts, and membranes.

Using Buckyballs To Cut Off Light! Novel Fullerene Materials with Unique Optical Transmission Characteristics

A simple rule governing the light transmission through a fullerene solution or solid is revealed, and a group of fullerene derivatives, glasses, and polymers are found to be able to continuously cut off lights of any wavelength in almost the entire UV and visible spectral region in a predictable and reliable manner. The solutions of aminated fullerenes 1−4 give structureless light transmission spectra well-resembling those of cutoff optical filters. The spectrum bathochromically moves with an increase in concentration (c), whose cutoff wavelength (λc) increases logarithmically with bc, i.e., λc = α log bc + k, where b is the path length and α and k are constants. The spectra are reproducible and stable, changing little over a long period of time. In the solutions, the fullerene molecules aggregate into nanoclusters and their average sizes increase with increasing concentration, suggesting that the formation and growth of the fullerene nanoaggregates are responsible for the concentratochromism. The chromic...

Radical-ion mechanism of optical limiting in fullerene solutions

The effect of photoinduced electron transfer with formation of a radical-ion pair on the characteristics of optical limiting of laser radiation in specially prepared multi-component fullerene solutions is studied. The limitation efficiency in such solutions increases due to absorption of laser radiation by molecules in a metastable state. The experimental results show that the spectral and time optical limiting ranges can be expanded due to formation of radical ions.

Solubilization and Purification of Single-Wall Carbon Nanotubes in Water by in Situ Radical Polymerization of Sodium 4-Styrenesulfonate

Because of outstanding electrical conductivity, thermal conductivity, and mechanical strength, single-wall carbon nanotubes (SWNT) have enormous potential in field emission displays, supercapacitors, molecular computers, and ultrahigh-strength materials.1,2 For optimal performance in most applications, the SWNT should be separated into individual tubes or bundles of only a few tubes. However, the as-prepared SWNT contain impurities of metal catalyst particles and amorphous carbon, and because of strong van der Waals attraction, the SWNT pack into bundles that aggregate into tangled networks. Dissolution of SWNT in water, which is important because of potential biomedical applications and biophysical processing schemes, has been facilitated by surfactants and polymers and by chemical modification.3-11 Here we report a method by which pristine SWNT are solubilized, separated from catalyst particles, and separated from excess dispersant to produce SWNT with grafted poly(sodium 4-styrenesulfonate) (PSS) as an aqueous solution that is stable indefinitely. The method is illustrated in Scheme 1. As in some other functionalizations of SWNT,12-14 the process requires no pretreatment. Debundling and functionalization of SWNT are achieved in one step with no high shear mixing or heavy sonication, which break down SWNT to shorter lengths.5,15 A mixture of 40 mg of pristine HiPco SWNT, 4.0 g of sodium 4-styrenesulfonate (NaSS), and 40 mg of potassium persulfate as a free radical initiator was stirred at 65 °C for 48 h. Catalyst residues and amorphous carbon were removed by gentle centrifugation, and excess unbound PSS was removed by ultrafiltration and ultracentrifugation. The final solution contained 68 mg of SWNT-PSS in 100 mL of water. A detailed procedure is in the Supporting Information. Elemental analysis (CHS) corresponded to 45 wt % of PSS in the SWNT/PSS composite. The 1H NMR spectra of the PSS in the ultrafiltrate and the SWNT-PSS were the same, which suggests that the molecular weight of the attached PSS is high. In control experiments, stirring pristine SWNT with preprepared PSS or with potassium persulfate and sodium p-toluenesulfonate but no monomer by the method used during the polymerization or sonicating in a cleaning bath failed to disperse the SWNT. SWNT also can be dispersed into water by surfactants and by high shear mixing or sonication with PSS, but large excesses of the surfactants or PSS are required.5,15 We attribute the stability of the SWNT with such a small amount of PSS to covalent bonding of the polymer to the SWNT. One attached polymer coil protects a large area of the SWNT surface from van der Waals attraction to other SWNT. By analogy to the addition of polystyryl radicals at diffusion-controlled rates to aggregates of [60]fullerene in solution,16 bundles of SWNT should also react with polymer radicals, although at lesser rate constants because of the lesser strain of the sidewalls of SWNT than of [60]fullerene. Additions of nonpolymeric radicals to SWNT are well-known.17 The distributions of diameters and lengths of the functionalized SWNT were analyzed by tapping mode atomic force microscopy (AFM). Figure 1 shows contour lengths from several hundred nanometers to several micrometers and a representative diameter of 1.2 nm. The range of diameters of pristine HiPco SWNT is 0.61.3 nm.18 Larger area AFM images and transmission electron microscopy (TEM) images at resolution too low to detect individual tubes show bundles of the SWNTPSS that are much smaller than the bundles of the pristine SWNT (Figures S1 and S2). TEM shows none of the catalyst particles that were abundant in the pristine SWNT (Figures S2a and 2b). The Raman spectrum of the functionalized SWNT in Figure 2a shows a disorder (D) band at 1315 cm-1 in addition to the radial breathing band (180-260 cm-1) and tangential (G) band at 1590 cm-1. The intensity of the D band is indicative of the degree of covalent functionalization of the nanotube framework. The radial breathing bands are shifted an average of 5 cm-1 to higher frequency by functionalization with the PSS, which indicates debundling during the polymerization. † Oklahoma State University. ‡ University of Oklahoma. § Rice University. * Corresponding author: e-mail wtford@okstate.edu. Figure 1. AFM height image of SWNT-PSS (3 μm × 3 μm). The arrows point to a 1.2 nm height difference.

Structural Features of Molecular-Colloidal Solutions of C60 Fullerenes in Water by Small-Angle Neutron Scattering

Highly stable and reproducible molecular-colloidal water solutions of C60 fullerenes (FWS) obtained by transferring fullerenes from an organic solution into an aqueous phase with the help of ultrasonic treatment are investigated by means of small-angle neutron scattering (SANS). A polydispersity in the size of detected particles up to 84 nm is revealed. These particles are slightly anisotropic and have a characteristic size of approximately 70 nm. Along with it, there are some indications that a significant part of fullerenes composes particles with the size of the order of 1 nm. The contrast variation based on mixtures of light and heavy water shows that the mean scattering length density of the particles is close to that of the packed fullerene associates as well as that the characteristic size of possible fluctuations of the scattering length density within the particles does not exceed 2 nm. A smooth surface resulting in the Porod law for the scattering is detected. A number of models discussed in the literature are considered with respect to the SANS data.

Photoinduced partial charge transfer between conjugated polymer and fullerene in solutions

Photoinduced charge transfer between a conjugated polymer and C60 and the related processes were investigated in dilute solutions. The substantial fluorescence quenching is correlated with the efficient exciton diffusion within the polymer chains, according to which a sphere-of-action mechanism is proposed. An emissive exciplex was found formed between the conjugated polymer and fullerene in a nonpolar solvent, indicating the occurrence of a photoinduced partial charge transfer process. The low-energy sites in the polymer are believed to play a crucial role in the partial charge transfer. The asymmetry of the exciplex provides a method for evaluating the tendency of photoinduced charge separation between the donor and the acceptor. This method allows screening candidates for photovoltaic applications.

Novel experimental arrangement developed for direct fullerene analysis by electrospray time‐of‐flight mass spectrometry

A novel electrospray setup was found effective for direct analysis of fullerene solutions by electrospray (ES) mass spectrometry. The electrospray capillary needle used for the analysis is equipped with a thin metal (copper, platinum or stainless steel) wire installed inside the capillary. The wire tip protrudes slightly from the capillary end. In this configuration the high electrical field formed by the wire tip stimulates a specific electrospray mode with a fine spray originating from the tip. The correlation of the acquired mass spectra with the magnified view of the spray at the capillary tip was investigated. The effective formation of fullerene ions in both negative and positive ion modes was observed in mass spectra only in the specific case of the electrospray originating from the wire tip. The fullerene di-anions observed in the negative ES mass spectra provide evidence for the electrochemical nature of this process occurring at the ES capillary tip. Observation of fullerene ions in mass spectra obtained using the suggested electrospray arrangement is assumed to be a consequence of the fine spray originating from the sharp metal wire tip. In this case the liquid/metal interface is near the Taylor cone apex.

OPTICAL SPECTROSCOPY AND NONLINEAR TRANSMITTANCE STUDY OF FULLERENE C60 IN MIXTURES WITH 2-CYCLOOCTYLAMINO-5-NITROPYRIDINE (COANP)

Characterization of the infrared absorption spectrum of the solutions of fullerene C 60 with 2-cyclooctylamino-5-nitropyridine additive has been performed with the focus on possible bonding with the amino-group of the additive. No occurrence of such bonding was found at normal conditions. Also no change of optical absorption in visible region and optical limiting of fullerene due to chemical bonding with the additive was detected. The resulting optical properties of the mixture were simply a sum of the properties of the components for a molar proportion of the additive to fullerene approaching 200:1.

Photon correlation spectroscopy and small angle neutron scattering studies on fullerene in solution

The aim of the present contribution is to characterize by photon correlation spectroscopy (PCS) fullerene in solution. We investigate fullerene in solution with organic solvents such as toluene, chloroform and CCl 4, observing that the hydrodynamics radius R H, extracted by the Stokes–Einstein relation, has the same value for all the investigated solutions. For comparison Small Angle Neutron Scattering (SANS) findings on fullerene/CS 2 solutions are presented. By using a spherical model, we are able to obtain the R g 's value and to compare the new value with the theoretical and experimental values existing in literature. The result highlights an almost total independence of the gyration radius on concentration.