Synthesis and characterization of new C60-PPV dyads containing carbazole moiety

New C₆₀ covalently linked PPV derivatives containing carbazole moiety poly{(2,5-di-pentoxyl-phenylene)-1,4-diylvinylene-3,6-[9-(1-azafulleroid-propyl)carbazolenevinylene]} (PPV-AFCAR) were synthesized and characterized. The polymers containing different percentage of C₆₀ were obtained through the percentage of azido unit being controlled by the initial feed ratio. Cyclic voltametric analysis showed that the electronic characteristic remained while it covalently attached to polymer by the cycloaddition reaction. The fluorescences of PPV moieties were strongly quenched due to the presence of fullerene.     

Synthesis of Buckminsterfullerene C60 functionalised core cross-linked star polymers

Buckminsterfullerene C₆₀ core functionalised core cross-linked star (CCS) polymers have been prepared for the first time, using atom transfer radical polymerisation and the arms-first approach. A simple and efficient method is presented which allows the construction of star polymers consisting of a large number of arms and multiple units of C₆₀ per core, far in excess of that obtained previously. The C₆₀ CCS polymers were characterised by gel permeation chromatography (GPC), UV-vis spectroscopy and cyclic voltammetry (CV). GPC revealed that the C₆₀ CCS polymers possess weight average molecular weights (M_w) ranging from 172-411 kDa and up to 30 arms per macromolecule. The average number of molecules of C₆₀ per CCS polymer core was found to be dependent on the C₆₀/PMMA ratio employed and was determined by UV-vis spectroscopy to range up to 6.2. CV revealed that, like pristine C₆₀, the C₆₀ CCS polymers possessed three reversible one electron reductions. However, the reduction potentials were positively shifted, implying that the electron affinity of these macromolecules is higher than pristine C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Recoil tritium-C60 interaction: a channel for endohedral encapsulation of tritium in C60

The introduction of tritium (T), with an initial kinetic energy of 2.7 MeV into the cavity of C₆₀ using recoil implantation is studied in a ⁶Li(n,α)T activated homogenized compound matrix of Li₂CO₃ and C_60. Radioactive endohedral T@C₆₀ could be detected through the liquid scintillation spectrometry coupled with high-pressure liquid chromatography (HPLC). Fast atom bombardment mass spectrometry provided evidence for the retainment of C₆₀ cage as against radiation damage. Solid state temperature-programmed desorption based on evolved gas showed the desorption of ³He gas (as a β⁻ decay product from T) from the endohedral C₆₀ cage at a higher temperature than the T₂ and T₂O trapped species at the defect sites and from the ordered crystallographic network of Li₂CO₃, respectively. The non-isothermal kinetics of the helium desorption, as a function of temperature evidenced a diffusion controlled process.     

Electrochemical behavior of C60 films and C60/lipid films in ionic liquids

Cyclic voltammograms (CVs) of C₆₀ films and C₆₀ embedded in cast films of triple-tailed cationic surfactant solutions and salt-free zero-charged cationic/anionic (catanionic) surfactant vesicles on glassy carbon electrode in a typical room-temperature ionic liquid (RT-IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), were examined. CVs show typically electrochemical oxidation and reduction. The salt-free zero-charged catanionic surfactant bilayer vesicles were determined by freeze-fracture transmission electron microscopy (FF-TEM) images and small-angle X-ray scattering (SAXS) measurements. The cast films of the salt-free zero-charged catanionic surfactant vesicles incorporated C₆₀ molecules were employed to study the electrochemical properties in RT-ILs, which would open new fields for the bulk electronic properties of fullerenes or their derivatives in ionic liquids.     

Synthesis of a hexagonal modification of C60 using cryoextraction

Samples of the hexagonal close-packed phase (h.c.p.) of fullerite C₆₀ with a low (less then 7%) content of more stable face-centered cubic (f.c.c.) phase were synthesized using cryoextraction with n-hexane. X-Ray diffraction analysis and thermogravimetry were applied for characterization of the samples. The role of n-hexane in the formation of the h.c.p. structure is discussed.     

Preparation and spectroscopic properties of chlorofullerenes C60Cl24, C60Cl28, and C60Cl30

We report easy preparation of recently discovered highly chlorinated fullerenes T_h-C₆₀Cl₂₄, C₁-C₆₀Cl₂₈, and D_3d-C₆₀Cl₃₀ in high-temperature reactions of C₆₀ with PCl₅ and ICl. Formation and interconversion of chlorofullerenes was investigated in details for C₆₀-ICl system. C₆₀Cl₂₈ is the least stable chlorofullerene that undergoes rearrangement (accompanied by partial chlorine elimination) into more stable T_h-C₆₀Cl₂₄ under more drastic reaction conditions (increased temperature and time of chlorination). T_h-C₆₀Cl₂₄ yields D_3d-C₆₀Cl₃₀ at temperatures above 220 °C via a sequence of rearrangements and further addition of chlorine. In contrast to the fullerene reaction with ICl, interaction of C₆₀ with PCl₅ is very selective with respect to formation of C₆₀Cl₂₄ in a wide temperature range. Solid-state electronic (UV-Vis) and vibrational (IR) spectra of chlorinated fullerenes C₆₀Cl₂₄, C₆₀Cl₂₈, C₆₀Cl₃₀ and fluorinated fullerenes C₆₀F₁₈ and C₆₀F₃₆ were recorded in the spectral range between 30 and 45,000 cm⁻¹. Raman spectra were also acquired for all investigated compounds. Moreover, molecular geometry of the C₆₀Cl₂₄ and its theoretical IR-absorption spectrum were calculated using B3LYP/STO-3G chemistry model.     

Ethylene physisorption on C60 fullerene

Monte Carlo computer simulation results on the adsorption of ethylene on C₆₀ fullerene are employed to locate the adsorption sites observed for the adsorption of other simple gases. The distributions of molecules according to the gas-solid interaction energy obtained from the simulations are in agreement with experimental results reported in the literature. We focused our attention on the isotherm obtained at 150 K. At this temperature, the molecules with a certain gas-solid energy have been identified and their location employed to find out the adsorption sites. This sort of distribution has been averaged over all the equilibrated configurations generated during the simulation. The results obtained confirm the assignment of adsorption sites previously reported for the adsorption of N₂, Ar, and CO₂. The distribution of molecules over the gas-gas interaction energy is also analyzed and the obtained results suggest that the adsorbed molecules prefer a T-shaped stacking. This conclusion is obtained through the analysis of the distributions with the aid of the gas-gas interaction potential. This observation agrees with recently published results by other authors. The information obtained from the microdensity profiles has also been employed to locate the adsorption sites.     

Evidence for C60 aggregation from solvent effects in [Ps-C60] molecular complex formation

Using a molecular probe positronium (Ps), Ps reaction rate constants (k) with C₆₀, a strong Ps acceptor, are determined for the formation of a donor-acceptor type molecular complex in solvents of varying surface tension (σ) and viscosity (η). Within the framework of Smoluchowski’s theory of diffusion, the calculated Stokes radius for C₆₀ in the different solvents deviated from the monomeric value, implying the existence of aggregated clusters in solution and using transmission electron microscopy, C₆₀ aggregation in carbon disulphide (CS₂) is observed with the formation of spherical fractal clusters of ∼90 nm size with aggregation number 1.7×10⁴ and a fractal dimension of 1.9 at a concentration of 0.5 mM. The fractal dimension of 1.9 revealed the mechanism of aggregation to proceed through a diffusion limited process with the estimated diffusion coefficient and the diffusion length of the aggregated cluster to be 2.27×10⁻⁶ cm²/s and 0.63 nm, respectively.     

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

We dissolve C₆₀, C₇₀ or C₈₄ molecules in benzene and change the fluid state from a gas–liquid two-phase region (25.0 °C) to the critical point (289.0 °C) and from the critical point to the original state (25.0 °C) along the gas–liquid coexistence curve. We find that particle-like and whisker-like nano/micro clusters, which are composed of C₆₀ molecules, deposit on the surface of a silicon substrate placed vertically in C₆₀/benzene solution during the temperature change, whereas no appreciable clusters are detected on the silicon substrate in either C₇₀/benzene or C₈₄/benzene solutions. The clusters, in which fcc lattice structures are formed by C₆₀ molecules, remain stable in the solution. The present result suggests that C₆₀ molecules can be separated and extracted from a mixture of C₆₀, C₇₀ and C₈₄ molecules dissolved in benzene.     

Synthesis of alkali-metal-doped C60 nanotubes

C₆₀ nanotubes have been synthesized by a solution-solution method. After degassing in a dynamic vacuum, the C₆₀ nanotubes doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C₆₀ nanotubes, forming A_xC₆₀ nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results.     

Molecular dynamics simulation of triaxial compression of C60 and C80 solids

Present work investigates the triaxial compression behavior of face-centered cubic C₆₀ and C₈₀ solids using molecular dynamics simulation. Second-generation empirical bond-order potential governs the atomic interactions within a C₆₀ or C₈₀ molecule, whereas van der Waals potential dominates the interactions between C₆₀ or C₈₀ molecules. The equilibrium lattice spacings for C₆₀ and C₈₀ solids are obtained as 14.26 Å and 15.56 Å, respectively. Investigation focuses on the effects of: (i) van der Waals potential, (ii) temperature and (iii) loading rate, on the bulk moduli and hydrostatic stress vs. volumetric strain curves of C₆₀ and C₈₀ solids. Our results showed that these properties are dependent on loading rate and the choice of van der Waals potential, but insensitive to temperature change.     

Fluorination of pressure-polymerized C60 phases

The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C₆₀ towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C₆₀ polymers showed partial decomposition to unfluorinated C₆₀ monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C₆₀F_x}_n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations.     

Cross-sectional structural analysis of C60 nanowhiskers by transmission electron microscopy

Cross-sectional observations of C₆₀ nanowhiskers (C₆₀NWs) were successfully conducted using the focused ion beam (FIB) method. The C₆₀NWs were observed to possess the core-shell structures with porous cores and dense surface thin layers. The size and number of pores decreased from the center to the surface, showing that the densification of C₆₀NWs proceeds from the surface to the center upon drying. A cross-sectional high-resolution transmission electron microscopy (HRTEM) image of a C₆₀NW showed a disordered structure comprising the domains with sizes on the order of 10 nm. The most frequently observed cross-sections were hexagons, reflecting the solvated hexagonal crystal structures of as-grown C₆₀NWs. From the observation of various cross-sectional shapes of C₆₀NWs with different diameters and crystallographic surface analysis, it is suggested that C₆₀NWs grow longer above a critical diameter D_c with the development of low-energy crystal surfaces.     

Stability of hexagonal modification of fullerite C60

Stability of the hcp modification of fullerite C₆₀ under heating, compression, and mechanical grinding was studied. It was established that uniaxial load and mechanical grinding caused transition of the hcp modification into more stable fcc modification, while no transition was observed upon heating or hydrostatic pressure. The results were discussed in terms of the theory of the deformation of solids.