Chromatographic properties of fullerene modified with liquid crystal p, p′-azoxyphenetol

Stationary phases for gas chromatography based on liquid crystal p,p′-azoxyphenetol applied onto Chromaton N-AW bearing a layer of C₆₀ fullerene were studied. The thermodynamic properties of the adsorption of n-alkanes and n-alcohols on the mesogen surface were studied at low occupancies. Test mixtures of structural isomers of substituted benzene and polycyclic aromatic hydrocarbons were analyzed in a wide temperature range from 100 to 240°C.     

Synthesis and characteristics of [60]fullerene polysiloxane stationary phase for capillary gas chromatography

A new type of fullerene-containing polysiloxane was synthesized by reacting [60]fullerene with azidopropyl polysiloxane directly. The polysiloxanes have been used successfully as stationary phases for capillary gas chromatography. They displayed high column efficiency, wide operational temperature and high thermostability, and exhibited unique selectivity for many organic substances, such as alkanes, alcohols, ketones and aromatic compounds. The stationary phase was especially suitable for separation of high boiling-point compounds like polycyclic aromatic hydrocarbons and phthalic esters, etc. It was also found that some alcoholic or aromatic positional isomers could be well separated on the column. The influence of the fullerene content on the separation was also investigated.     

Effect of nature of organic solvent on the absorption spectrum of C60 fullerene

Absorption spectrums of C₆₀ fullerene in 10 various organic solvents in the range of 300–620 nm was studied. In all the solvents the C₆₀ fullerene has four absorption maxima in the range under study. When an aromatic solvent has an ionization potential of 8.1 eV or lower a new additional absorption band appears in the absorption spectrum of C₆₀ fullerene, caused by the formation of a charge-transfer complex (CTC) of the solvent and C₆₀ fullerene.     

C60 fullerene, as ultraefficient quencher of singlet-excited adamantanone generated in photo-and chemiexcitation

Quenching of the fluorescence of Ad=O and its singlet-exited state (¹Ad=O*) generated in chemiluminescent reaction of adamantylideneadamantane-1,2-dioxetane (AdOOAd) termolysis by C₆₀ fullerene was detected and investigated. The “quenching efficiency-C₆₀ concentration” plots obtained from the decrease in the fluorescence and chemiluminescence intensities obey the Stern-Volmer law. The bimolecular rate constants (k _bim) were determined and the overlap integrals of the Ad=O fluorescence spectra with the C₆₀ absorption spectra (∫ _Ov) were calculated. Based on the nonconstant k _bim/∫_Ov ratios for different singlet-exited energy donors obtained for the ¹PAH*-C₆₀ systems (PAH are polycyclic aromatic hydrocarbons) and ¹Ad=O*-C₆₀, a conclusion is drawn that quenching of ¹Ad=O* by C₆₀ fullerene is a result of inductive-resonant singlet-singlet (major contribution) and exchange-resonant singlet-triplet (minor contribution) energy transfer. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1044–1046, May, 2007.     

An analysis of the structure of fullerene C70 by quantum-chemical methods

Hartree-Fock and density functional theory calculations showed that the B, C, D, and E fullerene C₇₀ cycles were not coplanar. The interrelation between acoplanarity and pyramidality of atoms was studied. The bond lengths, valence and torsion angles, and charges and chemical shifts of fullerene C₇₀ atoms were jointly analyzed. Most attention was given to the acoplanarity of hexagons E in the aromatic belt.     

Topochemical solid-state reactions and problems of selective synthesis of fullerene derivatives

The characteristic features of polyaddition of small functional groups to fullerenes are considered. The review summarizes the results of experimental and theoretical studies of topochemical solid-state fluorination of fullerene C₆₀ with inorganic variable-valence transition metal fluorides and elemental fluorine in chemically active matrices. The thermodynamic and kinetic aspects of the reactions and the factors responsible for selectivity are considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 32–50, January, 2005.     

Unique Separation Behavior of a C60 Fullerene‐Bonded Silica Monolith Prepared by an Effective Thermal Coupling Agent

Herein, we report a newly developed C₆₀ fullerene‐bonded silica monolith in a capillary with unique retention behavior due to the structure of C₆₀ fullerene. N‐Hydroxysuccinimide (NHS)‐conjugated C₆₀ fullerene was successfully synthesized by a thermal coupling agent, perfluorophenyl azide (PFPA), and assigned by spectroscopic analyses. Then, NHS‐PFPA‐C₆₀ fullerene was attached onto the surface of a silica monolith in a capillary. The capillary provided specific separation ability for polycyclic aromatic hydrocarbons in liquid chromatography by an effective π–π interaction. Furthermore, corannulene, which has a hemispherical structure, was selectively retained in the capillary based on the specific structural recognition due to the spherical C₆₀ fullerene. This is the first report revealing the spherical recognition ability by C₆₀ fullerene in liquid chromatographic separation.     

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine linked with fullerene

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine-fullerene dyad 2 has been described. While nonfluorinated phthalocyanine-fullerene dyad 1 showed an efficient property of intramolecular photoinduced electron transfer, dyad 2, regardless of its covalently linked dyad system, appears not to show any electronic communication between fullerene and phthalocyanine. This observation is presumably due to the strong electron withdrawing nature of 12 trifluoroethoxy groups; fluorine leads phthalocyanine to become an acceptor whose electronic accepting property is equivalent to that of fullerene. This is a unique example that fluorine can terminate electronic communication in the covalently fullerene-phthalocyanine dyad system.     

Investigation of reactions between [60]fullerene and molecular fluorine in a CoF2 matrix

Fluorination of [60]fullerene dispersed in a CoF₂ matrix with molecular fluorine was studied. The reaction was carried out in a mass spectrometer. The partial pressures of volatile products were continuously monitored at the constant fluorine inlet. The differences in the activation barriers of subsequent fluorination from C₆₀ to C₆₀F₄₄ were estimated. The conditions, at which C₆₀F₁₈ and C₆₀F₃₆ were formed selectively, were found. Based on a comparison between the fluorination of pure C₆₀ and C₆₀ dispersed in CoF₂ matrix, the role of a matrix in the selectivity of this process was elucidated.     

Effect of C<Subscript>60</Subscript> fullerene on the boiling point of its solutions in some aromatic solvents

Concentration dependences of the boiling points T _b ^exp of C₆₀ fullerene solutions in four aromatic solvents were determined. For benzene and p-xylene, processing of the increasing dependence in terms of the Raoult law enabled estimation of the cooperativity parameters of the interaction between fullerene and solvent molecules.     

Aromatic character of Oh-C24N24. A cavernous nitride fullerene bearing N4-macrocycle motifs

Spherical fullerenes offer noteworthy structures usually involving six- and five-membered faces, with application in technological issues. In this sense, cavernous spherical-like structures bearing larger holes provide interesting examples for further understanding of structure-properties relationship. Here, we explored the magnetic response of a proposed cavernous nitride fullerene, C₂₄N₂₄, which has a O_h-symmetry with six N₄-macrocyclic and eight 1,3,5-triazine faces displaying 48-π electrons. C₂₄N₂₄ exhibits a local aromatic behavior owing to the contrasting antiaromatic response of the N₄-macrocyclic faces and the aromatic character of the 1,3,5-triazine faces. Thus, the overall structure is ascribed as a local aromatic species, where the triazine faces exhibit the characteristic shielding cone for aromatic rings. Furthermore, the constructive combination of local shielding cones in C₂₄N₂₄ delivers a related shielding-cone response, as expected for a perfect aromatic cage. Hence, the local aromatic/nonaromatic/antiaromatic sections exhibit an additive or subtractive interaction, leading to a characteristic response inherent to the nature of the spherical cage. We expect that further study of the interplay between different aromatic and antiaromatic faces in fullerene-like cages can deliver interesting pseudo-aromatic or pseudo-antiaromatic spherical species.     

Face-to-face C6F5-[60]fullerene interaction for ordering fullerene molecules and application to thin-film organic photovoltaics

Treatment of [60]fullerene with potassium methylnaphthalenide and excess C(6)F(5)CH(2)Br afforded 1,4-bis(pentafluorobenzyl)[60]fullerene, the study of which showed that there is a face-to-face interaction between [60]fullerene and a perfluoro aromatic ring, allowing the molecule to be utilized for high-performance organic photovoltaic devices.     

Corannulene Chalcogenides

The introduction of chalcogen atoms into a polycyclic aromatic hydrocarbon structure is an established method to tune material properties. In the context of corannulene (C₂₀H₁₀), a fragment of fullerene C₆₀, such structural adjustments have given rise to an emerging class of functional and responsive molecular materials. In this minireview, our aim is to discuss the synthesis and properties of such chalcogen (sulfur, selenium, and tellurium) derivatives of corannulene.     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Extraction of fullerene mixture from fullerene soot with organic solvents

Investigation of extraction of fullerene mixture from the fullerene soot obtained by plasma erosion of graphite rod in helium atmosphere with different solvents such as α-chloronaphthalene, o-dichlorobenzene, o-xylene, toluene, benzene, carbon tetrachloride, and n-hexane at 25°C was carried out. Completeness and effectiveness of extraction as well as relative content of light (C₆₀, C₇₀) and heavy (C₇₆, C₇₈, C₈₄) fullerenes in the extract were evaluated.     

Effect of fullerene C<Subscript>60</Subscript> on the structure and mechanical characteristics of polyethylene: Technological aspect

On the basis of the literature data, a retrospective analysis of the thermodynamic characteristics of dissolution of fullerene C₆₀ in a series of single-ring aromatic solvents is presented. The effect of the molecular structure of a solvent on its dissolving capacity with respect to fullerene is studied. The parameter of the boiling temperature of the solvent normalized to its molecular mass is introduced. The correlation of this parameter with the dissolving capacity of the solvent is discussed. Special emphasis is placed on the effect of halogen-containing solvents on the dissolution of fullerene and indirectly on the development of the mechanical characteristics of films prepared from common solutions of fullerene and low-density polyethylene. For comparison, the films prepared from PE melts modified with low concentrations of fullerene are considered. The film structure is studied via X-ray analysis, optical microscopy, AFM, small-angle scattering of linearly polarized light, and DSC. The films with the maximum strength are prepared from solutions in halogen-containing solvents at a concentration of fullerene below 1 wt %. In this case, spherulites are 5–10 times smaller than those in the films cast from solutions in other solvents. In the films cast from common solutions of PE and fullerene in bromobenzene, crystal solvates C₆₀ · 2C₆H₅Br are formed. It seems that the formation of the crystal solvates binds the residual solvent and thus affects the mechanical behavior of the films, thereby eliminating the plasticizing effect of residual bromobenzene. Localization of fullerene in various regions of the supramolecular structure of the films is discussed, and the morphology of the separating regions of the crystal solvate fullerene phase is analyzed.     

DSC investigation of the polystyrene films filled with fullerene

Polystyrene composite films with different content of C₆₀?+?C₇₀ fullerene mix have been obtained from o-xylene solutions. The mass fraction of fullerene was varied from 0.01 to 0.1 mass%. The glass transition temperatures and specific heat capacities in range of 293?C423?K have been determined for the films by DSC method. The plasticization of the polymer is observed in thermal properties of the films under influence of small fullerene additions. The values of T _g and C _P decrease and thermal coefficient of heat capacity b increase as fullerene content increases up to 0.02 mass%. The effect of interaction between polymer and fullerene molecules on thermal properties becomes evident at higher fullerene content in range from 0.02 to 0.1 mass%. At this the values of T _g and C _P increase and b coefficient decrease with increasing content of fullerene. Concentration dependence of C _P and b values is less steep for polymer composite films in elastic state at temperatures above T _g. Molecular interactions in the composites are discussed in view of our-self and literature data.     

Lewis acid-assisted nucleophilic substitution of fullerene epoxide

[Structure: see text] A 1,4-bis(phenyl)-1,4-dihydro[60]fullerene resulting from an efficient nucleophilic substitution has been obtained by reaction of a fullerene epoxide, C60O, with nucleophilic aromatic compounds in the presence of boron trifluoride etherate as a Lewis acid.     

Photoreactions between [60]fullerene and various aromatic tertiary amines

The photoreactions of [60]fullerene with aromatic tertiary amines such as N,N-dimethylaniline and N,N-dimethyl-1-naphthylamine gave two or three types of [60]fullerene adducts. The reaction efficiency in the series of p-substituted N,N-dimethylanilines remarkably increased with increasing electron-donating properties of aromatic tertiary amines employed.     

Analytical potential of fullerene as adsorbent for organic and organometallic compounds from aqueous solutions

In this work, the analytical potential of C60 fullerene as a sorbent for organic and organometallic compounds from aqueous solutions was studied for the first time. Fullerene adsorbs many types of organic substances (e.g., N-methylcarbamates, phenols, polycyclic aromatic hydrocarbons, amines) with efficiencies that depend on the nature of the compound concerned and never exceed 60%. Conventional sorbents such as XAD-2 or polyurethane foam are more efficient than C60 for this purpose. Organometallic compounds (viz. metalocenes and organoleads) are quantitatively adsorbed on C60 via the formation of neutral complexes or chelates; the adsorption constant is dramatically increased by the use of classical reagents such as pyrrolidinedithiocarbamate or diethyldithiocarbamate. A complementary comparative study on the adsorption of organometallic complexes on RP-C18 and silica gel 100, among others, showed C60 to be superior as sorbent. All experiments in this work were carried out by using continuous flow configurations and gas chromatography-atomic absorption spectrometry techniques.