Solution ozonolysis of C<Subscript>70</Subscript>: stable products and chemiluminescence

For the first time the total and relative contents of the stable ozonolysis products of fullerene C₇₀ solutions were identified by IR spectroscopy and elemental and chemical analyses. At the 100% conversion of C₇₀ a mixture of products corresponding to the empirical formula C₇₀O_14.3H_0.21 (epoxides: polyketones: polyesters: secondary fullerene ozonides (SFOZ): acids = 1.07: 6: 6: 0.21: 1.02) is formed. The content of polyketones, polyesters, acids, and SFOZ increases during the whole ozonolysis time (1 h). The number of oxygen atoms in epoxides C₇₀O _n (n = 1–4) is lower than that in epoxides C₆₀O _n (n = 1–6) formed by the ozonolysis of fullerene C₆₀. The kinetic curve of accumulation of epoxides C₇₀O _n (n = 1–4) passes through a maximum, which is observed 0.5 min after the beginning of ozonolysis. No epoxides were identified among the products 3.5 min after the ozonolysis. The photoluminescence (PL) (λ_max = 645 and 685 nm) of fullerene polyketones in glassy EtO₂/EtOH solutions frozen at 77 K was observed. This PL is much brighter, than that of polyketones formed upon the ozonolysis of fullerenes C₆₀. For the first time the chemiluminescence (CL) was detected and studied upon the ozonolysis of C₇₀ solutions at 300 K. The CL emitters are excited states of fullerene polyketones. The CL spectrum is partially overlapped with the known CL spectrum appeared upon the ozonolysis of C₆₀ (λ_max = 685 nm) but contains the greater number of maxima (λ_max = 645 and 685 nm), which is related to a lower symmetry of the C₇₀ oxidation products.     

Formation of secondary fullerene ozonides in the ozonolysis of C60 solutions and chemiluminescence upon their hydrolysis

The formation of secondary fullerene ozonides (SFOs) in the ozonolysis of C₆₀ solutions in CCl₄ has reliably been determined for the first time; SFOs are accumulated during the whole ozonolysis time as a suspension in CCl₄. Hydrolysis of the SFOs results in chemiluminescence (CL) (I _max = 2.65·10⁸ photon s⁻¹ mL⁻¹), whose spectra contain maxima at 558, 608, and 685 nm. The most probable CL emitters are excited fullerene polyketones. Hydrogen peroxide was identified as a stable hydrolysis product of the SFOs by the color reaction with diphenylcarbazide and CL arisen upon the addition of an aqueous solution of FeSO₄·9H₂O to the hydrolyzate of the SFO. Chemiluminescence upon hydrolysis is a selective test for SFOs and allows one to find them in a complex mixture of the ozonolysis products of C₆₀. The rate constant and activation energy of SFO hydrolysis were determined from the kinetic measurements of CL. For SFO hydrolysis several probable reactions were proposed, including the formation of the CL emitters, and their heat effects were estimated using the PM3/RHF and AM1/RHF semiempirical methods for one-and two-cage model structures of SFOs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1322–1329, August, 2006.     

Fluorescence Quenching Study of Zinc Bisporphyrins by Fulleropyrrolidines and Their N-Oxides

Novel phenylene-bridged zinc bisporphyrins （1-4）, fulleropyrrolidines （C60-m, C60-h） and their N-oxides （C60-mo, C60-ho） were synthesized. The fluorescence quenching processes of bisporphyrins in toluene solution by fulleropyrrolidines and their N-oxides were investigated by steady-state fluorescence spectra. The fluorescence quenching constants proved that the fluorescence quenching ability was decreased as reduction of the pyrrolidine functional groups of fullerene surface： C60-h〉C60-m〉C60, and the fluorescence quenching ability was increased about 1.3-7.4 times by utilizing fulleropyrrolidine N-oxides （C60-mo, C60-ho） compared to fulleropyrrolidine compounds （C60-m, C60-h）. The results revealed photoinduced electron transfer （PET） efficiency between bispor-phyrin and fullerene derivatives could be tunable by change of functional groups on fullerene surface.     

Synthesis, structures, and properties of new thiophosphorylated fullerenopyrrolidines. First example of the Pishchimuka reaction in fullerene derivatives

The reactions of fullerene C₆₀ with thiophosphorylated mono-or dialdehydes and N-methylglycine in toluene afforded new thiophosphorylated fullerenopyrrolidines, including those containing the free aldehyde group. The purity and compositions of the reaction products were confirmed by MALDI-TOF mass spectrometry and HPLC. The structures of the reaction products were established by two-dimensional homo-and heterocorrelation NMR experi-ments. The properties of the products were studied by cyclic voltammetry and quantum chemical methods. The Pishchimuka rearrangement in thiophosphorylated derivatives of fullerenopyrrolidines was performed for the first time, and thiol esters of phosphonic acids of fullerenopyrrolidines were prepared. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 489–497, March, 2006.     

Quenching of electronically excited Ln3+* ions by C60 fullerene

Quenching of electronically excited states of Ln^3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)₃·H₂O (Ln = Tb, Eu) complexes by C₆₀ fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C₆₀ concentration obtained from data on the decrease in the photoluminescence intensity and Ln^3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln^3+* to C₆₀ fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln^3+* photoluminescence spectra with the C₆₀ absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C₆₀ in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.     

Products of reaction of fullerene C60 with fuming sulfuric acid studied by IR and ESR spectroscopy

The products of reaction of fullerene C₆₀ with fuming sulfuric acid were precipitated from a solution with water and triethylamine and studied by IR and ESR spectroscopies. A comparison of the obtained data with the spectra of fullerene, dimers C₁₂₀ and C₁₂₀O, and fullerene polymers produced by photopolymerization allowed the conclusion that fullerene polymers were formed by fullerene oxidation with fuming sulfuric acid.     

Selective reduction of fullerene C60 by metals in neutral and alkaline media. Interaction of C60 with KOH

The reduction of fullerene C₆₀ by Zn and Mg in DMF was studied both in the presence and absence of KOH. Fullerene C₆₀ was reduced in these systems to form the C₆₀ ^n– (n = 1, 2, and 3) anions. The anions were detected by optical and ESR spectroscopies. It was found that Mg reduced C₆₀ to the monoanion, Mg/KOH and Zn reduced C₆₀ to the dianion, and Zn/KOH reduced C₆₀ to the trianion. Like KCN, potassium hydroxide adds to fullerene upon interaction with C₆₀ in DMF. The reaction of C₆₀ with KOH in benzonitrile was accompanied by the generation of the fullerene monoanion. A possible mechanism of the formation of fullerene monoanions in the presence of KOH is discussed. The degradation of the C₆₀ ^n– anions in air was studied.     

Fullerene C60 Trichloromethylation Through CCl4 Plasmalysis or Sonolysis

The trichloromethylation of C₆₀ fullerene was achieved either under plasmalysis conditions, i.e. by arcing a solution of C₆₀ in CCl₄ between two graphite electrodes, or by sonolysis of C₆₀ in CCl₄. The resulting products were studied by UV–VIS and FT-IR spectroscopy as well as by thermogravimetric analysis in comparison to the trichloromethyl adducts formed by radiolysis or photolysis of C₆₀ in CCl₄. A reference study on the plasmalysis of pure CCl₄ has revealed the formation of carbon soot and hexachlorobenzene. The formation of the latter compound was suppressed when C₆₀ was present in CCl₄.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Reactions of chlorofullerene C60Cl6 with N-substituted piperazines

It was shown for the first time that reactions of C₆₀ halides with aliphatic amines provide a facile route for the synthesis of aminofullerenes, valuable precursors for water-soluble cationic fullerene derivatives. Particularly, chlorofullerene C₆₀Cl₆ and N-substituted piperazines were investigated in this work. It was shown that substitution of chlorine atoms in C₆₀Cl₆ by amine groups is accompanied by partial elimination of addends from the fullerene cage that yields mixtures of di-, tetra- and, hexaaminofullerenes as the final products. Separation of these mixtures by column chromatography resulted in isolation of pure 1,4-diaminofullerenes; this procedure gives much higher and more reproducible yields of these compounds than direct oxidative photoaddition of secondary amines to C₆₀. ESI mass spectrometry and NMR spectroscopy data showed that hexaaminofullerene isomers are major components in inseparable mixtures of polyaddition products. Polyaminofullerenes were found to be readily soluble in aqueous acids; these solutions are unstable because of a facile substitution of protonated amine groups with hydroxyls. Nevertheless, the use of other amine substrates in the investigated reaction can potentially allow the preparation of more stable water-soluble cationic fullerene derivatives for biological studies.     

Low-Cost Synthesis of Fullerene Derivatives

Refined mixed fullerenes were used as a reagent in known organic reactions instead of the pure fullerene C₆₀ with aim to find an alternative, low-cost method for the synthesis of fullerene derivatives potentially exhibiting photoconductive properties. The isolation of C₆₀ or C₇₀ in clean form without admixtures requires the use of large quantities of toluene or other nonpolar solvents, polluting the environment and multiplying the production cost. 1,3-Dipolar cycloaddition of azomethine ylide to fullerite was chosen because this reaction is one of the most widely used for fullerene functionalization, producing material possibly presenting photoinducing behavior. The data showed that the use of the cheaper mixed fullerenes instead of pure C₆₀ leads to the isolation of the same expected products with similar yields. The photoelectric properties of mixed fullerenes and their organic derivatives were also examined. A slightly semiconductive behavior was confirmed as well as a noticeable photoresponse.

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Fullerene‐Based Macro‐Heterocycle Prepared through Selective Incorporation of Three N and Two O Atoms into C60

A 14‐membered heterocycle is created on the C₆₀ cage skeleton through a multistep procedure. Key steps involve repeated PCl₅‐induced hydroxylamino N?O bond cleavage leading to insertion of nitrogen atoms, and also piperidine‐induced peroxo O?O bond cleavage leading to insertion of oxygen atoms. The hetero atoms form one pyrrole, two pyran, and one diazepine rings in conjunction with the C₆₀ skeleton carbon atoms. The fullerene‐based macrocycle showed unique reactivities towards fluoride ion and copper salts.     

Oxidation of fullerene C<Subscript>60</Subscript> with the system aluminum tri-<Emphasis Type="Italic">tert</Emphasis>-butoxide—<Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide

Oxidation of fullerene C₆₀ with the system aluminum tri-tert-butoxide-tert-butyl hydroperoxide, in which electron-excited dioxygen is generated, gave a complex mixture of fullerene oxides C₆₀O _x (x = 1–6). The pathways of their formation were proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 296–300, February, 2008.     

The reaction of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with fullerene C60

Heating (100 °C, toluene) or photolysis (Nd³⁺ : YAG laser, = 532 mil, benzonitrile) of a mixture of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (Hantsch ester) (1) and fullerene C₆₀ under anaerobic conditions results in the formation of fullerene hydrogenation products and ethyl 2,6-dimethylpyridine-3,5-dicarboxylate, which is the product of dehydrogenation of1, identified by IR spectroscopy and mass spectrometry. The triplet state of C₆₀ is quenched by the Hantsch ester.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2531–2534, October, 1996.     

Preparation and study of hydrides of fullerenes C60 and C70

Fullerene hydrides were prepared by hydrogenation of fullerences C₆₀ and C₇₀ using proton transfer from 9,10-dihydroanthracene to fullerene and were studied by mass spectrometry (electron impact, field desorption), IR, UV, and¹H and¹³C NMR spectroscopy. The main product of the hydrogenation of C₆₀ is C₆₀H₃₆, which is sufficiently stable. Hydrogenation of fullerene C₇₀ gives a series of polyhydrides C₇₀H _n (n=36–46), and the main product is C₇₀H₃₆. The dehydrogenation of C₆₀H₃₆ by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is not quantitative and results in the formation of fullerene derivatives along with C₆₀. The comparison of the IR and¹H and¹³C NMR spectral data for solid C₆₀H₃₆ with the theoretical calculations suggests that the fullerene hydride has aT-symmetric structure and contains four isolated benzenoid rings located at tetrahedral positions on the surface of the closed skeleton of the molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 4, pp. 671–678, April, 1997.     

Solvent effect on the kinetics of the free-radical polymerization of styrene in the presence of fullerene C60

The induction period in the kinetic curves of styrene polymerization in the presence of fullerene C₆₀ was found to increase significantly at a solvent (benzene, toluene, ortho-dichlorobenzene, CCl₄) concentration of ≥50 mol %. The free-radical polymerization rates of styrene in the presence of fullerene C₆₀ and solvents, the ratio of chain propagation and termination rate constants k _p /k ₀ ^1/2 , and the stoichiometric inhibition coefficient were determined.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

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.     

Features of the oxidation of C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerites as studied by IR spectroscopy

Features of the oxidation of C₆₀ and C₇₀ fullerites were studied by infrared spectroscopy. It was shown that for C₆₀ fullerite, the presence of toluene residue reduces the temperature at which oxidation starts. The form of the toluene (solvate or nonsolvate) is not important. A low-frequency shift in the valence C-O-C vibrations of C₇₀ fullerene due to local steric strains was discovered.     

Electrochemical formation and properties of two-component films of transition metal complexes and C60 or C70

The electrochemically active polymers have been formed during electro-reduction carried out in solution containing fullerenes, C₆₀ or C₇₀, and transition metal complexes of Pd(II), Pt(II), Rh(III), and Ir(I). In these films, fullerene moieties are covalently bounded to transition metal atoms (Pd and Pt) or their complexes (Rh and Ir) to form a polymeric network. All films exhibit electrochemical activity at negative potentials due to the fullerene cages reduction process. For all studied metal complexes, yields of formation of films containing C₇₀ are higher than yields of electrodeposition of their C₆₀ analogs. C₇₀ /M films also exhibit higher porosity in comparison to C₆₀/M layers. The differences in film morphology and efficiency of polymer formation are responsible for differences in electrochemical responses of these films in acetonitrile containing supporting electrolyte only. C₇₀/M films shows more reversible voltammeric behavior in negative potential range. They also show higher potential range of electrochemical stability. Processes of film formation and electrochemical properties of polymers depend on the transition metal ions or atoms bonding fullerene cages into polymeric network. The highest efficiency of polymerization was observed for fullerene/Pd and fullerene/Rh films. In the case of fullerene/Pd films, the charge transfer processes related to the fullerene moieties reduction in negative potential range exhibit the best reversibility among all of the studied systems. Capacitance performances of C₆₀/Pd and C₇₀/Pd films deposited on the porous Au/quartz electrode were also compared. Capacitance properties of both films are significantly affected by the conditions of electropolymerization. Only a fraction of the film having a direct contact with solution contributes to pseudocapacitance. Capacitance properties of these films also depend on the size of cations of supporting electrolyte. The C₇₀/Pd film exhibits much better capacitance performance comparison to C₆₀/Pd polymer.