Pentamethylated derivatives of [60]fullerene: X-ray structure of the C60Me5H and ESR spectroscopy evidence for the stable radical C60Me5

Single-crystal X-ray study of 6,9,12,15,18-pentamethyl-1,6,9,12,15,18-hexahydro(C₆₀-I_h)[5,6]fullerene (C₆₀Me₅H) has been reported. In crystal packing, the stacking self-organization of molecules is realized. It is concluded that the formation of such polar columns is a general rule for crystals of C₆₀R₅H independent of the nature of the R group. An ESR spectrum of the stable fullerenyl radical of the cyclopentadienyl-type, C₆₀Me₅, was observed in a sample of the pentamethylated[60]fullerene. Rotation of methyl groups around C-C bonds is restricted on the ESR scale time and therefore protons within each methyl group are non-equivalent.     

Catalyst free,visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C₆₀, followed by SET from the amine to the triplet excited state of C₆₀. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C₆₀ radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.     

Reactions of fullerene C60 with methyl methacrylate radicals: A density functional theory study

We have investigated the stepwise addition of four growing methyl methacrylate (MMA) radicals to C₆₀ fullerene, taking into account all possible types of the formed adducts. This reaction set is a reliable approximation for understanding the MMA polymerization process in the presence of C₆₀ fullerene. We have analyzed the structures of the fullerene-MMA adducts and energy parameters of their formation (heat effects and activation enthalpies). We found that up to three MMA growing radicals are favorably attached to C₆₀ as the fullerene-MMA trisadduct is a stable radical of the allyl type. It is inactive for further radical addition, and the elimination of the hydrogen atom from the growing MMA radical becomes preferable. The effects of steric factors and structures of the products of multiple growing MMA radical additions to C₆₀ on the radical polymerization of MMA in the presence of C₆₀ fullerene are considered.     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Photophysical Properties and Photoinduced Electron Transfer between[60]Fullerene—containing Cyclic Sulphoxide [C60—C60H8SO]and Tetrathiafulvalene（TTF） by Laser Flash Photolysis

Photoinduced electron transfer(PET) processes between C60-C6H8SO and Tetrathiafulvalene(TTF) have been studied by nanosecond laser photolysis.Quantrm yiekds(φet) and rate constants of electron transfer(ket) from TTF to excited triplet state of[60] fullerene-containing cyclic sulphoxide in benzonitrile(BN) have been evaluated by observing the transient absorption bands in the NIR region.With the decay of excited triplet state of [60]fullerene-containing cyclic suplhoxide,the rise of radical anion of [60]fullerene-containing cyclic sulphoxinde is observed.     

η5—π-Complexes of bowl-shaped precursors of C60 fullerene with MCp groups: stability estimates from DFT calculations. Complexes C21H9(MCp) n (n = 1—3; M = Fe,Ru)

Stability of the C₂₁H₉(MCp) _n (n = 1—3; M = Fe, Ru) complexes containing the C₂₁H₉ radical, a representative bowl-shaped precursor of C₆₀ fullerene, was estimated. The carbon skeleton of the radical comprises three pentagonal faces (pent). DFT calculations of the C₂₁H₉ radical and its complexes were carried out with full geometry optimization and the PBE exchange-correlation potential. The energies of the M—pent bonds were found to increase with an increase in n, being only slightly lower than those in the hypothetical icosahedral 12⁵—-C₆₀(MCp)₁₂ complexes and classical sandwich complexes M(Cp)₂. The increased stability of the C₂₁H₉(MCp) _n complexes was explained by greater involvement of the conjugated system of the polyhedral skeleton in the interaction.     

Quantum chemical modeling of the addition reactions of 1‐n‐phenylpropyl radicals to C60 fullerene

Modeling of the addition of various radicals to C₆₀ fullerene is currently an active research area. However, the radicals considered are not able to adequately model polymeric radicals. In this work, we have performed a theoretical study of the possible reactions of C₆₀ fullerene with 1‐n‐phenylpropyl radicals, which are used to model polystyrene radicals. Several possible ways of subsequent addition of up to four 1‐phenylpropyl radicals to C₆₀ have been analyzed, the structures of the intermediates have been defined and thermal properties, such as the activation enthalpies of the corresponding reactions, have been calculated using density functional theory with the approximation of PBE/3z. It is shown that the topology of the spin density distribution on the fullerenyl radical causes regioselectivity for further radical addition. According to the energetic characteristics of the reactions, we assume the possibility of formation of products of one‐, two‐, three‐, and four‐ addition of the growth radical to the fullerene core in radical polymerization of styrene in the presence of C₆₀ fullerene. © 2016 Wiley Periodicals, Inc.     

Reactions of excited fullerenes C60 and C70 studied by mass spectrometry

The transformation of the mass spectra of the laser-desorbed C₆₀ and C₇₀ samples with a successive increase in the laser power, resulting in an increase in the degree of excitation of C₆₀ (C₇₀) and in the number of the particles in the laser plume, was studied. Unusual metastable clusters (C₆₀ + C₂) and (C₇₀ + C₂) are formed even at a minimum laser power and begin to dissociate after 0.5 s following a short (3 ns) laser pulse. An increase in the laser power results in the appearance of peaks of metastable clusters C₆₂ (C₇₂) with the statistically normal lifetime without a delay of dissociation. A further increase in the laser power produces metastable clusters C_60k–2n and C_70k–2n (k = 2, 3) formed without a lag from the dimers and trimers of C₆₀ (C₇₀) by the ejection of a number of C₂ required for the stabilization of the C₂ molecules. The peak of C₇₀ appears simultaneously with the appearance of the (C₆₀)_2–2n peaks upon the laser desorption of pure C₆₀. These findings provide evidence for the growth of the excited fullerene clusters by coalescence and subsequent stabilization due to the ejection of a small fragment rather than by the implantation of C₂ into the fullerene framework. This mechanism of cluster growth should be taken into consideration in modeling fullerene formation in an electric arc reactor, because the clusters formed under these conditions have a substantial excess internal energy.     

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.     

[6,6]‐Open and [6,6]‐Closed Isomers of C70(CF2): Synthesis,Electrochemical and Quantum Chemical Investigation

Novel difluoromethylenated [70]fullerene derivatives, C₇₀(CF₂)_n (n=1–3), were obtained by the reaction of C₇₀ with sodium difluorochloroacetate. Two major products, isomeric C₇₀(CF₂) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C₇₀(CF₂) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C₇₀(CF₂) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C₇₀. In situ ESR spectroelectrochemical investigation of the C₇₀(CF₂) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C₇₀(CF₂) constitutes an interesting example of a redox‐switchable fullerene derivative.     

Unstable Isomer of C90 Fullerene Isolated as Chloro Derivatives,C90(1)Cl10/12

High‐temperature chlorination of C₉₀‐containing fullerene fraction resulted in the isolation and X‐ray structural characterization of C₉₀(1)Cl_10/12, the first derivatives of a relatively unstable isomer D_5h‐C₉₀(1) with a nanotubular shape. In the crystal structure, three isomers of both C₉₀(1)Cl₁₀ and C₉₀(1)Cl₁₂ with similar chlorination patterns co‐crystallize in the same crystallographic site. Thus, in contrast to the previous reports, D_5h‐C₉₀(1) is present, though with a low abundance, in the fullerene soot produced by arc‐discharge method with undoped graphite rods.     

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.     

Oligo‐ and poly(fullerene)s for photovoltaic applications: Modeled electronic behaviors and synthesis

The atom transfer radical addition polymerization (ATRAP) of fullerene to give poly(fullerene)s (PFs) for organic electronics is explored. Quantum chemistry maps the expected electronic behavior of PFs with respect to common electron acceptors, namely fullerene, phenyl‐C₆₁‐butyric acid methyl ester and its bis‐adduct, and mono‐ and bis‐indine‐fullerene derivatives. Surprisingly, it is found that PFs should demonstrate electron affinities and LUMO energy levels closer to the bis‐derivatives than the mono‐adducts, even though only one C₆₀ double‐bond is used in PF chain formation. A self‐consistent library of PFs is synthesized and a correlation between structural characteristics and molecular weights is found. While comonomers with –OC₁₆H₃₃ linear side‐chains lead to the highest known ATRAP molecular weights of 21000 g mol ^{? 1}, like‐for‐like, branched side‐chains permit syntheses of higher molecular weights and more soluble polymers. Of the series, however, PFs with ‐OC₁₂ side‐chains are expected to be of the greatest interest for opto‐electronic applications due to their ease of handling and highest regioregularity. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1345–1355     

C68 Fullerene Isomers,Anions, and their Metallofullerenes: Charge‐Stabilizing Different Isomers

The complete set of 6332 classical isomers of the fullerene C₆₈ as well as several non‐classical isomers is investigated by PM3, and the data for some of the more stable isomers are refined by the DFT‐based methods HCTH and B3LYP. C₂:0112 possesses the lowest energy of all the neutral isomers and it prevails in a wide range of temperatures. Among the fullerene ions modeled, C₆₈^2?, C₆₈^4? and C₆₈^6?, the isomers C₆₈^2?(C_s:0064), C₆₈^4?(C_2v:0008), and C₆₈^6?(D₃:0009) respectively, are predicted to be the most stable. This reveals that the pentagon adjacency penalty rule (PAPR) does not necessarily apply to the charged fullerene cages. The vertical electron affinities of the neutral C_s:0064, C_2v:0008, and D₃:0009 isomers are 3.41, 3.29, and 3.10 eV, respectively, suggesting that they are good electron acceptors. The predicted complexation energy, that is, the adiabatic binding energy between the cage and encapsulated cluster, of Sc₂C₂@C₆₈(C_2v:0008) is ?6.95 eV, thus greatly releasing the strain of its parent fullerene (C_2v:0008). Essentially, C₆₈ fullerene isomers are charge‐stabilized. Thus, inducing charge facilitates the isolation of the different isomers. Further investigations show that the steric effect of the encaged cluster should also be an important factor to stabilize the C₆₈ fullerenes effectively.     

High‐Potential Perfluorinated Phthalocyanine–Fullerene Dyads for Generation of High‐Energy Charge‐Separated States: Formation and Photoinduced Electron‐Transfer Studies

High oxidation potential perfluorinated zinc phthalocyanines (ZnF_nPcs) are synthesised and their spectroscopic, redox, and light‐induced electron‐transfer properties investigated systematically by forming donor–acceptor dyads through metal–ligand axial coordination of fullerene (C₆₀) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine‐ (Py) and phenylimidazole‐functionalised fullerene (C₆₀Im) derivatives to the zinc centre of the F_nPcs. The determined binding constants, K, in o‐dichlorobenzene for the 1:1 complexes are in the order of 10⁴ to 10⁵ M ^?1; nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6‐31G* method. The HOMO and LUMO levels are located on the Pc and C₆₀ entities, respectively; this suggests the formation of ZnF_nPc^.+–C₆₀Im^.? and ZnF_nPc^.+–C₆₀Py^.? (n=0, 8 or 16) intra‐supramolecular charge‐separated states during electron transfer. Electrochemical studies on the ZnPc–C₆₀ dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge‐separated states. The energy of the charge‐separated state for dyads composed of ZnF_nPc is higher than that of normal ZnPc–C₆₀ dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar‐energy harvesting and optoelectronic device building applications.     

Pressure effect on heterogeneous trifluoromethylation of fullerenes and its application

The first systematic study of heterogeneous fullerene trifluoromethylation using an innovative gradient-temperature gas-solid reactor revealed a significant effect of CF₃I pressure on the conversion of C₆₀ and C₇₀ into trifluoromethylated products and on the range of fullerene(CF₃)_n compositions that were obtained. The design of the reactor allowed us to lower the residence times of fullerene(CF₃)_n species in the hot zone which resulted in the significant differences in relative isomeric distributions as compared to the earlier methods. For the first time, gram quantities of trifluoromethylated fullerenes were prepared using the new reactor, and the selective synthesis of a single-isomer C₆₀(CF₃)₂ was developed. The relative reactivity of C₇₀ as a CF₃ radical scavenger was found to be much lower than that of C₆₀, especially at an early radical addition stage, which led to the cost-efficient synthesis of C₆₀(CF₃)₂ from a fullerene extract.     

Effect of fullerene on radical polymerization of vinyl acetate

The effect of fullerene (C₆₀) on the radical polymerization of vinyl acetate (VAc) with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was investigated kinetically and by means of ESR. C₆₀ was found to act as an effective inhibitor in the present polymerization. All C₆₀ molecules used were incorporated into poly(VAc) during polymerization. The relationship of induction period and initiation rate reveals that a C₆₀ molecule can trap 15 radicals formed in the polymerization system. The polymerization rate (R_p) after the induction period is given by R_p = k [MAIB]^0.6 [VAc]^2.0 (60 °C), which is similar to that observed in the absence of C₆₀. Stable fullerene radical (C) was observed in the polymerization system by ESR. The C concentration increased with time and was then saturated. The saturation time well corresponds to the induction period observed in the polymerization. About 20% of C₆₀ molecules added could survive as stable C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2572–2578, 2000     

Base-promoted reaction of C60Cl6 with thioamides: an access to [60]fullereno[1,9-d] thiazoles

Regioselective reaction of C₆₀Cl₆ with thioamides via a radical annulation to form fullereno thiazole derivatives is reported. The reaction is promoted by K₂CO₃, which might deprotonate thioamide to initiate a single electron transfer from thioamide anion to C₆₀Cl₆. The experiments with various thioamides establish the proposed base-promoted reaction as a facile route for synthesis of fullereno fused thiazole derivatives starting from C₆₀Cl₆, a prevalent synthon in fullerene chemistry. In addition, the tunable electrochemical properties of the fullereno thiazole products have been investigated for their potential photovoltaic application.     

Insulin Surface Acoustic Wave Immunosensor Based on Immobilized C60/Anti‐Insulin Antibody

Immobilized fullerene C₆₀/anti‐insulin antibody was prepared and applied in shear horizontal surface acoustic wave (SH‐SAW) immunosensors to detect insulin in aqueous solutions. The immobilizations of anti‐insulin onto fullerene were studied through a C₆₀/PVC coated SH‐SAW sensor system in liquid. The partially irreversible frequency response for an anti‐insulin antibody was observed by the desorption study, which implied that fullerene could chemically react with anti‐insulin. C₆₀/anti‐insulin coating materials were successfully prepared and identified with an FTIR spectrometer. The C₆₀/anti‐insulin coated SH‐SAW immunosensors were developed and applied for detection of insulin in aqueous solutions. Within the range of normal human insulin concentration, the SH‐SAW immunosensors immobilized with C₆₀/anti‐insulin exhibited linear frequency responses to the concentration of insulin with a sensitivity of 130 Hz/pM. The SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin showed a detection limit of 0.58 pM for insulin in aqueous solution. The interference of various common bio‐species in human blood, e.g. urea, ascorbic acid, tyrosine, and metal ions, to the SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin for insulin was investigated. These common bio‐species interferences showed nearly no interference to the SAW immunosensors coated with C₆₀/anti‐insulin. The reproducibility of the SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin for insulin was also investigated and is discussed.     

Sc2O@Td(19151)‐C76: Hindered Cluster Motion inside a Tetrahedral Carbon Cage Probed by Crystallographic and Computational Studies

A new cluster fullerene, Sc₂O@T_d(19151)‐C₇₆, has been isolated and characterized by mass spectrometry, UV/Vis/NIR absorption, ⁴⁵Sc NMR spectroscopy, cyclic voltammetry, and single‐crystal X‐ray diffraction. The crystallographic analysis unambiguously assigned the cage structure as T_d(19151)‐C₇₆, which is the first tetrahedral fullerene cage characterized by single‐crystal X‐ray diffraction. This study also demonstrated that the Sc₂O cluster has a much smaller Sc?O?Sc angle than that of Sc₂O@C_s(6)‐C₈₂ and the Sc₂O unit is fully ordered inside the T_d(19151)‐C₇₆ cage. Computational studies further revealed that the cluster motion of the Sc₂O is more restrained in the T_d(19151)‐C₇₆ cage than that in the C_s(6)‐C₈₂ cage. These results suggest that cage size affects not only the shapes but also the cluster motion inside fullerene cages.