C60 Dimer Research Articles

Reversible dimerization of [5,6]-C60O.

The recently discovered [5,6]-open isomer of C(60)O has been found to undergo facile dimerization to form a new C(2) symmetry isomer of C(120)O(2), which can be photodissociated with relatively high efficiency to regenerate monomeric [5,6]-C(60)O. High yield dimerization of [5,6]-C(60)O proceeds spontaneously in toluene solution near room temperature. On the basis of (13)C NMR spectroscopy, ab initio quantum computations, and HPLC retention patterns, the resulting C(120)O(2) product has been deduced to be a nonpolar dimer of C(2) symmetry in which the C(60)O moieties are linked by two single bonds between sp(3)-hybridized carbon atoms adjacent to oxygen atoms. Photophysical properties of this dimer have also been measured and compared to those of C(120), the [2 + 2]-dimer of C(60). The ground-state absorption spectrum of C(120)O(2) in toluene is slightly red-shifted relative to that of C(120), with a distinctive peak at 329 nm and an S(1)-S(0) origin band at 704 nm. Its fluorescence spectrum shows two major peaks at 718 and 793 nm. In room-temperature toluene, the measured triplet state intrinsic lifetime of this C(120)O(2) isomer is 34 +/- 2 micros, a value somewhat shorter than that of C(120) (44 micros). C(120)O(2) undergoes photodissociation from its triplet state to regenerate monomeric [5,6]-C(60)O with quantum yields of 2.5% at 24 degrees C and 43% at 70 degrees C. It can therefore serve as a stable reactant for photolytic production of [5,6]-C(60)O. As a simple fullerene adduct that reacts under mild conditions, [5,6]-C(60)O may prove useful in special synthetic applications. Solutions of [5,6]-C(60)O are also unique because they can provide mixtures of a fullerene monomer and its dimer in a dynamic balance controllable by adjustment of concentration, temperature, and optical irradiation.

Calorimetric study of crystalline dimer and polymerized phases of fullerene C60

By high precision dynamic calorimetry the temperature dependences of heat capacity C p 0 = f ( T ) for dimer of C 60 , orthorhombic and rhombohedral polymerized phases of fullerene C 60 were determined in the temperature range 300–650 K. Besides, endothermic transformations caused by the depolymerization of the polymerized (dimeric) phases of C 60 were studied and their standard thermodynamic characteristics a temperature interval, enthalpy, entropy and Gibbs function were analyzed. Based on the thermodynamic and oscillation spectroscopy data, it was established that the depolymerization proceeds completely and the products formed are a monomer fcc phase of C 60 . From the data of the present work and the heat capacity values measured by us earlier in a low-temperature interval, the thermodynamic functions of the substances, viz. the heat capacity C p 0 ( T ), enthalpy H 0 ( T )− H 0 (0), entropy S 0 ( T )− S 0 (0) and Gibbs function G 0 ( T )− H 0 (0), were calculated over the range from T →0 to (380–490) K at standard pressure. The results were discussed taking into account literature data. A sequence of a relative thermodynamic stability at 298.15 K and atmosphere pressure of the crystalline polymerized C 60 phases was arranged.

Turning Peapods into Double-Walled Carbon Nanotubes

AbstractThe formation pathway to double-walled carbon nanotubes (DWNTs) from C60 encased within single-walled carbon nanotubes (peapods) is introduced in this article. Onedimensionally arranged C60 molecules coalesce gradually within the nanotube and change the structure to C60 dimers, trimers, tetramers, and so on as intermediates. In addition to these interesting structural transformations visualized in the nanotube space, the nanotube itself is very stable, and this structural stability is very important when using the interior of the nanotube as the reaction field or the space for molecular storage. In terms of optical absorption, the lowest energy absorption band for DWNTs, ∼0.65 eV, shows broadened and downshifted features as compared with that of SWNTs.We expect that this opticalabsorption feature will lead to the use of DWNTs in absorbing devices for optical-fiber communications. The Raman experiments give new information about the frequency of the C-C stretching-mode vibration for nanotubes with diameters of less than ∼1 nm, which shows a decrease in vibration frequency with decreasing tube diameter. This diameter dependence can be explained by an admixture of sp3 character in the C-C interaction. Therefore, the electronic and mechanical properties of nanotubes with diameters of <1 nm are expected to be different from nanotubes of the ∼1-nm-diameter class, and we anticipate that new phenomena will occur in small-diameter tubes.

Nitrogen Radio Frequency Plasma Processing of Fullerenes

Nitrogen radio frequency (rf) plasma processing of C60 in the formation of the nitrogen endohedral complex (N@C60) and C60N adducts was fully examined with spectroscopic methodology and molecular orbital calculations. N@C60 formation was achieved using an internal parallel plate electrode type of capacitively coupled nitrogen rf plasma,1 whereas this was impossible when using an external ring electrode type of capacitively coupled rf nitrogen plasma. This experimental observation suggests that the formation of N@C60 in the internal parallel plate plasma system stems from the steep charge gradient around the rf cathode electrode induced by the self-bias effect, which promotes accelerated collisions of N+ with C60. Another important nitrogen rf plasma-induced process is the formation of C60N adducts. The formation and relative stabilities of internal and external C60N adducts and N@C60 were fully examined with the aid of MO calculations at a semiempirical approximation level, and the calculation was further extended to the plasma processing of C70. The calculation suggested that a C60 polymer is abundantly formed in a nitrogen rf plasma in which the nitrogen plays an important role in the intermolecular cross-linking of C60, derived from the radical addition and/or recombination reaction of the C60N adduct. The polymer formation was clearly supported by the observation of the peaks attributable to the nitrogen-containing C60 dimers in the time-of-flight mass spectra observed on the carbonaceous deposits formed in the nitrogen rf plasma.

Mechanochemical Synthesis of a Novel C60 Dimer Connected by a Germanium Bridge and a Single Bond.

ChemInformVolume 35, Issue 1 Isocyclic Compounds Mechanochemical Synthesis of a Novel C60 Dimer Connected by a Germanium Bridge and a Single Bond. Yasujiro Murata, Yasujiro Murata Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this authorAihong Han, Aihong Han Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this authorKoichi Komatsu, Koichi Komatsu Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this author Yasujiro Murata, Yasujiro Murata Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this authorAihong Han, Aihong Han Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this authorKoichi Komatsu, Koichi Komatsu Inst. Chem. Res., Kyoto Univ., Uji, Kyoto 611, JapanSearch for more papers by this author First published: 18 December 2003 https://doi.org/10.1002/chin.200401089AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume35, Issue1January 6, 2004 RelatedInformation

Photoemission spectral analysis of fullerene films polymerized by argon plasma treatment

Photoemission spectral analysis was carried out on plasma polymerized fullerene (C60) films prepared by sublimating C60 under an argon plasma. In the photoemission analysis, the overall distribution of the shallow valence band states of the plasma-treated C60 was compared with pristine C60. These changes suggest that the pi conjugation of the shallow valence band states of two C60 molecules is induced by polymerization during the plasma treatment. To investigate the changes in the onset of the shallow valence band states brought about by polymerization, the orbital energy levels in C60 dimers were examined using the semiempirical AM-1 method. Calculations showed that the highest occupied molecular orbital levels of the dimers were shallower than that of C60.

Photoconductivity of solid fullerene C60 film modified by laser irradiation

An improvement on photoconductivity of fullerene C60 film has been observed after modification of laser irradiation at room temperature or at about 100°C because some dimer, trimer and polymer of C60 have been formed under the laser irradiation. This leads to some change of charge transfer (CT) states and reduction on resistance to transport of photocarriers. Another important reason for the great increase on photoconductivity of C60 modified by laser irradiation at about 100°C (373 K) is thermal effect. Thermal treatment of the laser modified C60 thin film at above 100°C (373 K) for a few hours makes a great improvement on its photoconductivity because this treatment reduces trap centers for photocarriers resulted from an increase on its crystallinity and some change on its morphology. Oxygen has a great effect on photoconductivity reduction of the laser modified C60 thin film.

Single-crystal structural study of the pressure-temperature-induced dimerization of C $\mathsf{_{60}}$

We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 single-crystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.

C60 fullerene and its molecular complexes under axial and shear deformation

We have studied the pristine C60 and its molecular complexes with the organicdonors bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) andtetramethyltetraselenafulvalene (TMTSF) by means of ESR and Ramanspectroscopy at high pressure. The important changes in the ESR signal of C60were observed under axial pressure combined with shear deformation. It is shownthat the treatment at a anisotropic pressure of 4 GPa results in a reduction in thesymmetry of the C60 molecule and the formation of radicals. Treatment of themolecular complex of (ET)2·C60 at a pressure of ∼4.5 GPa and a temperature of150°C leads to the formation of C60 dimers. The Raman spectra of themolecular complex C60·TMTSF·2(CS2) were measured in situ at ambienttemperature and pressures up to 9.5 GPa. The pressure behaviour of the Ramanpeaks reveals singularity at 5.0 ± 0.5 GPa related to the softening andsplitting of some of the phonon modes. The residual softening of the Ag (2)mode is the same as in the case of KC60, which may be an indication that thetransition has a charge-transfer character, resulting in the formation of theC60−1anionic state charge-transfer complex.

Mechanochemical Synthesis of a Novel C60 Dimer Connected by a Silicon Bridge and a Single Bond.

Abstract A novel C60 dimer connected by a germanium bridge and a single bond was synthesized by the mechanochemical solid-state reaction using a high-speed vibration milling technique. The structural characterization was made by the 1H and 13C NMR, APCI mass, and UV-vis spectroscopy, and the presence of the electronic interaction between the two C60 cages was demonstrated by the electrochemical method.

Formation and isomerization of C120: considerations of symmetry, kinetics and thermodynamics

AbstractAn orbital‐symmetry analysis (OCAMS) of the dimerization of C60 to its stable (D2h) dimer 1 indicates that the reaction cannot proceed along a totally symmetric pathway but that the reaction‐path symmetry must be reduced at least to C2h. Similarly, one‐step conversion of 1 to its isomer 3 (also D2h), which has been proposed as an intermediate for the intercalation of helium atoms into C60, is also limited to a C2h pathway. As neither of these pathways is geometrically appropriate, it is predicted that both reactions proceed stepwise. Semi‐empirical computations (AM1/UHF) confirmed this prediction: in the dimerization, a transoid singlet biradical (2) is formed, and then closes readily to 1 after rotation about its newly formed bond. An intermediate (4) of C2v symmetry is detected along the pathway for isomerization of 1 to 3. THERMO computations (AM1/RHF) indicated that both dimers should be in thermal equilibrium with C60 at moderate temperatures, but that their equilibrium concentrations in the gas phase would be exceedingly small under thermally accessible conditions. The limitations of the computational method employed and their bearing on the reliability of the results are discussed. Copyright © 2002 John Wiley & Sons, Ltd.

Synthesis, X-ray structure, and properties of the singly bonded C60 dimer having diethoxyphosphorylmethyl groups utilizing the chemistry of C60(2-).

[reaction: see text] A singly bonded C60 dimer having a diethoxyphosphorylmethyl group on each C60 cage was obtained by the reaction of C60(2-) dianion with diethyl iodomethylphosphonate followed by the treatment with iodine. The precise structure of the dimer was determined for the first time by X-ray crystallography, and its homolytic dissociation as well as spectroscopic and electrochemical properties were clarified.

Reversible dimerization of C60 molecules in the crystal structure of the bis(arene)chromium fulleride [Cr(C7H8)]2C60.

Bis(toluene)chromium fulleride, [Cr(C(7)H(8))(2)]C(60), has been synthesized as a black microcrystalline powder from C(60) and [Cr(C(7)H(8))(2)] in toluene. [Cr(C(7)H(8))(2)]C(60) is an ionic compound in which the fullerene is negatively charged and the bis(toluene)chromium molecule positively charged. At T = 250 K a reversible first-order phase transition from a primitive cubic high-temperature phase to a triclinic low-temperature phase occurs. The high-temperature phase [Pm3 macro m, a = 9.9840 (1) A, T = 295 K] is composed of dynamically disordered fulleride anions and bis(toluene)chromium(I) cations in a CsCl-type arrangement. The triclinic low-temperature modification [P1 macro, a = 13.6414 (8), b = 13.8338 (7), c = 13.8548 (7) A, alpha = 91.830 (3), beta = 116.776 (2), gamma = 119.333 (2) degrees, T = 235 K] consists of ordered C(60) dimers and two crystallographically distinct bis(toluene)chromium entities.

Determination of the reaction rate constant and activation energy for pressure-induced 2+2 cycloaddition of the C60 fullerene

The kinetics of fullerene solid-phase dimerization proceeding through the 2+2 cycloaddition of C60 at a pressure of 1.5 GPa is investigated by vibrational spectroscopy in the temperature range 373–473 K. Kinetic curves for the formation of (C60)2 dimers are obtained using the analytical band at 796 cm−1 in the IR spectra of the (C60)2 dimer molecule. Under the assumption that the pressure-induced dimerization of C60 is an irreversible second-order reaction, the reaction rate constants are determined at different temperatures. The activation energy and the preexponential factor are found to be equal to 134±6 kJ/mol and (1.74±0.24)×1014 s−1, respectively.

Triplet State Dissociation of C120, the Dimer of C60

Triplet State Dissociation of C₁₂₀, the Dimer of C₆₀

Dimerization of C60: Symmetry Considerations

Orbital-symmetry analysis (OCAMS) of the dimerization of C60via [2+2] cycloaddition indicates that the reactant monomers should approach one another along a pathway in which C2h symmetry is conserved. Point-by-point computations (AM1/UHF) confirm this prediction: a low-energy pathway leads to a single-bonded dimer 2 with C2h symmetry. Closure to the stable D2h dimer 1 is effected by relatively facile rotation about the single bond. A similar symmetry analysis was performed on a second isomer 3 with D2h symmetry, the moieties of which are linked by two two-atom chains. It raises the possibility that 3, the so-called `window' isomer, may be interconvertible with 1 along a pathway that retains Ci (S2) symmetry. Although the computational results indicate that C60 is in thermal equilibrium with its stable dimer 1 at moderate temperatures, the latter is not observed in the gas phase for thermodynamic reasons. According to THERMO computations (AM1/RHF), the equilibrium is shifted strongly towards the monomer pair at temperatures where vaporization of the solid C60 is observed (>400°).

Theoretical Studies of the Structures and Stabilities of Dumbell-like Fullerene Dimers: C121

Three possible isomers of C121, i.e. [6,6]−[6,6] (1, D2d), [6,6]−[6,5] (2, Cs), and [6,5]−[6,5] (3, C2), were examined by ab initio MO calculations and a hybrid method of Hartree−Fock and DFT. The geometry optimizations gave closed-bond structures (methanofullerene) for all 6,6-bridge and open-bond structures (homofullerene) for all 6,5-bridge structures. Calculations of energies revealed that 2 is the most stable, while 1 is slightly less stable than 2 by Δ(ΔGf°(298.15 K)) = 2.521 kJ mol-1, and 3 is much less stable than 2 by Δ(ΔGf°(298.15 K)) = 21.777 kJ mol-1. That is explained by the difference of energy between a methanofullerene and a homofullerene, and the strain energy of the spirojunction at the central bridging carbon atom of C121. The predicted IR and Raman spectra of 1, 2, and 3 indicate that all of 1, 2, and 3 have the same six cage−cage vibrational modes. By comparing the predicted 13C NMR spectra of 1, 2, and 3, and the experimental 13C NMR spectra of C121 isolated by HPLC, we concluded that the structure of the C121 is 2, which is the first C60 dimer that has both a methanofullerene and a homofullerene moiety.

Properties of Photoexcited States of C180, a Triangle Trimer of C60

Abstract Photophysical properties of C180 “cis-2/cis-2/cis-2”, a triangle triad of C60, were investigated by various methods including a transient absorption spectroscopy. Fluorescence and triplet absorption spectra were similar to those of C120 (C60 dimer) and other 1, 2-adducts of C60. On the other hand, short fluorescence lifetime and small quantum yield for the intersystem crossing process indicate that the photophysical properties of C180 are affected by the non-radiative process in the singlet excited state.

Photophysical and Photochemical Properties of C120O, a C60 Dimer Linked by a Saturated Furan Ring

Photophysical and photochemical properties of C120O, a C60 dimer linked by a saturated furan ring, have been characterized by various time-resolved spectroscopic methods. A steady-state absorption band of C120O is blue-shifted compared with those of 1,2-adducts of C60 (C60R). The fluorescence lifetime and quantum yield were estimated to be 1.7 ns and 8.7 × 10-4, respectively, which are similar to those of C60R and C120. On the other hand, the lifetime of the triplet excited state (3C120O*) was estimated to be 0.16 μs, which is quite shorter than those of C60 (55 μs), C60R (24−29 μs), and C120 (23 μs). Furthermore, the quantum yield for the intersystem crossing process was as low as 0.48. These unusual triplet properties of 3C120O* indicate that the triplet excited C60 moiety in 3C120O* was influenced by an adjacent π-electron system of another C60 moiety in the ground state. Ground-state reduction of C120O was observed in the reaction with tetrakis(dimethylamino)ethylene, indicating the stable radical anion formation of C120O, in contrast to the unstable radical anion of C120. Photoinduced electron transfer from 1,4-diazabicyclo[2.2.2]octane to 3C120O* was confirmed by an observation of the transient absorption band of the radical anion of C120O in the near-IR region. Oxidation of C120O was also performed by employing a cosensitization method. The reaction rate constants of the both photoinduced reduction and oxidation were slightly smaller than those of C60 and C60R.

Pressure-induced dimerization kinetics of fullerene C60

Dimerization kinetics was studied for fullerene C60 by IR spectroscopy at a pressure of 1.5 GPa in the temperature range 373–473 K. The kinetic curves for the formation of a dimer (C60)2 were obtained using its analytical IR band at 796 cm−1. Under the assumption that pressure-induced C60 dimerization is a second-order irreversible reaction, the reaction rate constants were determined at different temperatures. The corresponding activation energy and preexponential factor were found to be 134±6 kJ/mol and (1.74± 0.24)×1014 s−1, respectively. The specific features of the solid-phase C60 dimerization in simple cubic and face-centered cubic fullerite phases are discussed.