Fullerene Dimers Research Articles

An Algebraic Analysis of Vibrational IR Spectra of Fullerene Dimer [(C70)2]2+ by Using U(2) Lie Algebra

An Algebraic Analysis of Vibrational IR Spectra of Fullerene Dimer [(C₇₀)₂]²⁺ by Using U(2) Lie Algebra

(Invited) Fullerene Cation-Mediated Demethylation/Cyclization to 5- and 7-Membered Cyclo[60]Fullerene Derivatives

This presentation reports on new cyclization reaction by using fullerene cation to obtain 5- and 7-membered cyclo[60]fullerene derivatives. In this talk, mainly we focused on development of methodology to obtain new fullerene derivatives utilizing cationic fullerene intermediate, and discussed reaction mechanism involving fullerene cation which can be coordinated by benzene rings or the oxygen atom, affording migration of the phenyl groups and activation of the methyl group of the methoxy group for demethylative cyclization.[1] Single-bonded fullerene dimers, (C60R)2 (R = (2-methoxyphenyl)dimethylsilylmethyl, (isopropoxy)dimethylsilylmethyl, and 2-methoxy-5-methylphenyl), afforded fullerene derivative cations (RC60 +) in the presence of an oxidant (I2, CuCl2, or CuBr2), leading to 5- and 7-membered cyclo[60]fullerene derivatives such as cyclo[60]fullerenes containing a Si–O bond, cyclo[60]fullerenes containing a C60–O bond, and dihydrobenzofurano[60]fullerene. The reaction mechanism involved thermal homolytic cleavage to give fullerene radical, oxidation of the radical to generate fullerene cation, and then demethylative cyclization in which the fullerene cationic centers interact with an aromatic group or the oxygen atoms of methoxy groups to produce the cyclized products. Obtained cyclo[60]fullerene derivatives were used in bulk-heterojunctoin organic solar cells and showed moderate power conversion efficiency and respectable open-circuit voltage. [1] Y. Matsuo, K. Ogumi, Y. Zhang, H. Okada, T. Nakagawa, H. Ueno, A. Gocho, E. Nakamura, J. Mater. Chem. A, in press. Figure 1

Silver(I)-Mediated Modification, Dimerization, and Polymerization of an Open-Cage Fullerene.

The reactions of the open-cage fullerene, MMK-9, with an open 12-membered ring on its surface and silver(I) salts have been examined. The structure of MMK-9 itself has been determined by single-crystal X-ray diffraction. MMK-9 reacts with silver trifluoroacetate in air to form the dimer, {MMK-9(OCH3)5Ag(AgO2CCF3)}2. Remarkably, five MeO groups have added to the surface of the open cage in a pattern that surrounds a pentagon immediately adjacent to the opening in the cage. Dioxygen has been implicated as the oxidant in this unusual addition of five groups to the open cage. Two silver ions connected to each other by a short argentophillic interaction reside at the core of the centrosymmetric dimer. The reaction of silver nitrate with MMK-9 yields the crystalline polymer, [{MMK-9(OCH3)5Ag(AgOCH3)}2·H2O]n. This polymer consists of dimeric {MMK-9(OCH3)5Ag}2 units that are connected into strands through silver ions, which are chelated by the amine functions of one open cage and bound in η2-fashion to a pair of carbon atoms on an adjacent open cage.

Raman study of the temperature-induced decomposition of the fullerene dimers C120

Raman spectra of the C120 crystalline fullerene dimers, synthesized by high-pressure/high-temperature (HPHT) treatment of the C60 fullerite, were measured at ambient and elevated temperatures (T>130°C) in order to study the kinetics of their thermal decomposition. Measurements exhibit an intensity decrease of the dimer-related pentagon pinch (PP) mode and an increase of the monomer’s one. The relative intensity of the dimer’s PP mode decreases exponentially with the thermal treatment time and becomes faster at elevated temperatures. The activation energy EA of the dimer decomposition, obtained from the Arrhenius dependence of the exponential decay time constant on temperature, is (1.71±0.06)eV.

(Invited) Charge Generation in Bulk-Heterojunctions Based on Fullerene Heterodimers

Organic photovoltaic (OPV) cells remain to be one of the most attractive approaches for utilization of solar energy showing gradually increasing conversion efficiency of 11%. Significant efforts were directed to the improvement of the electron donating (polymer) part of the bulk-heterojunction (BHJ) solar cells. On the other hand, less advancement has been made on the acceptor side. Recently, a few examples of soluble fullerene hetero- and homodimers based on C60 and C70 linked through chemical bridges have been developed and were shown to competitively perform in solar cells. However, the electronic structure of these fullerene dimers is not well understood. Thus, it is not known how those two fullerene molecules are electronically coupled in the dimer, i.e., whether the excited neutral state or anion state of the dimer is delocalized over the whole dimer or still localized only on one fullerene cage. We have experimentally shown that fullerene molecules in the C60-C70-heterodimer in solid films are strongly electronically coupled and the spin densities of the anion and excited triplet states are delocalized over the whole molecular dimer. However, in the frozen diluted solutions the fullerene cages in heterodimers are instead weakly coupled. The anion and triplet states of the dimers show the signature of individual C60 or C70 molecules. We explain this phenomenon by the presence of two different conformers in the solid-state films and in frozen solutions. Since the electronic coupling between fullerene molecules in the dimers is influenced by their packing in the blends, our observation provides insight into how to tune the electronic properties of the fullerene acceptors by proper adjustment of molecular bridge structures between fullerene cages to fix the desired conformation, which in turn may have an impact on the charge carrier generation efficiency in organic solar cells.

Potential energy of H2 inside the C116 fullerene dimerization: An atomic analysis

DFT method has proved useful for its ability to provide an atomic analysis of the dimerization of fullerene molecules. Such atomic analysis may provide information that is not available by experimental methods. Here, the structures of possible three isomers of C116 fullerene dimerization obtained from two C58 fullerene cages have been optimized using DFT method at the B3LYP/6-31G(d,p) level of theory. The orientation of C58 fullerene and bond reorganization during the dimerization process have been studied. The transition structures and energy barriers between the three isomers are obtained. The potential energies of the H2 molecule motion along and perpendicular to the axial dimer with possible rotational angles are calculated. Also, the 13C NMR chemical shifts and electron density distribution have been applied to distinguish between the C58 fullerene cages and the three isomers of C116 fullerene dimerization. Our results show that the C116 fullerene dimerization could be considered to be good candidate for hydrogen storage.

Effective magnetic coupling with strong spin frustration in (Ph3MeP+)(C60˙−) and reversible C60˙− dimerization in (Ph3MeP+)(C60˙−)·C6H5CN. Effect of solvent on structure and properties

Antiferromagnetic coupling of spins with spin frustration and fullerene dimerization are observed for (Ph3MeP+)(C60˙−) (left) and (Ph3MeP+)(C60˙−)·C6H5CN (right).

Morphological and electrical control of fullerene dimerization determines organic photovoltaic stability

Light induced fullerene dimerization is controlled by both the fullerene and polymer morphology of organic solar cells.

Charge transfer complexes of fullerenes containing C₆₀˙⁻ and C₇₀˙⁻ radical anions with paramagnetic Co(II)(dppe)₂Cl⁺ cations (dppe: 1,2-bis(diphenylphosphino)ethane).

The reduction of Co(II)(dppe)Cl2 with sodium fluorenone ketyl produces a red solution containing the Co(I) species. The dissolution of C60 in the obtained solution followed by the precipitation of crystals with hexane yields a salt {Co(I)(dppe)2(+)}(C60˙(-))·2C6H4Cl2 and a novel complex {Co(dppe)2Cl}(C60) (). With C70, only the crystals of {Co(dppe)2Cl}(C70)·0.5C6H4Cl2 () are formed. Complex contains zig-zag fullerene chains whereas closely packed double chains are formed from fullerenes in . According to the optical spectra and magnetic data charge transfer occurs in both and with the formation of the Co(II)(dppe)2Cl(+) cations and the C60˙(-) or C70˙(-) radical anions. In spite of the close packing in crystals, C60˙(-) or C70˙(-) retain their monomeric form at least down to 100 K. The effective magnetic moments of and of 1.98 and 2.27μB at 300 K, respectively, do not attain the value of 2.45μB expected for the system with two non-interacting S = 1/2 spins at full charge transfer to fullerenes. Most probably diamagnetic {Co(I)(dppe)2Cl}(0) and neutral fullerenes are partially preserved in the samples which can explain the weak magnetic coupling of spins and the absence of fullerene dimerization in both complexes. The EPR spectra of and show asymmetric signals approximated by several lines with g-factors ranging from 2.0009 to 2.3325. These signals originate from the exchange interaction between the paramagnetic Co(II)(dppe)2Cl(+) cations and the fullerene˙(-) radical anions.

The Influence of Alkali Metal Cation Size on the Formation and Dissociation of Crown Ether Fullerene Dimers in Electrospray Mass Spectrometry

Crown ether fullerenes, C60H(cr – H), form two different dimers in electrospray ionization mass spectrometry, a noncovalently bound, metal-bridged dimer [C60H(cr – H)]2M+, and a singly bonded fullerene dimer of the type (cr – H)–C60–C60–(cr – H)Mnn+, with n = 1, 2. In this work, the dependence of both the formation and the dissociation of these dimers on the respective sizes of the crown ether moiety (12cr4, 15cr5, 18cr6) and of the alkali metal ion (M+ = Li+, Na+, K+, Rb+, Cs+) is studied. The size ratio of crown ether cavity to metal cation size has a profound influence on the formation of the noncovalent dimers, [C60H(cr – H)]2M+. These are only formed if the cation is larger than the crown ether cavity. Also, the doubly charged, covalent dimers [C60(cr – H)]2M22+ show a dependence on the size ratio. The proposed formation mechanism involves the recombination of two C60(cr – H)M•+ radical cations, which can only occur if the repulsion between the two charges is sufficiently reduced by encapsulating the...

A V-shaped polyaromatic amphiphile: solubilization of various nanocarbons in water and enhanced photostability.

Nanocarbons are synthetic carbon-rich compounds with polyaromatic frameworks that have lately attracted attention as emerging functional materials. However, their extreme hydrophobicity and aggregation peculiarity, besides their shape and size diversities, precluded their study in solution, especially in "green" water. More convenient and general solubilizing methods of nanocarbon frameworks are required by using non-covalent supramolecular interactions. Here we report a protocol for solubilizing a wide range of nanocarbons, that is, fullerenes (C60 , C70 , C84 , and C120 ), polyarenes (tetracene, pentacene, perylene, coronene, and hexabenzocoronene), and carbon nanotubes (single-walled and multi-walled CNTs), in water through manual grinding with V-shaped polyaromatic amphiphiles. The obtained aqueous nanocomposites are composed of nanocarbons encircled by the polyaromatic frameworks of the amphiphiles through multiple aromatic-aromatic interactions. Notably, the encapsulated photosensitive nanocarbons, such as tetracene, pentacene, and fullerene dimer, exhibit unusual stability toward UV/Vis light.

Formation of {Co(dppe)}2{μ2-η(2):η(2)-η(2):η(2)-[(C60)2]} Dimers Bonded by Single C-C Bonds and Bridging η(2)-Coordinated Cobalt Atoms.

Coordination of two bridging cobalt atoms to fullerenes by the η(2) type in {Co(dppe)}2{μ2-η(2):η(2)-η(2):η(2)-[(C60)2]}·3C6H4Cl2 [1; dppe = 1,2-bis(diphenylphosphino)ethane] triggers fullerene dimerization with the formation of two intercage C-C bonds of 1.571(4) Å length. Coordination-induced fullerene dimerization opens a path to the design of fullerene structures bonded by both covalent C-C bonds and η(2)-coordination-bridged metal atoms.

Supramolecular photovoltaic cells utilizing inclusion complexes composed of Li+@C60 and cyclic porphyrin dimer

We have newly constructed supramolecular photovoltaic cells using inclusion complexes of lithium-ion-encapsulated [60]fullerene ( Li +@ C 60) and cyclic porphyrin dimers (M-CPDPy, M = H 4 and Ni 2). First, supramolecular inclusion complexes of Li +@ C 60 and M-CPDPy were prepared in MeCN/PhCN (3/1, v/v) by rapid injection method. The molecular aggregates with spherical nanoparticles demonstrated a broad absorption property in the visible region. The macroscopic structures were also estimated to be ca. 200 nm in diameter by transmission electron microscope (TEM) and dynamic light scattering (DLS) measurements. The photoelectrochemical solar cells composed of these assemblies on nanostructured SnO 2 electrode were fabricated by electrophoretic deposition method. The photoelectrochemical behavior of the nanostructured SnO 2 film of supramolecular nanoassemblies of Li +@ C 60 and M-CPDPy is significantly higher than those of the single component films ( Li +@ C 60 or M-CPDPy) and supramolecular inclusion complexes of pristine C 60 and M-CPDPy.

钠原子连接的C60富勒烯二聚物的等离激元激发

钠原子连接的C60富勒烯二聚物的等离激元激发

Hiding and recovering electrons in a dimetallic endohedral fullerene: air-stable products from radical additions.

Fullerenyl radicals can be generated by addition of a free radical to a fullerene surface, by nucleophilic addition followed by one-electron oxidation, or by thermal dissociation of singly bonded fullerene dimers. However, fullerenyl radicals are usually very reactive and generally cannot be isolated. On the contrary, we have found that the reactions of the dimetallic endofullerenes, La2@Ih-C80 and La2@D5h-C80, with 3-chloro-5,6-diphenyltriazine resulted in mono-addition of the triazinyl radical to the fullerene cages to yield isolable fullerenyl radicals. The unusual stability of these fullerenyl radicals arises from the confinement of the unpaired electron to an internal, metal-metal bonding orbital. Accordingly, the fullerene cage protects the radical center from other reactive species. Furthermore, we demonstrate that the fullerenyl radical adduct of La2@Ih-C80 reacts with toluene to afford additional benzylation. Interestingly, the benzylated derivative is diamagnetic in solution, while it forms a paramagnetic dimer when crystallized.

ChemInform Abstract: Polarizability as a Landmark Property for Fullerene Chemistry and Materials Science

AbstractReview: 257 refs.

Formation of Singly Bonded Fullerene Dimers in Electrospray Mass Spectrometry

The K+ adducts of the crown ether–[60]fullerene conjugate of the form (12cr4 – H)–C60–H are investigated by electrospray mass spectrometry (ESI-MS), focusing on the dimeric species produced from two different solvent mixtures. A singly bonded fullerene dimer of the type (12cr4 – H)–C60–C60–(12cr4 – H)K+ is generated in aprotic solvents, while in protic solvents, a metal-bridged, noncovalently bound dimer predominates. The dimerization reaction is proposed to occur during the ESI process via the radical intermediate (12cr4 – H)–C60•. The fragmentation behavior of the different dimers is studied by collision-induced dissociation (CID), showing characteristic product ions for each species.

1,8-Diazabicycloundecene-mediated Separation of Singly Bonded Fullerene Dimer and Application to Facile Preparation of C61H2

We investigated the complexation of a singly bonded fullerene dimer [C60(CH2SiMe2OiPr)]2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in order to develop facile separation of a fullerene derivative from the mixture of fullerene and its derivatives without the use of time consuming and expensive chromatographic techniques. Addition of DBU to a 1,2,4-trimethylbenzene (TMB) solution of C60 and [C60(CH2SiMe2OiPr)]2 afforded complexation only with [C60(CH2SiMe2OiPr)]2, leading to precipitation of the [C60(CH2SiMe2OiPr)]2-DBU complex. Decomplexation with 1,2-dichlorobenzene gave [C60(CH2SiMe2OiPr)]2 in 56% recovery. In addition, the [C60(CH2SiMe2OiPr)]2-DBU complex could be used for the synthesis of dihydromethano[60]fullerene C61H2.

Fullerene van der Waals oligomers as electron traps.

Density functional theory calculations indicate that van der Waals fullerene dimers and larger oligomers can form interstitial electron traps in which the electrons are even more strongly bound than in isolated fullerene radical anions. The fullerenes behave like "super atoms", and the interstitial electron traps represent one-electron intermolecular σ-bonds. Spectroelectrochemical measurements on a bis-fullerene-substituted peptide provide experimental support. The proposed deep electron traps are relevant for all organic electronics applications in which non-covalently linked fullerenes in van der Waals contact with one another serve as n-type semiconductors.

Communication: Embedded fragment stochastic density functional theory.

We develop a method in which the electronic densities of small fragments determined by Kohn-Sham density functional theory (DFT) are embedded using stochastic DFT to form the exact density of the full system. The new method preserves the scaling and the simplicity of the stochastic DFT but cures the slow convergence that occurs when weakly coupled subsystems are treated. It overcomes the spurious charge fluctuations that impair the applications of the original stochastic DFT approach. We demonstrate the new approach on a fullerene dimer and on clusters of water molecules and show that the density of states and the total energy can be accurately described with a relatively small number of stochastic orbitals.