Fullerene Dimers Research Articles

Formation dynamics of fullerene dimersC118+,C119+, andC120+

Dumbbell-shaped fullerene dimers ${C}_{118}^{+}$ and ${C}_{119}^{+}$ have recently been observed in mass spectra resulting from collisions between clusters of C${}_{60}$ molecules and keV He${}^{2+}$ or Ar${}^{2+}$ ions [H. Zettergren et al., Phys. Rev. Lett. 110, 185501 (2013) and F. Seitz et al., J. Chem. Phys. 139, 034309 (2013)]. To unveil the formation mechanisms of these fullerene dimers, systematic molecular dynamics (MD) simulations based on the self-consistent charge density functional tight-binding method have been performed for C${}_{n}^{+}$ + C${}_{60}$ ($n=58,59,60$) collisions following prompt atom knockouts by the fast ions. The statistics from the MD simulations indicate a much higher reactivity of ${C}_{59}^{+}$ and ${C}_{58}^{+}$ fragments compared to that of ${C}_{60}^{+}$. It is found that the covalently bonded dumbbell-shaped fullerene dimers ${C}_{118}^{+}$ and ${C}_{119}^{+}$ can be formed at very low-collision energies within 1 ps and are stable enough to survive on the microsecond time scale of the experiment. The thermodynamic and kinetic stabilities, as well as the bonding features, have been investigated for the most stable dumbbell dimers ${C}_{118}^{+}$, ${C}_{119}^{+}$, and ${C}_{120}^{+}$.

Fullerene Dimers Connected through C24and C36Bridge Cages

, for the first time, see Figure1. Then we investigate their electronic and magnetic pro-perties in comparison to those of their parents by calculatingHOMO–LUMO gaps, binding energies, and NICS indices.In fact, the synthesis and characterization of such fullerenedimers are of main interest due to their unique structural,magnetic, superconducting and mechanical properties,

Mobility of Long-Lived Fullerene Radical in Solid State and Nonlinear Temperature Dependence

A singly bonded fullerene dimer [C60R]2 in the solid state thermally generates a pair of fullerene radicals C60R(•) that dissociate reversibly and irreversibly upon heating and cooling of the solid. The temperature dependence of the electron mobility of the solid shows striking nonlinearity, caused by the dissociation of a strongly interacting radical pair into two free radicals, which interact with the neighboring fullerene molecules to increase the mobility 10 times to a value of 1.5 × 10(-3) cm(2) V(-1) s(-1). The nonlinearity is due to the plastic crystalline nature of fullerene crystals.

Electronic Structure of Fullerene Heterodimer in Bulk‐Heterojunction Blends

To increase performance of organic solar cells, the optimization of the electron‐accepting fullerenes has received less attention. Here, an electronic structure study of a novel covalently linked C60‐C70‐heterodimer in blend with the polymer PCDTBT (poly[9‐(1‐octylnonyl)‐9H‐carbazole‐2,7‐diyl]‐2,5‐thiophenediyl‐2,1,3‐benzothiadiazole‐4,7‐diyl‐2,5‐thiophenediyl) is presented. Upon optical excitation of polymer:heterodimer solid films, the unpaired electron is shared between both C60 and C70 cages. In contrast, in the solution the electron is localized on one half of the dimer. Electronic structure calculations reveal that for the C60‐C70‐heterodimer two nearly isoenergetic minima exist, essentially the cis and trans conformers, which are separated by a thermodynamically accessible rotational barrier. In the cis conformation, the edge‐to‐edge distance between the two cages is ca. 4 Å and an unpaired electron is shared between two dimer halves, while in the trans conformation the separation between the fullerene cages is larger and favors electron localization on one half of the heterodimer. By comparison with the experimental data, it is concluded that the cis conformation is preferable in films, and the trans conformation in solution. Modification of the linking molecular bridge opens the possibility to influence the electronic properties of fullerene dimers, which in turn may have an impact on the charge carrier generation efficiency in solar cells.

Plasmon excitation in C60 fullerene dimers

Plasmon resonances in C60 fullerene dimers are investigated using time-dependent density functional theory. Owing to larger separation between molecules, there exist capacitive coupling plasmon modes in fullerene dimers. With the decrease of the gap distance, low-energy capacitive coupling plasmon modes show red shift. When the gap distance further decreases, because of the electrons tunneling across the dimer junction, plasmon resonance modes of C60 fullerene dimers are significantly modified, and the charge transfer plasmon modes occur. C60 fullerene dimer is different from metallic nanostructures dimmer. As the gap distance is again reduced, the charge transfer plasmon modes are not blue-shifted, but they are further red-shifted. In the range of the visible spectrum, C60 fullerene dimmers have strong absorption peaks.

Polarizability as a landmark property for fullerene chemistry and materials science

The review summarizes data on dipole polarizability of fullerenes and their derivatives, covering the most widespread classes of fullerene-containing molecules (fullerenes, fullerene exohedral derivatives, fullerene dimers, endofullerenes, fullerene ions, and derivatives with ionic bonds).

NBS-promoted oxidation of fullerene monoradicals leading to regioselective 1,4-difunctional fullerenes.

We have demonstrated that NBS is able to promote the oxidation of fullerene monoradicals to form 1,4-difunctional fullerenes. The singly bonded fullerene dimers were used as fullerene monoradical precursors, which produced various 1,4-fullerenes with a wide range of functional groups in good to high yields with high regioselectivity in terms of cosolvents and nucleophiles.

Molecular structure and spectroscopic properties of a nickel-bridged {Ni(Ph3P)}2(μ2-η(2), η(2)-C60)2 dimer.

A compound containing fullerene dimers bonded through two nickel atoms, {Ni(Ph3P)}2(μ2-η(2),η(2)-C60)2·2C6H4Cl2 (1), has been obtained as single crystals. The fullerenes are neutral in 1 , showing a zero-valent state of Ni. The nickel atoms are bonded in an η(2) coordination mode with Ni-C distances of 2.001(3)-2.037(3) Å and a close approach of the fullerenes with a 9.716 Å center-to-center distance. The DFT calculations showed a diamagnetic singlet ground state for this dimer.

Structures and stabilities of asymmetric fullerene dimers: A density functional theory study

The molecular structure and the relative stability of asymmetric fullerene dimers were systematically investigated using density functional theory calculations. The most stable geometries for a directly-linked dimer of C130, and bridged dimers of C130O and C131 were identified among several isomers by using a total energy comparison. The relative stability of asymmetric dimers was defined by calculating the dissociation energy barrier of a fullerene dimer into two unit fullerenes. We found that the directly-linked asymmetric dimer C130 was not energetically stable and that the carbon-bridged dimer C131 was more stable than the oxygen-bridged dimer C130O. The electronic structures of the stable asymmetric dimers were also investigated.

Density Functional Theory Study on the Decay of Fullerenyl Radicals RC60•, ROC60•, and ROOC60• (R = tert-Butyl and Cumyl) and Polarizability of the Formed Fullerene Dimers

Currently, there are no comparative studies on the possible routes of decay of fullerenyl radicals. Such information is required for development of new synthetic approaches to the fullerene derivatives, obtained via radical reactions, and understanding mechanisms of oxidative destruction of fullerene-containing materials. In the present work, we have performed a theoretical study on the possible reactions of the selected fullerenyl radicals, generated in the well-known experimental systems. We consider three main routes for the radical decay: formation of fullerene bisadducts via XC60(•) + X(•) reactions, dimerization of XC60(•), and their interaction with molecular oxygen. The calculated heat effects explain the experimental regularities of fullerene radical reactions (e.g., the reversibility of the dimerization and low reactivity of fullerenyls toward molecular oxygen). We have found that the heat effects are maximal for the dimerization of ROOC60(•), so the interaction of C60 with peroxy radicals may provide more effective synthetic routes to the single-bonded C60 dimers compared to the known ones. Moreover, the exothermicity of ROO(•) addition to C60 is increased during the subsequent addition that allows reconsidering the reasons underlying C60 antioxidant activity. Additionally, polarizability and its nonadditivity of fullerene dimers XC60-C60X have been found. Guided by the calculated polarizabilities, we assume a new bistable system "fullerenyl ↔ dimer" for molecular machinery. Depending on the conditions, such a system can exist in two states differing by their response to external electric fields.

COLLISION DYNAMICS OF X@C60(X = He, Ne, Ar) AT LOW ENERGIES

In this paper, a semi-empirical molecular dynamics model is developed. The central collisions of C 60 + C 60 and X@C 60 + X@C 60 ( X = He , Ne , Ar ) at various incident energy are investigated within this model. The fullerene dimers like a "dumbbell" can be formed by a self-assembly of C 60 fullerene and X@C 60 ( X = He , Ne ) endohedral fullerenes, and the new fullerene structure like "peanut" can be formed by a self-assembly of Ar@C 60. It is found that Ar atom plays a great role in the collision of Ar@C 60 + Ar@C 60 because of its size effect. The energy effect is found that various incident energies cannot change the final structure at low energies if they are below a certain energy.

Energy alignment induced large rectifying behavior in endoheral fullerene dimers

Using the nonequilibrium Green's function formalism combined with density functional theory for quantum transport calculation, we have investigated the electronic transport properties of three endofullerenes Na@C60C60[@F, Na@C60C60, and F@C60C60. The results show that the electronic transport properties of these endofullerenes are strongly dependent upon the species inside the fullerene. A large rectifying behavior is observed in Na@C60C60, while Na@C60C60[@F and F@C60C60 can only present very weak rectification. It is revealed that the alignment between the molecular levels of two C60s moieties with the applied bias is the main cause of the large rectification in Na@C60C60.

Adsorption of Polar and Nonpolar Molecules on Isolated Cationic C60 , C70 , and Their Aggregates.

Physisorption on graphite, graphene, nanotubes, and other graphitic structures has been the subject of numerous studies, partly driven by interest in the nature of order in two-dimensional systems, their phase transitions, and the use of graphitic scaffolds for reversible storage of hydrogen at high volumetric density and low mass. In contrast, physisorption on individual fullerenes or small aggregates of fullerenes has remained largely unexplored, last but not least, because of technical challenges. A summary of recent progress in identifying specific adsorption sites on positively charged C60 , C70 , and their aggregates is given in this Minireview. Adsorption energies and storage capacities for helium, hydrogen, methane, oxygen, nitrogen, water, and ammonia are determined. Mass spectrometric data reveal the formation of a commensurate phase in which all hollow sites of C60 or C70 are occupied. This phase is identified for all nonpolar molecules, including oxygen, which does not form a commensurate phase on planar graphite. The polar molecules, on the other hand, do not wet fullerenes and they do not form this commensurate phase. A hierarchy of other distinct adsorption sites are identified for nonpolar molecules, namely, groove sites for fullerene dimers and beyond, and dimple sites for fullerene trimers and beyond. Furthermore, evidence is presented for the preferential adsorption of hydrogen and methane in registered sites on fullerene dimers. The interpretation of experimental data that merely count the number of preferred adsorption sites is aided by molecular dynamics simulations, which utilize interaction potentials derived from ab initio calculations to determine adsorption energies.

Magnetic Coupling in the Fullerene Dimer {Co(Ph3P)(C6H5CN)}2(μ2-η2:η2-C60)2 with Two Zerovalent Cobalt Atoms as Bridges

The magnetic metal-bridged fullerene dimer {Co(Ph3P)(C6H5CN)}2(μ2-η2,η2-C60)2 was synthesized for the first time and studied by X-ray crystallography and magnetic susceptibility methods. The dimers, in which two fullerene C60 cages are η2-bonded through two Co0 atoms (S = 1/2), have a triplet (S = 1) state and transfer to a diamagnetic singlet (S = 0) ground state below 50 K (J/kB = −28.6 K). The theoretical calculations show that C60 can work as an efficient spin coupler between paramagnetic metals.

ChemInform Abstract: Synthesis and Photovoltaic Properties of Acceptor Materials Based on the Dimerization of Fullerene C60 for Use in Efficient Polymer Solar Cells.

AbstractDimeric fullerne derivatives are shown to work as excellent n‐type material for polymer solar cells in combination with poly(3‐hexythiophene) or PTP7.

The Stability of Cosmic Fullerenes and Fullerenic Aggregates

AbstractEstablishing the stability of cosmic fullerenes and fullerenic aggregates is extremely relevant for a variety of reasons. For instance, the emission features of C60 and C70 fall in the same spectral region as the Un-identified InfraRed (UIR) bands, which they could contribute to. To be able to contribute to the UIR emission, however, fullerenes must be able to survive long enough against the destruction mechanisms operating in the interstellar medium. In this study we focus on the effects of collisional processing, i.e., the bombardment by energetic ions and electrons. A recent experimental/theoretical study has shown that ion collisions with C60 clusters result in the dissociation of the cluster with the simultaneous formation of covalent fullerene dimers, which could play a role as DIBs carriers. We present here our first results about the collisional processing of C60 molecules and clusters by H, He and C ions in interstellar shocks. We have adapted the models that have previously been developed to successfully treat the collisional processing of PAHs in space. The nature of the interaction and the similarities between PAHs and fullerenes make this approach appropriate. In addition, our study shows that the formation of covalent dimers following ion collisions with C60 clusters is compatible with the astrophysical conditions under consideration.

Regioselective [2 + 2] Cycloaddition of a Fullerene Dimer with an Alkyne Triggered by Thermolysis of an Interfullerene C–C Bond

Heating of a singly bonded fullerene dimer in the presence of an alkyne forms a cyclobutene structure on only one of the two fullerene moieties, through a stereo- and regioselective [2 + 2] cycloaddition. Experimental and theoretical data suggest that the reaction is triggered by cleavage of the interfullerene C-C bond and formation of a monomeric fullerene radical.

A two-step approach to the synthesis of N@C60 fullerene dimers for molecular qubits

We report the two-step synthesis of a highly soluble fullerene dimer, both for short reaction times and at the microscale. We apply this reaction scheme to starting materials that contain 15N@C60 and 14N@C60, and we demonstrate how, if applied to highly pure N@C60 in the future, this scheme may be used to produce (14N@C60)2 or (15N@C60)2 dimers in one step, and crucially 14N@C60–15N@C60 dimers in a second step. Such dimers represent isolated electron spin pairs that may be used to demonstrate entanglement between the spins. Additionally, CW EPR spectroscopy of the 15N@C60–C60 dimer in the solid state reveals permanent zero-field splitting (D = 14.6 MHz and E = 0.56 MHz).

Polarizability of C60 fullerene dimer and oligomers: the unexpected enhancement and its use for rational design of fullerene-based nanostructures with adjustable properties

The high polarizabilities of fullerene and its derivatives cause peculiarities in various physical and chemical processes in fullerene-containing systems. Their polarizabilities have been found to be efficient parameters for the design of nanostructures with desirable behavior. Unfortunately, the appropriate experimental data are scarce for most of the fullerene derivatives, due to their low availability or possible dissociation. At the same time, such information may be useful for C60-based nanotechnologies. We point our attention to the fullerene dimer and oligomers, which are novel and very promising compounds for nano-applications. We have performed the first density-functional theory study on the polarizability of fullerene derivatives (C60)n (n = 1–5) to elucidate how their structure affects the polarizability. In contrast to the concept of additivity, common in physical chemistry, the mean polarizability of (C60)n nonlinearly depends on the number of fullerene cores in their molecules, i.e. it violates the additivity. Similar to the other positive deviations from additive schemes, it has been called exaltation of polarizability. This effect is a result of the interaction of the π-electronic systems of fullerene cores in (C60)n and increases with their maximal remoteness. Experimental evidence of the exaltation is discussed. Thus, it agrees well with the enhancement of the polarizability of crystalline forms of C60 compared to molecular ones measured previously. Also, we have found a strong correlation between the calculated exaltations and the chemical properties of isomeric (C60)3, (C60)2 and its derivatives observed experimentally. The predicted enhancement has not been described previously and may be widespread among various nanostructures (for example, dimers of bowl-shaped hydrocarbons or other fullerenes). Insights into possible applications of the polarizability and its anisotropy to the molecular design and molecular machinery have been provided.

A study of the stretching vibrational spectroscopy of C120O and C120O2 by u(2) lie algebra

The vibrational energy levels of endohedral fullerene dimers C120O and C120O2 are calculated considering the local Hamiltonian of Morse potential using the algebra. Here each bond of the molecules is replaced by a corresponding Lie algebra and finally the Hamiltonian is constructed considering the interacting Casimir and Majorana operators. The fundamental stretching modes of vibration of both the dimmers C120O and C120O2 are then calculated using this Hamiltonian to compare the results of functional-based tight-binding (DF-TB) calculations.