C60 Dimer Research Articles

Thermal transport in fullerene-based molecular junctions: molecular dynamics simulations

We investigate phonon thermal transport of fullerene-based single-molecule junctions by employing classical molecular dynamics (MD) simulations. We compute the thermal conductances of C60 fullerene monomers, dimers, and trimers utilizing three distinct MD methods. We observe the equilibration dynamics in one approach, and employ two other nonequilibrium steady state simulation methods. We discuss technical aspects of each simulation technique, and show that their predictions for the thermal conductance agree. Our simulations reveal that while the thermal conductance of fullerene monomer and dimer junctions remains similar, that of trimer junctions experiences a significant reduction. This study could assist in the design of high-performing thermoelectric junctions, where low thermal conductance is desired.

Improving second-order Møller-Plesset perturbation theory for noncovalent interactions with the machine learning-corrected abinitio dispersion potential.

In this work, we utilize our recently developed machine learning (ML)-corrected abinitio dispersion (aiD) potential, known as D3-ML, which is based on the comprehensive SAPT10K dataset and relies solely on Cartesian coordinates as input, to address the dispersion deficiencies in second-order Møller-Plesset perturbation theory (MP2) by replacing its problematic dispersion and exchange-dispersion terms with D3-ML. This leads to the development of a new dispersion-corrected MP2 method, MP2+aiD(CCD), which outperforms other spin-component-scaled and dispersion-corrected MP2 methods as well as popular ML models for predicting noncovalent interactions across various datasets, including S66 × 8, NAP6 (containing 6 naphthalene dimers), L7, S12L, DNA-ellipticine, the C60 dimer, and C60[6]CPPA. In addition, MP2+aiD(CCD) exhibits comparable or even superior performance compared to the contemporary ωB97M-V functional. The limited performance of pure ML models for systems outside the training set or larger than those in the training set highlights their instability and unpredictability. Conversely, the outstanding performance and transferability of the hybrid MP2+aiD(CCD) method can be attributed to the fusion of the physical electronic structure method and a data-driven ML model, combining the strengths of both sides. This investigation firmly establishes MP2+aiD(CCD) as one of the most accurate and reliable fifth-order scaling correlated wave function methods currently available for modeling noncovalent interactions, even for large complexes. MP2+aiD(CCD) is expected to be reliably applicable in investigating real-life complexes at the hundred-atom scale.

Density functional theory study on the interaction of C60 fullerene with PCBM

Functionalized fullerenes are known as high-performance molecules. Herein, the interaction of C60 fullerene with Phenyl-C61-butyric-acid-methyl-ester (PCBM) is investigated by means of density functional theory method to elucidate the structures and electronic states of C60-PCMB complexes. C60-PCBM blends are typically used in solar cell. Studying the electronic structure of C60-PCBM is important for elucidating the mechanism of solar cells. The intermolecular distances for C60 and PCBM dimers were calculated to be 3.70 and 2.34 Å, respectively. In C60 dimer, the five membered ring of C60 interacted with the six membered ring of neighbour C60. Two hydrogen bonds between side chains of PCBM are connected in the PCBM dimer. The binding energies were 1.4 kcal mol−1 (C60 dimer) and 2.6 kcal mol−1 (PCBM dimer). In the C60-PCBM complex, five different structures were found to be stable. The binding energies were distributed in the range 1.6–3.7 kcal mol−1. The electronic states and excitation energies of C60-PCBM complexes and the basis set superposition error were discussed on theoretical results.

Negatively Charged Iron-Bridged Fullerene Dimer {Fe(CO)2-μ2-η2,η2-C60}22.

The interaction of {Cryptand(K+)}(C60•-) with Fe3(CO)12 produced {Cryptand(K+)}2{Fe(CO)2-μ2-η2,η2-C60}22-·2.5C6H4Cl2 (1) as the first negatively charged iron-bridged fullerene C60 dimer. The bridged iron atoms are coordinated to two 6-6 bonds of one C60 hexagon with short and long C(C60)-Fe bonds with average lengths of 2.042(3) and 2.088(3) Å. Fullerenes are close to each other in the dimer with a center-to-center interfullerene distance of 10.02 Å. Optical spectra support the localization of negative electron density on the Fe2(CO)4 units, which causes a 50 cm-1 shift of the C≡O vibration bands to smaller wavenumbers, and the C60 cages. Dimers are diamagnetic and electron paramagnetic resonance silent and have a singlet ground state resulting from the formation of an Fe-Fe bond in the dimer with a length of 2.978(4) Å. According to density functional theory calculations, the excited triplet state is higher than the ground state by 6.5 kcal/mol. Compound 1 shows a broad near-infrared band with a maximum at 970 nm, which is attributable to the charge transfer from the orbitals localized mainly on iron atoms to the C60 ligand.

Coupled Cluster Benchmarking of Large Noncovalent Complexes in L7 and S12L as Well as the C60 Dimer, DNA-Ellipticine, and HIV-Indinavir.

In this work, we report the benchmark binding energies of the seven complexes within the L7 data set, six host-guest complexes from the S12L data set, a C60 dimer, the DNA-ellipticine intercalation complex, and the largest system of the study, the HIV-indinavir system, which contained 343 atoms or 139 heavy atoms. The high-quality values reported were obtained via a focal point method that relies on the canonical form of second-order Møller-Plesset theory and the domain-based local pair natural orbital scheme for the coupled cluster with single double and perturbative triple excitations [DLPNO-CCSD(T)] extrapolated to the complete basis set (CBS) limit. The results in this work not only corroborate but also improve upon some previous benchmark values for large noncovalent complexes albeit at a relatively steep cost. Although local CCSD(T) and the largely successful fixed-node diffusion Monte Carlo (FN-DMC) have been shown to generally agree for small- to medium-size systems, a discrepancy in their reported binding energy values arises for large complexes, where the magnitude of the disagreement is a definite cause for concern. For example, the largest deviation in the L7 data set was 2.8 kcal/mol (∼10%) on the low end in C3GC. Such a deviation only grows worse in the S12L set, which showed a difference of up to 10.4 kcal/mol (∼25%) by a conservative estimation in buckycatcher-C60. The DNA-ellipticine complex also generated a disagreement of 4.4 kcal/mol (∼10%) between both state-of-the-art methods. The disagreement between local CCSD(T) and FN-DMC in large noncovalent complexes shows that it is urgently needed to have the canonical CCSD(T), the Monte Carlo CCSD(T), or the full configuration interaction quantum Monte Carlo approaches available to large systems on the hundred-atom scale to solve this dilemma. In addition, the performances of cheaper popular computational methods were assessed for the studied complexes with respect to DLPNO-CCSD(T)/CBS. r2SCAN-3c, B97M-V, and PBE0+D4 work well in large noncovalent complexes in this work, and GFN2-xTB performs well in π-π stacking complexes. B97M-V is the most reliable computationally efficient approach to predicting noncovalent interactions for large complexes, being the only one to have binding errors within the so-called 1 kcal/mol "chemical accuracy". The benchmark interaction energies of these host-guest complexes, molecular materials, and biological systems with electronic and medicinal implications provide crucial reference data for the improvement of current and future lower-cost methods.

Fully conjugated azacorannulene dimer as large diaza[80]fullerene fragment

A fully conjugated azacorannulene dimer with a large π-surface (76π system) was successfully synthesized from a fully conjugated bifunctional polycyclic aromatic azomethine ylide. This molecule represents an example of diaza[80]fullerene (C78N2) fragment molecule bearing two internal nitrogen atoms. X-ray crystallography analysis shows its boat-shaped structure with two terminal azacorannulenes bent in the same direction. The molecular shape leads to unique selective association with a dumbbell-shaped C60 dimer (C120) over C60 through shape recognition. Owing to its large π-surface and a narrow HOMO–LUMO gap, the azacorannulene dimer exhibits red fluorescence with a quantum yield of up to 31%. The utilization of the fully conjugated bifunctional azomethine ylide is a powerful method for the bottom-up synthesis of large multiazafullerene fragments, providing a step towards the selective total synthesis of multiazafullerenes.

Virtual vibrational spectrometer for sp2 carbon clusters and dimers of fullerene C60

A virtual vibrational spectrometer HF Spectrodyn, based on efficient software exploring unrestricted Hartree–Fock approximation, was used to perform computational spectrometry of C60, C66 and C70 carbon clusters as well as C60 dimers. All the species are presented as digital twins, the structure and properties of which were discussed. The obtained IR absorption and Raman scattering spectra are analyzed to point out strengths, limitations and ongoing developments of the virtual spectrometry.

Exohedral Functionalization of Fullerene by Substituents Controlling of Molecular Organization for Spontaneous C60 Dimerization in Liquid Crystal Solutions and in a Bulk Controlled by a Potential.

A study was carried out on the possibility of orderly and spontaneous dimerization at room temperature of C60 cages in fullerene liquid crystal fullerene dyads (R-C60). For this purpose, dyads with a structural elements feature supporting π-stacking and Van der Waals interactions were tested, due to the presence of terthiophene donors linked through an α-position or dodecyloxy chains. In addition, this possibility was also tested and compared to dyads with shorter substituents and the pristine C60. Research has shown that only in dyads with the features of liquid crystals, π-dimerization of C60 units occurs, which was verified by electrochemical and spectroelectrochemical (ESR) measurements. Cyclic voltammetry and differential voltammetry studies reveal π-dimerization in liquid crystal dyad solution even without the possibility of previous polymerization (cathodic or anodic) under conditions in the absence of irradiation and without the availability of reaction initiators, and even with the use of preliminary homogenization. These dyads undergo six sequential, one-electron reductions of π-dimer (R-C60···C60-R), where two electrons are added successively to each of the two fullerene cages and first form two radical anion system (R-C60)•−(R-C60)•− without pairing with the characteristics of two doublets. Similarly, the second reductions of π-dimer occur at potentials that are close to the reduction potential for the conversion to a system of two triplet dianions (R-C60)2−(R-C60)2−. Electron paramagnetic resonance spectra indicate a significant interaction between C60 cages. Interestingly, the strength of intermolecular bonds is so significant that it can overcome Coulombic repulsion, even with such highly charged particles as dianions and trianions. Such behavior has been revealed and studied so far only in covalently bonded C60 dimers.

Monte Carlo MP2-F12 for Noncovalent Interactions: The C60 Dimer.

A scalable stochastic algorithm is presented that can evaluate explicitly correlated (F12) second-order many-body perturbation (MP2) energies of weak, noncovalent, intermolecular interactions. It first transforms the formulas of the MP2 and F12 energy differences into a short sum of high-dimensional integrals of Green's functions in real space and imaginary time. These integrals are then evaluated by the Monte Carlo method augmented by parallel execution, redundant-walker convergence acceleration, direct-sampling autocorrelation elimination, and control-variate error reduction. By sharing electron-pair walkers across the supermolecule and its subsystems spanned by the joint basis set, the statistical uncertainty is reduced by one to 2 orders of magnitude in the MP2 binding energy corrected for the basis-set incompleteness and superposition errors. The method predicts the MP2-F12/aug-cc-pVDZ binding energy of 19.1 ± 4.0 kcal mol-1 for the C60 dimer at the center distance of 9.748 Å.

Fullerene Mechanochemistry: Serendipitous Discovery of Dumb‐Bell‐Shaped C120 and Beyond

AbstractThe serendipitous discovery of dumb‐bell‐shaped C120 under high‐speed vibration milling conditions is described. The mechanochemical protocol has been employed to synthesize the He‐, H2‐ or H2O‐encapsualted C120, the cross‐dimer C130, trimer C180, bridged C60 dimers as well as products from many other reactions of fullerenes, carbon nanotubes and graphenes. Mechanochemistry extended to various reactions of non‐fullerene molecules is briefly discussed. What is the most favorite and original chemistry developed in your research group?Mechanochemistry and fullerene chemistry.How do you get into this specific field? Could you please share some experiences with our readers?The poor solubility of fullerenes in common organic solvents prompts scientists to seek alternative protocol for fullerene chemistry. An idea of performing chemical reactions of fullerenes in the absence of any organic solvent was conceived when I was a guest research fellow in Kyoto University. That was how I first got into the mechanochemical reactions of fullerenes, and made the serendipitous discovery of fullerene dimer C120.How do you supervise your students?I encourage my graduate students to do scientific research of their ownideas within the scope of my group's research interests. I usually emphasize scientific rigor and intolerance of research misconduct to the graduate students when they first join my group. I provide them my guidance on how to do each piece of scientific work including detailed discussion of encountered problems, even spectral analysis and ChemDraw drawing, manuscript writing, etc.What is the most important personality for scientific research?Curiosity, creativity, and persistence.What are your hobbies?Sports, mainly jogging and running nowadays.How do you keep balance between research and family?My balance has heavily leaned toward work thanks to the understanding and support from my family.

Implications of Nitrogen Doping on Geometrical and Electronic Structure of the Fullerene Dimers

Main observation and conclusionBecause of its unsaturated bonds, C60 is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C60 dimers have been ambiguous for years. A quarter‐century after the discovery of azafullerene dimer (C59N)2, we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C59N)2 is elucidated specifically, revealing that the inter‐cage C—C single bond length of (C59N)2 is comparable with that of an ordinary C(sp3)‐C(sp3) single bond, and that the most stable conformer of (C59N)2 is gauche‐conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C59N)2 is optimized by a B3LYP‐D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C60)2 and its divalent anion. Additionally, the dissociation of (C59N)2 at 473 K under mass spectrometric conditions suggests the inter‐cage C—C bond is relatively weaker than an ordinary C—C single bond, which can be explained by the interaction energies of inter‐cages.

Electron-beam irradiation of photopolymerized C60 film studied using in situ scanning tunneling microscope, in situ Fourier-transform infrared spectroscopy, and first-principles calculations

We have examined the formation of a two-dimensional (2D) new carbon network by inducing the general Stone–Wales transformation between adjacent C60 molecules in a 2D dumbbell-type C60 polymer film. Structural changes in pristine C60 films after ultraviolet-visible (UV-vis) light and electron-beam (EB) irradiations were studied using in situ scanning tunneling microscope (STM) and in situ Fourier-transformed infrared (IR) spectroscopy, in combination with first-principles calculations based on density functional theory. Analyses of STM images and depth profiles found that three types of photopolymerized dumbbell-shaped dimers and trimers are formed on the surface layers of pristine C60 films: (i) [2+2] C60 dimers formed in a lateral direction, (ii) [2+2] dimerization of C60 between the first and second layers, and (iii) a triangular [2+2] C60 trimer along a lateral direction. As UV-vis light irradiation time increases, a comparison between experimental and theoretical IR spectra indicated that 2D dumbbell-shaped C60 polymers are formed within a few surface layers of the C60 film (in a similar manner, a 1D dumbbell-shaped polymer is also formed in a shallow space of the C60 film), whereas a [2+2] dumbbell-shaped dimer is formed in any bulk space of the film. Thereafter, when the EB was irradiated to the photopolymerized C60 film, the evolution of IR spectra with respect to EB irradiation time suggested that the 2D dumbbell-type C60 polymer is not decomposed but structurally changed to form a new network polymer.

Thermal magnetoresistance and spin thermopower in C60 dimers

We theoretically investigate the spin-related thermoelectric properties in C60 dimer bridged between zigzag graphene nanoribbon electrodes using the tight-binding model, equilibrium Green’s function method, and Landauer–Büttiker transport formalism. By applying a thermal gradient, our proposed device could generate a notable spin thermopower. Moreover, by switching the magnetization of the electrodes, different spin currents, and giant thermal magnetoresistance (MR) can be achieved. Interestingly, various types of C60 dimers also produce a thermal MR, which is sensitively modified by the gate voltages.

Pressure-Induced Dimerization of C60 at Room Temperature as Revealed by an In Situ Spectroscopy Study Using an Infrared Laser

Using in situ high-pressure Raman spectroscopy and X-ray diffraction, the polymerization and structure evaluation of C60 were studied up to 16 GPa at room temperature. The use of an 830 nm laser successfully eliminated the photo-polymerization of C60, which has interfered with the pressure effect in previous studies when a laser with a shorter wavelength was used as excitation. It was found that face-centered cubic (fcc) structured C60 transformed into simple cubic (sc) C60 due to the hint of free rotation for the C60 at 0.3 GPa. The pressure-induced dimerization of C60 was found to occur at about 3.2 GPa at room temperature. Our results suggest the benefit and importance of the choice of the infrared laser as the excitation laser.

Local dimerization and dedimerization of C60 molecules under a tip of scanning tunneling microscope: A first-principles study

The local dimerization and dedimerization of C60 molecules in a C60 thin film using a scanning tunneling microscopy (STM) [M. Nakaya et al. Adv. Mater. 22, 1622 (2010)] are promising techniques for realizing ultradense data storages. However, the detailed mechanism of the reversible topochemical reactions has not been clarified yet. Based on the density functional theory we explain the mechanism in terms of charging and electric-field effects on the molecules. The total-energy calculations reveal that when the C60 molecules in the surface layer are negatively charged, the dimerization is promoted and inter-layer dimers composed of two C60 molecules in different layers are formed dominantly over in-plane dimers. When the thin-film surface is positively charged or the inter-layer dimers are exposed to a strong electric field, a C60 monomer pair becomes more stable than a C60 dimer, and the dedimerization is promoted. These results predict competition between the dimerization and dedimerization of a negatively charged C60 binary system in a strong electric field, which is indeed confirmed by our STM experiments. In addition, the dedimerization induced in the electric field is discussed from the viewpoints of the intermolecular donor-acceptor interaction and the charge-dipole relaxation of a C60 binary system.

Double-Hybrid Functionals and Tailored Basis Set: Fullerene (C60) Dimer and Isomers as Test Cases.

A computational protocol making use of double hybrid functionals in conjunction with a recently developed basis set tailored to reproduce noncovalent interactions (hereafter named DH-SVPD) is here applied and tested for the evaluation of the properties of C60 fullerenes, namely intermolecular interactions in the weakly bound C60 dimer and relative stabilities of C60 isomers (as described by the C60ISO and iso-C60 data sets). The obtained results suggest that the DH-SVPD performance is very close to that obtained with empirical corrections and larger quadruple-ζ basis for the C60 dimer. In contrast, both approaches (tailored basis set and larger basis with empirical potential) do not reach the envisaged accuracy for the relative stabilities of C60 isomers. Nevertheless, this test well underlined how the DH-SVPD basis set is able to recover the performance obtained by coupling the DH functionals with empirical dispersion corrections and larger basis set, significantly reducing the computational effort for double hybrids and thus enabling expansion of their application domain to larger molecular systems.

Model potential study of non-valence correlation-bound anions of (C60)n clusters: the role of electric field-induced charge transfer.

A polarization model which accounts for electric field-induced charge transfer between fullerene molecules is introduced. Application of this model to the C60 dimer and trimer shows that intermolecular charge transfer makes a significant contribution to the polarizabilities of these clusters. This polarization model is incorporated into a one-electron Hamiltonian for describing non-valence correlation-bound anions, allowing us to further demonstrate that intermolecular charge transfer also results in increased stability of these anion states.

Bucky-corn: van der Waals composite of carbon nanotube coated by fullerenes

ABSTRACTCan a C60 layer cover a surface of single-wall carbon nanotube (SWCNT) forming an exohedral pure-carbon hybrid with only van der Waals interactions? The aim of the present paper is to address this question and to demonstrate that the fullerene shell layer in such a bucky-corn structure can be stable. Theoretical study of the structure, stability and electronic properties of bucky-corn hybrids is reported for the shell of C60 and C70 molecules on an individual SWCNT, C60 dimers on an individual SWCNT as well as C60 molecules on SWNT bundles. The geometry and total energies of the bucky-corn hybrids were calculated by the molecular dynamics method, while the density functional theory method was used to simulate the electronic band structures.

Transport properties of the H2O@C60-dimer-based junction

Theoretical predictions play an important role in finding potential applications in molecular electronics. Fullerenes have a number of potential applications, and the charge flow from a single C60 molecule to another becomes more versatile and more interesting after doping. Here, we report the conductance of two H2O@C60 molecules in series order and how the number of encapsulated water molecules influences the transport properties of the junction. Encapsulating an H2O molecule into one of the C60 cages increases the conductance of the dimer. Negative differential resistance is found in the dimer systems, and its peak-to-valley current ratio depends on the number of encapsulated H2O molecules. The conductance of the C60 dimer and the H2O@C60 dimer is two orders of magnitude smaller than that of the C60 monomer. Furthermore, we demonstrate that the conductance of the molecular junctions based on the H2O@C60 dimer can be tuned by moving the encapsulated H2O molecules. The conductance is H2O-position dependent. Our findings indicate that H2O@C60 can be used as a building block in C60-based molecular electronic devices and sensors.

Vis-Near-IR Spectroscopic and Time-Dependent DFT Study of Reduced Singly Bonded C60 Species.

Reduced fullerenes and fullerene derivatives exhibit intense absorptions in the vis-near-IR (vis-NIR) region. The absorptions are sensitive toward the addition pattern, number of addends, and oxidation state of the fullerene species and are used as an important benchmark for identifying anionic fullerene species. Similar absorptions are also shown for the reduced singly bonded C60 species, which are electronically different from reduced fullerene derivatives. However, much less work has been carried out on the vis-NIR spectroscopic study of the anionic singly bonded C60 species, likely due to the difficulty in controlled production of these species. Herein, we report the vis-NIR spectroscopic study of the mono- and dianions of the singly bonded C60 species (RC60(-), R(-)C60(-), and RC60(2-•)), which are selectively generated by controlled-potential bulk electrolysis (CPE) of the singly bonded C60 dimer and C60 oxazolino heterocycles. Time-dependent density functional theory (TD-DFT) calculations were performed to rationalize the experimental results.