(Ro)vibrational Spectroscopic Constants, Lifetime and QTAIM Evaluation of Fullerene Dimers Stability

The iconic caged shape of fullerenes gives rise to a series of unique chemical and physical properties; hence a deeper understanding of the attractive and repulsive forces between two buckyballs can bring detrimental information about the structural stability of such complexes, providing significant data applicable for several studies. The potential energy curves for the interaction of multiple van der Waals buckyball complexes with increasing mass were theoretically obtained within the DFT framework at ωB97xD/6-31G(d) compound model. These potential energy curves were employed to estimate the spectroscopic constants and the lifetime of the fullerene complexes with the Discrete Variable Representation and with the Dunham approaches. It was revealed that both methods are compatible in determining the rovibrational structure of the dimers and that they are genuinely stable, i.e., long-lived complexes. To further inquire into the nature of such interaction, Bader's QTAIM approach was applied. QTAIM descriptors indicate that the interactions of these closed-shell systems are dominated by weak van der Waals forces. This non-covalent interaction character was confirmed by the RDG analysis scheme. Indirectly, QTAIM also allowed us to confirm the stability of the non-covalent bonded fullerene dimers. Our lifetime calculations have shown that the studied dimers are stable for more than 1 ps, which increases accordingly with the number of carbon atoms.

Distributed Polarizability Model for Covalently Bonded Fullerene Nanoaggregates: Origins of Polarizability Exaltation

Polarizability exaltation is typical for (C₆₀)_n nanostructures. It relates to the ratio between the mean polarizabilities of (C₆₀)_n and C₆₀: the first one is higher than the n-fold mean polarizability of the original fullerene. This phenomenon is used in the design of novel fullerene compounds and the understanding of its properties but still has no chemical rationalization. In the present work, we studied the distributed polarizability of (C₆₀)₂ and isomeric (C₆₀)₃ nanoaggregates with the density functional theory method. We found that polarizability exaltation increases with the size of the nanostructure and originates from the response of the sp²-hybridized carbon atoms to the external electric field. The highest contributions to the dipole polarizability of (C₆₀)₂ and (C₆₀)₃ come from the most remote atoms of the marginal fullerene cores. The sp³-hybridized carbon atoms of cyclobutane bridges negligibly contribute to the molecular property. A similar major contribution to the molecular polarizability from the marginal atoms is observed for related carbon nanostructures isomeric to (C₆₀)₂ (tubular fullerene and nanopeanut). Additionally, we discuss the analogy between the polarizability exaltation of covalently bonded (C₆₀)_n and the increase in the polarizability found in experiments on fullerene nanoclusters/films as compared with the isolated molecules.

Covalently Bonded Fullerene Nano-Aggregates (C60)n: Digitalizing Their Energy–Topology–Symmetry

Fullerene dimers and oligomers are attractive molecular objects with an intermediate position between the molecules and nanostructures. Due to the size, computationally assessing their structures and molecular properties is challenging, as it currently requires high-cost quantum chemical techniques. In this work, we have jointly studied energies, topological (Wiener indices and roundness), and information theoretic (information entropy) descriptors, and have obtained regularities in triad ‘energy–topology–symmetry’. We have found that the topological indices are convenient to indicating the most and least reactive atoms of the fullerene dimer structures, whereas information entropy is more suitable to evaluate odd–even effects on the symmetry of (C60)n. Quantum chemically assessed stabilities of selected C120 structures, as well as linear and zigzag (C60)n, are discussed.

The influence of the configuration of the (C70)2 dimer on its rovibrational spectroscopic properties: a theoretical survey

A study of the spectroscopic properties of the buckyball dimer (C₇₀)₂ was performed, which involved mapping the potential energy curve of this system. The spectroscopic constants of the system were obtained using theoretical Dunham and discrete variable representation methods, as well as the Rydberg analytical function expanded to the sixth degree. Because the fullerenes in the dimer have both hexagonal and pentagonal faces, the properties of (C₇₀)₂ were examined for different system configurations. The fullerene dimerization process involves a weak interaction, possibly mediated by short-range components such as van der Waals forces. The differences between the spectroscopic constants of the various (C₇₀)₂ configurations and between their dissociation energies D_e were found to be rather small, which can be attributed to the dominant influence of the hexagonal faces of the fullerenes on the interaction between the fullerenes. These results should aid our understanding of the process of fullerene dimer formation and hopefully facilitate the development and application of new materials based on these dimers. Graphical Abstract Comparison of the potential energy curve and a schematic representation for the all (C₇₀)₂ fullerenes dimers configurations.

Comment on "Fullerene-based materials for solar cell applications: design of novel acceptors for efficient polymer solar cells--a DFT study" by A. Mohajeri and A. Omidvar, Phys. Chem. Chem. Phys., 2015, 17, 22367

Though a linear correlation has been recently reported between mean polarizabilities of the fullerene derivatives and open-circuit voltages of organic solar cells based on them, we demonstrate that there is no general dependence between these two values and some related quantities (anisotropy of polarizability and LUMO levels).

Reply to the 'Comment on "Fullerene-based materials for solar cell applications: design of novel acceptors for efficient polymer solar cells--a DFT study"' by D. S. Sabirov, A. O. Terentyev and I. S. Shepelevich, Phys. Chem. Chem. Phys., 2016, DOI

It is possible to predict the photovoltaic performance of fullerene derivatives based on their electronic/magnetic properties.

Strong electronic polarization of the C60 fullerene by imidazolium-based ionic liquids: accurate insights from Born–Oppenheimer molecular dynamic simulations

Fullerenes are known to be polarizable due to their strained carbon–carbon bonds and high surface curvature.

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).