Retro–Leapfrog and structure elucidation

Operations on maps are topological-geometrical tools used for transforming a given polyhedral tessellation. Investigation of fullerene structure often needs information on the original map which transformed into a larger molecular structure. Operations leading to the previous, smaller structures are called Retro-operations. They appear particularly useful in studies of structure elucidation or stability of series of fullerenes. The paper presents the first structure affiliation of the well-known C₆₀ fullerene to a family of Leapfrog fullerenes with relatedness being established by map operation. Thus, the tessellation of C₆₀ is described as an Archimedean, joint Sumanene-hexagon covering, in tetrahedral disposition. The other members of family show essentially the same covering and predicted good stability. Related Leapfrog fullerenes showing a disjoint Sumanene covering are also given.     

A combination of Clar number and Kekulé count as an indicator of relative stability of fullerene isomers of C<Subscript>60</Subscript>

Kekulé count is not as useful in predicting the thermodynamic stability of fullerenes as it is for benzenoid hydrocarbons. For example, the Kekulé count of the icosahedral C₆₀, the most stable fullerene molecule, is surpassed by its 20 fullerene isomers (Austin et al. in Chem Phys Lett 228:478–484, 1994). This article investigates the role of Clar number in predicting the stability of fullerenes from Clar’s ideas in benzenoids. We find that the experimentally characterized fullerenes attain the maximum Clar numbers among their fullerene isomers. Our computations show that among the 18 fullerene isomers of C₆₀ achieving the maximum Clar number (8), the icosahedral C₆₀ has the largest Kekulé count. Hence, for fullerene isomers of C₆₀, a combination of Clar number and Kekulé count predicts the most stable isomer.     

Water-soluble fullerenes using solubilizing agents, and their applications

Host–guest and supramolecular chemistry can produce water-solubilization of fullerenes such as C₆₀, C₇₀, and C_60/70 derivatives by hydrophobic interactions, CH–π interactions, and/or π–π interactions. For materials and biomedical applications, these water-soluble host–fullerene complexes must have the following important properties: (i) high solubility, (ii) high stability, and (iii) functionalization of the host–fullerene complex. These objectives can be achieved by selection of appropriate host molecules, development of novel solubilizing methods, and synthesis of functionalized host molecules. This review describes the introduction of a variety of host molecules that can solubilize fullerenes in water. In addition, we describe applications of host–fullerene complexes, in particular using photoinduced energy- and electron-transfer processes in water.     

Nuclear Reactions and Radionuclides in the Study of Fullerenes

Radiochemical techniques have been applied in various ways to the study of fullerenes and metallofullerenes for the past several years, and they have provided invaluable information pertaining to the stability, structures, and formation of the novel carbon material. This paper reviews those experimental results that have fully shown the usefulness and uniqueness of radionuclides demonstrated in the field of fullerene science.     

Computational Studies on Non‐covalent Interactions of Carbon and Boron Fullerenes with Graphene

First‐principles DFT calculations are carried out to study the changes in structures and electronic properties of two‐dimensional single‐layer graphene in the presence of non‐covalent interactions induced by carbon and boron fullerenes (C₆₀, C₇₀, C₈₀ and B₈₀). Our study shows that larger carbon fullerene interacts more strongly than the smaller fullerene, and boron fullerene interacts more strongly than that of its carbon analogue with the same nuclearity. We find that van der Waals interactions play a major role in governing non‐covalent interactions between the adsorbed fullerenes and graphene. Moreover, a greater extent of van der Waals interactions found for the larger fullerenes, C₈₀ and B₈₀, relative to smaller C₆₀, and consequently, results in higher stabilisation. We find a small amount of electron transfer from graphene to fullerene, which gives rise to a hole‐doped material. We also find changes in the graphene electronic band structures in the presence of these surface‐decorated fullerenes. The Dirac cone picture, such as that found in pristine graphene, is significantly modified due to the re‐hybridisation of graphene carbon orbitals with fullerenes orbitals near the Fermi energy. However, all of the composites exhibit perfect conducting behaviour. The simulated absorption spectra for all of the graphene–fullerene hybrids do not exhibit a significant change in the absorption peak positions with respect to the pristine graphene absorption spectrum. Additionally, we find that the hole‐transfer integral between graphene and C₆₀ is larger than the electron‐transfer integrals and the extent of these transfer integrals can be significantly tuned by graphene edge functionalisation with carboxylic acid groups. Our understanding of the non‐covalent functionalisation of graphene with various fullerenes would promote experimentalists to explore these systems, for their possible applications in electronic and opto‐electronic devices.     

Fullerene C60 derivatives as antimicrobial photodynamic agents

Functionalized fullerenes have shown interesting biomedical applications as potential phototherapeutic agents. The hydrophobic carbon sphere of fullerene C₆₀ can be substituted by cationic groups to obtain amphiphilic structures. These compounds absorb mainly UV light, but absorption in the visible region can be enhanced by anchoring light-harvesting antennas to the C₆₀ core. Upon photoexcitation, fullerenes act as spin converters by effective intersystem crossing. From this excited state, they can react with ground state molecular oxygen and other substrates to form reactive oxygen species. This process leads to the formation of singlet molecular oxygen by energy transfer or superoxide anion radical by electron transfer. Photodynamic inactivation experiments indicate that cationic fullerenes are highly effective photosensitizers with applications as broad-spectrum antimicrobial agents. In these structures, the hydrophobic character of C₆₀ improves membrane penetration, while the presence of positive charges increases the binding of the fullerene derivatives with microbial cells. Herein, we summarize the progress of antimicrobial photodynamic inactivation based on substituted fullerenes specially designed to improve the photodynamic activity.     

Hypercoordinated carbon in C-doped boron fullerenes: a quantum chemical study

The structures and stability of C-doped boron fullerenes with the three-dimensional arrangement of non-classical pentacoordinated quasi-flat carbon centers were studied using the density functional theory (DFT) B3LYP/6-311+G(d,p) method. The doping with carbon atoms in apical positions above the five-membered rings stabilizes the spherical boron fullerene forms due to multicenter interactions of p_z-orbitals of the carbons and adjacent boron atoms. Increasing in the size of the fullerene cluster is accompanied by change in the bonding pattern and by flattening of the hypercoordinated carbon centers. Endohedral metal atoms significantly affect on the structure and stability of the fullerene systems with hypercoordinated carbon centers.     

The Effect of Doping Different Heteroatoms on the Interaction and Adsorption Abilities of Fullerene

Density functional method has been employed to compare the interaction and adsorption abilities of simple and doped fullerenes with various heteroatoms (Al, B, Si, N, P, and S). Three sulfur‐containing molecules (H₂S, SO₂, and thiophene) were selected to study of their interactions with fullerenes. These interactions will be important in the design of new sensor, adsorption, and elimination of pollutants and chemical reactions. The calculated adsorption energies (E_ad) in the gas phase and solvents (water, using the polarized continuum model) showed that all adsorbates have exothermic interaction with all fullerenes. The maximum E_ad values were calculated for aluminum‐doped fullerene (AF) and nitrogen‐doped fullerene (NF), and the adsorption energies in solvent are not so different with those in the gas phase. Natural Bond Orbitals (NBO) calculations showed the complexes of AF and then boron‐doped fullerene (BF) have the highest E2 interaction energies, whereas simple fullerene (F) and phosphorus‐doped fullerene (PF) have the least E2 energies. Population analyses showed that doping by heteroatoms bearing extra electrons reduces the energy gap and this decrease is more than the decrease observed from doping by heteroatoms with electron defect. Moreover, the change in the energy gaps of the complexes, obtained from the density of states (DOSs) plots, showed that these structures could be used in sensor devices. All calculated data confirmed the better adsorption of SO₂ by fullerenes versus H₂S and thiophene and among all fullerenes, AF and then BF and NF are the best adsorbent for these structures.     

Quantum-Chemical Simulation of New Hybrid Nanostructures: Small Fullerenes C20 and C28 in Single-Walled Boron-Nitrogen Nanotubes

A quantum-chemical simulation of new hybrid nanostructures consisting of regular chains of the small fullerenes C₂₀ and C₂₈ encapsulated into the bulk of achiral zigzag single-walled boron-nitrogen nanotubes [(C₂₀,C₂₈)@BN-NT]. The electronic properties and the nature of interatomic bonds in these nanostructures are analyzed as a function of the fullerene and the distances between fullerenes in the chain and between fullerenes and tube walls. The electronic characteristics of hybrid nanostructures are compared with those of "isolated" fullerenes and nanotubes, and (C20,C28) + BN-NT structures simulating fullerene adsorption on tube surface as the initial stage of (C₂₀,C₂₈)@BN-NT formation.     

Incorporation of Pure Fullerene into Organoclays: Towards C60‐Pillared Clay Structures

In this work, we demonstrate the successful incorporation of pure fullerene from solution into two‐dimensional layered aluminosilicate minerals. Pure fullerenes are insoluble in water and neutral in terms of charge, hence they cannot be introduced into the clay galleries by ion exchange or intercalation from water solution. To overcome this bottleneck, we organically modified the clay with quaternary amines by using well‐established reactions in clay science in order to expand the interlayer space and render the galleries organophilic. During the reaction with the fullerene solution, the organic solvent could enter into the clay galleries, thus transferring along the fullerene molecules. Furthermore, we demonstrate that the surfactant molecules, can be selectively removed by either simple ion‐exchange reaction (e.g., interaction with Al(NO₃)₃ solution to replace the surfactant molecules with Al³⁺ ions) or thermal treatment (heating at 350 °C) to obtain novel fullerene‐pillared clay structures exhibiting enhanced surface area. The synthesized hybrid materials were characterized in detail by a combination of experimental techniques including powder X‐ray diffraction, transmission electron microscopy, X‐ray photoemission, and UV/Vis spectroscopy as well as thermal analysis and nitrogen adsorption–desorption measurements. The reported fullerene‐pillared clay structures constitute a new hybrid system with very promising potential for the use in areas such as gas storage and/or gas separation due to their high surface area.     

富勒烯合成化学研究进展

富勒烯是一类由12个五元环和若干六元环组成的笼状分子, 自20世纪80年代中期被发现以来就以其独特的结构和新奇的性质而成为科学界研究的热点, 25年来, 无论在基础研究还是在实际应用领域都有了长足的进步, 人们在发展富勒烯合成新方法和寻找富勒烯新结构方面做了大量的工作。本文对富勒烯的各种宏量合成方法进行了回顾, 并概述了迄今已发表的60余种富勒烯新结构,包括各种富勒烯空笼、内嵌富勒烯、富勒烯笼外修饰衍生物及氮杂富勒烯等结构。     

Fullerenes in Sol-Gel Materials

The family of fullerene molecules is composed of a large variety of compounds that have been synthesized following the discovery of C₆₀ in 1985. The chemistry of fullerenes, developed in these last years, has allowed designing the properties of this family of molecules for specific applications in materials science. One of the main tasks to build up solid state devices based on fullerenes is the synthesis of materials doped with a highly dispersed and homogeneous distribution of fullerenes. Many of the peculiar photophysical properties, such as the reverse saturable absorption used to obtain a solid state optical limiter, are in fact lost in the aggregates of fullerenes. Sol-gel processing allows preparing inorganic oxides and hybrid organic-inorganic materials at low temperatures and presents an interesting alternative to organic polymers to entrap molecules of the fullerene family in a solid matrix. Porous inorganic solids and aerogels are also important classes of materials that can be synthesized via sol-gel and can act as hosts of fullerenes. In the present article we have reviewed the main achievements of sol-gel processing of fullerene based nanocomposite materials.     

Stability of small fullerenes C n (n=36,40 and 60): A topological and molecular orbital approach

Summary By semi-empirical molecular orbital calculations stability of fullerenes was analyzed in terms of topological parameters, such as the number of special fragments and the number of three types of abutting bonds between two 5-membered rings. Relative stability was compared by AM1 method for all spectrally distinct closed-shell isomers of C₃₆ and C₄₀ fullerenes, and for some closed-shell isomers of C₆₀ fullerene. Molecular geometries of these fullerenes were also optimized. Their relative stabilities were well explained by the instability of abutting bonds.     

Structural interconnections and the role of heptagonal rings in endohedral trimetallic nitride template fullerenes

Recent experiments indicate that fullerene isomers outside the classical definition can also encapsulate metallic atoms or clusters to form endohedral metallofullerenes. Our systematic study using DFT calculations, suggests that many heptagon‐including nonclassical trimetallic nitride template fullerenes are similar in stability to their classical counterparts, and that conversion between low‐energy nonclassical and classical parent cages via Endo–Kroto insertion/extrusion of C₂ units and Stone–Wales isomerization may facilitate the formation of endohedral trimetallic nitride fullerenes. Close structural connections are found between favored isomers of trimetallic nitride template fullerenes from C₇₈ to C₈₂. It appears that the lower symmetry and local deformations associated with introduction of a heptagonal ring favor encapsulation of intrinsically less symmetrical mixed metal nitride clusters. © 2016 Wiley Periodicals, Inc.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.     

Benzene Adsorption on C<Subscript>24</Subscript>, Si@C<Subscript>24</Subscript>, Si-Doped C<Subscript>24</Subscript>, and C<Subscript>20</Subscript> Fullerenes

The absorption feasibility of benzene molecule in the C₂₄, Si@C₂₄, Si-doped C₂₄, and C₂₀ fullerenes has been studied based on calculated electronic properties of these fullerenes using Density functional Theory (DFT). It is found that energy of benzene adsorption on C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes were in range of –2.93 and –51.19 kJ/mol with little changes in their electronic structure. The results demonstrated that the C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes cannot be employed as a chemical adsorbent or sensor for benzene. Silicon doping cannot significantly modify both the electronic properties and benzene adsorption energy of C₂₄ fullerene. On the other hand, C₂₀ fullerene exhibits a high sensitivity, so that the energy gap of the fullerene is changed almost 89.19% after the adsorption process. We concluded that the C₂₀ fullerene can be employed as a reliable material for benzene detection.     

Functional Carbazole-Fullerene Complexes: A New Perspective of Carbazoles Acting as Nano-Octopus to Capture Globular Fullerenes

Fullerene host-guest constructs have attracted increasing attention owing to their molecular-level hybrid arrangements. However, the usage of simple carbazolic derivatives to bind with fullerenes is rare. In this research, three novel carbazolic derivatives, containing a tunable bridging linker and carbazole units for the capturing of fullerenes, are rationally designed. Unlike the general concave-convex interactions, fullerenes could interact with the planar carbazole subunits to form 2-dimensional hexagonal/quadrilateral cocrystals with alternating stacking patterns of 1 : 1 or 1 : 2 stoichiometry, as well as the controllable fullerene packing modes. At the meanwhile, good electron-transporting performances and significant photovoltaic effects were realized when a continuous C_60⋅⋅⋅C₆₀ interaction channel existed. The results indicate that the introduction of such carbazolic system into fullerene receptor would provide new insights into novel fullerene host-guest architectures for versatile applications.     

Mechanism of selection of perfect fullerenes in arc synthesis

Joint consideration of the gas flow dynamics in an arc chamber for fullerene production and fullerene assembly kinetics shows that the efficient fullerene annealing and the giant prevalence of magic fullerenes C₆₀ and C₇₀ are associated with the gas flow structure generated by the arc in the discharge chamber. Most nascent fullerenes are not immediately removed from the chamber; rather, they are entrained by closed gas flows. Analysis of fullerene annealing makes it possible to optimize fullerene production not only for arc parameters but also for chamber geometry.     

Fullerene-containing porphyrins: Synthesis and potential practical applications

The review focuses current research in the rapidly developing field of the chemistry of porphyrin–fullerene complexes. Recent advances in the synthesis, properties, and potential applications of these compounds are considered. An overview of the most popular methods to prepare porphyrin complexes with C₆₀ fullerene is given. The discussion of porphyrin?fullerene complexes includes the structures of noncovalently linked porphyrin?fullerenes along with covalently linked complexes. Much attention is paid to potential applications of porphyrin?fullerene conjugates.     

Exohedral Silicon Fullerenes: Si<Subscript>60</Subscript>Pn<Subscript>60</Subscript> and Si<Subscript>80</Subscript>Pn<Subscript>60</Subscript> (Pn = P,As, Sb and Bi)

Based on density functional theory (DFT) calculations, we predict that the icosahedral structures of the silicon fullerenes Si₆₀ and Si₈₀ can be stabilized by 12 exohedral pentagons of group V-A unit Pn₅ (Pn = P, As, Sb or Bi). The 12 pentagons can fully passivate the dangling bonds associated with 12 pentagonal Si₅ rings on the silicon fullerene cages, thereby resulting in stable exohedral silicon fullerenes Si₆₀Pn₆₀ and Si₈₀Pn₆₀. Properties of the eight Si₆₀Pn₆₀ and Si₈₀Pn₆₀ clusters, including harmonic vibrational frequencies, electron affinity (EA), the HOMO–LUMO gap and NICS values, are computed. We find that all eight Si₆₀Pn₆₀ and Si₈₀Pn₆₀ fullerenes possess relatively large HOMO–LUMO gaps, high electron affinities, and that the Si₆₀Pn₆₀ fullerenes exhibit weak aromaticity. Among eight clusters examined, the exohedral fullerene I _h-Si₆₀P₆₀ possesses the largest cohesive energy per atom. Ab initio molecular dynamics (AIMD) simulation is performed to demonstrate thermal stability of the hollow cage structure of Si₆₀P₆₀ at the room temperature.