A Series of Endohedral Metallo-BN Fullerene Superatomic Structures

Superatoms are crucial in the assembly of functional and optoelectronic materials. This study investigates the endohedral metallo-boron nitride [boron nitride (BN)] fullerenes U@B12N12, Cm@B12N12, and U@B16N16 in theory. Our findings confirm that U@B12N12, Cm@B12N12, and U@B16N16 are superatoms and their electronic configurations are 1P61S21D101F142P62S22D102F123P6, 1P61S21D101F141G161H162S22P62D102F12, and 1P61S21D101F142P62S22D102F14, respectively. Notably, the orbital energy levels in these superatoms exhibit a flipping phenomenon, deviating from those of previous superatom studies. Further, the orbital composition analyses reveal that superatomic orbitals 1S, 1P, 1D, and 1F mainly originate from BN cages, whereas the 2S, 2P, 2D, 2F, and 3P superatomic orbitals arise from hybridizations between BN cage orbitals and the 7s, 7p, 6d, and 5f orbitals of actinide atoms. And the energy gap of endohedral metallo-BN fullerene superatoms is reduced by introducing actinide atoms. Additionally, the analyses of ionization potentials and electron affinities show that U@B12N12, Cm@B12N12, and U@B16N16 have lower ionization potentials and higher electron affinities, suggesting decreased stability compared to that of pure BN cages. This instability may be linked to the observed flipping of the superatomic orbital energy levels. These insights introduce new members to the superatom family and offer new building blocks for the design of nanoscale materials with tailored properties.

Structure and vibrational properties of 1D molecular wires: from graphene to graphdiyne

Graphyne- and graphdiyne-like model systems have attracted much attention from many structural, theoretical, and synthetic scientists because of their promising electronic, optical, and mechanical properties, which are crucially affected by the presence, abundance and distribution of triple bonds within the nanostructures. In this work, we performed the two-step bottom-up on-surface synthesis of graphyne- and graphdiyne-based molecular wires on the Au(111). We characterized their structural and chemical properties both in situ (UHV conditions) through STM and XPS and ex situ (in air) through Raman spectroscopy. By comparing the results with the well-known growth of poly(p-phenylene) wires (namely the narrowest armchair graphene nanoribbon), we were able to show how to discriminate different numbers of triple bonds within a molecule or a nanowire also containing phenyl rings. Even if the number of triple bonds can be effectively determined from the main features of STM images and confirmed by fitting the C1s peak in XPS spectra, we obtained the most relevant results from ex situ Raman spectroscopy, despite the sub-monolayer amount of molecular wires. The detailed analysis of Raman spectra, combined with density functional theory (DFT) simulations, allowed us to identify the main features related to the presence of isolated (graphyne-like systems) or at least two conjugated triple bonds (graphdiyne-like systems). Moreover, other spectral features can be exploited to understand if the chemical structure of graphyne- and graphdiyne-based nanostructures suffered unwanted reactions. As in the case of sub-monolayer graphene nanoribbons obtained by on-surface synthesis, we demonstrate that Raman spectroscopy can be used for a fast, highly sensitive and non-destructive determination of the properties, the quality and the stability of the graphyine- and graphdiyne-based nanostructures obtained by this highly promising approach.

Synthesis of inter-[60]fullerene conjugates with inherent chirality

Coalescence of [60]fullerenes potentially produces hypothetical nanocarbon assemblies with non-naturally occurring topologies. Since the discovery of [60]fullerene in 1985, coalesced [60]fullerene oligomers have only been observed as transient species by transmission electron microscopy during an oligomerization process under a high electron acceleration voltage. Herein, we showcase the rational synthesis of covalent assemblies consisting of inherently chiral open-[60]fullerenes. The crystallographic analyses unveiled double-caged structures of non-conjugated and conjugated inter-[60]fullerene hybrids, in which the two [60]fullerene cages are bounds to each other through a covalent linkage. The former one further assembles via a heterochiral recognition so that four carbon cages are arranged in a tetrahedral manner both in solution and solid state. Reflecting radially-conjugated double π-surface nature, the inter-[60]fullerene conjugate exhibits strong electronic communication in its reduced states, intense absorption behavior, and chiroptical activity with a dissymmetry factor of 0.21 (at 674 nm) which breaks the record for known chiral organic molecules.

Extending on-surface synthesis from 2D to 3D by cycloaddition with C60

As an efficient molecular engineering approach, on-surface synthesis (OSS) defines a special opportunity to investigate intermolecular coupling at the sub-molecular level and has delivered many appealing polymers. So far, all OSS is based on the lateral covalent bonding of molecular precursors within a single molecular layer; extending OSS from two to three dimensions is yet to be realized. Herein, we address this challenge by cycloaddition between C60 and an aromatic compound. The C60 layer is assembled on the well-defined molecular network, allowing appropriate molecular orbital hybridization. Upon thermal activation, covalent coupling perpendicular to the surface via [4 + 2] cycloaddition between C60 and the phenyl ring of the molecule is realized; the resultant adduct shows frozen orientation and distinct sub-molecular feature at room temperature and further enables lateral covalent bonding via [2 + 2] cycloaddition. This work unlocks an unconventional route for bottom-up precise synthesis of three-dimensional covalently-bonded organic architectures/devices on surfaces.

Acceleration Effect of Bowl-Shaped Structure in Aerobic Oxidation Reaction: Synthesis of Homosumanene ortho-Quinone and Azaacene-Fused Homosumanenes

An oxidation reaction of hydroxyhomosumanene on silica gel providing homosumanene ortho-quinone and its synthetic application for azaacene-fused homosumanenes is described. Hydroxyhomosumanene is photochemically oxidized by air, when it is coated on silica gel; this aerobic oxidation proceeds faster than that of planar analogues. The difference of such reactivity was attributed to the unusual keto-enol tautomerization due to structural difference between planar and curved π-system. The homosumanene ortho-quinone was used in the synthesis of several azaacene-fused homosumanenes, azaacenohomosumanenes. X-ray diffraction analysis of the single crystals revealed their columnar stacking structures due to the interactions between each bowl. Azaacenohomosumanenes exhibited high electron affinity due to the combination of buckybowl and electron-deficient azaacene moieties.

Hollow Spherical Fullerene obtained by Kinetically Controlled Liquid-Liquid Interfacial Precipitation

Nanomaterials with hollow structures are expected to exhibit new functionalities for materials engineering. Here we report the fabrication of fullerene (C 60 ) spheres having different hollow structures by using a kinetically controlled liquid-liquid interfacial precipitation (KC-LLIP) method. For this purpose, 1,2-ethylenediamine (EDA) was used as a covalent cross-linker of C 60 molecules to form C 60 -EDA shells, while in-situ generated EDA-sulfur (EDA-S) droplets were applied as 'yolks' being eliminated by washing following formation of the yolk-shell structure, leading to hollow structures. Porous spheres, string hollow spheres, hollow spheres, and open hollow spheres have been synthesized by controlling the kinetics of nucleation of C 60 -EDA and the template EDA-S growth. Isopropanol was used as an additive to control the discrepancy in growth rates of C 60 -EDA and EDA-S. This facile KC-LLIP preparation method is expected to facilitate the large-scale fabrication and application of structured C 60 spheres in materials science and technology.

Fullerenes for the treatment of cancer: an emerging tool

Cancer is a most common cause of mortality globally. Available medicines possess severe side effects owing to their non-specific targeting. Hence, there is a need of an alternative in the healthcare system that should have high efficacy with the least side effects, also having the ability to achieve site-specific targeting and be reproducible. This is possible with the help of fullerenes. Fullerenes are having the unique physicochemical and photosensitizer properties. This article discusses the synthesis, functionalization, mechanism, various properties, and applications of C60 fullerenes in the treatment of cancer. The review article also addresses the various factors influencing the activity of fullerenes including the environmental conditions, toxicity profile, and future prospective.

Magnetic coupling induced by the interaction between endohedral metal borofullerenes

Superatom-assembled materials have highly tunable magnetic and electronic properties and parameters of clusters. Here, eight superatom dimers composed of two U@B₄₀ motifs have been studied by the density functional theory. Calculation results show that U@B₄₀ dimers exhibit spin antiferromagnetic coupling, spin ferromagnetic coupling and nonmagnetic, that is, the magnetic coupling is induced by the interaction between the U@B₄₀ superatoms. In addition, the monomers in U@B₄₀ dimers still retain the superatomic orbitals, and some of the super atomic orbitals disappear due to the interaction between monomers. The assembly based on U@B₄₀ induced a decrease in the energy gap. This study provides a basis for a deep understanding of controlling the cluster-assembled materials for tailoring their functionalities.

The studied eight U@B₄₀ superatom dimers show that they exhibit spin antiferromagnetic coupling, spin ferromagnetic coupling and nonmagnetic, that is, the magnetic coupling is induced by the interaction between the U@B₄₀ superatoms.

Environmental Applications of Sorbents, High-Flux Membranes of Carbon-Based Nanomaterials

Carbon-based nanomaterials have unique and controllable properties, making it possible to find and treat environmental challenges. There are several environmental applications for carbon-based nanoparticles: sorbents, membranes, antimicrobial agents, and sensors. According to this review, carbon-based nanomaterials have a variety of environmental benefits. This article also looks at prospective uses of nanomaterials in environmental systems, utilizing carbonaceous nanoparticles as a guide for their physical, chemical, and electrical properties.

Recent trends in covalent functionalization of 2D materials

Covalent functionalization of the surface is more crucial in 2D materials than in conventional bulk materials because of their atomic thinness, large surface-to-volume ratio, and uniform surface chemical potential. Because...

Toxicity and Antioxidant Activity of Fullerenol C60,70 with Low Number of Oxygen Substituents

Fullerene is a nanosized carbon structure with potential drug delivery applications. We studied the bioeffects of a water-soluble fullerene derivative, fullerenol, with 10-12 oxygen groups (F10-12); its structure was characterized by IR and XPS spectroscopy. A bioluminescent enzyme system was used to study toxic and antioxidant effects of F10-12 at the enzymatic level. Antioxidant characteristics of F10-12 were revealed in model solutions of organic and inorganic oxidizers. Low-concentration activation of bioluminescence was validated statistically in oxidizer solutions. Toxic and antioxidant characteristics of F10-12 were compared to those of homologous fullerenols with a higher number of oxygen groups:F24-28 and F40-42. No simple dependency was found between the toxic/antioxidant characteristics and the number of oxygen groups on the fullerene’s carbon cage. Lower toxicity and higher antioxidant activity of F24-28 were identified and presumptively attributed to its higher solubility. An active role of reactive oxygen species (ROS) in the bioeffects of F10-12 was demonstrated. Correlations between toxic/antioxidant characteristics of F10-12 and ROS content were evaluated. Toxic and antioxidant effects were related to the decrease in ROS content in the enzyme solutions. Our results reveal a complexity of ROS effects in the enzymatic assay system.

François Diederich (1952-2020): 40 Years of Organic Chemistry

François Diederich, Professor of Organic Chemistry and long-time Chair of the Editorial Board of Angewandte Chemie, sadly passed away on September 23, 2020. He will be remembered for his groundbreaking research in the chemistry of fullerenes and carbon-rich molecules, in supramolecular and medicinal chemistry, as an engaging teacher, and as a generous and fascinating human being.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

[2 + 1] Cycloaddition reactions of fullerene C60 based on diazo compounds

The most common variant of fullerene core functionalization is the [2 + 1] cycloaddition process. Of these, reactions leading to methanofullerenes are the most promising. They are synthesized in two main reactions: nucleophilic cyclopropanation according to the Bingel method and thermal addition of diazo compounds. This present review summarizes the material on the synthesis of monofunctionalized methanofullerenes - analogues of [60]PCBM - based on various diazo compounds. The main cyclopropanating agents for the synthesis of monosubstituted methanofullerenes, the optimal conditions and the mechanism of the [2 + 1] cycloaddition, as well as the practical application of the target products are analyzed.

Aggregation-free and high stability core-shell polymer nanoparticles with high fullerene loading capacity, variable fullerene type, and compatibility towards biological conditions

Fullerenes have unique structural and electronic properties that make them attractive candidates for diagnostic, therapeutic, and theranostic applications. However, their poor water solubility remains a limiting factor in realizing their full biomedical potential. Here, we present an approach based on a combination of supramolecular and covalent chemistry to access well-defined fullerene-containing polymer nanoparticles with a core-shell structure. In this approach, solvophobic forces and aromatic interactions first come into play to afford a micellar structure with a poly(ethylene glycol) shell and a corannulene-based fullerene-rich core. Covalent stabilization of the supramolecular assembly then affords core-crosslinked polymer nanoparticles. The shell makes these nanoparticles biocompatible and allows them to be dried to a solid and redispersed in water without inducing interparticle aggregation. The core allows a high content of different fullerene types to be encapsulated. Finally, covalent stabilization endows nanostructures with stability against changing environmental conditions.

The recent advancement of low-dimensional nanostructured materials for drug delivery and drug sensing application: A brief review

In this review article, we have presented a detailed analysis of the recent advancement of quantum mechanical calculations in the applications of the low-dimensional nanomaterials (LDNs) into biomedical fields like biosensors and drug delivery systems development. Biosensors play an essential role for many communities, e.g. law enforcing agencies to sense illicit drugs, medical communities to remove overdosed medications from the human and animal body etc. Besides, drug delivery systems are theoretically being proposed for many years and experimentally found to deliver the drug to the targeted sites by reducing the harmful side effects significantly. In current COVID-19 pandemic, biosensors can play significant roles, e.g. to remove experimental drugs during the human trials if they show any unwanted adverse effect etc. where the drug delivery systems can be potentially applied to reduce the side effects. But before proceeding to these noble and expensive translational research works, advanced theoretical calculations can provide the possible outcomes with considerable accuracy. Hence in this review article, we have analyzed how theoretical calculations can be used to investigate LDNs as potential biosensor devices or drug delivery systems. We have also made a very brief discussion on the properties of biosensors or drug delivery systems which should be investigated for the biomedical applications and how to calculate them theoretically. Finally, we have made a detailed analysis of a large number of recently published research works where theoretical calculations were used to propose different LDNs for bio-sensing and drug delivery applications.

The intermolecular anthracene-transfer in a regiospecific antipodal C60 difunctionalization

Ever since the discovery of fullerenes, their mono- and multi-functionalization by exohedral addition chemistry has been a fundamental topic. A few years ago, a topochemically controlled regiospecific difunctionalization of C₆₀ fullerene by anthracene in the solid state was discovered. In the present work, we analyse the mechanism of this unique reaction, where an anthracene molecule is transferred from one C₆₀ mono-adduct to another one, under exclusive formation of equal amounts of C₆₀ and of the difficult to make, highly useful, antipodal C₆₀ bis-adduct. Our herein disclosed dispersion corrected DFT studies show the anthracene transfer to take place in a synchronous retro Diels-Alder/Diels-Alder reaction: an anthracene molecule dissociates from one fullerene under formation of an intermediate, while undergoing stabilizing interactions with both neighbouring fullerene molecules, facilitating the reaction kinetically. In the intermediate, a planar anthracene molecule is sandwiched between two neighbouring fullerenes and forms equally strong 'double-decker' type π-π stacking interactions with both of these fullerenes. Analysis with the distortion interaction model shows that the anthracene unit of the intermediate is almost planar with minimal distortion. This analysis highlights the existence of simultaneous noncovalent interactions engaging both faces of a planar polyunsaturated ring and two convex fullerene surfaces in an unprecedented 'inverted sandwich' structure. Hence, it sheds light on new strategies to design functional fullerene based materials.

A facile approach to hydrophilic oxidized fullerenes and their derivatives as cytotoxic agents and supports for nanobiocatalytic systems

A facile, environment-friendly, versatile and reproducible approach to the successful oxidation of fullerenes (oxC₆₀) and the formation of highly hydrophilic fullerene derivatives is introduced. This synthesis relies on the widely known Staudenmaier’s method for the oxidation of graphite, to produce both epoxy and hydroxy groups on the surface of fullerenes (C₆₀) and thereby improve the solubility of the fullerene in polar solvents (e.g. water). The presence of epoxy groups allows for further functionalization via nucleophilic substitution reactions to generate new fullerene derivatives, which can potentially lead to a wealth of applications in the areas of medicine, biology, and composite materials. In order to justify the potential of oxidized C₆₀ derivatives for bio-applications, we investigated their cytotoxicity in vitro as well as their utilization as support in biocatalysis applications, taking the immobilization of laccase for the decolorization of synthetic industrial dyes as a trial case.

The Role of Functionalization in the Applications of Carbon Materials: An Overview

The carbon-based materials (CbMs) refer to a class of substances in which the carbon atoms can assume different hybridization states (sp1, sp2, sp3) leading to different allotropic structures -. In these substances, the carbon atoms can form robust covalent bonds with other carbon atoms or with a vast class of metallic and non-metallic elements, giving rise to an enormous number of compounds from small molecules to long chains to solids. This is one of the reasons why the carbon chemistry is at the basis of the organic chemistry and the biochemistry from which life on earth was born. In this context, the surface chemistry assumes a substantial role dictating the physical and chemical properties of the carbon-based materials. Different functionalities are obtained by bonding carbon atoms with heteroatoms (mainly oxygen, nitrogen, sulfur) determining a certain reactivity of the compound which otherwise is rather weak. This holds for classic materials such as the diamond, the graphite, the carbon black and the porous carbon but functionalization is widely applied also to the carbon nanostructures which came at play mainly in the last two decades. As a matter of fact, nowadays, in addition to fabrication of nano and porous structures, the functionalization of CbMs is at the basis of a number of applications as catalysis, energy conversion, sensing, biomedicine, adsorption etc. This work is dedicated to the modification of the surface chemistry reviewing the different approaches also considering the different macro and nano allotropic forms of carbon.

Carbon fragments as highly active metal-free catalysts for the oxygen reduction reaction: a mechanistic study

In metal-free carbon-fullerene-based or defective graphene-based electrocatalysts, pentagon rings are known to play a key role in boosting catalytic activities for the oxygen reduction reaction (ORR). However, the fundamental chemical mechanism underlying the remarkable catalytic effect of the pentagon rings towards the ORR is still not fully understood. Herein, we perform a comprehensive computational study of the catalytic activities of various carbon fullerenes and fullerene fragment species, all containing pentagon rings, by using the density functional theory (DFT) and computational hydrogen electrode (CHE) methods. We find that more active sites on carbon are associated with more neighbouring pentagon rings and stronger adsorption of the key intermediates of O*, OH* and OOH* for the ORR. Importantly, two C₆₀-based fragments, namely, C₆₀-frag1 and C₆₀-frag2l, show a very high activity towards the ORR, as both yield overpotentials as low as 0.389 and 0.407 V, and entail suitable adsorption free energy of OH* and OOH* species. These desirable chemical properties of fullerene fragments can be attributed to the high-energy HOMO orbitals, induced by the low-symmetry fullerene-fragment structures. Both the number of neighbouring pentagon rings and the degree of overall symmetry of the fragment appear to be the two important factors that can be adjusted for the design of optimal metal-free carbon electrocatalysts towards high ORR activities.

General One-step Synthesis of Symmetrical or Unsymmetrical 1,4-Di(organo)fullerenes from Organo(hydro)fullerenes through Direct Oxidative Arylation

A general one-step synthesis of symmetrical or unsymmetrical 1,4-di(organo)fullerenes from organo(hydro)fullerenes (RC₆₀H) is realized by direct oxidative arylation. The new combination of catalytic trifluoromethanesulfonic acid (TfOH) and stoichiometric o-chloranil is the first to be used to directly generate an R-C₆₀⁺ intermediate from common RC₆₀H. Unexpectedly, the in situ generated R-C₆₀⁺ intermediate is shown to be quite stable in whole ¹³C NMR spectroscopy characterization in the absence of cation quenching reagents. Because the direct oxidation of common RC₆₀H to form the corresponding R-C₆₀⁺ has never been realized, the present combination of TfOH and o-chloranil solves the challenges associated with the formation of stable RC₆₀⁺ cations from common RC₆₀H without any coordination of an R group.

[60]Fullerene for Medicinal Purposes, A Purity Criterion towards Regulatory Considerations

Since the early nineties countless publications have reported promising medicinal applications for [60]fullerene (C60) related to its unparalleled affinity towards free radicals. Yet, until now no officially approved C60-based drug has reached the market, notably because of the alleged dangers of C60. Nevertheless, since the publication of the effects of C60 on the lifespan of rodents, a myriad of companies started selling C60 worldwide for human consumption without any approved clinical trial. Nowadays, several independent teams have confirmed the safety of pure C60 while demonstrating that previously observed toxicity was due to impurities present in the used samples. However, a purity criterion for C60 samples is still lacking and there are no regulatory recommendations on this subject. In order to avoid a public health issue and for regulatory considerations, a quality-testing strategy is urgently needed. Here we have evaluated several analytical tools to verify the purity of commercially available C60 samples. Our data clearly show that differential scanning calorimetry is the best candidate to establish a purity criterion based on the sc-fcc transition of a C60 sample (Tonset ≥ 258 K, ∆sc-fccH ≥ 8 J g-1).

Easy, efficient and versatile one-pot synthesis of Janus-type-substituted fullerenols

An efficient one-pot synthesis for Janus-type fullerenol derivatives and how to characterize them is reported. This synthesis provides access to asymmetrically substituted fullerenol with five substituents on one pole of the fullerene and polyhydroxylation moieties, mostly ether and hydroxy groups, on the rest of the fullerene core. As substituents a broad variety of primary amines can be used to obtain Janus-type amphiphilic fullerenols in good to excellent yield. These fullerenol amphiphiles can serve as suitable precursors for further reactions resulting in new applications for fullerenols.

Are octahedral clusters missing on the carbon energy landscape?

We report a new class of carbon nanostructures at a lower sub-nano end of the size scale with a surprising stability, as compared to the well-known carbon fullerenes. The octahedral carbon clusters contain tetragonal rings, which, in spite of a common belief, prove to be an energy efficient means of plying graphene sheets to make three-dimensional spheroid shapes, similar to fullerenes. The two families of structures are shown to be competitive at small sizes (∼20 atoms) at room temperature, and for higher temperatures, at both small and large sizes (>200 atoms). Our calculations demonstrate that both vibrational and electronic spectra of these cluster families are similar, which thus might cloud their experimental identification. However, there is a sufficiently strong shift in vibrational frequencies below 160 and in the range of 600-800 cm^-1, which should help to identify different types of carbon clusters experimentally. We propose octahedral clusters and other structures containing tetragonal rings as viable structural elements and building units in inorganic chemistry and materials science of carbon along with fullerenes.

Hybrids of Fullerenes and 2D Nanomaterials

Fullerene has a definite 0D closed-cage molecular structure composed of merely sp2-hybridized carbon atoms, enabling it to serve as an important building block that is useful for constructing supramolecular assemblies and micro/nanofunctional materials. Conversely, graphene has a 2D layered structure, possessing an exceptionally large specific surface area and high carrier mobility. Likewise, other emerging graphene-analogous 2D nanomaterials, such as graphitic carbon nitride (g-C3N4), transition-metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and black phosphorus (BP), show unique electronic, physical, and chemical properties, which, however, exist only in the form of a monolayer and are typically anisotropic, limiting their applications. Upon hybridization with fullerenes, noncovalently or covalently, the physical/chemical properties of 2D nanomaterials can be tailored and, in most cases, improved, significantly extending their functionalities and applications. Here, an exhaustive review of all types of hybrids of fullerenes and 2D nanomaterials, such as graphene, g-C3N4, TMDs, h-BN, and BP, including their preparations, structures, properties, and applications, is presented. Finally, the prospects of fullerene-2D nanomaterial hybrids, especially the opportunity of creating unknown functional materials by means of hybridization, are envisioned.

Nucleophilic cyclopropanation of [60]fullerene by the addition–elimination mechanism

Information on the synthesis of monofunctionalized methanofullerenes C₆₀ obtained by the addition–elimination mechanism is generalized. The main reagents for cyclopropanation, mechanisms and optimal conditions for the processes, and the prospects for practical application of the products are considered.

Generalized material on the synthesis of monosubstituted methanofullerenes C₆₀, obtained by the addition–elimination mechanism.

Ionic-surfactants-based thermotropic liquid crystals

Ionic surfactants can be combined with various functional groups through electrostatic interaction, resulting in a series of thermotropic liquid crystals (TLCs).

Excitation-dependent electron exchange energy and electron transfer dynamics in a series of covalently tethered N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline - [C60] fullerene dyads via varying π-conjugated spacers

Femtosecond time-resolved fluorescence and transient absorption studies are reported for three newly synthesized covalently linked N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline (BBA) and pyrrolidinofullerenes (C60)-based donor-π conjugated bridge-acceptor dyads (D-B-A) as functions of the bridge length (7.1, 9.5 and 11.2 Å for Dyad-1, Dyad-2 and Dyad-3), dielectric constants of the medium and pump wavelengths. In polar solvent, ultrafast fluorescence quenching (kEET ≥ 2 × 1012 s-1) of the BBA moiety upon excitation of the BBA moiety (320 nm) is observed in the dyads and is assigned to a mechanism involving electron exchange energy transfer (EET) from 1BBA* to C60 followed by electron transfer from BBA to 1C60*. Cohesive rise and decay dynamics of conjugated BBA˙+-C60˙- anion pairs confirm the involvement of a distance independent adiabatic charge-separation (CS) process (kCS ≥ 2.2 × 1011 s-1) with near unity quantum efficiency (φCS ≥ 99.7%) and a distance-dependent non-adiabatic charge-recombination (CR) process [kCR ∼ (1010-108) s-1]. In contrast, excitation of the C60 moiety (λex = 430 to 700 nm) illustrates photoinduced electron transfer from BBA to 1C60*, involving non-adiabatic (diabatic) and distance-dependent CS (kCS in the range of 0.59-1.78 × 1011 s-1) with 98.86-99.6% (Dyad-3-Dyad-1) quantum efficiency and a CR process with kCR values [kCR ∼ (1010-108) s-1] up to three orders greater than kCS of the respective dyads. Both the processes, CS and CR, upon C60 excitation and the CR process upon BBA excitation show distance dependent rate constants with exponential factor β ≤ 0.5 Å-1, and electron transfer is concluded to occur through a covalently linked conjugated π bridge. Global and target analysis of fsTA data reveal the occurrence of two closely lying CS states, thermally hot (CShot) and thermally relaxed (CSeq) states, and two CR processes with two orders of different rate constants. Careful analysis of the kinetic and thermodynamic data allowed us to estimate the total reorganization energy and electronic coupling matrix (V), which decrease exponentially with distance. These novel features of the distance independent adiabatic CS process and the distance-dependent diabatic CR process upon donor excitation are due to extending the π-conjugation between BBA and C60. The demonstrated results may provide a benchmark in the design of light-harvesting molecular devices where ultrafast CS processes and long-lived CS states are essential requirements.

Rationalizing the Regioselectivity of the Diels-Alder Biscycloaddition of Fullerenes

The physical factors governing the regioselectivity of the double functionalization of fullerenes have been explored by means of density functional theory calculations. To this end, the second Diels-Alder cycloaddition reactions involving 1,3-butadiene and the parent C₆₀ fullerene as well as the ion-encapsulated system Li⁺@C₆₀ have been selected. In agreement with previous experimental findings on related processes, it is found that the cycloaddition reaction, involving either C₆₀ or Li⁺@C₆₀, occurs selectively at specific [6,6]-bonds. The combination of the activation strain model of reactivity and the energy decomposition analysis methods has been applied to gain a quantitative understanding into the markedly different reactivity of the available [6,6]-bonds leading to the observed regioselectivity in the transformation.

Unusual spin-polarized electron state in fullerene induced by carbon adatom defect

First-principles calculations show that a carbon adatom defect at the Def[5, 6] site on the surface of C₆₀ can produce a more stable spin-polarized singlet electronic state instead of a magnetic triplet state. This is clearly different from the cases of graphene and nanotubes. The mechanism results from the electron population of the adatom, which produces antiferromagnetic coupling around the C₆₀ cage and the adatom itself. Our calculations show the same phenomenon occurs in other IPR fullerenes, such as C₇₀ and C₈₀. These findings extend the understanding of the magnetic origin of pure carbon structures and are valuable for research related to the spin polarization of carbon systems.

Novel distyryl BODIPY–fullerene dyads: preparation, characterization and photosensitized singlet oxygen generation efficiency

Novel types of mono- and bis-distyryl-BODIPY–fullerene dyads, 6 and 7, were prepared by Bingel cyclopropanation.

Covalent functionalization of polyhedral graphitic particles synthesized by arc discharge from graphite

Occurrence of covalent functionalization of astralenes by radical addition.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Ultrafast charge-transfer in organic photovoltaic interfaces: geometrical and functionalization effects

Understanding the microscopic mechanisms of electronic excitation in organic photovoltaic cells is a challenging problem in the design of efficient devices capable of performing sunlight harvesting. Here we develop and apply an ab initio approach based on time-dependent density functional theory and Ehrenfest dynamics to investigate photoinduced charge transfer in small organic molecules. Our calculations include mixed quantum-classical dynamics with ions moving classically and electrons quantum mechanically, where no experimental external parameter other than the material geometry is required. We show that the behavior of photocarriers in zinc phthalocyanine (ZnPc) and C60 systems, an effective prototype system for organic solar cells, is sensitive to the atomic orientation of the donor and the acceptor units as well as the functionalization of covalent molecules at the interface. In particular, configurations with the ZnPc molecules facing on C60 facilitate charge transfer between substrate and molecules that occurs within 200 fs. In contrast, configurations where ZnPc is tilted above C60 present extremely low carrier injection efficiency even at longer times as an effect of the larger interfacial potential level offset and higher energetic barrier between the donor and acceptor molecules. An enhancement of charge injection into C60 at shorter times is observed as binding groups connect ZnPc and C60 in a dyad system. Our results demonstrate a promising way of designing and controlling photoinduced charge transfer on the atomic level in organic devices that would lead to efficient carrier separation and maximize device performance.

Highly hydroxide conductive ionomers with fullerene functionalities

A novel ionomer was designed that will not poison the catalyst in alkaline fuel cells, by incorporating for the first time N-methyl pyrrolidine-C60 cation in polymeric anion exchange ionomers. The resultant fullerene-based anion exchange ionomer shows an extremely high hydroxide conductivity (182 mS cm(-1)) at a low cation concentration (0.62 mmol g(-1)).

Synthetic Developments of Nontoxic Quantum Dots

Semiconductor nanocrystals, or quantum dots (QDs), are candidates for biological sensing, photovoltaics, and catalysis due to their unique photophysical properties. The most studied QDs are composed of heavy metals like cadmium and lead. However, this engenders concerns over heavy metal toxicity. To address this issue, numerous studies have explored the development of nontoxic (or more accurately less toxic) quantum dots. In this Review, we select three major classes of nontoxic quantum dots composed of carbon, silicon and Group I-III-VI elements and discuss the myriad of synthetic strategies and surface modification methods to synthesize quantum dots composed of these material systems.