Superhalogens inside fullerenes X@C2n (X = BO2, BeF3; 2n = 60, 70)

The exploration of endohedral fullerenes has garnered significant attention recently due to their distinctive chemical, electrochemical, and optoelectronic properties. Charge transfer, which usually occurs from encapsulated species to fullerenes, importantly affects the structures and properties of endohedral fullerenes. In this study, we theoretically investigated endohedral superhalogen fullerenes X@C2n (X = BO2, BeF3; 2n = 60, 70), in which the charge is reversely transferred from the fullerene to the superhalogen, by using density functional theory calculations and ab initio molecular dynamics simulations. Both natural population analysis and the quantum theory of atoms in molecules confirm about one electron transfer from the fullerene to the superhalogen, resulting in the formal valence state of X-@C2n+. Energy decomposition analysis on the interaction between the superhalogen and fullerene revealed that electrostatic energy contributes predominantly to the total interaction energy. These endohedral superhalogen fullerenes with cationic fullerenes were predicted to be able to serve as building blocks for one dimensional fullerene-based nanowires when combined with endohedral alkali-metallofullerenes with anionic fullerenes.

Formation of Doubly and Triply Charged Fullerene Dimers in Superfluid Helium Nanodroplets

Sequential ionization of fullerene cluster ions (C_{60})_{n}^{+} within multiply charged helium nanodroplets leads to the intriguing phenomenon of forming and stabilizing doubly and triply charged fullerene oligomers. While the formation of doubly charged dimers (C_{60})_{2}^{2+} has been predicted in earlier studies, the observation of even triply charged ones (C_{60})_{2}^{3+} is highly surprising. This remarkable resilience against Coulomb explosion is achieved through efficient cooling within the superfluid environment of helium nanodroplets and a sequential ionization scheme that populates covalently bound or physisorbed fullerene dimers. Calculations support the stability of four differently bonded (C_{60})_{2}^{2+} and (C_{60})_{2}^{3+} isomers and predict a low Coulomb barrier (<0.4  eV) preventing even dissociation of cold van der Waals complexes.

Electron Localization and Mobility in Monolayer Fullerene Networks

The novel 2D quasi-hexagonal phase of covalently bonded fullerene molecules (qHP C60), the so-called graphullerene, has displayed far superior electron mobilities, if compared to the parent van der Waals three-dimensional crystal (vdW C60). Herein, we present a comparative study of the electronic properties of vdW and qHP C60 using state-of-the-art electronic-structure calculations and a full quantum-mechanical treatment of electron transfer. We show that both materials entail polaronic localization of electrons with similar binding energies (≈0.1 eV) and, therefore, they share the same charge transport via polaron hopping. In fact, we quantitatively reproduce the sizable increment of the electron mobility measured for qHP C60 and identify its origin in the increased electronic coupling between C60 units.

Understanding the Electronic Structure and Chemical Bonding in the 2D Fullerene Monolayer

Recently synthesized two-dimensional (2D) monolayer quasi-hexagonal-phase fullerene (qHPC60) demonstrates excellent thermodynamic stability. Within this monolayer, each fullerene cluster is surrounded by six adjacent C60 cages along an equatorial plane and is connected by both C-C single bonds and [2 + 2] cycloaddition bonds that serve as bridges. In this study, we investigate the stability mechanism of the 2D qHPC60 monolayer by examining the electronic structure and chemical bonding through state-of-the-art theoretical methodologies. Density functional theory (DFT) studies reveal that 2D qHPC60 possesses a moderate direct electronic band gap of 1.46 eV, close to the experimental value (1.6 eV). It is found that the intermolecular bridge bonds play a crucial role in enhancing the charge flow and redistribution among C60 cages, leading to the formation of dual π-aromaticity within the C60 sphere and stabilizing the 2D framework structure. Furthermore, we identify a series of delocalized superatom molecular orbitals (SAMOs) within the 2D qHPC60 monolayer, exhibiting atomic orbital-like behavior and hybridization to form nearly free-electron (NFE) bands with σ/π bonding and σ*/π* antibonding properties. Our findings provide insights into the design and potential applications of NFE bands derived from SAMOs in 2D qHPC60 monolayers.

Structures, fundamental properties, and potential applications of low-dimensional C60 polymers and other nanocarbons: a review

Since carbon (C) atom has a variety of chemical bonds via hybridization between s and p atomic orbitals, it is well known that there are robust carbon materials. In particular, discovery of C60 has been an epoch making to cultivate nanocarbon fields. Since then, nanocarbon materials such as nanotube and graphene have been reported. It is interesting to note that C60 is soluble and volatile unlike nanotube and graphene. This indicates that C60 film is easy to be produced on any kinds of substrates, which is advantage for device fabrication. In particular, electron-/photo-induced C60 polymerization finally results in formation of one-dimensional (1D) metallic peanut-shaped and 2D dumbbell-shaped semiconducting C60 polymers, respectively. This enables us to control the physicochemical properties of C60 films using electron-/photo-lithography techniques. In this review, we focused on the structures, fundamental properties, and potential applications of the low-dimensional C60 polymers and other nanocarbons such as C60 peapods, wavy-structured graphene, and penta-nanotubes with topological defects. We hope this review will provide new insights for producing new novel nanocarbon materials and inspire broad readers to cultivate new further research in carbon materials.

Chemical properties of superatomic Li3O clusters from a density functional theory perspective: formation of chloride and adsorption behavior on graphynes

Superatomic clusters have received a lot of attention due to their ability to mimic the electronic configurations of individual atoms. Despite numerous studies of these clusters, their ability to mimic the chemical properties of individual atoms is still unclear. This also applies for Li3O/Li3O+ clusters which simulate the Na atom and its ion, but their capabilities to form a salt or be adsorbed on surfaces remain unexplored. In this work, a density functional theory investigation was performed to study the chemical formation and adsorption behavior of the superatomic Li3O cluster. The results show that Li3O mimics the chemical properties of the sodium element to form Li3O chloride and be adsorbed on graphdiyne and γ-graphyne with similar binding energy as the sodium adsorbate cases. Beyond the isolated cluster individuals, superatoms are demonstrated as elements from the 3D periodic table to construct compounds and attach onto solid surfaces.

Cinematographic study of stochastic chemical events at atomic resolution

The advent of single-molecule atomic-resolution time-resolved electron microscopy (SMART-EM) has created a new field of 'cinematic chemistry,' allowing for the cinematographic recording of dynamic behaviors of organic and inorganic molecules and their assembly. However, the limited electron dose per frame of video images presents a major challenge in SMART-EM. Recent advances in direct electron counting cameras and techniques to enhance image quality through the implementation of a denoising algorithm have enabled the tracking of stochastic molecular motions and chemical reactions with sub-millisecond temporal resolution and sub-angstrom localization precision. This review showcases the development of dynamic molecular imaging using the SMART-EM technique, highlighting insights into nanomechanical behavior during molecular shuttle motion, pathways of multistep chemical reactions, and elucidation of crystallization processes at the atomic level.

Boosting Photocatalytic Water Splitting of Polymeric C60 by Reduced Dimensionality from Two-Dimensional Monolayer to One-Dimensional Chain

The recent synthesis of monolayer fullerene networks (Hou, L., et al. Nature 2022, 606, 507) provides new opportunities for photovoltaics and photocatalysis because of their versatile crystal structures for further tailoring of electronic, optical, and chemical function. To shed light on the structural aspects of the photocatalytic water splitting performance of fullerene nanomaterials, we compare the photocatalytic properties of individual polymeric fullerene chains and monolayer fullerene networks from first-principles calculations. We find that the photocatalytic efficiency can be further optimized by reducing the dimensionality from two-dimensional (2D) to one-dimensional (1D). The conduction band edge of the polymeric C60 chain provides an external potential for the hydrogen reduction reaction much higher than that of its monolayer counterparts over a wider range of pH values, and there are 2 times more surface active sites in the 1D chain than in the 2D networks from a thermodynamic perspective. These observations identify the 1D fullerene polymer as a more promising candidate as a photocatalyst for the hydrogen evolution reaction in comparison to monolayer fullerene networks.

Spectroscopy of C60+ and C120+ in the mid-infrared

Infrared spectra of C60+ and C120+, obtained via helium messenger spectroscopy, are reported. For C60+, new absorption features have been found just above the discrete vibrational spectrum of the ion. The absorption profile, which is broad and contains little structure, is assigned to one or more electronic absorption transitions and is in good agreement with predictions from time-dependent density functional theory. It seems likely that the transitions observed correspond to excitation from the 2A1u electronic ground state to one or both of the low-lying 2E1u and 2E2u electronic states previously identified as dark states of C60+. These states presumably become optically bright through vibronic coupling and specifically the Jahn-Teller effect. In the case of C120+, the simplest positively charged oligomer of C60, we present the first vibrational spectrum of this ion. Through a comparison with theory, vibrational features are best explained by a peanut-shaped structure for C120+, maintained by covalent bonding between the two C60 units. We have also discovered electronic transitions for C120+, which, similar to C60+, lie just above the vibrational spectrum.

Diversity of platinum-sites at platinum/fullerene interface accelerates alkaline hydrogen evolution

Membrane-based alkaline water electrolyser is promising for cost-effective green hydrogen production. One of its key technological obstacles is the development of active catalyst-materials for alkaline hydrogen-evolution-reaction (HER). Here, we show that the activity of platinum towards alkaline HER can be significantly enhanced by anchoring platinum-clusters onto two-dimensional fullerene nanosheets. The unusually large lattice distance (~0.8 nm) of the fullerene nanosheets and the ultra-small size of the platinum-clusters (~2 nm) leads to strong confinement of platinum clusters accompanied by pronounced charge redistributions at the intimate platinum/fullerene interface. As a result, the platinum-fullerene composite exhibits 12 times higher intrinsic activity for alkaline HER than the state-of-the-art platinum/carbon black catalyst. Detailed kinetic and computational investigations revealed the origin of the enhanced activity to be the diverse binding properties of the platinum-sites at the interface of platinum/fullerene, which generates highly active sites for all elementary steps in alkaline HER, particularly the sluggish Volmer step. Furthermore, encouraging energy efficiency of 74% and stability were achieved for alkaline water electrolyser assembled using platinum-fullerene composite under industrially relevant testing conditions.

Organic photovoltaics: The current challenges

Organic photovoltaics are remarkably close to reaching a landmark power conversion efficiency of 20%. Given the current urgent concerns regarding climate change, research into renewable energy solutions is crucially important. In this perspective article, we highlight several key aspects of organic photovoltaics, ranging from fundamental understanding to implementation, that need to be addressed to ensure the success of this promising technology. We cover the intriguing ability of some acceptors to undergo efficient charge photogeneration in the absence of an energetic driving force and the effects of the resulting state hybridization. We explore one of the primary loss mechanisms of organic photovoltaics-non-radiative voltage losses-and the influence of the energy gap law. Triplet states are becoming increasingly relevant owing to their presence in even the most efficient non-fullerene blends, and we assess their role as both a loss mechanism and a potential strategy to enhance efficiency. Finally, two ways in which the implementation of organic photovoltaics can be simplified are addressed. The standard bulk heterojunction architecture could be superseded by either single material photovoltaics or sequentially deposited heterojunctions, and the attributes of both are considered. While several important challenges still lie ahead for organic photovoltaics, their future is, indeed, bright.

Long-range ordered porous carbons produced from C60

Carbon structures with covalent bonds connecting C₆₀ molecules have been reported^1-3, but their production methods typically result in very small amounts of sample, which restrict the detailed characterization and exploration necessary for potential applications. We report the gram-scale preparation of a new type of carbon, long-range ordered porous carbon (LOPC), from C₆₀ powder catalysed by α-Li₃N at ambient pressure. LOPC consists of connected broken C₆₀ cages that maintain long-range periodicity, and has been characterized by X-ray diffraction, Raman spectroscopy, magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, aberration-corrected transmission electron microscopy and neutron scattering. Numerical simulations based on a neural network show that LOPC is a metastable structure produced during the transformation from fullerene-type to graphene-type carbons. At a lower temperature, shorter annealing time or by using less α-Li₃N, a well-known polymerized C₆₀ crystal forms owing to the electron transfer from α-Li₃N to C₆₀. The carbon K-edge near-edge X-ray absorption fine structure shows a higher degree of delocalization of electrons in LOPC than in C₆₀(s). The electrical conductivity is 1.17 × 10^-2 S cm^-1 at room temperature, and conduction at T < 30  K appears to result from a combination of metallic-like transport over short distances punctuated by carrier hopping. The preparation of LOPC enables the discovery of other crystalline carbons starting from C₆₀(s).

A few-layer covalent network of fullerenes

The two natural allotropes of carbon, diamond and graphite, are extended networks of sp³-hybridized and sp²-hybridized atoms, respectively¹. By mixing different hybridizations and geometries of carbon, one could conceptually construct countless synthetic allotropes. Here we introduce graphullerene, a two-dimensional crystalline polymer of C₆₀ that bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet. We report charge-neutral, purely carbon-based macroscopic crystals that are large enough to be mechanically exfoliated to produce molecularly thin flakes with clean interfaces-a critical requirement for the creation of heterostructures and optoelectronic devices². The synthesis entails growing single crystals of layered polymeric (Mg₄C₆₀)_∞ by chemical vapour transport and subsequently removing the magnesium with dilute acid. We explore the thermal conductivity of this material and find it to be much higher than that of molecular C₆₀, which is a consequence of the in-plane covalent bonding. Furthermore, imaging few-layer graphullerene flakes using transmission electron microscopy and near-field nano-photoluminescence spectroscopy reveals the existence of moiré-like superlattices³. More broadly, the synthesis of extended carbon structures by polymerization of molecular precursors charts a clear path to the systematic design of materials for the construction of two-dimensional heterostructures with tunable optoelectronic properties.

Quantitative Characterization of Oxygen-Containing Groups on the Surface of Carbon Materials: XPS and NEXAFS Study

The results of the comparative quantitative study of oxygen-containing groups adsorbed on the surface of carbonized sponge scaffold (CSS), highly oriented pyrolytic graphite (HOPG), fullerite C60 and multi-walled carbon nanotubes (MWCNTs) introduced into a high vacuum from the atmosphere without any pre-treatment of the surface are discussed. The studied materials are first tested by XRD and Raman spectroscopy, and then quantitatively characterized by XPS and NEXAFS. The research results showed the presence of carbon oxides and water-dissociation products on the surfaces of materials. It was shown that main source of oxygen content (~2%) on the surface of HOPG, MWCNTs, and C60 powder is water condensed from the atmosphere in the form of an adsorbed water molecule and hydroxyl group. On the CSS surface, oxygen atoms are present in the forms of carbon oxides (4–5%) and adsorbed water molecules and hydroxyl groups (5–6%). The high content of adsorbed water on the CSS surface is due to the strong roughness and high porosity of the surface.

Time-Resolved Imaging of Stochastic Cascade Reactions over a Submillisecond to Second Time Range at the Angstrom Level

Many chemical reactions, such as multistep catalytic cycles, are cascade reactions in which a series of transient intermediates appear and disappear stochastically over an extended period. The mechanisms of such reactions are challenging to study, even in ultrafast pump-probe experiments. The dimerization of a van der Waals dimer of [60]fullerene producing a short carbon nanotube is a typical cascade reaction and is probably the most frequently studied in carbon materials chemistry. As many as 23 intermediates were predicted by theory, but only the first stable one has been verified experimentally. With the aid of fast electron microscopy, we obtained cinematographic recordings of individual molecules at a maximum frame rate of 1600 frames per second. Using Chambolle total variation algorithm processing and automated cross-correlation image matching analysis, we report on the identification of several metastable intermediates by their shape and size. Although the reaction events occurred stochastically, varying the lifetime of each intermediate accordingly, the average lifetime for each intermediate structure could be obtained from statistical analysis of many cinematographic images for the cascade reaction. Among the shortest-living intermediates, we detected one that lasted less than 3 ms in three independent cascade reactions. We anticipate that the rapid technological development of microscopy and image processing will soon initiate an era of cinematographic studies of chemical reactions and cinematic chemistry.

Relationship between molecular properties and degradation mechanisms of organic solar cells based on bis-adducts of phenyl-C61 butyric acid methyl ester

Environmental stability remains a major challenge for the commercialisation of organic solar cells and degradation pathways remain poorly understood. Designing materials for improved device stability requires an understanding of the relationship between the properties of the donor or acceptor molecule and different degradation mechanisms. Here we study the correlations between various molecular parameters of the fullerene derivative bis-PCBM and the degradation rate of polymer:bis-PCBM organic solar cells, based on the same carbazole-alt-benzothiadiazole polymer, in aerobic and anaerobic conditions. We compare eight high purity bis-PCBM isomers with different electronic, chemical and packing properties along with PCBM and the mixture of bis isomers. In the case of aerobic photodegradation, we find that device degradation rate is positively correlated to the LUMO energy of the bis-PCBM isomer and to the degree of crystallinity of the isomer, while the correlation of degradation with driving force for epoxide formation is unclear. These results support the idea that in these samples, aerobic photodegradation proceeds via superoxide formation by the photogenerated polaron on the fullerene, followed by further chemical reaction. In the absence of air, photodegradation rate is correlated with molecular structure, supporting the mechanism of microstructural degradation via fullerene dimerization. The approach and findings presented here show how control of specific molecular parameters through chemical design can serve as a strategy to enhance stability of organic solar cells.

Ionization and electron excitation of C60 in a carbon nanotube: A variable temperature/voltage transmission electron microscopic study

The destruction of specimen molecules by an electron beam (e-beam) is either beneficial, as in mass spectrometry capitalizing on ion formation, or deleterious, as in electron microscopy. In the latter application, the e-beam not only produces the specimen image, but also causes information loss upon prolonged irradiation. However, the atomistic mechanism of such loss has been unclear. Performing single-molecule kinetic analysis of C₆₀ dimerization in a carbon nanotube (CNT) under variable-temperature/voltage conditions, we identified three reactive species—that is, radical cation, singlet, and triplet excited states—reacting competitively as the voltage and the properties of the CNT were changed. The key enabler was in situ continuous recording of the whole reaction process, suggesting an upcoming new era of “cinematic chemistry.”

There is increasing attention to chemical applications of transmission electron microscopy, which is often plagued by radiation damage. The damage in organic matter predominantly occurs via radiolysis. Although radiolysis is highly important, previous studies on radiolysis have largely been descriptive and qualitative, lacking in such fundamental information as the product structure, the influence of the energy of the electrons, and the reaction kinetics. We need a chemically well-defined system to obtain such data and have chosen as a model a variable-temperature and variable-voltage (VT/VV) study of the [2 + 2] dimerization of a van der Waals dimer [60]fullerene (C₆₀) to C₁₂₀ in a carbon nanotube (CNT), as studied for several hundred individual reaction events at atomic resolution. We report here the identification of five reaction pathways that serve as mechanistic models of radiolysis damage. Two of them occur via a radical cation of the specimen generated by specimen ionization, and three involve singlet or triplet excited states of the specimen, as initiated by electron excitation of the CNT, followed by energy transfer to the specimen. The [2 + 2] product was identified by measuring the distance between the two C₆₀ moieties, and the mechanisms were distinguished by the pre-exponential factor and the Arrhenius activation energy—the standard protocol of chemical kinetic studies. The results illustrate the importance of VT/VV kinetic analysis in the studies of radiation damage and show that chemical ionization and electron excitation are inseparable, but different, mechanisms of radiation damage, which has so far been classified loosely under the single term “ionization.”

Interfacial Linkage and Carbon Encapsulation Enable Full Solution-Printed Perovskite Photovoltaics with Prolonged Lifespan

Simplified perovskite solar cells (PSCs) were fabricated with the perovskite layer sandwiched and encapsulated between carbon-based electron transport layer (ETL) and counter electrode (CE) by a fully blade-coated process. A self-assembled monolayer of amphiphilic silane (AS) molecules on transparent conducting oxide (TCO) substrate appeals to the fullerene ETL deposition and preserves its integrity against the solvent damage. The AS serves as a "molecular glue" to strengthen the adhesion toughness at the TCO/ETL interface via robust chemical interaction and bonding, facilitating the interfacial charge extraction, increasing PCEs by 77 % and reducing hysteresis. A PCE of 18.64 % was achieved for the fully printed devices, one of the highest reported for carbon-based PSCs. AS-assisted interfacial linkage and carbon-material-assisted self-encapsulation enhance the stability of the PSCs, which did not experience performance degradation when stored at ambient conditions for over 3000 h.

Probing Mechanistic Insights into Highly Efficient Lithium Storage of C60 Fullerene Enabled via Three-Electron-Redox Chemistry

Renewable organic cathodes with abundant elements show promise for sustainable rechargeable batteries. Herein, for the first time, utilizing C₆₀ fullerene as organic cathode for room-temperature lithium-ion battery is reported. The C₆₀  cathode shows robust electrochemical performance preferably in ether-based electrolyte. It delivers discharge capacity up to 120 mAh g^-1 and specific energy exceeding 200 Wh kg^-1 with high initial Coulombic efficiency of 91%. The as-fabricated battery holds a capacity of 90 mAh g^-1 after 50 cycles and showcases remarkable rate performance with 77 mAh g^-1 retained at 500 mA g^-1 . Noteworthily, three couples of unusual flat voltage plateaus recur at ≈2.4, 1.7, and 1.5 V, respectively. Diffusion-dominated three-electron-redox reactions are revealed by cyclic voltammogram and plateau capacities. Intriguingly, it is for the first time unveiled by in situ X-ray diffraction (XRD) that the C₆₀ cathode underwent three reversible phase transitions during lithiation/delithiation process, except for the initial discharge when irreversible polymerization in between C₆₀ nanoclusters existed as suggested by the characteristic irreversible peak shifts in both in situ XRD pattern and in situ Raman spectra. Cs-corrected transmission electron microscope corroborated these phase evolutions. Importantly, delithiation potentials derived from density-functional-theory simulation based on proposed phase structures qualitatively consists with experimental ones.

Ubiquitous organic molecule-based free-standing nanowires with ultra-high aspect ratios

The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems.

The role of spin in the degradation of organic photovoltaics

Stability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

A solid–liquid two-phase precipitation method for the growth of fullerene (C60) nanowires

A schematic diagram of the preparation of C60 nanowires by the solid–liquid two-phase precipitation method.

Hybrid Fullerene-Based Electron Transport Layers Improving the Thermal Stability of Perovskite Solar Cells

The structure-dependent thermal stability of fullerene electron transport layers (ETLs) and its impact on device stability have been underrated for years. Based on cocrystallographic understanding, herein, we develop a thermally stable ETL comprising a hybrid layer of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and [6,6]-phenyl-C₆₁-propylbenzene (PCPB). By tuning the weight ratios of PCBM and PCPB to influence the noncovalent intermolecular interactions and packing of fullerene derivatives, we obtained a champion device based on the 20PCPB (20 wt % addition of PCPB into the mixture of PCBM/PCPB) ETL and excellent thermal stability of 500 h under 85 °C thermal aging in a N₂ atmosphere in the dark. The present work exemplifies that cocrystallography can be a precise tool to probe the interaction and aggregation of fullerene derivatives in ETLs, and mixed fullerene derivatives can be sought as promising ETLs to enhance the long-term stability of perovskite solar cells under high-temperature working environments.

Electric-Field-Controllable Conductance Switching of an Overcrowded Ethylene Self-Assembled Monolayer

Molecular isomerism has been discussed from the viewpoint of the tiniest switch and memory elements in electronics. Here, we report an overcrowded ethylene-based molecular conductance switch, which fulfills all the essential requirements for implementation into electronic devices, namely, electric-field-controllable reversible conductance change with a molecular-level spatial resolution, robust conformational bistability under ambient conditions, and ordered monolayer formation on electrode surfaces. The conformational state of this overcrowded ethylene, represented by a folded or twisted conformer, is susceptible to external environments. Nanoscopic measurements using scanning tunneling microscopy techniques, together with theoretical simulations, revealed the electronic properties of each conformer adsorbed on Au(111). While the twisted conformer prevails in the molecularly dispersed state, upon self-assembly into a monolayer, a two-dimensional network structure of the folded conformer is preferentially formed due to particular intermolecular interaction. In the monolayer state, folded-to-twisted and its reverse isomerization can be controlled by the modulation of electric fields.

[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).

Significantly Enhanced Electrical Performances of Eco-Friendly Dielectric Liquids for Harsh Conditions with Fullerene

The eco-friendly vegetable liquid is increasingly used because of the growing demand for environmentally friendly dielectric liquid. A vegetable liquid/fullerene nanofluid was fabricated via ultrasonic processing with good dispersion of the fullerene nanoparticles. It was observed that a small amount of fullerene (~100 mg/L) can significantly improve the electrical properties of vegetable insulating liquid (dissipation factor decreased by 20.1%, volume resistivity increased by 23.3%, and Alternating Current (AC) dielectric breakdown strength increased by 8.6%). Meanwhile, the trace amount of fullerene is also able to improve the electrical performances (i.e., dissipation factor and electrical resistivity) of the vegetable nanofluid under harsh conditions of long-term thermal aging compared with the blank contrast. The reduced acid values (25%) and dissolved decomposition gases (58.2% for hydrogen) in the aged vegetable nanofluid indicate the inhibition of molecule decomposition of vegetable liquid with fullerene. The improved electrical performances and thermal resistance of the vegetable nanofluid contribute to the electron affinity of fullerene proved by calculation of electron density distribution on the surface. The thermogravimetric analysis of the nanofluid under different atmospheres interprets that the oxygen absorbed inevitably in the fullerene contributes to the performance deterioration of the nanofluids during the initial aging. This work provides a potential method towards eco-friendly dielectric liquid with great electrical performances for harsh environments.

A Promising Nano-Insulating-Oil for Industrial Application: Electrical Properties and Modification Mechanism

Despite being discovered more than 20 years ago, nanofluids still cannot be used in the power industry. The fundamental reason is that nano-insulating oil has poor stability, and its electrical performance decreases under negative impulse voltage. We found that C₆₀ nanoparticles can maintain long-term stability in insulating oil without surface modification. C₆₀ has strong electronegativity and photon absorption ability, which can comprehensively improve the electrical performance of insulating oil. This finding has great significance for the industrial application of nano-insulating oil. In this study, six concentrations of nano-C₆₀ modified insulating oil (CMIO) were prepared, and their breakdown strength and dielectric properties were tested. The thermally stimulated current (TSC) curves of fresh oil (FO) and CMIO were experimentally determined. The test results indicate that C₆₀ nanoparticles can simultaneously improve the positive and negative lightning impulse and power frequency breakdown voltage of insulating oil, while hardly increasing dielectric loss. At 150 mg/L, the positive and negative lightning impulse breakdown voltages of CMIO increased by 7.51% and 8.33%, respectively, compared with those of FO. The AC average breakdown voltage reached its peak (18.0% higher compared with FO) at a CMIO concentration of 200 mg/L. Based on the test results and the special properties of C₆₀, we believe that changes in the trap parameters, the strong electron capture ability of C₆₀, and the absorption capacity of C₆₀ for photons enhanced the breakdown performance of insulating oil by C₆₀ nanoparticles.

Self-Assembled Fullerene Crystals as Excellent Aromatic Vapor Sensors

Here we report the aromatic vapor sensing performance of bitter melon shaped nanoporous fullerene C₆₀ crystals that are self-assembled at a liquid-liquid interface between isopropyl alcohol and C₆₀ solution in dodecylbenzene at 25 °C. Average length and center diameter of the crystals were ca. 10 μm and ~2 μm, respectively. Powder X-ray diffraction pattern (pXRD) confirmed a face-centered cubic (fcc) structure with cell dimension ca. a = 1.4272 nm, and V = 2.907 nm³, which is similar to that of the pristine fullerene C₆₀. Transmission electron microscopy (TEM) confirmed the presence of a nanoporous structure. Quartz crystal microbalance (QCM) results showed that the bitter melon shaped nanoporous C₆₀ performs as an excellent sensing system, particularly for aromatic vapors, due to their easy diffusion through the porous architecture and strong π–π interactions with the sp²-carbon.

Direct observation of C60− nano-ion gas phase ozonation via ion mobility-mass spectrometry

Atmospheric pressure differential mobility analysis-mass spectrometry facilitates determination of nano-ion-neutral reaction rates approaching the collision controlled limit.

Spin density transfer from guest to host in endohedral heterofullerene dimers

The endohedral heterofullerenes (B@C₅₉B)₂, (B@C₅₉N)₂, (N@C₅₉B)₂ and (B@C₅₉N–N@C₅₉B) are investigated using dispersion corrected density functional theory.

Two-Dimensional Fullerene Assembly from an Exfoliated van der Waals Template

Two-dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom-up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C₆₀ as a polymerizable monomer. The C₆₀ building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C₆₀ monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C₆₀ . The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid.

Femtosecond Dynamics of Photoexcited C60 Films

The well known organic semiconductor C₆₀ is attracting renewed attention due to its centimeter-long electron diffusion length and high performance of solar cells containing 95% fullerene, yet its photophysical properties remain poorly understood. We elucidate the dynamics of Frenkel and intermolecular (inter-C₆₀) charge-transfer (CT) excitons in neat and diluted C₆₀ films from high-quality femtosecond transient absorption (TA) measurements performed at low fluences and free from oxygen or pump-induced photodimerization. We find from preferential excitation of either species that the CT excitons give rise to a strong electro-absorption (EA) signal but are extremely short-lived. The Frenkel exciton relaxation and triplet yield strongly depend on the C₆₀ aggregation. Finally, TA measurements on full devices with applied electric field allow us to optically monitor the dissociation of CT excitons into free charges for the first time and to demonstrate the influence of cluster size on the spectral signature of the C₆₀ anion.

Realizing Large-Area Arrays of Semiconducting Fullerene Nanostructures with Direct Laser Interference Patterning

We present a laser interference patterning method for the facile fabrication of large-area and high-contrast arrays of semiconducting fullerene nanostructures, which does not rely on a tedious application of sacrificial photoresists or photomasks. A solution-deposited phenyl-C₆₁-butyric acid methyl ester (PCBM) fullerene thin film is exposed to a spatially modulated illumination intensity, as realized by a two-beam laser interference. The PCBM molecules exposed to strong intensity are photochemically transformed into a low-solubility dimeric state, so that the nontransformed PCBM molecules can be selectively removed in a subsequent solution-based development step. Following brief exposure to green laser light (λ = 532 nm, t = 5 s, p = 0.17 W cm^-2) in the designed two-beam interference setup, and a 1 min development in a tuned acetone-chloroform solution, we realize well-defined and ordered PCBM nanostripe patterns with a fwhm line width of ∼200 nm and a repetition rate of ∼2.900 lines mm^-1 over a large area of 1 cm². We demonstrate that a desired high contrast is effectuated because the initial PCBM-dimer transformation rate is dependent on the square of the illumination intensity. The semiconducting functionality of the patterned fullerene is verified in a field-effect transistor experiment, where a typical PCBM nanostripe featured an electron mobility of 5.3 × 10^-3 cm² V^-1 s^-1 and an on/off ratio of 3 × 10³.

Chemical kinetics study through observation of individual reaction events with atomic-resolution electron microscopy

Single-molecule atomic-resolution real-time electron microscopic movie imaging is an emerging new tool for obtaining dynamic structural information on molecules and molecular assemblies. This method provides a hitherto inaccessible possibility to in situ observe the time evolution of chemical events at various temperatures from the beginning till the end, as demonstrated for the kinetics study of [2 + 2] cycloaddition of [60]fullerene molecules, which was found to occur via an excited state or via radical cation depending on the temperature. One unique feature of this methodology is that, by observing directly the reaction events, one can obtain information on the frequency of events unperturbed by molecular diffusion. With the obtained experimental data set, we provided the first experimental proof of what the quantum mechanical transition state theory predicted, in that isolated molecules behave as if all their accessible states were occupied in a random order. We also found that, under the 1-D reaction conditions, molecular-level information on a few hundred molecules suffices to deduce statistically meaningful kinetics data that match with those obtained by bulk experiments.

Direct Microscopic Analysis of Individual C60 Dimerization Events: Kinetics and Mechanisms

Modern transition state theory states that the statistical behavior of a chemical reaction is the sum of individual chemical events that occur randomly. Statistical analysis of each event for individual molecules in a three-dimensional space however is practically impossible. We report here that kinetics and mechanisms of chemical reactions can be investigated by using a one-dimensional system where reaction events can be observed in situ and counted one by one using variable-temperature (VT) atomic-resolution transmission electron microscopy (TEM). We thereby provide direct proof that the ensemble behavior of random events conforms to the Rice-Ramsperger-Kassel-Marcus theory, as illustrated for [2 + 2] cycloaddition of C₆₀ molecules in carbon nanotubes (CNTs). This method gives kinetic and structural information for different types of reactions occurring simultaneously in the microscopic view field, suggesting that the VT-TEM opens a new dimension of chemical kinetics research on molecules and their assemblies in their excited and ionized states. The study carried out at 393-493 K showed that pristine CNT primarily acts as a singlet sensitizer of the cycloaddition reaction that takes place with an activation energy of 33.5 ± 6.8 kJ/mol. On the other hand, CNT suffers electron damage of the conjugated system at 103-203 K and promotes a reactive radical cation path that takes place with an activation energy of only 1.9 ± 0.7 kJ/mol. The pre-exponential factor of the Arrhenius plot gave us further mechanistic insights.

Progress in Understanding Degradation Mechanisms and Improving Stability in Organic Photovoltaics

Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo-induced burn-in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long-term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long-term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo-induced burn-in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn-in effect.