Initial Fullerene Research Articles

Loosely Bounded Exciton with Enhanced Delocalization Capability Boosting Efficiency of Organic Solar Cells.

In organic solar cells (OSCs), electronacceptorshaveundergone multipleupdates, from the initial fullerene derivatives, to the later acceptor-donor-acceptor type non-fullerene acceptors (NFAs), and now to Y-series NFAs, based on which efficiencies have reached over 19%. However, the key property responsible for further improved efficiency from molecular structure design is remained unclear. Herein, the material properties are comprehensively scanned by selecting PC71BM, IT-4F, and L8-BO as the representatives for different development stages of acceptors. For comparison, asymmetric acceptor of BTP-H5 with desired loosely bounded excitons is designed and synthesized. It's identified that the reduction of intrinsically exciton binding energy (Eb) and the enhancement of exciton delocalization capability act as the key roles in boosting the performance. Notably, 100 meV reduction in Eb has been observed from PC71BM to BTP-H5, correspondingly, electron-hole pair distance of BTP-H5 is almost two times over PC71BM. As a result, efficiency is improved from 40% of S-Q limit for PC71BM-based OSC to 60% for BTP-H5-based one, which achieves an efficiency of 19.07%, among the highest values for binary OSCs. This work reveals the confirmed function of exciton delocalization capability quantitatively in pushing the efficiency of OSCs, thus providing an enlightenment for future molecular design.

Effect of fullerene C60 thermal and tribomechanical loading on Raman signals

Fullerene C60 powder was loaded by 1 N normal force and exposed to sliding under different frequencies for 15 min. It is shown that the velocity of the sliding movement determines the stability of the fullerene C60 powder. At slow velocity of movement with a frequency of 1 Hz under 1 N normal force, the fullerene C60 structure remains undamaged after 15 min sliding. On the contrary, high sliding velocities of 10 Hz and 50 Hz affected fragmentation of the fullerene C60, which resulted in a reduction of the coefficient of friction (COF). During sliding with 1 Hz, the friction reached the highest level with an average COF of 0.59 ± 0.03. The faster relative motion under 1 N normal force gave a lower average COF with 0.39 ± 0.03. The initial fullerene C60 powder formed a thick compressed layer in the tribomechanical loaded zone. As proven by Raman spectroscopy, operating the tribomechanical sliding test at 50 Hz stimulated the re-attraction of fresh C60 fullerene island onto the fragmented layer from outside of the loaded powder regions. The COF was increasing again up to 0.44 ± 0.04 for 1 N normal force and 50 Hz frequency. The fragmentation and decomposition of fullerene C60 with increasing sliding velocity is attributed to thermal heating up during fast relative movement. Raman spectra of the tribomechanical loaded fullerene C60 are compared with Raman spectra from slowly heated up C60 in air and with Raman spectra of laser irradiated fullerene C60.

Geometric modeling of midi-fullerene growth from C32 to C60

Axonometric projections together with the corresponding graphs for fullerenes are constructed in the range from 32 to 60. The growth of fullerenes is studied on the basis of a mechanism according to which a carbon dimer embeds in a hexagon of an initial fullerene. This leads to stretching and breaking the covalent bonds which are parallel to arising tensile forces. In this case, instead of a hexagon adjoining two pentagons, two adjacent pentagons adjoining two hexagons are obtained. As a result, there arises a new atomic configuration and there is mass increase of two carbon atoms. We considered the direct descendants of fullerene C32; namely, C2n, where n=17–30.

Geometric modeling of midi-fullerenes growth from C24 to C48

Axonometric projections together with corresponding graphs for fullerenes are constructed in the range from 24 to 48. The growth of fullerenes is studied on the basis of the mechanism, according to which a carbon dimer embeds in a hexagon of an initial fullerene. This leads to stretching and breaking the covalent bonds which are parallel to arising tensile forces. In this case, instead of the hexagon adjoining two pentagons, one obtains two adjacent pentagons adjoining two hexagons. As a result, there arises a new atomic configuration and there is mass increase of two carbon atoms. We considered direct descendants of fullerene C24; namely, C2n, where n=13–24.

Facile Method toward Hierarchical Fullerene Architectures with Enhanced Hydrophobicity and Photoluminescence.

A two-step self-assembly strategy has been developed for the preparation of fullerene hierarchical architectures. Typically, the precipitation method is utilized to synthesize the initial fullerene microstructures, and subsequently a drop-drying process is employed to facilitate the fullerene microstructures to self-assemble into the final hierarchical structures. Overall, this methodology is quite simple and feasible, which can be applied to prepare fullerene hierarchical structures with different morphological features, simply by choosing proper solvent. Moreover, the as-obtained C70 hierarchical structures have many superior properties over the original C70 microrods such as superhydrophobicity and unique photoluminescence behaviors, promising their applications as waterproof optoelectronics.

A Study of the Aromaticity of the Heterofullerene C24–2nBnNn(n = 3 or 6) and C12N12 Isomers

The global aromaticity of the heterofullerene C24–2nBnNn(n = 3 or 6) and C12N12 isomers formed from the initial C24 fullerene with D6 symmetry, has been investigated using both the topological resonance energy (TRE) and the percentage topological resonance energy (%TRE) methods. The local aromaticity was studied using the bond resonance energy (BRE) method. Analysis was made of the effects of the types, the numbers, and the arrangements of heteroatoms on the global and local aromaticity of the molecules under consideration. Our results obtained by the TRE and %TRE methods were compared with the nucleus independent chemical shift (NICS (0)) values at the cage center. We found that NICS(0) values were not suitable for estimating the global aromaticity of these compounds. It was expected that the inclusion of heteroatoms would decrease the antiaromaticity relative to the C24(D6) cage. Our BRE results show that the antiaromaticity is primarily related to the existence of highly reactive antiaromatic bonds in the molecule. We found that when a local structure within the cage had two nitrogen and one boron atom in the same pentagon ring, it played an important role in the global aromaticity of these compounds. Finally, we predicted the kinetic stability using the minimum BRE method.

有机芳香烃掺杂控制C60微/纳米晶形貌和发光

The luminescence intensity of initial fullerene is very low because of its high molecular symmetry. The key point to enhance the luminescence intensity of fullerene is to lower the molecular symmetry of fullerene,which could make the forbidden bands transition allowed. Herein,C60 nano /microcrystals were synthesized by the evaporation of C60 saturated solution in m-xylene,1,2,3-trichlorobenzene,1,2,4-trichlorobenzene,and 1,3,5-trichlorobenzene. The structures of C60 nanocrystals were controlled and their PL intensities were also highly enhanced by the introduction of different solvent.

Understanding High-Yield Catalyst-Free Growth of Horizontally Aligned Single-Walled Carbon Nanotubes Nucleated by Activated C60 Species

Our understanding of the catalyst-free growth of single-walled carbon nanotubes by chemical vapor deposition is limited. Toward improving our knowledge base, we conducted systematic investigations into the initial preparation of C(60) fullerenes as nucleation precursors for single-wall and even double-wall carbon nanotube fabrication. The role of the dispersing media is shown to be crucial and is related to the initial fullerene cluster size. Oxygen-based groups, in particular, epoxy groups, are shown to be vital prior to actual growth. Moreover, the presence of oxygen groups during the growth phase is necessary for tube development. We also demonstrate the possibility of fabricating the tubes in crossbar configurations with bespoke crossing angles in a single synthesis step, unlike other routes which require at least two synthesis steps. The systematic studies significantly advance our understanding of the growth mechanisms involved in all-carbon catalyst-free growth of single- and double-walled carbon nanotubes.

Pressure- and temperature-induced transformations in crystalline polymers of C60

The great advantage of the C60 molecule is its potential for polymerization, due to which the molecule can be the building block of new all carbon materials. In addition, it contains, both sp2 and sp3 hybridized carbon atoms, which allows synthesizing new carbon materials with desired physicochemical properties using both types of carbon bonding. The one- and two-dimensional polymeric phases of C60 are prototype materials of this sort. Their properties, especially polymerization under pressure and room temperature via covalent bonding between molecules belonging to adjacent polymeric chains or polymeric layers, can be used for further development of new materials. The present review focuses on the study of the pressure-induced polymerization and thermodynamic stability of these materials and their recovered new phases by in-situ high-pressure Raman and X-ray diffraction studies. The phonon spectra show that the fullerene molecular cage in the high-pressure phases is preserved, while these polymers decompose under heat treatment into the initial fullerene C60 monomer.

SYNTHESIS OF FULLEROPYRROLIDINE PYRIDINIUM SALTS BY FACILE ANION EXCHANGE AND THEIR SOLUBILITY

Several ionic fullerene salts have been prepared based on a fulleropyrrolidine pyridinium cation and four different anions. The initial ionic fullerene can be easily prepared by quaternization of a pyridine-appended fulleropyrrolidine derivative in high yield. Anion exchange is a simple procedure giving several different salts of varying polarity. In addition to their characterization, the quantitative solubility of these salts has been studied in seven different solvents, including an imidazolium ionic liquid.

Laser mass spectrometry study of the properties of fullerene structures

Fullerene films grown by various methods are studied using mass spectrometry. The mass spectra of the films formed onto an aluminum foil using thermal deposition (TD) or supersonic molecular beam (SMB) exhibit a small change in the mass peak distribution in the C120 dimer range as compared to the initial fullerene powder during desorption by laser radiation irrespective of the radiation wavelength (λ = 259, 518 nm). Under the action of laser radiation with wavelength λ = 259 nm, fullerene films grown on a silicon substrate with an SMB also exhibit a small change in the mass peak distribution in the C120 dimer range. At λ = 518 nm, the mass peak distribution in the dimer range shifts significantly toward small masses, so that the intensity maximum corresponds to M ≅ C102. This fact is assumed to be related to the polymerization of an SMB fullerene film caused by heating due to the absorption of laser radiation with a wavelength λ = 518 nm.

The thermodynamic properties of bis(η6-o-xylene)chromium(I) fulleride over the temperature range from T → 0 to 340 K

The temperature dependence of the heat capacity of bis(η6-o-xylene)chromium(I) fulleride, [(η6-(o-xylene))2Cr]+•[C60]•−, over the temperature range 6–340 K was measured on an adiabatic vacuum calorimeter. The low-temperature (20 K ≤ T ≤ 50 K) heat capacity was subjected to multifractal processing; conclusions about the heterodynamic character of the structure were drawn. The experimental data were used to calculate the standard thermodynamic functions Cp∘(T), H∘(T)-H∘(0), S∘(T), and G∘(T)-H∘(0) over the temperature range from T → 0 to 340 K and estimate the standard entropy of fulleride formation from simple substances at 298.15 K. The standard thermodynamic characteristics of [(η6-(o-xylene))2Cr]+•[C60]•− were compared with those of the initial fullerene C60.

Cathodoluminescence studies of C60 fullerene-based films and nanostructures

The objects of investigation in this work are submicron Cm fullerene-based films and fullerene nanostructures fabricated by electron-beam lithography. The set of techniques for studying the fullerenes is extended due to attraction of the spectral cathodoluminescence (CL) to either of the initial fullerene films or submicron net structures with period of about 0.9 μm, wall height 0.6 μm, and width about 0.4 μm.

C60 Degradation Effect on Polystyrene under the Fullerene‐Polymer Interaction

Study of the content of composite polystyrene‐fullerene samples prepared from solution by the solvent evaporation method have been performed with the size exclusion chromatography, translation diffusion, viscometry and electro‐optical Kerr effect techniques. It was established that polystyrene interacts with fullerene C60 in benzene without any special treatment at room temperature just after the mixing of polymer and fullerene solutions. The product of this interaction contains initial polystyrene and low molecular fullerene adducts that appear as a result of depolymerization of a significant part (up to 40 wt.%) of polymer chains.

Fullerene films deposited by evaporation in vacuum using spot-focused annular electron beam

A rapidly focused annular electron beam can provide for the effective evaporation of a fullerene mixture in a vacuum of ∼10−2 Pa. A 1-kW beam focused into a spot within 0.1–1 s produces explosive evaporation of a fullerene target at an extremely high efficiency of heating. A comparison of the Raman and electronic absorption spectra of the initial fullerene powder and a film deposited upon its evaporation shows that C60 and C70 fullerenes are evaporated without rupture of C-C covalent bonds. The electron beam evaporation in vacuum has been successfully used to obtain fullerene films on substrates with an area of ∼0.1 m2.

Pulse-Arc System for Investigation of Initial Fullerene Deposition

Abstract Since the discovery of fullerenes and carbon nanotubes, the deposits on arc electrodes produced at high gas pressure have been investigated intensely. Despite of the enthusiasm, little work was reported about the initial deposition processes. In principle, such processes could be followed by reducing the amount of products, i.e. a short discharge with a small current. In practice, however, this was prevented by two practical obstacles, arc instability and possible byproducts originated from reactions with remaining impurities in the vacuum chamber. In the present study, we reported a new kind of compact preparation system which allowed stable arc with a small current and a clean environment. Figure 1 shows a schematic diagram of the system. For higher arc stability, the system had a small cylindrical shape which would reduce the effect of convection. Both electrodes were aligned on the axis inside the cylinder and their gap was adjustable by a micrometer.

Fullerenes as nuclei of carbon black particles

The existing models for the structure and inception processes of carbon black particles are analyzed taking into account the experimental data on the cluster formation. A new model of the formation of carbon black particles is proposed. The inference is made that single-layer fullerenes being the minimum possible closed carbon black particles serve as nuclei of large-sized carbon black particles. These particles grow via the deposition of carbon layers on the surface of fullerenes with defects. The defects fulfill the role of seeds that give rise to the front of the layer growth. The defect-free fullerenes do not take part in the carbon black formation due to the thermodynamic stability as a result of structural perfection. The primary carbon black particles—globules—are many-layer formations with a hole in the center whose size and configuration match the size and configuration of the initial fullerene nucleus. The layers in the form of concentric spheroids inserted into each other are composed of distorted and defect carbon networks. The flatest parts of several outer layers of carbon black particles are the regions of the coherent X-ray scattering.

Nature of radiation-stimulated phase transformations of graphite nanotubules to fullerenes and onions

The proposed model furnishes an explanation of radiation-stimulated transformation of graphitic nanotubules under electron-beam irradiation at 300 keV energy. During irradiation graphitic nanotubules and graphitic petals of collapsed and curled into spherical fullerene nanoparticles with multilayer structure (onions). With the carbon nano-formations having developed surface, the superficial effects have to play a tangible role in the equilibrium and transition of phases. Estimations of the value of surface and pressure change from superficial stretch is indicative of spherical carbon nanoparticles formation to be preferable. The build-up of additional spheres around the initial fullerene (onion formation) and hence its radius increase gradually lowers the Laplace pressure.

96/04961 Surface fractal dimension of graphitized carbon black particles

Axonometric projections together with the corresponding graphs for fullerenes are constructed in the range from 32 to 60. The growth of fullerenes is studied on the basis of a mechanism according to which a carbon dimer embeds in a hexagon of an initial fullerene. This leads to stretching and breaking the covalent bonds which are parallel to arising tensile forces. In this case, instead of a hexagon adjoining two pentagons, two adjacent pentagons adjoining two hexagons are obtained. As a result, there arises a new atomic configuration and there is mass increase of two carbon atoms. We considered the direct descendants of fullerene C32; namely, C2n, where n = 17–30.

Crystalline Ropes of Metallic Carbon Nanotubes

Fullerene single-wall nanotubes (SWNTs) were produced in yields of more than 70 percent by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200degreesC. X-ray diffraction and electron microscopy showed that these SWNTs are nearly uniform in diameter and that they self-organize into "ropes," which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 angstroms. The x-ray form factor is consistent with that of uniformly charged cylinders 13.8 +/- 0.2 angstroms in diameter. The ropes were metallic, with a single-rope resistivity of <10(-4) ohm-centimeters at 300 kelvin. The uniformity of SWNT diameter is attributed to the efficient annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the strain energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly favor the metallic (10,10) tube with C5v symmetry and an open edge stabilized by triple bonds.