Fullerene Crystals Research Articles

Bimolecular Crystals of Fullerenes in Conjugated Polymers and the Implications of Molecular Mixing for Solar Cells

AbstractThe performance of polymer:fullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X‐ray diffraction is used to demonstrate the formation of stable, well‐ordered bimolecular crystals of fullerene intercalated between the side‐chains of the semiconducting polymer poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side‐chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2‐methoxy‐5‐(3′,7′‐dimethyloxy)‐p‐phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large‐scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation of fullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method of intentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications.

Auger investigation of fullerene nanowhiskers heat-treated at 400-800 degrees centigrade

Fullerene nanowhiskers were prepared from a toluene solution of C60 and isopropyl alcohol by a liquid-liquid precipitation method. The samples on the silicon (100) wafer were heated at the elevated temperatures ranging from 400 °C through 800 °C by an electron beam bombardment in an ultra-high vacuum, and their thermal stability was investigated with a scanning Auger-electron microprobe. At 400 °C fullerene nanowhiskers already got thinner, while bulky fullerene crystals still remained even at 800 °C. And many craters were observed around the fullerene crystals on the Si(100) substrate.

Growth mechanism of vertically aligned fullerene micro tubes prepared by the liquid-liquid interfacial precipitation method

C60-based materials such as FNWs and FNTs are new candidates for organic electronics and solar cells. Recently, a method to produce vertically-aligned fullerene microtube crystals (VFMTs) has been established. The VFMTs are exepected to be used as field emission devices, solar cells, fuel cells, and so forth. To realize such attractive applications, structures and arrangements of VFMTs should be controlled. In oder to know the growth mechanism of VFMTs, Scanning electron microscopy (SEM) observations were performed for several injection periods of VFMTs. In the initial stage of synthesis (IPA injection time of 60 min), vertically aligned thin non-tubular fullerene microwhiskers (VFMWs) formed on AAO substrates. The outer and inner diameter of VFMWs became increased with increasing the injected amount of IPA. And also the size of tube holes became larger. The tubular structures appeared at an injection time of around 90 min. At an injection time of 120 min, vertically aligned FMTs with hexagonal cross sections and holes were obtained and their diameter and structure did not change up to the final stage of injection time of 3 00 min.

Temperature dependence of the spectral profile and total intensity of the second-harmonic signal of the fullerene crystal

The temperature dependence of second-harmonic generation in crystalline fullerene is simulated based on a microscopic model of orientational disorder, with special emphasis on the vicinity of the phase transition. The temperature-induced changes of the total second-harmonic intensity and of the corresponding spectral profile are treated on equal footing within a consistent theoretical framework. In addition to the previously applied approach where superexchange-type exciton transfer via the charge transfer (CT) manifold was described phenomenologically, and alternative model invoking the CT states explicitly is proposed, giving deeper insight into the underlying physics. Both models yield very good agreement with experimental results.

形態制御可能な単分散C60ナノ結晶の創製

The preparation of fullerene fine crystals with uniform size and shape would permit the control of their specific electronic energy levels and the fabrication of materials with completely new properties. To this end, we have successfully fabricated, for the first time, shape- and size controlled C60 nanocrystals using a reprecipitation method developed in our laboratory. The C60 nanocrystals obtained were clearly monodisperse and came in an interesting diversity of shapes such as spherical, rodlike, fibrous, disk, and octahedral. We were able to selectively control these sizes and shapes by simply changing the combination of solvents used and the reprecipitation conditions.

Study of the Desensitizing Effect of Different [60]Fullerene Crystals on Cyclotetramethylenetetranitramine (HMX)

AbstractThree types of [60]fullerene crystals were obtained. The first one was the direct commercial [60]fullerene, and the other two were recrystallized from the first one in carbon bisulfide and in carbon bisulfide/petroleum ether, respectively. Scanning electron microscopy (SEM), X‐ray powder diffractometry (XRD), and FT‐IR spectrometry were used to study the physical characteristics of the crystals. The thermal stability of the three [60]fullerene crystals was studied by differential thermal analysis (DTA), and the effects of the three [60]fullerenes on the mechanical sensitivity and friction sensitivity of HMX were tested and analyzed. It was found that the three types of [60]fullerenes have different thermal stabilities, and the friction and impact sensitivities of HMX are reduced from 100% to 70% and to 60%, respectively when 1% [60]fullerene 3 was added in HMX.

Electrically controlled dynamic holographic gratings in fullerene C60-doped nematic liquid crystals

A new method to demonstrate the dynamic enhancement of the photorefractive effect in C60-doped homeotropically aligned 4-cyano-4′-pentyl-biphenyl (5CB) liquid crystals under the influence of an externally applied dc voltage is presented in the read-out process. We observed clear holographic images due to the transient diffraction efficiency enhancement controlled by the application of a dc voltage. The hidden gratings are due to a light-induced surface-charge modulation and amplified by the Carr–Helfrich effect in the presence of the electric field produced by the dc voltage. A qualitative analysis of the phenomenon, according to which the effective bulk voltage is modulated due to light-induced surface modifications, is proposed. We achieved the highest transient first-order diffraction efficiency of up to 40%. The effective nonlinear index coefficient is as large as 0.2 cm2 W−1.

Rotational dynamics and polymerization of C60 in C60-cubane crystals: A molecular dynamics study

We report classical and tight-binding molecular dynamics simulations of the C(60) fullerene and cubane molecular crystal in order to investigate the intermolecular dynamics and polymerization processes. Our results show that, for 200 and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations, while C(60) fullerenes show rotational motions. Fullerenes perform "free" rotational motions at short times (approximately < 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (approximately > 10 ps). The mechanisms underlying these dynamics are presented. Random copolymerizations among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure. Changes in the radial distribution function and electronic density of states indicate the coexistence of amorphous and crystalline phases. The different conformational phases that cubanes and fullerenes undergo during the copolymerization process are discussed.

High-pressure stability ofCs6C60

The ${\mathrm{Cs}}_{6}{\mathrm{C}}_{60}$ molecular crystal has been studied by Raman spectroscopy measurements and ab initio calculations under high pressure. The Raman scattering data have been collected from ambient pressure up to $45.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at room temperature. It is shown that the intercalation of cesium atoms in the ${\mathrm{C}}_{60}$ crystalline structure allows us to preserve the ${\mathrm{C}}_{60}$ molecules up to the maximum studied pressure, i.e., more than twice the amorphization pressure of the solid ${\mathrm{C}}_{60}$ fullerene crystal. The calculated pressure evolution of all the observed Raman mode frequencies is in good agreement with that obtained experimentally. In this work, the high-resolution measurements allow us to observe six Raman modes and several partners in doublets in addition to the Raman lines previously observed for the same system. The symmetry of all the observed modes has been identified through our calculations.

The mechanism of cell-damaging reactive oxygen generation by colloidal fullerenes

Because of the ability to induce cell death in certain conditions, the fullerenes (C 60) are potential anticancer and toxic agents. The colloidal suspension of crystalline C 60 (nano-C 60, nC 60) is extremely toxic, but the mechanisms of its cytotoxicity are not completely understood. By combining experimental analysis and mathematical modelling, we investigate the requirements for the reactive oxygen species (ROS)-mediated cytotoxicity of different nC 60 suspensions, prepared by solvent exchange method in tetrahydrofuran (THF/ nC 60) and ethanol (EtOH/ nC 60), or by extended mixing in water (aqu/ nC 60). With regard to their capacity to generate ROS and cause mitochondrial depolarization followed by necrotic cell death, the nC 60 suspensions are ranked in the following order: THF/ nC 60>EtOH/ nC 60>aqu/ nC 60. Mathematical modelling of singlet oxygen ( 1O 2) generation indicates that the 1O 2-quenching power (THF/ nC 60<EtOH/ nC 60<aqu/ nC 60) of the solvent intercalated in the fullerene crystals determines their ability to produce ROS and cause cell damage. These data could have important implications for toxicology and biomedical application of colloidal fullerenes.

Correlation of crystalline and structural properties of C60 thin films grown at various temperature with charge carrier mobility

Transistors fabricated from C60 films grown by hot wall epitaxy at higher substrate temperature, showed an order of magnitude increased charge carrier mobility up to 6cm2∕Vs. In this letter, the authors present an extensive study of morphology and crystallinity of the fullerene films using atomic force microscopy and grazing-incidence x-ray diffraction. A clear correlation of crystalline quality of the C60 film and charge carrier mobility was found. A higher substrate temperature leads to a single crystal-like faceted fullerene crystals. The high crystalline quality solely brings a drastic improvement in the charge carrier mobility. A gate voltage independent mobility is also observed in these devices which can be attributed to the highly conjugated nature of the C60 thin film.

Optical amplification in multilayer photorefractive liquid crystal films

Photorefractive two-beam coupling was performed in fullerene C60-doped nematic liquid crystal cell. Photorefractive gain coefficient as high as 1386cm−1 was obtained at an input pump power as weak as 16mW. However, the thin film nature led to a small gain of 16. By the use of several such cells stacked together to increase the overall interaction length, the optical gain was improved greatly, and the pump power to obtain the highest optical gain was reduced. At 1.2V, the highest gain of 141 was obtained for the 40μW signal at an input pump power of 12mW.

Ozone Reaction with Carbon Nanostructures 1: Reaction Between Solid C60 and C70 Fullerenes and Ozone

The exposure of powdered crystals of C60 and C70 fullerenes to ozone with an O3/O2 ratio of 9.7% w/w causes their immediate oxidation. The FT-IR spectroscopy shows the formation of CO2 and the accelerated disappearance of ozone. The infrared spectra of crystalline C60 and C70 powders that were exposed to ozone show absorption bands indicating that oxidation was accompanied by formation of alpha,beta-unsaturated carboxylic groups, aldehyde and other ketonic moieties. The spontaneous decay of O3 in the O3/O2 atmosphere monitored by FT-IR spectroscopy was found to follow a pseudofirst order kinetic law with k0 = 6.9 x 10(-5) s(-1). When powdered C60 is present in the system a k(C60)(1) = 2.0 x 10(-4) s(-1); k(C70)(1) = 1.4 x 10(-4) s(-1) for C70. The accelerated disappearance of O3 is due to its adsorption/reaction with the powdered fullerenes. After about approximately 1000 s the reaction enters in a second step wherein the disappearance of O3 slows down significantly due to the lack of further reaction sites on the powdered fullerene surfaces and due to accumulated CO2 in the gas phase which exerts an inhibitory effect in the ozone spontaneous decomposition.

Molecular Dynamics Simulation of Thermal Conductivity of Diamondoid Crystals

AbstractHydrocarbon molecules with diamond structure, called diamondoids have gain considerable interest as promising nanoscale building blocks. Very large mismatch between strong, covalent intramolecular bonding and weak intermolecular bonding suggests interesting phonon related properties for diamondoid crystal. We use molecular dynamics (MD) simulations to examine thermal transport of diamondoid crystals. In particular, thermal conductivity of small molecule adamantine and larger molecule pentamantane crystal is studied by equilibrium and non-equilibrium MD. The thermal conductivity of both materials is low, but comparable with that characterizing fullerene crystal.

Ordered Crystals of Fullerenes Produced by Cocrystallization with Halogenated Azatriquinacenes

The growth and structures of three new cocrystalsC9Cl6Br3N·C60, C9Cl6Br3N·C70, and C9Cl6H3N·3C70·3C6H5Clinvolving fullerenes and halogenated azatriquinacenes are reported. In each case, the fullerene is completely ordered and avoids the orientational disorder found in many crystalline fullerenes and fullerene cocrystals. In each structure, the upper Cl6 surface of the halogenated azatriquinacene molecule cups a fullerene. In C9Cl6Br3N·C60 and C9Cl6Br3N·C70, the molecules are arranged alternately in columns with the lower Br3 face of the azatriquinacene also interacting with a neighboring fullerene. In C9H3Cl6N·3C70·3C6H5Cl, one of the fullerenes is cupped by the upper surface of the azatriquinacene, while four chlorobenzene molecules also form a belt around it.

Nanostructural magnetism of polymeric fullerene crystals

The nature of magnetism in all-carbon crystals composed of polymeric layers of covalently bound fullerene (C60) molecules is considered. The results of quantum-chemical calculations performed using the unrestricted Hartree-Fock approximation and the semiempirical AM1 method are presented. It is shown that the exchange integrals J of both a free C60 molecule and a monomer unit of the polymer are too large ensure the required magnetic susceptibility of the fullerene crystal. However, the J value exhibits an approximately n-fold decrease for an oligomer molecule consisting of n C60 units. Therefore, in the case of large n, the exchange integral can be reduced to a low level sufficient to provide for a significant magnetic susceptibility. A nanosize (scaly) model of the observed magnetism is proposed that is consistent with recent experimental data, which are indicative of a nanostructural character of magnetic fullerene samples.

Structure-Controlled Self-Assembly of Impeller-Shaped Crystal on the Transition Metal Fullerene Complexes

Impeller-like transition metal fullerene crystals have been obtained by a very simple self-assembly method under mild conditions. None of the surfactants or other templates were needed in the process. The reaction temperature and solution concentrations can be used as an additional means to control the size and diameter of the fullerene crystals. Their morphologies and particle sizes were determined by field emission scanning electron microscopy (FESEM). Three new cocrystals of C60 fullerenes with transition metal diethyl dithiophosphates have been prepared and characterized by EA, IR, UV−vis, and 1H, 13C, and 31P NMR spectroscopy.

Recognition-controlled molecular crystals of fullerenes with cubane

Recognition-controlled molecular crystals of fullerenes with cubane

In situ Spectroelectrochemistry of C60 in Ordered Layers:Fullerene Crystals and Peapods

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Fullerene in a Metal-Organic Matrix: Design of the Electronic Structure

We present a theoretical study of a new hybrid compound, where the C60 molecules are encapsulated in a recently discovered metal-organic framework (MOF). Being placed in a rigid skeleton, the fullerene molecules form a cubic crystal, while the intermolecular distance of the fullerenes is tuned by the choice of appropriate organic linkers of the MOF structure. The resulting C60 crystal shows a density of conduction states considerably higher than any of the fullerene crystals considered so far, which is a key factor influencing the transition temperature of the superconducting state. This constitutes a new approach of tuning the density of states of a fullerene crystal.