C60 In Solution Research Articles

Facile Fabrication and Photolectrochemical Properties of Porphyrin–Fullerene Assemblies by Self-Assembly and Surface Sol–Gel Processes

Ultrathin photoelectric conversion films consisting of a porphyrin–fullerene photoredox pair were fabricated by the combined use of room-temperature covalent-bonding and surface sol–gel processes. First, cysteamine was self-assembled on an indium–tin-oxide (ITO) electrode. The cysteamine-modified electrode was then immersed in C60 solution, giving immobilization of C60 via bond formation between the amino group of cysteamine and C60. Next, the C60-modified electrode was dipped in 2-ethanolamine solution to implant the hydroxy group to the immobilized C60 via the bond formation between C60 and the amino group; thus, the hydroxy group was exposed as the outermost layer. Then, Ti(OBu)4 and tetracarboxyporphyrin (TCPP) were alternately assembled on the C60 layer by the surface sol–gel process, to give an assembly of TCPP, titanium oxide species [Ti(O)], and C60 on the ITO electrode. The double layering of TCPP–Ti(O) was possible. The spectral characterization of the films was carried out. In the presence of sacrificial reagents, anodic photocurrents were generated from these modified electrodes. The incorporation of the C60 layer resulted in the substantial enhancement of the photocurrents as compared with that of the TCPP layer alone, suggesting effective electron-transfer reactions between TCPP and C60 that contribute to the photocurrent increase. The photocurrents increased by the double layering of the TCPP and Ti(O) layers.

A Molecular Thermometer Based on the Delayed Fluorescence of C70 Dispersed in a Polystyrene Film

A new optical molecular thermometer, based on the thermally activated delayed fluorescence of C70 dispersed in a polystyrene film, was developed. In the presence of oxygen, the fluorescence intensity of the C70 film is essentially temperature independent in a wide range. In the absence of oxygen, however, the fluorescence intensity markedly increases with temperature. At room temperature (25 degrees C), and after degassing the sample, the fluorescence intensity of C70 increases 22 times, while at 100 degrees C the fluorescence intensity is increased by 70 times. With our system, the very weak fluorescence of C70 (phi(F) congruent with 5 x 10(-4), in toluene) can be increased up to 91 times (up to an estimated maximum value phi(F) = 0.046). The estimate value of the singlet-triplet gap (29 kJ mol(-1)) and the fluorescence lifetime (0.63 ns) of the C70 in film are in agreement with the values reported in the literature for C70 in solution. The values of the phosphorescence lifetime at room temperature (23 ms) and the quantum yield of triplet formation (0.989) were also determined. The system is completely reversible with respect to heating-cooling cycles.

Aqueous micellar solution of C60: Preparation, properties, and capability for generation of singlet oxygen

Conditions for preparing stable aqueous micellar solution of nonmodified fullerene C60 were optimized. The size distribution of the micellar particles was determined by transmission electron microscopy, and the negative charge of the micelles was proved. The mean particle diameter appeared to be ∼2.5 times smaller than that determined by dynamic light scattering. The possibility of generation of singlet oxygen in the modified system C60/H2O was demonstrated. The 1O2 luminescence signal at λ = 1268 nm lasts for ∼3 μs.

Crystal structure of the supramolecular adduct 2 C70·5 C6H5OH containing hydrogen-bonded rings of phenol

Hydrolysis of a solution of C70 in triphenylphosphite leads to the supramolecular adduct 2C70·5C6H5OH. The crystal structure was determined by single-crystal X-ray diffraction. The overall structure can be derived from the ThB4 structure type and described by a 32·4·3·4-net of C70 and hydrogen-bonded, ring-like tetramers and hexamers of phenol filling cube-like voids.

Exclusive Endo-Cavity Interplay of t-Bu-calix[6]arene with C70

Toluene solutions of fullerene C70 and t-Bu-calix[6]arene form a 2:1 inclusion complex that has been structurally authenticated using synchrotron source X-ray diffraction data. Remarkably, the fullerene is not included in the cavity of the calixarene, and this has implications in predicting the structures of fullerene complexes of other calixarenes and container molecules. The fullerenes shroud the exo surface of the calixarene at the van der Waals limit, with the fullerenes arranged into corrugated sheets, with each calixarene interdigitated at the upper rim with the upper rim of two other calixarenes, the macrocycles forming a bilayer separating the sheets of fullerenes.

Supramolecular Arrangement of C60 and Phenol into a Square Packing Arrangement of π‐π Interacting and Hydrogen‐Bonded Rods in C60·5C6H5OH

AbstractThe supramolecular adduct C60·5C6H5OH was obtained as single crystals by the slow hydrolysis of a solution of C60 in triphenylphosphite. The crystal structure was determined with atomic resolution by single‐crystal X‐ray diffraction [triclinic, space group P$\tilde {1}$, a = 1003.52(14) pm, b = 1011.71(14) pm, c = 1264.17(17) pm, α = 88.566(2) °, β = 84.026(2) °, γ = 83.485(2) °, V = 1.2681(3) nm3, Z = 1]. The overall structure can be described as a distorted square packing pattern of hydrogen‐bonded and π‐π interacting rods,1∞[C60(C6H5OH)4]. The fullerene molecules are fully ordered and the C–C bond lengths exhibit remarkably small variations within the 6:6 and 6:5 subsets. The results are discussed in the context of an analysis of reliable crystal structure data for several different fullerene co‐crystal compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Fluctuating Hydration Structure around Nanometer-Size Hydrophobic Solutes. I. Caging and Drying around C60 and C60H60 Spheres

The hydration structure around nanometer-size hydrophobic solutes is studied with molecular dynamics simulation by taking aqueous solutions of C60 and C60H60 as examples. In the hydration shell around a single C60 or C60H60, dipoles of simulated water molecules tend to be aligned to form the vortexlike coherent pattern which lasts for 100 ps, while individual water molecules stay within the hydration shell for about 10 ps. This structural pattern organized by fluctuating and diffusively moving molecules should be called a "fluctuating cage". In the narrow region between a pair of C60 molecules or a pair of C60H60 molecules, water density strongly fluctuates and is correlated to the mean force between solutes. The fluctuating caging and drying between solutes affect the hydrophobic interaction and dynamical behaviors of solutes.

Structurization of a solvent interacting with fullerene C60

Solutions of fullerene C60 in toluene and p-xylene were investigated by small-angle X-ray diffraction. In all small-angle scattering curves, the scattering intensity decreases to constant value IC with an increase in the scattering angle. The value of IC nonmonotonically depends on the fullerene concentration. The radii of gyration of scattering elements were determined by constructing small-angle X-ray diffraction patterns in Guinier coordinates.

On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C60 solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of IC with increase of scattering angle. The value of IC depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C60 in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C60 by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C60 solutions in good solvents are considered.

Preparation of Aqueous Colloidal Dispersion of C60 Fullerene

A method for preparing aqueous colloidal dispersions of C60 fullerene free of organic solvents is proposed. The size of dispersed particles is determined using the turbidity spectra. A solvatochromic effect is observed upon the addition of a C60 solution in toluene to a water-acetone mixture.

Effect of surface temperature on the concentration of C60/C70 molecules in dc arc discharge fullerene generator

Synthesis of C60, C70 and higher fullerenes was carried out at Pakistan Institute of Nuclear Science and Technology (PINSTECH) using dc arc discharge technique. High-performance liquid chromatography (HPLC) and UV–vis spectroscopy are employed to characterize the fullerenes. The toluene extracted fullerene solutions of the raw soot collected from four different regions (A–D) of dc arc discharge fullerene generator were compared with pure C60 toluene solution. Due to poor solubility of C60 in HPLC grade methanol, different fractions of methanol as a mobile phase with toluene were tried. The mobile phase composition of 80:20 methanol:toluene was found an optimal ratio to achieve the best separation factor of 1.246 between C60 and C70 fullerenes. Quantitative concentration is calculated from the HPLC and UV–vis spectra. The molarity of C60 carbon molecules for all the regions is calculated from the HPLC spectra by comparing the spectra of known molar solution of C60. The maximum concentration of C70 is found to be 21% in the region B that is nearer the arc zone and at a higher temperature than other regions. Both the techniques confirm the presence of C60, C70 and higher fullerenes in all the four regions with variation in concentration of C60 and C70. UV–vis spectra of the region C show the additional absorption bands at 285 and 305nm.

Effect of Fullerene C60 on Structuring of Toluene

Toluene solutions of fullerene C60 with concentrations of 0.001, 0.01, and 0.2 wt % were studied by small-angle X-ray diffraction analysis. The radii of gyration of scattering elements were determined from the small-angle diffraction patterns plotted in the Guinier coordinates.

Crystal Structure and Stablility of the Fullerene – Chalcogene Co‐Crystal C60Se8CS2

AbstractC60Se8CS2 was prepared, for the first time, by slow concentration of a solution of C60 and Se8 in carbondisulfide. The crystal structure (P21/c, a = 1330.05(17), b = 2900.6(4), c = 988.09(13) pm, b = 91.760(2)°; Z = 4; 8910 independent reflections; R1 = 0.073; wR2 = 0.186) contains fully ordered fullerene molecules. It may be derived from the NiAs‐structure‐type with Se8‐rings and CS2 filling the octahedral voids of the distorted hexagonal close packing of fullerene molecules. The results are completed by Raman‐spectroscopic and thermogravimetric investigations.

Gas-Phase Observation of Multiply Charged C60 Anions

Gas-phase observation of C60(1-), C60(3-), and C60(4-) anions generated at platinum and gold electrodes and detected by electrochemical/electrospray mass spectrometry is reported. The anions were electrochemically generated from solutions of C60 dissolved in toluene/acetonitrile as well as from reduction of C60 films on gold electrode surfaces. The gas-phase observation of C60(3-) and C60(4-), despite the fact that they have negative electron affinities, is a result of a Coulombic barrier to electron loss. The fact that C60(2-) was not detected in these experiments is ascribed to its limited solubility under the reaction conditions. These studies, which demonstrate the gas-phase kinetic stability of C60(3-) and C60(4-), illustrate the promise of electrochemical/electrospray mass spectrometry for the study of metastable anions.

Modulation of the Photophysical Properties of C60 by Electronic Confinement Effect

This research work reports on the incorporation of fullerene C60 in diverse inorganic and organic matrixes and how these different environments induce changes on the photophysical properties of the molecule depending on the cavity dimensions of the host. Indeed the fluorescence emission band of C60 experiences a progressive bathochromic shift with respect to C60 in solution as the cavity dimensions of the host decrease in going from the mesoporous material MCM41 to UTD-1 and Na-Y zeolites. This experimental observation, which has been documentarily confirmed by theoretical predictions and recent experimental results, is a reflection of the confinement effect imposed by the host. However, the most striking result reported in this work is that the fluorescence range accessible to this occluded species can be extraordinarily extended by confinement inside the neutral cages of a "dendritic box". The ability of the dendritic shell to create a microenvironment, modifying the properties of its functional core, allows the emission bands of C60 incorporated into a dendrimer to be effectively red-shifted with respect to their emission in solution, and, contrarily to other confined spaces of considerable hardness such as zeolites or the high surface material MCM41, the magnitude of this shifting is maximum and can be modulated under appropriate experimental conditions. This phenomenon has an enormous relevance since it can be exploited in future technological applications.

Light Scattering Study of Aqueous Poly(Vinyl)pyrrolidone–Fullerene C70 Solutions

It was shown by static and dynamic light scattering that poly(vinyl)pyrrolidone (PVP) molecules form large intermolecular complexes (clusters) with C70 in aqueous solutions. The molecular weights and dimensions of PVP–C70 clusters increase both with the increase of fullerene content and the molecular weight of the matrix PVP. However, two different diffusion coefficients were detected by dynamic light scattering. The slow mode was explained as diffusion of large PVP–C70 clusters. The fast mode represents free PVP molecules in solution. Dimensions of clusters revealed in aqueous PVP–C70 solutions are less than that for PVP–C60 by factor of 2.5–3.

Morphology of C60 nanotubes fabricated by the liquid–liquid interfacial precipitation method

Single crystalline C60 fullerene nanowhiskers are formed by adding isopropyl alcohol gently to fullerene saturated solutions. The method is called the liquid–liquid interfacial precipitation method. In the present study, observation using transmission electron microscope was made for C60 nanowhiskers with hollow structure, i.e. C60 fullerene nanotubes fabricated by the modification of liquid–liquid interfacial precipitation method using pyridine as solvent. After adding isopropyl alcohol to the C60 solution in the glass bottles, ultrasonic dispersion was applied for 1 min and then the bottles were kept at 10°C. Within 24 h, fibrous solids with the length larger than several millimeters and the diameters ranging from submicrons to 1ΰm were precipitated. For the transmission electron microscope study, the samples were pulverized by the ultrasonic dispersion. Under the transmission electron microscope, tubular morphology was usually observed for the whiskers with the diameters larger than 200 nm and hardly observed for those with the diameters smaller than 200 nm; both the C60 fullerene nanotubes and the fullerene C60 nanowhiskers were in crystalline state. Since partly tubular structures were sometimes observed at the end of the C60 fullerene nanowhiskers, the mechanism for the formation of tubular morphology is suggested to be a dissolution process after the crystal growth. When the samples were kept in the glass bottles for several hours after the pulverization, closing of nanotubes at the ends was observed for relatively smaller nanotubes in diameter. For relatively larger nanotubes in diameter, zigzag thinning of tube wall edges was observed. It is thus expected that subsequent growth or dissolution occurred at the end of the pulverized C60 nanotubes, which may be an effective way to control the shape of tubes. The C60 nanotubes presented here will be useful as adsorbents, catalysts, and membranes.

Solubility of C 60 fullerene in o-dichlorobenzene–tetrachloromethane mixtures

The solubility of C60 fullerene in o-dichlorobenzene–tetrachloromethane mixtures has been studied in a wide temperature range, and the thermodynamic functions of C60 solution have been calculated.

Transmission electron microscopy investigation of tubular and capsular needlelike crystals of C60 produced by the liquid–liquid interfacial precipitation method

Tubular and capsular needlelike crystals of C60 with a few hundreds nanometers to about one micrometer in diameter were discovered among the precipitates prepared by the liquid–liquid interfacial precipitation method. Addition of a small amount of (η2–C60)Pt(PPh3)2 to the toluene solution of C60 produced various morphologies of hollow C60 crystals. This paper gives the first report on the formation of structures we named “C60 nanotubes.”

Transmission electron microscopy investigation of fullerene nanowhiskers and needle-like precipitates formed by using C60 and (η2-C60)Pt(PPh3)2

Nanowhiskers and needle-like precipitates obtained by the liquid-liquid interfacial precipitation method for the systems of isopropyl alcohol and toluene solutions of C60 and (η2-C60)Pt(PPh3)2 were examined by transmission electron microscopy. Morphology of the C60 precipitates was remarkably changed by the addition of (η2-C60)Pt(PPh3)2 in the C60 toluene solution, and capsular needle-like crystals of C60 were formed. C60 cages were found to be directly contacted along the growth axis of (η2-C60)Pt(PPh3)2 needle-like crystals.