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Journal of Oleo ScienceCopyright ©2013 by Japan Oil Chemists’ SocietyJ. Oleo Sci. 62, (8) 541-553 (2013)

Self-Assembled Fullerene NanostructuresLok Kumar Shrestha1＊ , Rekha Goswami Shrestha2, Jonathan P. Hill1 andKatsuhiko Ariga1, 3

1 World Premier International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044 JAPAN

2 Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science 2641 Yamazaki, Noda, Chiba 278-8510, JAPAN

3 PRESTO & CREST, JST, 1-1 Namiki, Tsukuba 305-0044 JAPAN

1 INTRODUCTIONDesign of nanostructured materials whose properties

can be tailored across different length scales so that they can be utilized in different functional systems and nanode-vices fabrication is a current topic of great interest in the field of materials nanoarchitectonics. Self-assembly is one of the special techniques applied for the organization of functional molecules such as fullerenes, amphiphiles, pro-teins and peptides with molecular level precision in the preparation of functional systems. This technique enables the arrangement of building blocks into a variety of nano-structures on the micro to macroscopic length scales. Using the concept of materials nanoarchitectonics in com-bination with self-assembly, various building units have been assembled or organized/reorganized into hierarchic functional nanostructures. Assembly of the ideal zero-di-mensional building block fullerene（C60）into higher dimen-sional crystalline nanostructures and assembly of function-alized fullerenes into different mesostructures are good examples of the materials nanoarchitectonics concept.

Soon after its discovery in 19851）, C60 received tremen-dous attention due to its unique structure and properties. After several years of intensive research activity, C60 has regarded as a molecule having tremendous potential as a building block for molecular engineering, novel materials synthesis, supramolecular chemistry, and also medicinal chemistry2, 3）. The 20 hexagonal and 12 pentagonal rings

＊Correspondence to: Lok Kumar Shrestha, World Premier International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044 JAPANE-mail: SHRESTHA.Lokkumar@nims.go.jpAccepted April 25, 2013 (received for review March 31, 2013)Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 onlinehttp://www.jstage.jst.go.jp/browse/jos/　　http://mc.manusriptcentral.com/jjocs

compose an icosohedral（Ih）symmetric closed cage struc-ture of the C60 molecule（diameter～0.8 nm）. In C60, each carbon atom is bonded to three other carbon atoms through sp2 hybridized bonds with the tendency for double bonds not to be present at the pentagonal rings resulting in poor electron delocalization, i.e. C60 is not a superaromatic molecule. As a result, it behaves as an electron deficient molecule. The electron-accepting capability of C60 both in solid state and solution have permitted special uses in the formation of charge-transfer complexes and bulk hetero-junctions with suitable donors for the production of photo-current. The formation of charge-transfer salts with a number of donor groups or doping with metals has led to ferromagnetic4） or superconducting materials5）. C60 exhibits strong absorption bands in the UV region and weaker but significant bands in the visible region. Functionalized C60 retains these characteristics but, in addition, the absorp-tion of the derivatives extends further into the near-IR region demonstrating that C60 and its derivatives are very easily excited by low-energy light. This, combined with the fullerenes’ high electron affinities, makes these materials appealing for use in photoinduced electron transfer6） and also for applications in medicinal chemistry7）. Guldi and Prato8） have recently reviewed the excited-state properties of C60 derivatives.

C60 has also demonstrated excellent capabilities in the quenching of various free radicals compared to conven-

REVIEW

Abstract: This review briefly summarizes recent developments in fabrication techniques of shape-controlled nanostructures of fullerene crystals across different length scales and the self-assembled mesostructures of functionalized fullerenes both in solutions and solid substrates.

Key words: fullerene, self-assembly, nanostructures, liquid-liquid interfacial precipitation, nanowhiskers, nanotubes, nanosheets

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tional antioxidants9）. Many fullerene-based compounds have shown tremendous practical values biological systems10） although the highly hydrophobic character of C60

（it is water insoluble）limits its application in biomaterials’ field. This problem has been addressed by many materials chemists and water soluble fullerenes have been produced by appropriate substitution or functionalization with ionic and nonionic functional groups11）. Furthermore, amphiphil-ic fullerene derivatives have also been produced that can self-assemble into different mesostructures in solution or on a substrate12）. Water-soluble fullerene derivatives led to the discovery of the interactions between organofullerenes and DNA, proteins, and living cells. C60 can also be encap-sulated in supramolecular structures containing a host moiety, such as cyclodextrin, surfactants, gels, or poly-mers13）.

Needless to say significant advances in fullerene chemis-try have lead to a number of interesting developments in-cluding carbon nanotubes（CNTs）14）. This functional mole-cule requires assembly into well-ordered one dimensional（1D）or two dimenaional（2D）forms to promote its elec-tronic and optical properties and to construct electronic or photonic devices15－17）. It is therefore essential to know the intermolecular ordering of C60 molecules at the micro and macroscopic level for the production of dimension-con-trolled nanostructures of C60

18）.In this review, we briefly summarize the recent develop-

ment of the production of low to higher dimensional nano-structured fullerene（C60）crystals over different length scales and focussing on solution-based approaches and dif-ferent self-assembled mesostructures of functionalized fullerenes.

2 NANOSTRUCTURED CRYSTALLINE FULLERENESNano-sized C60 crystals have received much attention

and are considered to be intermediate states between mol-ecules and bulk materials. Hierarchical assembly of C60 into nanocrystals（or nanoparticles）offers unique properties with potential to be used in device fabrication. Bulky parti-cles without any unified shape of pristine C60 have the in-teresting property of forming crystalline assemblies of various well-defined morphologies and sizes depending on the method of molecular assembly. Various synthetic ap-proaches have been explored to make 1D or 2D nanostruc-tures of C60. Templating, slow evaporation, and vapor-solid processes are the commonly employed methods to produce C60 crystals19－24）. Similarly other processes, such as layer-by-layer assembly and electrophoretic deposition have also been applied to assemble fullerene nanoparticles25, 26）.

In addition to the aforementioned methods, precipitation either in the bulk or at interface is also important and is the most extensively employed method used for the pro-

duction of tailored nanostructured crystalline C6027, 28）. Mi-

yazawa and coworkers have developed a liquid-liquid inter-facial precipitation（LLIP）method for growing low dimensional nanowhiskers or hollow tubular structures from solution under ambient conditions29, 30）. It should be noted that if diameters of the 1D rod structure is in the range of hundreds of nanometers to a few microns and lengths reach several hundreds of microns then they are referred to as C60 nanowhiskers. In contrast to CNTs, C60 nanowhiskers do not contain any internal hollow spaces. Rather, whiskers are composed of many C60 molecules bonded through a combination of van der Waals interac-tions and chemical bonds. Miyazawa et al. have also ex-tended this method to produce 2D hexagonal and polygo-nal shaped nanosheets31, 32）. Very recently, we extended this method to produce giant microcrystals with macro-pores at their surfaces and also succeeded in fabricating, for the first time, hexagonal-shaped crystalline fullerene with bimodal pore structures33, 34）. Furthermore, we utilized this method for the unusal formation of 3D highly crystal-line cubic-shape crystals of C60-fullerene-Ag（I）organome-tallic heteronanostructure［C60｛AgNO3｝5］, which showed irreversible structural rearrangement upon gentle washing with aliphatic alcohols resulting in the formation of unique-ly structured formations of well-oriented C60 microcrys-tals35）.

In solution-based crystal formation methods, the crystal formation mechanism is suggested to be driven by super-saturation related to the low C60 solubility in alcohols（known as an antisolvent or a poor solvent for C60）. There-fore, the solubility of C60 is a key parameter for good and poor solvent selection. Rods or needles grow in arbitrary directions through the LLIP process at the interface of sat-urated C60 in toluene and isopropyl alcohol（IPA）. In depth investigations on the production of structure controlled crystalline fullerene have confirmed the fact that the mor-phology and size of crystalline assembly of C60 largely depend on the synthetic route, concentration of C60 in solu-tion, crystallization temperature, and mixing ratio of anti-solvent and solvent particularly in the precipitation method. Formation of 1D rods and 2D plate-like morpholo-gies from slow evaporation of C60 solution and vapor depo-sition, respectively, can be taken as a good example. In the following section, we discuss recent advances for the lower to higher dimensional nanostructured crystalline fullerene by solution-driven assembly methods.

A very simple method for producing so-called zero-di-mensional C60 nanoclusters is the solvent-exchange method in which C60 molecules dissolved in a good solvent assemble into particle type（pseudo sphere or irregular shape parti-cles）nanocrystals upon solvent removal or during solvent exchange. Recently this method has been extended to the fabrication of higher dimensional C60 nanocrystals by opti-mizing synthetic conditions. Work of Deguchi et al.36） can

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be taken as a good example of the formulation of stable aqueous dispersions of fullerenes（C60 and C70）consisting of nearly spherical shaped nanoclusters by simply injecting a saturated solution of fullerene in tetrahydrofuran（THF）into water followed by THF removal by purging gaseous ni-trogen. At that time, it was the first example of the stable dispersion of C70 in water. From transmission electron mi-croscopy（TEM）observations they found fairly monodis-perse clusters of C60 and C70 displaying low dimensional morphology（see Fig. 1）. High resolution transmission elec-tron microscopy（HR-TEM）revealed the polycrystalline nature of the clusters. They found that the dispersion is very easy to perform and exhibits excellent colloidal stabil-ity without any stabilizing agent. No precipitation was ob-served even after storage in the dark at room temperature over long periods（at least 9 months of preparation）. It was found that the surface of the cluster is negatively charged and the electrostatic repulsion between the negatively charged cluster surfaces is important for the stability of the dispersions. The method proposed by Deguchi et al. is a simple route to produce stable dispersions of colloidal C60 and C70 in water, which are certainly suitable for the study of biomedical applications of fullerenes.

In solvent-exchange methods, THF is the most common-ly employed solvent for the production of colloidal disper-sions of C60 nanocrystals. Rapid mixing of a THF solution of C60 into water followed by evaporative removal of the THF controls the particle size by varying the liquid-phase addi-tion rate. Various other solvents have been used with or without THF for the production of sub-100 nm low dimen-sional C60 nanoclusters. Other examples can be found else-where37, 38）. Recently Park et al.39） investigated the critical effect of solvent geometry on the morphology of C60 pre-

pared by a drop-drying process at room temperature. They found a critical correlation between the solvent geometry and the geometry of the self-assembled C60 crystals. Al-though a clear mechanism of such crystal formation was not clear, they found that pseudo nD solvent guides C60 molecules to self-assemble into n-1D morphology. That is, pseudo 3D（p3D）solvents guide C60 molecules to self-as-semble into p2D hexagonal disk structures, and that p2D and p1D solvents result in p1D C60 wire and p0D C60 dot structures, respectively. They found that when a C60 solu-tion in p3D tetrahedral carbon tetrachloride was dropped and dried, 2D hexagonal nanosheets were observed. On the other hand, when a C60 solution in linear chain n-hexane（p1D structure）was drop-dried, spherical 0D C60 crystals were observed.

We noticed that morphology of fullerene crystals fabri-cated using solvent-exchange method is not very well defined in particular for lower or 0D morphology. Most re-ported examples have been mostly particle type and were not of perfect 0D morphology. Masuhara and coworkers40） have recently reported fine fullerene crystals with unique shapes including perfect 0D fullerene nanoballs using a re-precipitation method. The 0D spherical nanostructures having average size～100 nm were fabricated by injecting 200 μL of 1 mM C60 solution in m-xylene into 10 mL of IPA solution at 353 K and aging the mixture at room tempera-ture（see Fig. 2a）. On the other hand, nanoballs having sizes in the range of 300-500 nm were fabricated by inject-ing 200 μL of C60 solution in pyridine（0.3 mM）into 10 mL ethanol solution at room temperature（Fig. 2b）. The nano-spheres and nanoballs were apparently monodisperse.

Herein, we discuss 1D fullerene nanowhiskers and nano-tubes. Fullerene nanowhiskers are generally rodlike or needlelike 1D crystals having diameters＜1 μm and length several tens of μm to hundreds of nm. These structures are the most investigated nanostructures of C60 and have been prepared by several different approaches. Slow evaporation is one of the methods used to produce 1D nanorods. In this method, C60 solutions in organic solvents are evaporated at a controlled rate at a particular temperature. The aspect ratio can be controlled by adjusting the solvent evaporation

Fig. 1　 Low dimensional fullerene nanocrystals fabri-cated by the so-called solvent exchange method: (a) TEM image C60 nanocrystal, and (b) the same for C70. Reproduced with permission from Langmuir 17, 6013-6017 (2001). © (2001) American Chemical Society.

Fig. 2　�Schematic model demonstrating 0D fullerene nanostructures: (a) nanospheres obtained from IPA/m-xylene system, and (b) nanoballs fabri-cated from ethanol/pyridine systems.

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kinetics, physical properties of solvents（vapor pressure, solubility of C60 etc.）, temperature, etc. Usually, very long high aspect ratio 1D rods of C60 crystals can be synthesized using this method. Bulk precipitation and drop drying method also yields 1D crystal. Volume ratio of poor sol-vents with C60 solutions, concentration of C60, and solvents nature have been pointed out as crucial parameters in the control of the dimensions of 1D rods prepared by the pre-cipitation method. On the other hand, as mentioned earlier, in the drop-drying method solvent structure is crucial to control the geometry of C60 crystals produced. Drop-drying of C60 solution prepared in so-called p2D solvents usually results in the formation of p1D C60 wires. For example, 1D C60 wires were formed from a C60 solution prepared using m-xylene, a representative p2D benzene series solvent with methyl functional groups meta to each other. Similar 1D C60 wires were obtained upon drop-drying C60 solutions of mesitylene and 1,3-dichlorobenzene, which have similar structures to m-xylene, except for the multiplicity and type of functional groups. These results of Park et al.39） confirmed that C60 molecules are specifically guided to self-assemble into 1D morphologies upon evaporation of benzene series solvents, as long as they have functional groups 120° apart, regardless of the polarity, size and number of the functional groups. The method of Park and coworkers may provide guidelines for the production of multidimensional fullerene nanostructures required for nanodevice fabrication.

Recently, use of the LLIP method is becoming more widespread for the production of nanostructures of C60 particularly for growth of 1D nanowhisker of C60 crystals due to the ease of synthesis under ambient conditions. Furthermore, the possibility of doping various elements into nanowhiskers and easy production of multicomponent fullerene nanowhiskers composed of different kinds of fullerene molecules are another advantage of the LLIP method. The basic concept of the LLIP method is to use a liquid-liquid interface as nucleation site for crystals. Mi-yazawa et al.29） used an interface between a concentrated solution of C60 in toluene and isopropyl alcohol（IPA）to produce a needlelike morphology of C60 with single crystal-line structure having diameters of about 250 nm and lengths in the range of several tens of microns. The largest ratio of length to diameter reached 4000. It has been found that the intermolecular distance within C60 nanowhiskers is shorter along the growth axis than in pristine C60 crystals indicating the formation of strong bonding between C60 molecules. It was anticipated that the fullerene nanowhis-kers polymerize via a “2＋2” cycloaddition in the close-packed［110］direction29）. An initial model of C60 nanowhis-kers where the C60 molecules are chained by the “2＋2” cycloaddition along the whisker growth axis was proposed by Miyazawa and is presented in Fig. 3. This model is based on the fact that the intermolecular distance of C60 mole-

cules in C60 nanowhiskers was found to be shortened by a few percent along the growth axis than that of pristine C60 crystals based on a transmission electron microscope（TEM）observations. This shortening is anticipated to be caused by the polymerization of C60 caused by electron beam irradiation.

These C60 nanowhiskers usually have a face-centered cubic（fcc）crystal structure with growth direction parallel to［110］and the overall morphology of C60 crystals is found to depend on the combinations of antisolvent and solvent, their volume ratios, and also the presence of water41）. However, the solvated hexagonal close packed（hcp）struc-ture of C60 nanowhisker has also been occasionally ob-served depending on the combination of antisolvent and solvent. Solvated crystals grown at an interface of IPA with a saturated solution of C60 in m-xylene can be taken as one example42）. These solvated hcp C60 nanowhiskers were transformed into fcc structure upon evaporation of solvent/or heating the sample. Minato and Miyazawa pointed out that the kinetics of hcp-to-fcc structure transformation depend on vapor pressure of solvent; higher vapor pres-sures lead to more rapid transformation. For example, the hcp to fcc structural transformation occurred more rapidly in toluene than in m-xylene. Entrapment of solvent mole-cules in the crystals in the initial production stage is ex-pected to be responsible for the formation of hexagonal solvated C60 nanowhiskers. Solvents could be easily removed by heat treatment.

Investigations have shown that fabrication of fullerene nanotubes is rather difficult compared to fullerene nanowhiskers. Generally, two types of tubular structures of fullerene crystals have been observed. One is partially hollow around the edge of 1D structures and the other is hollow throughout. Masuhara et al. found that, in addition to the crystal size, overall concentration of C60 also causes the formation of a hollow structure although the tubes were short～2-5 μm. They observed hollow structures upon injecting 300 μL C60 solution in m-xylene（2 mM）into

Fig. 3　 A body-centered tetragonal (bct) model of 1D C60 nanowhisker polymerized via “2 + 2” cyclo-addition of C60 molecules. Reprinted with per-mission from J. Mater. Res. 17, 83-88 (2002), © 2002, Materials Research Society.

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10 mL of 2-propanol, otherwise, solid C60 rods were ob-served upon injection C60 solution below 300 μL. Ji et al.43） also observed single crystalline submicrometer C60 tubes with highly uniform size by using a solvent-induced and surfactant assisted self-assembly technique. Although they pointed out that length and length-to-width ratio of the tubes can be controlled by varying the concentration of C60 in the stock solution and the mixing ratio of antisolvent and C60 solution. Lengths of nanotubes were found to be in the range of a few microns（～5 μm）. A major contribution to the production of long fullerene nanotubes came from Miyazawa and coworkers. They fabricated very long（length in the range of few hundreds microns）single crystalline nanotubes of not only C60 but also of C70 using LLIP method. They also found that the C60 nanotubes sometimes grow to extreme lengths into the millimeter length scale with outer diameters of several hundreds of nanometers and inner diameters of several tens of nanometers to a few hundreds of nanometers. These nanotubes showed good uniformity and linearity. The same group succeeded to fab-ricate vertically aligned fullerene microtubes by slowly in-jecting IPA solution into a saturated solution of C60 in toluene through an alumina membrane44）. The length of the vertically aligned C60 microtubes reached about 500 μm and their planar density and diameter could be controlled by changing the growth conditions, such as the injection rate of IPA and the amount of the C60 solution.

Regarding the dimensions of 1D nanostructures of C60 crystals, usually volume ratio of antisolvent and C60 solu-tion and concentration of C60 in the stock solution play a crucial role. At fixed volume ratio, increasing C60 concen-tration decreases the length and width of derived C60 rods and tubes. Ji et al.43） carefully addressed the effect of C60 concentration and volume ratio of antisolvent and C60 solu-tion on the dimensions of 1D C60 crystals using IPA and m-xylene systems. At fixed 1:1 volume ratio of IPA and C60 so-lution in m-xylene, increasing C60 concentration from 0.75 to 1.2 mgmL－1 formed C60 rods with average length ca. 25 to 3.0 μm and width 447 to 406 nm, respectively. On the other hand, at fixed concentration of 1.2 mgmL－1 increas-ing volume ratio of IPA and C60 solution in m-xylene from 1:1 to 1:3 modulated the shapes of C60 crystal from rods to tubes. The lengths of rods and tubes were essentially the same at ca. 3 μm but their widths increased from 406 to 811 nm（see Fig. 4）.

Miyazawa’s group proposed a modification of the LLIP method to produce fullerene nanowhiskers and nanotubes having lengths hundreds of μm in a relatively short period of time～2 h45）. They divided nucleation stage and crystal growth stage. For nucleation stage, saturated C60 solution was mixed with a small amount of alcohol and for the growth stage C60 was precipitated in the nucleated solution by injecting alcohol to the bottom of the solution at a con-trolled flow rate using a syringe pump. The widths were

found in the range 200-500 nm. They also succeeded to control the diameter of C60 nanowhiskers by changing the area of the liquid-liquid interface, which could be done by simply altering the reaction glass bottle size. Increasing the internal diameter of the glass bottle, i.e., increase in the area of liquid-liquid interface, increases the overall diame-ter of nanowhiskers. For example, the mean diameter of C60 nanowhiskers grown at an IPA and toluene interface

Fig. 4　 SEM images of C60 rods (a-d) and tubes (e-g) at different concentration of C60 in m-xylene and at different volume ratio of IPA and C60 solution: (a) Typical SEM images of C60 rods at 1:1 vol-ume ratio and 0.75 mgmL–1 C60 in m-xylene, (b) C60 rods from 1.0 mgmL–1 C60 in m-xylene, (c) low and (d) high magnification SEM images of from 1.2 mgmL–1 C60 in m-xylene, (e) SEM im-ages of C60 tubes obtained at volume ratio of 1:2 and 1.0 mgmL–1 C60, (f) tubular structure ob-tained at volume ratio of 1:2 and 1.2 mgmL–1 C60, (g) show a tubular feature obtained at vol-ume ratio of 1:3 and 1.2 mgmL–1 C60, and (h) TEM image demonstrating tubular structure. Adopted with permission from J. Phys. Chem. C 111, 10498-10502 (2007) © 2007, American Chemical Society.

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was increased from 222 to 579 nm upon increasing the in-ternal diameter of the glass bottle from 17 and 32.4 mm46）. Details of the dimension controlled fabrications of C60 nanowhiskers or nanotubes from a variety of antisolvents and solvents and using different methods have been re-cently summarized elsewhere47）.

Next we briefly discuss 2D crystals. Fabrication of a 2D plate like morphology of fullerene crystals particularly by solution based methods has been sparsely reported in comparison to the 1D structures. Physical vapor deposition methods have been mostly used to make 2D thin films of C60

48）. Highly selective disk-shaped 2D single crystalline C60 reported by Shin et al.49） is another good example of vapor deposition processes for synthesis of 2D crystals of C60. A C60 solvate formed upon storing C60 solution in trichloro-bromomethane（BrCCl3）in dark for a week, which showed interpenetrated hexagonal shape single crystals of C60. 2BrCCl3, may be the first example of fabrication of 2D C60 crystals based on a solution method50）. The average size of the hexagonal shaped 2D crystals was about 100 μm with thicknesses of a few microns. The group of Miyazawa re-ported the first example of very thin（so called transpar-ent）hexagonal shaped C60 nanosheets by the LLIP method at an IPA and carbon tetrachloride（CCl4）interface31）. They could tailor the average size of the nanosheets by simply changing the type of alcohols though thickness remained essentially unchanged. For example, hexagonal shape nanosheet with a diameter～7.5 μm was observed in the IPA/CCl4 system, whereas the diameter decreased to～2.5 μm and 500 nm, respectively with ethanol and methanol. The same group also fabricated polygonal shaped 2D crys-tals including hexagons and rhombuses by altering solvent molecular structures32）. As mentioned earlier, Park et al.39） produced 2D crystals of C60 by a drop-drying method from a so-called pseudo 3D geometry solvent such as CCl4 and SnCl4, which also supports the results of Miyazawa and co-workers. Figure 5 shows representative SEM images of 2D crystals produced by using LLIP method.

Regarding the 3D morphology of fullerene crystals, Choi and coworkers51） recently reported high-definition cube-shaped crystals of C70, which were synthesized by the LLIP and precipitation methods from a mixture of a solution of C70 in mesitylene and IPA. Formation of local mesitylene cavities, which are instantaneously generated when IPA is

added to the C70/mesitylene solution, was expected to be the key factor for C70 cube formation. Due to the low solu-bility of C70 in IPA, the local concentration of C70 in the me-sitylene cavities is increased upon addition of IPA in C70/mesitylene solution. Therefore, instant nucleation of C70 occurs in the mesitylene cavities. This mixed-solvent-medi-ated nucleation phenomenon is similar to the traditional recrystallization process and the synthesis of various self-crystallized C60 structures. Once C70 molecules are localized in the cavity of mesitylene, which is surrounded by IPA, mesitylene guides C70 molecules to self-crystallize into cubes. They found that the average size of the C70 cubes decreases with increasing the amount of IPA and the con-centration of C70 in the starting solution. Their results support the hypothesis that the addition of IPA induces local cavities of mesitylene in which C70 molecules are lo-calized and their self-crystallization is guided. It should be noted that the size of the cavity should become smaller as the amount of IPA increases as a result; the average size of the resulting cube crystal is then also smaller. The decrease in the size of the cube with the C70 concentration is due to the increased number of nucleation sites. The average size of C70 cubes was ca. 2.05 μm.

Another contribution to the fabrication of cube-shape C70 crystals came from Yao et al.52）. They fabricated cube shape C70 microcrystals by using a fast solvent-assisted evapora-tion method by selectively using aromatic solvents with halogen radicals as a controller. The C70 cubes were of rather polydispersed sizes ranging from several hundred nanometers to tens of micrometers（＞30 μm）. It was found that when the size of the cubic crystals was larger than～10 μm, the cube crystals formed usually have a concave pyramid and some of them have a polycrystalline flower-like shape.

To our knowledge, a perfect cubic shape 3D morphology of C60 crystal is still absent from the literature. However, assembly of 1D nanorods or nanotubes of C60 has been shown to yield 3D nanostructures53）. We have also found a similar aggregation of 1D nanorods or nanotubes into a flower-like morphology in the presence of surfactants in the antisolvent. These 3D flower-shaped C60 crystals have hexagonal close packed structure and show intense photo luminescence（PL）compared to pristine C60

54）. Our group very recently succeeded to fabricate highly crystalline cube-shaped crystals of C60-fullerene-Ag（I）organometallic heteronanostructure［C60｛AgNO3｝5］, which undergoes irre-versible structural rearrangement upon exposure to low molecular weight al iphatic alcohols（ in particular 1-butanol）yielding a uniquely structured formation of well-oriented C60 nano/microcrystals（‘bucky cubes’）35）. The mechanism of rearrangement represents a supramolecular analogue of topotactic processes more commonly associat-ed with some purely inorganic materials, such as maghe-matite, where chemical changes can occur with addition or

Fig. 5　 SEM images of 2D C60 crystals grown at liquid-liquid interface as typical examples. Adopted with permission from J. Am. Chem. Soc. 131, 6372-6373. © 2009 American Chemical Society

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loss of materials. Hence, C60｛AgNO3｝5, undergoes a super-topotactic transformation from a crystalline organometallic complex to well-ordered cube-shaped arrays of needle-like C60 crystals which reflect the original cubic crystal mor-phology an internal structure.

3 S E L F - A S S E M B LY O F F U N C T I O N A L I Z E D FULLERENESHerein, we discuss the self-assembly of functionalized

fullerenes into different mesostructures in solution. As we have mentioned earlier, owing to its highly hydrophobic character, fullerene C60 is insoluble in water, which limits its practical applications. However, this extremely hydro-phobic C60 molecule can be made water soluble by func-tionalizing with charged groups such as carboxylic acids or amines and, hence, its theoretical importance and potential applications are improved55, 56）. Ravi et al.57） recently re-viewed several synthetic routes proposed to functionalize C60 to increase its solubility and processibility. Derivatizing C60 with different functional groups, solubilizing and encap-sulating through the formation of complexes with surfac-tants, cyclodextrins, calixerenes, Tween-20, phospholipids, and liposomes, and producing charge-transfer（CT）complex with organic compounds bearing electron donat-ing groups through electron donor and acceptor interaction are the most commonly employed synthetic routes to func-tionalize C60. After suitable functionalization or modifica-tion of C60 into an amphiphilic molecule its self-assembly behavior in different solvent systems has been investigated in detail with emphasis on its potential impact for the de-velopment of functional materials. For example, Jeng et al.58） observed monodisperse spherical type aggregates having a radius of gyration of about 2.0 nm in dilute solu-tions of starlike hexaanionic fullerene derivatives, C60［CH2］4

SO3Na］6（star-ionomer）. SAXS and SANS studies showed that the interparticle interaction between the aggregates is much weaker and insensitive to the temperature and con-centration characteristics of hard-sphere type interactions common in surfactant micelles. The hydrophobic behavior of star-ionomer was expected to be responsible for the for-mation of monodisperse aggregates. Sano et al.59） have also synthesized novel amphiphilic C60 derivatives with two am-monium headgroups（so called bola-amphiphilic C60: sche-matic molecular structure is presented in Fig. 6a）and ob-served self-assembled spherical vesicles with average diameter in the range of 20-50 nm from the dilute aqueous solution of this bola-amphiphilic C60（3-10 mM）（see Fig. 6）. Vesicular dispersion was obtained by applying simple ultra-sonication to the mixture. This novel aggregation was an-ticipated to be caused by the hydrophobic interaction pro-duced by the fullerene moieties exposed to water molecules by the disordered alkyl tails. Wilson and cowork-

ers60） obtained experimental evidence of nanoscale aggre-gates formed by e,e,e-tris-malonic acid-C60（or C3）in water, which was commonly assumed to exist as discrete mole-cules solubilized in aqueous solution. Figure 7 shows the molecular structure of C3 and electron micrographs of the aggregates at different magnifications. The aggregates were polydisperse having sizes in the range of 40-80 nm. The size was independent of concentration and tempera-ture, but strongly dependent on pH between pH 4-8. The aggregates increased in size with decreasing pH. For in-stance, the average hydrodynamic diameter of the aggre-gates formed by C3 increased from about 90 to 380 nm at a fixed concentration 5 mgmL－1 at 25℃. This increase with pH has been explained by considering the effect of proton dissociation of the C3 malonic acid groups. They also con-firmed that it is the aggregates of C3, which are responsible for their neuroprotective action in cells, not the individual C3 molecules.

Geckeler et al.61） synthesized water-soluble mono-6-aza-6-deoxy-β -cyclodextrin-C60（C60 is covalently bonded to β -cyclodextrin via a bridging nitrogen atom）, which exhib-ited unusual aggregation behavior in solution. The average particle size increased from 0.55 to 3.255 μm with decreas-ing concentration of the solution from 0.216 to 0.01 mM. This unusual phenomenon was related to the diffusivity of

Fig. 6　 (a) Molecular structure of bola-amphiphilic C60, (b) schematic model of vesicle, and (c-f) elec-tron micrographs of the derived vesicles at dif-ferent magnifications. Adopted with permission from Langmuir 16, 3773-3776 (2000) © 2000 American Chemical Society.

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the particles. Dilution led to a reduction in the viscosity and a corresponding increase in the diffusivity of the parti-cles, which facilitated the interaction between clusters leading to cluster-cluster aggregation. The group of Naka-mura investigated association behavior of potassium salt of pentaphenyl fullerene（Ph5C60K）in water62）. Using a laser light scattering（LLS）technique they found that in aqueous solution the hydrocarbon anions Ph5C60

－ associate into bi-layers forming stable spherical vesicles with an average radius of gyration of about 17 nm. The critical aggregation concentration was found to be extremely low（＜10－7 moles per liter）. However, the average aggregation number of as-sociated particles in these large spherical vesicles was about 1.2×104. The same group has shown that the attach-ment of five aromatic groups to one pentagon of a C60 mol-ecule produces deeply conical molecules, which can stack into polar columnar assemblies63）. The stacking was ex-pected to be driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighboring molecule in the same column. Interestingly they found that the packing pattern is maintained upon extending the aromatic groups by attaching flexible aliphatic chains, which thereby result-ed in the formation of compounds with thermotropic and lyotropic liquid crystalline properties demonstrating the possibility of designing a range of new polar liquid crystal-line materials. Liquid crystalline properties of selected self-

assembled fullerene derivatives can be found elsewhere and in the references therein64, 65）. Nakamura and cowork-ers recently reported that fullerene anions featuring a non-polar/polar/nonpolar ternary motif spontaneously form ves-icles exposing their nonpolar fluorous chains to the aqueous environment. Average diameter of vesicles was ca. 36 nm66）. They found that these vesicles tightly yet nonco-valently bind fluorous molecules on their surfaces. In con-trast to lipid vesicles that easily lose their structural integ-rity upon removal from aqueous solution, their vesicles were very robust and retained their spherical shape even on a solid substrate under high vacuum. They looked like nanometer-sized hollow Teflon balls. When the vesicle solu-tion was coated and dried on a hydrophilic surface（Indium tin oxide）, it become water-insoluble and made the surface water-repellent（contact angle ca. 111.7°）similar to a Teflon surface demonstrating the possible utility of the vesicle surface as a scaffold for molecular display, the interior for molecular delivery, and the solution for macroscopic surface modification. In subsequent work, Nakamura and coworkers synthesized twenty potassium complexs of fullerene anion amphiphiles having overall structure non-polar/polar/nonpolar and investigated their abilities to form bilayer vesicles in water67）. The complexes were penta-［（4-substituted）phenyl］［60］fullerene anions, where the 4-substituents included alkyl groups ranging from methyl to icosanyl groups and perfluoromethyl, perfluorobutyl, and perfluorooctyl groups. They found that despite the hy-drophobicity of the fullerene moiety（nonpolar part）and alkyl/perfluoroalkyl chains（second nonpolar part）, all com-pounds except for the one with perfluoromethyl groups were soluble in water due to the centrally located fullerene cyclopentadienide（polar part）and spontaneously formed a vesicle of 25-60 nm diameter with a narrow unimodal size distribution. The vesicles were stable upon heating to 90℃ or standing over a year in air, as well as on a solid substrate in air or in vacuum, maintaining their spherical form. The vesicle membrane consists of an interdigitated bilayer of the amphiphile molecules, in which the nonpolar fullerene part is at the interior and the other nonpolar part is exposed to water. Note that the exposure of nonpolar parts of an amphiphile to water is an unusual phenomenon in surfactant science and it is beyond common sense. However, this fact was well supported by experiments. These vesicles, in particular those bearing icosanyl chains, exhibited the smallest water permeability coefficient ever found for a self-assembled membrane in water. Figure 8 shows SEM images of vesicles on indium tin oxide（ITO）surface formed by the fullerene anion bearing five perfluo-rooctyl chains（Rf8K）as a typical example. As can be seen in Fig. 8a, the Rf8K vesicles uniformly cover a wide area of the ITO substrate. A closer look at the SEM image（Fig 8b）reveals that the vesicles sit on the grain boundaries of the ITO surface to maximize contact with the surface. The 30°

Fig. 7　 Cryo-TEM micrograph of the aggregates formed by the C3 solution at different magnifications. Inset of panel (a) shows schematic molecular structure of C3. Adopted with permission from Nano Lett. 4, 1759-1762 (2004) © 2004 Ameri-can Chemical Society.

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tilted side view（Fig. 8c）confirms this observation and also indicates that the vesicles largely retain their spherical structures under the rather harsh SEM conditions of 10－5 Pa, which demonstrates the unusual robustness of the fullerene vesicle. The average diameter of the Rf8K vesicle particles was ca. 35.6 nm. The attractive features of these vesicles are that they are morphologically stable, monodis-persed, nanosized, spherical hollow objects, which can be prepared by a simple method without any purification. They can also be used to modify solid surfaces. It is antici-pated that these nonpolar/polar/nonpolar type amphiphiles will open a new avenue in research on nano-sized compart-ment structures in solution and on solid surfaces.

In the study of supramolecular assemblies of fullerene derivatives, Georgakilas et al.68） found that ionic fullerene derivatives, which are relatively soluble in polar solvents, self-organize into different morphological nanostructures such as spheres, nanorods, and nanotubes in water de-pending on the side chain appendage of the fullerene spheroid. Guldi et al.12） discussed the organization of fuller-ene derivatives in bulk, at interfaces, and on substrates. They highlighted that the proper combination of the hydro-phobic fullerene core with hydrophilic functional groups（both ionic and nonionic）potentially leads to organized structures whose sizes range from nanometer to microme-ter length scales. The main driving force of such spontane-ous assembly is the amphiphilic character of the fullerene derivatives. They pointed out that, similarly to the conven-tional surfactant systems, supramolecular assembly, dimen-sions and the functions of the fullerene derivatives depend on the following parameters: （a）hydrophilic-hydrophobic balance, （b）the effect of the environment, typically provid-ed by solvents, （c）the interface at which the aggregation occurs, and（d）the solvation process. The influence of these effects on the fullerene supramolecular assemblies can be found elsewhere69）.

Nakanishi et al.70） reported 1D lamellae of fullerene de-rivatives bearing long alkyl chains. The 1D structure epi-taxially oriented along the highly oriented pyrolytic graphite（HOPG）lattice. They could tune the distance

between adjacent nanowires at the nanometer length scale by the molecular design. They presented an approach to direct the assembly of C60 groups on graphite in a predict-able way using alkanes as structure-directing components, covalently bonded to C60 and explored the polymorphism of fullerene assemblies by using the two different intermo-lecular forces, namely π-π interactions of C60 and van der Waals interactions of aliphatic chains. The same group also reported novel micron size flowerlike supramolecular as-semblies of fullerene-based molecules bearing long alkyl chains71）. In the following work, Nakanishi and coworkers observed that a novel N,N-dimethylfulleropyrrolidinium iodide（ionic fullerene derivative derived from further func-tionalization of the N-methylfulleropyrrolidine）form a variety of functional and polymorphic self-assembled structures both from solution and on substrate72）. They ob-served that these ionic fullerene derivatives due to π-π, van der Waals, and electrostatic interactions hierarchically or-ganized into flake-like microparticles with high water repel-lency, doughnut-shaped objects with rough surfaces, and long 1D C60 nanowires（＞1μm）. The flakelike microparti-cles due to surface roughness in nanometer length scale showed water repelling properties giving a static water contact angle of～140°, which is about 10° lower than that observed from microflowers formed by the parent fullerene amphiphile, i.e. N-methylfulleropyrrolidine. The authors mentioned that the difference in water repellency is due to different surface roughnesses. Figure 9 shows typical SEM

Fig. 8　 (a) SEM images of Rf8K vesicles on ITO under ca. 10–5 Pa. (b) Magnified view of panel a, and (c) a different area of the same sample as viewed with a 30° tilt of the sample stage. Adopted with permission from J. Am. Chem. Soc. 133, 6364-6370 (2011) © 2011 American Chemical Soci-ety.

Fig. 9　 Typical SEM and AFM images of flakelike mic-roparticles and 1D nanowires of N,N-dimethyl-fulleropyrrolidinium iodide. Adopted with per-mission from Langmuir 27, 7493-7501 (2011). © 2011 American Chemical Society.

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images of flake-like microparticles formed by N,N-dimeth-ylfulleropyrrolidinium iodide by slow addition of excess methanol solution into its concentrated solution in dichlo-romethane and typical AFM images of nanowires of the N,N-dimethylfulleropyrrolidinium iodide obtained by spin-coating of its 10 μM solution in dichloromethane on HOPG substrate. As can be seen in AFM images, N,N-dimethylful-leropyrrolidinium iodide forms extremely large areas of 2D lamellar domains composed of the 1D C60 nanowires with lengths of over 1.0 μm. The periodic separation of the nanowires is ca. 7.3 nm, which is almost exactly twice the molecular length of N,N-dimethylfulleropyrrolidinium iodide in a fully extended conformation（3.7 nm）. Moreover, a cross-sectional line analysis reveals that the average height difference within the lamellae is 0.38 nm, which is close to the difference between the diameter of C60 and the height of a flat- lying alkyl chain layer on the HOPG surface. These results indicate that the organization of N,N-dimethylfulleropyrrolidinium iodide within nanowires is similar to that of N-methylfulleropyrrolidine, with the C60 moieties organized in a zigzag conformation and the ali-phatic chains localized in between70）.

In the study of supramolecular assembly of fullerene gly-coconjugates in aqueous solution, Kato et al.73） found small supramolecular aggregates（spherical micelles type）having particle size of about 4 nm. These spherical micelles with an extremely narrow size distribution represent supramo-lecular sugar balls, which have potential for biomedical ap-plications. Nurmawati et al.74） outlined a synergistic self-as-sembly of fullerenes（C60）and functionalized poly（p-phenylene）（PPP）to develop nanofibers with high aspect ratios. Nanostructured PPP-C60 hybrids were prepared by direct casting of a dilute solution on solid substrates and on water under ambient conditions. When a solution of the mixture of C60 and PPP polymer（C12PPPOH）（1:1, 0.5 mgmL－1 in toluene）was cast onto a solid substrate, unidi-rectional crystallization of nanohybrid material having nanofibrous morphology with high aspect ratios was observed（see Fig. 10）.

Nanofibers that have an average diameter of about 35 nm and length of 30-50 μm aggregate to form whiskers. The observed high aspect ratio of 1050 is comparable to typical aspect ratios of CNTs. The HR-TEM images shown in Fig. 10c, d shows regular lattice fringes in the nanonee-dles spanning along the growth axis. They explained that planarization of the polymer backbone through potential O-H-O hydrogen bonds and optimum alkyl chain crystalli-zation played an important role in the molecular level or-dering of C12PPPOH during the whisker formation. The first step of the multiscale assembly of the whisker formation involves a molecular level polymer C60 assembly driven by π-π stacking of the conjugated backbone of the polymer and the fullerene, resulting in the nanofibers. Murthy and coworkers75） have recently demonstrated first example of

solubilization of C60 in water by complexation with disac-charides in mixed homogeneous solvent system. The com-plexation of hydrophobic water-insoluble C60 dissolved in nonpolar solvent toluene and extremely water-soluble di-saccharides dissolved in polar solvent DMSO resulted in a unique self-assembled highly crystalline water-soluble C60-disaccharide complex with average particle size ca. 60 nm. Their results highlight the potential application of water-soluble C60-disaccharide complex in biomedical applica-tions.

4 CONCLUDING REMARKSIn this review we have briefly summarized recent devel-

opments in the production of shape-controlled fullerene nano/microcrystals by solution-based approaches. Facile syntheses of fullerene crystals having different morphology such as fullerene spheres, fullerene nanowhiskers and nanotubes, fullerene nanosheets, and assembly of fullerene nanorods or nanotubes in three-dimensional assemblies are discussed. Moreover, supramolecular assembly of function-alized fullerenes（fullerene derivatives）into different meso-structures（micelles, liquid crystals, and vesicles）both in solution and substrate was discussed.

Fig. 10　 (a) SEM image of whiskers casted from hybrid toluene solution (0.5 mgmL–1) of 1:1 C60: C12PPPOH, (b) side view of an individual nanowhiskers showing multiple fibers, (c) HR-TEM image, and (d) magnified HR-TEM of se-lected area. Adopted with permission from ACS Nano 2, 120-127 (2008). © 2008 American Chemical Society.

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ACKNOWLEDGEMENT This work was also partly supported by World Permier

International Research Center Initiative（WPI Initiative）, MEXT, Japan and the Core Research for Evolutional Science and Technology（CREST）program of Japan Science and Technology Agency（JST）, Japan.

References and Notes1） Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.;

Smalley, R. E. C60: Buckminsterfullerene. Nature 318, 162-163（1985）.

2） Prato, M.［60］Fullerene chemistry for materials sci-ence applications. J. Mater. Chem. 7, 1097-1109（1997）.

3） DaRos, T.; Prato, M. Medicinal chemistry with fuller-enes and fullerene derivatives. Chem. Commun. 663-669（1999）.

4） Allemand, P. M.; Khemani, K. C.; Koch, A.; Wudl, F.; Holczer, K.; Donovan, S.; Gruner, G.; Thompson, J. D. Organic Molecular Soft Ferromagnetism in a Fuller-ene-C60. Science 253, 301-303（1991）.

5） Schön, J. H.; Kloc, C.; Haddon, R. C.; Batlogg, B. A Su-perconducting field-effect switch. Science 288, 656-658（2000）.

6） Martín, N.; Sánchez, L.; Llescas, B.; Pérez, I. C60-based electroactive organofullerenes. Chem. Rev. 98, 2527-2547（1998）.

7） Ros, T. D.; Prato, M. Medicinal chemistry with fuller-enes and fullerene derivatives. Chem. Commun. 663-669（1999）.

8） Guldi, D. M.; Prato, M. Excited-state properties of C60 fullerene derivatives. Acc. Chem. Res. 33, 695-703（2000）.

9） Krusic, P. J.; Wasserman, E.; Keizer, P. N.; Morton, J. R.; Preston, K. F. Radical reactions of C60. Science 254, 1183-1185（1991）.

10） Bisaglia, M.; Natalini, B.; Pellicciari, R.; Straface, E.; Malorni, W.; Monti, D.; Franceschi, C.; Schettini, G. C3-Fullero-tris-methanodicarboxylic acid protects cere-bellar granule cells from apoptosis. J. Neurochem. 74, 1197-1204（2000）.

11） Nakamura, E.; Isobe, H. Functionalized fullerenes in water. The first 10 years of their chemistry, biology, and nanoscience. Acc. Chem. Res. 36, 807-815（2003）.

12） Guldi, D. M.; Zerbetto, F.; Gerogakilas, V.: Prato, M. Ordering fullerene materials at nanometer dimensions. Acc. Chem. Res. 38, 38-40（2005）.

13） Diederich, F.; Gómez-López, M. Supramolecular fuller-ene chemistry. Chem. Soc. Rev. 28, 263-277（1999）.

14） Iijima, S. Helical microtubules of graphitic carbon. Na-ture 354, 56-58（1991）.

15） Thompson, B. C.; Fréchet, J. M. J. Polymer-Fullerene

Composite Solar Cells. Angew. Chem. Int. Ed. 47, 58-77（2007）.

16） Segura, J. L.; Martín, N.; Guldi, D. M. Materials for or-ganic solar cells: The C60/π-conjugated oligomer ap-proach. Chem. Soc. Rev. 34, 31-47（2005）.

17） Hoppe, H.; Sariciftci, N. S. Morphology of polymer/fullerene bulk heterojunction solar cells. J. Mater. Chem. 16, 45-61（2006）.

18） Babu, S. S.; Möhwald, H. T. Nakanishi, Recent progress in morphology control of supramolecular fullerene as-semblies and its application. Chem. Soc. Rev. 39, 4021-4035（2010）.

19） Liu, H.; Li, Y.; Jiang, L.; Luo, H.; Xiao, S.; Fang, H.; Li, H.; Zhu, D.; Yu, D.; Xu, J.; Xiang, B. Imaging as-grown［C60］fullerene nanotubes by template technique. J. Am. Chem. Soc. 124, 13370-13371（2002）.

20） Gan, H.; Liu, H.; Li, Y.; Gan, L.; Jiang, L.; Jiu, T.; Wang, N.; He, X.; Zhu, D. Fabrication of fullerene nanotube arrays using a template technique. Carbon 43, 195-213（2005）.

21） Céolin, R.; Tamarit, J. Ll.; López, D. O.; Barrio, M.; Agafonov, V.; Allouchi, H.; Moussa, F.; Szwarc, H. A new hexagonal phase of fullerene C60. Chem. Phys. Lett. 314, 21-26（1999）.

22） Ogawa, S.; Furusawa, H.; Watanabe, T.; Yamamoto, H. Observation of condesed structure of C60 assembled from solution. J. Phys. Chem. Solids 61, 1047-1050（2000）.

23） Geng, J.; Zhou, W.; Skelton, P.; Yue, W.; Kinloch, I. A.; Windle, A. H.; Johnson, B. F. J. Am. Chem. Soc. 130, 2527-2534（2008）.

24） Briseno, A. L.; Mannsfeld, S. C. B.; Ling, M. M.; Liu, S.; Tseng, R. J.; Reese, C.; Roberts, M. E.; Yang, Y.; Wudl, F.; Bao, Z. Patterning organic single-crystal transistor arrays. Nature 444, 913-917（2006）.

25） Dinh, T.; Shon, Y-S. Direct assembly of photorespon-sive C60-Gold nanoparticle hybrid films. ACS Applied Materials & Interfaces, 1, 2699-2702（2009）.

26） Jeon, H. G.; Ryo, S.; Sugiyama, T. Oh, I.; Masuhara, H.; Asahi, T. Fullerene C60 nanostructures having inter-penetrating surfaces prepared by electrophoretic de-position of C60 nanoparticles in water. Chem. Lett. 36, 1160-1161（2007）.

27） Kasai, H.; Nalwa, H. S.; Oikawa, H.; Okada, S.; Matsu-da, H.; Minami, N.; Kakuta, A.; Ono, K. Mukoh, A. Na-kanishi, H. A novel preparation method of organic mi-crocrystal. Jpn. J. App. Phys. 31, L1132-L1134（1992）.

28） Jin, Y.; Curry, R. J.; Sloan, J.; Hatton, R. A.; Chong, L. C.; Blanchard, N.; Stolojan, V.; Kroto, H. W.; Silva, S. R. P. Structural and optoelectronic properties of C60 rods obtained via a rapid synthesis route. J. Mater. Chem. 16, 3715-3720（2006）.

29） Miyazawa, K.; Kuwasaki, Y.; Obayashi, A.; Kuwabara, M.

L. K. Shrestha, R. G. Shrestha, J. P. Hill et al.

J. Oleo Sci. 62, (8) 541-553 (2013)

552

C60 nanowhiskers formed by the liquid-liquid interfa-cial precipitation method. J. Mater. Res. 17, 83-88（2002）.

30） Miyazawa, K. Synthesis and properties of fullerene nanowhiskers and fullerene nanotubes. J. Nanosci. Nanotechnol. 9, 41-50（2009）.

31） Sathish, M.; Miyazawa, K. Size-tunable hexagonal fullerene（C60）nanosheets at the liquid-liquid interface. J. Am. Chem. Soc. 129, 13816-13817（2007）.

32） Sathish, M.; Miyazawa, K.; Hill, J. P.; Ariga, K. Solvent engineering for shape-shifter pure fullerene（C60）. J. Am. Chem. Soc. 131, 6372-6373（2009）.

33） Shrestha, L. K.; Hill, J. P.; Miyazawa, K.; Ariga, K. Mix-ing antisolvents induced modulation in the morpholo-gy of crystalline C60. J. Nanosci. Nanotechnol. 12, 6380-6384（2012）.

34） Shrestha, L. K.; Yamauchi, Y.; Hill, J. P.; Miyazawa, K.; Ariga, K. Fullerene Crystals with Bimodal Pore Archi-tectures Consisting of Macropores and Mesopores. J. Am. Chem. Soc. 135, 586-589（2013）.

35） Shrestha, L. K.; Sathish, M.; Hill, J. P.; Miyazawa, K.; Tsuruoka, T.; Sanchez-Ballester, N.; Honma, I.; Ji, Q.; Ariga, K. Alcohol-induced Rearrangement of Olm-stead’s Crystalline Ag（I）-Fullerene Heteronanostruc-ture yields ‘Bucky Cubes’J. Mater. Chem. C 1, 1174-1181（2013）.

36） Deguchi, S.; Alargova, R. G.; Tsujii, K. Stable disper-sions of fullerenes, C60 and C70 in water. Preparation and characterization. Langmuir 17, 6013-6017（2001）.

37） Hilburn, M. E.; Murdianti, B. S.; Maples, R. D.; Wil-liams, J. S.; Damron, J. T.; Kuriyavar, S. I.; Ausman, K. D. Synthesizing aqueous fullerene colloidal suspen-sions by new solvent-exchange methods. Colloid and Surfaces A: Physicochem. Eng. Aspects 401, 48-53（2012）.

38） Maples, R. D.; Hilburn, M. E.; Murdianti, B. S.; Kore-alege, R. S. H.; Williams, J. S.; Kuriyavar, S. I.; Ausman, K. D. Optimized solvent-exchange synthesis method for C60 colloidal dispersions. J. Colloid Interface Sci. 370, 27-31（2012）.

39） Park, C.; Song H. J.; Choi, H. C. The critical effect of solvent geometry on the determination of fullerene（C60）self-assembly into dot, wire, and disk structutres. Chem. Commun. 4803-4805（2009）.

40） Masuhara, A.; Tan, Z. Kasai, H. Nakanishi, H.; Oikawa, H. Fullerene fine crystals with unique shapes and con-trolled size. Jpn. J. App. Phys. 48, 050206-1-3（2009）.

41） Miyazawa, K.; Hotta, K. The effect of solvent ratio and water on the growth of C60 nanowhiskers. J. Cryst. Growth 312, 2764-2770（2010）.

42） Minato, J.; Miyazawa, K. Solvated structure of C60 nanowhiskers. Carbon 43, 2837-2841（2005）.

43） Ji, H-X.; Hu, J-S.; Tang, Q-X.; Song, W-G.; Wang, C-R.;

Hu, W-P.; Wan, L-J.; Lee, S-T. Controllable preparation of submicrometer single-crystal C60 rods and tubes trough concentration depletion at the surface of seeds. J. Phys. Chem. C 111, 10498-10502（2007）.

44） Cha, S. I.; Miyazawa, K.; Kim, J-D. Vertically well-aligned C60 microtubes crystal array prepared using a solution-based, one-step process. Chem. Mater. 20, 1667-1669（2008）.

45） Cha, S. I.; Miyazawa, K.; Kim, Y. K.; Lee, D. Y.; Kim, J-D. Kinetically controlled fabrication of C60 1-dimen-sional crystals. J. Nanosci. Nanotechnol. 11, 3374-3380（2011）.

46） Wakahara, T.; Miyazawa, K.; Nemoto, Y. Ito, O. Diame-ter controlled growth of fullerene nanowhiskers and their optical properties. Carbon 49, 4644-4649（2011）.

47） Shrestha, L. K.; Ji, Q. Mori, T.; Miyazawa, K.; Yamau-chi, Y.; Hill, J. P.; Ariga, K. Fullerene Nanoarchitecton-ics: from Zero to Higher Dimensions. Chem. Asian J. in press DOI: 10.1002/asia.201300247.

48） Deutsch, D.; Tarábek, J.; Krause, M.; Janda, P. Dunsch, L. Nanostructuring of C60 fullerene thin films. Carbon 42, 1137-1141（2004）.

49） Shin, H. S.; Yoon, S. M.; Tang, Q.; Chon, B.; Joo, T. Choi, H. C. Highly slelective synthesis of C60 disks on graphite substrate by a vapor-solid process. Angew. Chemi. Intl. Ed. 47, 693-696（2008）.

50） Barrio, M.; López, D. O.; Tamarit, J. L1, Espeau, P. Céolin, R. Allouchi, H. Solid-state studies of C60 sol-vates formed in the C60-BrCCl3 system. Chem. Mater. 15, 288-291（2003）.

51） Park, C. Yoon, E.; Kawano, M.; Joo, T.; Choi, H. C. Self-crystallization of C70 cubes and remarkable enhance-ment of photoluminescence. Angew. Chem. Int. Ed. 49, 9670-9675（2010）.

52） Yao, M.; Fan, X.; Liu, D.; Liu B. Wågberg, T. Synthesis of differently shaped C70 nano/microcrystals by using various aromatic solvents and their crystallinity-de-pendent photoluminescence. Carbon 50, 209-215（2012）.

53） Jeong, J.; Kim, W-S.; Park, S-I.; Yoon, T-S.; Chung, B. H. Synthesis and characterization of various shaped C60 microcrystals using alcohols as antisolvents. J. Phys. Chem. C 114, 12976-12981（2010）.

54） Shretha, L. K.; Hill, J. P.; Tsuruoka, T. Miyazawa, K.; Ariga, K. Surfactant-assisted assembly of fullerene（C60）nanorods and nanotubes formed at liquid-liquid interface. Langmuir 29, 7195-7202（2013）.

55） Tokuyama, H.; Yamago, S.; Nakamura, E.; Shiraki, T.; Sugiura, Y. Photoinduced biochemical activity of fuller-ene carboxylic acid. J. Am. Chem. Soc. 115, 7918-7919（1993）.

56） Cassell, A. M.; Scrivens, W. A.; Tour, J. M. Assembly of DNA/fullerene hybrid materials. Angew. Chem. Int. Ed. 37, 1528-1531（1998）.

Self-Assembled Fullerene Nanostructures

J. Oleo Sci. 62, (8) 541-553 (2013)

553

57） Ravi, P.; Dai, S.; Wang, C.; Tam, K. C. Fullerene con-taining polymers: a review on their synthesis and su-pramolecular behavior in solution. J. Nanosci. Nano-technol. 7, 1176-1196（2007）.

58） Jeng, U-S.; Lin, T-L.; Tsao, C-S.; Lee, C-H.; Canteenwa-la, T.; Wang, L. Y.; Chiang, L. Y.; Han, C. C. Study of ag-gregates of fullerene-based ionomers in aqueous solu-tions using small angle neutron and X-ray scatering. J. Phys. Chem. B 103, 1059-1063（1999）.

59） Sano. M.; Oishi, K.; Ishi-i, T.; Shinkai, S. Vesicle forma-tion and its fractal distribution by bola-amphiphilic［C60］fullerene. Langmuir 16, 3773-3776（2000）.

60） Sitharaman, B.; Asokan, S.; Rusakova, I.; Wong, M. S.; Wilson, L. J. Nanoscale aggregation properties of neu-roprotective carboxyfullerene（C3）in aqueous solution. Nano Lett. 4, 1759-1762（2004）.

61） Samal, S.; Geckeler, K. E. Unexpected solute aggrega-tion in water on dilution. Chem. Commun. 2224-2225（2001）.

62） Zhu, S.; Burger, C.; Chu, B.; Sawamura, M.; Nagahama, N.; Toganoh, M.; Hackler, U. E.; Isobe, H.; Nakamura, E. Spherical bilayer vesicles of fullerene-based surfac-tants in water: a laser light scattering study. Science 291, 1944-1947（2001）.

63） Sawamura, M.; Kawai, K.; Matsuo, Y.; Kanie, K.; Kato, T.; Nakamura, E. Stacking of conical molecules with a fullerene apex into polar columns in crystals and liq-uid crystals. Nature 419, 702-705（2002）.

64） Zhong, Y-W.; Matsuo, Y.; Nakamura, E. Lamellar assem-bly of conical molecules possessing a fullerene apex in crystals and liquid crystals. J. Am. Chem. Soc. 129, 3052-3053（2007）.

65） Matsuo, Y.; Nakamura, E. Selective multiaddition of or-ganocopper reagents to fullerenes. Chem. Rev. 108, 3016-3028（2008）.

66） Homma, T.; Harano, K.; Isobe, H.; Nakamura, E. Nano-meter-sized fluorous fullerene vesicles in water and on

solid surface. Angew. Chem. Int. Ed. 49, 1665-1668（2010）.

67） Homma, T.; Harano, K.; Isobe, H.; Nakamura, E. Prepa-ration and properties of vesicles made of nonpolar/po-lar/nonopolar fullerene amphiphiles. J. Am. Chem. Soc. 133, 6364-6370（2011）.

68） Georgakilas, V.; Pellarini, F.; Prato, M.; Guldi, D. M.; Melle-Franco, M. Supramolecular self-assembled fullerene nanostructures. PNAS 16, 5075-5080（2002）.

69） Zhang, E-Y.; Wang, C-R. Fullerene self-assembly and supramolecular nanostructures. Curr. Opin. Colloid & Interface Sci. 14, 148-156（2009）.

70） Nakanishi, T.; Miyashita, N.; Michinobu, T.; Wakayama, Y. Tsuruoka, T.; Ariga, K.; Kurth, D. G. Perfectly straight nanowires of fullerene bearing long alkyl chains on graphite. J. Am. Chem. Soc. 128, 6328-6329（2006）.

71） Nakanishi, T.; Ariga, K.; Michinobu, T.; Yoshida, K.; Takahashi, H. Teranishi, T.; Möhwald, H. Kurth, D. G. Flower-shaped supramolecular assemblies: hierarchi-cal organization of a fullerene bearing long aliphatic chains. Small 3, 2019-2033（2007）.

72） Li, H.; Hollamby, M.; Seki, T.; Yagi, S.; Möhwald, H.; Na-kanishi, T. Multifunctional, polymporphic, ionic fuller-ene supramolecular materials: self-assembly and ther-motropic properties. Langmuir 27, 7493-7501（2011）.

73） Kato, H.; Böttcher, C.; Hirsch, A. Sugar balls: synthesis and supramolecular assembly of［C60］fullerene glyco-conjugates. Eur. J. Org. Chem. 2659-2666（2007）.

74） Nurmawati, M. H.; Ajikumar, P. K.; Renu, R. Sow, C. H.; Valiyaveettil, S. Amphiphilic poly（p-phenylene）-driven multiscale assembly of fullerenes to nanowhiskers. ACS Nano 2, 1429-1436（2008）.

75） Bhoi, V. I.; Kumar, S.; Murthy, C. N. The self-assembly and aqueous solubilization of［60］fullerene with disac-charides. Carbohydrate Res. 359, 120-127（2012）.