Ambipolar to Unipolar Conversion in C70/Ferrocene Nanosheet Field-Effect Transistors.

Organic cocrystals, which are assembled by noncovalent intermolecular interactions, have garnered intense interest due to their remarkable chemicophysical properties and practical applications. One notable feature, namely, the charge transfer (CT) interactions within the cocrystals, not only facilitates the formation of an ordered supramolecular network but also endows them with desirable semiconductor characteristics. Here, we present the intriguing ambipolar CT properties exhibited by nanosheets composed of single cocrystals of C70/ferrocene (C70/Fc). When heated to 150 °C, the initially ambipolar monoclinic C70/Fc nanosheet-based field-effect transistors (FETs) were transformed into n-type face-centered cubic (fcc) C70 nanosheet-based FETs owing to the elimination of Fc. This thermally induced alteration in the crystal structure was accompanied by an irreversible switching of the semiconducting behavior of the device; thus, the device transitions from ambipolar to unipolar. Importantly, the C70/Fc nanosheet-based FETs were also found to be much more thermally stable than the previously reported C60/Fc nanosheet-based FETs. Furthermore, we conducted visible/near-infrared diffuse reflectance and photoemission yield spectroscopies to investigate the crucial role played by Fc in modulating the CT characteristics. This study provides valuable insights into the overall functionality of these nanosheet structures.

Fullerene C70/porphyrin hybrid nanoarchitectures: single-cocrystal nanoribbons with ambipolar charge transport properties.

In recent years, supramolecular cocrystals containing organic donors and acceptors have been explored as active components in organic field-effect transistors (FETs). Herein, we report the synthesis of novel single-cocrystal nanoribbons with ambipolar charge transport characteristics from C70 and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin (3,5-TPP) in a 3 : 2 ratio. The C70/3,5-TPP nanoribbons exhibited a new strong absorption band in the near-infrared region, indicating the presence of charge-transfer interactions between C70 and 3,5-TPP in the cocrystals. We elucidated the mechanism of the charge-transport properties of the nanoribbons using photoemission yield spectroscopy in air and theoretical calculations. A strong interaction between porphyrins in the one-dimensional porphyrin chains formed in C70/3,5-TPP nanoribbons, which was confirmed by single-crystal X-ray diffraction, plays a crucial role in their hole transport properties.

One-Dimensional Fullerene/Porphyrin Cocrystals: Near-Infrared Light Sensing through Component Interactions.

Recently, organic donor-acceptor (D-A) cocrystals have attracted special interest as functional materials because of their unique chemical and physical properties that are not exhibited by simple mixtures of their components. Herein, we report the preparation of one-dimensional novel D-A cocrystals from C60 and 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin (3,5-TPP); these cocrystals have near-infrared (NIR) light-sensing abilities, despite each of their component molecule individually having no NIR light-sensing properties. Micrometer-sized rectangular columnar C60-3,5-TPP cocrystals were produced by a simple liquid-liquid interfacial precipitation method. The cocrystals exhibit a new strong transition in the NIR region indicative of the existence of charge-transfer interactions between C60 and 3,5-TPP in the cocrystals. The C60-3,5-TPP cocrystals showed n-type transport characteristics with NIR light-sensing properties when the cocrystals were incorporated in bottom-gate/bottom-contact organic phototransistors, revealing that organic cocrystals with suitable charge-transfer interaction are useful as functional materials for the creation of novel NIR-light-sensing devices.

Young's Modulus of Fullerene C60-C70 Alloy Crystalline Nanowhiskers.

Crystalline nanowhiskers (NWs) composed of fullerene C60 and C70 molecules, i.e., alloy NWs, were synthesized by a liquid-liquid interfacial precipitation method. The nominal composition of C70 ranged from 0 to 40 mass%. The bending tests of the alloy NWs were performed inside a high-resolution transmission electron microscope, and the deformation behavior was observed in situ. The bending force acting on the NWs were measured simultaneously by an optical deflection method, and the Young's modulus was estimated from the resulting force-flexure curves. The average Young's modulus was found to increase to approximately 30 GPa as the C70 composition was increased to the solubility limit. In contrast, the Young's modulus decreased with increasing NW diameter caused by the addition of C70.

Regulating Higher-Order Organization through the Synergy of Two Self-Sorted Assemblies.

The extracellular matrix (ECM) is the natural fibrous scaffold that regulates cell behavior in a hierarchical manner. By mimicking the dynamic and reciprocal interactions between ECM and cells, higher-order molecular self-assembly (SA), mediated through the dynamic growth of scaffold-like nanostructures assembled by different molecular components, was developed. Designed and synthesized were two self-sorted coumarin-based gelators, a peptide molecule and a benzoate molecule, which self-assemble into nanofibers and nanobelts, respectively, with different dynamic profiles. Upon the dynamic growth of the fibrous scaffold assembled from peptide gelators, nanobelts assembled from benzoate gelators transform into a layer-by-layer nanosheet, reaching ninefold increase in height. By using light and an enzyme, the spatial-temporal growth of the scaffold can be modified, leading to in situ height regulation of the higher-order architecture.

Thermal decomposition of fullerene nanowhiskers protected by amorphous carbon mask.

Fullerene nanostructures are well known for their unique morphology, physical and mechanical properties. The thermal stability of fullerene nanostructures, such as their sublimation at high temperature is also very important for studying their structures and applications. In this work, We observed fullerene nanowhiskers (FNWs) in situ with scanning helium ion microscopy (HIM) at elevated temperatures. The FNWs exhibited different stabilities with different thermal histories during the observation. The pristine FNWs were decomposed at the temperatures higher than 300 °C in a vacuum environment. Other FNWs were protected from decomposition with an amorphous carbon (aC) film deposited on the surface. Based on high spacial resolution, aC film with periodic structure was deposited by helium ion beam induced deposition (IBID) on the surface of FNWs. Annealed at the high temperature, the fullerene molecules were selectively sublimated from the FNWs. The periodic structure was formed on the surface of FNWs and observed by HIM. Monte Carlo simulation and Raman characterization proved that the morphology of the FNWs was changed by helium IBID at high temperature. This work provides a new method of fabricating artificial structure on the surface of FNWs with periodic aC film as a mask.

Superconductivity in alkali-doped fullerene nanowhiskers.

Superconductivity in alkali metal-doped fullerene nanowhiskers (C60NWs) was observed in K3.3C60NWs, Rb3.0C60NWs and Cs2.0Rb1.0C60NWs with transition temperatures at 17, 25 and 26 K, respectively. Almost full shielding volume fraction (~80%) was observed in K3.3C60NWs when subjected to thermal treatment at 200 °C for a duration of 24 h. In contrast, the shielding fraction of Rb3.0C60NWs and Cs2.0Rb1.0C60NWs were calculated to be 8% and 6%, respectively. Here we report on an extensive investigation of the superconducting properties of these AC60NWs (A = K3.3, Rb3.0 and Cs2.0Rb1.0). These properties are compared to the ones reported on the corresponding conventional (single-crystal or powder) K-doped fullerene. We also evaluated the critical current densities of these C60NWs using the Bean model under an applied magnetic field up to 50 kOe.

Vortex-aligned fullerene nanowhiskers as a scaffold for orienting cell growth.

A versatile method for the rapid fabrication of aligned fullerene C60 nanowhiskers (C60NWs) at the air-water interface is presented. This method is based on the vortex motion of a subphase (water), which directs floating C60NWs to align on the water surface according to the direction of rotational flow. Aligned C60NWs could be transferred onto many different flat substrates, and, in this case, aligned C60NWs on glass substrates were employed as a scaffold for cell culture. Bone forming human osteoblast MG63 cells adhered well to the C60NWs, and their growth was found to be oriented with the axis of the aligned C60NWs. Cells grown on aligned C60NWs were more highly oriented with the axis of alignment than when grown on randomly oriented nanowhiskers. A study of cell proliferation on the C60NWs revealed their low toxicity, indicating their potential for use in biomedical applications.

Synthesis of fullerene nanowhiskers using the liquid-liquid interfacial precipitation method and their mechanical, electrical and superconducting properties.

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C60, C70, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C60 (fullerene) nanowhiskers (C60NWs) exhibit superconducting behavior. Potassium-doped C60NWs have realized the highest superconducting volume fraction of the alkali metal-doped C60 crystals and display a high critical current density (Jc) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid-liquid interfacial precipitation method.

Adsorption of amino acids by fullerenes and fullerene nanowhiskers.

We have investigated the adsorption of some amino acids and an oligopeptide by fullerene (C60) and fullerene nanowhiskers (FNWs). C60 and FNWs hardly adsorbed amino acids. Most of the amino acids used have a hydrophobic side chain. Ala and Val, with an alkyl chain, were not adsorbed by the C60 or FNWs. Trp, Phe and Pro, with a cyclic structure, were not adsorbed by them either. The aromatic group of C60 did not interact with the side chain. The carboxyl or amino group, with the frame structure of an amino acid, has a positive or negative charge in solution. It is likely that the C60 and FNWs would not prefer the charged carboxyl or amino group. Tri-Ala was adsorbed slightly by the C60 and FNWs. The carboxyl or amino group is not close to the center of the methyl group of Tri-Ala. One of the methyl groups in Tri-Ala would interact with the aromatic structure of the C60 and FNWs. We compared our results with the theoretical interaction of 20 bio-amino acids with C60. The theoretical simulations showed the bonding distance between C60 and an amino acid and the dissociation energy. The dissociation energy was shown to increase in the order, Val < Phe < Pro < Asp < Ala < Trp < Tyr < Arg < Leu. However, the simulation was not consistent with our experimental results. The adsorption of albumin (a protein) by C60 showed the effect on the side chains of Try and Trp. The structure of albumin was changed a little by C60. In our study Try and Tyr were hardly adsorbed by C60 and FNWs. These amino acids did not show a different adsorption behavior compared with other amino acids. The adsorptive behavior of mono-amino acids might be different from that of polypeptides.

Nanoporous carbon tubes from fullerene crystals as the π-electron carbon source.

Here we report the thermal conversion of one-dimensional (1D) fullerene (C60) single-crystal nanorods and nanotubes to nanoporous carbon materials with retention of the initial 1D morphology. The 1D C60 crystals are heated directly at very high temperature (up to 2000 °C) in vacuum, yielding a new family of nanoporous carbons having π-electron conjugation within the sp(2)-carbon robust frameworks. These new nanoporous carbon materials show excellent electrochemical capacitance and superior sensing properties for aromatic compounds compared to commercial activated carbons.

High-temperature calcined fullerene nanowhiskers as well as long needle-like multi-wall carbon nanotubes have abilities to induce NLRP3-mediated IL-1ß secretion.

Because multi-wall carbon nanotubes (MWCNTs) have asbestos-like shape and size, concerns about their pathogenicity have been raised. Contaminated metals of MWCNTs may also be responsible for their toxicity. In this study, we employed high-temperature calcined fullerene nanowhiskers (HTCFNWs), which are needle-like nanofibers composed of amorphous carbon having similar sizes to MWCNTs but neither metal impurities nor tubular structures, and investigated their ability to induce production a major proinflammatory cytokine IL-1ß via the Nod-like receptor pyrin domain containing 3 (NLRP3)-containing flammasome-mediated mechanism. When exposed to THP-1 macrophages, long-HTCFNW exhibited robust IL-1ß production as long and needle-like MWCNTs did, but short-HTCFNW caused very small effect. IL-1ß release induced by long-HTCFNW as well as by long, needle-like MWCNTs was abolished by a caspase-1 inhibitor or siRNA-knockdown of NLRP3, indicating that NLRP3-inflammasome-mediated IL-1ß production by these carbon nanofibers. Our findings indicate that the needle-like shape and length, but neither metal impurities nor tubular structures of MWCNTs were critical to robust NLRP3 activation.

Fullerene nanoarchitectonics: from zero to higher dimensions.

The strategic design of nanostructured materials, the properties of which could be controlled across different length scales and which, at the same time, could be used as building blocks for the construction of devices and functional systems into new technological platforms that are based on sustainable processes, is an important issue in bottom-up nanotechnology.Such strategic design has enabled the fabrication of materials by using convergent bottom-up and top-down strategies. Recent developments in the assembly of functional fullerene (C60) molecules, either in bulk or at interfaces, have allowed the production of shape-controlled nano-to-microsized objects that possess excellent optoelectronic properties, thus enabling the fabrication of optoelectronic devices. Because fullerene molecules can be regarded as an ideal zero-dimensional (0D) building units with attractive functions, the construction of higher-dimensional objects, that is, 1D, 2D, and 3D nanomaterials may realize important aspects of nanoarchitectonics. This Focus Review summarizes the recent developments in the production of nanostructured fullerenes and techniques for the elaboration of fullerene nanomaterials into hierarchic structures.

Fullerene crystals with bimodal pore architectures consisting of macropores and mesopores.

A new class of fullerene (C(60)) crystals with bimodal pore architectures consisting of macropores and mesopores was synthesized by using a liquid-liquid interfacial precipitation (LLIP) method involving an interface between isopropyl alcohol (IPA) and a saturated solution of C(60) in a mixture of benzene and carbon tetrachloride (CCl(4)). By varying the mixing fraction of CCl(4) in benzene, the porosity and electrochemically active surface area can be flexibly controlled.

Surfactant-assisted assembly of fullerene (C60) nanorods and nanotubes formed at a liquid-liquid interface.

Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcrystals at the liquid-liquid interface. C60 crystals were grown using a liquid-liquid interfacial precipitation (LLIP) method by layering surfactant solution in butanol with a saturated solution of C60 in benzene. In the LLIP method, it is suggested that the crystal formation mechanism is driven by supersaturation related to the low C60 solubility in alcohol. We found that the dimensions of the synthesized C60 flowers depend on the concentration and surfactant type. In the absence of surfactant (i.e., in the butanol/benzene system), 1D C60 nanowhiskers (nanorods) and C60 nanotubes (diameter 400 nm-2 µm and length 5-20 µm) are obtained. However, when surfactants are incorporated into the system flowerlike microcrystals consisting of C60 nanotubes are observed. For instance, crystals grown at the interface of a 0.01% diglycerol monolaurate (C12G2) nonionic surfactant in butanol with benzene lead to the formation of flower-shaped microcrystals of average sizes in the range of 10-35 µm. To the best of our knowledge, this is the first example of the surfactant-assisted assembly of C60 crystals. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have shown that fullerene flowers have a hexagonal structure with cell dimensions of a = 2.539 nm and c = 1.021 nm, which differ from that of pristine C60. Mixtures of flower-shaped C60 crystals and free-standing C60 nanotubes are found in the 0.1% C12G2/butanol system. However, clusters or giant aggregates of nanowhiskers lacking any specific shape are observed in the 1% C12G2/butanol system although these crystals exhibit hexagonal close-packed structures. Flower-shaped C60 microcrystals are also observed with anionic surfactants cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC). C60 flowers obtained from 0.01% CTAB and 0.01% CTAC also exhibit hexagonal structures with cell dimensions of a = 2.329 nm and c = 1.273 nm, a = 2.459 nm and c = 0.938 nm, respectively. Our C60 flowers exhibit intense photoluminescence (PL) and a blue-shifted PL intensity maximum compared to the same parameters for pristine C60, demonstrating the potential to control the optoelectronic properties of fullerene-based nanostructures.

Mixing antisolvents induced modulation in the morphology of crystalline C60.

We present systematic studies of the synthesis of fullerene (C60) crystals with diverse morphologies by liquid-liquid interfacial precipitation (LLIP) method based on different alcohols as antisolvents and aromatic benzene as a solvent. C60 crystals are grown at liquid-liquid interface of mixed isopropyl alcohol (IPA) and tertiary butyl alcohol (TBA) with C60 solution in benzene. The role of mixing IPA and TBA on the morphology of C60 crystal is investigated. One dimensional (1 D) C60 nanowhiskers and polygon-shaped 2D sheets have been grown with individual IPA/benzene and TBA/benzene system, respectively. However, C60 crystals of different morphology (1D, 2D or both), and the self-assembly of nano-sized C60 into micron-sized crystals could be obtained upon mixing IPA and TBA and it is the mixing ratio which determines the morphology. Raman scattering and power X-ray diffraction measurements have shown that these materials are crystalline with cubic and hexagonal structures.

Synthesis of oriented bundle fibers of fullerene C70 crystal nanotubes.

We synthesized oriented bundle fibers of C70 crystal nanotubes (NTs) by a liquid-liquid interfacial precipitation method. The bundle fibers were characterized by transmission electron microscopy and scanning electron microscopy. We deduced that in the formation process, bundle fibers of C70 nanowhiskers (NWs) precipitate initially, and then elution occurs in the interior region of each NW to form C70 NT bundle fibers.

Superconducting fullerene nanowhiskers.

We synthesized superconducting fullerene nanowhiskers (C(60)NWs) by potassium (K) intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x) in the range between 1.6 and 6.0 in K-doped C(60) nanowhiskers (K(x)C(60)NWs), while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K(3.3)C(60)NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C(60)) crystal was less than 1%. We report the superconducting behaviors of our newly synthesized K(x)C(60)NWs in comparison to those of K(x)C(60) crystals, which show superconductivity at 19 K in K(3)C(60). The lattice structures are also discussed, based on the x-ray diffraction (XRD) analyses.

Fullerene/cobalt porphyrin hybrid nanosheets with ambipolar charge transporting characteristics.

A novel supramolecular nanoarchitecture, comprising C(60)/Co porphyrin nanosheets, was prepared by a simple liquid-liquid interfacial precipitation method and fully characterized by means of optical microscopy, AFM, STEM, TEM, and XRD. It is established that the highly crystalline C(60)/Co porphyrin nanosheets have a simple (1:1) stoichiometry, and when incorporated in bottom-gate, bottom-contact field-effect transistors (FETs), they show ambipolar charge transport characteristics.

Synthesis and characterization of fullerene nanowhiskers by liquid-liquid interfacial precipitation: influence of C60 solubility.

Fullerene nanowhiskers (FNWs) composed of C(60) fullerene molecules were prepared using the liquid-liquid interfacial precipitation (LLIP) method in the carbon-disulfide (CS(2)) and isopropyl alcohol (IPA) system. The electron microscopic images reveal the formation of non-tubular FNWs. The X-ray diffraction (XRD) pattern studies indicate the presence of fcc crystalline structure and unusual triclinic structure in the FNWs. The selected area electron diffraction pattern (SAED) analysis demonstrates the existence of triclinic and electron beam assisted fcc to tetragonal crystalline phase transformation. The formation of triclinic structure might be validated due to the partial polymerization of FNWs at C(60) saturated CS(2)-IPA interface. The high solubility of C(60) in CS(2) solvent system results in partial polymerization of FNWs. The polymerization of fullerene molecules in the FNWs has been further confirmed using Raman spectroscopy.