C60 Chains Research Articles

Packing C60 in boron nitride nanotubes.

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.

Crystal structures of polymerized fullerides AC60, A=K, Rb, Cs, and alkali-mediated interactions

Starting from a model of rigid interacting C60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account (i) van der Waals interactions and electric quadrupole interactions between C60 monomers on different chains as well as (ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions (i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C60 chains in planes (001). The interactions (ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C60 monomers interact with induced quadrupoles due to excited electronic d-states of the alkalis. Both interactions (ii) lead to an effective orientation-orientation interaction between the C60 chains and always favor the ferrorotational structure I2/m, where C60 chains have a same orientation. The structures Pmnn for KC60 and I2/m for Rb- and CsC60 are the result of a competition between the direct interaction (i) and the alkali-mediated interactions (ii). In Rb– and CsC60 the latter are found to be dominant, the preponderant role being played by the quadrupolar electronic polarizability of the alkali ions.

Electrical and thermal properties of C60-filled single-wall carbon nanotubes

We report measurements of electrical resistivity, thermopower, and thermal conductivity of highly C60-filled single-wall carbon nanotubes and unfilled controls, from 1.5 to 300 K. The data suggest that the C60 chains provide additional conductive paths for charge carriers, increase the rate of phonon scattering, and block interior sites from sorbing other gas molecules.

Energetics and electronic structures of encapsulated C60 in a carbon nanotube.

We report total-energy electronic structure calculations that provide energetics of encapsulation of C60 in the carbon nanotube and electronic structures of the resulting carbon peapods. We find that the encapsulating process is exothermic for the (10,10) nanotube, whereas the processes are endothermic for the (8,8) and (9,9) nanotubes, indicative that the minimum radius of the nanotube for the encapsulation is 6.4 A. We also find that the C(60)@(10,10) is a metal with multicarriers each of which distributes either along the nanotube or on the C60 chain. This unusual feature is due to the nearly free electron state that is inherent to hierarchical solids with sufficient space inside.

A Theoretical Study of the Pressure-Induced Dimerization of C60 Fullerene

We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+2] cycloaddition of double bonds. The possible crystal packings of (C60)2 molecules are calculated by minimization of the lattice energy with a bond charge intermolecular potential model proved successful in the previous C60 studies. The set of dimer lattices that were derived from the fcc lattice was used to construct the initial structures for minimization. The final structures found this way, although belonging to various space-group symmetries, retain approximately fcc arrangement of the constituting C60 cages. On the other hand, the structure obtained from the dimer motif observed in the o-dichlorobenzene solvate of (C60)2 exhibits a hcp-like C60 arrangement. The more energetically stable hcp-type dimer seems not to form due to the high potential barrier separating the fcc and hcp structures. The relative stability of the predicted structures changes significantly under pressure. Some of the dimer structures are remarkably similar to the respective theoretical monomeric and polymeric C60 structures studied previously. On this basis we propose that the respective structures are connected states in the possible conversion paths from pristine C60 to its various polymerization products. One of the dimer structures is geometrically favorable for the formation of the higher C60 chain oligomers as well as of the infinite polymer.

Synthesis and characterization of [60]fullerene-based nonlinear optical polyacrylonitrile derivatives

Nonlinear Optical (NLO) materials have gained increasing interest, particularly in the past decades, for their realized and potential applications in many fields of photonics, optical communication and laser technology. Along with metallophthalocyanines and mixed metal clusters [1], C60 and other fullerenes have emerged as promising candidate materials for the nonlinear optical applications owing to their intrinsic NLO properties which primarily originate from their largeπ electron conjugations and strong electron affinity [2]. However the ability to fabricate NLO devices based on C60 has been limited due to its poor processability and multiaddition of organic group [3]. Therefore, the main key to the development of C60-based NLO materials is to synthesize highly soluble C60 derivatives with excellent NLO properties under very mild conditions. Very recently, studies on the optical limiting (OL) property (one of the NLO responses) of simple blends of [60]fullerene and polymer (i.e., [60]fullerene-doped polymer) have grown rapidly. Although doping of C60 into polymer matrices may bring about enhancement of nonlinear response, there are, however, problems associated with this approach. These problems stem from the tendency for the dopant molecules to aggregate in the solid state, leading to difficulty in achieving homogeneous dispersions and ultimately phase separation at high loadings [4]. Polymeric modification of fullerene can overcome these problems. So far, only a few articles reported such work concerning C60 polymeric derivatives [5, 6]. For this reason, we synthesized the highly soluble [60]fullerene-based polyacrylonitrile (PAN) derivatives with different C60 contents using a previously reported one-pot experiment procedure [7, 8], and described initial results of an investigation into their third-order nonlinear optical response by optical-heterdyne-detected optical-Kerr-effect (OHDOKE) technique. The parent polymer PAN and the soluble C60acrylonitrile (C60-AN) copolymers with C60 wt % of ∼12% and ∼18% were synthesized as shown in Scheme 1 under a purified argon atmosphere. The resultant polymers were redissolved in N,N-dimethylformamide (DMF), filtered to remove any unreacted C60 and trace of cross-linking product (if any), and reprecipitated with methanol to give the powder product (the purification procedure was repeated twice). Its color is closely related to the fullerene content in the copolymer: the higher the content, the deeper the product’s color. These copolymer structures were characterized by a variety of physical methods, including ultraviolet-visible (UV-Vis) absorption, electron spin resonance (ESR), differential scanning calorimeter analysis (DSC), Fourier transform infra-red (FT-IR), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The UV-Vis absorption spectra in DMF of C60-AN copolymers differ greatly from that of pure PAN. For the former, its spectrum with only one sharp absorption peak at 295 nm(s) keeps essentially transparent at wavelengths longer than 400 nm, whereas in the copolymer with high C60 content, except for the peak at 295 nm, two new peaks at 257 nm (m, shoulder) and 264 nm(s), which are ascribed to the characteristic absorption for the covalent attachment of C60 to the PAN backbone, were observed. In contrast to the light-yellow exhibited by the pure PAN, the color of copolymers gradually changes from brown to black as the C60 content increases. Obviously, the covalent attachment of C60 to the PAN chains leads to the enhancement of the absorption degree at longer wavelengths. This implies that there should be somewhat electronic interaction between C60 and PAN chains. As discussed for the UV-Vis absorption spectra, there exists considerable difference in electronic structure

Interfullerene vibrations in the polymeric fulleride CsC60

The CsC60 fulleride at low temperatures comprises linear chains of C60– ions; the interball C–C vibrations in the chains are observed by temperature-dependent neutron spectroscopy and disappear when the transition to the high-temperature cubic phase occurs.

Three-dimensional electronic instabilities in polymerized solid AC60.

The low-temperature structure of A1C60 (A=K, Rb) is an ordered array of polymerized C60 chains, with magnetic properties that suggest a non-metallic ground state. We study the paramagnetic state of this phase using first-principles electronic-structure methods, and examine the magnetic fluctuations around this state using a model Hamiltonian. The electronic and magnetic properties of even this polymerized phase remain strongly three dimensional, and the magnetic fluctuations favor an unusual three-dimensional antiferromagnetically ordered structure with a semi-metallic electronic spectrum.