C60 Chains Research Articles

Boosting Photocatalytic Water Splitting of Polymeric C60 by Reduced Dimensionality from Two-Dimensional Monolayer to One-Dimensional Chain.

The recent synthesis of monolayer fullerene networks (Hou, L., et al. Nature 2022, 606, 507) provides new opportunities for photovoltaics and photocatalysis because of their versatile crystal structures for further tailoring of electronic, optical, and chemical function. To shed light on the structural aspects of the photocatalytic water splitting performance of fullerene nanomaterials, we compare the photocatalytic properties of individual polymeric fullerene chains and monolayer fullerene networks from first-principles calculations. We find that the photocatalytic efficiency can be further optimized by reducing the dimensionality from two-dimensional (2D) to one-dimensional (1D). The conduction band edge of the polymeric C60 chain provides an external potential for the hydrogen reduction reaction much higher than that of its monolayer counterparts over a wider range of pH values, and there are 2 times more surface active sites in the 1D chain than in the 2D networks from a thermodynamic perspective. These observations identify the 1D fullerene polymer as a more promising candidate as a photocatalyst for the hydrogen evolution reaction in comparison to monolayer fullerene networks.

Electromechanical Switching of a C60 Chain in a Nanogap

Electromechanical switching in fullerene C60 nanochains, introduced in the device as a C60 pyrrolidine tris-acid (CPTA) film, was realized in nanogap electrodes with ∼20 nm separation. Unlike microscale C60 channels, a conductive C60 chain spontaneously formed in the nanogap without electron beam irradiation. The initial current flow was likely due to electron hopping through the CPTA molecules. A higher voltage generated a nonlinear current and caused a rapid current step to drastically generate a large current flow. A further high current generated a sudden current reduction recognized as the negative differential resistance, suggesting a resistance state change from a low state to a high state. At the high-resistance state, a step-like current increase changed the nanochain conduction to the low-resistance state. The high- to low-resistance state switching was reproducible, and a sequential input voltage executed a binary resistance switching operation at room temperature. From the switching voltage and current values, the switching energy for the C60 chain in the nanogap was estimated to be approximately several milliwatts, most probably caused by the polymerization and depolymerization of the conductive C60 chain.

Structure and Dynamics of Carbon Buckyballs Encapsulated to Single-Walled Carbon Nanotubes

The structural and dynamical attributes of C60 chains inserted inside Single Walled carbon Nanotubes (SWNT) have been investigated by x-ray and neutron refraction, and inelastic neutron scattering (INS). The mensuration have been performed on a large mass of a very high quality carbon peapods sample. We showed that powder refraction could hardly give definitive response on the way the C60s are bonded inside SWNT. However, the comparison of the neutron-derived generalized compression of states (GDOS) of the inserted C60 peas with the GDOS of the same objects derived from lattice dynamics computations led to unambiguous results. The witnessing of excitations in the 8-15 meV span is a clear evidence for the presence strong bonds among C60s in the sample. In the same time, the witnessing of a very weak quasi-elastic signal may be relevant to rotational motions of C60 monomers inside the SWNT. These results suggest that peapods are built of a mixed phase of C60 monomers and C60 n-mers.

C60 layer growth on intact and Tl-modified Si(1 1 1)5 [formula omitted] 2-Au surfaces

The Si(1 1 1)5 × 2-Au surface comprises a quasi-one-dimensional surface reconstruction consisting of Au stripes mediated by honeycomb Si chains. In the present study, using STM observations we explored adsorption of thallium (Tl) onto Si(1 1 1)5 × 2-Au surface as well as growth of C60 layers on Tl-modified and intact Si(1 1 1)5 × 2-Au surfaces. Analysis of the results was based on the recently proposed KK model of Si(1 1 1)5 × 2-Au surface [Kwon and Kang, PRL 113 (2014) 086101]. It was found that intact Si(1 1 1)5 × 2-Au surface produces a poor template effect on the overgrown C60 layers which have a close-packed-like structure without distinct ordering. In contrast, the C60 layers grown on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface where Tl atoms occupy various adsorption sites on the honeycomb Si chains have a well-ordered quasi-one-dimensional structure consisting of straight C60 chains. Ordering of the C60 molecules is a result of an intricate interplay between adsorbed C60 molecules with each other and with a substrate surface. Separation between neighboring C60 chains is dictated by the periodicity of the underlying Si(1 1 1)5 × 2-Au template, while the C60-C60 spacing within the chains of ∼12 Å that is ∼3.2a0 reflects the peculiarity of the C60-C60 intermolecular interaction on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface. Structural information on (Au, Tl)/Si(1 1 1) and C60/(Au, Tl)/Si(1 1 1) systems gained in the present study can be useful for the prospective works on elucidating the ways to control electronic properties of the Si(1 1 1)5 × 2-Au surface using atomic and molecular adsorbates.

Preparation and Characterization of C60/Graphene Hybrid Nanostructures.

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We present methods for depositing and passively manipulating C60 molecules on rippled graphene that advance the pursuit of realizing applications involving 1D C60/graphene hybrid structures. The techniques applied in this exposition are geared towards high vacuum systems with preparation areas capable of supporting molecular deposition as well as thermal annealing of the samples. We focus on C60 deposition at low pressure using a homemade Knudsen cell connected to a scanning tunneling microscopy (STM) system. The number of molecules deposited is regulated by controlling the temperature of the Knudsen cell and the deposition time. One-dimensional (1D) C60 chain structures with widths of two to three molecules can be prepared via tuning of the experimental conditions. The surface mobility of the C60 molecules increases with annealing temperature allowing them to move within the periodic potential of the rippled graphene. Using this mechanism, it is possible to control the transition of 1D C60 chain structures to a hexagonal close packed quasi-1D stripe structure.

Energetics and electronic structures of chemically decorated C60 chains

We studied the energetics and electronic structures of one-dimensional molecular chains of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) using the density functional theory (DFT). Our DFT calculations show that the binding energies of PCBM range from 90 to 300 meV, depending on not only the intermolecular spacing but also the intermolecular arrangements owing to the interaction between functional groups and C60. The electronic structure of PCBM chains are also sensitive to the mutual arrangements of PCBM in their chain structure. The calculated effective masses of the conduction band range from 0.58 to 634.97me, giving rise to anisotropic transport properties in their condensed phase.

Deficiencies in Repair of Double–Standard DNA/RNA- Binding Molecules Identified in Many Types of Solid and Liquid Tumors Oncology in Human Body for Advancing Cancer Immunotherapy Using Computer Simulations and Data Analysis

We have recently discovered that deficiencies in repair of double– standard DNA/RNA–binding molecules identified in many types of solid and liquid tumors oncology in human body for advancing cancer immunotherapy at their upper rims bind tightly to double– standard DNA/RNA–binding molecules, irrespective of their number of base–pairs. For this aim, we have synthesized a various Fullerene Nano molecules, which have central C20, C60, C240, C540, C960, C2160 and C3840 Carbon chains [1-7]. In spite of their increasing lipophilicity, these compounds could all be dissolved completely in aqueous HEPES (4–(2–hydroxyethyl)–1–piperazineethanesulfonic acid) buffer with 50% added methanol. The binding constants among double–standard DNA/RNA–binding molecules and the above mentioned various Fullerene Nano molecules, were in the same range. That means the length of the spacer have not a great influence on the binding site. In this editorial, we have to change the spacer to the nucleic acids derivatives, which bind probably in the major groove of double–standard DNA/ RNA–binding molecules. The new various Fullerene Nano molecules were characterized by 1HNMR, 13CNMR, 31PNMR, Attenuated Total Reflectance Fourier Transform Infrared (ATR–FTIR), FT–Raman, UV– Vis and HR Mass spectroscopies. After the synthesis of the first Fullerene Nano molecule, we have found that in this type of various Fullerene Nano molecules, the binding constant between double–standard DNA/RNA– binding molecules group (a) and double–standard DNA/RNA–binding molecules group (b) was greater than the latter.

Theoretical Insight into the Internal Quantum Efficiencies of Polymer/C60and Polymer/SWNT Photovoltaic Devices

The internal quantum efficiency (IQE) of an organic photovoltaic device (OPV) is proportional to the number of free charge carriers generated and their conductivity per absorbed photon. However, both the IQE and the quantities that determine it, for example, electron–hole binding, charge separation, electron–hole recombination, and conductivity, can only be inferred indirectly from experiments. Using density functional theory, we calculate the excited-state formation energy, charge transfer, and zero-bias conductance in the singlet ground state and triplet excited state across polymer/fullerene and polymer/single-walled carbon nanotube (SWNT) OPV donor/acceptor bulk heterojunctions. Specifically, we compare polythiophene (PT) and poly(3-methylthiophene-2,5-diyl) (P3MT) as donors and C60 chains with (6,4), (6,5), and (10,5) SWNTs as acceptors. We find the conductivity increases substantially for both the excited triplet relative to the singlet ground state and for PT compared with P3MT due to the increased charge transfer and the resulting improvement in donor/acceptor level alignment. Similarly, the (6,4) SWNT, with a larger SWNT band gap and greater conductivity than fullerenes, provides the highest conductivities of 5 and 9% of the theoretical maximum for electron and hole carriers, respectively. This work has important implications for both the optimization of polymer/SWNT bulk heterojunctions and the design of new OPV bulk heterojunctions in silico.

Structures and structure-related electronic properties of new C60(CF3)10 isomers

Abstract The largest collection of well-characterized homoleptic fullerene derivatives C60(X)n is for X = CF3 and n = 2–18. The largest subset of these with a given composition is the set of 27 isomers of C60(CF3)10. The X-ray structures of five of them were reported previously. In this paper we report the X-ray structures of, and extensive DFT calculations on, eight additional C60(CF3)10 isomers and the electrochemical reduction potentials of eight of the (now) 13 structurally-characterized isomers. The connections between their molecular structures (i.e., their addition patterns), the positions, extents of delocalization, and relative energies of their DFT-predicted LUMOs, and their first reduction potentials are compared and contrasted with each other and with the previously reported isomers. It is shown that addition patterns that produce the greatest number of non-terminal double bonds in fullerene pentagons are the best electron acceptors and tend to exhibit relatively small HOMO–LUMO gaps. A detailed analysis of the nearest-neighbor packing patterns in the 13 X-ray structures reveals significant differences in the number of nearest neighbor fullerene molecules and differences in the ranges of fullerene centroid⋯centroid distances even when the number of nearest neighbors is constant. Nevertheless, ten solvent-free structures exhibit nearly equally-efficient lattice packing arrays as far as crystal density is concerned. When the addition pattern results in two sterically-accessible C(sp2)6 hexagons on the fullerene surface, a one-dimensional chain of electronically-coupled nearest-neighbor C60(CF3)10 molecules is formed.

Thermal transport in one-dimensional superlattice and quasicrystal chains: Fullerene phononic crystal

In order to investigate the thermal transport in one-dimensional (1D) superlattice and quasicrystal chains, the simple harmonic-oscillator model and the C60 chains model, are studied through non-equilibrium molecular dynamics simulation. In the simple harmonic-oscillator model, we construct a simple periodic harmonic-oscillator chain by using two different stiffness coefficients alternatively. It is found that its thermal conductivity is smaller than in non-periodic chains, no matter which stiffness coefficient is used in the non-periodic chains. In order to test if this is true in a real material structure, a superlattice C60 chain is constructed by connecting perfect and defective C60 alternatively. The calculation outcome of the C60 chains coincides with the results of the simple harmonic-oscillator model, that the thermal conductivity of the superlattice C60 chain is smaller than that of perfect and defective crystal C60 chains. Besides this, we also studied the thermal transport properties of the quasicrystal C60 chain, which consists of a random defective C60 molecular structure. It is found that the thermal conductivity of the quasicrystal structure is far less than that of the crystal and superlattice chains. The phonon spectra of the perfect, defective and superlattice C60 chain are provided to give corresponding supports. Our results also propose a controllable method for the thermal management in nanoscale materials.

Temperature Evolution of Quasi-one-dimensional C60 Nanostructures on Rippled Graphene.

We report the preparation of novel quasi-one-dimensional (quasi-1D) C60 nanostructures on rippled graphene. Through careful control of the subtle balance between the linear periodic potential of rippled graphene and the C60 surface mobility, we demonstrate that C60 molecules can be arranged into a quasi-1D C60 chain structure with widths of two to three molecules. At a higher annealing temperature, the quasi-1D chain structure transitions to a more compact hexagonal close packed quasi-1D stripe structure. This first experimental realization of quasi-1D C60 structures on graphene may pave a way for fabricating new C60/graphene hybrid structures for future applications in electronics, spintronics and quantum information.

Depressing thermal conductivity of fullerene by caging rare gas

We have investigated the thermal conductivity of C60 and its derivatives caged with rare gas by using the nonequilibrium molecular dynamics method. It is reported that embedding C60 with different rare gas atoms has a significant impact on its thermal conductivity. We analyze the phenomenon through the phonon spectra of rare gas atom and the C–C bonds length of C60. When the number of atoms inside the C60 increases, the phonon spectra band width of rare gas expands and the length of C–C bonds becomes longer, which contributes to the depression of the thermal conductivity of C60. The method is applied to control the thermal conductivity of C60 chains, which maybe a kind of potential materials in thermal circuits. Our results also provide a controllable method for the thermal management in nanoscale materials.

Effects of nanobuds and heat welded nanobuds chains on mechanical behavior of carbon nanotubes

This study reports an investigation on the effects of nanobuds and heat welded nanobuds chains (C60 chains attached or embedded on the surface of a SWCNT) on the mechanical properties of carbon nanotubes by molecular dynamics (MD) simulations. The bond order change and the stress concentration in the distorted connection area of nanobuds when C60 attaches to the surface of the SWCNT are first studied. Then the effect of multiple randomly scattered and attached C60 fullerenes on the ultimate tensile strength of SWCNT is discussed. It is found that both nanobuds and heat welded nanobuds chains lower the ultimate tensile strength of individual defect-free SWCNT. However, the mean post-peak strength of the CNT (after necking) is significantly enhanced by heat welded nanobuds chains. Moreover, the ultimate tensile strength of the SWCNT with vacancy defects does not decrease by heat welded nanobuds chains; interestingly, the maximum tensile strength of the SWCNTs bundles with intertube bridging and vacancy defects even can be enhanced by more than 20% by heat welded nanobuds chains.

Radical spin interaction in one-dimensional chains of decamethyl C60

Based on density functional theory, we examine the energetics and electronic structure of chains of decamethyl C60 with two stacking conformations. The decamethyl C60 chains possess various spin configurations arising from the combinations of intramolecular and intermolecular spin interactions. The antiparallel spin arrangement within and between molecules is the ground state, and the intramolecular spin interaction is four times larger than the intermolecular interaction. These decamethyl C60 chains possess small dispersion bands near the Fermi level arising from the π states distributed on pentagonal rings, which are well separated from each other because of segmentation by the attached methyl groups.

Coordination Complexes of Pentamethylcyclopentadienyl Iridium(III) Diiodide with Tin(II) Phthalocyanine and Pentamethylcyclopentadienyl Iridium(II) Halide with Fullerene C60– Anions

Synthetic approaches to iridium complexes of metal phthalocyanines (Pc) and fullerene anions have been developed to give three types of complexes. The compound{(Cp*IrIIII2)SnIIPc(2−)}·2C6H4Cl2 (1) (Cp* is pentamethylcyclopentadienyl) is the first crystalline complex of a metal phthalocyanine in which an iridium(III) atom is bonded to the central tin(II) atom of Pc via a Sn–Ir bond length of 2.58 Å. In (TBA+)(C60•–){(Cp*IrIIII2)SnIIPc(2−)}·0.5C6H14 (2), the {(Cp*IrIIII2)SnIIPc(2−)} units cocrystallize with (TBA+)(C60•–) to form double chains of C60•– anions and closely packed chains of {(Cp*IrIIII2)SnIIPc(2−)}. Interactions between the fullerene and phthalocyanine subsystems are realized through π–π stacking of the Cp* groups of {(Cp*IrIIII2)SnIIPc(2−)} and the C60•– pentagons. Furthermore, the spins of the C60•– are strongly antiferromagnetically coupled in the chains with an exchange interaction J/kB = −31 K. Anionic (TBA+){(Cp*IrIICl)(η2-C60–)}·1.34C6H4Cl2 (3) and (TBA+){(Cp*IrIII)(η2-C60–)}·1.3C6H4Cl2·0.2C6H14 (4) are the first transition metal complexes containing η2-bonded C60– anions, with the Cp*IrIICl and Cp*IrIII units η2-coordinated to the 6–6 bonds of C60–. Magnetic measurements indicate diamagnetism of the {(Cp*IrIICl)(η2-C60–)} and {(Cp*IrIII)(η2-C60–)} anions due to the formation of a coordination bond between two initially paramagnetic Cp*IrIICl or Cp*IrIII groups and C60•– units. DFT calculations support a diamagnetic singlet ground state of 4, in which the singlet–triplet energy gap is greater than 0.8 eV. DFT calculations also indicate that the C60 molecules are negatively charged.

C60 chain phases on ZnPc/Ag(111) surfaces: Supramolecular organization driven by competing interactions.

Serpentine chain C60 phases were observed in scanning tunneling microscopy (STM) images of C60 layers on zinc phthalocyanine (ZnPc) or pentacene covered Ag(111) and Au(111) surfaces. This low-density, quasi-one-dimensional organization contrasts starkly with the close-packed hexagonal phases observed for C60 layers on bare metal substrates. STM was employed to perform a detailed investigation of these chain structures for C60/ZnPc/Ag(111) heterolayers. Motivated by the similarity of these chain phases, and the chain and stripe organization occurring in dipole-fluid systems, we investigated a model based on competing van der Waals attractions and electrostatic repulsions between C60 molecules as an explanation for the driving force behind these monolayer phases. Density functional theory (DFT) calculations revealed significant charge transfer to C60 from the Ag(111) substrate, through the intervening ZnPc layer, inducing electrostatic interactions between C60 molecules. Molecular dynamics simulations performed with attractive van der Waals interactions plus repulsive dipole-dipole interactions reproduced the C60 chain phases with dipole magnitudes consistent with DFT calculations.

Optical Generation and Detection of Polaronic States in PCBM

Photoinduced charge transfer from an indium tin oxide (ITO) contact into [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) is measured. For both, charge-transfer peaks are observed for a series of excitation energies below the absorption edge. If charge transfer is blocked using a tunnel barrier or an applied electric field, then the peaks disappear. The observed transitions are similar to those predicted by theoretical calculations of the absorption spectra for negatively charged C60 and C70 chains. This observation suggests that charge transfer occurs preferentially at the polaronic transition energies, providing a new means for polaronic state spectroscopy.

Prediction of ultra-high ON/OFF ratio nanoelectromechanical switching from covalently-bound C60 chains

Applying a first-principles computational approach, we have systematically analyzed the effects of [2+2] cycloaddition oligomerization of fullerene C60 chains on their junction electronic and charge transport properties. For hypothetical infinite C60 chains, we first establish that the polymerization can in principle increase conductance by several orders of magnitude due to the strong orbital hybridizations and band formation. On the other hand, our simulations of the constant-height scanning tunneling microscope (STM) configuration shows that, in agreement with the recent experimental conclusion, the junction electronic structure and device characteristics are virtually unaffected by the C60 chain oligomerization. We further predict that the switching characteristics including even the ON/OFF-state assignment will sensitively depend on the substrate metal species due to the Fermi-level pinning at the substrate-side contact and the subsequent energy level bending toward the STM tip-side contact. We finally demonstrate that a force-feedbacked nanoelectromechanical approach in which both of the C60–electrode distances are kept at short distances before and after switching operations can achieve a metal-independent and significantly improved switching performance due to the Fermi-level pinning in both contacts and the large intrinsic conductance switching capacity of the C60 chain oligomerization.

Sharp organic interface of molecular C60 chains and a pentacene derivative SAM on Au(788): A combined STM & DFT study

Controlling the molecular structure of the donor–acceptor interface is essential to overcoming the efficiency bottleneck in organic photovoltaics. We present a study of self-assembled fullerene (C60) molecular chains on perfectly ordered 6,13-dichloropentacene (DCP) monolayers forming on a vicinal Au(788) surface using scanning tunneling microscopy in conjunction with density functional theory calculations. DCP is a novel pentacene derivative optimized for photovoltaic applications. The molecules form a brick-wall patterned centered rectangular lattice with the long axis parallel to the monatomic steps that separate the 3.9nm wide Au(111) terraces. The strong interaction between the C60 molecules and the gold substrate is well screened by the DCP monolayer. At submonolayer C60 coverage, the fullerene molecules form long parallel chains, 1.1nm apart, with a rectangular arrangement instead of the expected close-packed configuration along the upper step edges. The perfectly ordered DCP structure is unaffected by the C60 chain formation. The controlled sharp highly-ordered organic interface has the potential to improve the conversion efficiency in organic photovoltaics.

Solvent-Assisted Self-Assembly of Fullerene into Single-Crystal Ultrathin Microribbons as Highly Sensitive UV–Visible Photodetectors

The size, shape, and crystallinity of organic nanostructures play an important role in their physical properties and are mainly determined by the self-assembling kinetics of molecular components often involving the solvent conditions. Here, we reported a kinetically controlled self-assembly of C60 assisted by the solvent carbon bisulfide (CS2) into single-crystal ultrathin microribbons of 2C60·3CS2, upon mixing the poor solvent isopropyl alcohol with a C60/CS2 stock solution. Surface energy calculations reveal that these microribbons represent a kinetically favored high-energy state as compared with the thermodynamically stable shape of prismatic rods. High-resolution transmission electron microscopy observations clarify that association of CS2 at the nucleation stage helps to guide and rigidify the formation of π-π stacking 1D chains of C60 through the surrounding CS2 cage-like structures, which further act as glue, boosting lateral assembly of as-formed 1D chains into untrathin 2D microribbon single crystals. Precise control over the thickness, width, and length of 2C60·3CS2 microribbons was achieved by manipulation of the growth kinetics through adjusting the solvent conditions. Upon heating to 120 °C, sublimation of CS2 components results in fcc C60 microribbons. We found that both microribbons of solvated monoclinic 2C60·3CS2 and pure fcc C60 exhibit highly sensitive photoconductivity properties with a spectral response range covering UV to visible. The highest on/off ratio of two-terminal photodetectors based on single ribbons reaches around 250, while the responsitivity is about 75.3 A W(-1) in the UV region and 90.4 A W(-1) in the visible region.