C60 Monomer Research Articles

Novel [60]fullerene polymers: Part 2: Synthesis and polymerisation processes through acrylation of N-(4-hydroxyphenyl)-o-hydroxy-2-phenyl fulleropyrrolidine derivatives and their monomers

Following on from part 1 of this paper where linear C60 polymers were synthesised, part 2 describes the synthesis of crosslinked and branched chain C60 polymers so that the amount of C60 content in the polymer, the number averaged molecular weight “Mn” and the weight averaged molecular weight “Mw” may be increased. This paper reviews the method in which fulleropyrrolidines were prepared by [3 + 2] cycloaddition of azomethine ylides to [60]fullerene cage through the use of N-(4-hydroxyphenyl) glycine in conjunction with benzaldehyde derivatives. Numerous types of [60]fullerene polymers were synthesised through fulleropyrrolidine acrylic monomers. In this study, the cycloaddition process was selected because it provides a powerful tool for fullerene functionalisation, as a result very stable cycloadducts are formed. The addition of azomethine ylide was found to provide a versatile method for the derivatization of [60]fullerene. In this case, the synthesis of functionalised C60 and novel branched chain and crosslinked network of fullerene polymers has been investigated. The first step in this study was to prepare dihydroxy fulleropyrrolidines by [3 + 2] cycloaddition of azomethine ylide to [60]fullerene. The fulleropyrrolidine monomer having multiple functional groups was put up by the reaction of –OH groups of fulleropyrrolidine with acryloyl chloride in the presence of a base in an alcoholic solution. FT-IR, Mass spectra,1H NMR and UV techniques were used to characterise the reaction products obtained. Benzoyl Peroxide was used as a free radical initiator to polymerise the monomer in dimethylformamide. DMF is a highly suitable solvent for this procedure because both C60 monomer and polymer are soluble. In this work, the process parameters such as time of reaction, reaction temperature, mole ratio, type of solvent, and quantity of reagents used were varied in so as to obtain the highest yields of fulleropyrrolidines, monomers and polymers.

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.

Raman Spectroscopy of AgNO3 Complex Encapsulated Fullerene (C60) Microcube

Ag+-fullerene (C60) hybrid microcrystal is synthesized by a liquid-liquid interfacial precipitation, which shows the broadened and weakened Raman bands, relative to original C60 monomers. Our experimental results, combined with numerical calculation implicate that charge transfer and overlap orbitals between Ag+ and C60 steered this dramatic change of Raman response, due to greatly reduced molecular symmetry and redistributed electron density. Density functional theory (DFT) calculations rationalize the degenerated Raman spectra of Ag+-exohedral fullerene conjugate through ƞ1 (C1-top) and ƞ2 (C2-bridge) sites, elucidating that the binding nature (π-5 s and d-π*) shifts partially from electrostatic to covalent bond. This study is expected to render a general and easily accessible Raman approach in deciphering transition metal ion-fullerene interactions.

Local dimerization and dedimerization of C60 molecules under a tip of scanning tunneling microscope: A first-principles study

The local dimerization and dedimerization of C60 molecules in a C60 thin film using a scanning tunneling microscopy (STM) [M. Nakaya et al. Adv. Mater. 22, 1622 (2010)] are promising techniques for realizing ultradense data storages. However, the detailed mechanism of the reversible topochemical reactions has not been clarified yet. Based on the density functional theory we explain the mechanism in terms of charging and electric-field effects on the molecules. The total-energy calculations reveal that when the C60 molecules in the surface layer are negatively charged, the dimerization is promoted and inter-layer dimers composed of two C60 molecules in different layers are formed dominantly over in-plane dimers. When the thin-film surface is positively charged or the inter-layer dimers are exposed to a strong electric field, a C60 monomer pair becomes more stable than a C60 dimer, and the dedimerization is promoted. These results predict competition between the dimerization and dedimerization of a negatively charged C60 binary system in a strong electric field, which is indeed confirmed by our STM experiments. In addition, the dedimerization induced in the electric field is discussed from the viewpoints of the intermolecular donor-acceptor interaction and the charge-dipole relaxation of a C60 binary system.

The influence of driving force on intramolecular electron transfer: A theoretical study of subphthalocyanine‐AzaBODIPY‐C60 supramolecular triad

AbstractThe driving force of electron transfer is one of important factors for initializing inter‐ and intramolecular charge separation. In this work, the main goal is to understand how driving force determines electron transfer pathway in subphthalocyanine‐AzaBODIPY‐C60 supramolecular triad. Experimental observations have suggested that there are only two intramolecular charge transfer states (subPC+‐AzaBODIPY−‐C60 and subPC+‐AzaBODIPY‐C60−) after photon absorption, where subPC is the donor. Through the calculations by using tuned long range corrected density functionals with polarizable continuum model, we find two more new intramolecular charge transfer states: subPC−‐AzaBODIPY+‐C60 and subPC‐AzaBODIPY+‐C60−, where AzaBODIPY is the donor. We compare the HOMO/LUMO energy of subPC, AzaBODIPY, and C60 monomers to their corresponding orbital energy in the triad. The results indicate that the driving force (HOMO/LUMO energy offsets) is not enough for electron transfer from AzaBODIPY to subPC or C60, which can explain why subPC−‐AzaBODIPY+‐C60 and subPC‐AzaBODIPY+‐C60− intramolecular charge transfer states cannot be observed in the experiment. In addition, this work may provide a simple and practical method to find the intramolecular charge transport pathway of a supramolecule.

Pyrene-based amphiphile regulated C60 aggregation in monolayers and Langmuir–Blodgett films

The advantage of using Langmuir–Blodgett (LB) method in assembling thin films is mainly the effective controlling the orientation of the molecules and deposition of mono- and multilayer films with an organized and ordered layer structure. In this paper, we have studied the interactions between C60 and a kind of pyrene-based amphiphile, N, N’-bis(octadecyl)-L-(1-pyrenebutyric acid)-glutamic diamide (abbreviated as LPG) in monolayers and in LB films by surface-pressure isotherms, CD spectroscopy, fluorescence spectroscopy, and atomic force microscopy (AFM). It has been found that the existing state of C60 was closely related to the mixing ratio of C60 to LPG. Miscibility and AFM image investigation revealed that C60 molecules were embedded into the LPG monolayer as monomers when the mole fraction of C60 was below 0.33 (molar ration of LPG to C60 is 2:1). Meanwhile, the inserting of C60 disturbed the packing of LPG. As a result, the magnitude of supramolecular chirality, which was derived from the self-assembly of LPG, decreased with the addition of C60. When more C60 molecules were mixed with LPG, they have to form three dimensional aggregates due to high adhesive energy. The donor-acceptor interaction between pyrene moieties and C60 was supposed to be the driving force to disperse C60 in LPG monolayer. A reasonable mechanism of the transition from C60 monomers to aggregates in LPG monolayer was also proposed.

Fullerene polymer film as a highly efficient photocatalyst for selective solar fuel production from CO2

ABSTRACTC60‐based polymeric systems have been constantly anticipated for sustainable solar energy conversion. Reported, herein is a C60 polymer film as visible light active photocatalyst for efficient and selective reduction of CO2 for the first time. The C60 polymer photocatalyst is synthesized via covalent coupling of C60 monomer units consisting of tetra substituted C60‐pyrene conjugates through spacer groups. The synthesized C60 polymer photocatalyst possesses an extended network of well‐defined repeating monomer units with good stability and visible light‐induced photocatalytic activity. The enhanced visible light harvesting ability of C60 polymer photocatalyst reasonably yields it with higher catalytic ability than its monomer unit. The C60 polymer film photocatalyst upon coupling with the biocatalyst carries out highly selective visible light driven reduction of CO2 to HCOOH (239.46 μmol). The tandem way of incorporating C60 into visible light active polymeric films for continuous use may be highly rewarding for their extended photocatalytic activity for solar fuel production from CO2. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48536.

Complex interplay between formation routes and natural organic matter modification controls capabilities of C60 nanoparticles (nC60) to accumulate organic contaminants

Accumulation of organic contaminants on fullerene nanoparticles (nC60) may significantly affect the risks of C60 in the environment. The objective of this study was to further understand how the interplay of nC60 formation routes and humic acid modification affects contaminant adsorption of nC60. Specifically, adsorption of 1,2,4,5-tetrachlorobenzene (a model nonionic, hydrophobic organic contaminant) on nC60 was greatly affected by nC60 formation route – the formation route significantly affected the aggregation properties of nC60, thus affecting the available surface area and the extent of adsorption via the pore-filling mechanism. Depending on whether nC60 was formed via the “top-down” route (i.e., sonicating C60 powder in aqueous solution) or “bottom-up” route (i.e., phase transfer from an organic solvent) and the type of solvent involved (toluene versus tetrahydrofuran), modification of nC60 with Suwannee River humic acid (SRHA) could either enhance or inhibit the adsorption affinity of nC60. The net effect depended on the specific way in which SRHA interacted with C60 monomers and/or C60 aggregates of different sizes and morphology, which determined the relative importance of enhanced adsorption from SRHA modification via preventing C60 aggregation and inhibited adsorption through blocking available adsorption sites. The findings further demonstrate the complex mechanisms controlling interactions between nC60 and organic contaminants, and may have significant implications for the life-cycle analysis and risk assessment of C60.

Transport properties of the H2O@C60-dimer-based junction

Theoretical predictions play an important role in finding potential applications in molecular electronics. Fullerenes have a number of potential applications, and the charge flow from a single C60 molecule to another becomes more versatile and more interesting after doping. Here, we report the conductance of two H2O@C60 molecules in series order and how the number of encapsulated water molecules influences the transport properties of the junction. Encapsulating an H2O molecule into one of the C60 cages increases the conductance of the dimer. Negative differential resistance is found in the dimer systems, and its peak-to-valley current ratio depends on the number of encapsulated H2O molecules. The conductance of the C60 dimer and the H2O@C60 dimer is two orders of magnitude smaller than that of the C60 monomer. Furthermore, we demonstrate that the conductance of the molecular junctions based on the H2O@C60 dimer can be tuned by moving the encapsulated H2O molecules. The conductance is H2O-position dependent. Our findings indicate that H2O@C60 can be used as a building block in C60-based molecular electronic devices and sensors.

Size distributions of fullerene surface clusters

We present an exactly solvable generalization of the rate equation model for irreversible growth with size-independent capture numbers which includes desorption of monomers. It is shown that the universal size distribution shapes depend on the sole parameter, the ratio between the characteristic diffusion and adsorption areas. We perform a statistical analysis of the scanning tunneling microscopy images of C60 clusters deposited onto In-modified Si(1 1 1)√3 × √3-Au surfaces at different temperatures and deduce the experimental size distributions. These distributions have an essentially asymmetric shape with a much faster decay toward larger sizes. Fitting the data with theoretical distribution shapes yield the estimates for some important kinetic parameters, in particular, the temperature-dependent diffusion lengths and effective lifetimes of C60 monomers.

Effects of the preparation method and humic-acid modification on the mobility and contaminant-mobilizing capability of fullerene nanoparticles (nC60)

Colloidal fullerene nanoparticles (nC60) in aquatic environments may significantly affect the transport and risks of hydrophobic organic contaminants by serving as a contaminant carrier. The objective of this study was to understand how the combined variables of the preparation method and natural organic matter modification of nC60 might affect the mobility and contaminant-mobilizing capability of nC60, by affecting the physicochemical properties of nC60. We found that an nC60 sample prepared by sonicating C60 powder in deionized water (son_nC60) was much less mobile in saturated sandy soil columns than an nC60 sample prepared by solvent-exchanging from toluene to water (tol_nC60), because son_nC60 was considerably larger in size. However, son_nC60 exhibited greater capability to bind 2,2',5,5'-polychlorinated biphenyl (PCB), likely because its loosely packed structures rendered more pore spaces, which were favorable adsorption sites for PCB. Forming nC60 samples in Suwannee River humic acid (SRHA) solution (instead of deionized water) only moderately affected the mobility of nC60, but had very significant effects on the contaminant-binding capability of nC60, especially when nC60 was prepared using the solvent exchange method. Adding SRHA after the formation of nC60 had varied effects on the mobility and contaminant-binding capability of nC60, but the fundamental mechanism seems to be linked to how and to what extent SRHA had affected the aggregation/packing of C60 monomers. An important environmental implication is that nC60 formed under different environmental conditions might have vastly different effects on contaminant transport and risks.

Ions colliding with clusters of fullerenes—Decay pathways and covalent bond formations

We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C60 molecules following collisions with Ar(2+), He(2+), and Xe(20+) at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C60]n(+) → C60(+)+(n-1)C60 evaporation model. Excitation energies in the range of only ~0.7 eV per C60 molecule in a [C60]13(+) cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar(2+) and He(2+) collisions, we observe very efficient C119(+) and C118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C59(+) or C58(+) and C60 during cluster fragmentation. In the Ar(2+) case, it is possible to form even smaller C120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe(20+) collisions.

Pressure- and temperature-induced transformations in crystalline polymers of C60

The great advantage of the C60 molecule is its potential for polymerization, due to which the molecule can be the building block of new all carbon materials. In addition, it contains, both sp2 and sp3 hybridized carbon atoms, which allows synthesizing new carbon materials with desired physicochemical properties using both types of carbon bonding. The one- and two-dimensional polymeric phases of C60 are prototype materials of this sort. Their properties, especially polymerization under pressure and room temperature via covalent bonding between molecules belonging to adjacent polymeric chains or polymeric layers, can be used for further development of new materials. The present review focuses on the study of the pressure-induced polymerization and thermodynamic stability of these materials and their recovered new phases by in-situ high-pressure Raman and X-ray diffraction studies. The phonon spectra show that the fullerene molecular cage in the high-pressure phases is preserved, while these polymers decompose under heat treatment into the initial fullerene C60 monomer.

The local-field factor and microscopic cascading: a self-consistent method applied to confined systems of molecules

We use a simplified self-consistent method to address nonlinear-optical cascading phenomena, which shows added microscopic cascading contributions in high-ordered nonlinear susceptibilities through fifth order. These cascading terms in the microscopic regime encompass all possible scalar cascading configurations. The imposition of geometric constraints further influences the predicted cascading contributions and opens up additional design parameters for nonlinear-optical materials. These results are used in approximating the effective fifth-order susceptibility in thin films of C60 monomers of varying thickness and concentration.

Stability of functionalized C60 paramagnetic dimers and monomers

Density functional theory is used to calculate the bond dissociation energy to cleave the C60C60 bond of the paramagnetic X–C60C60–X and X–C60C60 dimers where X is F, OH, O and H. The results show that these dimers would not be stable much above room temperature and therefore cannot constitute the paramagnetic phase needed to form the observed ferromagnetism which has been shown to be stable up to 800K. The calculated bond dissociation energies to remove an F, OH or H from a single C60 are large suggesting that they could be the source of the unpaired spin needed for the high temperature ferromagnetism.

High Temperature Depolymerization of the 2D-R Polymer of C60 Studied by Raman Spectroscopy

Raman spectra of the two-dimensional rhombohedral (2D-R) polymer of C60 were measured at ambient conditions after 0.5 hour of treatment at various elevated temperatures in order to study the process of polymer degradation. The 2D-R polymer is stable up to ∼510 K, while at higher temperatures an intermediate state appears where the initial 2D-R polymer coexists with inclusions of tetragonal-like (T-like) and orthorhombic-like (O-like) oligomers, as well as C60 dimers and monomers. The polymeric material changes drastically its composition after treatment at ∼560 K resulting in the domination of C60 monomers.

Raman study of the temperature-induced decomposition of the two-dimensional rhombohedral polymer of C60 and the intermediate states formed

Raman spectra of single crystalline two-dimensional rhombohedral (2D-R) polymer of C60 were measured at ambient conditions after its high temperature treatment (HTT) in order to study the polymer decomposition process. The data obtained indicate that the 2D-R polymer remains stable after 0.5h treatment up to ∼503K, while at higher temperatures a material transformation takes place. New Raman lines appear in the Raman spectrum after HTT in the range of 513–553K, related to the Ag(2) pentagon pinch (PP) mode of 2D tetragonal-like (2D-T-like) and 1D orthorhombic-like (1D-O-like) oligomers as well as to C60 dimers and monomers, typical for an intermediate state of partially decomposed 2D-R polymer. Above 553K, the material changes completely and its new composition is dominated by C60 monomers with some possible inclusion of C60 dimers. The activation energy of the 2D-R polymer decomposition, obtained from the dependence of the decomposition time on the treatment temperature, is EA=1.76±0.07eV/molecule.

First-principles study of a single C60 cluster adsorbed on KBr(1 0 0)

Atomic and electronic structure of the C60 monomer adsorbed KBr(100) surface has been studied by using density-functional theory calculations. We found that a single C60 cluster favors an adsorption configuration where a hexagon ring of C60 adsorbs atop the surface K atom. The energy gain by adsorption is as small as 0.37eV, and the resulting structural modifications of the C60 cluster and the KBr(100) substrate are negligible. Calculated density of states and charge characters indicate that this structure is stabilized by a weak interaction between the p-orbitals of interfacial C and Br atoms. The present calculations are found to be useful in understanding the structural properties of a close-packed C60 monolayer phase grown on KBr(100) in a recent atomic force microscopy study.

Topochemical 3D Polymerization of C60 under High Pressure at Elevated Temperatures

Fullerene C60 monomer crystals were compressed to a face-centered cubic (fcc) phase with a lattice parameter of a = 11.93(5) A and a micro-Vickers hardness of 4500 kg/mm2 using high-pressure and high-temperature conditions of 15 GPa at 500-600 degrees C. The hardness is compatible with that of cubic boron nitride (c-BN), suggesting the formation of a 3D C60 polymer. The single-crystal X-ray structural analysis revealed that each C60 molecule in the polymer was linked to the 12 nearest neighbors by [2+2] cycloaddition between the common pentagon-hexagon (56) edges. However, ab initio geometry optimization and molecular dynamics calculations suggested that the 3D polymer should have a rhombohedral structure with the space group of R containing [3+3] cycloaddition between the pentagons of C60 molecules within the plane perpendicular to the 3-fold axis. The higher apparent symmetry of fcc was observed as an averaged structure of different orientations of the rhombohedral structure. The R structure can be derived by only a slight rotation of each C60 unit in the (111) plane of the fcc structure. The band-structure calculation suggested that the 3D polymer (R) was a semiconductor; the activation energy for the electrical conductivity was experimentally determined to be 0.25 eV at 550 K.

Photochemical and Photophysical Properties of Three Carbon-Bridged Fullerene Dimers: C121 (I, II, III)

The photochemical and photophysical properties of the three C121 isomers (I, II, III) were investigated with MADLI-TOF-MS, UV-vis spectra, fluorescence spectra, absorption spectra of their DMA complexes, and theoretical calculations. The three isomers of C121 (I, II, III) have different stabilities under laser irradiation, but isomer I and isomer II show good stability against the heat-induced conversion between different isomers: No conversion between the isomers was found after heating the mixture of isomer I and isomer II at 353 K for 12 h in Ar atmosphere. The results of UV-vis absorption and fluorescence spectra indicate that interactions between two C60 moieties of C60=C=C60 in the ground and singlet states are not significant, C121 (I, II, III) behaves as an electron-acceptor similar to C60. These indicate that the formation of the fullerene chain structure (e.g., C60=C=C60) does not disturb the photochemical and photophysical properties of the C60 monomer itself, even that the properties were enhanced by the formation of the polymer. This is significant for the C60 polymer in photochemical or photoelectronic applications in which C60=C=C60 can be an excellent basic unit of polymers.