Series Of Fullerenes Research Articles

Silvery fullerene in Ag102 nanosaucer.

Despite the discovery of a series of fullerenes and a handful of noncarbon clusters with the typical topology of I h-C60, the smallest fullerene with a large degree of curvature, C20, and its other-element counterparts are difficult to isolate experimentally. In coinage metal nanoclusters (NCs), the first all-gold fullerene, Au32, was discovered after a long-lasting pursuit, but the isolation of similar silvery fullerene structures is still challenging. Herein, we report a flying saucer-shaped 102-nuclei silver NC (Ag102) with a silvery fullerene kernel of Ag32, which is embraced by a robust cyclic anionic passivation layer of (KPO4)10. This Ag32 kernel can be viewed as a non-centered icosahedron Ag12 encaged into a dodecahedron Ag20, forming the silvery fullerene of Ag12@Ag20. The anionic layer (KPO4)10 is located at the interlayer between the Ag32 kernel and Ag70 shell, passivating the Ag32 silvery fullerene and templating the Ag70 shell. The t BuPhS- and CF3COO- ligands on the silver shell show a regioselective arrangement with the 60 t BuPhS- ligands as expanders covering the upper and lower of the flying saucer and 10 CF3COO- as terminators neatly encircling the edges of the structure. In addition, Ag102 shows excellent photothermal conversion efficiency (η) from the visible to near-infrared region (η=67.1%±0.9% at 450nm, 60.9%±0.9% at 660nm and 50.2%±0.5% at 808nm), rendering it a promising material for photothermal converters and potential application in remote laser ignition. This work not only captures silver kernels with the topology of the smallest fullerene C20, but also provides a pathway for incorporating alkali metal (M) into coinage metal NCs via M-oxoanions.

Insight into the Origin of Trapping in Polymer/Fullerene Blends with a Systematic Alteration of the Fullerene to Higher Adducts.

The bimolecular recombination characteristics of conjugated polymer poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,5-bis 3-tetradecylthiophen-2-yl thiazolo 5,4-d thiazole)-2,5diyl] (PDTSiTTz) blended with the fullerene series PC60BM, ICMA, ICBA, and ICTA have been investigated using microsecond and femtosecond transient absorption spectroscopy, in conjunction with electroluminescence measurements and ambient photoemission spectroscopy. The non-Langevin polymer PDTSiTTz allows an inspection of intrinsic bimolecular recombination rates uninhibited by diffusion, while the low oscillator strengths of fullerenes allow polymer features to dominate, and we compare our results to those of the well-known polymer Si-PCPDTBT. Using μs-TAS, we have shown that the trap-limited decay dynamics of the PDTSiTTz polaron becomes progressively slower across the fullerene series, while those of Si-PCPDTBT are invariant. Electroluminescence measurements showed an unusual double peak in pristine PDTSiTTz, attributed to a low energy intragap charge transfer state, likely interchain in nature. Furthermore, while the pristine PDTSiTTz showed a broad, low-intensity density of states, the ICBA and ICTA blends presented a virtually identical DOS to Si-PCPDTBT and its blends. This has been attributed to a shift from a delocalized, interchain highest occupied molecular orbital (HOMO) in the pristine material to a dithienosilole-centered HOMO in the blends, likely a result of the bulky fullerenes increasing interchain separation. This HOMO localization had a side effect of progressively shifting the polymer HOMO to shallower energies, which was correlated with the observed decrease in bimolecular recombination rate and increased “trap” depth. However, since the density of tail states remained the same, this suggests that the traditional viewpoint of “trapping” being dominated by tail states may not encompass the full picture and that the breadth of the DOS may also have a strong influence on bimolecular recombination.

(Invited) Endohedral Fullerene Hybrids: From Gold Nanoparticles to Graphene

Endohedral fullerenes are at the forefront of nanotechnology due to their rich electronic structure. In this talk I will focus on some examples of endohedral fullerenes used in hybrid nanostructures with other nanomaterials. For example, gold nanoparticles have been found to significantly increase or alternatively quench the photoluminescence of dyes, enhance the Raman scattering of organic molecules and the photocatalytic activity of semiconductors. We have reported for the first time the use of the singlet oxygen sensor green for the evaluation of the generation of singlet oxygen from a series of fullerenes (including endohedral fullerenes) and gold nanoparticle hybrids. The C70 mono adducts appear to be more efficient sensitizers compared to C60 in accordance with previous studies that were based on the 1270 nm emission of the singlet oxygen. Lu3N@C80 had a performance somewhat between the two empty cages. Overall, pyrene derivatives appeared to be efficient photo-sensitizers, especially when coupled with gold nanoparticles, with the 2.24 and 3.48 times increase on the fluorescence intensity.I will also elaborate on how Gd-based metallofullerene (Gd3N@C80) molecules can be used to create single adatoms and nanoclusters on a graphene surface. We have shown that endohedral metallofullerenes can adhere to graphene surfaces at temperatures well above their bulk sublimation point, indicating that the surface bound metallofullerenes have strong adhesion to dangling bonds on graphene surfaces. The ability to create dispersed single Gd adatoms, and Gd nanoclusters on graphene may have impact in spintronics and magnetism.Endohedral metallofullerenes continue to fascinate us with their versatility and attractive electronic properties.

(Invited) Endohedral Fullerene Hybrids: From Gold Nanoparticles to Graphene

Endohedral fullerenes are at the forefront of nanotechnology due to their rich electronic structure. In this talk I will focus on some examples of endohedral fullerenes used in hybrid nanostructures with other nanomaterials. For example, gold nanoparticles have been found to significantly increase or alternatively quench the photoluminescence of dyes, enhance the Raman scattering of organic molecules and the photocatalytic activity of semiconductors. We have reported for the first time the use of the singlet oxygen sensor green for the evaluation of the generation of singlet oxygen from a series of fullerenes (including endohedral fullerenes) and gold nanoparticle hybrids. The C70 mono adducts appear to be more efficient sensitizers compared to C60 in accordance with previous studies that were based on the 1270 nm emission of the singlet oxygen. Lu3N@C80 had a performance somewhat between the two empty cages. Overall, pyrene derivatives appeared to be efficient photo-sensitizers, especially when coupled with gold nanoparticles, with the 2.24 and 3.48 times increase on the fluorescence intensity.I will also elaborate on how Gd-based metallofullerene (Gd3N@C80) molecules can be used to create single adatoms and nanoclusters on a graphene surface. We have shown that endohedral metallofullerenes can adhere to graphene surfaces at temperatures well above their bulk sublimation point, indicating that the surface bound metallofullerenes have strong adhesion to dangling bonds on graphene surfaces. The ability to create dispersed single Gd adatoms, and Gd nanoclusters on graphene may have impact in spintronics and magnetism.Endohedral metallofullerenes continue to fascinate us with their versatility and attractive electronic properties.

Chlorination-Promoted Skeletal Transformations of Fullerenes.

Classical fullerenes are built of pentagonal and hexagonal rings, and the conventional syntheses produce only those isomers that obey the isolated-pentagon rule (IPR), where all pentagonal rings are separated from each other by hexagonal rings. Upon exohedral derivatization, the IPR fullerene cages normally retain their connectivity pattern. However, it has been discovered that high-temperature chlorination of fullerenes with SbCl5 or VCl4 can induce skeletal transformations that alter the carbon cage topology, as directly evidenced by single crystal X-ray diffraction studies of the chlorinated products of a series of fullerenes in the broad range of C60 to C102. Two general types of transformations have been identified: (i) the Stone-Wales rearrangement (SWR) that consists of a rotation of a C-C bond by 90°, and (ii) the removal of a C-C bond, i.e., C2 loss (C2L). Single- or multistep SWR and/or C2L transformations afford either classical non-IPR fullerenes bearing fused pentagons (highlighted in red in the TOC picture) or nonclassical (NCx) fullerenes with x = 1-3 heptagonal rings (highlighted in blue in the TOC picture) often flanked by fused pentagons. Several subtypes of the SWR and C2L processes can be further discerned depending on the local topology of the transformed region of the cage. Under the chlorination conditions, the non-IPR and NC carbon cages that would be energetically unfavorable and mostly labile in their pristine state are instantaneously stabilized by chlorination of the pentagon-pentagon junctions and by delimitation of the original spherical π-system into smaller favorable aromatic fragments. The significance of the chlorination-promoted skeletal transformations within the realm of fullerene chemistry is demonstrated by the growing body of examples. To date, these include single- and multistep SWRs in the buckminsterfullerene C60 and in the higher fullerenes C76(1), C78(2), C82(3), and C102(19), single and multistep C2Ls (i.e., cage shrinkage) in C86(16), C88(33), C90(28), C92(50), C96(80), C96(114), and C102(19), and multistep combinations of SWRs and C2Ls in C88(3), C88(33), and C100(18), (IPR isomer numbering in parentheses is according to the spiral algorithm). Remarkably, an IPR precursor can give rise to versatile transformed chlorinated fullerene cages formed via branched pathways. The products can be recovered either in their initial chlorinated form or as more soluble CF3/F derivatives obtained by an additional trifluoromethylation workup. Reconstruction of the skeletal transformation pathways is often complicated due to the lack of the isolable intermediate products in the multistep cases. Therefore, it is usually based on the principle of selecting the shortest pathways between the starting and the final cage. The quantum-chemical calculations illustrate the detailed mechanisms of the SWR and C2L transformations and the thermodynamic driving forces behind them. A particularly important aspect is the interplay between the chlorination patterns and the regiochemistry of the skeletal transformations.

Enhanced photocatalytic activity of anatase-TiO2 nanoparticles by fullerene modification: A theoretical and experimental study

A series of fullerene (C60)-modified anatase TiO2 (a-TiO2) nanocomposites with different weight loadings of C60 were successfully synthesized by a simple solution phase method. The as-prepared C60@a-TiO2 nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET), UV–vis diffuse reflectance absorption spectra (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The photocatalytic degradation of methylene blue (MB) by the neat a-TiO2 and C60@a-TiO2 nanocomposites was investigated under UV-A light irradiation, demonstrating that C60 effectively enhances the photocatalytic activity of a-TiO2 nanoparticles with an optimal amount of 2.0wt%. By combining with the density functional theory (DFT) calculations, we investigated the electronic structures of C60@a-TiO2 hetero-interfaces to reveal the underlying principle of the C60 loading on the photocatalytic activity. It was found that the incorporation of C60 on the a-TiO2 surface not only narrowed the band gap, but also introduced an additional doping state between the valance and conduction band. Therefore, the presence of intermediate electronic state will in turn contribute to the efficient charge separation and enhanced light adsorption for the C60@a-TiO2 nanocomposites, resulting in an improved photocatalytic performance.

Systematic Construction and Calculation of Electronic Properties of Fullerene Series Related by Rotational Symmetry: From Fullerenes to Bicapped Nanotubes.

The results herein demonstrate that the methods of circumscribing and the facile calculation of Hückel molecular orbital (HMO) eigenvalues by mirror-plane fragmentation have a broad application in the construction of carbon cluster series and the systematic study of trends in their electronic properties. In comparing open-ended nanotubes and their isomeric elongated fullerenes (bicapped nanotubes), we show that the former are more aromatic but the latter are more conjugated and that progressive elongation increases aromaticity and conjugation in both. Recursion equations that will allow one to obtain the eigenvalues to all 5-endcapped nanotubes are given.

(Invited) Photoinduced Electron Transfer Processes of Trifluorinated Molecules Dispersed in Conjugated Polymer Films and at Interfaces with Swcnts

The use of a Marcus formulation to describe photo-induced electron transfer processes in the complex blends of conjugated polymers and fullerenes associated with organic photovoltaics is rare. The conventional approach considers the polymer and fullerene to form a type II band offset similar to a picture for two inorganic semiconductors. A motivation for this presentation is to ask whether this simple model is correct and only the energetics need be considered when examining the driving force for the photo-induced electron transfer process. Or whether a re-organization energy is also required to describe the effect and therefore an optimum driving force is required to realize high charge separation yields. This presentation will describe two studies using a series of trifluoromethylfullerenes (TMFs) dispersed at low concentration in a conjugated polymer film or in a bilayer forming an interface with a layer of chiral-pure single-walled carbon nanotubes (SWCNTs). The fullerene series provides exquisite control over a wide range of reduction potentials of the fullerene, and can thus influence the driving force for photo-induced electron transfer studies. In both experiments, the use of the electrodeless technique of flash photolysis, time-resolved microwave conductivity (fp-TRMC) which provides a sensitive probe of the yield and kinetics of charges generated in both systems.

Topological Invariants of Nanocones and Fullerenes

The Timisoara-eccentricity (TM-EC) index of a molecular graphis defined as the sum of  i i i over all at- oms i in � , where  i,  i and  i are the degree, eccentricity and the number of atoms at distance  i from atom i. The topo- logical efficiency index ofis defined as = 2W / Nw , where W denotes the Wiener index, w is the minimal vertex contribution and N is the number of carbon atoms. This paper is devoted to the study of nanocones and fullerenes by these new graph in- variants. It is proved that the TM-EC index of a fullerenecan be bounded by a polynomial of degree 2, for twelve infinite series of fullerenes. It is also shown that in one pentagonal carbon nanocone with exactly 5n 2 + 10n + 5 carbon atoms, we have   1.24 and TM - EC = 280n 3 + 385n 2 + 195n + 40. Finally, we examine the dual of this nanocone and prove that we have   1.24 and TM - EC = 70n 3 + 20n 2 - 5n.

Fullerene-ionic-liquid conjugates: a new class of hybrid materials with unprecedented properties.

A modular approach has been followed for the synthesis of a series of fullerene-ionic-liquid (IL) hybrids in which the number of IL moieties (two or twelve), anion, and cation have been varied. The combination of C60 and IL give rise to new unique properties in the conjugates such as solubility in water, which was higher than 800 mg mL(-1) in several cases. In addition, one of the C60 -IL hybrids has been employed for the immobilization of palladium nanoparticles through ion exchange followed by reduction with sodium borohydride. Surprisingly, during the reduction several carbon nanostructures were formed that comprised nano-onions and nanocages with few-layer graphene sidewalls, which have been characterized by means of thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM-EDAX), and high-resolution transmission electron microscopy (HRTEM). Finally, the material thus obtained was successfully applied as catalyst in Suzuki and Mizoroki-Heck reactions in a concentration of just 0.2 mol %. In the former process it was recyclable for five runs with no loss in activity.

Solvent-free Sc3N@C80-Ih and Its Precursor Cocrystal with Toluene

Solvent-free Sc3N@C80-Ih was prepared for the first time in high quality microcrystalline form via thermal decomposition of its toluene cocrystal. The production route and structural studies of both materials are presented. The structures were determined by x-ray powder diffraction, and confirmed by cohesion energy calculations. The solvent-free endohedral fullerene forms face centered cubic crystals with lattice parameter a = 15.611 Å and the molecules are orientationally disordered. This is a new member of the high-symmetry isostructural expansion series of fullerenes. The parent cocrystals precipitated from toluene possess 1:1 stoichiometry; their structure is orthorhombic of Cmcm space-group. At room temperature the toluene molecules are located in large cavities in a severely disordered way. A symmetry lowering phase transition is observed on cooling indicating the dynamic nature of the disorder. The decomposition, assisted by toluene diffusion at elevated temperatures, is also analyzed in detail.

Synthesis and properties of fullerene (C60) substituted cyclophosphazene derivatives

A series of fullerene (C60) substituted cyclophosphazene derivatives (2a–4a) were synthesized for the first time by 1,3-dipolar cycloaddition of the 1-formylphenoxy (aryloxy)cyclotriphosphazenes (2–4) (aryloxy=phenoxy, 1-naphthoxy and 1-pyrenoxy) and C60. All the obtained compounds were characterized by 1H NMR, 13C NMR, 31P NMR, UV–Vis, fluorescence spectroscopy, MALDI-TOF and elemental analysis. The thermal behaviors of the synthesized compounds were investigated by Thermal Gravimetric Analysis (TGA).

Trap‐Assisted Recombination via Integer Charge Transfer States in Organic Bulk Heterojunction Photovoltaics

Organic photovoltaics are under intense development and significant focus has been placed on tuning the donor ionization potential and acceptor electron affinity to optimize open circuit voltage. Here, it is shown that for a series of regioregular‐poly(3‐hexylthiophene):fullerene bulk heterojunction (BHJ) organic photovoltaic devices with pinned electrodes, integer charge transfer states present in the dark and created as a consequence of Fermi level equilibrium at BHJ have a profound effect on open circuit voltage. The integer charge transfer state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor–acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap‐assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed.

Topological Wiener Indices and Polynomials of C<SUB>84</SUB> Fullerene Nanocage

The Wiener index is the most popular topological index used as an invariant molecular descriptor in the study of structures and physiochemical properties of molecules. Here, Wiener index and its modifications, hyper-Wiener and Harary indices, as well as Hosoya and hyper-Hosoya polynomials are studied over C 84 fullerene nanocage which is the third most abundant member of the higher fullerene series with two major structures known as stable C84, D2 (22) and D2d (23). The computation of Wiener indices and polynomials of isomers C84–D2 (22) and C84–D2d (23) is implemented using graph algorithms which employ the isomer’s molecular graphs. Our results show that the isomer C84–D2 (22) has greater Wiener and topological efficiency indices than isomer C84-D2d (23), which indicates that the isomer C84–D2d (23) has greater compactness and stability than isomer C84–D2 (22). These results are consistent with the experimental observations and further confirmed by the lower Harary index of isomer C84–D2 (22). The greater Wiener index of isomer C84–D2 (22) also suggests that its boiling point would be higher than that of isomer C84–D2d (23).

Electronic structure and bandgap engineering of CdTe nanotubes and designing the CdTe nanotube–fullerene hybrid nanostructures for photovoltaic applications

The electronic structure of CdTe nanotube–fullerene nanocomposites has been explored. Within this context, the structural and electronic properties of isolated 100 faceted CdTe nanotubes (NTs) with hexagonal cross-sections were first investigated using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. The possibility of band gap engineering of clean CdTe nanotubes is explored by varying either the size or wall thickness of the NTs. However, the efficient modification of the band gap can be attained by introducing the molecular states of fullerene into the band gap region of the CdTe NTs. The effects of the modulation of the band alignment through the variation in the wall thickness of the CdTe NTs on the electron injection rate from the NT to C60 in hybrid systems have been explored and we also found that the light harvesting efficiency of these nanohybrids can be maximized by increasing the concentration of the C60–thiol moieties. The position of the electronic energy levels offers information about the electronic structure of the hybrid systems such as whether it constructs type I or type II hetero-junctions, which bears key information for their application in photovoltaics. We also studied the electronic structure of CdTe–fullerene hybrid nanostructures with a series of fullerenes of different compositions.

Hot electron production and diffuse excited states in C70, C82, and Sc3N@C80 characterized by angular-resolved photoelectron spectroscopy

Angular-resolved photoelectron spectroscopy using wavelength-tuneable femtosecond laser pulses is presented for a series of fullerenes, namely, C70, C82, and Sc3N@C80. The photoelectron kinetic energy distributions for the three molecules show typical thermal electron spectra with a superimposed peak structure that is the result of one-photon ionization of diffuse low-angular momenta states with electron density close to the carbon cage and that are related to so-called super atom molecular orbitals. Photoelectron angular distributions confirm this assignment. The observed structure is less prominent compared to the thermal electron background than what was observed in C60. It can be concluded that hot electron emission is the main ionization channel for the larger and more complex molecules for these excitation conditions.

Spectroscopy of Fullerenes, Fulleranes and PAHs in the UV, Visible and Near Infrared Spectral Range

AbstractThe spectra of fullerenes C60 and C70, higher fullerenes C76, C78 and C84 and hydrogenated fullerenes (fulleranes) were studied in laboratory in the UV and in the visible spectral range and could be used for searching and recognizing these molecules in space. Furthermore, the radical cation spectra of all the mentioned fullerene series and also of a series of large and very large polycyclic aromatic hydrocarbons (PAHs) were generated in the laboratory and studied in the near infrared spectral range.

Synthesis and studies of methyl ester substituted thieno-o-quinodimethane fullerene multiadducts for polymer solar cells

A new series of fullerene (C60) multiadducts of methyl ester substituted thieno-o-quinodimethane were synthesized for polymer solar cells (PSCs). The synthesized 5-methyl ester thieno-o-quinodimethane fullerene (C60) multiple adducts, such as METFMA (mono-adduct), METFBA (bis-adduct) and METFTA (tris-adduct), showed good solubility in toluene, CHCl3 and ODCB. Their molecular structures were confirmed by 1H, 13C NMR, UV–visible spectroscopy, DSC, TGA and HRMS Cyclic voltammetry revealing a lowest unoccupied molecular orbital (LUMO) energy level of −3.65eV for METFMA, −3.53eV for METFBA and −3.42eV for METFTA, which is higher than that of PC61BM. The higher LUMO energy level of METFMA, METFBA and METFTA resulted in an enhancement of the open-circuit voltages (Voc) of PSCs. Device of the multiple adduct acceptors was blended with a P3HT donor with the configuration, ITO/PEDOT/P3HT:acceptor/LiF/Al, using METFMA, METFBA, METFTA and PC61BM as the electron acceptor. The optimal photovoltaic performances were achieved using METFBA and METFTA with power conversion efficiencies of 3.00% and 2.93%, respectively. These results were comparable to the device conducted with P3HT:PC61BM (3.42%) under the same conditions.

On the Radical Cation Spectra of Fullerenes and Fulleranes. Part 1: C60, C70,C76, C78 and C84

The radical cation of the fullerene series C60, C70,C76, C78 and C84 were generated in oleum (fuming sulphuric acid with 30% free SO3) and analyzed by electronic absorption spectroscopy. A general agreement was found between the fullerenes radical cation spectra generated in oleum and those described in the literature and produced in other conditions. An attempt to correlate the radical cation transition of C60, C70, C76, C78 and C84 in oleum with their ionization potential was proposed.

Interaction Between Fullerenes and Single-Wall Carbon Nanotubes: The Influence of Fullerene Size and Electronic Structure

A series of fullerenes and endohedral metallofullerenes peapods have been synthesized by supercritical method in high filling rate. The interaction between SWNTs and various kinds of fullerenes (C60, C70, C78, C84) and metallofullerenes (Gd@C82, Er@C82, Ho@C82, Y@C82) has been further investigated. The slight blue shift of G-band in Raman spectra with respect to pristine SWNTs was attributed to the charge transfer from SWNTs to fullerenes cage. The obvious RBM shift strongly depended on the distance between the inner wall of the SWNTs and the fullerene cage and also partly associated with the electronic structure of the fullerene. These results indicated that the interaction between fullerenes and SWNTs, which was considered to be the van de walls interaction, can be influenced by the cage size and the kind of fullerenes.