Adducts Of C60 Research Articles

Rigid Tether Directed Regioselective Synthesis and Crystallographic Characterization of Labile 1,2,3,4-Bis(triazolino)[60]fullerene and Its Thermolized Derivatives.

Labile bis-triazoline adducts of C60 are supposed to be the precursors of bis-azafulleroids, but the formation mechanism is still unclear because of the incomplete isolation of the thermolized products and the lack of X-ray structures. A rigid-tethered reagent 1,2-bis(azidomethyl)benzene (1) was used to regioselectively synthesize the labile 1,2,3,4-bis(triazolino)[60]-fullerene (2), the structure of which was determined by single-crystal X-ray crystallography. Further thermolysis of 2 produces four products (3 a-3 d), which were all characterized by X-ray crystallography. Although 3 a and 3 b have traditional bis-azafulleroid structures, as proposed previously, 3 c and 3 d show unprecedented structures with either the coexistence of [5,6]-open and [6,6]-closed patterns or an oxidized structure with an 11-membered ring on the cage. A thermolysis mechanism is proposed to clarify long-term confusion about the transformation process from bis-triazoline adducts to bis-azafulleroids of C60 .

Evidence of charge-remote fragmentation in protonated [60]fulleropyrrolidine multi-adducts

[60]fulleropyrrolidine derivatives (Prato adducts of C60) with up to three ligands were protonated by electrospray ionization (ESI) and the collision-induced dissociation (CID) behaviour of these ions was studied with a quadrupole ion trap mass spectrometer. The systems under investigation showed distinctly different fragmentation behaviour for the neutral and the protonated ligands regarding both extent of fragmentation and pattern. This provided a means to distinguish reactions at the site of the charge from those occurring remote from it. In fact, evidence of charge-remote fragmentation (CRF) was obtained, with the neutral, charge-remote ligands showing efficient fragmentation and the protonated ligand largely resisting decomposition.

Synthesis of Isomerically Pure Multi‐aniline C60 Adducts with Cyclopentadienyl Addition Pattern

Unlike aliphatic amines, anilines cannot react directly with fullerenes to form isomerically pure fullerene multi‐adducts. In the present work several anilino C60 derivatives are prepared through BiCl3‐mediated replacement reactions of C60 derivatives that contain secondary amino addends. All new anilino C60 derivatives have a cyclopentadienyl addition pattern and contain multiple anilino addends up to 5.

Synthesis of Enantiopure T-Symmetrical [6:0]-Hexakis Adducts of C60 Equipped with 1,2-Glycol Substituted cyclo-Monomalonate Addends.

The synthesis of T-symmetrical [6:0]-hexakis adducts of C60 bearing enantiopure cyclo-monomalonate addends equipped with 1,2-glycol groups masked as isopropylidene acetals is presented. The deprotection of the acetals afforded functional fullerene building blocks bearing six 1,2-glycol moieties in an octahedral geometry as connection sites with appropriate linear organic spacers targeting 3D chiral extended networks with cubic building units. Evaluation of the experimental results revealed the advantageous synthetic accessibility to hexakis adduct (-)-9 which carries six homochiral C12 cyclo-monomalonate addends.

VOC enhancement in polymer solar cells with isobenzofulvene–C60 adducts

We report the use of isobenzofulvene–C60 adducts in bulk heterojunction organic solar cells, synthesized via the [4 + 2] cycloaddition of C60 with an in situ generated isobenzofulvene intermediate. The LUMO energy levels of these adducts are 20–180 meV higher than that of PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). This large increase of the LUMO level is attributed to cofacial π-orbital interactions between the fullerene surface and the isobenzofulvene π–system (aromatic ring and double bond). Raised LUMO levels of fullerenes, together with their desirably slow recombination dynamics, led to higher open-circuit voltages (VOC) in bulk heterojunction polymer solar cells (up to 0.75 V for bisadducts) relative to cells tested in parallel using the well-known PCBM as the fullerene acceptor. In addition to enhanced VOC, the short-circuit current densities (JSC) were improved in the devices containing the epoxide analogs of the isobenzofulvene–C60. Notably the epoxide derivative of the monoadduct (IBF–Ep) exhibited ∼20% enhancement of power conversion efficiency (PCE) compared to reference P3HT:PCBM solar cells. A combination of optical and electronic methods was used to investigate the origin of the PCE enhancement observed with these new fullerene acceptors with particular attention to the increased VOCs.

Charge separated states and singlet oxygen generation of mono and bis adducts of C60 and C70

We present a series of fullerene derivatives and a study on their photoluminescence properties, complete with their efficiency as singlet oxygen generation photosensitizers. We demonstrate the intramolecular charge transfer between pyrene donor and fullerene acceptor. The opposite effect in decay lifetime measurements is observed for the mono and bis adducts of C60 and C70 for the first time, indicating an interplay between charge-separation and locally excited states. A monoexponential decay was observed for the mono adduct of C60 and the bis adduct of C70, while a biexponential decay was observed for the bis adduct of C60 and the mono adduct of C70. The effect of these molecules as sensitizers of the singlet oxygen radical was tested using detailed 3D excitation photoluminescence maps. A quenching of the singlet oxygen for the C60-mono and C70-bis adducts was observed while a strong photosensitizing effect was observed for the C60-bis and C70-mono adducts.

Synthesis and photochromic properties of fullerene C60 adducts with dithienylethenes

A number of adducts of C60 with dithienylethenes were synthesized for the first time using the Prato reaction and their photochromic properties studied. It was found that the positions of the absorption bands for the ring-closed forms of diarylethenes incorporated fullerene adducts and the efficiency of their photochromic transformations were dependent on the nature of the substituents on the second thiophene ring.

Self‐Assembled Giant Vesicles Formed by Type I [3:3]‐Hexakis Adducts of C60 Equipped with Enantiomerically Pure cyclo‐Monomalonate Addends

AbstractAn efficient route for the synthesis of two amphiphilic type I [3:3]‐hexakis adducts of C60 equipped with enantiopure cyclo‐monomalonate addends was explored. Studies on their self‐assembling behavior by TEM and SEM revealed that minor modification of the size and chemical nature of their glycol‐substituted monomalonate addends and, consequently, of the shape of these giant molecules significantly influences their corresponding self‐assembling architectures.

Dispersion interaction stabilizes sterically hindered double fullerenes.

By state-of-the-art quantum chemical methods, we show that for bulky functional groups like cyclohexane, [20]fullerene, dodecahedrane, and C60, the attractive dispersion interaction can have a greater impact on stereochemistry than the repulsive steric effect, making the compact isomer the more stable one. In particular, for the double C60 adduct of pentacene 1, the syn isomer should be the main product instead of the anti one inferred in the original synthesis experiment (Y. Murata et al., J. Org. Chem. 1999, 64, 3483). With and without dispersion interactions taken into account, the Gibbs energy difference ΔG(syn-anti) is -6.36 and +1.15 kcal mol(-1), respectively. This study reminds us that dispersion interactions as well as electrostatic or hyperconjugation effects, etc. can lead to some unusual stereochemical phenomena.

Regioselectivity in multiple cycloadditions to fullerene C60: vibronic coupling density analysis

We theoretically investigate multiple cycloadditions of butadienes to fullerene C60 with the concept of vibronic coupling density (VCD) as a reactivity index. Recently, we have clarified that C60 bears ethylene moieties at its reactive sites as functional groups, on the basis of VCD. In this study, we calculate the VCDs of C60 adducts with n butadienes (n=1, …, 5) and show that the ethylene moieties are conserved with almost the same distributions as those in C60. The VCD analysis predicts that the hexakisadduct with a six-fold axis is finally obtained, which is consistent with experimental observations.

Synthesis, Characterization, and Electron-Transfer Processes in Indium Ferrocenyl-Containing Porphyrins and Their Fullerene Adducts

Three new indium(III) tetra- and penta(ferrocenyl)-substituted porphyrins of the general formula XInTFcP [X = Cl(-), OH(-), or Fc(-); TFcP = 5,10,15,20-tetraferrocenylporphyrin(2-); Fc = ferrocene] have been prepared and characterized by UV-vis, magnetic circular dichroism (MCD), (1)H, (13)C, 2D, and variable-temperature NMR spectroscopy, as well as elemental analysis. Molecular structures of the ClInTFcP, FcInTFcP, and FcInTFcP@4C60 complexes were determined by X-ray crystallography with the last compound being not only the first example of a C60 adduct to the organometallic porphyrins but also the first structure in which organometallic porphyrin antennas intercalated into four electron-transfer channels. The electronic structures and relative energies of individual atropisomers, as well as prospective electron-transfer properties of fullerene adducts of XInTFcP complexes, were investigated by the Density Functional Theory (DFT) approach. Redox properties of XInTFcP complexes were investigated using electrochemical (CV and DPV), spectroelectrochemical, and chemical oxidation approaches. Electrochemical experiments conducted in low-polarity solvent using noncoordinating electrolyte were crucial for the sequential oxidation of ferrocene substituents in XInTFcP compounds. In agreement with DFT calculations, the axial ferrocene ligand in FcInTFcP, with direct In-C σ-bond has a 240 mV lower oxidation potential compared to the first oxidation potential for equatorial ferrocene substituents connected to the porphyrin core. The first equatorial ferrocene oxidation process in all XInTFcP complexes is separated by at least 150 mV from the next three ferrocene based oxidations. The second, third, and fourth redox processes in the ferrocene region are more closely spaced. The addition of the bulky axial ferrocene ligand results in significantly larger rotational barriers for equatorial ferrocene substituents in FcInTFcP compared to the other complexes and leads to better defined redox waves in cyclic voltammetry (CV) and differential pulse voltammetry (DPV) experiments. Mixed-valence compounds of the general formula [XInTFcP](n+) (n = 1, 2) were observed and characterized by spectroelectrochemical and chemical oxidation approaches. In all cases, the presence of the intense intervalence charge transfer (IVCT) bands associated with the oxidation of a single equatorial ferrocene substituent were detected in the NIR region confirming the presence of the iron-based mixed-valence species and suggesting long-range metal-metal coupling in the target systems. The resulting data from the mixed-valence [XInTFcP](n+) (n = 1, 2) complexes matched very closely to the previously reported MTFcP and metal-free poly(ferrocenyl)porphyrins and were assigned as Robin and Day Class II mixed-valence compounds.

Cyclobutadiene–C60 Adducts: N‐Type Materials for Organic Photovoltaic Cells with High VOC

AbstractNew tetraalkylcyclobutadiene–C60 adducts are developed via Diels–Alder cycloaddition of C60 with in situ generated cyclobutadienes. The cofacial π‐orbital interactions between the fullerene orbitals and the cyclobutene are shown to decrease the electron affinity and thereby increase the lowest unoccupied molecular orbital (LUMO) energy level of C60 significantly (ca. 100 and 300 meV for mono‐ and bisadducts, respectively). These variations in LUMO levels of fullerene can be used to generate higher open‐circuit voltages (VOC) in bulk heterojunction polymer solar cells. The tetramethylcyclobutadiene–C60 monoadduct displays an open‐circuit voltage (0.61 V) and a power conversion efficiency (2.49%) comparable to the widely used P3HT/PCBM (poly(3‐hexylthiophene/([6,6]‐phenyl‐C61‐butyric acid methyl ester) composite (0.58 V and 2.57%, respectively). The role of the cofacial π‐orbital interactions between C60 and the attached cyclobutene group was probed chemically by epoxidation of the cyclobutene moiety and theoretically through density functional theory calculations. The electrochemical, photophysical, and thermal properties of the newly synthesized fullerene derivatives support the proposed effect of functionalization on electron affinities and photovoltaic performance.

静電塗布法によるフラーレン誘導体の薄膜形成における印加電圧と膜質の関係

Thin films of fullerene derivative were prepared by an electrospray deposition (ESD) method using six types of fullerene derivatives (a series of [6,6]-Phenyl-C61-butyric acid ester and adducts of C60 with indene). The optimized conditions for fabricated thin films were investigated by ESD process using 1.0 mg/mL diluted solutions of the fullerene derivatives : the spray diameter as a function of the supply rate by changing the applied voltages. In all the cases, the spray diameters increased with increasing applied voltage reaching the maximum diameter (Dmax) at the voltage (VDmax) and decreasing for higher voltage. The scanning electron microscope observation of the successfully fabricated thin films showed the imbricated structure formed by the stacking of fullerene derivative sheets. The atomic force microscope image revealed that the highest density of imbricated structure was obtained at VDmax, and the root-mean-square roughness of the film surface decreased sharply reaching at the voltage. These findings suggest that the ESD method is expected to be effective to prepare a fullerene derivative thin film for the production of organic devices.

Intramolecular versus intermolecular electronic interactions between [5,6]-open and [6,6]-closed C60 adducts with exTTF

Intramolecular and intermolecular electronic interactions are important concepts for fabricating fullerene-based nanostructures such as bulk heterojunction (BHJ) solar cells and supramolecular assemblies. To ascertain differences of the molecular interactions depending on the electronic characteristics of the fullerene adducts, we have synthesized and investigated the [5,6]-open and [6,6]-closed adducts of C60, which are covalently linked to π-extended tetrathiafulvalene (exTTF) by a flexible σ-bond chain. The two adducts were synthesized by means of cycloaddition reactions and were characterized using spectroscopic methods such as MALDI-TOF mass spectrometry and NMR spectroscopy. Electronic properties of the [5,6]-open and [6,6]-closed adducts were investigated in the ground and excited states using steady-state absorption spectroscopy, cyclic and differential pulse voltammetry (CV and DPV), fluorescence spectroscopy, and femtosecond time-resolved absorption spectroscopy. DFT calculations of the two adducts predict that the flexible bridge between C60 and exTTF enables a closer proximity than the interlayer distance of graphite (3.35 A), which dictates considerable π–π interactions. In comparing the [5,6]- and [6,6]-adducts, it is noteworthy to mention that the [6,6]-adduct revealed longer lifetimes of the photochemically formed radical ion pair states than that of the [5,6]-adduct, which is in contrast to results of recent investigations related to the photodynamics of [5,6]- and [6,6]-adducts of C60. Titration experiments using references, namely [5,6]- and [6,6]-PC61BM, inferred that the [6,6]-adduct gives rise to stronger electronic interactions with exTTF than the [5,6]-adduct. Comprehensive understanding of the different molecular properties, which the [5,6]- and [6,6]-adducts exhibit, provides valuable information regarding the morphology and/or the electronic properties of C60-based nanocomposites, such as C60-based BHJ solar cells or supramolecular assemblies.

π-Conjugated molecular heterojunctions with multi[60]fullerene: photophysical, electrochemical, and photovoltaic properties

A series of well-defined D–π-B–A C60 adducts containing three chromophores and their corresponding precursors were facilely developed as organic photovoltaic materials. The photophysical and electrochemical properties indicated that effective photo-induced intramolecular and/or intermolecular energy transfer and charge transfer were formed from the donor chromophores to the C60 moiety in thin films. Solution processed molecular heterojunction solar cells using 12 as active layer were fabricated with 2.0% monochromatic efficiency. Our results showed that further exploration might lead the way toward high-efficient solution-processed single molecular solar cell materials based on conjugated oligomer covalent to fullerene units.

Anthracene and Anthracene:C60 Adduct-Terminated Monolayers Covalently Bound to Hydrogen-Terminated Silicon Surfaces

Anthracene monolayers covalently bound to hydrogen-terminated n-type Si(100) surfaces have been prepared from the attachment of an amine-substituted anthracene derivative to a preassembled acid-terminated alkyl monolayer using carbodiimide coupling. The anthracene headgroups were then used as anchoring sites for C60 following [4 + 2] Diels–Alder cycloaddition. After cycloaddition of C60 on the anthracene layer, the surface roughness determined by atomic force microscopy increased from 3.0 ± 0.7 to 5.0 ± 1.0 Å and the morphology showed uniformly distributed globular features a few nanometers high. Cyclic voltammograms of the anthracene-modified monolayer in the dark were characterized by an ill-defined reversible system at E°′ = −2.05 V vs saturated calomel electrode (SCE), which compares well with the value determined for the anthracene derivative in solution on a platinum electrode. Furthermore, the surface coverage of attached anthracene units was estimated to be (4.6 ± 0.3) × 10–10 mol cm–2, which is consistent with a densely packed monolayer. In contrast, the voltammogram of the C60-modified monolayer did not show multiple reversible one-electron transfers characteristic of the anthracene:C60 adduct. Instead, one irreversible cathodic peak at −1.50 V followed by a reversible system at −2.15 V was observed. These electrochemical differences between surface-confined and dissolved species are assigned to reduced charge transfer kinetics between the underlying semiconductor and bound C60 within a certain potential range. This hypothesis is consistent with the flat band potential Efb value of −0.80 ± 0.05 V vs SCE, determined from capacitance measurements. Moreover, scanning electrochemical microscopy (SECM) measurements in feedback mode provided clear evidence for the electroactive properties of bound C60. The SECM approach curves suggest that both the anthracene and anthracene:C60 layers displayed good conductivity, presumably by electron hopping between adjacent redox sites.

Novel bis-C60 derivative compared to other fullerene bis-adducts in high efficiency polymer photovoltaic cells

We report the application of novel mono- and bis-o-quino-dimethane C60 (oQDMC60) adducts in bulk heterojunction photovoltaic devices. When blended with poly(3-hexylthiophene), the fullerene adducts presented here have an enhanced open-circuit voltage of 640 mV and 820 mV, while preserving high short-circuit current and fill factor, resulting in efficiencies of 4.1% and 5.2%, respectively. Detailed assessment of material properties relevant to photovoltaic devices such as energy levels, charge carrier mobility, absorption and solubility further complements the evaluation. Increased fullerene solubility hindering phase segregation in blends with bis-oQDMC60 has been circumvented by an in-depth morphology optimization assisted by absorption spectroscopy, X-ray reflectivity and atomic force microscopy. This optimized preparation could also serve as a guide for implementation of similar fullerene derivatives. Furthermore, we compare bis-oQDMC60 to previously reported fullerene bis-adducts to provide insight into this emerging class of materials.

ChemInform Abstract: Formation of C60 Adducts with Two Different Alkyl Groups via Combination of Electron Transfer and SN2 Reactions.

ChemInform Abstract: Formation of C60 Adducts with Two Different Alkyl Groups via Combination of Electron Transfer and SN2 Reactions.

Stable and Unstable 6,6‐ and 5,6‐ Closed and Open Adducts of Fullerene C60

DFT/PBE/TZ2P research of total energy of various adducts at variation of 5,6‐ and 6,6‐ bond was carried out. On the basis of the analysis of local minima, the conclusion on structures stability and instability was drawn. Acyclic and cyclic derivatives containing 4‐6‐membered rings are established to form the closed adducts only. Thus the [6,6]‐closed structures are 15–18 kcal/mole more stable than [5,6]‐closed. The [6,6]‐closed adducts with strained 3‐membered cycles and their [5,6]‐open isomers are found to be stable. The analysis of strain energy is accomplished.

Water-Solubility, Antioxidant Activity and Cyctochrome C Binding of Four Families of Exohedral Adducts of C60 and C70

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