Fullerene Core Research Articles

60]Fullerene adducts with improved electron acceptor properties [In Process Citation

The synthesis of C(60)-based dyads in which the C(60) core is covalently attached to a strong electron acceptor moiety such as quinones, TCNQ or DCNQI derivatives, has been carried out by 1, 3-dipolar cycloaddition of "in situ" generated azomethyne ylides or nitrile oxides to C(60). As expected, the obtained pyrrolidino[3', 4':1,2][60]fullerenes exhibit reduction potentials of the C(60) framework which are cathodically shifted in comparison with the parent C(60). In contrast, isoxazolo[4',5':1,2][60]fullerenes show reduction waves for the fullerene core that are anodically shifted in comparison with the parent C(60), which indicates that they are remarkably stronger acceptors than C(60).The electron acceptor organic addend also undergoes an anodic shift due to the electronic interaction with the C(60) moiety. The molecular geometry of pyrrolidinofullerenes has been calculated at the semiempirical PM3 level and reveals a highly distorted geometry for the acceptor moiety in compound 13, and a most stable conformation in which both dicyanomethylene units are far away from the C(60) surface.

Synthesis of two pentaarylated [60]fullerene derivatives Ar5C60‐H (Ar = p‐MeC6H4, m‐MeC6H4) and their novel electrochemical properties

AbstractThrough one pot reaction of C60 with organocopper/magnesium reagent ( p‐MeC6H4 )2 CuMgBr or ( m ‐ MeC6 H4 )2‐CuMgBr prepared from CuBr‐Me2S and p‐MeC6H4MgBr or m‐MeC6H4 MgBr and subsequent quenching with aqueous NH4Cl, two pentaarylated [ 60 ] fullerene derivatives (p‐MeC6H4)5 C60H (1) and (m‐MeC6H4)5 C60H (2) have been synthesized in 94% and 96% yields, respectively. While known compound 1 prepared via this improved method is unambiguously identified, new compound 2 is fully characterized by elemental analysis, IR, UV‐vis, 1H NMR and 13C NMR spectroscopies. Additionally, electrochemical study shows that the two [60] fullerene derivatives 1 and 2 in dichloromethane solution display two sequential one‐electron reductions which are shifted by about 0.4 V towards more negative potential values with respect to free C60. Such remarkable cathodic shift is attributed to the multiple breakage of the double‐bond conjugation within the Fullerene core.

Synthesis of a Biotinated Lipofullerene as a New Type of Transmembrane Anchor

As a prototype for a new class of lipid membrane components, the lipophilic fullerene derivative (so-called lipofullerene) 1 was synthesized and characterized. This mixed [1:5]-hexakisadduct consists of ten long alkyl chains within five didodecyl malonate addends and a linker malonate carrying a (+)-biotin unit as part of an amphiphilic spacer. The malonates are attached to the fullerene core in an octahedral addition pattern, which was achieved by two successive cyclopropanation sequences with the functional precursor malonate 8 and dodecyl malonate 10. The final step of the synthesis of 1 was the attachment of activated biotin 5 with the deprotected precursor 11. Binding experiments followed by reflectometric interference spectroscopy [RIfS] proved the capability of 1 to bind specifically the protein streptavidin (SA) through the biotin unit. The amphiphilic behavior of 1 was demonstrated by Langmuir Blodgett (LB) film investigations.

Synthesis of fluorous fullerene adducts: reversible solubilization of fullerenes in perfluorinated solvents

Fullerene (C60) Diels-Alder adducts with perfluoroalkylated 1,3-cyclopentadiene (1a,b) were synthesized and studied. The perfluoroalkylated cyclopentadiene was found to be less reactive toward C60 than cyclopentadiene itself, possibly because of the electron-withdrawing effect of the side chain. Because of the same effect, the temperature of the retro-Diels-Alder reaction for the fluorinated adducts was lower (70 degrees C) than the reported value (95 degrees C) for the cyclopentadiene adducts of C60. Higher adducts of the fluorous diene and C60 were found to be soluble in perfluorohexane and to show visible partitioning between organic (toluene) and fluorous phases. Also, the Diels-Alder addition of the fluorous diene was accompanied by extensive oxidation of the fullerene core, as revealed by MALDI-TOF data.

Reactions of photoexcited C 60 with weak organic acids. Novel method for the derivatization of fullerenes

Pyrex-filtered irradiation of C 60 solutions in liquid diphenylmethane in the absence of oxygen is shown to result in Ph 2CH ⋅ radicals, which further react with the electron-deficient C 60 to give Ph 2CH–C 60H n ( n=1, 3, 5). The fullerene ground state to 3 C 60 transition is suggested to be accompanied by the increase of the fullerene solvation affecting thus the acidity of methylene hydrogens in Ph 2CH 2 as well as the feasibility of their dissociation. Also, photolysis of C 60 solutions in weakly acidic phenylacetylene is shown to lead to the addition of a varying number of phenylethinyl groups to the fullerene core.

Anomalies of Glass Transition: Manifestation in fullerene core polystyrene stars

Segmental dynamics around Tg in the 4- and 6-arm fullerene (C60) core star-like polystyrenes with different preset arm lengths was studied by DSC as compared to that in the linear PS and PS/C60 blend. The ‘anomalies’ in glass transition behavior were found for the stars including both suppression and facilitation of segmental motion, and pronounced dynamic heterogeneity within a transition range. The results are interpreted in terms of breakdown of intermolecular cooperativity of segmental motions and PS-C60 interactions.

Photoinduced Charge Separation and Stabilization in Clusters of a Fullerene−Aniline Dyad

Fullerene−bridge−aniline dyad and the model fulleropyrrolidine compound form stable, optically transparent clusters in mixtures (3:1) of acetonitrile and toluene. Ground- and excited-state properties of the clusters of the dyad and the model compound are compared with their corresponding monomeric forms. Clustering of the dyad as well as the model compound exhibits a red-shifted emission maximum (λmax ∼ 738 nm) compared to their monomeric forms (λmax ∼ 714 nm). The electron transfer from the appended electron donor moiety to the parent fullerene core in the dyad cluster is evident from the decreased (∼80%) fluorescence yield. The formation of fullerene radical anion (absorption maximum at 1010 nm) with a lifetime of several hundreds of microseconds was further confirmed using nanosecond laser (337 nm) flash photolysis experiments. In contrast, the dyad molecules in their monomeric form did not yield any detectable yield of C60 radical anion following laser pulse excitation. The failure to observe any char...

Oxyfunctionalization of Non-Natural Targets by Dioxiranes. 3.(1) Efficient Oxidation of Buckminsterfullerene C(60) with Methyl(trifluoromethyl)dioxirane.

By employing methyl(trifluoromethyl)dioxirane (1b), the stepwise oxyfunctionalization of C(60) can be carried out with high conversions (>90%) under mild conditions (0 degrees C); the products have been compared with those produced by the oxidation of C(60) with m-chloroperoxybenzoic acid. Along with the previously characterized oxide C(60)O, a wider set of higher oxidation products is obtained by using 1b; among these, regioisomeric dioxides C(60)O(2) are isolated in good overall yield (40%). One of the dioxides is predominant (yield 23%), corresponding to a C(s)()-symmetry dioxide previously well characterized and presenting the epoxide functionalities in close proximity over the 6:6 ring junctions. The oxidation with dioxirane 1b also produces sufficient quantities of trioxides, so that mixtures of C(60)O(3) regioisomers can be isolated. The main trioxide fraction was found amenable to spectroscopic characterization; the (13)C NMR spectra indicates that the sample consists of two possible regioisomers, one having C(s)(), and the other C(2) symmetry. In both, the three epoxide rings are assembled over 6:6 ring junctions and in close proximity to each other; this shows that, in the ensuing sequential O-transfers from the dioxirane to the fullerene framework, the 6:6 carbon-carbon double bonds adjacent to an existing epoxide functionality are more easily oxidized. The whole of the spectroscopic data indicate that the fullerene core remains intact and no rupture of the cage occurs following oxidation at the trioxide level.

Activity of water-soluble fullerenes towards OH-radicals and molecular oxygen

bis-functionalized C60 carrying negatively charged carboxyl groups, C60[C(CO−2)2]2, or positively charged quaternary ammonium groups, C60(C4H10N+)2, have been shown to exhibit high water-solubility without cluster formation. This renders them excellent targets for free radical attack and energy transfer reactions in aqueous environment. Absolute rate constants on the order of 8×109 M−1 s−1 and 1.5×109 M−1 s−1 have been measured for the addition of OH radicals to the fullerene core and for the formation of 1O2 through triplet excited states of the fullerenes, respectively, for a variety of bis-functionalized stereoisomers. Comparatively lower rates have been observed for the corresponding energy transfer reactions with γ-cyclodextrin-encapsulated (C60/γ-CD, C60C(CO−2)2/γ-CD, and C60[C(OCH2CH2)3CH3]2/γ-CD), and water-soluble poly-functionalized fullerenes (e,e,e-C60[C(CO−2)2]3, C60[(CH2)4SO3H]6, and C60(OH)18). The latter three also exhibited a lower reactivity towards OH radicals. In case of the γ-CD complexes, OH reacted exclusively with the macromolecular host.

Triplet-State Properties and Singlet Oxygen Generation in a Homologous Series of Functionalized Fullerene Derivatives

The main properties of the triplet states and the yields of singlet oxygen generation for a series of methano[60]fullerene adducts with increasing numbers of substituents were determined. The triplet properties investigated are energies, triplet−triplet absorption spectra, extinction coefficients, and quantum yields. A strong correlation is observed between several triplet properties and the topology of the fullerene core. Successive fragmentation of the chromophore of the parent C60 results in higher triplet energies and lower triplet quantum yields. In addition, singlet oxygen quantum yields (φΔ) were determined for all adducts and decrease as the area of the conjugated fullerene core decreases.

Formation of an Effective Opening within the Fullerene Core of C(60) by an Unusual Reaction Sequence.

A large hole in a fullerene: The addition of dioxygen to the highly reactive 1,4-diaminobutadiene moiety of 1, formed from the reaction of C(60) with a rigid diazidobutadiene, results in the very efficient formation of an open fullerene (see the space-filling model) with the largest orifice created so far on a fullerene. The opening may be large enough to allow the smallest atoms, molecules, or ions to pass through.

Fullerene core star-like polymers 2. Preparation from fullerenes and linear or cyclic monoaminopolyethers

Fullerene core star-like polymers have been synthesized by reacting C 60 with methyl ethers of polyoxypropylene or polyoxyethylene and crown ethers having amino end-group. Depending on the starting mole ratio (C 60/polyether=1, 3 or 10), products with different average number of polyether branches were prepared. The solubility of the derivatives was modulated by varying the number and the hydrophilicity of the grafted polyether chains.

Palm-tree and dumbbell like polystyrene structures based on C 60

By reacting anionic polymers such as polystyryllithium with C 60, “living” hexa-adducts have been prepared and used to initiate the anionic polymerization of vinyl monomers. If styrene is used as the monomer, only one chain is growing out from the fullerene core producing a “palm-tree” type structure. The outgrowing chain bearing on its end a carbanion, could be reacted with the coupling agent dibromoparaxylene to form “dumbbell” like macromolecules where two 6 branched PS stars are connected together by a PS chain of controlled length.

Bucky Light Bulbs: White Light Electroluminescence from a Fluorescent C60 Adduct−Single Layer Organic LED

Recently it was reported that a C60 adduct, Th-hexapyrrolidine (THP, Figure 1a), has a substantial yellow-green fluorescence.1 The photophysical properties of THP are atypical of C60 and its derivatives.2 The fluorescence of C60 and its monoadducts is very weak, with reported quantum yields on the order of 10-4.3-6 The origin of the fluorescence properties of THP may be due to a reduction of conjugation within the fullerene core leading to higher excitation energies and larger single-triplet gaps. The result is a displacement of the spectrum to the blue, a small reduction of the excited-state S1 f T1 intersystem crossing, an increase in the rate of singlet state radiative decay (fluorescence rate), and a decrease in the rate of triplet decay to the ground state (T1 f S0) by thermal deactivation.1 Due to the photophysical properties of THP, we have utilized it as a chromophore in the fabrication of a white light organic LED. Though lightly n-doped as well as pristine fullerene C60 was shown to exhibit electroluminescence with apparent decomposition,7 to the best of our knowledge, this is the first time electroluminescence has been obserVed from a C60 deriVatiVe, an unprecedented result in light of the fact that C60 is universally an efficient luminescence quencher.8 Traditionally, organic electroluminescent devices are multilayered, with the electron-transport, hole-transport and emissive materials segregated.9 In contrast, we fabricated the organic LEDs by blending THP (emissive material) with a hole transport material, poly(9-vinylcarbazole) (PVK), and an electron-transport material, 2,5-bis-(4-naphthyl)-1,3,4-oxadiazole (BND), to form a single-layer device (Figure 1). This molecularly-doped polymer device configuration has been used by others.10-14

Palm Tree- and Dumbbell-Like Polymer Architectures Based on C60

By reacting 6 PSLi per C60 molecule, fairly pure star-shaped polymers with six branches and six carbanions located on the fullerene core are obtained. Only one of these six carbanions is able to initiate the anionic polymerization of styrene or isoprene leading to well-defined palm tree-like architectures (PSa)6C60PSb or (PS)6C60PI. At its end, the out-growing chain bears a carbanion that has been allowed to react with the coupling agents dibromo-p-xylene and dibromohexane to produce the dumbbell-like structures, (PSa)6C60PSb-pX-PSbC60(PSa)6 and (PS)6C60PI-Hex-PIC60(PS)6. If C60 itself is allowed to react with the “living” palm tree, a third fullerene molecule is introduced in the center of the macromolecular architecture.

Electron Transfer Studies With Fullerenes Incorporated Into Artificial Lipid Bilayer Membranes

A systematic variation of functionalizing addends, covalently linked to the fullerene core, has been probed in light of facilitating fullerene incorporation into artificial lipid bilayer membranes. Electron transfer studies, by means of time-resolved pulse radiolysis, show that structurally balanced fullerene derivatives were successfully incorporated into various vesicular matrices which, in turn, enabled a very efficient fullerene reduction by hydrated electrons and *CH 2 OH radicals.

Similarity of glass transition anomalies in fullerene core polymer stars and block copolymers

Glass transitions have been studied by differential scanning calorimetry (DSC) in atactic polystyrene (PS) and polydimethylsiloxane (PDMS), when covalently attaching their chains differing in length to `rigid walls,' fullerene C 60 (or C 70) `balls' in stars or polyimide (PI) blocks in block copolymers. A number of common anomalies were observed including complication and multiple broadening of the glass transition range, both to higher and lower temperatures, decreases in activation parameters, arising out of the heterogeneity of segmental dynamics. The results are interpreted as proceeding from (a) the common segmental origin of α- and β-relaxations and a breakdown of intermolecular cooperativity of segmental motions; (b) confinement of chains to nanometer-scale spaces, and (c) the `rigid wall' effect.

Matrix-assisted laser-induced gas-phase aggregation of C 60 oxides

Matrix-assisted laser desorption/ionisation of C 60 oxides, in conjunction with reflectron time-of-flight mass spectrometry, leads to an unprecedented gas-phase aggregation resulting in the formation of C 120O n − · . products. The analysis of the product distribution obtained for oxides of varying oxygen content strongly suggests that the structures of these species are closely related to oxo-bridged isolated fullerene cages rather than to species featuring a fused giant fullerene core.

Synthesis and Electrochemical Properties of New C60-Acceptor and -Donor Dyads

The synthesis of new C60-acceptor and C60-donor dyads 6−8 by facile and irreversible [4+2]cycloadditions of anthraquinone- and anthraquinodimethane-based dienes with C60, as well as by direct oxidative amination of C60 with N, N′-dimethyl-o-phenylenediamine is described. The complete electrochemical characterization and ESR-spectroscopic data of the C60-acceptor dyads allows an unambiguous assignment of the location of each reduction step to one or other of the electroactive groups. The locations of the first oxidation and reduction events in all type A and -B systems investigated in this study correspond to the PM3-calculated HOMOs of the neutral species or the SOMOs of the singly reduced species. Whereas the anthraquinone moiety in 6 is a weaker acceptor than C60, the introduction of the more electron-withdrawing cyanoimino groups at the 9,10-positions of the anthracene unit in the dyad 7 causes the first reduction to take place on the addend. This experimental and computational study has shown that both the C60-acceptor dyad 7 and the C60-donor dyad 8 are suitable precursors for the synthesis of the proposed type-D triads, which contain both a donor and an acceptor building block attached to the fullerene core in a stereochemically defined arrangement.

ChemInform Abstract: Macrocyclization on the Fullerene Core: Direct Regio‐ and Diastereoselective Multi‐Functionalization of [60]Fullerene, and Synthesis of Fullerene‐Dendrimer Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.