Fullerene Moiety Research Articles

TR-EPR of single and double spin-labeled C60 derivatives in frozen matrices

Time-resolved electron paramagnetic resonance spectra of two single spin-labeled and two double spin-labeled C60 derivatives in frozen solution are recorded with pulsed laser excitation and 100 ns time resolution. Quartet and quintet excited species are detected which arise from the electron spin coupling of the triplet excited fullerene moiety with the unpaired spin(s) of the nitroxide label(s). Despite the similar molecular structure, in both series of single and double labeled derivatives a different behavior was found, which is due to substantial difference of the energy of exchange coupling.

Synthesis, Photophysical and Photovoltaic Properties of New [60]Fullerene Pyrrolidine Derivatives

Two new [60]fullerene pyrrolidine derivatives 2 and 3 were synthesized and characterized by 1H NMR, 13C NMR and MS. Their photophysical processes have been investigated by using laser flash photolysis. The experiments show quenching of oligomer singlet excited state and the evidence of the fullerene singlet excited emission. And the intramolecular of electron transfer and also energy transfer of 2 and 3 occurred and the triplet excited state of fullerene moiety in 2 and 3 have different lifetime due to their different structures. A photovoltaic device using compound 2 as the only photoactive material has also been investigated which showed the energy conversion efficiency is 0.011%.

Synthesis of fullerene-substituted oligo(phenylenebutadiyndiyl)

A diethynylbenzene monomer substituted with two fullerene moieties has been prepared, and its oligomerization performed in the presence of phenylacetylene as end-capping reagent afforded the corresponding end-capped mono- and di-mer with an oligo(phenylenebutadiyndiyl) (OPB) conjugated backbone substituted with two and four fullerene subunits, respectively.

Prolongation of the Lifetime of the Charge-Separated State at Low Temperatures in a Photoinduced Electron-Transfer System of [60]Fullerene and Ferrocene Moieties Tethered by Rotaxane Structures

A rotaxane tethering both fullerene (C60) and ferrocene (Fc) moieties (abbreviated as (C60;Fc)rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C60;Fc)rotax+, the C60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C60 and Fc in (C60;Fc)rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C60*-;Fc*+)rotax+ is formed mainly via the excited triplet state of C60 in polar solvents. The lifetime of (C60*-;Fc*+)rotax+ was evaluated to be 20 ns in dimethylformamide (DMF) at room temperature. With lowing temperature, the lifetime of (C60*-;Fc*+)rotax+ extends to 270 ns in DMF at -65 degrees C, due to the structural changes leaving C60*- and Fc*+ at a relatively long distance in the low-temperature region.

Redox Active Two-Component Films of Palladium and Covalently Linked Zinc Porphyrin–Fullerene Dyad

Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C60 covalently linked to zinc meso-tetraphenyloporphyrin, ZnPC60, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnPC60/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties.

Photophysical and Electrochemical Properties of meso,meso‐Linked Oligoporphyrin Rods with Appended Fullerene Terminals

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Photocurrent increase by doping a liquid crystal host with a functionalized fullerene

Doping a photoconductive mesogenic material with a small amount of functionalized fullerene significantly increases the photocurrent. LESR studies show the appearance of a long‐lived charge‐separated state under light illumination, with a negative charge on the fullerene moiety. This confirms that in the system studied the fullerene unit acts as an electron trap. In the lamellar structure of the liquid crystalline phase the fullerene units and mesogenic cores are separated, which ensures better space separation between negative and positive charges. As a result the charge recombination is slowed and the photocurrent is amplified.

Resonance Energy Transfer in New Fullerene–Coumarin Diads

The fluorescence properties of new [60] and [70] fullerene-coumarin diads are studied. These diads were synthesized by covalently linking a coumarin dye to a fullerene (C60 or C70) by a cyclopropanation reaction. The absorption and fluorescence spectra, quantum yields and lifetimes of the diads are reported. The fluorescence quenching of the coumarin moiety by the fullerene was observed in all diads, indicating the occurrence of resonance energy transfer between the coumarin and fullerene moieties.

Conformations and Electronic Structures of Axially Coordinated Fullerene−Porphyrin−Fullerene Triad (C60CHCOO)2−Sn(IV) Porphyrin

The conformational (cis and trans) stability and electronic structures of (C(60)CHCOO)(2)-Sn(IV) porphyrin, recently synthesized as a novel fullerene-porphyrin-fullerene triad linked by metal axial coordination, have been studied by ab initio calculations. The cis conformer was found to be slightly more stable than the trans by 1.38 kcal/mol in the neutral compound. Upon the addition of an electron to the triad, the relative stability of the cis conformer was found to be higher (3.29 kcal/mol) than that in the neutral one. From the investigation of frontier molecular orbitals, for the cis conformer, it was found that the electrons are localized in HOMO of the porphyrin, while the electrons are localized in LUMO of the syn-fullerene. For the trans conformer, it was found that the electrons are localized in HOMO of the porphyrin, while the electrons are localized in LUMO of one of the two fullerene moieties, and the electrons are localized in LUMO2 of the other fullerene moiety, but the LUMO and LUMO2 have the same orbital energy. Thus, the PET may take place unidirectionally in the cis conformer from the porphyrin to the syn-fullerene, while it is bidirectional from the porphyrin to both of the fullerene moieties.

Electron and Energy Transfer in Rotaxanes and Catenanes Incorporating Fullerene, Porphyrin and Ferrocene Moieties

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Porphyrin–fullerene photosynthetic model systems with rotaxane and catenane architectures

Abstract Routes for the synthesis of a series of [2]rotaxanes and [2]catenanes incorporating porphyrin, ferrocene and fullerene moieties by the Sauvage metal template technique are described. Photophysical studies on these materials show that excitation of the porphyrin component causes a series of events along an energy gradient leading to long-lived long distance charge-separated radical pair states with lifetimes as long as 32 μs in tetrahydrofuran solution at ambient temperatures. To cite this article: D.I. Schuster et al., C. R. Chimie 9 (2006) .

60]Fullerene–acene chemistry: a review

Abstract Acenes represent interesting platforms on which to add [60]fullerenes via Diels–Alder cycloaddition reactions. For unsubstituted acenes, the most reactive positions are the center-most rings. Large acenes can accommodate more than one [60]fullerene cycloaddition and these reactions become facile once suitable directing substituents (e.g. phenyl groups) are added to the acene. In these cases, [60]fullerenes add in a syn-diastereoselective fashion due to favorable π–π stacking interactions between adjacent [60]fullerene moieties. The π–π stacking interactions provide further stabilization to these adducts. Several cis-bis[60]fullerene–acene adducts have been prepared in modest to excellent yield and one cis,cis-tris[60]fullerene–heptacene adduct has also been prepared. To cite this article: J.B. Briggs and G.P. Miller, C. R. Chimie 9 (2006).

PH-responsive, self-assembling nanoparticle from a fullerene-tagged poly(l-glutamic acid) and its superoxide dismutase mimetic property

In this study, we describe the fabrication of novel fullerene-containing peptide-nanoparticles through self-assembly. A water-soluble, poly(l-glutamic acid)-attached fullerene was newly synthesized and the conformation and self-assembling property in water were examined by using circular dichroism, FTIR, UV, atomic force microscopy, and dynamic light scattering measurements. In the lower pH region (<6.8), the fullerene peptide self-assembles into nanoparticles that are ca. 100–200 nm in diameter. These nanoparticles are rich in α-helices, and stacking interaction of fullerene moieties contributes to the stability of the high-order structure. In addition, these particle sizes can be easily controlled by changing pH that results in causing the conformational transition of PLGA segment. Finally, the fullerene-containing nanoparticle is confirmed to be capable of removing the biologically important superoxide radical in comparison with the superoxide dismutase.

Synthesis and fluorescence properties of [60] and [70]fullerene–coumarin dyads: Efficient dipole–dipole resonance energy transfer from coumarin to fullerene

New [60] and [70]fullerene–coumarin dyads were prepared by covalently linking a coumarin dye to a fullerene (C60 or C70) via a 1,3-dipolar cycloaddition reaction of azomethine ylides or by a cyclopropanation reaction of fullerenes with malonate derivatives. These dyads were spectroscopically characterized and their fluorescence properties studied. Fluorescence quenching of the coumarin fluorophore in the dyads results from efficient dipole–dipole resonance energy transfer from the coumarin moiety to the fullerene moiety.

Synthesis and characterization of photoresponsive diphenylaminofluorene chromophore adducts of [60]fullerene

A class of acceptor–keto–donor structures as hindered 9,9-di(3,5,5-trimethylhexyl)-2-diphenylaminofluoreno-methano[60]fullerene C60(>DPAF-C9) and the related bisadducts C60(>DPAF-C9)2 and C60(>DPAF-C2)2 were synthesized. They are derivatives of multiphoton absorptive C60(>DPAF-C2) showing enhanced cross-sections of simultaneous two-photon absorption under laser excitation at 800 nm in nanosecond region. Molecular synthesis of these C60–DPAF conjugates involved the covalent attachment of a diphenylaminofluorene moiety to methano[60]fullerene via a keto linkage for increasing molecular acceptor–donor polarization of the chromophore in conjunction with the fullerene cage. Preparation of 7-(1,2-dihydro-1,2-methanofullerene[60]-61-carbonyl)-9,9-dialkyl-2-diphenylaminofluorene C60(>DPAF-Cn) involved cyclopropanation of C60 with a key synthon 7-α-bromoacetyl-9,9-dialkyl-2-diphenylaminofluorene. Synthesis of this synthon was achieved by a three-steps procedure starting from 2-bromofluorene via dialkylation at C9 of the fluorene ring, attachment of a diphenylamino group at C2 of dialkylfluorene, and Friedel–Craft acylation of the α-bromoacetyl group at C7 of diphenylaminofluorene. All C60–DPAF derivatives were fully characterized with the chemical structures confirmed by various spectroscopic analyses and validated by the single-crystal structural analysis data of C60(>DPAF-C2). Strong solvent-sensitive fluorescence quenching phenomena of C60(>DPAF-C2), C60(>DPAF-C9), and C60(>DPAF-C9)2 were noticed, showing no fluorescence band above 700 nm in more polar solvents, such as DMF, PhCN, and THF, while in less polar solvents (toluene, CHCl3, and CS2) a fullerenyl fluorescence band at 700–710 nm was observed. It was attributed to the occurrence of electron transfer via the singlet excited state of the fullerene moiety 1C60*(>DPAF-Cn) in the former group of the solvents. On the contrary, energy transfer processes from DPAF-Cn moiety to the fullerene cage are favored in the latter group of the solvents.

Photoinduced Processes in a Tricomponent Molecule Consisting of Diphenylaminofluorene−Dicyanoethylene−Methano[60]fullerene

Photoinduced intramolecular processes in a tricomponent molecule C60(>(CN)2-DPAF), consisting of an electron-accepting methano[60]fullerene moiety (C60>) covalently bound to an electron-donating diphenylaminofluorene (DPAF) unit via a bridging dicyanoethylenyl group [(CN)2], were investigated in comparison with (CN)2-DPAF. On the basis of the molecular orbital calculations, the lowest charge-separated state of C60(>(CN)2-DPAF) is suggested to be C60*-(>(CN)2-DPAF*+) with the negative charge localized on the fullerene cage, while the upper state is C60(>(CN)2*--DPAF*+). The excited-state events of C60(>(CN)2-DPAF) were monitored by both time-resolved emission and nanosecond transient absorption techniques. In both nonpolar and polar solvents, the excited charge-transfer state decayed mainly through initial energy-transfer process to the C60 moiety yielding the corresponding 1C60, from which charge separation took place leading to the formation of C60*-(>(CN)2-DPAF*+) in a fast rate and high efficiency. In addition, multistep charge separation from C60(>(CN)2*--DPAF*+) to C60*-(>(CN)2-DPAF*+) may be possible with the excitation of charge-transfer band. The lifetimes of C60*-(>(CN)2-DPAF*+) are longer than the previously reported methano[60]fullerene-diphenylaminofluorene C60(>(C=O)-DPAF) with the C60 and DPAF moieties linked by a methanoketo group. These findings suggest an important role of dicyanoethylenyl group as an electron mediating bridge in C60(>(CN)2-DPAF).

Synthesis of fullerohelicates and fine tuning of the photoinduced processes by changing the number of addends on the fullerene subunits

Two fullerene-substituted m-phenylene-bis-phenanthroline ligands have been prepared. The synthesis of the first derivative ( L1 ) is based on an esterification reaction between a C s symmetrical cis-2 fullerene bis-adduct bearing a carboxylic acid function and a bis-phenanthroline alcohol ( 5 ). The second ligand ( L2 ) has been obtained by reaction of a bis-phenanthroline malonate ( 9 ) and C 60 under Bingel conditions. The copper(I) complexes of L1 and L2 have been prepared by treatment with a slight excess of Cu(CH 3CN) 4BF 4. NMR spectroscopy and mass spectrometry analysis have unambiguously shown that these complexes are bis-copper(I) helicates substituted with two fullerene moieties. The photophysical properties of the copper(I) complexes Cu 2(L1) 2 and Cu 2(L2) 2 have been investigated. In both systems photoinduced electron transfer from the central metal-complexed unit to the external fullerenes may occur, in principle, by excitation of both moieties. However, this is found to be the case only for the methanofullerene system Cu 2(L2) 2 . Unexpectedly, for Cu 2(L1) 2 , photoexcitation of the peripheral carbon spheres is followed by regular internal deactivation. Possible reasons for this behavior are examined in light of current theories for photoinduced energy and electron transfer.

Supramolecular complexes obtained from porphyrin–crown ether conjugates and a fullerene derivative bearing an ammonium unit

A methanofullerene derivative with an ammonium subunit ( 1 ) has been prepared and its ability to form a supramolecular complex with a porphyrin–crown ether conjugate evidenced by NMR, UV–vis, electrospray mass spectrometry (ES-MS) and luminescence experiments. Interestingly, in addition to the ammonium–crown ether recognition, intramolecular stacking of the fullerene moiety and the porphyrin subunit has been evidenced. Due to this additional recognition element, the association constant for the supramolecular complex is increased by two orders of magnitude when compared to the K a values found for the complexation of 1 with benzo-18-crown-6. Finally, non-covalent systems resulting from the association of cation 1 with porphyrin derivatives bearing two crown ether subunits have been investigated. Intramolecular C 60–porphyrin interactions have also been evidenced within these supramolecular complexes. As a result, the 2:1 complexes are very stable as shown by the ES-MS studies.

Self-assembly of a C60 derivative bearing an ammonium unit with porphyrin-crown ether conjugates

Our recent progresses in the synthesis and the study of supramolecular porphyrin-fullerene conjugates are reported. In particular, we show that π-stacking of the two chromophores can have a dramatic effect on recognition interactions in non-covalent C 60-porphyrin ensembles. Specifically, a supramolecular complex has been obtained from a porphyrin-crown ether conjugate and a methanofullerene derivative bearing an ammonium function. In addition to the ammonium-crown ether interaction, intramolecular stacking of the fullerene moiety and the porphyrin subunit has been evidenced in the supramolecular system. Due to this additional recognition element, the association constant ( K a ) for the complex is increased by two orders of magnitude when compared to K a values previously found for complexation of the fullerene-ammonium derivative with other crown ethers. Finally, non-covalent systems resulting from the association of the fullerene-ammonium derivative with porphyrins bearing two crown-ether subunits have been investigated. Intramolecular C 60-porphyrin interactions have also been observed within these supramolecular arrays. As a result, the 2:1 complexes are very stable.

Fullerene non-linear excited state absorption induced by gold nanoparticles light harvesting

Au nanoparticles can be synthesized in solution by a laser ablation methodology which allows to obtain funtionalized metal nanoparticles with a disulfide fullerene derivative in a simple one step process. The supramolecular system is shown to be an efficient non-linear absorbers of 532 nm nanosecond laser pulses. The mechanism of the non-linear absorption is shown to proceed through a light harvesting step by the metal nanoparticles and an efficient energy transfer to the fullerene moieties which absorb in a non-linear regime through their triplet states.