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We present a study of the static polarizability for the tubular fullerenes C60 + i · 10, where i = 0–5, and the closely related [5,5] carbon nanotube, using time-dependent (current)-density-functional theory. Comparing the results obtained within the conventional adiabatic local-density approximation with those obtained using the Vignale–Kohn current-dependent exchange-correlation functional it is found that the extra long-range exchange-correlation effects described by the current-density functional are important to consider, especially for the longest fullerenes. For all systems studied the current-density functional results are in good agreement with experiment, and the agreement with available ab initio self-consistent-field results and results from a point–dipole interaction model is much better than when using the adiabatic local-density functional. � 2004 Elsevier B.V. All rights reserved.

We report the synthesis of a novel charge-transporting polymer based on the charge-transport unit N,N‘-diphenyl-N,N‘-bis(3-methylphenyl)-[1,1‘-biphenyl]-4,4‘-diamine (TPD). Introducing approximately 30 wt % of the liquid electro-optic molecule 4-(N,N-diethylamino)-2-fluoro-(Z)-β-methyl-(E)-β-nitrostyrene (FDEAMNST) and small amounts of C60 makes this polymer photorefractive. A full photorefractive characterization is presented. In this composite a rather large electro-optic effect is observed due to the efficient plasticization by the electro-optic molecules of the host polymer. The diffraction efficiency and gain coefficient (3.4% and 50 cm-1, respectively) are rather low. This is attributed to a low space-charge field due to a very low trap density, which is in agreement with a 90° phase-shift between the illumination pattern and the refractive index grating. To increase the trap density, molecules with a low ionization energy were dispersed in the composite.

Unlike the addition of a second equivalent of diazoalkane to C60, which does not show marked selectivity, the addition of azides to C60 shows chemo and regio selectivity [4]. Utilization of this unique selectivity, led us to the preparation of the first heterofullerene ‘C59N’ in bulk quantity [5, 6]. Herein we report on its synthesis and mechanism of formation. We also describe the application of this procedure for the formation of higher heterofullerene analogs, i.e. ‘C69N’ isomers [7] and introduce methodology that opens a viable route to the functionalization of azafullerenes [8]. The azafullerene (C59N)2 can be synthesized from C60 in three steps. The initial step in the formation of azafullerenes is the 1,3-dipolar cycloaddition of 2methoxyethoxymethyl azide (MEM-azide) [9]. Not unlike the addition of diazoalkane, the addition of an alkyl azide to C60 occurs across the [6,6] bond. At room temperature, the initially formed triazoline can be isolated in 35-40% yield. Thermolysis of the triazoline, followed by concomitant loss of nitrogen, gives rise to azafulleroids and fulleroaziridines. Fulleroaziridines and azafulleroids can also be obtained directly from C60 at higher reaction temperatures (160-180°C).

The photocurrent in conjugated polymer-fullerene blends is dominated by the dissociation efficiency of bound electron-hole pairs at the donor-acceptor interface. A model based on Onsager's theory of geminate charge recombination explains the observed field and temperature dependence of the photocurrent in $\mathrm{P}\mathrm{P}\mathrm{V}\ensuremath{\mathbin:}\mathrm{P}\mathrm{C}\mathrm{B}\mathrm{M}$ blends. At room temperature only 60% of the generated bound electron-hole pairs are dissociated and contribute to the short-circuit current, which is a major loss mechanism in photovoltaic devices based on this material system.

We have studied the morphology of different heterogeneous samples containing poly [2-methoxy,5-(3',7'-dimethyl-octyloxy)]-p-phenylene-vinylene (MDMO-PPV) and either fullerene (C(60)) or 6,6-phenyl C(61)-butyric acid methyl ester (PCBM) using atomic force microscopy in the shear force detection mode or pulsed-force mode and near-field scanning optical microscopy. These investigations confirm the large influence of preparation conditions on the morphology. Systematic variation of the layer thicknesses in two-layer samples indicate that fluoresecence quenching is restricted to ail interface layer with a thickness of about 40 nm. (C) 2003 Published by Elsevier B.V.

The heterofullerene ion C(59)N(+) is formed efficiently in the gas phase during fast atom bombardment mass spectroscopy of a cluster-opened N-MEM (N-methoxyethoxy methyl) ketolactam. This transformation is shown to occur also in solution in the presence of strong acid, affording biazafullerenyl (C(59)N)(2) in good yield. It is proposed that the azafullerene dimer is formed upon in situ reduction of the highly reactive azafulleronium ion. The isolation and characterization of biazafullerenyl opens a viable route for the preparation of other heterofullerenes in solution.

Fullerene and azafullerene films were studied by electron energy loss spectroscopy in reflection geometry. Compared to C 60 , (C 59 N) 2 multilayers show additional vibrational modes that are characteristic of the dimer structure. The (C 59 N) 2 is semiconductor-like and giant optically allowed excitonic transitions are found in the gap in drastic contrast with C 60 . The azafullerene monolayer on Cu(1 1 1) no longer shows the presence of dimers, indicating monomer adsorption. Similarly to C 60 , azafullerene molecules in contact with the metal substrate receive a transferred charge between two and three electrons. However, the C 59 N appears more covalently bound to Cu because it decomposes when heated above 660 K while C 60 only desorbs.

Ultrafast spectroscopic studies using an optical excitation of a conjugated polymer by sub-10-fs pulses are reported. Phonon modes which are strongly coupled to the electronic excitation of the conjugated polymer are directly observed as coherent oscillations during the pump-probe experiment, mirroring the resonant/nonresonant Raman spectrum of the conjugated polymer. In composites of a conjugated polymer with a fullerene the primary photoexcitation is found to be an ultrafast photoinduced electron transfer. We are able to time resolve for the first time the kinetics of this charge transfer process with a forward transfer time of around tau (et) similar to 45 fs.

The emission of small (hydrogenated) carbon cluster ions: CnHm+ (n = 2-22) upon highly charged Xeq+ (q = 20- 14) impact on C-84 surfaces is studied by means of time-of-flight secundary ion mass spectrometry. The respective stage of hydrogenation/protonation of a certain carbon cluster ion C-n(+) is a strong indication for its geometrical structure. From the cluster ion yield as a function of cluster size it can be concluded, that the hydrogenation takes place after the initial carbon cluster formation. The carbon clusters seem to be emitted as art entity in agreement with "equilibrium" and "shock wave" models.

In this contribution we discuss photo-induced electron transfer in conjugated polymer/fullerene composites and compare this with light induced effects in pure components. Two overlapping LESR lines are observed, from positive polarons on the polymer chains and negative charges on the fullerene moieties. Microwave power saturation studies show different relaxation times for these two spins, giving clear evidence for independent spins. The unusually high relaxation rate of the fullerene monoanionic spins is of intrinsic origin and discussed in terms of a splitting of the T 1u level by a Jahn-Teller type distortion as proposed in the literature. We observed two distinct contributions to LESR signals, a prompt and a persistent one. Excitation light intensity dependence of the prompt contributions into P + and C 60 − ESR signals is of bimolecular type (I 0.5 ) and implies the mutual annihilation within (P + …C 60 − ) pair. The persistent contribution is found to be excitation intensity independent and proposed to originate from deep traps due to disorder.

We present studies of the electronic structure of polymerized orthorhombic and dimerised using electron energy-loss spectroscopy in transmission. From the C1s excitation spectra a reduced density of π ? states is ob- served for polymerized . This is in contrast to and can be explained by the different type of 'doping' and by the different bonding between the fullerene molecules in the two systems. Additional information about the optical prop- erties was obtained from the low energy loss function. Using a Kramers-Kronig analysis, the dielectric function, (e), and the optical conductivity, (σ), have been derived. e and the onset of the spectral weight have been compared between the polymer, the dimer and . This onset of spectral weight is found to be at : and : for o- and for , respectively.

One approach to endohedral complexes would comprise controlled opening of the fullerene, encapsulation of the guest material, and restoration of the original fullerene structure, a strategy that Hawkins very likely considered in his pioneering work on osmylation of C{sub 60} and C{sub 70}. Here we report the first regioselective and efficient synthetic method for severing two adjacent bonds in C{sub 60}. Reaction of C{sub 60} with azides yields [5.6]azafulleroids in good yields. In the azafulleroid, one C-C bond is cleaved and the C=C bonds adjacent to the nitrogen atom are susceptible to regiospecific formation of bisazafulleroids. The previously reported elegant work on the self-sensitized photooxygenation of certain C{sub 60} adducts was applied to N-methoxyethoxymethyl (MEM)-substituted [5.6]azafulleroid 1 to afford the ring-opened N-MEM-ketolactam 3 in high yield. Compound 3 is stable under the reaction conditions; no new products were detected after 4 h of photooxygenation in ODCB at 25-30{degree}C. Thereafter, methylene blue was added as a sensitizer, and the photooxygenation was resumed; no further reaction occurred within 5 h. The work presented here can be considered a first step toward the controlled opening of the fullerene cage. 14 refs., 1 fig.

It is well known that many non-degenerate ground state conjugated polymers like PPV derivatives show an ultrafast electron transfer to fullerenes upon photoexcitation. In this work we investigate the photoexcited states of fullerene - carbazolyl substituted PDA composites and compare them to the pristine components. We report the finding of photoexcited spins as well as charges in one asymmetric carbazolyl substituted PDA, the CPDO (poly(1-N-carbazolyl-penta-1,3-diyne-5-ol)). While PIA FTIR measurements show strong IRAV bands for this material, LESR studies on the same samples reveal photoexcited spins. Although CPDO samples show a dark ESR signal, which is well known for the topochemical polymerization, photoexcitation studies clearly reveal, that the LESR does not come from photoinduced polymerization. No enhancement of LESR signal is found for mixtures of CPDO and fullerenes, in our case a special solubilized fullerene, PCBM. We conclude therefore, that even PDA which show photoexcited charges and spins, do not exhibit a photoexcited charge transfer to fullerenes.

The enantiomers of the first cagewise inherently asymmetric C 60 derivative, i.e. N-MEM (MEM = 2-methoxyethoxymethyl) keto lactam 1, have been separated by HPLC and their chiroptical properties compared with data obtained from C 60 derivatives that are dissymmetric or asymmetric due to chiral addends.

We present electron energy-loss spectroscopy studies in transmission of the electronic structure of (C59N)2. The overall broadening observed for the π-derived structures in the low energy-loss function of (C59N)2 when compared to C60 is due to the reduced symmetry of the heterofullerene. The optical gap of (C59N)2 is about 1.4 eV, slightly smaller than that of C60 (1.8 eV). Using a Kramers-Kronig analysis the dielectric function in the low energy region was calculated. A static dielectric function at zero energy of ∼ 5.6 is found.