Konstantinos Kordatos

Controlled production of aligned-nanotube bundles

Carbon nanotubes might be usefully employed in nanometre-scale engineering and electronics. Electrical conductivity measurements on the bulk material, on individual multi-walled and single-walled nanotubes and on bundles of single-walled nanotubes have revealed that they may behave as metallic, insulating or semiconducting nanowires, depending on the method of production—which controls the degree of graphitization, the helicity and the diameter. Measurements of Youngs modulus show that single nanotubes are stiffer than commercial carbon fibres. Methods commonly used to generate nanotubes—carbon-arc discharge techniques, catalytic pyrolysis of hydrocarbons and condensed-phase electrolysis—generally suffer from the drawbacks that polyhedral particles are also formed and that the dimensions of the nanotubes are highly variable. Here we describe a method for generating aligned carbon nanotubes by pyrolysis of 2-amino-4,6-dichloro-s-triazine over thin films of a cobalt catalyst patterned on a silica substrate by laser etching. The use of a patterned catalyst apparently encourages the formation of aligned nanotubes. The method offers control over length (up to about 50 μm) and fairly uniform diameters (30–50 nm), as well as producing nanotubes in high yield, uncontaminated by polyhedral particles.

Langmuir–Blodgett and layer-by-layer films of photoactive fullerene–porphyrin dyads

The fabrication of high quality, robust and photoactive ITO electrodes—in the form of well-defined two- and three-dimensional films—is reported following the Langmuir–Schafer (LS) and the layer-by-layer (LBL) methods. In the LS approach C60-NiP multilayers were transferred from the air–water interface, while the LBL approach utilizes electrostatic and van der Waals interactions for the step-by-step deposition of individual C60-NiP molecules out of solution. These complementary techniques allow control over the thickness and composition of the films at a molecular level and guarantee the specific alignment and the orientation of the incorporated donor–acceptor system. Modified ITO electrodes were probed in photocurrent experiments, in which the LBL-modified electrodes reveal smaller photon to current conversion efficiencies relative to the LS-modified electrodes.

Absorption spectra of the mono-adduct and eight bis-adduct regioisomers of pyrrolidine derivatives of C60

Abstract Absorption spectra of the pyrrolidine N -mTEG (mTEG=CH 2 CH 2 OCH 2 CH 2 OCH 2 CH 2 OCH 3 ) mono-adduct and eight bis-adducts of C 60 were studied in the 230–800 nm spectral range. The five-membered ring adducts contain an apex nitrogen atom. A theoretical discussion in terms of the effective electronic structures and transitions of these species shows that a filiation between spectra of C 60 , and its pyrrolidine mono- and bis-adduct derivatives can be expected and rationalised. Allowed transitions in the ultraviolet are related to fullerene core electronic transitions and are observed to be little affected in energy and in transition strength by the mono-adduct, apart from band splitting or broadening associated with the lowered molecular symmetry with respect to C 60 , whereas in the visible region, the transitions related to C 60 forbidden transitions are significantly modified by the adduct. The bis-adducts have similar general spectral behaviour to that of the mono-adduct, with differences that reflect the relative position of the two addends but are found to be not dependent on membership of any of the three formal symmetry groups into which the bis-adducts can be classified. The second pyrrolidine adduct reinforces the perturbation of the forbidden and, to a lesser extent, the allowed transitions of the fullerene core. From a comparison with the spectra of C 60 [C(COOEt) 2 ] and its bis-adducts, it was concluded that the N atom in the pyrrolidine five-membered ring adduct is a less efficient blocker of through-bond and/or through-space communication than the sp 3 carbon atom in Bingel–Hirsch methanofullerenes.

A glutathione amperometric biosensor based on an amphiphilic fullerene redox mediator immobilised within an amphiphilic polypyrrole film

A novel biosensor for the amperometric detection of glutathione is proposed in which glutathione reductase is coupled to a pyrrolofullerene bis-adduct playing the role of redox mediator between electrode and enzyme. The adoption of a simple procedure for realizing the immobilization of the redox mediator, together with the enzyme, within a polypyrrole film cast onto a glassy carbon electrode, was made possible by the amphiphilic properties of the fullerene derivative. The biosensor showed a fast and reproducible response to glutathione and, because of its lower sensitivity, a wider linear range with respect to a similar device based on a diffusional redox mediator.

Triplet state properties of N-mTEG(60)fulleropyrrolidine mono and bisadduct derivatives

Abstract Laser flash photolysis and pulse radiolysis techniques were used to determine triplet state properties of N -mTEG[60]fulleropyrrolidine mono and bisadduct derivatives (FP) (mTEG=CH 2 CH 2 OCH 2 CH 2 OCH 2 CH 2 OCH 3 ) in benzene. These properties include the triplet absorption spectra between 550 and 900 nm, quantum yields of triplet photosensitized singlet oxygen production ( Φ Δ ) and triplet molar absorption coefficients ( e T ) with the assumption that the quantum yield of triplet formation ( Φ T ) is equal to Φ Δ . Our results demonstrate that the triplet properties depend on the number of addends and the addition pattern.

Cathodoluminescence of fullerene C60

Fullerenes are not automatic candidates for luminescence analyses due to their highly absorptive nature. Consequently, very few luminescence experiments have been performed on fullerenes. This paper focuses on the luminescence properties of commercially available C60 when bombarded by electrons (cathodoluminescence) and, to a lesser extent, x-rays (radio- thermoluminescence) between 20 and 270 K. Wavelength resolved luminescence signals have been recorded as a function of temperature. CL experiments reveal pronounced anomalies that truncate the emission spectrum between 155 and 170 K. Other less pronounced anomalous features are detected at 70 and 245 K. These dramatic changes in the luminescence spectra are cautiously interpreted to be manifestations of phase transitions and support the view that cathodoluminescence (CL) can be used to monitor for phase transitions in fullerenes. The luminescence signals offer information on the mechanisms of the relaxation processes, including changes in charge trapping energies and emission spectra.

Neutron diffraction study of the polymeric structure of

High-resolution neutron powder diffraction is used to authenticate that the fulleride undergoes on cooling an incomplete structural phase transition from a primitive cubic to a monoclinic phase (space group , lattice constants at 2.5 K: a = 13.707(2) A, b = 14.466(2) A, c = 9.366(1) A, ). Very short interfullerene C-C contacts are identified, providing evidence for the presence of bridging bonds whose distances refine to A. The C-C bonds are inclined to the c axis by and lie within the bc plane. The stability of the ground state polymeric structure and the kinetics of the monomer polymer transformation are influenced by the charge state of the fulleride ions, the steric crowding associated with the dopant alkali ions and the relative orientational state adopted by neighbouring fullerides in the precursor monomer phase.

Synthesis of Fullerene Derivatives for Incorporation in Sol-Gel Glasses

We report on the synthesis of fullerene derivatives containing a trialkoxysilane moiety that exhibit enhanced solubility in solvents commonly used for sol-gel processing. These derivatives have been successfully embedded in glassy bulk samples and thin films that show very promising optical limiting properties.

Electrochemical properties of soluble fullerene derivatives

Abstract The family of fullerene derivatives obtained by 1,3-dipolar cycloaddition of azomethine ylides to C 60 is colloquially termed fulleropyrrolidines. In this paper, we report the synthesis and the electrochemical properties of a series of fulleropyrrolidine derivatives. All compounds are characterized by the presence of a solubilizing mTEG group. In addition, a derivative containing a thiophene moiety, covalently attached to the pyrrolidine ring has been studied. Cyclic voltammetry measurements, performed also at low temperatures, allowed the observation of five fullerene-centered reductions for all the species. Adsorption phenomena, however, were found associated to the last reduction processes in the thiophene–fulleropyrrolidine conjugate. Moreover, thanks to the increased solubility of the latter species in polar solvents (acetonitrile–dichloromethane mixtures) its anodic polymerization was carried out, leading to a conducting film still retaining the redox properties of the fullerene derivative.

Novel Functional Fullerene Materials: Fullerenes as Energy Acceptors

Summary. Fullerene derivatives exhibit absorption throughout the UV/Vis region up to 750 nm. This feature is important for easy excitation. Once excited, fullerenes may become both electron and energy acceptors. The distinction between these two pathways depends strongly on the partner involved (donor) and on the conditions employed (solvent, etc.).