David A. Britz

Noncovalent interactions of molecules with single walled carbon nanotubes

In this critical review we survey non-covalent interactions of carbon nanotubes with molecular species from a chemical perspective, particularly emphasising the relationship between the structure and dynamics of these structures and their functional properties. We demonstrate the synergistic character of the nanotube-molecule interactions, as molecules that affect nanotube properties are also altered by the presence of the nanotube. The diversity of mechanisms of molecule-nanotube interactions and the range of experimental techniques employed for their characterisation are illustrated by examples from recent reports. Some practical applications for carbon nanotubes involved in non-covalent interactions with molecules are discussed.

Low temperature assembly of fullerene arrays in single-walled carbon nanotubes using supercritical fluids

Molecules assembled inside nanotubes to form 1D arrays exhibit functional properties different to the bulk crystal and have been proposed for many applications ranging from catalysis to quantum computing. We have discovered that single-walled carbon nanotubes can be efficiently filled with fullerenes in supercritical fluids at temperatures as low as 30–50 °C. Despite the low solubility of fullerenes in supercritical fluids, the nanotube filling was particularly effective in supercritical carbon dioxide producing Cn@SWNT structures in 70% yield at 50 °C. This method was also applied for functionalized and endohedral fullerenes and allows insertion of thermally unstable molecules which would be impossible to insert in nanotubes using standard techniques. We discuss the advantages of using supercritical fluids as compared to conventional solvents and propose mechanisms for fullerene encapsulation at low temperatures.

Selective host–guest interaction of single-walled carbon nanotubes with functionalised fullerenes

Exohedrally functionalised fullerenes have been inserted in single-walled carbon nanotubes (SWNTs) with the aid of supercritical carbon dioxide to form peapods; C(61)(COOEt)(2) are encapsulated in SWNTs in high yield, whereas C(61)(COOH)(2) aggregate via hydrogen bonding to form a supramolecular complex, which sterically hinders encapsulation and causes it to adhere to the exterior surface of the SWNTs.

Controlled orientation of ellipsoidal fullerene C70 in carbon nanotubes

Density functional theory calculations predict two orientations for ellipsoidal C70 fullerenes inside single-walled carbon nanotubes (SWNTs) of different sizes: transverse orientation for C70 in (11,11) nanotubes (d=14.9 A) and longitudinal orientation for C70 in (10,10) nanotubes (d=13.6 A). SWNTs with these diameters have been prepared and filled with the C70 fullerenes, and characterized by Raman spectroscopy and high-resolution transmission electron microscopy, showing the orientations predicted by theory.

Chemical reactions inside single-walled carbon nano test-tubes

We report the application of SWNTs as templates for forming covalent polymeric chains from C(60)O reacting inside SWNTs; the resulting peapod polymer topology is different from the bulk polymer in that it is linear and unbranched.

Synthesis and reactivity of N@C60O

The endohedral fullerene epoxide N@C60O was synthesised, isolated by High Performance Liquid Chromatography (HPLC), and characterised by Electron Spin Resonance (ESR). This nitrogen radical displays predominantly axial symmetry characteristics as expected for a monoadduct, evidenced by a zero-field splitting D parameter of 6.6 MHz and an E parameter of 0.5 MHz in powder at 77 K. Photo- and thermally-activated silencing of the nitrogen radical were observed, the latter showing the evolution of a new spin signal during heating at 100 degrees C. We suggest that loss of nitrogen spin is due to coupling with a radical formed by opening of the epoxide ring. This implies that the reaction of C60O with C60 in the solid state proceeds via a radical, rather than ionic, intermediate.

Ordering and interaction of molecules encapsulated in carbon nanotubes

Abstract A clear understanding of the interactions between the building blocks of self-assembled molecular materials is essential for rational design of functional nanostructures. Intermolecular interactions have been investigated for three different classes of fullerenes in single-walled carbon nanotubes (SWNTs); van der Waals molecule – molecule and molecule – SWNT interactions control the geometry of the molecular arrays inside nanotubes; electrostatic intermolecular forces influence the alignment of polar endohedral fullerenes M@C82; and hydrogen bonding between functionalised fullerenes has a significant effect on the selectivity of insertion of functionalised fullerenes into SWNTs.

Inserting Fullerene Dimers into Carbon Nanotubes: Pushing the Boundaries of Molecular Self‐assembly

Carbon nanotubes can encapsulate several molecular species forming one‐dimensional crystals. Using previously reported methods we produced directly‐bonded, asymmetric C60‐C70 dimers and oxygen‐bridged dimers of the type C60‐O‐C60. We present here microscopic evidence of filling single‐walled carbon nanotubes (SWNTs) with the above fullerene dimers. The most important filling constraint is found to be the nanotube size. SWNTs with diameters around 1.6 nm incorporate dimers considerably more easily than SWNTs with smaller diameters. This kind of molecular self‐assembly opens up the potential for using nanotubes and fullerenes for nanodevices.