Piecing Together Large Polycyclic Aromatic Hydrocarbons and Fullerenes: A Combined ChemTEM Imaging and MALDI-ToF Mass Spectrometry Approach.

Motivated by their importance in chemistry, physics, astronomy and materials science, we investigate routes to the formation of large polycyclic aromatic hydrocarbon (PAH) molecules and the fullerene C60 from specific smaller PAH building blocks. The behaviour of selected PAH molecules under electron (using transmission electron microscopy, TEM) and laser irradiation is examined, where four specific PAHs-anthracene, pyrene, perylene and coronene-are assembling into larger structures and fullerenes. This contrasts with earlier TEM studies in which large graphene flakes were shown to transform into fullerenes via a top-down route. A new combined approach is presented in which spectrometric and microscopic experimental techniques exploit the stabilisation of adsorbed molecules through supramolecular interactions with a graphene substrate and enable the molecules to be characterised and irradiated sequentially. Thereby allowing initiation of transformation and characterisation of the resultant species by both mass spectrometry and direct-space imaging. We investigate the types of large PAH molecule that can form from smaller PAHs, and discuss the potential of a "bottom-up" followed by "top-down" mechanism for forming C60.

Oxygen, sulfur and selenium terminated single-walled heterocyclic carbon nanobelts (SWHNBs) as potential 3D organic semiconductors.

Carbon nanomaterials such as polyaromatic hydrocarbons (PAHs), graphene, fullerenes and nanotubes are on the frontline of materials research due to their excellent physical properties, which in recent years, have started to compete with conventional inorganic materials in charge transfer based applications. Recently, a variety of new structures such as single-walled carbon nanobelts (SWCNBs) have been conceived, however, to date only one 'all-phenyl' example has been synthesised, due to problems with their stability and the challenging synthetic methodologies required. This study introduces a new class of phenacene-based SWCNBs and their chalcogenide derivatives, forming the new sub-class of single-walled heterocyclic carbon nanobelts (SWHNBs) which are expected to be both more stable and easier to synthesise than the all carbon analogues. Subsequent theoretical examination of the structure-property relationships found that unlike the small-molecule acene homologues (tetracene, pentacene etc.) which become more reactive with addition of oxygen, an increase in the molecular size of the SWCNBs actually stabilises the HOMO energy level, in correlation with the increasingly negative nuclear independent chemical shift (NICS) calculations of their cylindrical aromaticities. The FMO energies of the phenacene SWCNBs are similar to that of the nanobelt reported by Itami and co-workers, but those of the SWHNBs are deeper and thus more stable. The sulfur derivative of one SWHNB was found to give hole-charge transfer mobilities as high as 1.12 cm2 V-1 s-1, which is three orders of magnitude larger than the corresponding unsubstituted SWCNB (3 × 10-3 cm2 V-1 s-1). These findings suggest the candidates are air-stable and potentially high-performing organic semiconductors for organic thin film transistor (OTFT) devices, while the structure-property relationships uncovered here will aid the design and synthesis of future three-dimensional organic nanomaterials.

A one-pot-one-reactant synthesis of platinum compounds at the nanoscale.

The preparation of inorganic nanomaterials with a desired structure and specific properties requires the ability to strictly control their size, shape and composition. A series of chemical reactions with platinum compounds carried out within the 1.5 nm wide channel of single-walled carbon nanotubes (SWNTs) have demonstrated the ability of SWNTs to act as both a very effective reaction vessel and a template for the formation of nanocrystals of platinum di-iodide and platinum di-sulphide, materials that are difficult to synthesise in the form of nanoparticles by traditional synthetic methods. The stepwise synthesis inside nanotubes has enabled the formation of Pt compounds to be monitored at each step of the reaction by aberration-corrected high resolution transmission electron microscopy (AC-HRTEM), verifying the atomic structures of the products, and by an innovative combination of fluorescence-detected X-ray absorption spectroscopy (FD-XAS) and Raman spectroscopy, monitoring the oxidation states of the platinum guest-compounds within the nanotube and the vibrational properties of the host-SWNT, respectively. This coupling of complementary spectroscopies reveals that electron transfer between the guest-compound and the host-SWNT can occur in either direction depending on the composition and structure of the guest. A new approach for nanoscale synthesis in nanotubes developed in this study utilises the versatile coordination chemistry of Pt which has enabled the insertion of the required chemical elements (e.g. metal and halogens or chalcogens) into the nanoreactor in the correct proportions for the controlled formation of PtI2 and PtS2 with the correct stoichiometry.

Switching intermolecular interactions by confinement in carbon nanotubes.

The encapsulation of trityl-functionalised C60 molecules inside carbon nanotubes drastically affects the intermolecular interactions for this species. Whilst the orientations of molecules in the crystal are often controlled by thermodynamics, the molecular orientations in nanotubes are a result of kinetic control imposed by the mechanism of entry into and encapsulation within the nanotube.

Self-assembly of a sulphur-terminated graphene nanoribbon within a single-walled carbon nanotube.

The ability to tune the properties of graphene nanoribbons (GNRs) through modification of the nanoribbon's width and edge structure widens the potential applications of graphene in electronic devices. Although assembly of GNRs has been recently possible, current methods suffer from limited control of their atomic structure, or require the careful organization of precursors on atomically flat surfaces under ultra-high vacuum conditions. Here we demonstrate that a GNR can self-assemble from a random mixture of molecular precursors within a single-walled carbon nanotube, which ensures propagation of the nanoribbon in one dimension and determines its width. The sulphur-terminated dangling bonds of the GNR make these otherwise unstable nanoribbons thermodynamically viable over other forms of carbon. Electron microscopy reveals elliptical distortion of the nanotube, as well as helical twist and screw-like motion of the nanoribbon. These effects suggest novel ways of controlling the properties of these nanomaterials, such as the electronic band gap and the concentration of charge carriers.