Robert C. Haddon

Molecular functionalization of carbon nanotubes and use as substrates for neuronal growth

Carbon nanotubes are strong, flexible, conduct electrical current, and can be functionalized with different molecules, properties that may be useful in basic and applied neuroscience research. We report the first application of carbon nanotube technology to neuroscience research. Methods were developed for growing embryonic rat-brain neurons on multiwalled carbon nanotubes. On unmodified nanotubes, neurons extend only one or two neurites, which exhibit very few branches. In contrast, neurons grown on nanotubes coated with the bioactive molecule 4-hydroxynonenal elaborate multiple neurites, which exhibit extensive branching. These findings establish the feasability of using nanotubes as substrates for nerve cell growth and as probes of neuronal function at the nanometer scale.

Diffraction Symmetry in Crystalline, Close-Packed C60

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the soccer ball model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.

Thermal hysteresis in dithiadiazolyl and dithiazolyl radicals induced by supercooling of paramagnetic liquids close to room temperature: a study of F3CCNSSN and an interpretation of the behaviour of F3CCSNSCCF3

The trifluoromethyl-substituted dithiadiazolyl and dithiazolyl radicals, F3CCNSSN (1) and F3CCSNSCCF3 (2) associate through pi*-pi* covalent and electrostatic S delta+...N delta- interactions in the solid state, but melt with a dramatic volume increase to generate paramagnetic liquids; these radicals exhibit thermal hysteresis, which arises through a meta-stable super-cooled liquid state, close to room temperature.

Reactivity, spectroscopy, and structure of reduced fullerenes

Abstract Reduced fullerenes, the simplest covalent derivatives of the fullerene family of carbon allotropes, provide an excellent context for the study of the fundamental chemical reactivity of fullerenes. We have developed a general method for the formation of a number of these compounds. Using Zn(Cu) reduction, we have access to pure samples of several isomerically pure C 60 H n and C 70 H n species. We have completely assigned the 13 C NMR spectrum of C 60 H 6 and have assigned the majority of the resonances in C 60 H 2 .

The isolation, characterisation, gas phase electron diffraction and crystal structure of the thermally stable radical [CF3CSNSCCF3]˙

The first structural characterisation of a heterocyclic free radical in all phases has been achieved. 4,5-Bis(trifluoromethyl)-1,3,2-dithiazol-2-yl, [CF3CSNSCCF3]˙ n4d, a 7π radical, was prepared quantitatively on reduction of [4d][AsF6] with various reducing agents. It is a blue gas over a green paramagnetic liquid [19F NMR δ n−59.7], which freezes to a diamagnetic black-green solid. There is a remarkably large volume increase on melting implying that the liquid consists of discrete monomeric radicals, and consistently there is no tendency to dimerise in CCl3F solution and the vibrational spectra attributable to the monomer are essentially identical in all phases. The thermodynamic properties obtained for the vapourisation, sublimation and melting processes are very similar to those of related diamagnetic materials. 4d is remarkably thermochemically robust giving decomposition products identical to those from photochemical decomposition, a quantitative mixture of CF3CSSCCF3 (and its oligomers) and CF3CNSNCCF3. The reaction chemistry is described. The crystal structure shows radical 4d to be a planar heterocyclic ring which associates in the solid as a diamagnetic tetramer. The structure of the gaseous monomer determined by electron diffraction is very similar to that in the solid phase. Comprehensive physical measurements were made including the UV-visible spectra of the bright blue solutions, variable temperature magnetic susceptibility and quantitative variable temperature ESR spectra both of which confirm a phase change from a diamagnetic solid to a paramagnetic liquid on melting, the vibrational spectra, and the photoelectron spectrum of the gaseous free radical. A study of the behavior of RCSNSCR˙ (Rxa0=xa0H, CH3 or CF3) given by the reduction of RCSNSCR+ on increase of concentrations of radical is reported, including the isolation of HCSNSCCF3˙ at low temperature. The experimental and calculated [UMPW1PW91/6-31+G*] structures of 4d are in good agreement. These and related calculations also support the interpretation of the vibrational and photoelectron spectra, and the thermodynamic properties of 4d, as well as provide possible explanations for the relative stabilities of RCSNSCR˙, and imply that the weak intramolecular interactions in 4d in the solid state are largely ionic Sδ+⋯Nδ− interactions.

Electric Current Induced Light Emission from C60

We report the luminescence of C60 crystals and films due to the passage of an electrical current. The current-voltage behavior is highly non-linear with light-emission beyond a threshold voltage. The emission spectrum is featureless and resembles black-body radiation with an effective temperature on the order of 1700 K. We report experiments aimed at distinguishing between electro- and thermoluminescence.

Molecular components of the bulk electronic structure of organic conductors: A soft X-ray absorption and soft X-ray emission spectroscopy approach

Abstract The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using soft X-ray absorption (SXA) and soft X-ray emission (SXE) spectroscopy. These techniques are powerful probes of the site and angular-momentum resolved partial density of states (PDOS) for both occupied and unoccupied states. Therefore these spectroscopies are particularly suited for an analysis of the density of states of multi-atomic, complex materials as the ET-based organic conductors, allowing site-specific electronic structure to be measured. We present a preliminary picture of the electronic structure of κ-ET 2 Cu(SCN) 2 and κ-ET 2 Cu[N(CN) 2 ]Br as measured by SXE and SXA performed at the C1s and N1s core levels.