Photoinitiated release of an aziridinium ion precursor for the temporally controlled alkylation of nucleophiles.

A photo-activatable aziridinium precursor has been developed to investigate the possibility of a photo-initiated traditional nucleophilic reaction. The photolysis of a quaternary amine yields a tertiary amine and has allowed us to temporally control aziridinium formation and subsequent alkylation of a colorimetric nucleophilic reporter molecule. We have also used this photo-initiated reaction to alkylate a sulfhydryl group. This new photo-initiated alkylation strategy is water-soluble and expands the toolkit of photo-activated crosslinkers for protein labeling research.

Single-walled carbon nanotubes as excitonic optical wires.

Although metallic nanostructures are useful for nanoscale optics, all of their key optical properties are determined by their geometry. This makes it difficult to adjust these properties independently, and can restrict applications. Here we use the absolute intensity of Rayleigh scattering to show that single-walled carbon nanotubes can form ideal optical wires. The spatial distribution of the radiation scattered by the nanotubes is determined by their shape, but the intensity and spectrum of the scattered radiation are determined by exciton dynamics, quantum-dot-like optical resonances and other intrinsic properties. Moreover, the nanotubes display a uniform peak optical conductivity of approximately 8 e(2)/h, which we derive using an exciton model, suggesting universal behaviour similar to that observed in nanotube conductance. We further demonstrate a radiative coupling between two distant nanotubes, with potential applications in metamaterials and optical antennas.

On-chip Rayleigh imaging and spectroscopy of carbon nanotubes.

We report a novel on-chip Rayleigh imaging technique using wide-field laser illumination to measure optical scattering from individual single-walled carbon nanotubes (SWNTs) on a solid substrate with high spatial and spectral resolution. This method in conjunction with calibrated AFM measurements accurately measures the resonance energies and diameters for a large number of SWNTs in parallel. We apply this technique for fast mapping of key SWNT parameters, including the electronic-types and chiral indices for individual SWNTs, position and frequency of chirality-changing events, and intertube interactions in both bundled and distant SWNTs.