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The nonlinear optical response of gold particles (with 2.5, 9, or 15 nm radius) prepared by γ-radiolysis in water solution and stabilized by poly(vinyl alcohol) is size-dependent. The 2.5 nm clusters do not limit light transmission even at very high fluence of nanosecond laser pulses, while the larger clusters strongly limit the laser beam transmission at 530 nm. The threshold of limitation and the amplitude depend on the size of the particles. The rise of the optical limiting effect is measured by picosecond laser spectroscopy. For the largest particles, it lasts 1 ns. The limitation effect is attributed to large light-scattering centers induced by the pulse around the initial particles.

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We report on a new, original and efficient method for pi-stacking functionalization of single-wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single-wall carbon nanotubes and porphyrin molecules. We developed a micelle-swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non-water-soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.

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The photoisomerization of disperse red 1 (DR1) in polymethylmethacrylate thin films is demonstrated by monitoring the refractive index variations by the attenuated total reflection method. Absorption spectrum measurements give a confirmation of this phenomenon. The kinetics of photoisomerization and of thermal relaxation are nonexponential. Some other molecules are studied. As in solution, azobenzene derivatives (N—N) produce reversible isomerization while dimethylaminonitrostilbene, a stilbene derivative (C—C), exhibits no thermal cis→trans relaxation.