Phthalocyanines have remarkable chemical and thermal stability and offer tremendous architectural flexibility in their structure, facilitating the tailoring of physical, optoelectronic, and chemical parameters. In this paper, we summarize experimental measurements of nonlinear optical absorption in a comprehensive representative series of modified phthalocyanines substituted with various central metals and peripheral functional groups. Rate equations are used to analytically solve the static‐state conditions that simulate the excited‐state dynamics that result from the nonlinear excited‐state absorption, and this solution is fitted to the experimental data. General molecular engineering trends relating the optical limiting performance of these compounds to their structural characteristics are also explored and discussed.

Due to their ease of fabrication and monodisperse, metallic nature, molybdenum-sulfur-iodine nanowires are an interesting alternative to carbon nanotubes for some applications. However very little is known about the solubility of these materials. In this work we have investigated the solubility of Mo(6)S(4.5)I(4.5) nanowire soot in a range of common solvents by performing sedimentation studies and microscopic and spectroscopic characterization. A sedimentation equation was derived showing that the concentration of any insoluble dispersed phase decreases exponentially with time. We find that in all solvents, Mo(6)S(4.5)I(4.5) nanowire soot contains three phases, two of which are insoluble with one stable phase. Microscopy and spectroscopy show that the first insoluble phase is associated mainly with spherical impurities and sediments rapidly out of solution resulting in purification. The second phase appears to consist of insoluble nanowire bundles and sediments more slowly, eventually leaving a stable dispersion of nanowire bundles. The stably dispersed bundles tend to be smaller than their insoluble counterparts. The best solvents studied were 2-propanol and dimethylformamide. Microscopy studies showed that, in the case of 2-propanol, sonication significantly reduced the bundle size relative to the unsonicated bulk. However, during sedimentation, large quantities of bundles were observed to reaggregate to form larger bundles which subsequently sedimented out of solution. In general, the sedimentation properties of the various phases did not vary significantly with concentration indicating that the insoluble nanowires are intrinsically insoluble. However, the diameter of the stably dispersed bundles decreased with concentration, until very small bundles consisting of only two or three nanowires were observed at concentrations below 0.003 mg/mL. In addition, stable composite dispersions were produced by mixing the nanowires with poly(vinylpyrrolidone) in 2-propanol opening the way for the formation of polymer/inorganic nanowire composites.

Single-wall carbon nanotubes are severely restricted by the fact that they exist in bundles. In addition, their interaction with other materials is poorly understood. In this work a new spectroscopic method is described to measure the ratio of free polymer to nanotube-bound polymer in SWNT/polymer solutions. This ratio is highly nonlinear and can be described by a model based on polymer−nanotube adsorption/desorption kinetics. In combination with the experimental data, this model shows that the nanotube bundles decrease in size as the concentration is reduced. Individual nanotubes are stable at low concentration, as supported by atomic force microscopy data. In addition, the model allows the indirect measurement of the polymer−nanotube binding energy at 1.1 eV per molecule. In principle, this method is generic and can be used to monitor dispersions of any metallic nanomaterials in suitable, luminescent organic solutions.

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We report a method for the fabrication of phthalocyanine particles with dimensions in the nanoscale regime. Phthalocyanines are of particular interest as reversed saturable absorption-based optical limiters. By fabricating phthalocyanine particles of nanometer sizes, we found intermolecular effects to strongly influence the linear and nonlinear optical properties. Linear optical studies, including absorption and emission spectroscopy, were used to investigate the interactions between the molecules inside the particles. The Z-scan technique was employed to examine the optical limiting effects in phthalocyanine nanoparticles compared to solutions of the corresponding molecules. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies were performed to further investigate the particle structure. Furthermore, X-ray diffraction measurements were made to probe the molecular alignment in the nanoparticle.

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The fabrication of a polymer and carbon nanostructure composite material is reported. A comprehensive material investigation of this stable dispersed system is presented. The fabrication technique and characterization steps are described where it was found that multiwalled carbon nanotubes and other clearly defined carbon nanostructures were stably dispersed in the polymer matrix. The properties of the material are investigated to characterize the carbon phases present. Experimental measurements of optical limiting of nanosecond laser pulses by a range of these composite materials in solution are reported. These composites were varied according to carbon nanostructure mass content. The experiments were performed using an open aperture z-scan apparatus with 6 ns Gaussian pulses at 532 nm from a frequency-doubled Q-switched Nd:YAG laser. Saturation of the optical limiting was reached at carbon nanostructure mass percentages in excess of 3.8%, relative to the polymer mass. Mechanistic implications of the optical limiting are investigated via angular dependent scattering measurements.