Nonlinear absorption, refraction, and optical limiting by a series of monoaxially chloro- and aryl-substituted indium(III) phthalocyanines are described. The absorption cross sections and temporal evolution of the low-lying excited states are also reported. A large nonlinear absorption that increased with wavelength between 500 and 590 nm was observed in each material. The nanosecond nonlinear absorption and the optical limiting are shown to be dominated by a strong excited state absorption from an orientationally averaged triplet state. We derive and experimentally confirm the relation between the molecular absorption cross sections and the fluence-dependent nonlinear absorption coefficients. The effective nonlinear refraction on the nanosecond time scale was reduced because the electronic contribution to the nonlinear refractive index was of the opposite sign from the thermal contribution. An optical limiter using the new material, p-(trifluoromethyl)phenylindium(III) tetra-tert-butylphthalocyanine [(t-Bu)4PcIn(p-TMP)], showed a much lower threshold for optical limiting and a much lower transmission at high fluences than previously reported indium phthalocyanine limiters. This improved optical limiting was due both to the larger nonlinear absorption coefficient and to the design of the limiter device. The optical properties of the In phthalocyanine moiety were found to be surprisingly robust to structural changes in the axial position.

Micro/nanolayer coextrusion was used to fabricate polycarbonate (PC)/poly(vinylidene fluoride) (PVDF) layered films with significantly reduced dielectric losses while maintaining high energy density. The high-field polarization hysteresis was characterized for layered films as a function of PVDF layer thickness (6000 to 10 nm) and composition (10 to 70 vol % PVDF), and was found to decrease with decreasing layer thickness and PVDF content. To gain a mechanistic understanding of the layer thickness (or nanoconfinement) effect, wide-angle X-ray diffraction, polarized Fourier transform infrared spectroscopy, and broadband dielectric spectroscopy were employed. The results revealed that charge migration, instead of dipole flipping, was responsible for the hysteresis in multilayered films. The absence of PVDF dipoleflipping was attributed to the nonuniform electric field distribution in the layered structure, where the field in PVDF layers were calculated to be significantly lower than that in PC layers due to large contrast in dielectric constant (∼3 for PC versus ∼12 for PVDF). The charges were likely to be impurity ions in the form of catalyst residue or surfactants from suspension polymerization. The characteristics of the dielectric spectroscopy relaxation indicated that ions mostly existed in the PVDF layers, and PC/PVDF interfaces prevented them from entering adjacent layers. Therefore, as the layer thickness decreases to nanometer scales, the amount of ion movement, dielectric loss, and hysteresis were decreased. This study provides clear evidence of the nanoconfinement effect in multilayered films, which advantageously decreases the hysteresis loss.

The performance of an optical limiter based on Pb-tetrakis(cumylphenoxy)phthalocyanine, a robust organic material with a large χ(3) and figure of merit, χ(3)/α0, is described. In an f/5 limiter with a sample transmission of 0.68, the threshold for limiting was 8±2 nJ and the dynamic range was greater than a factor of 103. The threshold for the PbPc(CP)4 limiter was ∼15 times smaller and the high intensity transmission ∼4–5 times lower than an equivalent limiter based on a thermal nonlinearity.

There is a need in electronic systems and pulsed power applications for capacitors with high energy density. From a material standpoint, capacitive energy density improves with increasing dielectric constant and/or breakdown strength. Current state-of-the-art polymeric capacitors are, however, limited in that their dielectric constant is low (2–4). Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complementary properties: one with a high breakdown strength (polycarbonate) and one with a high dielectric constant (polyvinylidene fluoride-hexafluoropropylene). As opposed to the monolith controls, multilayered films with various numbers of layers and compositions subjected to a pulsed voltage exhibit treeing patterns that hinder the breakdown process. Consequently, substantially enhanced breakdown strengths are measured in the mutilayered films. It is further shown, by varying the overall film thickness, that the charge at the tip of the needle electrode is a key parameter that controls treeing. Based on the acquired data, a breakdown mechanism is formulated to explain the increased dielectric strengths. Using the understanding gained from these systems, selection and optimization of future layered structures can be carried out to obtain additional property enhancements.

Using a transmission-spectrum-based method, the refractive index of a 50 μm thick sample of poly(methyl methacrylate) (PMMA) was measured as a function of wavelength. To mitigate the effects of nonplane-parallel surfaces, the sample was measured at 16 different locations. The technique resulted in the measurement of index at several thousand independent wavelengths from 0.42 to 1.62 μm, with a relative RMS accuracy <0.5×10(-4) and absolute accuracy <2×10(-4).

The recognition that eye lenses in nature often employ a gradient refractive index to enhance the focusing power and to correct aberrations has motivated us to construct a synthetic lens using the layered concept encountered in biological lenses. The result is a highly flexible technology for the fabrication of gradient-refractive index lenses that is based on a method of polymer forced assembly. Polymeric nanolayered films with incremental differences in the refractive index are assembled according to a prescribed design and molded into the desired shape. The exceptional flexibility of the process lies in the wide range of lens shapes and index profiles that can be realized. A lens with any refractive index distribution can be achieved within the refractive index range of available coextrudable optical materials.

The dimerization and tendency to form higher aggregates of two isomeric metal-free phthalocyanine compounds with tetracumylphenoxy peripheral substitution at the alpha (1 or 4, 5 or 8, 9 or 12, 13 or 16) and beta (2 or 3, 6 or 7, 10 or 11, 14 or 15) positions has been analysed by spectroscopic measurements. The dimerization constants in chloroform solution are 1.3 × 101 M −1 and 7.0 × 103 M −1 respectively. At concentrations greater than 10−3 M , the beta phthalocyanine isomer forms a spectroscopically resolvable higher aggregate. Q-band spectra of the dimer of each isomer and of the aggregate of the beta isomer in chloroform solution were generated. Comparison of these spectra with the corresponding thin film spectra of each isomer indicates that the stronger tendency toward aggregation of the beta isomer extends into the solid state. The difference in aggregating tendency of the two isomers was attributed to a steric constraint of the alpha isomer that restricts conformational freedom and, consequently, hinders formation of dimer and higher order complexes.

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