Arthur W. Snow

Optical limiter using a lead phthalocyanine

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.

Off‐resonant third‐order optical nonlinearities of metal‐substituted phthalocyanines

The third‐order optical susceptibility of the Pt, Pb, and metal‐free tetrakis(cumylphenoxy)phthalocyanines was measured by degenerate four‐wave mixing at 1.064 μm, far from strong absorption bands. Metal substitution strongly enhances the off‐resonant χ(3). The χ(3)xxxx for Pt‐phthalocyanine (2×10−10 esu) and Pb phthalocyanine (2×10−11esu) is about 45 times and 5 times that of the metal‐free form (4×10−12 esu), respectively.

The Alpha Substitution Effect on Phthalocyanine Aggregation

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 × 101M−1 and 7.0 × 103M−1 respectively. At concentrations greater than 10−3M, 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, hinde...

Derivatives of phthalocyanine prepared for deposition as thin films by the Langmuir-Blodgett technique☆

Abstract Film pressure versus area data for a series of organic derivatives of phthalocyanine are presented in detail. Classical monomolecular films were not observed. Compounds studied include tetraphenoxy, dicumylphenoxy and tetracumylphenoxy, tetraoctadecoxy and tetraneopentoxy phthalocyanine. Spread films of metal-substituted tetracumylphenoxy phthalocyanines that contained iron, cobalt, nickel, copper, zinc, palladium, platinum and lead were also examined along with 1:1 mole ratio mixed films of these compounds with octadecanol. Mixed films with varying mole ratios of nickel tetracumylphenoxy phthalocyanine and octadecanol are also described. On the basis of these data and considerations of recent studies of tetra- tert -butyl phthalocyanine by other investigators, a stacked phthalocyanine structure is indicated. The stack axis is not parallel to the plane of the film.

Trace Chemical Vapor Detection Using SAW Delay Line Oscillators

The resonant frequencies of SAW delay line oscillators are shown to be very sensitive to the presence of thin organic films that are deposited onto the delay line surface. Theory suggests that the sensi- tivity of the SAW device to mass loading depends on the square of the resonant frequency. This dependence has been studied experimentally using devices resonating at 31, 52, and 112 MHz that were coated with organic films of precisely controlled composition and thickness. The mass sensitivity of SAW oscillators can be exploited to make very sen- sitive chemical sensors if an appropriate sorptive coating is applied to the device. Results obtained from a delay line oscillator operating at 290 MHz (the highest frequency SAW chemical sensor reported to date) suggest that the rapid detection of organic vapors at concentra- tions substantially below 100 parts per billion (by volume) is readily achievable.

Synthesis, aggregation behavior and nonlinear absorption properties of lead phthalocyanines substituted with siloxane chains

The synthesis and characterization of polysiloxane substituted metal-free and lead phthalocyanines are described. These materials form a class of isotropic liquid phthalocyanines that combine a large nonlinear absorption with an exceptionally large nonlinear thermal refractive effect. These materials effectively couple the nonlinear absorption characteristics of the phthalocyanine (Pc) moiety with the thermorefractive properties typical of siloxanes. The room temperature index of these phthalocyanines can be varied by the choice of the siloxane substituent. Furthermore, the siloxane substituents are effective at inhibiting aggregation of the phthalocyanine rings. The observed aggregation constants in toluene solutions are very small and only a small degree of aggregation is observed even in the pure liquid phthalocyanines. Nonlinear transmission, z-scan, transient absorption and degenerate four-wave mixing studies confirm that the Pb substituted materials possess a broad spectral region of induced absorption with nonlinear absorption coefficients similar to that observed from other lead substituted phthalocyanines. The observed ground state molar absorption coefficients of the siloxy phthalocyanines are somewhat smaller than comparable alkyl substituted phthalocyanines. Taken together, these properties make these materials very useful for practical nonlinear optical applications. The coupling of siloxane chains to the Pc rings represents a promising way to achieve some important properties that are difficult to achieve by other means.

THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF METALLO-PHTHALOCYANINES

This paper discusses the third-order nonlinear optical (NLO) properties of metal-free, lead and transition metal phthalocyanines, as well as scandium, yttrium and lanthanide bisphthalocyanines measured by time-resolved degenerate four-wave mixing at 1064 nm. The study focuses on the structure-property relationships and explores the possible mechanisms leading to the enhanced third-order optical nonlinearity measured for this interesting class of NLO materials.

Oligooxyethylene liquid phthalocyanines

A series of methyl-terminated oligooxyethylene (CH3(OCH2CH2)nO, n = 8.8)-substituted phthalocyanines with peripheral substitution at four β positions, at four α positions and at the eight α positions was synthesized and structurally characterized. These compounds are isotropic liquids above 10 °C. Non-linear optical properties of the tetra-α- and tetra-β-substituted compounds were examined. Both are reverse saturable absorbers in the visible region of the spectrum, but the tetra-α-substituted compound has the larger non-linear absorption coefficient and can be a useful optical limiter in cases where a non-volatile liquid is desirable.

Morphology and properties of Langmuir films containing tetrakis(cumylphenoxy) phthalocyanines

Abstract Tetrakis(cumylphenoxy) phthalocyanine, H 2 Pc(Cp) 4 , and the family of related compounds containing transition metal ions in the center of the macrocyclic ring, MPc(Cp) 4 , will spread from organic solvents to give pressure vs. area isotherms typical of monolayers, but classical monomolecular films are not formed. Mixed films containing a classical component as a transfer promoter, such as stearamide, produce Langmuir-Blodgett (LB) multilayers of better quality than the MPc(Cp) 4 compounds alone. As a structural model, a simple mixed film containing stacked, ordered MPc(Cp) 4 molecules was originally postulated, but more recent observations by transmission electron microscopy and by IR reflectance-absorbance spectroscopy have revealed a more complex and less well-ordered morphology than previously suspected. In mixed films transferred by the LB technique, a two-dimensional colloidal dispersion of MPc(Cp) 4 aggregates is formed. Disk-like aggregates more than one monomolecular layer thick are observed in single-component films and are also seen dispersed in the second component of mixed films. Differential scanning calorimetry also suggests a significant degree of phase separation in the two-component LB films. Small melting point depressions relative to the melting points of single-component monolayers indicate that the melting points of two-component films containing MPc(Cp) 4 are determined by the transfer promoters.

Scaling Properties of Gold Nanocluster Chemiresistor Sensors

The effect of geometric scaling on the performance of metal-insulator metal-ensemble (MIME) chemiresistors based on gold nanoclusters is investigated. The ultrasmall size of the nanoclusters is shown to enable extreme scaling of the sensors with reductions in area of at least a factor of 104 over conventional MIME devices. If the operating voltage is held constant, the absolute sensitivity of the devices is found to remain essentially unchanged by the geometric scaling. Interestingly, this occurs despite the fact that contact resistance appears to play a significant role in the smallest devices. The detection limit of the sensors is set by a signal-to-noise ratio, and because 1/f noise tends to dominate, reduction in sensor size raises the noise floor, leading to a degradation in the detection limit. Because of the importance of the 1/f noise, optimal performance will be obtained by operating the sensors under ac conditions with filtering. Despite the degradation in performance that results from scaling, nanocluster-based chemiresistors of reduced size can still be advantageous because of the possibility of achieving vapor-sensing systems of substantially reduced size, power, complexity, and cost, as well as new applications, e.g., for sensor arrays