Michael S. DeClue

High-speed photorefractive polymer composites

Two photorefractive polymer composites are presented that exhibit the fastest response times reported to date by an order of magnitude (τg≈5 ms at 1 W/cm2), while maintaining large gain coefficients (Γ≈230 and 130 cm−1). These materials show promise for video-rate optical processing applications. The factors limiting the photorefractive speed in these materials are investigated.

Spectroscopic determination of trap density in C60-sensitized photorefractive polymers

Abstract A new and simple method for the determination of the trap density in C 60 -sensitized photorefractive polymers is presented. We show that the radical anion of C 60 acts as the primary photorefractive hole trap, using the strong near-infrared absorption of C 60 − to quantify the anion concentration in situ. The spectroscopically determined concentration correlates well with the photorefractive trap density obtained from analysis of the photorefractive performance. In our model, optical irradiation is needed to activate the trapping sites, and the nonlinear optical chromophore acts as a temporary reservoir for the photogenerated holes (compensator). This model is further clarified using cyclic voltammetry.

Interactions between Catalysts and Amphiphilic Structures and their Implications for a Protocell Model

One of the essential elements of any cell, including primitive ancestors, is a structural component that protects and confines the metabolism and genes while allowing access to essential nutrients. For the targeted protocell model, bilayers of decanoic acid, a single-chain fatty acid amphiphile, are used as the container. These bilayers interact with a ruthenium-nucleobase complex, the metabolic complex, to convert amphiphile precursors into more amphiphiles. These interactions are dependent on non-covalent bonding. The initial rate of conversion of an oily precursor molecule into fatty acid was examined as a function of these interactions. It is shown that the precursor molecule associates strongly with decanoic acid structures. This results in a high dependence of conversion rates on the interaction of the catalyst with the self-assembled structures. The observed rate logically increases when a tight interaction between catalyst complex and container exists. A strong association between the metabolic complex and the container was achieved by bonding a sufficiently long hydrocarbon tail to the complex. Surprisingly, the rate enhancement was nearly as strong when the ruthenium and nucleobase elements of the complex were each given their own hydrocarbon tail and existed as separate molecules, as when the two elements were covalently bonded to each other and the resulting molecule was given a hydrocarbon tail. These results provide insights into the possibilities and constraints of such a reaction system in relation to building the ultimate protocell.

Polysiloxane-bound ligand accelerated catalysis: a modular approach to heterogeneous and homogeneous macromolecular asymmetric dihydroxylation ligands

Polysiloxane acts as a modular scaffold for macromolecular reagent development. Two separate components were covalently integrated into one material, one constituent provided reagent functionality, the other modulated solubility. In particular cinchona alkaloid based ligands used in the osmium tetroxide catalyzed asymmetric dihydroxylation (AD) reaction were covalently attached to commercially available polysiloxane. To enhance the reactivity of these polymeric ligands, multifunctional reagents were designed to include both the cinchona alkaloid and an alkoxyethylester solubilizing moiety providing random co-polymers. While the mono-functional materials led to heterogeneous conditions, the bi-functional polymers resulted in homogeneous reaction mixtures. Although both reagent types provided diol products with excellent yield and selectivity (>99% ee in nearly quantitative yield) the homogeneous analog has nearly twice the reactivity. Every repeat unit in the heterogeneous material was functionalized along the polysiloxane backbone while approximately half of these sites contained ligand in the homogeneous version. This approach led to macromolecular catalysts with high loadings of ligand and therefore materials with very low equivalent weights. Although these polymers are highly loaded they do maintain reactivity on a par with their free ligand counterpart. Using straightforward purification techniques (i.e. precipitation, simple filtration, or ultrafiltration) these polymeric ligands were easily separated from diol product and reused multiple times. Polysiloxane is a viable support for the catalysis of AD reactions and may provide a generally useful backbone for other catalytic systems.

Organic photorefractive material design strategies

We seek to improve the performance of organic photorefractive (OPR) systems by implementing two different design philosophies. In one strategy polysiloxane-based charge transport polymers are used to explore the requirement of a low glass transition temperature. These polymers allow construction of low Tg composites without plasticizcer and additionally may have higher charge mobility than poly(n-vinyl carbazole).The other strategy entails the use of small-molecule organic glasses composed of covalently attached charge transport and non-linrar optical chromophore moieties. Both classes of materials are characterized by holographic, photoconductive, and ellipsometric methods.

A new charge transporting polymer for photorefractive applications

Summary form only given. Since the first observation of photorefractivity in a polymer, there has been continued interest in these polymers for applications including data storage, phase conjugation, pattern recognition, imaging through turbid media, laser-based-ultrasound detection, image amplification and novelty filtering. Although many materials published show promising performance, there is still a great need for improved materials. We present a novel hole transport polymer the combines the hole transporter tri-benzyl amine with the polysiloxane backbone, abbreviated as PSX-TBA. Methoxy substituents were added to improve compatibility with polar chromophore dopants.