Session VB

Tuesday, May 17th

Session VB:


The Performance of Hybrid Titania/Silica-derived Xerogels as Active Antifouling/Fouling-release Surfaces Against the Marine Alga Ulva linza: in Situ Generation of Hypohalous Acids

Corey Damon, Caitlyn Gatley, Meredith Lang, Josh Beres, and Mike Detty

University at Buffalo, Department of Chemistry

Marine biofouling is the accumulation of biological organisms on submerged surfaces. Biofouling on ship hulls leads to an increase in roughness and drag, with subsequent loss of range and speed; a major problem for maritime industry. Hull coatings that discourage settlement (antifouling, AF) or minimize adhesion (fouling release, FR) of fouling organisms represent two approaches to combat biofouling.  Sol-gel-derived xerogel coatings incorporating organically modified silanes (ORMOSILs) have shown promise as FR coatings and have previously been modified to incorporate organochalcogenide catalysts for the oxidation of bromide with hydrogen peroxide (H2O2). The catalytic oxidation of halides with H2O2 found in aquatic environments can produce hypohalous acids in situ, which have known biocidal effects and discourage settlement of aquatic species. Grafting of transition metals to mesoporous silica has also provided catalysts for the oxidation of halide salts with H2O2; albeit only under acidic conditions. Active xerogels incorporating transition metals have been prepared which catalyze the oxidation of both bromide and chloride with H2O2 at the pH of seawater (pH 8), the first evidence of chloride oxidation at oceanic conditions. Biological assays performed with the green alga Ulva linza yielded a significant reduction in zoospore settlement and increase in sporeling removal for active coatings relative to catalyst-free coatings in the presence of H2O2, indicating AF properties have been introduced to a FR surface. The impact of transition metals and ORMOSILs on xerogel surface characteristics was evaluated by contact angle analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy.


Covalently Linked Quantum Dot Heterostructures: Evidence for Photoinduced Charge Transfer

Justin Nasca and David F. Watson

University at Buffalo, Department of Chemistry

Semiconductor quantum dots (QDs) boast many properties that make them of interest to researchers. In particular, their size-dependent optical properties, high oscillator strengths, and possibilities to undergo multiexciton generation (MEG) and hot carrier extraction render QDs worthwhile from a solar energy conversion standpoint. Recent research in our lab has focused on employing established carbodiimide chemistry to tether QDs to each other through the formation of a covalent bond between capping groups. Using this chemistry offers one main advantage; the coupling of two QDs together is selective (i.e. QD “A” can only form a covalent linkage with QD “B”). This talk will highlight recent research efforts to covalently tether ZnSe QDs to CdS QDs. The following topics will be discussed: (1) Surface modification and synthesis of ZnSe and CdS QDs; (2) Characterization of modified QDs through the use of attenuated total reflectance (ATR) infared spectroscopy and steady state emission and (3) evidence for photoinduced charge transfer through the use of steady state emission. Over a period of approximately 5 days, measurable trap-state emission associated with CdS was quenched by 51% while over the same time period, mixed dispersions where no amide linkage is possible was quenched by 7%. These data suggest that a type-II interface is formed between ZnSe and CdS and upon excitation of either QD, charge separation takes place. These results suggest that covalently linking QDs to form a type-II interface may be beneficial towards solar energy conversion. Further characterization of these heterostructures is necessary to elucidate the type of charge transfer as well as the kinetics of charge separation.


Are Two Switches Better Than One: Design and Synthesis of Photo-responsive Molecules for Metal-Organic Frameworks

Travis Mitchell, Ian M. Walton, Jordan M. Cox, and Jason B. Benedict

University at Buffalo, Department of Chemistry

In recent years, the development and research of crystalline solids containing permanent porosity has gained much recognition throughout the scientific community. These materials, which include metal-organic frameworks (MOFs), zeolitic imidazole frameworks (ZIFs), and porous coordination polymers (PCPs), have potential applications in catalysis, electrochemistry, chemical separations, and gas sequestration. By incorporating photochromic moieties into the framework of these materials, through which the local chemical environment of the void space can be externally controlled using a specific wavelength of light, the application of these materials can be further enhanced. Previously, our group has synthesized photochromic linkers with a dithienylethene based photochromic system containing a phenanthrene backbone in which the linker is functionalized at the 2,7 position of the phenanthrene with either a pyridyl group or carboxylic acid group using what we designate as the Pinacol Route for synthesis. This presentation will highlight a new synthetic route that yields a unique dithienylethene capable of undergoing two distinct photochemical reactions. This photochrome, [(Z)-1,2-bis(2-methyl-5-(pyridin-4-yl)thiophen-3-yl)-1,2-diphenylethene] (BPyDTS), contains both a stilbene and a dithienylethene photochromic moiety. Single Crystal X-Ray Diffraction (SCXRD) revealed that the two photoactive carbons involved in the dithienylethene photo-reaction do not possess the proper geometry required for the solid-state reaction to occur. Single crystals of BPyDTS do, however, show a change in absorbance under UV irradiation at 365 nm potentially indicating photo-chemical reactivity of the stilbene group in the single crystalline phase. BPyDTS does undergo a reversible photochemical ring closing reaction in solution that is likely associated with the dithienylethene group.


Electrochemical Rectification Towards Redox Mediators by Porphyrin Molecular Multilayer Films for Application in Dye-Sensitized Solar Cells

Marissa Civic, Samantha J. Donovan, and Peter H. Dinolfo

Rensselaer Polytechnic Institute

We have designed a method utilizing copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry to assemble light-harvesting arrays for use in dye-sensitized solar cells (DSCs). This rapid method produces uniform, multilayer films with highly controllable photophysical and electrochemical characteristics. Modification of these properties is critical in order to pursue replacement of the most commonly used iodide/triiodide redox mediator, which limits the maximum achievable efficiency for DSCs, with alternatives that utilize an outer-sphere redox mechanism. Tailoring DSC design to allow for these mediators is of great interest in order to improve device function.  We have found our films possess an electrochemical rectifying property allowing charge transfer to the redox mediator while blocking recombination with the electrode surface. Herein we study the effectiveness of the rectification capabilities of our films, as well as examine factors such as rates of charge transfer and mediator-dye interactions. Our focus is highly relevant, as it offers an interesting method to possibly improve DSC devices by further utilizing the dye component already present in current designs.


Vibrational Study of Fullerene and Supported Jacobsen's Catalyst on Various Substrates Using Vibrational Sum Frequency Generation Spectroscopy.

Dennis Elsenbeck, Sushanta Das, and Luis Velarde

University at Buffalo, Department of Chemistry

Surface specific study of catalytic interfaces is an area of interest for scientists across various disciplines.  We made use of spatial and temporal overlap of broadband IR and narrowband VISIBLE pulses to generate sum frequency generation (SFG) to selectively obtain information for these interfaces.  We used a tunable visible laser to scan the fullerene/substrate interface using both insulating and conducting surfaces.  We present qualitative and quantitative trends across the visible range used and provide some of the clearest and most advanced fullerene SFG spectra to date.  We also SFG to probe a supported organometallic catalyst in the methyl, carbonyl, and fingerprint region.  We observed the oxomanganese stretching mode of oxidized Jacobsen's catalyst, the species responsible for the catalysts function as an expoxidation facilitator.  Using this data we can provide orientational information as well as catalytic information directly at the surface of the support.