Linking molecular structure with excited-state photochemical dynamics is crucial for engineering efficient organic solar cells and related photochemical applications. Two molecular dye systems are currently under investigation in our lab: carboalkoxyphenylporphyrins in solution-cast thin films and a new family of highly fluorescent thiazolothiazole viologen dyes. The singlet exciton diffusion lengths of solution-cast porphyrin thin films with various alkyl chain lengths have been examined. Modifications of peripheral solubilizing groups help orientate porphyrins in solution processed thin films and influence molecular orientation. The photoluminescent singlet decay lifetime of pristine porphyrin films and films lightly doped with [6,6]-phenyl-C61-butryic acid methyl ester (PCBM) were used in a 3D exciton diffusion Monte Carlo simulation to extract the exciton diffusion parameters and the nanocomposition. Longer alkyl chain derivatives yielded increased PL decay lifetimes and lengthened exciton diffusion lengths (L_D) for octyl and hexyl containing porphyrin derivatives. GIWAXS and XRD data indicates that molecular organization is strongly dependent upon the peripheral carboalkoxy substituent, and that nematic molecular organization resulted in an increase in the exciton diffusion length. Our findings are an important step toward a deeper understanding of the exciton diffusivity and molecular packing relationship. We have also synthesized a class of extended viologen dye structures that incorporate a thiazolo[5,4-d]thiazole backbone. The dyes exhibit both reversible yellow to dark blue electrochromism and high fluorescence quantum efficiency that is deactivated upon electrochemical reduction. The fused bicyclic thiazolothiazole heterocycle allows the alkylated pyridinium groups to remain planar, strongly affecting their electrochemical properties. The electrochromic and strongly fluorescent properties make these materials attractive for molecular electronics, biomolecular sensing, and other photochemical applications.

 

Although “ordered” organic π-conjugated assemblies outperform “disordered” ones in many optoelectronic device applications, we are far from being able to port the well-understood supramolecular recipes of π-systems from solution to solid-state device environments. For the past several years we have been exploring hydrogen bond (H-bond) directed self-assembly of π-systems along these lines, for example, to enhance their absorption and charge transport properties for organic photovoltaic (OPV) applications. Various examples of oligothiophenes outfitted with heterocycles capable of forming H-bonded “rosettes” will be discussed in this context. The second part of the talk will introduce new monomers derived from [2.2]paracyclophane (pCp) that are capable of robust H-bond directed self-assembly into one-dimensional nanostructures in solution and the solid state. The design introduces transannular (intramolecular) H-bonds between pairs of pseudo-ortho-positioned amides as a way to preorganize the molecules for intermolecular H-bonding with two neighbors. The result is formation of homochiral, one-dimensional pCp stacks that show supramolecular polymer signatures in solution.

Abstract: The philosophy of science studies how individual scientific concepts, models, theories, and experiments all influence the development of scientific knowledge. My research in the philosophy of nanoscience applies methods from philosophy of science to understanding how problems raised by nanoscience have changed our understanding of concepts, theories, and models from physics, materials science, and inorganic chemistry. For instance, studying the synthesis, simulation, and characterization of mixed-metal nanoclusters raises questions about whether these objects count as alloys. In this talk, I examine some keys questions from philosophy of science for chemistry and nanoscience and highlight some results from my approach to answering these questions. Bio: Julia Bursten is a second-year assistant professor of philosophy at the University of Kentucky specializing in philosophy of the physical sciences. Her research studies how theories and models work in nanoscience, chemistry, and materials science, and why theories in these sciences often work differently than theories in areas like quantum physics and biology.

This presentation will highlight two platforms recently developed in the Sagle group which combine lipids and plasmonic nanoparticles.  The first platform involves sandwiching a liposome between a planar gold surface and a gold colloid to generate a biocompatible, highly enhancing surface enhanced Raman spectroscopy (SERS) substrate.  Our initial characterization of these novel substrates investigates substrate stability, temperature inside the liposome component, SERS activity inside the liposome, SERS mechanism and reproducibility.  The substrates are shown to be stable to laser irradiation and exhibit a temperature increase of only 20 degrees Celsius inside the liposome component.  The SERS enhancement of dye residing in the liposome component was found to be 8 x 10⁶, higher than expected considering the dye molecules are at least 4 nm from either gold surface.  Finite Difference Time Domain (FDTD) calculations reveal that the field enhancements inside the liposome are uniform with the major contributing factor being long range coupling between the gold nanoparticle and the mirror.  Lastly, these substrates show greater reproducibility than typical SERS substrates in which dye is sandwiched between two metallic surfaces, and are expected to allow for the non-perturbative measurement of biological molecules in their native state, freely diffusing in solution.  The second platform involves interfacing a gold nanodisc array with solid supported lipid bilayers for label-free biosensing of membrane-associated proteins.  This platform is shown to have superior sensitivity due to elongated gold nanodics (exhibiting greater sensitivity than typical nanoparticle arrays) and an ultrathin silica layer above the nanodiscs, enabling the lipid bilayer to reside close to the nanoparticle surface.  Further studies currently underway are using this platform with silver nanodiscs to carry out label-free SERS measurements of lipid components in the freely diffusing bilayer.

 

Abstract: Recently, dye-sensitized solar cells (DSCs) were shown to be the highest power conversion efficiency technology of any solar cell technology when using photons from the beginning of the solar spectrum until 700 nm. Two key directions are apparent in further elevating this technology: (1) broadening the spectral window used, and (2) efficiently subdividing the spectrum further for multijunction devices which can be used in combination with many solar cell technologies. Progress toward designing optimal panchromatic organic sensitizers to use NIR photons based on physical organic concepts such as proaromaticity and cross conjugation will be discussed. Additionally, the design and realization of a series sequential multijunction dye sensitized solar cell (SSM-DSC) system for effective photon management will be discussed. Ongoing research to optimize this system based on transition metal redox shuttle design and high voltage organic dye design will be analyzed. The SSM-DSC system coupled with electrocatalysts as solar-to-fuel systems has been shown to power water splitting and CO₂ reduction coupled with water oxidation from a single illuminated area without external bias.

Jared Delcamp
Assistant Professor 
University of Mississippi
Department of Chemistry & Biochemistry

The economic viability of the petrochemical industry is predicated on the simultaneous production of chemicals and fuels, with high volumes of low value fuel addressing the strategic energy needs of the US, and high value chemicals providing the industry’s critical economic foundation. This operational model would be ideal for the growing biorefining industry, but even after years of effort, biofuels remain the biorefinery’s primary focus, as the breadth and sophistication of technology for biobased chemical production lags far behind that of the petrochemical industry. Further, the recent precipitous drop in oil prices and the development of new sources of non-renewable raw materials further threatens to marginalize the biofuel industry as a minor player in energy production. Thus, the incorporation of chemical products as part of the biorefinery’s overall manufacturing strategy becomes even more important, but the choices of targets to be pursued must also demonstrate a good fit with the context set by the current petrochemical industry. Equally important is the ability to demonstrate that the chemical targets chosen and the necessary methodology for their production can adapt to this unexpected shift in the chemical industry. This presentation will provide a brief situational analysis of the interplay between current energy prices, biorefinery development and choice of chemical targets. Efforts to develop technology tailored to fit within this scenario for the conversion of renewable building blocks to high value chemicals able will also be described. Efforts to better understand the structure of lignin will enable expanded use of a valuable source of carbon. Alternative systems navigate the multiple substructural units present in lignin, and afford new oxidation chemistry using environmentally benign reagents. We will overview this work and discuss how its inclusion within a larger fuel/chemical production scenario can help enable a successful and viable biorefining industry.

 

Schedule of Events - March 31, 2017
8:00 a.m.	Registration & Continental Breakfast Gallery, W.T. Young Library
8:50 a.m.	Welcome
9:00 a.m.	John A. Rogers, PhD Materials for Biodegradable Electronics Auditorium, W.T. Young Library
10:00 a.m.	Break (refreshments available)
10:30 a.m.	Zhenan Bao, PhD Skin-Inspired Organic Electronic Materials and Devices Auditorium, W.T. Young Library
11:30 a.m.	Lunch & Break
1:00 p.m.	George Malliaras, PhD Interfacing with the Brain using Organic Electronics Auditorium, W.T. Young Library
2:00 - 2:30 p.m.	Coffee Break & Poster Session Set-up
2:30 - 3:15 p.m.	Alon Gorodetsky PhD, Naff Young Investigator Dynamic Materials Inspired By Cephalopods Auditorium, W.T. Young Library
3:15 - 4:30 p.m.	Poster Session Jacobs Science Building

For additional information, click here.

Protein-carbohydrate recognition phenomena illustrated through simulation and thermodynamic calculations

 

Christina M. Payne, Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY

 

Carbohydrates are the most abundant biological molecules on Earth and play important roles in metabolism, cell wall structure, and cellular-level processes; they also happen to be one of the most structurally diverse natural substrates, constructed from a variety of chemically distinct monosaccharides and glycosidic linkages. In response to this diversity, carbohydrate-binding proteins have evolved many different structural approaches to enable recognition of complex carbohydrate substrates. Molecular simulation and free energy calculations, coupled with structural and biochemical observations, can provide extraordinary resolution of molecular-level protein-carbohydrate recognition mechanisms. In this talk, I describe two recent studies wherein we used molecular modeling to reveal the underpinnings of experimentally-observed protein-carbohydrate recognition phenomena. In the first example, we will examine the recognition mechanisms of b-sandwich carbohydrate binding modules (CBMs), a non-catalytic domain of carbohydrate-active enzymes. Counterintuitively, our results suggest these CBMs accommodate cello-oligomers in a bi-directional fashion, and the approximate structural symmetry of the substrate enables such promiscuity. In the second example, we will look at the substrate recognition mechanisms of a mammalian glycoprotein and biomarker, YKL-40, associated with chronic inflammatory diseases and a multitude of cancers. Identification of the lectin’s physiological ligand and biological function has proven experimentally difficult. Using a multifaceted computational approach, we evaluated the feasibility of binding several different polysaccharide and collagen peptide ligands; hyaluronan was revealed as the likely physiological ligand, consistent with associated in vivo expression levels. In general, our approaches reveal valuable fundamental insights into the complex solid and soluble carbohydrate substrate recognition mechanisms of biomolecules, the findings of which hold considerable promise in advancing lignocellulosic biotechnology, glycome mapping tools, and pharmaceutical antagonist design.