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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 ����vlog�ٷ���� 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 ����vlog�ٷ���� & 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.

PV-Powered Semiconductor electrochemical reactor systems: applications for wastewater treatment in the developing world

Michael R. Hoffmann

California Institute of Technology, Engineering & Applied Science, Linde-Robinson Labs, Pasadena, California 91125

 

The Hoffmann Group has developed, tested, and implemented transportable reactor systems that have been designed for the onsite treatment and disinfection of domestic wastewater.  After pre-treatment with a sequential anaerobic/aerobic baffled bioreactor, the effluent is processed sequentially through semiconductor electrochemical arrays where the chemical oxygen demand and microbial loads are reduced to below international reuse standards.  Special mini-reactors are used to convert grey water for reuse as handwashing water.   The treated black water is recycled into flush water reservoirs without discharge to the surrounding environment.   Human wastewater can be clarified with the elimination of suspended particles along with >95% reduction in the chemical oxygen demand and a total elimination of fecal coliforms, E. coli, viruses, and total coliforms.  Enteric organism disinfection is achieved for bacteria and viruses via anodic reactive chlorine generation from in situ chloride oxidation coupled with cathodic reduction of water to form molecular hydrogen. Improvement of the performance and durability of the core semiconductor anodes along with materials modifications to lower their production costs are ongoing. Third and fourth-generation prototypes are undergoing field-testing in locations that lack conventional urban infrastructure for wastewater discharge and treatment.  The packaged treatment systems can operate without an external source of electricity or fresh water.  Manufacturing and field-testing is underway in China and India.   Two Caltech-China joint-venture companies, Eco-San and Entrustech, have been established in Yixing, China to manufacture solar-powered units for the developing world and electrochemical reactor systems for commercial use. Additional industrial collaborations have been established in India with ERAM Scientific and with the Kohler Company (USA/India) for production of units to be used in urban and peri-urban environments in India. Larger-scale units have been built for use in South Africa and Southern China.

 

Rebekah Ison, Anne Filson, Gary Rohrbacher from UK's College of Design will be presenting this week's seminar.

“Pragmatism and Imagination: Designing a Carbon Refinery”

Anne Filson

This talk will showcase several student algae projects developed in undergraduate architecture studios, using them to explain the potential of cross-disciplinary academic collaborations. 

 

“The Problem is the Solution”

Gary Rohrbacher

This talk will describe the work of the Atomic Cities Research Group in several design research studios conducted between 2010 and 2016. The studios propose hopeful futures for the Paducah Gaseous Diffusion Plant site, and the City of Paducah in Western Kentucky.

 

"From SEE(E)D to (S)STEM"

Rebekah Ison

This is a project exploring collaboration among scientists, engineers, entrepreneurs, educators and designers to develop didactic tools to promote sustainability, science, technology, engineering and mathematics.

Refreshments will be served at this event.

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Semiconductor photocatalysis: mechanisms, photocatalytic performances and lifetime of redox carriers

Faculty Advisor: Dr. Marcelo Guzman