Photoinduced electron transfer (ET) reactions are simplified versions of what happens in photosynthesis and an understanding of these interactions could be applied to studying alternative energy sources and light interactions in biological systems. Mixed valence compounds are model systems to study ET between the metals when excited by ultrafast laser pulses. In this study we synthesized and spectroscopically characterized mixed valence complexes such as [(CN)₅Fe^II-CN-Ru^III(NH₃)₅]^- (RuFe), [(NC)₅Ru^II-CN-Pt^IV(NH₃)₄-NC-Ru^II(CN)₅]^4- (RuPtRu), and [(NC)₅Fe^II-CN-Pt^IV(NH₃)₄-NC-Fe^II(CN)₅]^4- (FePtFe). These complexes are analyzed for purity with Fourier transform infrared spectroscopy (FT-IR) by viewing CN stretching frequencies. Spectra of the solvent effects were studied of these complexes in formamide, D₂O, and DMSO-d₆ with FT-IR and UV-Vis. Spectra of the solvent effects show shifts in the peak position and shape depending on solvent composition, signifying changes in metal-metal charge transfer (MMCT) absorption band with UV-Vis and shifts in CN stretches with FT-IR. Optimizing synthesis can maximize yield and understanding of solvent effects can be applied to the study of ET reactions. This work can be used as the basis for further studies of MMCT reactions in ultrafast spectroscopies.

Concerted proton-electron transfer (CPET) is the movement of both an electron and a proton in one kinetic step of a chemical reaction. This mechanism can explain the observed lower reaction barriers than would be expected by a consecutive step-by-step mechanism. The study of such reactions can help with the elucidation of the electronics involved in processes such as capture of energy in solar cells. The octahedral ruthenium complex [Ru^II(en*)₂(bpy)](PF₆)₂ (en* = 1,1,2,2-tetramethylethylenediamine , bpy = 2,2’-bipyridine) is studied with various quinone compounds. The proposed reaction is the two-electron oxidation of ruthenium with loss of two protons from neighboring en* nitrogen atoms with production of hydroquinone, or catechol, and the corresponding deprotonated Ru(IV) complex. The oxidation of ruthenium is due to two nitrogen atoms now requiring an electron from the metal center while previously having a dative Ru-N interaction. Ortho-quinones are of special interest due to the possibility of a 2 e^-, 2 H⁺ coupled reaction. The described reaction is observed under some circumstances as is the coordination of the quinone to the ruthenium along with loss of an en* ligand, forming a Ru(III) radical species that can be observed by EPR spectroscopy. Reactions were followed in nonprotic solvents such as THF and acetone to prevent solvent interference and products were confirmed by ¹H NMR spectroscopy and EI mass spectrometry. Steric and electronic effects were explored with various substituted quinones along with light and thermal effects on the reactions. CPET mechanisms for some of the attempted reactions are supported by UV/visible spectroscopy kinetics data.

Starch is an abundant and naturally occurring polysaccharide produced by a variety of plants. By itself starch does not have desirable mechanical properties, and therefore has limited applications. However with some modification this renewable resource has potential for a range of applications. To improve the mechanical properties of starch and extend its application, we aim to modify corn starch through graft copolymerization with other renewable resources. Poly(L-lactic acid) (PLLA) is a well known polymer derived from renewable resources with suitable mechanical properties for a wide range of applications. We have successfully synthesized copolymers, starch-g-PLLA, by reacting gelatinized cornstarch with L-lactic acid in the presence of a stannous octoate catalyst. Reactions were carried out at 90°C under vacuum, and the resulting copolymers purified by Soxhlet extraction to remove residual lactic acid. Spectral analysis has confirmed the copolymer structure via FTIR Spectroscopy, 1H FT-NMR and 13C FT-NMR Spectroscopy. Polymer surface morphology was characterized using Scanning Electron Microscopy (SEM) and thermal properties were investigated using Differential Scanning Calorimetry (DSC). By varying the amount of L-lactic acid to starch and optimizing gelatinization, polymers with varying mechanical properties and hydrophilicity should be obtained.

Generating electricity directly from sunlight is an attractive solution to our current energy problems. However, the high cost of processing the materials for silicon photovoltaics has limited the widespread use of this technology. Solution processable semiconducting organic polymers could offer an inexpensive route to utilizing this clean and abundant energy source, but devices made from these materials are currently too inefficient to be economically viable. Photovoltaic devices utilize energy from an absorbed photon to generate free charge carriers, producing an electric current. Some losses in efficiency may occur during the separation of charge carriers, which is driven by the built-in electric field of the device. The built-in field is generally assumed to arise from the difference in electrode work functions, but is also dependent on interfacial effects such as dipole layers. Other researchers have shown that chemical modification of indium tin oxide (ITO) electrode surfaces with self-assembled monolayers of organic molecules (SAMs) changes the ITO work function. Correlation of the built-in field of photovoltaic device structures with these work function measurements for several different SAM molecules may give information about the presence or absence of physical and chemical interactions between the SAM and the polymer. Such information could help direct the use of SAMs to improve the efficiency of such devices. We are able to measure the built-in field directly using electroabsorption spectroscopy. Initial work has been conducted to determine an ITO/SAM/polymer/metal structure that allows repeatable measurement of the built-in field. The built-in fields of structures using phosphonic acid SAMs and the polymer P3HT are being measured, and future work will extend these measurements to other conjugated polymers.

Most dye-sensitized solar cells that are currently being investigated use titanium oxide nanoparticle films to optimize light scattering and maximize the surface area where light is absorbed. These films are about 15 micrometers thick and are usually produced using a doctor blade method or screen printing techniques on a fluorine tin oxide (FTO) glass substrate followed by annealing at 450 degrees Celsius. This research investigates a new method where electrophoretic deposition (EPD), which is a common industrial process that has only recently been applied to dye-sensitized solar cells, is used to create P25 titanium oxide nanoparticle (commercial brand of titanium oxide nanoparticles) films while using magnesium nitrate as an electrolyte. Thus far the method has not been perfected and efficiencies of 2 % have only been achieved in this work. By optimizing the film morphology, thickness, and other film characteristics, which are easily tunable while using EPD, it is anticipated that efficiencies of 3 to 5 % can be achieved with good adhesion to the FTO glass substrate and desirable micro- and nanostructure providing the solar cell industry with an alternative method to creating dye-sensitized solar cells.  Before this comes to fruition, problems such as electrolyte contamination in the film and cracking of the film as a result of capillary action must be solved.  Thus far, other electrolytes that would evaporate during annealing have been tried with no positive results. Soaking the films in a solution to remove the electrolyte after deposition is being pursued.

Organic light emitting diodes (OLEDs) based on solution-processable conjugated polymer thin films are an attractive replacement for traditional inorganic LEDs due to their lower cost and ability to be made into flexible displays. OLEDs, however, have yet to be optimized for their maximum external quantum efficiency (EQE), the ratio of photons emitted to the electrons injected into the device. The EQE is in part limited by the photoluminescence quantum yield (PLQY) of the emissive polymer thin film. It has been reported that the inclusion of metal nanoparticles near the polymer films enhances their fluorescence through the excitation of localized surface plasmon resonances (LSPRs) in the metal nanoparticles. The enhancements in the local electromagnetic fields associated with LSPR excitation result in an increased radiative decay rate, and therefore a decreased fluorescence lifetime of nearby polymer. Here we study the effects of silver nanoprisms on the PLQY and fluorescence lifetime of emissive polymer thin films spin coated onto optically dense metal nanoparticle films. Preliminary measurements indicate that the presence of these particles in direct contact with the polymer film decreases both the PLQY and fluorescence lifetime. Ongoing work is investigating the role of spectral overlap between the LSPR spectrum and the polymer emission spectrum, a spacer layer between the nanoprisms and the polymer film, and the use of nanoprisms synthesized via different protocols.