Matching Items (5)
Filtering by
- All Subjects: Photoelectrochemistry
- All Subjects: Transfer
- Creators: Gust, Devens
Description
The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis.
ContributorsBrennan, Bradley J (Author) / Gust, Devens (Thesis advisor) / Moore, Thomas A. (Committee member) / Allen, James P. (Committee member) / Arizona State University (Publisher)
Created2012
Description
The work described in the thesis involves the synthesis of a molecular triad which is designed to undergo proton coupled electron transfer (PCET) upon irradiation with light. Photoinduced PCET is an important process that many organisms use and the elucidation of its mechanism will allow further understanding of this process and its potential applications. The target compound designed for PCET studies consists of a porphyrin chromophore (also a primary electron donor), covalently linked to a phenol-imidazole (secondary electron donor), and a C60 (primary electron acceptor). The phenol-imidazole moiety of this system is modeled after the TyrZ His-190 residues in the reaction center of Photosystem II (PS II). These residues participate in an intermolecular H-bond between the phenol side chain of TyrZ and the imidazole side chain of His-190. The phenol side chain of TyrZ is the electron transfer mediator between the oxygen evolving complex (OEC) and P680 (primary electron donor) in PSII. During electron transfer from TyrZ to P680*+, the phenolic proton of TyrZ becomes highly acidic (pKa~-2) and the hydrogen is preferentially transferred to the relatively basic imidazole of His-190 through a pre-existing hydrogen bond. This PCET process avoids a charged intermediate, on TyrZ, and results in a neutral phenolic radical (TyrZ*). The current research consists of building a molecular triad, which can mimic the photoinduced PCET process of PSII. The following, documents the synthetic progress in the synthesis of a molecular triad designed to investigate the mechanism of PCET as well as gain further insight on how this process can be applied in artificial photosynthetic devices.
ContributorsPatterson, Dustin (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Skibo, Edward B (Committee member) / Arizona State University (Publisher)
Created2011
Description
Converting solar energy into electricity is a reasonable way to ameliorate the current untenable energy situation. One way to harness solar energy is to mimic the mechanisms already present in natural photosynthesis. A key component of many artificial photosynthetic systems is the linker connecting the dye to an electrode. Studying the associated electron transport process is important for improving linker efficiency. Similarly it is important to be able to control the electron transfer to the dye from a water oxidation catalyst, and to be able to improve the lifetime of the charge separated state. Natural photosynthesis provides a blueprint for this in the tyrosine-histidine pair in photosystem II. In this work, research on these topics is described.
ContributorsTomlin, John Jacob (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Kodis, Gerdenis (Committee member) / Arizona State University (Publisher)
Created2015
Description
As sunlight is an ideal source of energy on a global scale, there are several approaches being developed to harvest it and convert it to a form that can be used. One of these is though mimicking the processes in natural photosynthesis. Artificial photosynthetic systems include dye sensitized solar cells for the conversion of sunlight to electricity, and photoelectrosynthetic cells which use sunlight to drive water oxidation and hydrogen production to convert sunlight to energy stored in fuel. Both of these approaches include the process of the conversion of light energy into chemical potential in the form of a charge-separated state via molecular compounds. Porphyrins are commonly used as sensitizers as they have well suited properties for these applications. A high potential porphyrin with four nitrile groups at the beta positions, a β-cyanoporphyrin (CyP), was investigated and found to be an excellent electron acceptor, as well as have the necessary properties to be used as a sensitizer for photoelectrosynthetic cells for water oxidation. A new synthetic method was developed which allowed for the CyP to be used in a number of studies in artificial photosynthetic systems. This dissertation reports the theories behind, and the results of four studies utilizing a CyP for the first time; as a sensitizer in a DSSC for an investigation of its use in light driven water oxidation photoelectrosynthetic cells, as an electron acceptor in a proton coupled electron transfer system, in a carotene-CyP dyad to study energy and electron transfer processes between these moieties, and in a molecular triad to study a unique electron transfer process from a C60 radical anion to the CyP. It has been found that CyPs can be used as powerful electron acceptors in molecular systems to provide a large driving force for electron transfer that can aid in the process of the conversion of light to electrochemical potential. The results from these studies have led to a better understanding of the properties of CyPs, and have provided new insight into several electron transfer reactions.
ContributorsAntoniuk-Pablant, Antaeres' Dawn (Author) / Gust, Devens (Thesis advisor) / Moore, Ana L (Committee member) / Ghirlanda, Giovanna (Committee member) / Arizona State University (Publisher)
Created2015
Description
There is surprisingly little scientific literature describing whether a hockey slap shot positively or negatively transfers to a driving golf swing. Golf and hockey use a similar kinematic sequence to send the ball / puck towards a target, but does that directly translate to positive skill transfer between the two sports, or are there other important factors that could result in a negative skill transfer? The aim of this study is to look further into the two kinematic sequences and determine their intertask skill transfer type. A field experiment was conducted, following a specific research design, in order to compare performance between two groups, one being familiar with the skill that may transfer (hockey slapshot) and the other group being unfamiliar. Both groups had no experience in the skill being tested (driving golf swing) and various data was collected as all of the subjects performed 10 golf swings. The results of the data analysis showed that the group with experience in hockey had a higher variability of ball distance and ball speed. There are many factors of a hockey slapshot that are likely to develop a negative intertask skill transfer, resulting in this group's high inconsistency when performing a golf swing. On the other hand, the group with hockey experience also had higher mean club speed, showing that some aspects of the hockey slapshot resulted in a positive skill transfer, aiding their ability to perform a golf swing.
ContributorsLarson, Finn Althea (Author) / Peterson, Daniel (Thesis director) / Cryer, Michael (Committee member) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05