Matching Items (4)
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- All Subjects: Artificial Photosynthesis
- Creators: Gust, Devens
Description
The first chapter reviews three decades of artificial photosynthetic research conducted by the A. Moore, T. Moore, and D. Gust research group. Several carotenoid (Car) and tetrapyrrole containing molecules were synthesized and investigated for excitation energy transfer (EET), photoregulation, and photoprotective functions. These artificial photosynthetic compounds mimicked known processes and investigated proposed mechanisms in natural systems. This research leads to a greater understanding of photosynthesis and design concepts for organic based solar energy conversion devices. The second and third chapters analyze the triplet energy transfer in carotenoid containing dyads. Transient absorption, time-resolved FTIR and resonance Raman spectra revealed that in a 4-amide linked carotenophthalocyanine dyads the Car triplet state is shared across the larger conjugated system, which is similar to protein complexes in oxygenic photosynthetic organisms. In a carotenopurpurin dyad (CarPur) a methylene ester covalent bond prevents the purpurin (Pur) from influencing the Car triplet based on the transient absorption, time-resolved FTIR and resonance Raman spectra. Thus CarPur resembles the antenna proteins from anoxygenic photosynthetic bacteria. Additional examples of carotenoporphyrin dyads further demonstrates the need for orbital overlap for ultrafast triplet energy transfer and the formations of possible intramolecular charge transfer state. The fourth chapter studies a 4-amino phenyl carotenophthalocyanine and its model compounds using high temporal resolution transient absorption spectroscopy techniques. EET from the Car second excited (S2) state to the phthalocyanine (Pc) was determined to be 37% and a coupled hot ground state (S*)/Pc excited state spectrum was observed. Excitation of the tetrapyrrole portion of the dyad did not yield any kinetic differences, but there was an S* signal during the excited states of the dyad. This demonstrates the EET and photoregulating properties of this artificial photosynthetic compound are similar to those of natural photosynthesis. The last chapter covers the synthesis of silicon Pc (SiPc) dyes and the methods for attaching them to gold nanoparticles and flat gold surfaces. SiPc attached to patterned gold surfaces had unperturbed fluorescence, however the selectivity for the gold was low, so alternative materials are under investigation to improve the dye's selectivity for the gold surface.
ContributorsWongCarter, Katherine (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2014
Description
Non-photochemical quenching (NPQ) is a photoprotective regulatory mechanism essential to the robustness of the photosynthetic apparatus of green plants. Energy flow within the low-light adapted reaction centers is dynamically optimized to match the continuously fluctuating light conditions found in nature. Activated by compartmentalized decreases in pH resulting from photosynthetic activity during periods of elevated photon flux, NPQ induces rapid thermal dissipation of excess excitation energy that would otherwise overwhelm the apparatus’s ability to consume it. Consequently, the frequency of charge separation decreases and the formation of potentially deleterious, high-energy intermediates slows, thereby reducing the threat of photodamage by disallowing their accumulation. Herein is described the synthesis and photophysical analysis of a molecular triad that mimics the effects of NPQ on charge separation within the photosynthetic reaction centers. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies were used to demonstrate reversible quenching of the first singlet excited state affecting the quantum yield of charge separation by approximately one order of magnitude. As in the natural system, the populations of unquenched and quenched states and, therefore, the overall yields of charge separation were found to be dependent upon acid concentration.
ContributorsPahk, Ian (Author) / Gust, Devens (Thesis advisor) / Gould, Ian (Committee member) / Mujica, Vladimiro (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
Humanity’s demand for energy is increasing exponentially and the dependence on fossil fuels is both unsustainable and detrimental to the environment. To provide a solution to the impending energy crisis, it is reasonable to look toward utilizing solar energy, which is abundant and renewable. One approach to harvesting solar irradiation for fuel purposes is through mimicking the processes of natural photosynthesis in an artificial design to use sunlight and water to store energy in chemical bonds for later use. Thus, in order to design an efficient energy conversion device, the underlying processes of the natural system must be understood. An artificial photosynthetic device has many components and each can be optimized separately. This work deals with the design, construction and study of some of those components. The first chapter provides an introduction to this work. The second chapter shows a proof of concept for a water splitting dye sensitized photoelectrochemical cell followed by the presentation of a new p-type semiconductor, the design of a modular cluster binding protein that can be used for incorporating catalysts, and a new anchoring group for semiconducting oxides with high electron injection efficiency. The third chapter investigates the role of electronic coupling and thermodynamics for photoprotection in artificial systems by triplet-triplet energy transfer from tetrapyrroles to carotenoids. The fourth chapter describes a mimic of the proton-coupled electron transfer in photosystem II and confirms that in the artificial system a concerted mechanism operates. In the fifth chapter, a microbial system is designed to work in tandem with a photovoltaic device to produce high energy fuels. A variety of quinone redox mediators have been synthesized to shuttle electrons from an electron donor to the microbial system. Lastly, the synthesis of a variety of photosensitizers is detailed for possible future use in artificial systems. The results of this work helps with the understanding of the processes of natural photosynthesis and suggests ways to design artificial photosynthetic devices that can contribute to solving the renewable energy challenge.
ContributorsBrown, Chelsea L (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Woodbury, Neal (Committee member) / Arizona State University (Publisher)
Created2015