Dissertationen: „Artificial photosynthesis“

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Ro, Youngju. „Molecular complexes for artificial photosynthesis“. Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS412/document.

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Le développement de sources d’énergie renouvelables telles que les combustibles solaires est une question cruciale dans le contexte actuel du réchauffement de la planète. L'eau est une source abondante, respectueuse de l'environnement, bon marché et abondante en électrons et en protons nécessaires à la production de combustible. Par conséquent, l'oxydation de l'eau activée par la lumière est une étape clé de la photosynthèse artificielle et le développement de catalyseurs efficaces, robustes et durables constitue un objectif important pour les chimistes. Dans la première partie de cette étude, nous nous concentrons sur le développement de tels catalyseurs basés sur des complexes métalliques à base de métaux de la première série des éléments de transition tel que le cuivre pour cette étude. L'électrocatalyse et la photocatalyse par oxydation de l'eau ont été étudiées. La deuxième partie du travail concerne la formation de paires d'ions entre les espèces à double charge opposée du catalyseur complexe et de l'accepteur d'électrons et du photosensibilisant et du catalyseur complexe. Cette étude devrait apporter des preuves solides de l'influence de chaque composant du photosystème par l'association et la dissociation de paires d'ions.Dans la troisième partie, nous étudions un système synthétique sensibilisant-catalyseur capable de photoactiver une molécule d’eau liée à l’unité catalytique par le biais d’une oxydation à deux électrons et à deux protons, réalisant toute la caractérisation photophysique de la dyade. Par conséquent, l’étude des complexes moléculaires pour la photosynthèse artificielle fournit diverses orientations pour développer le rendement d’utilisation de l’énergie solaire
Development of renewable energy sources like solar fuels is a crucial issue in the actual context of global warming. Water is an environmentally friendly, cheap and abundant source of the electrons and protons needed for fuel production. Therefore, light-activated water oxidation is a key step in artificial photosynthesis and the development of efficient, robust and sustainable catalysts is an important goal for chemists. In the first part of this study, we focus on the development of such catalysts based on earth abundant copper complexes. The water oxidation electrocatalysis and photocatalysis were investigated. The second part of the work concerns the ion pair formation between the oppositely double charged species of complex catalyst and electron acceptor and Photosensitizer and complex catalyst are investigated. This study should bring solid evidence on the influence of each component in photosystem through the ion pair association and dissociation. In the third part, we study a synthetic sensitizer-catalyst system that can photoactivate a water molecule bound to the catalytic unit through a two-electron, two-proton abstraction, performed all the photophysical characterization of the dyad. Therefore, studying molecular complexes for artificial photosynthesis provides diverse direction to develop the utilization efficiency of solar energy

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Bazzan, Irene. „Molecular Catalysis towards Artificial Photosynthesis“. Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424626.

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The 21st century is a time of unprecedented uncertainty for the energy sector: a secure, clean, continuous and equally distributed source of energy is fundamental to global economic growth and human development. Nowadays, being able to find a real substitute to fossil fuels represents a fascinating challenge. Among possible alternatives, renewable sources seems to better fit the energetic demand and solar energy is by far the largest exploitable. However, it has to be captured, converted and conveniently stored. Inspired by Nature, artificial photosynthesis is a process aimed at efficiently converting sunlight energy into alternative fuels such as hydrogen or other different reduced form of carbon. This artificial system is characterized by an articulate scheme of events, terminating with redox reactions that need to be efficiently catalysed. The project of this thesis aims to study the development of new catalytic, molecular and Earth-abundant based systems for redox processes in artificial photosynthesis. For our goals, photo-activated systems are preferred in order to better mimic the light-driven activation in an ideal artificial device. Moreover, multi and mono metallic active sites in catalysts structure are considered, inspired by several efficient examples in literature. The work is mainly focused on water oxidation reaction, being still considered the bottleneck of artificial photosynthesis; however also preliminary studies on CO2 reduction have been examined. First, a Cobalt-based oxo cluster, [Co4(μ3-O)4(μ-O2CCH3)4(pyridine)4] has been studied as a molecular catalyst for water oxidation in a light activated system with Ru(bpy)32+ as photosensitizer and S2O82- as sacrificial donor. The species has been characterized through different analytic techniques and tuning electronic substituents properties, structure-activity correlations have been investigated by cyclic voltammetry and laser flash photolysis. Moreover, a synthetic approach to modify the structure of the species has been evaluated in order to design no covalent dyads between the catalyst and the photosensitizer exploiting π−π interactions. Other Cobalt-based species with high nuclearity and totally inorganic ligands (polyoxometalates, POMs) have been studied in water oxidation catalysis. In particular, complexes [Co9(H2O)6(OH)3(PW9O34)3]16-, [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(SiW8O31)3}]5- and [{Co4(OH)3PO4}4(PW9O34)4]16- have been investigated with laser flash photolysis and in the photo-activated system. Interesting mechanistic insights have been reached thanks to the analysis of these species. Moreover, during the thesis work a novel single site Copper-based compound with a tetraazacyclotetradecane ligand has been proposed as water oxidation catalyst. In particular, the species has been characterized among the electrochemical system and the catalytic behaviour has been explored by means cyclic voltammetry, electrolysis and photoelectrochemical experiments. With the aim of the development of a sunlight activated water splitting device, for the first time in this thesis work a Copper molecular species has been examined in combination with light. Results seem to be preliminary interesting for further studies on azamacrocyclic Copper-based molecular species. Finally, dealing with the catalysis of CO2 reduction some studies have been performed with a POM-based complex, [Cu(SiW11O39)]6-. Cyclic voltammetry experiments have been run in order to evaluate the possible catalytic activity of the compound in CO2 reduction. The aim of this thesis work is to suggest a method to achieve a better understanding of the analysed topic through optimized experimental conditions and mechanistic insights.
Il 21° secolo appare come un momento di enorme incertezza per il settore energetico: un’energia sicura, pulita, continua ed equamente distribuita risulta necessaria per la crescita economica e lo sviluppo della società umana. Riuscire a trovare un’adatta alternativa ai combustibili fossili costituisce una sfida affascinante per l’avanzamento scientifico. Considerando diverse possibilità, le risorse rinnovabili sembrano essere in grado di rispondere meglio alla richiesta energetica e fra queste, l’energia solare è sicuramente la più sfruttabile, però deve essere raccolta, convertita e conservata. Ispirandosi alla Natura, la fotosintesi artificiale è una soluzione in grado di convertire efficientemente l’energia derivante dalla luce solare in combustibili alternativi come idrogeno o altre forme ridotte di carbonio. Questo sistema artificiale presenta una struttura articolata di eventi, che terminano con reazioni di ossidoriduzione che necessitano un’efficiente catalisi. All’interno del panorama descritto, questo progetto di tesi è quindi focalizzato nello sviluppo di nuovi sistemi molecolari basati su metalli abbondanti sulla superficie terrestre in grado di catalizzare processi redox coinvolti nella fotosintesi artificiale. Lo studio di sistemi foto indotti è stato privilegiato, poiché si avvicina maggiormente all’ attivazione da parte della luce di un ideale sistema artificiale. Inoltre, ispirandosi ai numerosi esempi presenti in letteratura, i catalizzatori considerati sono basati su strutture con centri attivi sia multi che mono metallici. Il lavoro è maggiormente focalizzato sulla reazione di ossidazione dell’acqua, considerata ancora la problematica maggiore nel processo di fotosintesi artificiale, ma sono stati presi in considerazione anche studi preliminari per la catalisi della reazione di riduzione di CO2. Inizialmente, un osso cluster di Cobalto, [Co4(μ3-O)4(μ-O2CCH3)4(pyridine)4] è stato esaminato come catalizzatore molecolare in un sistema foto attivato con Ru(bpy)32+ come fotosensibilizzatore e S2O82- come donatore sacrificale. La specie è stata caratterizzata mediante diverse tecniche analitiche e variando le proprietà elettroniche dei sostituenti, correlazioni fra la struttura e l’attività sono state investigate con voltammetria ciclica e laser flash fotolisi. Inoltre, un approccio sintetico volto alla modifica strutturale del catalizzatore è stato valutato per progettare diadi non covalenti tra la specie stessa e il fotosensibilizzatore sfruttando interazioni π−π. Altre specie ad alta nuclearità, contenenti Cobalto e con leganti totalmente inorganici (poliossometallati, POMs) sono stati valutati per la catalisi di ossidazione dell’acqua. In particolare i complessi [Co9(H2O)6(OH)3(PW9O34)3]16-, [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(SiW8O31)3}]5- e [{Co4(OH)3PO4}4(PW9O34)4]16- sono stati investigati nel sistema foto attivato e con laser flash fotolisi. Interessanti informazioni di meccanismo sono state ottenute grazie allo studio di questi composti. Inoltre, durante il lavoro di tesi un nuovo composto basato su un unico atomo di Rame e un legante tetraazaciclotetradecano è stato proposto come catalizzatore per ossidazione dell’acqua. In particolare, la specie è stata caratterizzata nel sistema elettrochimico e la sua attività catalitica è stata valutata mediante voltammetria ciclica, elettrolisi ed esperimenti fotoelettrochimici. Con lo sguardo volto allo sviluppo di un dispositivo per water splitting attivato dalla luce solare, in questa tesi per la prima volta è stata esaminata una specie molecolare di Rame in combinazione con la luce. I risultati ottenuti sembrano aprire la strada a nuove linee di ricerca legate a specie molecolari di Rame con leganti macrociclici azotati. Infine, per quanto riguarda la catalisi della reazione di riduzione di CO2, un complesso di Rame con legante POM è stato selezionato, [Cu(SiW11O39)]6-, ed esperimenti di voltammetria ciclica sono stati effettuati per valutarne l’attività catalitica. Questo lavoro di tesi si propone di indicare un metodo di lavoro per ottenere una migliore comprensione dell’argomento trattato, attraverso l’ottimizzazione delle condizioni sperimentali e approfondimenti riguardanti il meccanismo dei processi in esame.

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Yamamoto, Masanori. „Studies on Molecule‐Based Artificial Photosynthesis“. 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225562.

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Berg, Katja E. „Bimetallic model compounds for artificial photosynthesis /“. Stockholm, 1997. http://www.lib.kth.se/abs98/berg0109.pdf.

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Liu, Rui. „Nanostructured Semiconductors for High Efficiency Artificial Photosynthesis“. Thesis, Boston College, 2013. http://hdl.handle.net/2345/3160.

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Thesis advisor: Dunwei Wang
Photosynthesis converts solar energy and stores it in chemical forms. It is one of the most important processes in nature. Artificial photosynthesis, similar to nature, can provide us reaction products that can potentially be used as fuel. This process promises a solution to challenges caused by the intermitted nature of solar energy. Theoretical studies show that photosynthesis can be efficient and inexpensive. To achieve this goal, we need materials with suitable properties of light absorption charge separation, chemical stability, and compatibility with catalysts. For large-scale purpose, the materials should also be made of earth abundant elements. However, no material has been found to meet all requirements. As a result, existing photosynthesis is either too inefficient or too costly, creating a critical challenge in solar energy research. In this dissertation, we use inorganic semiconductors as model systems to present our strategies to combat this challenge through novel material designs of material morphologies, synthesis and chemical reaction pathways. Guided by an insight that a collection of disired properties may be obtained by combining multiple material components (such as nanostructured semiconductor, effective catalysts, designed chemical reactions) through heterojunctions, we have produced some advanced systems aimed at solving fundamental challenges common in inorganic semiconductors. Most of the results will be presented within this dissertation of highly specific reaction routes for carbon dioxide photofixation as well as solar water splitting
Thesis (PhD) — Boston College, 2013
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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Álvarez, Prada Luis Ignacio. „Ruthenium and Platinum Nanoparticles For Artificial Photosynthesis“. Doctoral thesis, Universitat Autònoma de Barcelona, 2021. http://hdl.handle.net/10803/673692.

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La creixent demanda energètica, necessària per a cobrir les necessitats d’una població cada vegada més nombrosa, ha accelerat el canvi climàtic en les últimes dècades, a causa de l’ús predominant de combustibles fòssils, que a més de contaminants són finits i estan mal distribuïts globalment. Això ha propiciat l’interès per emprar energies més netes. Així, prenent la naturalesa com a exemple, sorgeix la Fotosíntesi Artificial, una forma d’emmagatzemar la ingent energia solar que rebem a la Terra en forma d’enllaços químics en diferents substàncies. Aquest procés inclou, a més a més de l’oxidació de l’aigua a dioxigen, la reacció de reducció de protons i la reducció de CO2, obtenint-se, respectivament, dihidrogen i productes derivats del carboni com són el metà o el metanol. En tots dos casos es requereix l’ús d’un catalitzador per fer el procés eficient, i un material fotoactiu que desencadeni el procés induït per la llum. En el Capítol I, es desenvolupa encara més la problemàtica del canvi climàtic i l’estat actual dels processos de reducció de protons i CO2, fent èmfasi en l’ús de semiconductors com el nitrur de carboni com a material fotoactiu i de nanopartícules metàl·liques com a catalitzadors. Es destaca, a més, l’ús del mètode organometàl·lic per a la preparació d’aquests catalitzadors, en condicions suaus de reacció i amb un gran control sobre les seves característiques físiques i químiques. En el Capítol II, s’exposen els objectius d’aquest treball, centrats en el disseny, caracterització multitècnica i l’ús de materials basats en nanopartícules metàl·liques per dur a terme aquests processos. En el Capítol III, es preparen nanopartícules de ruteni emprant diferents lligands com estabilitzadors, observant diferències en la seva activitat i estabilitat electrocatalítica en la reducció de protons, relacionats amb les seves propietats i composició. En el capítol IV, es fa servir carbur de nitrogen grafític mesoporós (mpg-CN) com a material fotoactiu per a la reducció de CO2 fotoinduïda. Es comprova l’efecte que té la incorporació de nanopartícules de platí al semiconductor, millorant notablement l’eficiència i la selectivitat del procés. En el Capítol V, torna a utilitzar-se mpg-CN però amb nanopartícules de ruteni i platí per a la fotoreducció de protons. Les nanopartícules de ruteni es preparen de diferents maneres, utilitzant lligands estabilitzadors, materials de carboni o directament en el semiconductor. Es comprova que, independentment de la tècnica, l’eficiència catalítica observada és similar en tots aquests sistemes, i molt inferior a l’obtinguda amb Pt. Les observacions catalítiques es recolzen amb estudis fotofísics. En el Capítol VI, es preparen nanopartícules de Pt suportades en quatre materials de carboni diferents (nanohorns y nanotubs de carboni, òxid de grafè reduït i grafit), que són incorporades a un sistema de detecció electroanalítica, essent eficaces per a la detecció de parabens a nivells ultratraça. Finalment, en el Capítol VII s’exposen les conclusions globals.
La creciente demanda energética, necesaria para cubrir las necesidades de una población cada vez más numerosa, ha acelerado el cambio climático en las últimas décadas, debido al empleo predominantemente de combustibles fósiles, que además de contaminantes son finitos y están mal distribuidos globalmente. Esto ha propiciado el interés por emplear energías más limpias. Así, tomando la naturaleza como ejemplo, surge la Fotosíntesis Artificial, una forma de almacenar la ingente energía solar que recibimos en la Tierra en forma de enlaces químicos en diferentes sustancias. Este proceso incluye, además de la oxidación de agua a dioxígeno, la reacción de reducción de protones y la reducción de CO2, obteniéndose, respectivamente, dihidrógeno y productos derivados del carbono como metano o metanol. En ambos casos se requiere el empleo de un catalizador para hacer el proceso eficiente, y un material fotoactivo que desencadene el proceso inducido por la luz. En el Capítulo I, se desarrolla aún más la problemática del cambio climático y el estado actual de los procesos de reducción de protones y CO2, señalando el empleo de semiconductores como el nitruro de carbono como material fotoactivo y de nanopartículas metálicas como catalizadores. Se destaca, además, el empleo del método organometálico para la preparación de estos catalizadores, en condiciones suaves de reacción y con un gran control sobre sus características físicas y químicas. En el Capítulo II, se exponen los objetivos de este trabajo, centrados en el diseño, caracterización multitécnica y uso de materiales basados en nanopartículas metálicas para llevar a cabo estos procesos. En el Capítulo III, se preparan nanopartículas de rutenio empleando diferentes ligandos como estabilizadores, observando diferencias en su actividad y estabilidad electrocatalítica en la reducción de protones, relacionados con sus propiedades y composición. En el Capítulo IV, se emplea carburo de nitrógeno grafítico mesoporoso (mpg-CN) como material fotoactivo para la reducción fotoinducida de CO2. Se comprueba el efecto que tiene la incorporación de nanopartículas de platino al semiconductor, mejorando notablemente la eficiencia y la selectividad del proceso. En el Capítulo V, vuelve a utilizarse mpg-CN pero con nanopartículas de rutenio y platino para la fotorreducción de protones. Las nanopartículas de rutenio se preparan de diferentes maneras, utilizando ligandos estabilizadores, materiales de carbono o directamente en el semiconductor. Se comprueba que, independientemente de la técnica, la eficiencia catalítica observada es similar en todos estos sistemas, y muy inferior a la obtenida con Pt. Las observaciones catalíticas se respaldan con estudios fotofísicos. En el Capítulo VI, se perparan nanopartículas de Pt soportadas en cuatro materiales de carbono diferentes (nanohorns y nanotubos de carbono, óxido de grafeno reducido y grafito), que son incorporadas a un sistema de detección electroanalítica, mostrándose eficaces para la detección de parabenos a niveles de ultratraza. Finalmente, en el Capítulo VII se exponen las conclusiones globales.
The increasing energy demand, necessary to meet the needs of the growing world population, has accelerated climate change in recent decades, due to the predominantly use of fossil fuels, which in addition to being pollutants are non-renewable and ill-distributed. This has aroused interest in cleaner energetic alternatives. Thus, taking Nature as an example, Artificial Photosynthesis emerges as a way to store the enormous amount of solar radiation received by the Earth, in the form of chemical bonds of a fuel. This process includes, besides the oxidation of water to dioxygen, the reduction of protons and the reduction of CO2, obtaining, respectively, dihydrogen and products derived from carbon such as methane or methanol. In both cases, the use of a catalyst is required to make the process efficient, and a photoactive material that triggers the process induced by light. Chapter I further develops the problem of climate change and the current state of the proton and CO2 reduction processes, pointing out the use of semiconductors such as carbon nitride as photoactive material and metallic nanoparticles as catalysts. In addition, the use of the organometallic method for the preparation of these catalysts is highlighted, under mild reaction conditions and with great control over their physical and chemical features. In Chapter II, the objectives of this work are exposed, centered on the design, multi-technique characterization and testing of materials based on metallic nanoparticles to carry out these processes. In Chapter III, ruthenium nanoparticles are prepared using different ligands as stabilizers, observing differences in their activity and electrocatalytic stability in the reduction of protons, related to their physical properties and composition. In Chapter IV, mesoporous graphitic nitrogen carbide (mpg-CN) is used as a photoactive material for photoinduced CO2 reduction. The effect of the loading of platinum nanoparticles to the semiconductor is tested, notably improving the efficiency and selectivity of the process. In Chapter V, mpg-CN is used again but with ruthenium and platinum nanoparticles for the photoreduction of protons. Ruthenium nanoparticles are prepared in different ways, using stabilizing ligands, carbon materials or directly deposited in the semiconductor. It is found that, regardless of the technique, the observed catalytic efficiency is similar in all these systems, and much lower than the performance of Pt. The catalytic observations are supported by photophysical studies. In Chapter VI, Pt nanoparticles supported on four different carbon materials (carbon nanohorns, carbon nanotubes, reduced graphene oxide and grahpite) are prepared and incorporated into an electroanalytical sensing platform, proving effective for the detection of parabens at ultra-trace levels. Finally, in Chapter VII the global conclusions are presented.
Universitat Autònoma de Barcelona. Programa de Doctorat en Química

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GOBBATO, THOMAS. „Bio-inspired Nano-Architectures for Artificial Photosynthesis“. Doctoral thesis, Università degli Studi di Trieste, 2023. https://hdl.handle.net/11368/3041030.

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Among the possible technologies for artificial photosynthesis, photoelectrochemical cells possess the advantage to decouple the overall water splitting reaction into the related semi-reactions enabling the study and optimization of the single process. In this Thesis a novel approach towards artificial photosystems design has been reported. The quantasome approach is a unique bio-inspired design strategy that pair down to essentials the PSII mimicry by shaping an innovative supramolecular material with the essential components of the quantasome: a light-harvesting antenna and a catalytic reaction center embedded in a unique ensemble. Bonchio, Prato and co-workers reported the very first example of an artificial quantasome (QS), a supramolecular artificial photosystem designed for light-induced water oxidation reaction. This innovative material is composed of a bis-cationic perylene bisimide photosensitizer (PBI2+) and a deca-anionic state-of-the-art water oxidation catalyst (Ru4POM). The artificial quantasome assembly forms in water, exploiting the complementary electrostatic interactions and hydrophobic-hydrophilic properties of the two selected molecular building blocks resulting in a supramolecular material (QS) with a definite chromophore to catalyst stoichiometry of 5:1. The structural characterization of this artificial quantasome (QS) and its building blocks, using state-of-the-art techniques of scanning probe microscopy and electron microscopy, is reported. The experiments performed point out to a lamellar structure of the supramolecular material resembling the self-organization of the natural enzyme PSII. This project aimed also at the synthesis of new artificial photosystems, indeed innovative hydrophilic photosynthetic materials are obtained by a combined supramolecular and click-chemistry strategy. The designed synthetic procedure adopted relies on click-chemistry functionalization of the N-terminal positions of PBI scaffolds. The functionalization of the N-terminal positions of a PBI scaffold set the parallelism with the natural antennae, that via N-terminal loops interactions modulate the structure of PSII-LHCII supercomplexes. Both new chromophores PBIn-TEGlock and PBI-TEGunlock present and estimated potential of the excited state suitable to drive photo-assisted water oxidation. Moreover, the synthetic route here reported is envisaged to maintain the positive peripherical charges on the molecular structures obtained in order to exploit complementary electrostatic interaction with Ru4POM water oxidation catalyst (WOC). The interactions of these new antennae with Ru4POM WOC yield unprecedented artificial quantasomes (QS-TEGlock, QS-TEGunlock) with tetraethylene glycol (TEG) functionalization. Photoelectrocatalytic characterization of the new artificial quantasomes is reported by coupling the supramolecular materials with state-of-the-art “inverse opal” indium tin oxide (IO-ITO) substrates. IO architectures are selected because their structure is reported to promote internal light scattering, due to the intrinsic geometry of the 3D-photoconductive lattice. QS-TEGlock exhibits a superior response for all the conditions explored, reporting a 340% photocurrent enhancement with respect to QS. In order to decouple the hydrophilic effect of TEG terminals from their cross-linking impact photoelectrocatalytic characterization of QS-TEGunlock is achieved. It is found that the decoration of the PBI chromophores with TEG residues, with or without cross-linking, can leverage the quantasome hydration and facilitate water oxidation reaction. Formation of TEG-templated hydration shells is verified by Raman microscopy of water exposed photoanodes.11 The presence of TEG-templated hydration shells sets a parallelism with natural PSII water channels. The added value of TEG cross-linkers is probed under prolonged photoelectrolysis whereby the unlocked structure reports a major photocurrent loss with respect to the locked one.
Among the possible technologies for artificial photosynthesis, photoelectrochemical cells possess the advantage to decouple the overall water splitting reaction into the related semi-reactions enabling the study and optimization of the single process. In this Thesis a novel approach towards artificial photosystems design has been reported. The quantasome approach is a unique bio-inspired design strategy that pair down to essentials the PSII mimicry by shaping an innovative supramolecular material with the essential components of the quantasome: a light-harvesting antenna and a catalytic reaction center embedded in a unique ensemble. Bonchio, Prato and co-workers reported the very first example of an artificial quantasome (QS), a supramolecular artificial photosystem designed for light-induced water oxidation reaction. This innovative material is composed of a bis-cationic perylene bisimide photosensitizer (PBI2+) and a deca-anionic state-of-the-art water oxidation catalyst (Ru4POM). The artificial quantasome assembly forms in water, exploiting the complementary electrostatic interactions and hydrophobic-hydrophilic properties of the two selected molecular building blocks resulting in a supramolecular material (QS) with a definite chromophore to catalyst stoichiometry of 5:1. The structural characterization of this artificial quantasome (QS) and its building blocks, using state-of-the-art techniques of scanning probe microscopy and electron microscopy, is reported. The experiments performed point out to a lamellar structure of the supramolecular material resembling the self-organization of the natural enzyme PSII. This project aimed also at the synthesis of new artificial photosystems, indeed innovative hydrophilic photosynthetic materials are obtained by a combined supramolecular and click-chemistry strategy. The designed synthetic procedure adopted relies on click-chemistry functionalization of the N-terminal positions of PBI scaffolds. The functionalization of the N-terminal positions of a PBI scaffold set the parallelism with the natural antennae, that via N-terminal loops interactions modulate the structure of PSII-LHCII supercomplexes. Both new chromophores PBIn-TEGlock and PBI-TEGunlock present and estimated potential of the excited state suitable to drive photo-assisted water oxidation. Moreover, the synthetic route here reported is envisaged to maintain the positive peripherical charges on the molecular structures obtained in order to exploit complementary electrostatic interaction with Ru4POM water oxidation catalyst (WOC). The interactions of these new antennae with Ru4POM WOC yield unprecedented artificial quantasomes (QS-TEGlock, QS-TEGunlock) with tetraethylene glycol (TEG) functionalization. Photoelectrocatalytic characterization of the new artificial quantasomes is reported by coupling the supramolecular materials with state-of-the-art “inverse opal” indium tin oxide (IO-ITO) substrates. IO architectures are selected because their structure is reported to promote internal light scattering, due to the intrinsic geometry of the 3D-photoconductive lattice. QS-TEGlock exhibits a superior response for all the conditions explored, reporting a 340% photocurrent enhancement with respect to QS. In order to decouple the hydrophilic effect of TEG terminals from their cross-linking impact photoelectrocatalytic characterization of QS-TEGunlock is achieved. It is found that the decoration of the PBI chromophores with TEG residues, with or without cross-linking, can leverage the quantasome hydration and facilitate water oxidation reaction. Formation of TEG-templated hydration shells is verified by Raman microscopy of water exposed photoanodes.11 The presence of TEG-templated hydration shells sets a parallelism with natural PSII water channels. The added value of TEG cross-linkers is probed under prolonged photoelectrolysis whereby the unlocked structure reports a major photocurrent loss with respect to the locked one.

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Tran, Anh. „Ruthenium-manganese complexes as models for artificial photosynthesis /“. Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3169.

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Johansson, Olof. „Ruthenium(II) Polypyridyl Complexes : Applications in Artificial Photosynthesis“. Doctoral thesis, Stockholm : Institutionen för organisk kemi, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-93.

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PIZZOLATO, ERICA. „New Molecules and Nano-materials for Artificial Photosynthesis“. Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908179.

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The Thesis project has been focused on innovative synthetic systems for artificial photosynthesis. This is a complex photocatalytic architecture that allows the conversion of solar light into chemical energy, enabling water splitting into hydrogen and oxygen under visible light irradiation. With the principal aim of orchestrating physical and chemical interfaces, a great research effort is currently dedicated at the optimization of the envisaged molecular components, including light-antennae, photosensitizers and multi-redox catalysts, as independent building blocks, together with their arrangement within nano-structured environments that define geometry, morphology and surface properties of the resulting photosynthetic system. In this Thesis, novel systems for photocatalytic water oxidation have been investigated, focusing on the design of catalyst-photosensitizers dyads by covalent (Chapter 2) or supramolecular strategies (Chapter 3). A final goal is the integration of these photosynthetic dyads on electroactive semiconductor surfaces, for the development of regenerative photoanodes (Chapter 4). The PhD work has been developed along three main research lines: 1) The synthesis and characterization of a novel covalent dyad based on a Co(II) catalyst and a Ru(II) photosensitizer moiety (E. Pizzolato et al. Phys. Chem. Chem. Phys. 2014, 16, 12000). Combined electrochemical and photophysical studies reveal that photoinduced, redox events involving the two metal centres occur within a short timescale of 15 ps, confirming efficient electronic interactions between the two units and functional water oxidation activity (Chapter 2). 2) The study of a novel supramolecular assembly, combining an organic metal-free bis-cationic perylene bisimide (PBI) photosensitizer with a totally inorganic anionic polyoxometalate (Ru4POM). This latter represents the state-of-the-art of molecular catalysts for water oxidation. This PBI self-assembles in water into 1-D structures and it provides one of the strongest photo-generated oxidant E(PBI*2+/1+) = 2.20 V vs NHE; its combination with Ru4POM is driven by electrostatic interactions and leads to the formation of a 2D porous hybrid architectures with a nano-lamellar sub-structure, alternating organic-inorganic molecular domains. This innovative supramolecular architecture shows: i) an ordered supramolecular structure; ii) fast photoinduced electron transfers (ET) in a 100 ps timescale (in the natural system, ET occur in the 40 µs-1.6 ms range); iii) oxygenic activity under visible light in neutral aqueous solution (E. Pizzolato et al. “Perylene bisimides-oxygenic/polyoxometalates photosynthetic assemblies”, manuscript in preparation) (Chapter 3). 3) The fabrication of composite photoanodes combining the photoactive PBI/Ru4POM nano-hybrid with nanocrystalline tungsten-oxide (nanoWO3) as the semiconductor acceptor layer. The photoelectrode demonstrates catalytic activity upon illumination with visible light (λ > 450 nm) in slightly acidic electrolyte (pH 3), with a maximum photocurrent density of 75 µA/cm2 at 1.20 V vs NHE and an Absorbed Photon to Current Efficiency (APCE) of 1.30%, superior to literature benchmark of 0.8% for PBI-sensitized photoelectrodes with IrO2 as oxygen evolving catalyst (Chapter 4). This result paves the way to further improvement concerning the decoration of the semiconductor surface to boost the photocatalytic performance and to improve the photoelectrode robustness.

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CECCONI, BIANCA. „Artificial Photosynthesis: Molecular Approaches for Photocatalytic Hydrogen Production“. Doctoral thesis, Università degli Studi di Milano-Bicocca, 2016. http://hdl.handle.net/10281/100472.

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The humankind today needs to face an epochal transition from a fossil fuel to a renewable source-based economy. Renewable sources are our chance to build a clean world with unlimited and widespread energy. Nowadays renewable energies could be properly harvested to produce electricity, while the development of a future clean fuel is less advanced. Since our energetic consumption is made essentially of fuels we need to build devices to transform renewable energy, such as solar radiation, into chemical energy of bonds. A promising future fuel is hydrogen since its carbon footprint is zero and it can be obtained from an abundant source such as water. Nature, through the photosynthesis, could inspire us to build our feed in the form of fuels. In this research project DSSC (dye-sensitized solar cells) have been modified to produce chemical energy instead of electricity. Attention has been focused on hydrogen production semi-reaction, thus the use of a sacrificial electron donor has been adopted. Such system is composed of TiO2 nanoparticles covered by a reduction catalyst and a metal-free organic sensitizer to harvest the visible spectrum of solar radiation. The aim of this research has been the development of molecular approaches to provide efficient light harvesting systems and reduction catalysts. Molecular design allowed a fine tuning of materials properties and a deep understanding of structure/performances relationships. The first part of the project has focused on designing push-pull structures to harvest visible light portion of solar spectrum. Fine molecular tuning of metal-free dyes afforded enhanced performances depending on the kind of modification. We modified a known phenothiazine dye in the donor, spacer and acceptor units in order to derive structure/performances relationships. Enhanced light harvesting properties and photo-stability have been afforded through π-spacer modification with various mono- and polycyclic simple and fused thiophene derivatives, while decoration of the donor core with glycolic or sugar chains gave better hydrophilicity and surface wettability. Lastly hydroxamic acids have been introduced as alternative anchoring groups to give stronger ester bonds on TiO2 surface and prevent hydrolysis in aqueous media. The second part of the research has concerned the study of cobaloximes as alternative noble metal free reduction catalysts. Starting from a mini-library of cobaloximes bearing various equatorial bridges, axial ligands, and starting oxidation numbers, molecular structure/efficiency studies have been done, while UV/Vis spectroscopy has been used to investigate the nature of the eventual Co(I) species transiently formed. For cobaloximes a Co(I) species is hypothesized but not confirmed in photocatalytic experiments and optimization of efficiency and stability of new catalysts need a deep understanding of the catalytic cycle in order to intervene in the critical intermediates.

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Parra, Puerto Andrés. „Towards Artificial Photosynthesis: Photoelectrochemical CO2 Reduction to Solar Fuels“. Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/347965.

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This thesis is devoted to prove the concept of the CO(2) reduction to CH(4) with a decreasing in the voltage requirements using a photocatalytic mechanism. Subsequently, part of the solar energy is transferred to the reaction, obtaining an improvement in the total energy balance. The work developed intends first, to take advantage of the know features of the photoactive nanostructured materials obtained by anodization and hydrothermal synthesis (allowing to obtain better surface areas and improving the photon collection, light photosynthetic reactions). Second investigate the copper and copper oxide cathodes for the CO(2) electroreduction activity to CH(4) (dark photosynthetic reactions) using a complete cell to understand the parameters involved in the process and the products selectivity for each cathodes. And third the implementation of the photoanode and cathode in a photoelectrochemical complete cell. Respect the photoactive materials we are going to talk about TiO(2) based nanostructured materials for water splitting. The first TiO(2) nanostructuration under study are nanotubes obtained by anodization of a Titanium foil using organic electrolytes. The TiO(2) crystal phase obtained by this technique was anatase. The next step in this material was the surface modification to improve the efficiency. To obtain this improvement the anodization process was done using two electrolytes in different steps. As sequence a porous surface with an increment in the surface area was obtained. After, the photoelectrochemical measurements were done in 1 M of sodium hydroxide (NaOH) under AM 1.5G illumination source to observe the photoactivity of these samples. The second nanostructured materials under study were TiO(2) nanorods obtained by hydrothermal synthesis over a conductive glass substrate, Fluorine Tin Oxide (FTO). The nanorods using this technique have rutile structure. An optimization of two parameters involved in the hydrothermal synthesis was studied: (1) initial titanium precursor concentration and (2) increasing the chlorine concentration to obtain larger and thinner rods. To enhance the photoactivity of TiO(2) we try to incorporate other materials inside the structure. The materials selected were: tin which improves the charge carriers, vanadium which allows the absorption in the visible range and nitrogen doping to enhance the efficiency in the photoactivity of the material. Concerning to methane production study, a discussion about the electrochemical CO(2) reduction activity over a copper based electrode using a hydrogen carbonate as supporting electrolyte was done, where the positive ions used are sodium and potassium. The first electrode selected is a pristine copper due to the interest of the methane production. The samples were characterized by scanning electronic microscopy (SEM) and X-Ray diffraction (XRD) to visualize the surface morphology and the crystal structure of the electrode. Afterwards, the electrochemical process is studied to understand the activity of these electrodes. Chronopotentiostatic (CP) experiments were done at different current densities to observe the activity as a function of the reached potential. The second electrode under study was a copper oxide cathode. In the electrochemical experiments an effect was studied related to the electrochemical reduction of the different copper oxide layers generated during the thermal synthesis, leading to a catalytically active copper that enables carbon dioxide reduction. With this type of electrodes a time- dependence test was done to carefully study these crystallographic changes. Finally, another important variable for CO(2) conversion was studied, the humidification of the CO(2) gas stream before the introduction in the electrochemical cell with the impact on the faradaic efficiency of the process. In the implementation in the PEC cell an evaluation of the photoanode and cathode was done. In this evaluation, the external potential requirements were studied concerning about the energy consumption and the benefit from the photoactivated process.
Esta tesis se ha desarrollado con el objetivo de probar el concepto de la reducción del dióxido de carbono a metano, mediante una reducción de los potenciales necesarios usando un mecanismo fotocatalítico. Parte de la energía solar es transferida a la reacción obteniendo una mejora en el balance energético total. El trabajo desarrollado se focaliza primero en el estudio de materiales nanoestructurados fotoactivos basados en dióxido de titanio obtenidos por anodización, generando nanotubos, y por síntesis hidrotermal obteniendo nanohilos sobre un sustrato conductor transparente, los cuales permiten obtener mayores superficies activas mejorando la colección de fotones, similar a las reacciones luminosas en la fotosíntesis. En segundo lugar, se ha estudiado la electroreducción del dióxido de carbono a metano usando cátodos de cobre y oxido de cobre (similar a las reacciones oscuras de la fotosíntesis). Usando el cobre como cátodo, se ha observado la obtención de metano a diferentes densidades de corriente aplicadas para poder observar la productividad respecto al potencial medido. Para el caso de los cátodos de óxido de cobre, no se ha encontrado producción de metano pero si de etileno. En estos cátodos se ha observado un efecto proveniente de la reducción de las capas de los diferentes óxidos de cobre, generados en la síntesis térmica, hacia un cobre catalíticamente activo para la reacción de reducción del dióxido de carbono. Este efecto se ha estudiado profundamente mediante un estudio de los cambios cristalográficos y superficiales a determinados tiempos. Finalmente, se ha estudiado el efecto de la humidificación del dióxido de carbono (gas) previa a la entrada a la celda electroquímica. Como parte final se ha realizado una evaluación energética de los fotoánodos generados por síntesis hidrotermal y de los cátodos basados en cobre estudiados, para poder implementar ambos en una celda fotoelectroquímica completa. En esta parte se ha estudiado los valores de los potenciales externos necesarios para que se pueda dar la reacción, asumiendo un 100% de eficiencia hacia la producción de metano para los cátodos de cobre y de etileno para los de óxido de cobre.

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Goberna, Ferrón Sara. „Novel molecular catalysts for water oxidation: towards artificial photosynthesis“. Doctoral thesis, Universitat Rovira i Virgili, 2013. http://hdl.handle.net/10803/129180.

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L’objectiud’aquesta tesi és el desenvolupamenticaracteritzacióde nouscatalitzadors per a l’oxidació d’aigua a partir complexos metàl•lics, especialment amb metalls de la primera sèrie de transició. En el segon capítol d’aquesta tesi s’explora la activitat catalítica homogènia per a l’oxidació d’aigua d’un compost de ruteni d’enllaç metall-metall, [Ru2(μ-O2CCH3)4]. Aquest catalitzador esta estabilitzat perlligands disponibles i de baix cost, per tant no requereix el disseny delligands orgànics. El tercer capítol d’aquesta tesi estudia l’activitatcatalítica d’un nou compost de cobalt basat en la química dels polioxometalts: [Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]16− (Co9). Els nostres experiments demostren que aquest compost és un catalitzador homogeni per a l’oxidació d’aigua produïda químicament, electroquímicament o induïda per llum. En el quart capítol d’aquesta tesi es relata la preparacióicaracterització d'unpolímerbasaten un compost de cobalt de tipus blau de Prússia, hexacianoferratde cobalt (CoHCF),queposseeixmoltes delescaracterístiquesclau: es formaa partir de metalls abundants, funcionaa pHneutreicondicions ambientalsi ésrobust.
The objective of this thesis is the development and characterization of new catalysts for the oxidation of water from metal complexes, especially first row transitionmetals. In the second chapter of this thesis we explore the homogeneous catalytic oxidation of water with a metal-metal bonded ruthenium compound [Ru2(μ-O2CCH3)4]. This catalyst is stabilized by available and inexpensive ligands, so it does not require the design of organic ligands. The third chapter of this thesis report the catalytic activity of a new cobalt compound based on polioxometalate chemistry [Co9(H2O)6(OH)3( HPO4 )2(PW9O34)3]16-( Co9). Our experiments show that this compound is a homogeneous catalyst for the oxidation of water produced chemically, induced by light or electrochemically. The fourth chapter of this thesis describes the preparation and characterization of a Prussian blue type polymer: cobalt hexacyanoferrate (CoHCF), which posses many of the key features necessaries for a viable WOC: it is formed from inexpensive metals, it works at neutral pH and ambient conditions and it is robust.

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Gil, Sepulcre Marcos. „Ru, Co and Ca-based catalysts for artificial photosynthesis“. Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/462105.

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La fotosíntesis artificial ofrece una alternativa al panorama energético actual, basado en el consumo de combustibles fósiles. Tratando de emular la fotosíntesis de las plantas, este campo de estudio trata de utilizar la luz solar para producir electrones, protones y oxígeno a partir del agua, para más tarde utilizar los electrones para producir hidrógeno u otros combustibles, y almacenar de esta forma la energía solar en forma de enlaces químicos. Para hacer energéticamente viables estos dos procesos es necesario el uso de catalizadores, comúnmente basados en metales de transición. En el primer capítulo se introduce brevemente la motivación que ha llevado a la realización de la tesis, discutiéndose también los aspectos mecanísticos más relevantes de la catálisis de oxidación de agua, así como la reducción de protones, dando una visión general de los catalizadores en ambos campos más relevantes hasta la fecha. El segundo capítulo se centra en los objetivos de este trabajo. El objetivo principal de esta tesis es la síntesis y caracterización estructural y electroquímica de varios catalizadores de Ru, Cu y Co, y el posterior estudio de su reactividad en catálisis de oxidación de agua y/o reducción de protones. El objetivo final es comprender sus mecanismos de reacción y los factores que afectan a su actividad catalítica para ayudar al diseño futuro de catalizadores más eficientes y robustos. En el tercer capítulo se presenta la síntesis, caracterización y reactividad de una nueva familia de complejos de Ru. Un estudio espectroscópico y cinético detallado ha permitido identificar la formación de nuevas especies tras oxidación de los complejos en soluciones acuosas, las cuales tienen una implicación directa en su comportamiento en catálisis de oxidación de agua. El cuarto capítulo aborda la síntesis y caracterización de una nueva familia de complejos de Cu, estudiándose su reactividad en catálisis de oxidación de agua y comparándose con la de los complejos de cobre más relevantes reportados hasta la fecha en la bibliografía. Finalmente, en el quinto capítulo se presenta la desactivación de un cluster molecular de CoII/CoIII cuando este se somete a potenciales de reducción, dando lugar a la formación de nanopartículas de CoO o CoO(OH) depositadas sobre un electrodo de carbono. Dichas nanopartículas han sido probadas en catálisis de reducción de protones y su reactividad relacionada con su morfología y naturaleza. En el sexto capítulo se incluyen las conclusiones más relevantes del trabajo realizado. Finalmente, el último capítulo contiene un anexo que incluye otros trabajos realizados y publicados durante esta tesis relacionados con el tema principal de esta tesis.
Artificial photosynthesis offers a viable alternative to the actual energetic model based mainly in the consumption of fossil fuels. Trying to emulate the photosynthesis process in higher plants, this area of study attempts to use sunlight in order to produce electrons, protons and oxygen from water, with the aim of using the released electrons for producing hydrogen or other useful fuels. Within this context, the use of catalysts usually based in transition metals is necessary to make these two processes viable. The first chapter contains a brief introduction about the motivation for the research presented in this thesis. The most relevant general mechanistic aspects for water oxidation (WO) as well as proton reduction catalysis are also presented, giving a general view of most relevant catalysts reported to date. The second chapter is focused in the objectives of this work. The main goal of this PhD thesis is the synthesis and the structural and electrochemical characterization of a series of Ru, Co and Cu-based catalysts and the ulterior study of their reactivity towards water oxidation and/or proton reduction catalysis. The final objective is to fully understand the mechanistic pathways and the factors that affect their catalytic performance for helping in the future rational design of more efficient and robust catalysts. In the third chapter, the synthesis, characterization and reactivity of a new family of Ru complexes is presented. A series of detailed electrochemical, spectroscopic and kinetic studies allows the identification of new species formed after oxidation of the complexes in aqueous solution that proved to be key for further understanding their catalytic behavior in water oxidation. The fourth chapter presents the synthesis and characterization of a new family of Cu complexes. Their reactivity towards water oxidation has been studied and compared with that of the most relevant Cu-based WO catalysts reported in the literature. Finally, in the fifth chapter we present the deactivation of a CoII/CoIII molecular cluster after application of reductive potentials, giving rise to the formation of CoO or CoO(OH) nanoparticles deposited onto a glassy carbon electrode. The ability of these nanoparticles for reducing protons has been tested, and their catalytic performance discussed on the basis of the nature of the species obtained and their morphology . In the sixth chapter the most relevant conclusions of this work are discussed. Finally, the last chapter includes an annex containing other works that have been carried out and published during this PhD thesis and that are closely related with the work carried out during the PhD.

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Tran, Anh. „Ruthenium-Manganese Complexes as Model Systems for Artificial Photosynthesis“. Doctoral thesis, KTH, Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3169.

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Karlsson, Susanne. „Single and Accumulative Electron Transfer – Prerequisites for Artificial Photosynthesis“. Doctoral thesis, Uppsala universitet, Kemisk fysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-122206.

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Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabsorption and electron transfer is further used for the oxidation of water and reduction of carbon dioxide to sugars. The work presented in this thesis is part of an interdisciplinary effort aiming at a functional mimic of photosynthesis. The goal of this project is to utilize sunlight to produce renewable fuels from sun and water. Specifically, this thesis concerns photoinduced electron transfer in donor(D)-photosensitizer(P)-acceptor(A) systems, in mimic of the primary events of photosynthesis. The absorption of a photon typically leads to transfer of a single electron, i.e., charge separation to produce a single electron-hole pair. This fundamental process was studied in several molecular systems. The purpose of these studies was optimization of single electron transfer as to obtain charge separation in high yields, with minimum losses to competing photoreactions such as energy transfer.Also, the lifetime of the charge separated state and the confinement of the electron and hole in three-dimensional space are important in practical applications. This led us to explore molecular motifs for linear arrays based on Ru(II)bis-tridentate and Ru(II)tris-bidentate complexes. The target multi-electron catalytic reactions of water-splitting and fuel production require a build-up of redox equivalents upon successive photoexcitation and electron transfer events. The possibilities and challenges associated with such processes in molecular systems were investigated. One of the studied systems was shown to accumulate two electrons and two holes upon two successive excitations, without sacrificial redox agents and with minimum yield losses. From these studies, we have gained better understanding of the obstacles associated with step-wise photoaccumulation of charge and how to overcome them.

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Anderlund, Magnus. „Dinuclear Manganese Complexes for Artificial Photosynthesis : Synthesis and Properties“. Doctoral thesis, Stockholm : Dept. of organic chemistry, Stockholm university, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-396.

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Zhang, Haoyu. „Studies of zeolite-based artificial photosynthetic systems“. Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1203019490.

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Planas, Roure Nora. „Ruthenium polypyridyl complexes relevant to the catalytic processes in artificial photosynthesis“. Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/33515.

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Una de les estratègies en el campde la fotosíntesis artificial consisteix en un sistema modular en que els diferents components indispensables d’un un aparell funcional són estudiats de manera independent per al seu futur acoblament. Aquesta tesi s’ha centraten la sintesis i caracterització d’una sèrie de nous compostos mono- i dinuclears de ruteni amb lligands de tipus polipiridil. S’ha estudiat l’aplicabilitat d’aquests nous compostos com a catalitzadors en processos tant importants com son l’oxidació d’ aigua a oxigen molecular i la reduccio de diòxid de carboni a àcid fòrmic. També, s’han estudiat en gran detall les propietats d’origen supramolecular detectades en els compostos dinuclears, fomentat per la directa implicació d’aquest tipus d’interaccions en els processos catalítics estudiats.
Artificial photosynthesis seeks to functionally mimik the photosynthetic process carried out by nature, and combine the energy from the sun with water to obain a “solar” fuel like hydrogen. One of the strategies in the field, consists on a modular approach in which all the components needed are studied independently, in view of their future assembly in a final operative device. This thesis has been focused on the synthesis and characterization of a series of new mono and dinuclear ruthenium componud with polylpyridylic ligands. The aplication of these new compounds as catalysts in very important processes such as water oxidation and CO2 reduction has been studied. Additionally, the suprmolecular properties detected in the dinuclear compounds has been studied in great detail, which has been promoted by the direct implication of such type of interactions in the catalytic processes studied.

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Stolper, Thorsten. „Theoretical Studies of Ru- and Re-based Catalysts for Artificial Photosynthesis“. Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-002E-E346-F.

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Berglund, Baudin Helena. „Electron and Energy Transfer in Supramolecular Complexes Designed for Artificial Photosynthesis“. Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5033-4/.

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Wolpher, Henriette. „Ruthenium(II) polypyridyl complexes in supramolecular systems relevant to artificial photosynthesis /“. Stockholm : Department of Organic Chemistry, Ahrrenius Laboratory, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-417.

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Stephani, Carolynn Kay. „Artificial Photosynthesis: An Investigation of Silicon Nanowires in Nickel Catalyzed Carboxylation“. Thesis, Boston College, 2014. http://hdl.handle.net/2345/3863.

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Thesis advisor: Kian L. Tan
Thesis advisor: Dunwei Wang
Silicon nanowires are utilized to harvest the energy from visible light. The introduction of a nickel pre-catalyst, 1, allows for this energy to be stored in chemical bonds, which are subsequently used in the carboxylation of 4-octyne
Thesis (MS) — Boston College, 2014
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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Arismendi, Romero Graciela. „Photosystem II and artificial photosynthesis: looking for an alternative energy source“. Revista de Química, 2013. http://repositorio.pucp.edu.pe/index/handle/123456789/99765.

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Con la elucidación de la estructura cristalina del Fotosistema II (PSII) se ha dado un paso importante en la búsqueda de nuevas alternativas de energía ambientalmente amigables. El intento de imitar la reacción que caracteriza a la fotosíntesis (para poder generar combustibles poco contaminantes), podría representar una nueva oportunidad en la reducción de nuestra dependencia de los combustibles fósiles.
With the elucidation of the crystal structure of photosystemII (PSII), an important step in the search for new environmentally friendly energy alternatives has been taken. The attempt to imitate the characteristic reaction of photosynthesis (in order to manufacture ecologically friendly fuels) could represent a new opportunity to reduce our dependence on fossil fuels.

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Zhang, Ketian. „Mixed ion and electron conducting polymer composite membranes for artificial photosynthesis“. Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121607.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references.
Inspired by the fact that OH- has a very high mobility in water, highly conductive OH⁻conducting membranes were developed for alkaline water electrolysis. The membranes were semi-interpenetrating networks of crosslinked poly(vinyl alcohol) (PVA) and a polycation miscible with PVA. It is analogous to aqueous strong base solution. The polycation is a OH- containing polymer; PVA solvates this polycation and facilitates the ion conduction via Grotthuss mechanism. The membrane with proper composition has an exceptionally high OH⁻ conductivity of 151 mS/cm, 6.51 times as high as the commercial membrane Neosepta AHA. At the same time, the hydrogen bonds and covalent crosslinks in the system give this membrane a high tensile strength of 41 MPa in the wet state, 46% higher than the Neosepta AHA membrane. Insight in the ion conduction mechanism was gained by spectroscopic studies and the measurement of OH- conduction activation energy.
This material system is also highly anion perm-selective, a feature critical to sustaining the pH gradient in bipolar membrane based artificial photosynthesis devices. A highly transparent mixed proton and electron conducting membrane was developed. The Nafion and reduced graphene oxide (rGO) were chosen as the proton conducting polymer matrix and the electrically conductive filler respectively. The filler has a high aspect ratio. As predicted by simulations, it will have low percolation threshold if homogeneously dispersed. To achieve this homogeneity, water-aided mixing was employed followed by fast freezing in liquid nitrogen. Though rGO is a light absorber, the extremely low percolation threshold (0.1%) allows us to achieve sufficient electrical conductivity with only a small volume fraction of rGO. Therefore, the membrane was highly transparent in addition to its ability to conduct both electrons and protons.
Detailed modeling of the energy loss from conduction, light absorption, and gas crossover was conducted, showing that this material system is promising for the artificial photosynthesis application.
by Ketian Zhang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

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Wang, Xia. „Artificial Photosynthesis : Carbon dioxide photoreduction and catalyst heterogenization within solid materials“. Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET025/document.

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Dans le contexte du réchauffement climatique et de l’usage abusif de combustibles fossiles, la recherche de sources d’énergie propres et durables est l’un des défis les plus importants de notre époque. Récemment, le stockage d’énergie solaire par la réduction de CO2 a fait l’objet d’un nouvel intérêt. Bien que la réduction de CO2 en carburants liquides ou gazeux soit une question à la fois fascinante et fondamentale, sa mise en œuvre dans les dispositifs technologiques reste très difficile à cause de la grande stabilité de CO2 et du caractère endergonique de sa transformation. On outre, les réactions impliquent multiples électrons et protons et ainsi demandent des catalyseurs efficaces et stables pour diminuer les barrières cinétiques importantes.Cette comprend deux parties. Après une introduction, la première partie décrit des études sur des catalyseurs homogènes en combinaison avec un photosensibilisateur, soit séparément soit connecté par liaison covalente. Grâce à la possibilité de les modifier par synthèse et à leur facile caractérisation, les photosystèmes moléculaires homogènes sont plus modulables et peuvent permettre un meilleur contrôle de la sélectivité des réactions et l’étude des mécanismes réactionnels.Cependant, les catalyseurs moléculaires ne peuvent être facilement transposés pour des applications à plus large échelle dans un contexte industriel. En effet, les catalyseurs homogènes sont moins stables et plus difficilement recyclables que les catalyseurs hétérogènes. Dans ce contexte, l’intégration de catalyseurs moléculaires au sein d’un support solide a l’avantage de maintenir leur activité catalytique tout en permettant une séparation et un recyclage plus faciles. La deuxième partie de cette thèse porte donc sur l’immobilisation de catalyseurs moléculaires dans les matériaux. Le but ultime de cette thèse est d’incorporer à la fois le catalyseur et le photosensibilisateur dans le support solide
In the context of global warming and the necessary substitution of renewable energies (solar and wind energy) for fossil fuels, efficient energy-storage technologies need to be urgently developed. Recently, energy storage via the reduction of CO2 has seen renewed interest. Although reduction of CO2 into energy-dense liquid or gaseous fuels is a fascinating fundamental issue, its practical implementation in technological devices is highly challenging due to the high stability of CO2 and thus the endergonic nature of its transformation. Furthermore, the reactions involve multiple electrons and protons and thus require efficient catalysts to mediate these transformations.The objective of this thesis is to investigate different strategies for the storage of solar energy in chemical compounds, through visible-light-driven CO2 reduction. This thesis comprises of two main parts. After an introduction, the first part describes the investigation of homogeneous catalysts in combination with a photosensitizer, either separately or connected covalently. Due to the easily-tunable synthesis and facile characterization of molecular catalysts, homogeneous photosystems are more controllable and can give deep insight into product selectivity and mechanistic issues.With regards to future applicability, however, homogeneous catalysis often suffers from additional costs associated with solvents, product isolation and catalyst recovery, amongst other factors. The integration of molecular catalysts into solid platforms offers the possibility to maintain the advantageous properties of homogeneous catalysts while moving towards practical system designs afforded by heterogeneous catalysis. The second part of this thesis is therefore the immobilization of molecular catalysts within solid materials, namely MOFs and PMO. The ultimate goal of this thesis is to incorporate both catalyst and photosensitizer into the solid support

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GALLONI, PIERLUCA. „Construction of electron-active complex systems as model for artificial photosynthesis“. Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2004. http://hdl.handle.net/2108/202905.

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La fotosintesi artificiale è un obiettivo ambizioso per la scienza moderna, che richiede una comprensione completa dei sistemi naturali. La comprensione di tutte le diverse reazioni del sistema è uno degli aspetti fondamentali nella ricerca chimica, fisica e biologica. Lo studio delle reazioni di trasferimento elettronico tra un accettore e un donatore è un punto cruciale, sia per lo sviluppo di sistemi artificiali sintetici, sia per possibili applicazioni nella costruzione di dispositivi elettronici e materiali fotosensibili. Lo scopo di questa tesi è stato quello di investigare reazioni di trasferimento elettronico e di energia, per avere informazioni riguardo le leggi che regolano questi sistemi complessi, usando diversi sistemi donatore-accettore, tra i quali particolare attenzione è stata rivolta al C60 come accettore e al ferrocene come donatore. Il lavoro sintetico è stato una parte importante della tesi, richiedendo tempo per ottimizzare le condizioni di reazione, le procedure di purificazione e per la completa caratterizzazione dei prodotti. Numerosi nuovi composti sono stati sintetizzati e sono state migliorate le rese per alcuni prodotti noti da letteratura. Un aspetto importante del lavoro ha riguardato lo studio dell’interazione tra donatore e l’accettore in alcune delle diadi ottenute, sia allo stato fondamentale, sia nello stato eccitato. Tra i vari risultati, i più interssanti possono essere riassunti nei seguenti punti. a) Un andamento peculiare emerge dagli esperimenti fotofisici e computazionali e dalle misure elettrochimiche e degli spettri di assorbimento nelle diadi fluorene-fullerene: cambia l’interazione, cambiando la posizione del fluorene che lega il fullerene. b) Risultati molto interessanti sono stati ottenuti quando ferrocene e fullerene sono uniti tramite legame spiro, dando una diade dalla geometria rigida. Difatti, confrontando le proprietà nello stato eccitato di questa diade con quelle della N-metil-2-ferrocenil-[3,4]-fulleropirrolidina, con maggiore libertà conformazionale, è stata osservata una reazione di trasferimento elettronico più veloce, indice di una maggiore interazione tra i due componenti. c) In diadi supramolecolari composte da ZnSalen e N-metil-2-piridil-[3,4]-fulleropirrolidina è stato osservato un efficiente trasferimento di energia. Questo sistema può essere usato come modello nei sistemi impiegati nella cattura della luce. d) Un efficiente trasferimento di elettroni avviene tra la tetraferrocenilporfirina di zinco e la N-metil-2piridil-[3,4]-fulleropirrolidina in una diade supramolecolare, come è stato osservato tramite la spettroscopia transiente, dove un tempo di vita di 800 ps della specie eccitata a separazione di carica è stato ottenuto in un solvente apolare come il toluene. In conclusione, sono stati ottenuti nuovi sistemi per lo studio delle reazioni di trasferimento di energia e di elettroni, che sono stati studiati usando diversi approcci sperimentali. I risultati possono essere di aiuto sia per una miglior comprensione dei fenomeni naturali, sia per lo sviluppo e la costruzione di dispositivi fotosensibili.
Artificial photosynthesis is an ambitions target of modern science that obviously requires a complete understanding of natural photosynthesis. The understanding of all steps involved is one of the most important topic in chemical, biological, and physical research. The study of electron transfer reaction between donor and acceptor molecules is a crucial key point, both for development of artificial photosynthesis and for application in electronic devices and photosensible materials. The aim of this thesis was to investigate electron and energy transfer reactions, as source of information about the mechanisms that rule this complex reaction, using different donor-acceptor systems, among which attention have been focused at C60 as acceptor and ferrocene as donor. Synthetic work constituted a major task in this thesis, requiring several attempts in order to optimize reaction conditions, purification procedures and full characterization of products. A number of new compounds was obtained together with improved yields of known products. Another important aspect of the work involved investigation of donor-acceptor interaction in some of the dyads, both in ground and in excited states. Among all the results, the most significant ones may be summarized in the following points. a) A peculiar behaviour emerged from photophysical and computational experiments, electronic spectra and electrochemical measurements of fluorene-fullerene dyads. Different interaction was the result of changing the position through which the two moieties are connected. b) Very interesting results emerged when a frozen structure was obtained from connecting ferrocene and fullerene moieties in a rigid assembly. In fact, in comparison with a dyad with flexible connection, a faster electron transfer rate - and therefore an enhanced interaction - was observed in the excited state. c) Efficient energy transfer was observed with supramolecular (ZnSalen)-(N-methyl-2-pyridyl-[3,4]fulleropyrrolidine) dyads. This system can be used as a good model for light harvesting model. d) Very efficient electron transfer reaction occurred between zinctetraferrocenylporphyrin and pyridylfulleropyrrolidine in supramolecular (ZnFc4Porph)-(N-methyl-2-pyridyl-[3,4]-fulleropyrrolidine) dyad, as observed by transient spectroscopy, even in non polar solvent such as toluene. In conclusion, new good systems for energy an electron transfer were obtained and investigated by different approaches. They can be used to reach a deeper knowledge of complex phenomena that rule natural photosynthesis as well as to build photosensible devices.

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Lim, Gary Lloyd Nogra. „Elucidation of Photoinduced Energy and Electron Transfer Mechanisms in Multimodular Artificial Photosynthetic Systems“. Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984185/.

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Multimodular designs of electron donor-acceptor systems are the ultimate strategy in fabricating antenna-reaction center mimics for artificial photosynthetic applications. The studied photosystems clearly demonstrated efficient energy transfer from the antenna system to the primary electron donor, and charge stabilization of the radical ion pair achieved with the utilization of secondary electron donors that permits either electron migration or hole transfer. Moreover, the molecular arrangement of the photoactive components also influences the route of energy and electron transfer as observed from the aluminum(III) porphyrin-based photosystems. Furthermore, modulation of the photophysical and electronic properties of these photoactive units were illustrated from the thio-aryl substitution of subphthalocyanines yielding red-shifted Q bands of the said chromophore; hence, regulating the rate of charge separation and recombination in the subphthalocyanine-fullerene conjugates. These multicomponent photosystems has the potential to absorb the entire UV-visible-NIR spectrum of the light energy allowing maximum light-harvesting capability. Furthermore, it permits charge stabilization of the radical ion pair enabling the utilization of the transferred electron/s to be used by water oxidizing and proton reducing catalysts in full-scale artificial photosynthetic apparatuses.

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Hegner, Franziska Simone. „Experimental and theoretical investigation of Prussian blue-type catalysts for artificial photosynthesis“. Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/666291.

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Bachmeier, Andreas S. J. L. „Metalloenzymes as inspirational electrocatalysts for artificial photosynthesis : from mechanism to model devices“. Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:eb1e648d-3a55-48ee-bd6e-c3212e65bac0.

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Artificial photosynthesis, an important route towards future supply of renewable energy, seeks to convert sunlight into storable chemical energy such as fuels. Building upon the principles of biological solar energy conversion, artificial photosynthesis can be broken down into four essential processes: harvesting of visible light, charge (electron-hole) separation, oxidation of water to dioxygen, and fuel formation. Importantly, unlike natural photosynthesis, artificial photosynthesis is solely dedicated to efficient formation of fuels and is not restricted by the availability of arable land. Both water oxidation and fuel formation require efficient and selective catalysts. This work utilises certain metalloenzymes, which have evolved to catalyse fuel-generating reactions such as the formation of H2 or the reductive activation of CO2 to carbon-based fuels with unmatched efficiencies. In contrast to most artificial catalysts, these enzymes are composed solely of abundant elements and operate efficiently at neutral pH. Thus, although not suitable for scale-up, they can be used to mimic conditions under which future devices will have to operate and provide design criteria for the components of applied technologies. In this thesis, physico-chemical techniques are used to study the mechanism of [FeFe]-hydrogenases, the most proficient H2 evolving catalysts that rival platinum in activity, by investigating how reversible inhibitors intercept transient enzyme states. The interaction of fuel-forming enzymes with light-absorbing semiconductor electrodes is also explored, leading to the construction of a photoelectrochemical cell for the selective, light-driven reduction of CO2. Furthermore, this thesis demonstrates that metalloenzymes can be used to establish new directions in artificial photosynthesis research, driving endergonic organic reactions such as specific C=C hydrogenation.

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Lee, Hyunjung. „DESIGN AND PHOTOCHEMICAL STUDIES OF ZEOLITE-BASED ARTIFICIAL PHOTOSYNTHETIC SYSTEMS“. The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1039117753.

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De, Tovar Villanueva Jonathan. „Pd and Co-based (nano)catalysts for C-C coupling and artificial photosynthesis“. Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/565829.

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Berggren, Gustav. „Mimicking nature synthesis and characterisation of manganese complexes of relevance to artificial photosynthesis /“. Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-108526.

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NIORETTINI, Alessandro. „Electroreduction of carbon dioxide over nanostructured metallic cathodes: a route towards artificial photosynthesis“. Doctoral thesis, Università degli studi di Ferrara, 2023. https://hdl.handle.net/11392/2504901.

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Come è ormai ben noto i livelli di anidride carbonica nell’atmosfera stanno costantemente aumentando a causa delle attività umane contribuendo ogni giorno di più all’incremento dell’effetto serra la cui lotta rappresenta attualmente una delle più grandi sfide per la società contemporanea. In questo contesto la conversione elettrocatalitica dellaCO2 rappresenta un’interessante approccio a questo problema dal momento che permette di pensare a quello che fino ad oggi non può essere considerato altrimenti se non un prodotto di scarto, come ad una nuova ed interessante risorsa virtualmente ad impattoambientale nullo. Attraverso i processi riduttivi proposti in questo lavoro è infatti possibile accedere a molecole di grande importanza industriale ed energetica e dall’elevato valore aggiunto come ad esempio acido formico, metano e Syngas (una miscela di CO ed H2 alla base dei processi industriali di tipo Fisher-Tropsch utilizzati per la sintesi di idrocarburi). Tra i molti metalli che manifestano attività catalitica in questi processi il rame occupa sicuramente un ruolo centrale. Il lavoro principale esposto in questa tesi è infatti incentrato nello sviluppo di tecniche nuove ed innovative per incrementare la selettività di questo metallo attraverso procedure di nanostrutturazione e funzionalizzazione con diverse specie metalliche. Una delle vie maggiormente percorsa consiste nella formazione controllata di ossidi di rame sottoposti poi ad una successiva riduzione nello stesso ambiente di CO2R. Numerose strategie sono state riportate in letteratura a questo proposito. Sulla base di questi lavori è descritto un metodo puramente elettrochimico ed innovativo per la sintesi di interfacce rame-indio dalle ottime proprietà catalitiche. Questo tipo di catodi è stato studiato nel dettaglio e caratterizzato morfologicamente ed elettrochimicamente permettendo di poter osservare efficienze riduttive in grado di eccedere il 70% in solo monossido di carbonio con una conseguente selettività verso il Syngas attorno al 100% dipendentemente dal potenziale applicato e dalla quantità di indio fissata sulla superficie. La letteratura in merito ad elettrodi Cu-In è tuttora molto limitata, in particolare i catodi Cu-In descritti in questa tesi sono in grado di produrre selettivamente miscele di Syngas ideali per la sintesi di metanolo ed aldeidi (oltre che di idrocarburi a più elevato peso molecolare) a potenziali particolarmente accessibili contenuti in una finestra che va da -1.3V a -1.6V vs SCE con delle correnti associate compatibili per applicazioni su più ampia scala. Durante questo lavoro di ricerca sono stati sperimentati anche diversi altri metalli per la funzionalizzazione delle interfacce di rame, in particolare risultati interessanti sono stati ottenuti anche con la deposizione di Cerio, che ha modificato la selettività verso la produzione del metano con efficienze massime osservate attorno al 40%. Inoltre grazie ad una collaborazione con l’università di Milano è stato possibile studiare le caratteristiche di particolari catodi in oro depositati su FTO tramite PLD che si sono dimostrati particolarmente selettivi nei confronti del CO e dell’acido formico. La deposizione PLD ha infatti permesso di accedere a nuove e peculiari nano strutture non ottenibili tramite le tecniche tradizionali di deposizione. Sono infatti descritte interfacce decorate da nanostrutture di forma colonnare e porosa, quest’ultima particolarmente selettiva per miscele di Syngas 40% CO e 60% H2 (ideale per la sintesi di idrocarburi a vario range di pesi molecolari) prodotte a potenziali relativamente blandi attorno a -1.1V vs SCE. Il lavoro contenuto in questa tesi di dottorato è stato oggetto di pubblicazioni su riviste di settore ed ha portato al deposito di un brevetto italiano ed europeo grazie alla collaborazione con realtà industriali interessate all’applicazione di questo tipo di tecnologie.
The level of carbon dioxide in the atmosphere is constantly growing mainly due to anthropogenic activities causing the well known greenhouse effect that represent one of the greatest challenges to contemporary society. On this regard electroreduction of CO2 represents an appealing strategy to rethink a waste and an environmentally dangerous product as an innovative feedstock for the formation of value-added carbon neutral compounds. Among metal electrodes able to catalyze such process, copper plays a central role. The work of this thesis focuses into the development of new and innovative strategies aimed at tuning Cu selectivity comprise nanostructuring and alloying with heterometals. One of the more investigated nanostructuring strategies consist in the controlled formation of Cu oxides, which then undergo to a re-reduction in CO2R conditions. Several strategies have been reported for the oxidation of Cu foils’ surface. In this contribution, are reported straightforward electrochemical methods for the formation of Cu-In interfaces. The latter were fully characterized and then used as cathodes for CO2 electroreduction, leading to the selective production of Syngas with efficiencies that exceed 70% only for carbon monoxide, whose composition varies upon changing the applied bias and Indium content. Literature examples of copper-indium nanostructured catalysts for CO2R are now still limited.[5] In particular, the proposed Cu-In cathode in this work is able to efficiently catalyze gaseous mixtures compatible with the Fischer-Tropsch synthesis of methanol or aldehydes, that are produced at a relative low (i.e. -1.3 V vs SCE up to -1.6 V vs SCE) applied bias with the development of interesting stable current densities. During this research work was investigated the co-functionalization of also other metallic species than indium such as Cerium that was able to drive the selectivity of the copper interface towards an enhanced production of methane (up to 40% in faradic efficiency). Furthermore, thanks to a collaboration with the Milan University a detailed study of gold nanostructures deposited via PLD on FTO substrates was also performed leading to the development of a particularly efficient electrocatalyst for the production of Syngas and formic acid. In particular with the pulsed laser deposition it was possible to generate particular nanostructures that are not achievable by standard synthetic methodologies, two of these were found to be interesting in terms of catalytic performance. In fact the study was centered into the description of a columnar cathodic interface and a “foam” like surface, the latter was the most interesting due to it’s selectivity towards a Syngas mixture of 40% CO and 60% H2 at a low applied bias of -1.1V vs SCE, ideal for the synthesis of hydrocarbons with a wide range of molecular weight. The work described in this thesis leads to the publications in multiple scientific journal and the deposition of an Italian and European patent due to the collaboration of interested industries in the application of this know how, on this regard also a lot of specific studies were carried out with the aim of clarify the technoeconomic potential of this technology and the possibility to scale up from the laboratory scale to a plant simulation not only in theory but also with the design and development of larger electrochemical cells and setup.

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Bruce, Jared. „Surface Functionalization of Silicon Microwires for Use in Artificial Photosynthetic Devices“. American Chemical Society, 2014. http://hdl.handle.net/1993/30301.

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Integrated photoelectrochemical water splitting with sunlight is one possible solution to growing global energy needs. Integration of catalysts, photoabsorbers and a membrane require low barriers to charge dissipation if a free standing device structure is to be achieved. The n-type/PEDOT:PSS junction has be identified as the major resistive component and constitutes a large barrier to charge dissipation. In this thesis, the modification of the interface between n-type Si/PEDOT:PSS was achieved by growing a highly – doped region at the contact between the wire and the membrane to reduce voltage loss at the junction from 300 mV to 130 mV. In addition, modification of the surface using a thiophene moiety is observed to decrease the voltage loss from 300 mV to 30 mV. Formation of an insulating silicon oxide on the methyl functionalized surface of the microwires identified a need for characterization of planar silicon samples representative of the sides of the microwires. Si (110), (211) and (111) crystal faces were functionalized with a methyl group and showed different resistance to oxidation. The Si (111) surface was the most resistant while the Si (211) surface was observed to be the least resistant to ambient oxidation.

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Mongwaketsi, Nametso Precious. „Studies on porphyrin-based nanorods for artificial light harvesting applications“. Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86772.

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Thesis (PhD)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The work presented in this thesis throws light on the supramolecular approach in exploration of bi-porphyrin nanorods system wherein self-assembly plays an important role. Porphyrin based nanorods were synthesized via self-assembly of meso-tetrakis (4-phenylsulfonicacid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin. Understanding the sizes and growth mechanism of the porphyrin nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of the porphyrin nanorods by ionic self- assembly. This study demonstrated that aggregates of the di- acid form of meso-tetrakis (4-phenylsulfonic acid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin resulted in porphyrin nanorods with diameters between 20 nm and 60 nm, and μm in lengths. Enhanced optical properties illustrated the potential for slightly modifying the method of synthesis to influence the physical and optical properties of porphyrin nanorods. The porphyrin nanorods reflectance data demonstrated that these structures are good absorbers of light and therefore could potentially be used to harvest light. The nonlinear optical (NLO) properties of the porphyrin nanorods were investigated for the first time in this study by second and third harmonic generation techniques. Such study was influenced by the fact that porphyrins have great thermal stability and extended -conjugated macro cyclic ring which give them large nonlinear optical effects. The NLO results showed that the porphyrin nanorods may have many potential uses in photonic applications due to larger third order nonlinear susceptibility. Single molecule spectroscopy was also used to investigate the dynamics of intermolecular and intramolecular processes. Porphyrin nanorods were incorporated into polymer matrices to achieve an arrangement where they can be directly used as a device. The assembly of porphyrin nanorods on track-etched membranes was achieved through altering the surface charge of the respective membranes. Porphyrin nanorods-polymer composites were produced using latex technology and electrospinning techniques. The fibres were characterized with respect to morphology and optical properties.
AFRIKAANSE OPSOMMING: Die werk wat in hierdie tesis beskryf word werp lig op die supramolekulêre benadering in die ondersoek van bi-porfirien nano-silinders waarin self-versameling ‘n belangrike rol speel. Porifirien nano-silinders was voorberei via self-versameling van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien. Dit is belangrik om die meganismes wat verband hou met die groei en grootte van die nano-silinder struktuur te ondersoek. Dit het ‘n invloed op die self-versameling asook die uiteindelike toepassing. Spectroskopiese en mikroskopiese studies was uitgevoer om die effek van tyd, konsentrasie en oplosmiddel op die selfversamelling te bestudeer. Die studie dui daarop dat bondels van die disuur vorm van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien het gelei tot porfirien nano-silinders met lengtes tussen 20 nm en 60 nm asook in die mikro meter skaal. Verhoogde optiese eienskappe het die potensiaal om effense veranderinge in die metode om die nano-silinders voor te berei om sodoende ‘n groter invloed op die fisiese en optiese einskappe te hê. Die reflektansie data wys dat hierdie strukture goeie absorbsies van lig toon en daarom geskik sal wees om lig te stoor. Die nie-liniêre optisie (NLO) eienskappe van die profirien nano-silinders was vir die eerste keer ondersoek deur middel van tweed en derde hormoniese generasie tegnieke. Hierdie studie was beïnvloed deur die feit dat porfiriene goeie stabiliteit by hoë temperatuur en ‘n verlengde -gekonjugeerde makro-sikliese ring bevat wat dan groot nie-liniêre optiese effekte gee. Die NLO resultate wys dat die profirien nano-silinders groot potensiaal het in die gebruik van fotoniese toepassings as gevolg van derde orde nie-liniêre vatbaarheid. Enkel molekuul spektroskopie was ook gebruik om die dinamika van intermolekulêre en intramolekulêre prosesse te ondersoek. Porfirien nano-silinders was geïnkorporeer in polimeer matrikse om ‘n eweredige verspreiding te verkry en om direk as ‘n toestel te gebruik. Die versameling van porfirien nano-silinders op baan-ingeëtse membrane was bereik deur die verandering in oppervlak lading van die membrane. Porfirien nano-silinder / polimeer samestellings was verkry deur lateks tegnologie en elektrospin tegnieke. Die vesels was gekarakteriseer in terme van morfologie en optiese eienskappe.

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Abrahamsson, Malin L. A. „Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis : Studies in Solution and on Electrode Surfaces“. Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5154-3/.

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Mirmohades, Mohammad. „Insight into Catalytic Intermediates Relevant for Water Splitting“. Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-281447.

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Catalysis is an important part of chemistry. This is also reflected in the chemical industry where 85-90 % of all products are made catalytically. Also nature employs catalysts, i.e. enzymes, for its reactions. To improve on the already existing catalysts one can learn a lot from nature which often uses earth-abundant elements in the enzymes which have also been optimized and finely tuned for billions of years. To gain a deeper understanding of both enzymatic and artificial catalysis one needs to investigate the mechanism of the catalytic process. But for very efficient catalysts with turnover frequencies of several thousand per second this is not easy, since an investigation of the mechanism involves resolving intermediates in the catalytic cycle. The intermediates in these instances are short-lived corresponding to their turnover frequencies. A maximum turnover frequency of 1,000 s-1 e.g. means that each catalyst goes through the whole catalytic cycle in 1 ms. Therefore time-resolved techniques are necessary that have a faster detection speed than the turnover frequency of the catalyst. Flash photolysis is a spectroscopic technique with an instrument response function down to 10 ns. Coupling this technique with mid-infrared probing yields an excellent detection system for probing different redox and protonation states of carbonyl metal complexes. Since many catalysts as well as natural enzymes involved in water splitting are metal carbonyl complexes this is an ideal technique to monitor the intermediates of these catalysts. Chapter 3 covers the investigation of [FeFe] hydrogenases, enzymes that catalyze the reduction of protons to hydrogen in nature. Chapter 4 investigates the intermediates of biomimetic complexes, resembling the active site of natural [FeFe] hydrogenases. Chapter 5 covers the insights gained from investigating other catalysts which are also involved in water splitting and artificial photosynthesis.

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Borgström, Magnus. „Controlling Charge and Energy Transfer Processes in Artificial Photosynthesis : From Picosecond to Millisecond Dynamics“. Doctoral thesis, Uppsala University, Department of Physical Chemistry, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6017.

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This thesis describes an interdisciplinary project, where the aim is to mimic the initial reactions in photosynthesis. In photosynthesis, the absorption of light is followed by the formation of charge-separated states. The energy stored in these charge-separated states is further used for the oxidation of water and reduction of carbon dioxide. In this thesis the photo-induced processes in a range of supramolecular complexes have been investigated with time resolved spectroscopic techniques. The complexes studied consist of three types of units; photosensitizers (P) capable of absorbing light, electron acceptors (A) that are easily reduced and electron donors (D) that are easily oxidised. Our results are important for the future design of artificial photosystems, where the goal is to produce hydrogen from light and water.

Two molecular triads with a D-P-A architecture are presented. In the first one, a photo-induced charge-separated state was formed in an unusually high yield (φ>90%). In the second triad, photo-irradiation led to the formation of an extremely long-lived charge-separated state (τ = 500 ms at 140K). This is also the first synthetically made triad containing a dinuclear manganese unit as electron donor.

Further, two sets of P-A dyads are presented. In both, the expected photo-induced reduction of the electron acceptor is diminished due to competing energy transfer to the triplet state of the acceptor.

Finally, a P-P-A complex containing two separate photosensitizers is described. The idea is to produce high-energy charge-separated states by using the energy from two photons.

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Borgström, Magnus. „Controlling charge and energy transfer processes in artificial photosynthesis : from picosecond to millisecond dynamics /“. Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6017.

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41

Moberg, Simon. „Artificial photosynthesis - 4-Aminobenzoic acids effect on charge transfer in a photo catalytic system“. Thesis, Uppsala universitet, Materialteori, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-390835.

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Artificial photosynthesis is used to harvest solar energy and store it in the form of chemical bonds. The system of interest in this study does this by splitting water into hydrogen and oxygen gas through a plasmon assisted process, collective oscillations from free electron gas. This is a renewable way to store energy that could be used as an alternative to fossil based fuel. In this study, a small part of this photo catalytic system is studied, namely the interaction between plasmonically active silver nanoparticles (Ag NPs) transferring photo-excited electrons via a linker molecule, 4-aminobenzoic acid (pABA). The pABA linker molecule transfers charge from the Ag surface to a semiconductor and a catalyst performing the water splitting. The pABA can bind in different ways onto the Ag-surface and the aim of this study is to examine which bond is strongest and which best enables charge transfer. To this purpose three systems where simulated quantum mechanically using a supercomputer. The total free energy of the systems was computed and compared. Out of the three studied binding sites, the hollow-site bond (pABA binding to three silver atoms) was found to have the lowest energy, meaningit's the strongest of the possible bonds. Additionally it was found that the band gap (the energy needed to transfer charge) for the pABA decreased when bound to the Ag-surface. The hollow-site bound pABA also had the smallest band gap, meaning it requires the least energy to transfer a charge and should therefore be the best bond fitted for the photo catalytic system.
Artificiell fotosyntes används för att absorbera solenergi och förvara den i formen av kemiska bindningar. Systemet som används i denna studie gör detta genom att splittra vatten till vätgas och syrgas genom en plasmon assisterad process. Detta är ett förnyelsebart sätt att förvara energi och kan användas som ett alternativ till fossila bränslen. I denna studie studeras en liten del utav detta fotokatalytiska system nämligen interaktionen där plasmonaktiva silvernanopartiklar (Ag NPs) överför foto-exciterade elektroner genom molekyllänken 4-aminobensoesyra (pABA). Molekyllänken pABA överför laddning från silverytan till en halvledare och en katalys som utför splittringen av vattnet. pABA kan binda på olika sätt tillen silveryta och denna studie syftar till att undersöka vilken utav bindningarna som är starkast och vilken som effektivast överför laddning. För att göra detta simulerades tre system kvantmekaniskt med hjälp av en superdator, ett system för varje sorts bindning. Den totala fria energin av systemen beräknades och jämfördes. Av de tre undersökta bindningarna hadehollow-site bindningen (pABA som binder till tre silveratomer) längst energi, vilket betyder att det är den starkaste av bindningarna. Utöver detta så visade det sig att bandgapet (energin som krävs för att överföra laddning) minskade för pABA när den var bunden till Ag-ytan. Hollow-site bundet pABA hade även minst bandgap, vilket betyder att den kräver minst energi för att överföra laddning och är därmed den mest effektiva bindningen för det fotokatalytiska systemet.

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LUISA, ALESSANDRA. „Metallo-porphyrins: key active players in molecular artificial photosynthesis and homogeneous photocatalytic hydrogen production“. Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908012.

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Contemporary society demands innovative answers to the environmental and energetic issue. A remarkably promising and widely discussed route to achieve this intent is based on artificial photosynthesis, i.e. the conversion of light into fuels by molecules that mimic the natural photosystems. The main aim of this thesis is the design, synthesis and characterization of new metal-chromophore supramolecular conjugates for photocatalytic applications, with specific focus on the homogeneous generation of molecular hydrogen. Particular attention was given to water soluble noble-metal-free systems, in order to meet both environment and cost requirements. Herein are described manifold applications of metallo-porphyrins for hydrogen photoreduction: as photosensitizer units in multi-component photoactive systems, as chromophores in antenna systems, and as catalysts, while offering at the same time a variety of structural handles for the assembling of the active partners.

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Ozcan, Ozlem. „Artificial Photosynthesis: Dye Assisted Photocatalytic Reduction Of Carbon Dioxide Over Pure And Platinum Containing Titania“. Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606313/index.pdf.

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The aim of this study is to test the limits of photocatalytic reduction of CO2 over Pt and light harvesting dye promoted TiO2 films under UV and visible light. Thick and thin TiO2 film catalysts are coated onto 1 cm long glass beads via a common sol-gel procedure and dip coating technique. TiO2 thin films were promoted by Pt and three different light harvesting molecules: RuBpy (Tris (2,2&rsquo
&ndash
bipyridyl) ruthenium (II) chloride hexahydrate) , BrGly (1,7-dibromo-N,N&rsquo
-(t-butoxycarbonyl-methyl)-3,4:9,10-perylene-diimide) and BrAsp (1,7-dibromo-N,N&rsquo
-(S-(1-t-butoxy-carbonyl-2-t-butoxycarbonyl-methyl)-ethyl)- 3,4:9,10-perylenediimide). Their SEM, XRD, UV-Vis spectroscopy and hydrogen chemisorption characterizations are performed. Reaction tests are performed for the catalysts under UV and visible light. The only quantifiable reaction product was methane. With RuBpy containing catalysts hydrogen production was observed under UV light, but not quantified. The results indicated that Pt addition resulted in higher yields in UV experiments. The presence of light harvesting molecules resulted in increase in photocatalytic activity for thin films, whereas it resulted in no change or decrease for the thick films. The latter case may occur due to the UV filtering effect of these dyes. Use of dyes (with visible range absorption bands) as promoters made visible light excitation possible. This resulted in photocatalytic activity under visible light, which was not observed with unpromoted and Pt promoted TiO2 thin film catalysts. Under visible light methane was the only quantified photoreduction product. CO evolution was also observed, but not quantified. The photocatalytic activities of the dye promoted TiO2 were in the order of RuBpy~BrAsp>
BrGly. The methane yields of visible light experiments were one order of magnitude lower than the ones under UV light.

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Lippert, Cameron A. „Redox-active ligand-mediated radical coupling reactions at high-valent oxorhenium complexes: reactions relevant to water oxidation for artificial photosynthesis“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41199.

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The making and breaking of O-O bonds has implications ranging from artificial photosynthesis and water oxidation to the use of O₂ as a selective, green oxidant for transformations of small molecules. Oxidative generation of O₂ from coupling of two H₂O molecules remains challenging, and well defined systems that catalytically evolve O₂ are exceedingly rare. Recent theoretical studies have invoked metal oxyl radicals (L[subscript n]M=O*) containing a singly occupied M-O π-type orbital as precursors to O-O bond forming events in both biological and synthetic water oxidation catalysts. However, the lack of stable metal oxyl complexes makes it difficult to explore and understand this hypothesis. The activation of dioxygen (breaking of O-O bonds) to produce terminal metal oxos also remains a challenge. There is an inherent kinetic barrier to the spin-forbidden reactions of triplet dioxygen, and features that engender selective O₂ reduction are not easily transferable from system to system. The primary thrust of this thesis work has been to elaborate new methods to generate well-defined metal oxyl radicals for studies of their reactions in radical bond-forming reactions similar to the radical coupling hypothesis of water oxidation. A library of >20 5- and 6-coordinate high-valent oxorhenium complexes containing redox-inert and redox-active ligands has been prepared. The complexes containing redox-active ligands have shown the ability for ligand-mediated radical coupling reactions. Mechanistic studies of bimetallic O₂ homolysis (the microscopic reverse of water oxidation) and nitroxyl radical deoxygenation at five-coordinate oxorhenium(V) reveal that, in both net 2e⁻ reactions, coupling to a redox-active ligand lowers the kinetic barrier to the reaction by facilitating formation and stabilization of 1e⁻ oxidized intermediates. Coordinatively unsaturated high-valent oxorhenium complexes containing redox-active ligands direct bond-forming reactions towards the metal center. This is undesirable towards the goal of forming O-O bonds. To address this problem coordinatively saturated Re(V) and Re(VII) complexes were prepared. Oxidation of these species by chemical oxidants allowed for the isolation of "masked" oxyl species. These complexes showed reactivity towards Si and trityl radicals to produce new Si-O and C-O bonds, whereas their closed-shell congeners were inert. We have successfully developed a method for the preparation and isolation of "masked" oxyl radicals and shown their utility in ligand-mediated radical coupling reactions.

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NATALI, Mirco. „SUPRAMOLECULAR SYSTEMS FOR ARTIFICIAL PHOTOSYNTESIS“. Doctoral thesis, Università degli studi di Ferrara, 2014. http://hdl.handle.net/11392/2389046.

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Artificial photosynthesis, i.e., conversion of solar energy into fuels, represents one of the most promising research fields which could potentially provide clean and renewable sources of energy for a sustainable development of the future generations. Among several possibilities, water splitting into molecular hydrogen and oxygen is one of the most challenging and appealing reaction schemes. Taking inspiration from nature several functional units are required to this aim: (i) an antenna system, responsible for light harvesting, (ii) a charge separating system, where the absorbed energy is converted into an electrochemical potential (electron/hole pair), and (iii) appropriate catalyst units, capable of stepwise storing the photogenerated electrons and holes in order to drive multi-electron transfer processes at low activation energy. In the present thesis several points regarding both the photoinduced oxidation and reduction of water as well as charge separation are studied. In more detail, three different classes of water oxidation catalysts are examined, namely tetrametallic polyoxometalate, tetracobalt cubanes, and single-site cobalt salophen complexes, within light-activated catalytic cycles involving tris(bipyridine) ruthenium and persulfate as photosensitizer and sacrificial electron acceptor, respectively. Particular attention is paid to the evaluation of the interactions between the catalyst and the sensitizer and to the kinetics of both photochemical and thermal electron transfer steps. Concerning water reduction, the following systems are investigated: a self-assembling reductant/sensitizer/catalyst triad based on an aluminum pyridylporphyrin central unit, a cobaloxime catalyst, and an ascorbate electron donor, a cationic cobalt porphyrin catalyst in the presence of tris(bipyridine) ruthenium as sensitizer and ascorbic acid as electron donor, and a PAMAM dendrimer decorated with ruthenium polypyridine dyes at the periphery and inside of which platinum nanoparticles have been grown. Beside the optimization of the photocatalytic performance, detailed insights into the photoinduced hydrogen evolving mechanism are carefully provided. Finally, a triad system for photoinduced charge separation, based on a naphthalene bisimide electron acceptor, a zinc porphyrin electron donor, and a ferrocene secondary electron donor, connected via 1,2,3- triazole bridges, is also described. Detailed photophysical investigation of the system will show an unusual behavior with respect to photoinduced electron transfer. Results obtained from a side-project in the field of molecular electronics will be also discussed, where photoinduced electron transfer processes are used to different aims.

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Karlsson, Erik. „Catalysts for Oxygen Production and Utilization : Closing the Oxygen Cycle: From Biomimetic Oxidation to Artificial Photosynthesis“. Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-56917.

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This thesis describes the development and study of catalysts for redox reactions, which either utilize oxygen or hydrogen peroxide for the purpose of selectively oxidizing organic substrates, or produce oxygen as the necessary byproduct in the production of hydrogen by artificial photosynthesis. The first chapter gives a general introduction about the use of environmentally friendly oxidants in the field of organic synthesis, and about the field of artificial photosynthesis. The second chapter describes a computational study of the mechanism of palladium-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes. The proposed mechanism, which was supported by DFT calculations, involves an unusual water attack on a (π-allyl)palladium complex. The third chapter describes a computational study of the oxidation of unfunctionalized hydrocarbons, ethers and alcohols with hydrogen peroxide, catalyzed by methyltrioxorhenium (MTO). The mechanism was found to proceed via rate-limiting hydride abstraction followed by hydroxide transfer in a single concerted, but highly asynchronous, step as shown by intrinsic reaction coordinate (IRC) scans. The fourth chapter describes the use of a new hybrid (hydroquinone-Schiff base)cobalt catalyst as electron transfer mediator (ETM) in the palladium-catalyzed aerobic carbocyclization of enallenes. Covalently linking the two ETMs gave a fivefold rate increase compared to the use of separate components. The fifth chapter describes an improved synthetic route to the (hydroquinone-Schiff base)cobalt catalysts. Preparation of the key intermediate 5-(2,5-hydroxyphenyl)salicylaldehyde was improved by optimization of the key Suzuki coupling and change of protecting groups from methyl ethers to easily cleaved THP groups. The catalysts could thus be prepared in good overall yield from inexpensive starting materials. Finally, the sixth chapter describes the preparation and study of two catalysts for water oxidation, both based on ligands containing imidazole groups, analogous to the histidine residues present in the oxygen evolving complex (OEC) and in many other metalloenzymes. The first, ruthenium-based, catalyst was found to catalyze highly efficient water oxidation induced by visible light. The second catalyst is, to the best of our knowledge, the first homogeneous manganese complex to catalyze light-driven water oxidation.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted.

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47

Thorne, James E. „Understanding the Limitations of Photoelectrochemical Water Splitting“. Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:108257.

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Thesis advisor: Dunwei Wang
Artificial photosynthesis is achieved by placing a semiconductor in water, where photoexcited charges generate a photovoltage at the surface of the semiconductor. However, solar to fuel efficiencies of earth abundant metal oxides and metal nitrides remain limited by their low photovoltages. Many different treatments have been used to improve the photovoltages of semiconductors, such as photocharging, surface regrowths, or the addition of heterogeneous catalysts. However, in these treatments, it remains unclear whether the enhanced photovoltage arises from improved kinetics or energetics. In many of the following studies, the surface kinetics of different semiconductors are measured in order to quantify how surface kinetics are related to the photovoltage of these materials. Different spectroscopic measurements are made along with detailed analysis of the Fermi level and quasi Fermi level in order to corroborate the kinetic data with energetic data. Together, this dissertation explores a multitude of methods and procedures that demonstrate how the photovoltage of semiconductors can be understood and manipulated for photoelectrochemial artificial photosynthesis
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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48

Thomas, Michael Brandon. „Donor-Acceptor Systems: Photochemistry and Energy Harvesting Applications“. Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703335/.

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Donor-acceptor systems have unique properties that make them ideal candidates for solar energy harvesting through mimicry of natural photosynthesis. This dissertation is focused on unraveling those unique properties in various types of donor-acceptor systems. The systems investigated are categorized as closely linked, push-pull, supramolecular, and multi-unit. As part of the study, photosynthetic analogues based on BF2-chelated dipyrromethene (BODIPY), porphyrin, phthalocyanine, truxene, ferrocene, quinone, phenothiazine (PTZ), perylenediimide (PDI), fullerene (C60), dicyanoquinodimethane (DCNQ), tetracyanobutadiene (TCBD), and triphenylamine (TPA) are investigated. The effects of proximity between donor-acceptor entities, their geometrical orientation relative to each other, push-pull character of substituents, and competitive energy and electron transfer are examined. In all systems, primary events of photosynthesis are observed, that is absorption and energy transfer and/or electron transfer is witnessed. Ultrafast transient absorption spectroscopy is utilized to characterize the photo-induced events, while other methods such as steady-state luminescence, cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and computational calculations are used to aid in the characterization of the donor-acceptor systems, in particular their applicability as solar energy harvesters.

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Neupane, Bhanu. „Excited state electronic structure, excitation energy transfer, and charge separation dynamics in various natural and artificial photosynthetic systems containing zinc and magnesium chlorins“. Diss., Kansas State University, 2011. http://hdl.handle.net/2097/13105.

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Doctor of Philosophy
Department of Chemistry
Ryszard J. Jankowiak
This dissertation reports the low temperature frequency domain spectroscopic study of three different natural pigment protein complexes and one artificial antenna system. The main focus of this work is to better understand electronic structure, excitation energy transfer (EET), and electron transfer (ET) dynamics in these systems that could have impact on achieving higher efficiency in future artificial solar cells. In the first part of this dissertation, electronic structure and EET pathways in isolated intact CP43 prime protein complex, which is isolated from Cyanobacterium synechocystis PCC 6803 grown under iron stressed conditions, are investigated using low-temperature absorption, fluorescence, fluorescence excitation, and hole-burning (HB) spectroscopies. This work suggests that, in analogy to the CP43 complex of PSII core, CP43 prime possesses two quasi-degenerate low energy states, A prime and B prime. The various low-temperature optical spectra are fitted considering an uncorrelated EET model. This work suggests that for optimal energy transfer from CP43 prime to PSI, the A prime and B prime state chlorophylls belonging to each CP43 prime should face towards the PSI core. The second part of dissertation reports the photochemical HB study on novel Zinc bacterial reaction center (Zn-RC) from Rhodobacter sphaeroides and its β-mutant (Zn-β-RC). This study shows that ET in the two samples is similar; however, the quantum efficiency of charge separation in the mutant decreases by 60 %. This finding suggests that the coordination state of the HA site zinc bacteriochlorophyll does not tune the active branch ET. Simultaneous fits of various optical spectra using experimentally determined inhomogeneity provides more reliable electron phonon coupling parameters for the P870 state of both RC samples. In the last part of this dissertation, EET in a novel artificial antenna system (ethynyl linked chlorophyll trefoil, ChlT1) is investigated. EET time in ChlT1 is ~2 ps. ChlT1 in MTHF/ethanol glass forms four different types of aggregates, A1-A4. The EET time in A1 and A2 type aggregates slows down only by a factor of 5 and 7, respectively. This study suggests that ChlT1 and its aggregates can be used as efficient antenna systems in designing organic solar cells.

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Song, Baiyun. „Studies on High Potential Porphyrin-fullerene Supramolecular Dyads“. Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc407825/.

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Photoinduced electron transfer in self-assembled via axial coordination porphyrin-fullerene dyads is investigated. Fullerene functionalized with imidazole and fullerenes functionalized with pyridine are chosen as electron acceptors, while zinc pophyrin derivatives are utilized as electron donors. The electron withdrawing ability of halogen atoms make the porphyrin ring electrophilic, which explained the binding of (F20TPP)Zn with fullerene derivatives having the highest binding constant around 105M-1. Another important observation is that the fullerene imidazole binding to zinc pophyrin had higher stability than fullerene pyridine-porphyrin dyad. Computational DFT B3LYP-21G(*) calculations are used to study the geometric and electronic structures. The HOMO and LUMO was found to be located on the porphyrin and fullerene entities, respectively. Photoinduced electron transfer is investigated by the steady-state absorption and emission, differential pulse voltammetry, and nanosecond and femtosecond transient absorption studies. The measurements provided the same conclusion that the increasing number of the halogen atoms on the porphyrin ring leads to the higher binding of porphyrin-fullerene supramolecular dyads and efficient charge separation and charge recombination processes.

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