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Dissertationen zum Thema „Photochemistry“

Autor: Grafiati

Veröffentlicht am 4. Juni 2021

Zuletzt aktualisiert am 16. November 2024

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1

Bones, David Lawrence. „Liquid Aerosol Photochemistry“. Thesis, University of Canterbury. Chemistry, 2008. http://hdl.handle.net/10092/1500.

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Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

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2

Firth, S. „Low temperature photochemistry“. Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378979.

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3

Rapley, P. A. „Photochemistry of thiophthalimides“. Thesis, Open University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371027.

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4

Niederjohann, Britta. „Photochemistry of small molecules“. [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972767398.

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5

Karlsson, Daniel. „Photochemistry of Phenyl Halides“. Doctoral thesis, Uppsala universitet, Institutionen för fotokemi och molekylärvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8602.

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We have studied fundamental aspects of photo-induced dissociation kinetics and dynamics in several phenyl halides. By combining femtosecond pump-probe measurements with ab initio calculations we are able to account for several observations. In mixed phenyl halides, the dissociation kinetics is found to be dependent on the nature, the number, and the position of the substituents, and also on the excitation wavelength. A surprisingly large reduction in the dissociation time constant, compared to that of bromobenzene (~30 ps), is observed when having two or more fluorine atoms. For example, in bromopentafluorobenzene a subpicosecond time constant is obtained. This can be explained by a significant lowering of the repulsive potential energy curves (PEC) along the C-Br bond. However, several of the experimental results cannot be accounted for by one-dimensional PECs. Therefore, we suggest a refined model for the dissociation, in which the excited states of the same spin multiplicity are coupled by employing multidimensional potential energy surfaces. This model has been explicitly evaluated by quantum dynamics simulations in the case of 3-BrFPh, and it seems to be capable of capturing the main features in the measured kinetics. Thereby we are also able to clarify the role of spin-orbit coupling in these molecules.

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6

Haynes, Anthony. „Intermediates in organometallic photochemistry“. Thesis, University of Nottingham, 1989. http://eprints.nottingham.ac.uk/27829/.

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CHAPTER 1: A background to the techniques of matrix isolation, liquid xenon solution and flash photolysis with fast IR detection is presented. The application of infrared spectroscopy in structural studies of metal carbonyl compounds is also discussed. Chapter 2: Photolysis of((nu5-C5R5)Pt(CO))2 (R=H, Me) in frozen gas matrices results in production of ((nu5-C5R5)Pt2(mu-CO)). 13CO enrichment and polarised photochemistry show that the photoproduct contains a single symmetrically bridging CO group. Photolysis of (CpNi(mu-CO))2 in frozen gas matrices results in formation of CP2Ni2(CO) with a terminal CO ligand. The stability these dinuclear photoproducts in room temperature solution has been investigated using fast TRIR spectroscopy. Photolysis in CO matrices leads to M-M bond cleavage and reaction with CO to give Pt(CO)4 or Ni(CO)4 as the final product. CHAPTER 3: Photolysis of Os2(CO)9 or OS2(CO)8- - (mu-nu1, nu1-C2H4) in frozen gas matrices leads to formation of Os2(CO)8, which has only terminal CO groups. The thermal and photochemical reactivity of Os2(CO)a towards CO, N2 and C2H4 is investigated. Photolysis using plane polarised light provides confirmation of the C2v structure of Os2(CO)9, and gives evidence favouring a D2h structure for Os2(CO)8. Prolonged UV photolysis of Os2(CO)9 in CO matrices leads to cleavage of the Os-Os bond and production of Os(CO)5. CHAPTER 4: The mechanism of the photochemical deoligomerisation of FpSiMe2SiMe3 is investigated using a variety of techniques. The reaction is shown to proceed via two photochemical steps. Primary CO-loss is followed by intramolecular trapping to give a silyl(silylene) intermediate. The second step involves expulsion of an SiMe2 fragment and coordination of a ligand. L. to give CpFe(CO)(L)SiMe3 (L = CO, PPh3,C2H4 or N2). CHAPTER 5: A study of the photochemistry of Fp-disilyl complexes containing beta-silyl hydrogens implies beta-H transfer from Si to Fe as the dominant process following photodissociation of CO. The product, a metalladisilacyclopropane or nu2-disilene complex, is implicated as an intermediate in the photochemical formation of FpH in this system. CHAPTER 6: The experimental techniques and spectrometers used in this research are described. along with a discussion of the theory and advantages of FTIR spectroscopy.

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7

Banks, C. P. „Aspects of polymer photochemistry“. Thesis, University of Hertfordshire, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384083.

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8

Sanderson, Jason Terry. „Studies in organic photochemistry“. Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393200.

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9

McCallum, Terry. „Radical Adventures in Photochemistry“. Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37825.

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A field in bloom: photoredox catalysis has allowed chemists access to highly reactive intermediates via the photo-mediated excitation of transition metal complexes and organic dyes for the mild generation of free radicals. These complexes and dyes are designed based on Nature’s blueprints of light-harvesting biomolecules that transform solar energy (photons) into chemical energy during photosynthesis. Light-mediated chemical activation is regarded as one of the most sustainable forms of chemical activation being that the energy provided by the sun is considered renewable and largely underutilized and presents an attractive avenue for research and development of new transformations that are mild, efficient, and waste-limiting in organic synthesis. Radical chemistry and photochemistry are united in their inherent ability to undergo single (or photoinduced) electron transfers by one-electron reaction modes. Combining these unique fields, photoredox catalysis has emerged as a mild and efficient alternative to classic alkyl radical generation using hazardous initiators and organostannanes. Photoredox catalysis has been dominated by ruthenium- and iridium-based polypyridyl complexes. These complexes are limited by their inherent redox potentials, restricting their reactivity towards relatively activated bonds. Nonactivated bromoalkanes and arenes are considered challenging substrates to engage using redox chemistry and typically only accessible in the realm of organostannane chemistry. Described herein are the efforts towards the discovery of free radical based organic transformations derived from nonactivated bromoalkanes and arenes mediated by photochemical excitation of polynuclear gold(I) complexes as photoredox catalysts. This work represents some of the first uses of a photoredox catalyst in the reduction of substrates having such high reduction potentials and offers a practical and useful alternative to classic radical reactions mediated by initiators (peroxides, persulfates, and azo compounds) and toxic organostannanes (Bu3SnH). Using gold based photoredox catalysts, the research conducted has provided many methodological advancements for the mild and efficient formation of carbon-carbon bonds using nonactivated bromoalkanes and a large collection of radical acceptors. Establishing the use of these photoexcited polynuclear gold(I) complexes in the context of classic radical reactions in organic synthesis was important for their validation as useful photocatalysts. First, the Ueno-Stork cyclization of nonactivated bromoalkanes was used to demonstrate the powerful reducing capabilities of the excited-state gold(I) complexes. Next, a photo-mediated variant of the Appel reaction was described, where the transformation of an alcohol to a bromoalkane was achieved using carbontetrabromide and N,N-dimethylformamide through the intermediacy of a Vilsmeier-Haack reagent. In combination with the hydrodebromination chemistry developed with photoexcited polynuclear gold(I) complexes, a photo-mediated one-pot formal deoxygenation reaction of alcohols was described; a useful alternative to the organostannane mediated Barton-McCombie deoxygenation reaction. Finally, in the field of medicinal chemistry, the functionalization of heteroarenes is of high interest for the discovery of drug candidates and bioactive molecules. In this respect, one of the most useful reactions for the functionalization of heteroarenes by alkyl radicals is the Minisci reaction using silver salts, carboxylic acids, and persulfates. Detailed are the efforts for the development of a photo-mediated redox-neutral improvement of the Minisci reaction, needing only gold(I) photocatalyst and nonactivated bromoalkane in the presence of heteroarenes. Overall, the work described in this thesis represents the push for mild and efficient alternatives to the relatively harsh conditions and/or toxic reagents and byproducts associated with classic radical chemistry. These studies demonstrate the ability to control highly reactive alkyl radical intermediates with the goal of their broader application in synthetic organic chemistry. The use of photoexcited polynuclear gold(I) complexes as potent reductants compared to ruthenium- and iridium-based polypyridyl complexes is illustrated through the genesis of highly reactive alkyl radicals from nonactivated bromoalkanes.

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10

Sugita, Akihiro. „Multiphoton spectroscopy and photochemistry“. Kyoto University, 2001. http://hdl.handle.net/2433/150656.

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11

Wang, Jing. „Two-photon Induced Photochemistry“. Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195094.

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Two-photon absorption is the process in which a molecule absorbs two photons simultaneously. The two key advantages of two-photon processes over one-photon processes are the possibility of excitation of materials with high three-dimensional spatial resolution and deep light-penetration into absorbing materials. Based on bond-cleavage reactions activated by photon-induced intramolecular electron transfer, two-photon activatable acid and radical initiators and two-photon removable protecting groups have been successfully designed and synthesized for photopolymerization and three-dimensional microfabrication and for biomedical photo-triggers. The optical and chemical properties of synthesized molecules, such as quantum yield of acid generation, initiation efficiency of photopolymerization, and photolysis efficiency, have been studied by using a variety of physical and analytical techniques under one-photon conditions. The two-photon characteristics and applications of these molecules are being investigated in collaboration with other groups.

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12

Yen, Chun-Wan. „Plasmonic photochemistry on the nanoscale“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41085.

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When nanoparticles are small in size compared to the wavelength of incident light, a localized surface plasmon resonance occurs. For certain noble metals, such as gold and silver, this frequency occurs in the visible or near IR range, and therefore it can be utilized for many important applications. Only silver and gold nanoparticles were utilized in this thesis work, and they were used in application for three separate files: environment, catalysis, and energy.

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13

Bishenden, Elizabeth. „Mode-selective photochemistry of OClO“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq28270.pdf.

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14

Smith, Richard S. „Photochemistry of 3,5-dimethoxybenzyl acetate“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0021/MQ57326.pdf.

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15

Desikan, Vasumathi. „Photochemistry of dibenzothiophene-based sulfilimines“. [Ames, Iowa : Iowa State University], 2007.

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16

Bruce, James I. „Supramolecular photochemistry of lanthanide complexes“. Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308689.

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17

Roscini, Claudio. „Reaction Control in Organic Photochemistry“. Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521102.

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18

Higgins, Christina Mary. „Tropospheric photochemistry of organic nitrates“. Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627967.

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The research presented in this thesis explores the tropospheric photochemistry of various organic nitrates (RON02). Interest in the atmospheric community has flourished regarding these species due to their potential role in tropospheric oxidation processes. Initially, a brief introduction to the atmosphere is given and followed by a more detailed description of the tropospheric chemistry surrounding the formation and destruction of RON02. Cavity ring-down spectroscopy was employed to determine the N02 quantum yields from the photoexcitation of organonitrates at tropospherically relevant wavelengths between 290 and 315 nm. Alkyl nitrate (methyl, ethyl, n-propyl and isopropyl nitrate) photolysis was found to have pressure-independent N02 quantum yield of unity. The photolysis of an unsaturated dinitrate species at 290 nm was estimated to have a quantum yield of ~ 0.25. Gas and liquid phase RON02 absorption cross-sections were shown to decrease steeply with increasing wavelength (320 - 240 nm). These absorption cross-sections were combined with quantum yields to estimate atmospheric lifetimes. Theoretical calculations were performed to explore the electronic ground and excited state structures of alkyl nitrates and multifunctional nitrates. DFTIB3L YP calculations struggled to reproduce the energies of charge transfer transitions in multi functional nitrates and the CAM-B3L YP level of theory was shown to be more suitable. Global abundance and distribution of organonitrates was analysed using the global chemistry transport model, STOCHEM, with comparison made between model and field measured data. In general, the model reproduced field measured RON02 mixing ratios, highlighting the soundness of the peroxy radical and NOx budgets used in the model. Finally, the atmospheric fate of the organonitrates studied is discussed.

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19

Cubbage, Kara. „Synthetic photochemistry of tethered maleimides“. Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.547843.

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20

Knox, Christopher James Henry. „The photochemistry of liquid aerosols“. Thesis, University of Canterbury. Chemistry, 2002. http://hdl.handle.net/10092/6076.

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The photochemistry of liquid aerosols has been investigated with the aim of using the physical properties of liquid aerosols to enhance the reactivity of photochemical and photocatalytic systems. The properties of aerosols that enhance reactivity are summarised under four headings: the optics of micro droplets, diffusion into small particles, surface and interfacial reactivity, and capillarity effects. A range of systems have been developed for the photochemistry of liquid aerosols. A number of photocatalytic systems have been studied and a significant enhancement in the photolysis of molybdenum hexacarbonyl has been observed, relative to the liquid phase. A computational study of the light intensity distribution inside liquid aerosols droplets in photochemical and photocatalytic systems has been carried out. Large enhancements of the internal field intensity relative to the incident field have been observed. It is proposed that the internal intensity distributions are the source of the increased rate of molybdenum hexacarbonyl photolysis. A model has been proposed for gas-liquid transfer, based on the capillary wave motion of the liquid surface.

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21

Thomas, Dawn Ann. „Matrix photochemistry of stratospheric species“. Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318039.

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22

Costa, Monica Ferreira da. „Mercury photochemistry in natural waters“. Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338305.

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23

Gadd, G. E. „Organometallic photochemistry at low temperatures“. Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304331.

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24

Reeman, Stuart Michael. „Adsorbate photochemistry of small molecules“. Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318275.

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25

Richards, Andrew Maurice. „Photochemistry of novel aluminium complexes“. Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236925.

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26

Smith, Carina Alice. „The atmospheric photochemistry of formaldehyde“. Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432746.

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27

Ponczek, Milena. „Understanding Atmospheric Mineral Dust Photochemistry“. Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1190.

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Les minéraux absorbent la lumière proche des UV (comme TiO2, Fe2O3, MgO) présents dans les aérosols minéraux interagissent avec les gaz traces présents dans l'atmosphère et peuvent initier une nouvelle chimie hétérogène photo-induite potentiellement significative et actuellement peu documentée. Cette thèse vise à aborder différentes questions sur la réactivité des poussières minérales vers les composés organiques et évaluer l'impact de ces interactions sur plusieurs aspects des sciences de l'atmosphère. Nous avons étudié expérimentalement l'interaction physico-chimique d'aérosols minéraux, purs ou revêtus de matériaux organiques/inorganiques avec des gaz traces de plusieurs familles chimiques (alcools, cétones, acides carboxyliques), dans des conditions simulées proches de l'environnement reel (concernant l'humidité, la concentration en phase gazeuse, la longueur d'onde et l'intensité de l'irradiation, la pression et la température) évaluant les effets des conditions ambiantes sur la cinétique de capture et la génération de produits en phase gazeuse. Dans l'ensemble, nos résultats montrent clairement que les reactions photochimique des poussières minérales doit être considéré comme une source de composés réactifs et comme un processus clé affectant leur action sur la nucléation de la glace et les noyaux de condensation des nuages
Minerals that absorb light near UV/Vis present in dust aerosols interact with trace gases in the atmosphere and can initiate a new and potentially significant photo-induced heterogeneous chemistry, which is currently poorly documented. This thesis aims to address different issues of mineral dust reactivity towards organic compounds and, therefore, assesses the impact of these interactions on several aspects of atmospheric sciences. We investigated experimentally the physicochemical interaction of mineral aerosols (synthetic and natural), pure or coated with organic/inorganic materials with trace gases from several chemical families (alcohols, ketones, carboxylic acids, etc.), under simulated conditions close to the real environment (regarding to humidity, concentration in the gas phase, wavelength and intensity of irradiation, pressure and temperature). In a first approach, we studied the uptake of oxygenated organics onto different dust proxies such as SiO2, TiO2 and Arizona test dust (ATD) evaluating the effects of ambient conditions on the uptake kinetics and product generation. Then, we discussed the chemistry of 5 dicarboxylic acids (C4-C8) on ATD particles upon UV-A irradiation monitoring products in the gas phase as well as those whose stay adsorbed on the particulate phase. Lastly, we investigated the influence of nitrate anions on the uptake of acetone on ATD and SiO2 and in the photochemical product formation of glutaric acid on ATD. Overall, our results clearly show that photochemical processing of dust aerosols should be considered as a source of reactive compounds and as a key process affecting their action as ice nucleation and cloud condensation nuclei

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28

Zhuang, Bo. „Fundamental Processes in Flavoprotein Photochemistry“. Thesis, Institut polytechnique de Paris, 2022. https://tel.archives-ouvertes.fr/tel-03789651.

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Les flavines sont des dérivés de la vitamine B2 qui forment un groupe de chromophores très polyvalents présents dans une grande variété d'enzymes et de protéines photoréceptrices. Elles peuvent adopter trois états redox différents avec divers états de protonation, menant à au moins cinq formes physiologiquement pertinentes, avec des spectres d'absorption électronique distincts. Malgré les propriétés photophysiques diverses des cofacteurs flavine, il n'y a que très peu de flavoprotéines naturellement photoréactives. La grande majorité des flavoprotéines remplissent des fonctions physiologiques non générées par la lumière ("non-photoactives"), bien que des réactions d'oxydoréduction photo-induites ultra-rapides et réversibles entre les flavines et les résidus proches s’y produisent largement, ce qui peut être considéré comme "auto-quenching" photo-protectrice. Ces dernières décennies, l'étude des flavoprotéines a connu un essor pour leurs applications photocatalytiques et photo-biotechnologiques. De plus, une nouvelle approche émergeant dans le développement de nouveaux photocatalyseurs à partir de flavoenzymes canoniques "non-photoactives" utilise la photochimie de flavines réduites au lieu de l'état de repos oxydé. En outre, des implications pratiques de la photochimie d'espèces de flavine encore différentes sont envisagées, mais une compréhension fondamentale de leurs mécanismes est requise. Dans cette thèse, par l'application de spectroscopie d'absorption et de fluorescence ultrarapide combinée avec des simulations moléculaires et d’approches de chimie quantique, une variété de processus photochimiques fondamentaux dans les flavoprotéines est étudiée. Tout d'abord, la photoréduction des flavines oxydées a été revisitée dans une flavoprotéine, la ferrédoxine-NADP+ oxydoréductase (FNR), ayant des configurations des réactifs très compactes, permettant la formation ultrarapide de paires de radicaux intermédiaires. La combinaison de techniques expérimentales et de modélisation a permis une évaluation détaillée de l'influence de l'environnement sur les propriétés spectrales des radicaux anioniques de flavine et cationiques d'acide aminé (tyrosine ou tryptophane). Par ailleurs, nous avons étudié la photochimie de flavines liées aux protéines dans différents états chimiques largement inexplorés dans la littérature. Il est démontré que la photooxydation des radicaux anioniques de flavine, qui agissent comme des intermédiaires de réaction dans de nombreuses réactions biochimiques, se produit efficacement en ~100 fs dans plusieurs flavoprotéines oxydases. Ce processus, qui est effectivement l'inverse de la photoréduction bien connue de la flavine oxydée, pourrait constituer une voie de désactivation universelle. Les propriétés de l'état excité des flavines complétement réduites ont été étudiées dans plusieurs systèmes FNR où elles sont impliquées comme intermédiaires fonctionnels, et comparées à celles en solution. Des informations précieuses concernant leurs structures électroniques et la flexibilité des flavines ont été obtenues et comparées avec des simulations atomiques, avec des implications catalytiques importantes. Enfin, un phénomène de photo-dissociation sans précédent a été révélé pour un complexe de transfert de charge non covalent de la flavine et d'un inhibiteur dans la flavoenzyme sarcosine oxydase monomérique. Ce processus se produit sur une échelle de temps de quelques centaines de femtosecondes et peut être attribué à une isomérisation photoinduite bien définie de l'inhibiteur. Dans l'ensemble, les résultats décrits, qui incluent la découverte de deux processus photochimiques jusqu'alors non documentés dans les flavoprotéines, élargissent le répertoire de la photochimie impliquant des cofacteurs de flavine. Ce travail peut ouvrir de nouvelles voies pour l'exploration de la photochimie des flavines avec, à terme, des implications pratiques possibles comme nouveaux photocatalyseurs et outils optogénétiques
Flavins are derivatives of vitamin B2 that form a highly versatile group of chromophores found in a large variety of enzymes and photoreceptor proteins. They can adopt three different redox states with various protonation states, leading to at least five physiologically relevant forms, with distinct electronic absorption spectra. Despite the diverse photophysical properties of the flavin cofactors, there are only very few natural photo-responsive flavoproteins. The vast majority of flavoproteins perform non-light-driven physiological functions (“non-photoactive”), although ultrafast, reversible photoinduced redox reactions between flavins and surrounding residues still widely occur in these systems, which can be viewed as photo-protective “self-quenching”. The past few decades have seen a blooming in the study of flavoproteins for their photocatalytic and photo-biotechnological applications. Moreover, a newly emerging approach in the development of novel photocatalysts from canonical “non-photoactive” flavoenzymes is making use of the photochemistry of reduced flavins instead of the oxidized resting state. Furthermore, practical implications of photochemistry of yet different flavin species are envisaged, but a basic understanding of their mechanisms is still required. In this thesis, applying ultrafast absorption and fluorescence spectroscopy combined with molecular simulations and quantum chemistry approaches, a variety of fundamental photochemical processes in flavoproteins is investigated. First the photoreduction of oxidized flavins was revisited in a flavoprotein, ferredoxin-NADP+ oxidoreductase (FNR), with closely packed reactant configurations, allowing ultrafast formation of intermediate radical pairs. Combining experimental and modeling techniques allowed a detailed assessment of the influence of the environment on the spectral properties of both the anionic flavin and the cationic amino acid (tyrosine or tryptophan) radicals. We further investigated the photochemistry of protein-bound flavin species in different chemical states that are largely unexplored in the literature. It is demonstrated that photooxidation of anionic flavin radicals, which act as reaction intermediates in many biochemical reactions, efficiently occurs within ~100 fs in several flavoprotein oxidases. This process, effectively the reverse of the well-known photoreduction of oxidized flavin may constitute a universal decay pathway. The excited-state properties of fully reduced flavins were studied in several FNR systems where they are involved as functional intermediates, and compared with those in solution. Valuable information concerning their electronic structures and the flavin flexibility was obtained and compared with atomic simulations, with important catalytic implications. Finally, an unprecedented photo-dissociation phenomenon was revealed for a non-covalent charge transfer complex of flavin and a inhibitor in the flavoenzyme monomeric sarcosine oxidase. This process occurs on the timescale of a few hundred femtoseconds and can be attributed to a well-defined photoinduced isomerization of the inhibitor. Altogether, the described findings, which include the discovery of two hitherto undocumented photochemical processes in flavoproteins, expand the repertoire of photochemistry involving flavin cofactors. This work may open new avenues for the exploration of flavin photochemistry with ultimately possible practical implications as novel photocatalysts and optogenetic tools

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29

Gan, Daqing. „Aqueous photochemistry of 1,4-benzoquinones and their possible role in the photochemistry of natural organic matter“. College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2180.

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Thesis (Ph. D.)--University of Maryland, College Park, 2005.
Thesis research directed by: Chemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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30

Jansen, Lisinka M. G. „Photochemistry and photophysics of azo dyes“. Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/28271.

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The photodegradation of azo dyes in solution and on cotton has been investigated. This is a major problem, because of the widespread use of this class of dyes to dye cotton. The photochemical pathways leading to photo degradation and the properties of the excited states and photophysical deactivation processes were studied. Many of the commercially used azo dyes are 1-aryl-2-naphthols with one or more azo groups which undergo azo-hydrazone tautomerism.

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31

Cowley, Nicholas John. „The mechanistic photochemistry of 4-hydroxybenzophenone“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq20620.pdf.

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32

Leibovitch, Mordechai. „Asymmetric synthesis in solid state photochemistry“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25090.pdf.

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33

Smith, Kenneth Christopher. „Photochemistry of urea/ketone inclusion compounds“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq24919.pdf.

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34

Delaney-Luu, Michelle Marie. „The photochemistry of substituted poly(acrylophenones)“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33362.pdf.

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35

Volkov, Victor Vitorovich. „Bacteriorhodopsin excited state dynamics and photochemistry“. Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/26308.

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36

Taylor, Tammye L. „UV photochemistry of synthetic model peptides“. Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/26966.

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37

Iqbal, Azhar. „Towards understanding the photochemistry of tyrosine“. Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3735/.

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The H-atom detachment driven through the 1πσ* states of biological chromophores containing an X-H bond (where X = N or O) upon UV absorption is ubiquitous in nature. Understanding the role of this dissociative state in the chromophores and their respective amino acids following UV excitation would enable a step change towards establishing a better understanding of the mechanisms of photostability of larger peptides in the gas-phase. The work presented in this thesis focuses on the H-atom elimination of phenol and indole, the chromophores of the amino acids tyrosine and tryptophan, respectively. The H-atom elimination has also been carried out in tyrosine and its sub-units p-ethylphenol and tyramine upon excitation at 200 nm. In all these systems the O-H bond fission on the phenol ring results in a range of H-atoms kinetic energy release. Using a combination of femtosecond pump-probe spectroscopy, time-offlight mass spectroscopy (TOF-MS) and velocity map ion imaging (VMI) reveals that H-atom elimination in all these systems occurs on an ultrafast timescale (~200 fs) for both fast and slow H-atoms. This casts considerable doubt over the previously assigned statistical origin of the slow H-atoms and suggests direct pathways to their formation. The H-atom kinetic energy spectrum in tyrosine also implies that H-atom elimination is occurring through the same coordinate i.e. O-H bond as exhibited by it’s phenol chromophore, thus confirming the active participation of the 1πσ* states from the chromophore of the amino acid to the amino acid itself. These findings are of great importance enabling one to compare these results with existing calculations on the chromophores which often model the system in an isolated environment. These results also provide ground work for more complex calculation to be carried out, in particular on the amino acids and the di/tri peptides.

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38

Rowland, Glenn Anthony. „The photochemistry of sulfuric acid aerosols“. Thesis, University of Canterbury. Chemistry, 2001. http://hdl.handle.net/10092/5949.

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We report here the experimental investigation of several photochemical reactions that may occur in concentrated sulfuric acid droplets in the clouds of the planet Venus. It was found that the irradiation of 80-100wt.% sulfuric acid aerosol with 193nm light in the presence of carbon monoxide resulted in the formation of carbon dioxide and either the formation or destruction of sulfur dioxide. The measured quantum yield for carbon dioxide formation is 0.011±0.010. Various instrumental techniques for determining the size and number density of aerosol droplets were utilised in an attempt to generate a stable, monodisperse sulphuric acid aerosol. Concentrated sulfuric acid solutions were irradiated with 178.3nm, 184.9nm, 193.3nm and 253.7nm light in order to investigate the UV photochemistry of the bulk liquid. No significant photochemistry was observed. The reactions occurring in sulfuric acid aerosol at 193nm were attributed to multiphoton processes, permitted by the optical focussing effects observed in small droplets. Irradiation of solutions of Fe(II) in 98wt.% sulfuric acid solution with 193nm or 248nm light results in the formation of Fe(III). Under the same conditions, the reduction of Fe(III) is also observed. The presence of sulfur dioxide increases the initial rate of the reaction, and dissolved oxygen is consumed in the initial stages. A qualitative mechanism for the photochemical interconversion of Fe(II) and Fe(III) in concentrated sulfuric acid is proposed, which incorporates the effect of sulfur dioxide and oxygen on the reaction.

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39

Kennedy, Graham Robert Alexander. „Laser photochemistry of jet-cooled molecules“. Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/621.

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40

Fletcher, S. C. „Polarized photochemistry and binuclear metal carbonyls“. Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356518.

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41

Lees, Alistair J. „Photophysics and photochemistry of organometallic complexes“. Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417484.

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42

Wilkes, J. „Photochemistry of small adsorbates on surfaces“. Thesis, University of Huddersfield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286052.

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43

Shields, C. J. „Matrix photochemistry with plane-polarised light“. Thesis, University of Strathclyde, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372121.

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44

Kunanandam, Suren. „Spectroscopy and photochemistry of arylazonaphtol dyes“. Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423732.

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45

Haddleton, D. M. „Photochemistry of some metal-ethane complexes“. Thesis, University of York, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374165.

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46

Birch, D. „The aqueous photochemistry of small peptides“. Thesis, Open University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383637.

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47

Willasey-Wilsey, Sarah Louise. „The photochemistry of unsaturated carbonyl compounds“. Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309739.

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48

Bushby, Lisa Marie. „Photochemistry and photophysics of lanthanide complexes“. Thesis, Durham University, 2001. http://etheses.dur.ac.uk/4208/.

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Luminescent lanthanide complexes have proven to be a productive area of research due in essence to their unique emission properties enabling their use in a variety of applications. A major drawback to using lanthanides is their low extinction coefficients, so that the antenna effect is often used to overcome this problem. In this way, the antenna chromophore absorbs incoming radiation and transfers the energy to the ion, leading to indirect excitation of the lanthanide. Understanding this mechanism of energy transfer is of fundamental importance both for the theory of the photophysical processes, and for the development of more efficient materials. In this thesis, many of the areas of both the population and the deactivation of the lanthanide excited states are discussed. The time resolved data of the Tm(^3+) ion in a variety of solvents and chelate systems have been measured, and the effects of deuteration on the decay kinetics investigated. The mechanism of energy transfer is followed by detailed kinetic measurements of a complex with a benzophenone containing chromophore. The calculation of the pure radiative lifetime allowed the efficiency of each of the steps involved in the sensitisation process to be determined for the first time. Changing the coordination environment around the ion, even slightly, by the addition of a single CH(_2) group into the arm of the ligand affects the oscillator strength of the hypersensitive transitions in both the Eu(^3+) and Tb(^3+) complexes, and influences the efficiency of energy transfer. Intramolecular sensitisation of Eu(^3+) ions by acetophenone containing ligands was investigated in a series with increasing electron donating ability of the chromophore. It was found that the efficiency of energy transfer increases with the polarity of the antenna, but that in the case of a dimethylamino substituted ligand, the solvent also has a profound effect on the intensity of Eu(^3+) emission. Energy transfer to bound Eu(^3+) and Tb(^3+) ions in aqueous micellar systems is demonstrated, with the process dependent on the hydrophobic properties of the chromophore and the properties of the surfactant. Photoinduced electron transfer reactions are found to occur in ethoxybenzyl substituted complexes with the emission from the chromophore and from the lanthanide ion dependent upon the lanthanide reduction potential and the AG value of both the forward and backward electron transfer reactions.

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49

Mitchell, Lorna J. „Exploiting the photochemistry of the quinones“. Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/32977/.

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This thesis will focus on two main research areas with the aim of developing and exploring the solar photochemical reactivity of quinones. In Chapter One, a review of quinone photochemistry is presented; this includes both cycloaddition reactions and hydrogen abstraction reactions. After a review of the relevant literature, the aims of the research are outlined and placed into context. Chapter Two details the development of a green photo Friedel-Crafts acylation for the preparation of acylated hydroquinones, which serve as versatile precursors for the synthesis of numerous biologically active quinone natural products. After a review of the relevant literature, the results of the research are discussed. Key achievements include the development of an accessible and ‘greener’ synthetic protocol employing a ‘sun-mimicking’ light source and trifluorotoluene as solvent. The factors influencing the regiochemical outcome of the acylation are also discussed. In Chapter Three, the photochemical oxidising ability of p-benzoquinone in both stoichiometric and substoichiometric quantities is investigated. In the introduction, a short review of the oxidising ability of the quinones - particularly DDQ - is presented and the enhanced oxidising ability of p-benzoquinone upon irradiation is discussed. The potential breadth of this underexploited oxidising ability is then investigated in the use of alcohol oxidation and C-H functionalisation protocols. Chapter Four summarises the results obtained in the thesis and outlines scope for further research in the area. In Chapter Five, full experimental details for the research are presented.

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50

Karabaeva, Kanykey E. „Photochemistry of Masked Pyrene-4,5-Dione“. Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1371083757.

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