Thèses sur le sujet « Charge tranfer »

Long-distance radical cation transport was studied in DNA condensates where linearized pUC19 plasmid was ligated to an oligomer and transformed into DNA condensates with spermidine. DNA condensates were detected by Dynamic Light Scattering and observed by Transmission Electron Microscopy. Introduction of charge into the condensates causes long-distance charge migration, which is detected by reaction at the remote guanines. The efficiency of charge migration in the condensate is significantly less than it is for the corresponding oligomer in solution. This result is attributed to a lower mobility for the migrating radical cation in the condensate, caused by inhibited formation of charge-transfer-effective states. Radical cation transport was also studied in DNA condensates made from an oligomer sandwiched between two linearized plasmids by double ligation. Unlike the single ligated plasmid condensates, the efficiency of charge migration in the double ligated plasmid-condensates is high, indicative of local structural and conformational transformation of the DNA duplexes. Organic monomer units having extended ð-conjugation as part of a long conducting polymer was synthesized and characterized. The monomer units were covalently attached to particular positions in DNA oligonucleotides by either the convertible nucleotide approach or by phosphoramidite chemistry. Successful attachment of the monomer units to DNA were confirmed by mass spectral analysis. The DNA-conjoined monomer units can self assemble in the presence of complementary sequences which act as templates that can control polymer formation and structure. By this method the para-direction of the polymer formation can be enforced and may be used to generate materials having nonrecurring, irregular structures.

When the thickness of an oxide film is below a nm (few atomic layers) the interaction with the metal substrate, together with structural and morphology changes, can lead to completely different chemistry with espect to thicker films and can lead to new and unprecedented phenomena. This thesis focuses on the study of the structure and properties of different ultrathin oxide films epitaxially grown on metal subtrates and their interactions with adsorbed metal atoms and clusters.

La perspective d'une société utilisant l'énergie de la lumière du soleil pour séparer la molécule d'eau en dihydrogène et en dioxygène, ces deux gaz servant de moyens de stockage et de vecteurs d'énergie, nécessite de nombreux développements. En particulier, il est nécessaire de choisir un matériau pouvant absorber la lumière et transférer son énergie aux charges électriques afin de générer un courant électrique. Parmi toutes les possibilités, ce mémoire étudie l'applicabilité des bâtonnets semiconducteurs de tailles nanométriques constitués d'un cœur de séléniure de cadmium et d'une coquille de sulfure de cadmium. Profitant des méthodes décrites ces dernières années et d'une méthodologie de fonctionnalisation, les objets obtenus présentent une grande monodispersité et peuvent être dispersés en milieu aqueux. Les propriétés photoélectrochimiques des nanobâtonnets sont explorées par microscopie électrochimique. Cette méthode permet de déterminer s'il y a un transfert de charge entre des molécules en solution et un substrat constitué des bâtonnets, et le cas échéant son sens. Ainsi les nanoparticules, soumises à une excitation lumineuse, transfèrent des électrons vers les molécules dans l'ensemble des cas explorés, révélant ainsi un caractère plus réducteur que la para-benzoquinone. Ce transfert est réalisé d'autant plus rapidement que le rapport entre la longueur et le diamètre des bâtonnets augmente, jusqu'à un optimum, mais aussi que la taille de la couche organique isolante les recouvrant diminue, comme l'ont révélé des suivis de réduction d'une sonde rédox moléculaire colorée, la résazurine. Ces charges ont été mises à profit pour fonctionnaliser les nanoparticules, au travers de la réduction d'un pont disulfure ou d'un sel d'or. Enfin des stratégies ont été explorées pour permettre aux particules de réaliser la réduction photosensibilisée de l'eau, au travers de la synthèse d'une cobaloxime, un catalyseur moléculaire, ou de la réduction de sels métalliques à propriété catalytique tels que le cobalt et le nickel
The development of a society based on solar energy requires a way to store it. One possibility consists in water splitting that needs a material to collect and transform the energy contained in light beam in an electric charges movement. Among all possibility, we hereby explore the applicability of nanometers-sized semiconductor rods composed of a cadmium selenide core and a cadmium sulfide shell. Based on methods already developed and a new functionalization methodology, the obtained particles exhibit a high monodispersity and can be dispersed in water, a useful property for the final purpose. Their photo-electrochemical properties have been explored by electrochemical microscopy that allowed to determine whether there is charge transfer between mediators in solution and quantum rods deposited as substrate and its direction. It reveals that under light irradiation and in all cases herein experimented, they transfer electrons to the mediators, making them more reductive than para-benzoquinone. This transfer is fastened when the ratio between the length and the diameter of the rods increased until an optimum, but also when the width of the organic isolating shell decreases, as revealed by time-resolved reduction of resazurin, a colored rédox molecular probe. These charge transfer have been used to functionalize particles by reduction of a disulfide bridge or a gold salt. Finally, strategies have been explored to make these quantum rods able to photosensibilized water reduction through synthesis of a cobaloxime, a molecular catalyst, or metal salt reduction as cobalt and nickel known to exhibit catalytic activity

Ce travail porte sur la neutralization résonnante d’ions Li+ sur des métaux et agrégatsmétalliques supportés. La neutralization sur Pd(100) a été étudié, pour différentsparamètres. La neutralisation s’avère très efficace sur cette surface avec un travail desortie grand et est en contradiction avec ce qu’on attend dans le cadre des modèlestraditionnels. Il est proposé qu’une description du processus RCT modifié, issued’études précédentes sur des métaux nobles, doit être utilisé. Dans celle ci desprocessus de neutralisation survenant à des distances atome- surface faible ont lieu etaussi un comportement adiabatique du système aux faible énergies de collisions mèneà une neutralization efficace.Les résultats de l’étude des processus de transfert d’électrons lors de l’interactiond’ions de Li+ avec des agrégats d’or supporté sur HOPG avec Al2O3 sont présentés etdiscuté. L’imagerie STM pour les agrégats d’or supporté sur un substrat HOPG viergeet aussi un substrat de HOPG bombardé par des ions de AR sont présentés. Lesobservations révèlent que agrégats d’or forment préférentiellement des chaines 1D lelong des marches sur HOPG vierge. Dans le cas de HOPG bombardé, la taille et lahauteur des agrégats sont dépendants des défauts de surface.Nous avons trouvé que la neutralisation est très efficace sur les petits agrégats et engénéral est beaucoup plus grande que sur des surfaces de cristaux d'or. Nous montronsdes effets liés à la nature du substrat, comme dans le cas de l’alumine ou le cas desdifférences observées sur des chaines d’agrégats sur HOPG vierge et les agrégatsformés sur des défauts
The present work investigates the neutralization of Li+ ions on metals and supportedmetal clusters. Neutralization on a transition metal surface Pd (100) for differentparameters was studied. Highly efficient neutralization on this surface with a highwork functions was observed and contradicts our traditional views on resonant chargetransfer (RCT) mechanism. A modified RCT picture involving new neutralizationprocesses occurring at a short atom-surface distance and an adiabatic behaviourleading to efficient neutralization at large distances, that has emerged from previousstudies on noble metal surfaces appears in qualitative agreement with our data.The experimental results on the dependence of the Li neutralization on the Auclusters supported on different substrates are reported and discussed. As acomplement to this, a STM study into the morphology of Au nanoparticles on apristine HOPG substrate as well as Ar+ ions sputtered HOPG substrate has beenperformed. The observations reveal that Au clusters preferentially form onedimensional chains along steps on pristine HOPG. In the case of Ar+ ions sputteredHOPG substrate, the size and height of cluster are dependent on surface defects.We found that neutralization is very efficient on small clusters and in general muchlarger than on surfaces of gold crystals. We demonstrate existence of strongdifferences as a function of cluster support type as in case of alumina supports orcluster chains on HOPG and clusters on defects on HOPG terraces

Structural analyses of DNA oligonucleotides indicate the presence of bound water molecules in the major and minor grooves of DNA. These water molecules participate in DNA charge transfer by their reaction with guanosine radical cation to form 7,8-dihydro-8-oxo-guanine (8-oxoG), which when treated with a base leads to DNA strand cleavage. We probed the reaction of guanosine radical cation with water with series of alkyl substituted cytidines and thymidines by incorporating the modified nucleosides into anthraquinone linked DNA duplexes and irradiating them with UV light at 350 nm. The incorporation of these hydrophobic substituents disrupt the DNA spine of hydration, and we have observed that these modifications in the major and minor groove do not effect the trapping or long distance hopping of radical cations in DNA. The second part of the work reported herein examines the role of charged nucleosides in long range charge transfer in duplex DNA. DNA methylation is a naturally occurring process mediated by enzymes responsible for such functions in biological systems. Hypermethylation of DNA can also occur as a result of environmental alkylating agents leading to mutation of the affected cells. Methylation of the ring nitrogen of a purine base can introduce a positive charge in the ring resulting in the cleavage of the glycosidic bond of the nucleoside. To understand the role of a charged nucleoside on charge transfer in DNA, we designed and synthesized cationic nucleoside mimics, which were incorporated into anthraquinone-linked DNA strands and irradiated at 350 nm. The presence of the cationic bases on the duplexes inhibits the migrating hole from hopping along the DNA strand, and induces a prominent local structural distortion of the DNA as a result of the charged nucleobase.

Une compréhension sans cesse plus pointue des processus élémentaires de transferts de charges et d’énergie, qui sont à la base même de nombreux processus biologiques, permet non seulement l’élaboration mais aussi l’amélioration de la mise au point de molécules photoactives utiles dans différentes applications. C'est le cas (i) de systèmes moléculaires et supramoléculaires destinés à mimer efficacement la photosynthèse, ou encore (ii) de molécules photoactives capables d’interagir avec des macromolécules biologiques et d’induire une transformation de ces biomolécules. C’est dans ce cadre général que s’inscrit l’élaboration de nouveaux complexes polyazaaromatiques de Ru(II) capables d’interagir avec la double hélice d’ADN et de photoréagir avec sa base la plus réductrice, la guanine, par transfert d’électron photoinduit. C’est sur la base de ces processus que des nouveaux agents antitumoraux photoactivables ont pu être développés. L’utilisation de complexes de Ru(II) dans le design d’entités supramoléculaires polymétalliques destinées à jouer le rôle de collecteurs de lumière et permettant ainsi de mimer les systèmes d’antennes naturels s’intègre également dans cette démarche.

L’ensemble de notre travail s’est concentré sur ces deux domaines d’applications. Par l’étude de différents processus de transfert de charges/d’énergie au sein des complexes seuls (processus intramoléculaires) ou en interaction avec un environnement spécifique (processus intermoléculaires), nous avons souhaité mettre en évidence l’intérêt de l’utilisation d’un nouveau ligand plan étendu, le tpac, au sein de complexes du Ru(II). Un tel ligand permet en effet de conférer d’une part une affinité élevée des complexes résultants pour l’ADN, et d’autre part, de par sa nature pontante, de connecter des unités métalliques entre elles au sein d’entités supramoléculaires de taille importante.

Les propriétés photophysiques de quatre complexes basés sur le ligand plan étendu tpac, le [Ru(phen)2tpac]2+ (P) et son homologue dinucléaire le [(phen)2Ru tpac Ru(phen)2]4+ (PP) (à base de ligands ancillaires phen), ainsi que le [Ru(tap)2tpac]2+ (T) et son homologue dinucléaire le [(tap)2Ru tpac Ru(tap)2]4+ (TT) (à base de ligands ancillaires tap), ont été étudiées et comparées entre elles.

L’examen de ces propriétés, d’abord pour les complexes seuls en solution, en parallèle avec celles de complexes dinucléaires contenant un ligand pontant PHEHAT, a permis de mettre en évidence l’importance de la nature du ligand pontant utilisé. Ces résultats ont ainsi révélé qu’un choix judicieux du ligand pontant permet de construire des entités de grande taille capables de transférer l’énergie lumineuse vers un centre (cas du ligand PHEHAT), ou, au contraire, de relier entre elles des entités ne s’influençant pas l’une l’autre d’un point de vue photophysique (cas du ligand tpac).

Les propriétés des complexes du tpac, étudiés cette fois en présence de matériel génétique (mononucléotide GMP, ADN ou polynucléotides synthétiques), se sont révélées très différentes selon que le complexe portait des ligands ancillaires phen (P, PP) ou tap (T, TT). Seuls les complexes à base de tap sont en effet photoréactifs envers les résidus guanine. Nous avons dès lors focalisé cette partie de notre travail sur les deux complexes T et TT. Cette photoréaction, ainsi que le transfert d’électron photoinduit entre ces complexes excités et la guanine, ont pu être mis en évidence par différentes techniques de spectroscopie d’émission tant stationnaire que résolue dans le temps, ainsi que par des mesures d’absorption transitoire dans des échelles de temps de la nano à la femto/picoseconde. L’étude du comportement photophysique des complexes en fonction du pH a en outre révélé de manière très intéressante que, pour des études en présence d’ADN, la protonation des états excités des complexes devait être considérée. Les résultats de cette étude nous ont fourni des pistes quant à l’attribution des processus observés en absorption transitoire.

Le transfert d’électron a également fait l’objet d’une étude par des méthodes théoriques. Ces calculs ab initio ont permis de mettre en évidence une faible influence de l’énergie de réorganisation sur la vitesse de transfert d’électron, qui semble dépendre plus sensiblement de la non-adiabaticité du processus, mais surtout de l’énergie libre de la réaction et d’un éventuel couplage à un transfert de proton.

L’ensemble des résultats obtenus avec les complexes T et TT en présence de matériel génétique, qui, de manière assez inattendue, sont très semblables, indiquent que ces complexes présentent tous deux un grand intérêt pour le développement de nouvelles drogues antitumorales photoactivables.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Electrospinning is a method of producing nano structured material from a polymer solution or melt using high strength electric fields. It is a process that has yet to find extensive industrial application yet shows promise if obstacles such as low rate of production overcome perhaps by more complete theoretical modelling. This work examines the effects of adding an ionic salt to a solution of poly(vinyl alcohol) in water. The direct effect was an increase the charge density and electric current. It was found that an increase in charge density decreases the mass deposition rate and forms a thinner initial jet. When the sign of the charge on the polymer solution was changed from positive to negative the charge density increased and the initial jet diameter and mass deposition rate also decreased. It was proposed that a smaller radius of curvature is formed by the Taylor cone at higher charge densities resulting in a smaller “virtual orifice”. The extent of the bending instability was explored and it was found that adding ionic salt results in a decrease in the bending instability resulting in thicker fibres. Changing the sign of the charge on the polymer solution from positive to negative resulted in an increase in the bending instability and resulted in thinner fibres. The charge transfer mechanisms used in different electrospinning models are explored and some assumptions not explicitly stated are discussed. From this discussion a generalized equation describing the charge transport mechanisms is proposed.

Using X-ray photoelectron (XPS) and X-ray absorbtion spectroscopy (XAS) we demonstrate charge transfer at an interface between two transition metal phthalocyanines, MnPc and F16CoPc, resulting in charged MnPc + and F16CoPc -, species. Density functional theory calculations reveal that a hybrid state is formed between the two types of phthalocyanines, which causes this charge transfer. For the hybrid state the Mn3dxz interacts with the Co 3dz2 orbital leading to a two-level system. Moreover, we have prepared mixed films out of this pair, which were characterized also by means of electron energy-loss spectroscopy. Our data reveal the formation of MnPc/F16CoPc charge transfer dimers in analogy to the heterojunction. The electronic excitation spectrum of these blends is characterized by a new low energy excitation at 0.6 eV.

Experimental measurements ol N₂ resonant charge transfer cross sections were performed. It was found that the energy of electrons used to produce the N₂⁺ ions is an important variable with respect to cross section. An examination of the experimental precision was performed and it was found that the precision of measurement was insufficient to determine the exact form of this relationship. The effect of ion energy (collisional energy) was too small to be seen. Modulated detection was used to improve precision and permit measurement at high noise levels. A description of the apparatus is provided. Consideration of other systems and the suitability of their resonant charge transfer reactions for experimental investigation is discussed. Various theoretical models for estimation of cross section were examined.
M.S.

Résumé : Le travail de recherche présenté dans ce mémoire fut inspiré par le processus de la photosynthèse qui se produit chez les plantes. Au cours de ce processus l’énergie solaire est convertie en énergie chimique via différentes étapes de transferts d’électrons et d’énergie. En maîtrisant bien ces concepts, de nombreuses applications, telles que les cellules photovoltaïques ou les DEL (Diodes électro-luminescentes) peuvent être améliorées. Pour se faire, il est important d’optimiser les propriétés des matériaux existants (oligomères, polymères, etc…) en préparant des systèmes conjugués plus efficaces, mais aussi de pleinement comprendre les processus qui s’y produisent (processus de transferts d’électrons et d’énergie photo-induist). La série d’oligomères et de polymères présentée dans ce mémoire le sont pour leurs applications dans des systèmes photoniques. Dans cette optique, ce mémoire a été divisé en cinq grands chapitres. Le premier présente les principes théoriques de la photophysique. Le second présente le suivi du transfert d’énergie T[indice inférieur 1] dans les états triplets, T[indice inférieur 1], une dyade constituée de la tétraphénylporphyrine de zinc(II), [ZnTPP], et de la bis(phénylpyridinato)(bipyridine) d’iridium(III), [Ir], chromophores liés avec un pont trans-diéthynylbis(phosphine)-platine(II). Malgré que cette dyade soit entièrement conjuguée et qu’elle soit constituée d’un donneur ([ZnTPP]) et d’un accepteur ([Ir]), aucun transfert d’énergie T[indice inférieur 1] [Ir] → S[indice inférieur 1]/T[indice inférieur 1] [ZnTTP] n’a été observé. Ce résultat fut attribué à l’absence de recouvrement des orbitales moléculaires entre la HSOMO(donneur*) et la HSOMO(accepteur), LSOMO(accepteur) and LSOMO (donneur*) (mécanisme de Dexter). Ainsi, l’échange d’électrons est impossible. Ce chapitre suggère que l’équation de Dexter, k[indice inférieur Dexter] = KJexp(-2r[indice inférieur DA]/L) ne reste qu’une approximation. Ce travail a été publié dans ChemComm (2013, 49, 5544-5546). Le troisième chapitre présente le transfert d’énergie singulet beaucoup lent qu’attendu se produisant dans une dyade constituée d’une porphyrine de zinc(II) avec une porphyrine base libre liées par un pont palladium(II) (trans-PdI[indice inférieur 2]). Sachant que cette dyade est entièrement conjuguée et que la distance entre les deux centres de masse des porphyrines est relativement courte, ce système aurait dû présenter un transfert d’énergie très rapide, d’après la théorie de Förster. Dans ce cas, ce comportement a été expliqué par le faible recouvrement des orbitales frontières (OM) du donneur et de l’accepteur. Ce travail a été accepté le 2014-05-26 dans Chemistry – A European Journal (chem.201403146). Le quatrième chapitre rapporte une étude du transfert d’énergie ultra-rapide (650 fs) entre des états singulets dans une dyade composé d’une porphyrine de zinc(II) (le donneur) et une porphyrine base libre (l’accepteur) liées à l’aide d’un pont de palladium ([beta],[beta]--trans-Pd(NH)[indice inférieur 2](CO)[indice inférieur 2]). Ces résultats ont été attribués à la présence d’un couplage fort entre les OM du donneur et de l’accepteur et de la très faible contribution (atomique) du Pd(II) vers ces OM. Cette dyade montre la plus rapide constante de transfert d’énergie k[indice inférieur ET] que nous connaissons pour des dyades similaires contentant un fragment métallique. Les résultats du troisième et quatrième chapitre montrent que la théorie de Förster tel quel ne suffit pas pour prédire les vitesses de transferts d’énergie dans certains systèmes : d’autres facteurs doivent être pris en compte. Ce travail a été soumis dans JACS ( ja-2014-061774, 19-6-2014). Dans le cinquième chapitre de ce mémoire, la synthèse du bis(-[alpha]-(amino(4-éthynylbenzene (triméthylsilane)(R))))bis(4-éthynylbenzene-(triméthylsilane))quinone diimine (R= H, Boc) comme modèle pour des polymères conjugués et non-conjugués contenant le colorant porphyrine a été proposée. Le corps du composé désiré (tétrakis(4-éthynlyphenyl)quinone-1,4-diimine-2,5-diamine) a montré un transfert de charge partant des groupes terminaux riches en électrons une la benzoquinone centrale plus pauvre. La nature de l’émission fut observée uniquement à 77K pour le cas où R = H et fut attribuée à de la fluorescence. À température ambiante, l’intensité était trop faible pour être observée. Dans le cas où R = Boc, aucune emission n’a été détectée. Malheureusement, le composé espéré ne fut pas obtenu, le procédé de synthèse employé engendra uniquement la forme réduite. Cette forme fut malgré tous analysé, et ne présenta pas de transfert de charge ni de communication entre les différents chromophores. Ceci a été expliqué simplement par le fait que la conjugaison est brisée quand ce composé est sous sa forme réduite. Ce travail sera soumis au Journal of Inorganic and Organometallic Polymers and Materials. // Abstract : The research work presented in this master thesis is inspired by the photosynthetic process occurring in plants where solar energy is converted into chemical energy via several energy and electron transfer processes. In the light of these concepts, several applications such as solar cells and light emitting diodes can be improved. To do so, we need to optimize the properties of polyads, oligomers and polymers to device more efficient conjugated materials as well as developing a full understanding of the photo-induced energy and electron transfer processes that occur. Several organometallic oligomers and polymers are presented in this thesis due to their potential photonic applications. In this respect, this master thesis has five chapters. The first one introduces some theoritical principles of photophysics. The second one presents the monitoring of triplet state (T[subscript 1]) energy transfer in a dyad that consists of zinc(II)tetraphenylporphyrin, [ZnTPP], and bis(phenylpyridinato)-(bipyridine)iridium(III), [Ir], chromophores linked by a platinum(II) containing bridge. Despite the conjugation in this dyad and the presence of the [ZnTPP] energy donor and the [Ir] energy acceptor species, no T[subscript 1] [Ir] → S[subscript 1]/T[subscript 1] [ZnTTP] energy transfer occurs. This result was explained by the absence of MO overlap between HSOMO(donor*) and HSOMO(acceptor), LSOMO(donor*) and LSOMO(acceptor) , and hence no efficient double electron transfer exchange (i.e. Dexter mechanism) is likely to occur. This chapter suggested that Dexter formulation, k[subscript Dexter] = KJexp(-2r[subscript DA]/L), appears as an approximation. This work has been published in ChemComm (2013, 49, 5544-5546). The third chapter shows an unexpected slow singlet energy transfer in a dyad built upon a zinc(II)porphyrin and the corresponding free base chromophores linked by a palladium(II)- containing bridge (trans-PdI[subscript 2]), despite the presence of conjugation and the relative short center-to-center distance. This behavior was explained by two factors, the first is the lack of large molecular orbitals (MOs) overlaps between the frontier MOs of the donor and acceptor, and thus preventing a double electron exchange to occur through the trans-PdI[subscript 2] bridge. The second factor affected the energy transfer is the electronic shielding induced by the presence of this same linker, namely the electron rich iodides, preventing the two VI chromophores to fully interact via their transition dipoles. This work has been accepted on 2014-05-26 in Chemistry-A European Journal (chem.201403146). The fourth chapter reports an ultrafast singlet energy transfer (650 fs) in a dyad composed of a zinc(II)porphyrin (donor) and a free base porphyrin (acceptor) [beta],[beta]-linked via trans- Pd(NH)[subscript2](C=O)[subscript 2]. These results were explained by the presence of strong MO couplings of the donor and acceptor and the very weak atomic contribution of the Pd(II) atom to this MO. This dyad shows the fastest energy transfer rate k[subscript ET] among other similar dyad systems incorporating a bridge either in the form of a metal fragment or carbon-based. The results of these third and fourth chapters showed that the Förster mechanism is not enough to account for the energy transfer in some systems and other factors affect that transfer. This work has been submitted in JACS ( ja-2014-061774, 19-6-2014). In chapter 5, the synthesis of bis-[alpha]-(amino(4-ethynylbenzene (trimethylsilane)(R))bis(4- ethynylbenzene-(trimethylsilane))quinone diimine (R = H, Boc) as a model for conjugated and unconjugated porphyrin dye polymers was proposed. The central core of the desired compound, tetrakis(4-ethynlypenyl)quinone-1,4-diimine-2,5-diamine, provided evidence for a charge transfer interaction from the electron richer terminal groups to be more electron poorer benzoquinone ring. The nature of the emission of the core compound was found to be fluorescence at 77K for the case R = H but was too weak to be observed at 298K. No emission was detected for the case R = Boc. Unfortunately, the synthetic route of the desired compound gave the reduced form. The analyses of the reduced compound showed the complete absence of the charge transfer or any communication between the different chromophores due to the broken conjugation between the porphyrin units in the reduced product. This work will be submitted to Journal of Inorganic and Organometallic Polymers and Materials.

This work details the simulation of charge transfer at ultramicrointerfaces. A novel algorithm is presented for the simulation of electrochemical techniques applied to both ultramicrodisc and ultramicropipette electrodes. Numerical Method. The simulations employ the Crank-Nicolson finite differences or the Alternating Direction Implicit (ADI) method extended to include expansion of the space grid in two dimensions, a n-point current calculation and implicit determination of boundary conditions. The effects are determined of; point separation, choice of grid expansion equation, boundary conditions and relative number of points on electrode and in solution. Also, diffusion geometry, time increment, and the stability of the algorithm are considered in detail. The various methods currently available to model electrochemical response at ultramicrointerfaces are discussed, together with their limitations and a suggested protocol for their use. Computing. All programs are written in FORTRAN and all calculations performed in double precision. Source codes were compiled and run on the Edinburgh Multi-Access System (EMAS). Electrochemical techniques. Techniques simulated include cyclic voltammetry and chronoamperometry at macro, ultramicrodisc and ultramicropipette electrodes, including asymmetric sweep voltammetry at ultramicropipette electrodes. Results are presented for both reversible and quasi-reversible charge transfer. Effects of sweep rate, electrode radius, charge transfer coefficient and rate of charge transfer are studied. Disc and pipette electrochemical responses are compared over a range of experimental parameters. The simulation method presented is fast, accurate and stable over a wide range of experimental parameters and is easily adapted to different electrode geometries and experimental techniques.

Die Reaktionspfade und Reaktionsdynamik photoinduzierter bimolekularer Ladungstransferreaktionen werden mit Hilfe der ultraschnellen polarisationsabhängigen UV-Pump/IR-Probe-Spektroskopie charakterisiert. Allgemein akzeptierte Modelle zur Beschreibung von bimolekularen Elektrontranserreaktionen nehmen an, dass Ladungstrennung in polaren Lösungsmitteln zu zwei Arten von Ionenpaaren führt, den lockeren (LIPs) und den engen Ionenpaaren (TIPs). TIPs und LIPs können durch die Beobachtung von Schwingungsmoden spektroskopisch unterschieden werden. Allerdings deuten die multiplen Zeitskalen sowohl für die Bildung von TIPs als auch LIPs darauf hin, dass eine Unterscheidung in zwei Arten von Ionenpaaren mit definierter Geometrie eine erhebliche Vereinfachung ist. TIPs und LIPs sind vielmehr als Grenzfälle zu betrachten, zwischen derer eine kontinuierliche Verteilung verschiedener Ionenpaare existiert. Die Natur der Ionenpaare wird durch die Verteilung der neutralen Reaktionspaare vor Initiation der Reaktion bestimmt. Außerdem wird gezeigt, dass TIPs höchst anisotrop sind. Die Wichtigkeit der beidseitigen Orientierung der Reaktanten wird dabei offengelegt. Weiterhin wird erstmalig ein femtosekundenspektroskopischer Beweis für die Existenz von Kohlensäure in wäßriger Lösung präsentiert. Eine Photosäure wurde verwendet, um die ultraschnelle Protonierung von Bikarbonat optisch auszulösen. Kohlensäure wurde bisher als Feststoff in Eismatrizen und in der Gasphase detektiert. Da Kohlensäure als Intermediat zwischen Kohlenstoffdioxid und Bikarbonat postuliert wird, ist ihre Charakterisierung von immenser Bedeutung für das Verständnis grundlegender Säure-Base Chemie von Karbonaten in wäßriger Lösung. Die Analyse der zeitabhängigen Signale unter Verwendung eines theoretischen Modells erlaubt die Bestimmung der bimolekularen Reaktionsdynamik. Dies ermöglicht einen Einblick in die Säure-Base Chemie von Kohlensäure.
The reaction pathways and dynamics of photoinduced bimolecular charge transfer reactions are characterised with ultrafast polarisation-sensitive UV-pump/IR-probe-spectroscopy. Generally accepted models for bimolecular electron transfer reactions suppose that charge separation in polar solvents leads to two geminate ion pairs, namely loose (LIPs) and tight ion pairs (TIPs). By monitoring vibrational marker modes TIPs and LIPs can be distinguished spectroscopically. However, multiple time scales for the formation of TIPs and LIPs indicate that a distinction between two kinds of ion pairs with well-defined geometries is a considerable simplification. TIPs and LIPs should rather be regarded as limiting cases, as there is a continuous distribution of different ion pairs between these two limits. The crucial parameter governing the nature of the ion pairs is the distribution of neutral reaction pairs subsequent to initiation of the reaction. Furthermore, TIPs are found to be highly anisotropic, revealing the importance of mutual orientation of the reactants. This thesis also presents for the first time femtosecond infrared spectroscopic results proving the existence of carbonic acid in aqueous solution. A photoacid is used to optically trigger the ultrafast protonation of bicarbonate. Carbonic acid has only been detected as solid existing in ice matrices and in the gas phase, so far. Because carbonic acid is often postulated as intermediate between carbon dioxide and bicarbonate its characterisation is of substantial support in understanding fundamental acid-base chemistry of carbonates in aqueous solution as well as in biophysical situations. Analysing the time-dependent signals using a theoretical model to describe bimolecular reaction dynamics an on-contact proton transfer reaction rate is derived. This gives an insight into the acid-base chemistry of carbonic acid.

Cette thèse traite du transfert du muon entre l'hydrogène muonique et d'autres atomes et molécules. Récemment, Adamczak et al. ont proposé une méthode de mesure de la structure hyperfine de l'état fondamental de l'hydrogène muonique basée sur la dépendance énergétique du taux de transfert muonique sur l'oxygène. Réalisées dans les années 90 au Paul Scherrer Institut, des expériences ont en effet indiqué que le taux de transfert sur l'oxygène semblait augmenter d'un facteur 4 entre des énergies de collision thermiques (0.04 eV) et épithermiques (0.12 eV). Nos calculs avaient pour première motivation de vérifier ce comportement. Pour étudier cette dépendance du taux de transfert, nous avons utilisé une méthode de résolution de l'équation de Schrödinger indépendante du temps du type close-coupling. Nous avons ainsi mis en oeuvre un formalisme utilisant les coordonnées hypersphériques elliptiques étendu pour traiter le cas d'un moment angulaire total différent de zéro. Nous avons utilisé ce formalisme pour calculer le processus de transfert sur l'oxygène et le néon. Dans ces deux cas, l'accord avec les résultats expérimentaux est excellent. Finalement, la dépendance énergétique du taux de transfert sur le néon suggère de préférer plutôt le néon à l'oxygène pour réaliser l'expérience de mesure de la structure hyperfine de l'hydrogène muonique. Les effets isotopiques (lorsque l'hydrogène muonique est remplacé par le deutérium muonique) sont aussi parfaitement reproduits et expliqués pour l'azote, l'oxygène et le néon.

An approximate analytical expression for the current potential characteristic for charge transfer at a microdisc interface under steady state conditions is given for reversible, quasireversible and irreversible kinetics. The quasireversible expression is proposed as a simple means for analysis of experimental voltammograms thus gaining access to the potential dependent forward rate constant and the charge transfer coefficient, α. It is used to analyse simulated data and the results compared to the simulation parameters. The mathematics of the linear diffusion of cyclic voltammetry for electron transfer at the Interface between Two Immiscible Electrolyte Solutions (ITIES) is addressed, and the numerical solution of the resulting integral equation is evaluated. The results show how the cyclic voltammograms for reversible electron transfer at the ITIES vary when different ratios of reactants and products are used, and how these differ from the classical reversible cyclic voltammograms. A microhole formed by eximer laser ablation in a polyester membrane is proposed as a useful support for a micro-ITIES providing symmetrical diffusion characteristics analogous to an inlaid disc electrode. This support (and also regular arrays of microholes) has been used to obtain symmetrical steady state voltammograms for the transfer of the acetylcholine cation from water to 1,2-dichloroethane. A micro-ITIES suported at the tip of a micropipette has been used to study the transfer of alkali metal ions assisted by crown ethers which gave a lower limit for the pseudo first order interfacial transfer rate constants of 10^-2 cm s^-1, and provided data on the complexation constants of Li^+ , Na^+ , K^+ Rb^+ and Cs^+ with dibenzo-18-crown-6. The oxidations of di-n-butylferrocene and ferrocene by hexacyanoferrate III at the ITIES were investigated using both microinterfaces supported at the tip of a micropipette, and large interfaces.

In this project a number of synthetic procedures were investigated with a view to preparing a new type of charge transfer polymer system having a structure based on that of side chain liquid crystal polymers, in that the hoped for polymer was composed of charge transfer acceptors connected to a polymer backbone via a flexible alkyl spacer linkage. As part of this work new charge transfer complexes were prepared some of which have shown possible novel properties, such as, co-operative magnetic effects and film forming capabilities. Finally, in order to characterise materials prepared, a Faraday magnetic susceptibility balance and instrumentation for measuring electrical conductivity has been built.

Interfacial charge transfer between metal oxides and organic semiconductors has been found to limit the efficiency of organic optoelectronic devices. Although a number of investigations of inorganic/organic systems exist, very few generally applicable rules for oxide/organic interfaces have been developed and many questions about these systems remain unanswered. Thus the studies presented in this dissertation were designed to improve the understanding of the fundamental interface physics of metal oxide/organic systems. Single molecule fluorescence microscopy was employed to determine the charge transfer mechanism while photoelectron spectroscopy was used to determine the energy level alignment of model systems. Additional computational studies allowed the examination of the properties of the charged organic molecules involved in charge transfer and modeling of the molecule-surface interaction. Calculations of the ground state properties and excited state transitions of the neutral and singly charged states of a modified perylene molecule were performed to provide insight into the orbitals of the initial and final states involved in the interfacial charge transfer process. The design and implementation of a novel UHV single molecule microscope is described. This microscope was used to observe the excited state charge transfer between a modified perylene molecule and Al₂O₃ (0001). The charge transfer mechanism was identified as involving activated trapping and detrapping of the defect derived states within the Al₂O₃ band gap, which resulted in the observation of strongly distributed kinetics for this system. The influence of defects and adsorbates on the electronic structure of ZnO and its interface with organic semiconductors was determined from photoelectron spectroscopy. Modified perylene molecules were found to have strong chemisorptive interactions with the ZnO surface involving charge transfer from defect derived ZnO states to the LUMO, while magnesium phthalocyanine molecules appear to have only weak physisorptive interactions with the ZnO surface. The interfacial investigations of the organic/oxide systems demonstrate the rich defect structure present in metal oxides. In both cases, defects were found to control the interfacial interactions between the metal oxide surface and the modified perylene molecules. Thus the manipulation of these defects states is of fundamental importance for optoelectronic device design.

Le dopage non covalent de nanostructures carbonées par transfert de charge depuis/vers des molécules donneuses ou acceptrices (EDA) ou bien par des molécules d’acide sulfurique H2SO4, est considéré comme potentiellement intéressant pour de nombreuses applications. Parmi celles-ci on peut citer: capteur chimique, transistor à effet de champ, et d’autre l'électronique. Cependant, d'un point de vue théorique, on en sait peu au sujet de ces processus de transfert de charge par électrons ou par trous.Dans un premier temps, nous nous sommes intéressés à l’interaction entre des molécules d’acide sulfurique et des nanostructures modèles, car elles sont capables de doper des nanotubes, de s’intercaler dans le graphite et même d’aligner les tubes dans une phase nématique, ce qui pourrait mener à la création de matériaux composites à forte valeur ajoutée.Bien que certaines études théoriques DFT ont été menées récemment, leurs résultats restent source de confusion. Par exemple, même s’il est rapporté un transfert de charge entre une molécule de H2SO4 et un plan de graphène, tous nos efforts pour reproduire ces calculs ont été infructueux. Nous proposons dans ce travail de thèse, un mécanisme de réaction qui expliquent la "protonation" des parois du tube, tel que proposé dans la littérature. Enfin nous proposons un scénario possible pour une meilleure compréhension de la structuration à grande échelle des molécules d'acide autour de points d'ancrage, telles que des défauts, de la structure carbonée
Non-covalent doping of carbon nanostructures by charge transfer from/to donor/acceptor molecules (EDA) or by H2SO4 molecules, be it with holes or electrons, is usually thought as potentially interesting for many applications of carbon based nano-devices. However, from a theoretical point of view, little is known about such “charge transfer” processes.Employing first-principles method based on Density Functional Theory (DFT), we have studied in details, and proposed a model to rationalize, the interaction between a prototypical donor molecule the tetrathiafulvalene (TTF), a standard acceptor organic molecule, tetracyanoethylene (TCNE) and carbon nanostructures: graphene layer and SWNTs with various chiral indices. Main results concern structural and thermodynamic aspects including dispersion forces effects, and evidently electronic structure modifications of the nanostructures. Various adsorption modes and concentration effects have been investigated. At very low coverage values, we have reported a charge transfer between graphene and TCNE or TTF. Moreover, we have shown that the charge transfer can be enhanced by increasing the concentration of those two EDA molecules, as it has been demonstrated experimentally. Those results are beneficial for comprehending the nonchemical doping mechanism in graphene structure by means of charge transfers. Considering the interaction between these prototypical molecules and carbon nanotubes, we have found that charge transfers tend to decrease while the curvature of nanotube is increasing. Besides, a strong influence of the metallic/semi-conductor character of the SWNTs can be observed and be explained by the change of polarisability of the curved carboneous substrates. Additionally, we have studied the adsorption properties of sulfuric acid molecules, in its non-hydrated form, on carboneous nanostructures. Against the common believe, no charge transfer is observed in the H2SO4@graphene or H2SO4@CNTs cases, even at very high concentrations. Instead, in order to elucidate the origin of p-doping observed experimentally, we have proposed that molecule is responsible of the reversible doping. Besides we have shown that a proton transfer could cause the experimental phenomenon of crystallization of H2SO4 molecules on SWNT’s surface. Finally in such process, defects like vacancy are of first importance, since they could provide anchorage points for hydrogen atoms. The results of the present work will certainly help to understand the charge transfer and doping mechanism of carbon nanostructures by means of non-covalent functionalization, which is a promising method for their future applications

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007.
Laren M. Tolbert, Committee Member ; Uzi Landman, Committee Member ; Nicholas V. Hud, Committee Member ; David M. Collard, Committee Member ; Gary B. Schuster, Committee Chair.

Most quasi-one-dimensional (quasi-1D) quarter-filled organic charge-transfer solids (CTS) with insulating ground states have two thermodynamic transitions: a high-temperature metal-insulator transition followed by a low-temperature magnetic transition. This sequence of transitions can be understood within the 1D Peierlsextended Hubbard (PEH) model. However, in some quasi-1D CTS both transitions occur simultaneously in a direct metal to spin-gapped insulator transition. In this second class of materials the organic stack bond distortion pattern does not follow the pattern of a second dimerization of a dimer lattice. These materials also display charge ordering of a large amplitude below the transition. Using quantum Monte Carlo methods we show that the same PEH model can be used to understand both classes of materials, however, within different parameter regions. We discuss the relevance of our work to experiments on several quarter-filled conductors, focusing in particular on the materials (EDO-TTF) 2X and (DMEDO-TTF) 2X.

In this thesis, we model electronic states, charge transfer and charge transport in organic semiconductors (OSCs). We are interested in the effect of chemical structure, molecular packing and different types of disorder on the charge transport in these materials, which is an important factor determining the efficiencies of devices made with OSCs. This is an intrinsically multiscale problem, and we use computational methods than span length and time-scales. We investigate the effect of molecular packing and crystal structure on charge carrier mobility in molecular crystals. We also model the electron mobility in disordered small molecules containing different defects to find the effect of these defects on the performance of devices. We perform electronic structure calculations to investigate the HOMO and LUMO levels in the presence of different defects, as well as to generate absorption, photoluminescence and infrared spectra to compare to experimental spectra. We develop a computationally efficient method for modelling polarons in organic semiconductors within a tight-binding framework. We apply the method to large assemblies of fullerene molecules generated with coarse-grained molecular dynamics. The method allows us to explore the effect of energetic and configurational disorder, as well as polaron formation, on the density of states and size of charge states in these systems. We further develop a method for calculating transfer integrals between molecules or molecular fragments, based on performing calculations of molecular orbitals in a counterpoise basis set. We apply it to calculating intramolecular transfer integrals and transfer integrals between donor and acceptor molecules at interfaces in organic photovoltaics, and between dopant and host molecules.

Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010.
Committee Chair: Bredas, Jean-Luc; Committee Member: Kippelen, Bernard; Committee Member: Marder, Seth; Committee Member: Orlando, Thomas; Committee Member: Sherrill, David. Part of the SMARTech Electronic Thesis and Dissertation Collection.

As a hydrophilic biopolymer, a DNA molecule is surrounded by water molecules in aqueous solution. The charge hopping mechanism indicates the competition between radical cation quenching by water molecules and migration along DNA partially determines the distance and efficiency of charge transport in DNA. Lipid can effectively bind DNA to induce hydrophobic environment around the DNA helix and reduce the water contact with bases in the DNA duplex. Therefore, the effect of water molecules on charge transport can be studied by comparison between nature DNA and DNA-lipid complexes. We synthesized several cationic lipids with various lengths of dialkyl chain (2, 8, 18) and spermine (Sp4+) binding core in this research, which posses strong DNA binding affinity due to their multi-charged spermine head-groups. Among those, C8GlySp4+ and C2GlySp4+ can form stable complex with DNA oligomer in aqueous solution, characterized by time dependent UV and CD spectrometry. C2GlySp4+ showed the similar inhibition on oxidative damage in GG steps as spermine while C8GlySp4+ demonstrated much more significant prohibitive effect at the same concentration. Since all the lipids bear the same binding core, they should afford the similar binding affinity towards DNA duplexes. we attributed the observation to the longer length of dialkyl group in C8GlySp4+, which can more effectively shield the DNA duplex from the water molecules than either spermine or C2GlySp4+. A kinetic model based on phonon-assist polaron hopping mechanism was proposed to rationalize the experimental results. The finding may give insight on the protection of DNA oxidative damage by reducing the access of the water molecule to DNA duplex and may have potential impact on the application of DNA as conducting biopolymer and protection of DNA in biological system.

This thesis is concerned with the preparation of floating films of electrically conductive organic charge-transfer complexes and their subsequent transfer to solid substrates by the Langmuir-Blodgett (LB) technique. Characterisation of the morphology (using ellipsometry, surface profiling, optical and scanning electron microscopy, energy dispersive spectroscopy and optical absorption spectroscopy) and electrical properties (at room temperature and low temperature) of the resulting multilayer structures is discussed. Three different systems were investigated: (i) mixed films containing the long chain tetrathiafulvalene (TTF) derivative octadecanoyl-TTF (ODTTF) and either octadecanoic acid (OA) or pentacosa-10,12-diynoic acid (PA); (ii) pure films of the charge-transfer complex Ν-octadecylpyridiniura-bis-(4,5-dimercapto-1,3-dithiole-2- thione) palladium (Ci8Py-Pd(dmit)2); and (iii) pure films of the charge-transfer complex N-octadecylpyridinium-bis-(4,5-dimercapto-1,3-dithiole-2-thione) nickel (CigPy- Ni(dmit)2). Some interesting electrical properties were observed in these films. Also, Ci8Py-Ni(dmit)2 has been incorporated as the active layer in a thin film field effect transistor structure. Carrier mobility values of 1.9 ± 0.5 x l0(^-5) cm(^2) V(^-1) S(^-1) and 0.3 ± 0.1 cm(^2) V(^-1) s-(^-1) were calculated from the device characteristics, before and after doping with iodine, respectively In the case of films containing ODTTF, a maximum room temperature in-plane dc conductivity after iodine doping of 2±lxl0(^-2) S cm(^-1) was recorded. This conductivity was found to be strongly dependent on the molar ratio of the two components present in the film. The behaviour has been explained using two-site percolation models. For C(_18)Py-Pd(dmit)(_2) and C(_18)Py-Ni(dmit)(_2), the properties of the floating layers and transferred films were found to be influenced by the exact experimental conditions. Ci8Py-Pd(dmit)(_2) films were conductive as deposited, with a stable maximum room temperature in-plane dc conductivity value of 1.5±1.0xl0(^-l) S cm(^-1). C(_18)Py-Ni(dmit)(_2) samples became conductive after exposure to iodine vapour, with a stable peak conductivity value of 1.3±0.8 x10(^-1)S cm(^-1).

Die vorliegende Dissertation beschäftigt sich mit dem elektrochemischen Verhalten verschiedener Ferrocenyl-substituierter Thiophene. Dabei wird sich zunächst mit dem elektrochemischen Verhalten der Serie der Ferrocenylthiophene beschäftigt, die Anzahl der Ferrocenyleinheiten variiert von n = 1 – 4. Die Abhängigkeit der elektronischen Eigenschaften von numerischen und konstitutionellen Veränderungen der redox-aktiven Gruppen wird evaluiert. Daraus resultierend wird sich einer eingehenderen Untersuchung und Modifikation des 2,5-Diferrocenylthiophen-Motivs zugewandt. Diese Modifikationen werden im Kontext möglicher Ladungstransferprozesse zwischen den Ferrocenyleinheiten in den verschiedenen Redoxzuständen und unter Beeinflussung durch den Thiophen-Brückenliganden diskutiert. Es folgen des Weiteren Ausführungen zu Substitutionen an den Ferrocenylen (Einführung elektronen-ziehender Funktionalitäten) sowie der Vergleich zwischen einer Thiophen- und der Ethylendioxythiophen-Brückeneinheit. Anschließend wird sich mit der elektronischen Variation des Brückenliganden durch die Einführung von N-haltigen Substituenten befasst. In den abschließenden Kapiteln wird der Einfluss zusätzlicher σ- (Fischercarben-Komplexe) oder π-gebundener ([Ru(η5-C5H5)]+/[Ru(η5-C5Me5)]+) Übergangsmetallkomplexfragmente auf Ladungstransferwechselwirkungen im 2,5-Diferrocenylthiophen in verschiedenen Redoxzuständen beleuchtet.

Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin
Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Charge transfer (CT) complexes have been used in a number of radiation polymerisation processes including grafting and curing. The complexes studied include donor (D) monomers like vinyl ethers and vinyl acetate (VA) with acceptor (A) monomers such as maleic anhydride (MA). Both UV and EB have been utilised as radiation sources. The complexes are directly grafted to these substrates in the presence of radiation. The complexes yield novel copolymers when radiation cured with concurrent grafting improving the properties of the finished product. The term cure grafting has been proposed for this concurrent grafting process. Studies in basic photografting work to complement the cure grafting have been proposed. The role of solvent in grafting is discussed, particularly the effect of aromatics in photografting to naturally occurring trunk polymers like wool and cellulose. The effect of the double bond molar ratio (DBMR) of the DA components in grafting is examined. The ultraviolet (UV) conditions for gel formation during photografting, hence the importance of homopolymer yields in these processes is reported. A plausible mechanism to explain the results from this photografting work is proposed. The significance of these photografting studies in the related field of curing, especially in UV and ionising radiation (EB) systems, is discussed. EB curing and cure grafting of charge transfer (CT) monomer complexes is investigated. The EB results are compared with UV curing and cure grafting of the same complexes. The work has been extended to include EB/UV curing and cure grafting of thiolene systems. The significance of these results in the potential commercial application of these complexes is discussed. Variables affecting the UV/EB curing and cure grafting of thiolenes on cellulose have been studied. These include effect of varying the type of olefin, increasing the functionality of the thiol, use of acrylate monomers and oligomers in hybrid systems, altering the surface structure of the cellulose and finally the role of air in these processes particularly with EB. Photopolymerisation of the thiol-enes in bulk has also been investigated. The thesis content is based on the published work of 14 research papers over the course of the project.

Thesis (Ph.D.)--University of Western Sydney, 2008.
Thesis submitted to the University of Western Sydney, College of Health and Science, School of Natural Sciences, in fulfilment of the requirements for admission to the Doctor of Philosophy. Includes bibliography.

There is a need for monolithic devices capable of spatial resolution in imaging and ionizing radiation detection. In this thesis, a GaAs acoustic charge transport device (ACT) was studied for this purpose. A new method of charge injection has been demonstrated for the ACT. Using near-infrared optical pulses incident through thin semi-transparent chromium windows, electron-hole-pairs were separated by the electric field in a depleted n-type channel region of the device. For light penetration less than the depth of the electron potential minimum, and for small injection levels, calculations indicated that electrons and holes were separated at their saturation velocities. Holes moving toward the surface of the substrate could recombine with electrons at an evaporated Schottky metal plate. Electrons moving toward the channel centre were bunched and transported by the electric field coupled to a <110> propagating surface acoustic wave (SAW) on (100) cut GaAs. Quantum efficiency, defined as the number of electrons collected at the output per incident photon on the GaAs surface, was greater than 9% at an optical wavelength of 730 nm. When compensation was made for the loss and reflection due to the chromium windows, the quantum efficiency was in excess of 24%. Charge transfer efficiency was greater than 0.992 with the ACT clocked at 360 MHz. The demonstrated optical injection technique may be of use in future ACT imaging devices.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

La demande énergétique de l’humanité augmente rapidement et ne montre aucun signe de ralentissement. Parallèlement à cette problématique, l'utilisation abusive de combustibles fossiles est l'une des principales causes d'augmentation de la concentration de CO₂ dans l'atmosphère. Ces problèmes doivent être résolus en termes de limitation des émissions de CO₂ et de recherche de sources d'énergie renouvelables pour remplacer les combustibles fossiles. De nos jours, l’énergie solaire est l’une des sources d’énergie renouvelables les plus efficaces. La conversion de l'énergie de la lumière solaire en électricité dans le photovoltaïque ou en énergie chimique par le biais de processus photocatalytiques implique invariablement un transfert d'énergie photo-induit et un transfert d'électrons. Dans ce contexte, l'objectif de la thèse est d'étudier les processus photo-induits dans les photosystèmes moléculaires utilisant la photolyse par flash laser. Le premier thème de cette thèse porte sur l’étude du transfert monoélectronique dans des systèmes de dyades donneur-accepteur en vue d’optimiser l’efficacité de la séparation des charges et de son application dans la cellule solaire organique photovoltaïque. Le deuxième thème de cette thèse porte sur l’étude de deux systèmes modèles de photosynthèse artificielle étudiés pour la possibilité d’une accumulation de charge par étapes. Ensuite, différents systèmes photocatalytiques, développés pour la photoréduction du CO₂, ont été étudiés. La compréhension des processus photo-induits devraient permettre l’amélioration de l'efficacité de la réduction du CO₂ dans les systèmes photocatalytiques pratiques
The energy demand of humanity is increasing rapidly, and shows no signs of slowing. Alongside this issue, abuse using fossil fuels is one of the main reasons which leads to an increase in atmospheric CO₂ concentration. These problems have to be solved in terms of both limiting CO₂ emission and finding renewable energy sources to replace fossil fuels. Nowadays, solar energy appears as one of the most effective renewable energy sources. Conversion of solar light energy to electricity in photovoltaics or to chemical energy through photocatalytic processes invariably involves photoinduced energy transfer and electron transfer. In this context, the aim of the thesis focuses on studying photoinduced processes in molecular photosystems using laser flash photolysis. The first theme of this thesis focus on studying single electron transfer in Donor-Acceptor Dyad systems towards optimization efficiency of charge separation and application in the photovoltaic organic solar cell. In the second theme of this thesis, two model systems of artificial photosynthesis were investigated to assess the possibility of stepwise charge accumulation on model molecules. A fairly good global yield of approximately 9% for the two charge accumulation on MV²⁺ molecule was achieved. Then, different photocatalytic systems, which have developed for CO₂ reduction, were studied. Understanding of the photoinduced processes is an important step toward improving the efficiency of reduction of CO₂ in practical photocatalytic systems