Développer de nouvelles sources d’énergie respectueuses de l’environnement est un des enjeux majeur de nos sociétés développées. Pour espérer la pérennité de notre espèce sur cette planète, il est indispensable de développer les sources d'énergie renouvelable ; permettant de nous affranchir de la dépendance aux énergies fossiles polluantes et dont les stocks s’épuisent. Il appartient aux scientifiques d’apporter leurs contributions à cet important défi que l’on appelle la transition énergétique et pour ça d’aider à développer une énergie idéale qui ne produirait pas de déchet polluant, serait très efficace et largement disponible. L'énergie solaire représente un excellent candidat car elle est de loin la plus abondante et prometteuse source d’énergie propre. D'importants efforts sont donc menés pour développer les technologies solaires, notamment la photosynthèse artificielle.La photosynthèse artificielle a vu le jour il y a une centaine d’années et fait l’objet de beaucoup d’intérêt et de recherche. Cette technologie cherche à imiter la photosynthèse naturelle réalisée par les plantes; et cela afin de stocker l’énergie provenant du Soleil dans des composés utilisables par l’Homme. La photosynthèse artificielle consiste en l’élaboration de systèmes synthétiques capables sous impulsion lumineuse de réaliser la décomposition de l’eau de manière catalytique, pour générer du dihydrogène ou des produits issus de la réduction du CO2, que l’on appelle combustibles solaires car à haut potentiel énergétique. En effet, la photosynthèse débute par la photo-catalyse de l’oxydation de l’eau, qui permet d’extirper les électrons et les protons des molécules d’eau. Ce sont ces électrons et protons qui seront utilisés par un catalyseur pour produire les combustibles solaires.Depuis peu, une véritable volonté de comprendre les mécanismes qui ont lieu lors de ces réactions catalysées semble apparaitre. Ces réactions mettent en jeu des transferts électroniques multiples photo-induits et cela rend leur étude assez compliquée. Grâce à des avancées technologiques importantes, nous avons étudié de manière plus approfondies plusieurs systèmes photo-catalytiques afin d’en tirer des savoirs permettant de rationaliser le design et d’améliorer les capacités des futurs systèmes développés. Ces avancées techniques ont été possibles grâce à des collaborations interdisciplinaires entre des chimistes et des physiciens et ont permis de développer un montage d’absorption transitoire « double-pump» afin de caractériser les espèces transitoires formées et de retracer les mécanismes lors de deux transferts électroniques photo-induits successifs.Dans la seconde partie de ce travail, de nouveaux catalyseurs ont été développé pour la réaction de photo-catalyse de l’oxydation de l’eau. La majorité des études menées jusqu’ici sur le sujet ont porté sur des systèmes moléculaires, mais le manque de robustesse et de réutilisabilité des catalyseurs homogènes a poussé la recherche vers le domaine des matériaux. Ainsi depuis une quarantaine d’années des systèmes photo-catalytiques hétérogènes ont été développé. Nous avons explorés deux types de matériaux, des nanoparticules catalyseurs dans des systèmes photo-catalytiques, et des polymères qui à eux seuls sont capables de réaliser l’ensemble des fonctions nécessaires à la photo-catalyse d’une réaction telle que l’oxydation de l’eau sous irradiation de lumière visible.Ainsi au cours de cette thèse nous avons tenté par deux approches d’avancer les connaissances et le développement de la photosynthèse artificielle. Une solution encore peu développée au problème énergétique auquel notre société fait face est le recours aux combustibles solaires, et il est grand temps que la recherche avance et que la transition énergétique s’impose plus efficacement et largement. / Developpment of environment-friendly sources of energy is one of the stakes major for our societies. To hope for the sustainability of Humans on Earth, it is essential to change our consumer habits on energetics by breaking our dependance on fossil fuels, which use leads to ecological desasters and which stocks are running out. The key of this important challenge is the growth of renewable energy sources, and this is called energy transition. The ideal energy would not produce any polluting waste, would be efficient and widely available. Solar energy is an excellent candidate because it is by far the most abundant and promising source of clean energy. Thus, important efforts are made to developp the solar technologies, including artificial photosynthesis.Artificial photosynthesis was created a century ago and is the focus of many interests and researchs. This technology aims at mimicking the natural photosynthesis realized by plants ; and that in order to store the energy coming from the Sun irriadiation in compounds that can be used at demand. Artificial photosynthesis consists in the elaboration of synthetic systems able under light impulsion to realize the water splitting/decomposition reactions in a catalytique way, generating hydrogène or CO2 reduction products, which are called solar fuels thanks to their high energetic potentials. Indeed, photosynthesis begins with the photo-catalysis of water oxidation, which extirpates the electrons and protons of water molecules. And it is these electrons and protons which will be used to produce the solar fuels.Recently, a real commitment to understand deaply the mechanisms that take place during these catalysed reactions seems to appear. These transformations involve multiple photo-induced electron transfers and it returns their study relatively complicated. Thanks to technological breakthroughs, we studied in a thorough way several photocatalytic systems to draw knowledges ; allowing the rationalisation of the design and then the efficiency improvement of future developped systems. These technical advances were possible thanks to interdisciplinary collaborations between chemists and physicists and led to the developpment of a set-up of « double-pump » transient absorption, that enables to characterize the transient species formed and to track down the pathways during two successive photoinduced electron transfers.In the second part of this work, new catalysts were developped for the photocatalysis of water oxidation reaction. The big majority of the studies led so far on this subject concerned molecular systems, but the lack of robustness and reusability of homogeneous catalysts pushed the research towards materials area. Since about forty years, heterogeneous systems were developped for photocatalysis of several reactions. We explored two types of materials, nanoparticules as catalyst in photocatalytic systems ; and polymers that are able on their own to realize all the functions required for the photocatalysis of a reaction such as water oxidation under visible light irradiation.Thus, during this PhD we tried by two approaches to increase the knowledges and the development of artificial photosynthesis. A solution that is still under-developped to fix the energetic issue our society is facing to, is the use of solar fuels ; and it’s imperative for the research to move forward and that energy transition prevails more effectively and widely.

Accurate energetic modeling of large molecular systems is always desired by chemists. For example, ligand-protein binding simulations and enzymatic catalysis studies all involve with a small energy difference. The energetic accuracy depends largely on a proper handling of electronic correlations. Molecular mechanics (MM) methods deliver a parameterized Newtonian treatment to these problems. They show great capability in handling large calculations but give only qualitatively good results. Quantum mechanics (QM) methods solve Schrödinger equations and exhibit much better energy accuracy, though the computational cost can be prohibitive if directly applied to very large systems. Fragment-based methods have been developed to decompose large QM calculations into fragment calculations. However, most current schemes use a self- consistent field (SCF) method on fragments, in which no electronic correlation is accounted for. The super-system energy is computed as a sum of fragment energies plus two-body corrections and, possibly, three-body corrections (a "body" is a fragment). Higher order corrections can be added. Nevertheless, many problems require the treatment of high order electronic correlations. The coupled-cluster (CC) theory is the state-of-the-art QM method for handling electronic correlations. The CC wavefunction contains correlated excitations up to a given truncated level and coincidental excitations for all possible electronic excitations. It is a brilliant way of including more electronic correlations while maintaining a low-order scaling. In the proposed excitonic coupled-cluster (X-CC) theory, substantial modifications have been made to allow CC algorithms to act on the collective coordinates of fragment fluctuations to obtain super-system energy. The X-CC theory is designed to achieve accurate energetic modeling results for large chemical systems with much improved affordability and systematic improvability. The test system used in this work is a chain of beryllium atoms. A 30-fragment X-CCSD(2) calculation delivered matching accuracy with traditional CCSD method. An X-CCSD(2) calculation on a chain of 100 bonded fragments finished in 7 hours on a single 2.2 GHz CPU core. The X-CC scheme also demonstrates the ability in handling charge transfer problems. Due to the use of fluctuation basis in the test cases, the excitonic algorithms can be easily generalized to inhomogeneous systems. This will be investigated in future work.

Over the last five years, charge-coupled devices (CCD) have been improved dramatically in terms of sensitivity, manufacturability and particularly, cost. This has enabled them to be used economically in many more industrial and commercial electronic imaging processes. They are found in products ranging from video cameras to satellite-based camera systems. This has sparked my interests in these devices, and with a great deal of encouragement from Dr. Turpin, I decided to base my Master's thesis/project on a CCD. The project was mainly based on the design of the electronics and optics needed to support a CCD. The particular circuit design which I used other designs which are available. Many of the designs are microprocessor- based, which tends to limit the speed of operation of the imaging process. Other circuits employ specially coded memory chips to implement the required logic processes, but again, the speed of operation is limited by the access times of the memory chips. The circuit employed in the project uses only logic gates and flip flops, and is probably one of the fastest circuits available for the capture of single-frame images.

In the present work, charge transfer in organic semiconductors is investigated by means of photoemission spectroscopy. Organic charge transfer systems consist of electron donors and acceptors and in some cases exhibit new electronic properties that are not observed in the individual constituents. Examples are metallic conductivity and changed optical or transport gaps. The main focus were interfaces between donor and acceptor molecules that were prepared as thin films by thermal evaporation in ultra-high vacuum. In particular, the strong electron acceptor F6TCNNQ was combined with several scientifically relevant donors, with the aim of achieving a large charge transfer. As reference systems, potassium doped F6TCNNQ and the interface between F6TCNNQ and gold were studied. In both systems, a large electron transfer to F6TCNNQ with similar spectroscopic signatures was observed. The investigated organic interfaces all showed charge transfer that manifested itself in form of changes in the core levels of F6TCNNQ that were similar for each system. Also, new occupied states in the former gaps of the molecules were found. For every investigated interface the Fermi energy was pinned above the respective highest occupied molecular orbitals which entails semiconducting behaviour and no metal-like delocalised charge carriers. For the combination of F6TCNNQ and dibenzopentacene, a blended film was prepared by co-deposition and compared with the corresponding interface. It was found that the electronic properties of the blend are initially determined by electrostatic interactions, whereas annealing leads to a large charge transfer due to a temperature induced change of molecular orientation. Moreover, the acceptors F2TCNQ and F16CoPc were used in order to compare systems with the same donor and different acceptors. Differences in the degree of charge transfer and interface morphology were observed. The last part of this work addresses the electronic properties of an organic rectifier that was fabricated by collaboration partners. It is built up of an organic heterojunction of two phtalocyanines (CuPc and F16CoPc) between two gold contacts. The energy level alignment across the device and the charge transfer reactions at the different interfaces are discussed with regard to the functionality of the device.

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It is known that organic monolayers on solid surfaces can enable electronic properties that are absent in the bulk of the solid materials. Often, once the organic film come into the contact with a solid surface, the established electronic interaction at their interface remains undisturbed. However, using a redox-active organic monolayer creates the possibility for modulating the extent and the direction of the interfacial charge transfer, establishing a switch at the interface. The theme of this thesis is investigation of the interfacial interaction of different redox states of a molecular switch, phenyl-capped aniline tetramer (PCAT) with iron oxide and graphite surfaces and their potential application in electronic devices. The nucleation and growth of submonolayer films of different oxidation states of PCAT on iron oxide surface was studied. Using atomic force microscopy and scaling island size distribution method the surface diffusion parameters of these islands were evaluated. Using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy the changes in these organic monolayers before and after interaction with iron oxide were demonstrated. However, these techniques were unable to provide similar data from the solid surface side of the interface. Instead, we were able to demonstrate the changes in the iron oxide film as a result of interfacial charge transfer using electrical conductivity measurement techniques. Based on this information a microfluidic chemical sensor based on the interface of pencil film and PCAT for quantification of free chlorine in drinking water was constructed. Using XPS and UV-vis spectroscopy it was shown that the interaction the organic monolayer with sodium hypochlorite solution leads to the development of positive charges on the backbone of PCAT. This electrostatic charge can affect the charge transport in the pencil film causing the modulation of electrical conductivity of the film. The presented work demonstrates alternative pathways for the design of novel hybrid electronic devices based on thin molecular film and solid surfaces. / Thesis / Doctor of Philosophy (PhD)

Ultrafast charge and electron transfer, primary events in artificial photosynthesis, are key in solar energy harvesting. This dissertation provides insight into photo-induced charge and electron transfer in the donor and acceptor constructs built using a range of donor and acceptor entities, including transition metal dichalcogenides (TMDs, molybdenum disulfide (MoS2), and tungsten disulfide (WS2)), N-doped graphene, diketopyrrolopyrrol (DPP), boron-dipyrromethene (BODIPY), benzothiadiazole (BTD), free base and metal porphyrins, zinc phthalocyanine (ZnPc), phenothiazine (PTZ), triphenylamine (TPA), ferrocene (Fc), fullerene (C60), tetracyanobutadiene (TCBD), and dicyanoquinodimethane (DCNQ). The carefully built geometries and configurations of the donor and (D), acceptor (A), with a spacer in these constructs promote intramolecular charge transfer, and intervalence charge transfer to enhance charge and electron transfer efficiencies. Steady-state UV-visible absorption spectroscopy, fluorescence and phosphorescence spectroscopies, electrochemistry (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)), spectroelectrochemistry (absorption spectroscopy under controlled potential electrolysis), transient absorption spectroscopy, and quantum mechanical calculations (density functional theory, DFT) are used to probe ground and the excited state events as well as excited state charge separation resulting in cation and anion species. The current findings are useful for the increased reliance on renewable energy resources, especially solar energy.