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Doctor of Philosophy / Department of Chemistry / Daniel A. Higgins / This doctoral thesis covers the synthesis, preparation, and characterization of a series of four perylene diimide derivatives, and the nanofibrous composite materials formed by these perylene diimides when complexed with oppositely charged polyelectrolytes. The perylene diimides include a symmetric dication (TAPDI2+), a symmetric dianion (PDISO32-), and two singly charged asymmetric varieties (C11OPDI+ and C7OPDI+) that contain a hydrophilic head group and hydrophobic ether tail. For all studies presented in the following chapters, poly(acrylate) (PA-) or poly(diallyldimethylammonium) chloride (PDDA+) are used as the polyelectrolytes (PEs). The patterned deposition of sheer aligned, nanofibrous material within a fluidic device is conclusively demonstrated. Thin films of the nanofibrous composite are prepared from aqueous solutions of the semiconducting perylene diimides and oppositely charged polyelectrolyte precursors. By sequentially exposing a clean glass substrate to the cationic and anionic precursor solutions, a thin film of composite material is deposited in a layer-by-layer fashion. By utilizing electrostatic self-assembly (ESA) and layer-by-layer (LbL) procedures, precise control of film thickness and optical density are obtained. The effect of perylene diimide structure and charge on resultant composite film morphology is explored. Through spectroscopic and microscopic studies of bulk perylene diimide solutions and composite thin films, it was determined that the formation of these fibrous materials is dependent on the aggregation of the PDI within the precursor solutions. The molecular orientation of the perylene diimide within the composite nanofiber was determined to be perpendicular to the fiber long axis. For the special case of C7OPDI+/PA- composite, flow induced fiber alignment was observed for both dip coated and flow coated samples. The influence of solution flow profile, PE molecular weight (MW), and PDI structure on deposition efficiency, macroscopic and microscopic morphology, and the potential for nanofiber alignment are investigated. Film formation mechanisms involving two unique routes are also presented.

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.

There is currently a great interest to develop and market organic electronic devices, and theoretical models are needed to provide physical insight and quality predictions when designing these materials. Many organic molecules absorb in the UV-vis region of light, and therefore, UV-vis spectroscopy is a relatively simple tool that can help experimentalists "see" the packing arrangements of the molecules within each material, as long as there is a solid theoretical understanding of the photophysics that links the interactions between molecules to changes in optical features. For example, the Kasha spectral shifts have been used for decades to identify J-aggregate and H-aggregate packing arrangements from red- and blue- spectral shifts, respectively. The innate presence of vibronic coupling in organic molecules gives rise to a unique set of additional spectral signatures that are far more reliable than the Kasha spectral shifts for inferring packing arrangements. Moreover, the Kasha shifts are based entirely on Coulomb coupling between molecules, which leads to the creation of delocalized Frenkel excitons. For many π-conjugated organic molecules, however, dispersion forces in π-conjugated chromophores encourage close packing distances of about 3.5-4 Å between organic monomers, which further introduces intermolecular couplings beyond the Coulomb coupling, due to intermolecular charge transfer (CT). Therefore, much theoretical research has focused on incorporating all these effects through a Frenkel-CT-Holstein Hamiltonian, in order to better understand how different packing arrangements within a given material can be identified through specific changes in steady-state absorption and photoluminescence features. In this thesis, the Frenkel-CT-Holstein model is specifically applied to study the absorption and photoluminescent spectra of various derivatives of perylene diimide (PDI), which are of great interest as non-fullerene acceptors in organic photovoltaic design. PDIs display a plethora of packing arrangements and corresponding spectral signatures just by varying the substituents within the PDI core. This thesis first aims to understand the exciton band structure of two different PDI micro-crystals that both experience similar Frenkel-CT interference, but with one system displaying dominant Coulomb interactions while the other undergoes dominant Frenkel-CT coupling. Both are close to what is called a “null”-point, and the work in this thesis explores the photoluminescent signature as a reliable means to track which side of the “null”-point the Frenkel-CT interference lies. While the Frenkel-CT-Holstein model is successful in modeling mostly absorption spectra of aggregates composed of PDI monomers, one challenge has been that aggregates of PDIs often exhibit so-called excimer features in their photoluminescence spectra, which the model cannot account for. Systems that emit broad, structureless and red-shifted excimer peaks typically display inefficient exciton transport in organic semiconductors. The bulk of this thesis has been to expand the model to account for excimer emission, which is made possible by utilizing a Holstein-Peierls (HP) Hamiltonian that incorporates the effects of both local vibronic coupling and nonlocal Frenkel-CT coupling to intermolecular motions within a dimer. The experimental spectra for two different PDI dimer systems that display different excimer features is successfully reproduced with the new theory. This thesis concludes by analyzing how nonlocal coupling, which account for changes in the Frenkel-CT mixing along an intermolecular vibrational mode, can lead to various types of excimers. Different phase relations within the electron and hole nonlocal coupling parameters can combine with different phase relations within the electron and hole Frenkel-CT coupling parameters, leading to a rich array of excimer properties, especially when combined with the additional effects of Coulomb coupling, as well as local intermolecular vibronic coupling, which can either enhance or diminish the excimer photoluminescence. Overall, the Holstein-Peierls approach offers insight into the roles of Frenkel and CT excitons in excimer formation, and highlights the importance of the magnitude and phase of the intermolecular electron and hole transfer integrals in the ground and excited state geometries in producing distinct excimer features. The model provides further insight into the origin of excimers, which lays a foundation for future theoretical and experimental studies in designing organic materials. / Chemistry

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Chemisorption of an organic monolayer to tune the surface properties of a transparent conductive oxide (TCO) electrode can improve the performance of organic electronic devices that rely on efficient charge transfer between an organic active layer and a TCO contact. Here, a series of perylene diimides (PDIs) was synthesized and used to study relationships between monolayer structure/properties and electron transfer kinetics at PDI-modified indium-tin oxide (ITO) electrodes. In these PDI molecules, one of the imide substituents is a benzene ring bearing a phosphonic acid (PA) and the other is a bulky aryl group that is twisted out of the plane of the PDI core. The size of the bulky aryl group and the substitution of the benzene ring bearing the PA were both varied, which altered the extent of aggregation when these molecules were absorbed as monolayer films (MLs) on ITO, as revealed by both attenuated total reflectance (ATR) and total internal reflection fluorescence spectra. Polarized ATR measurements indicate that, in these MLs, the long axis of the PDI core is tilted at an angle of 33-42 degrees relative to the surface normal; the tilt angle increased as the degree of bulky substitution increased. Rate constants for electron transfer (k(s,opt)) between these redox-active modifiers and ITO were determined by potential-modulated ATR spectroscopy. As the degree of PDI aggregation was reduced, k(s,opt) declined, which is attributed to a reduction in the lateral electron self-exchange rate between adsorbed PDI molecules, as well as the heterogeneous conductivity of the ITO electrode surface. Photoelectrochemical measurements using a dissolved aluminum phthalocyanine as an electron donor showed that ITO modified with any of these PDIs is a more effective electron-collecting electrode than bare ITO.

Le contrôle de la morphologie de la couche active en optoélectronique organique représente un objectif majeur du fait de son impact sur la stabilité et les performances des dispositifs. En particulier, le degré d'autoorganisation d'un mélange de deux composés à caractère donneur (D) et accepteur (A) d’électrons, ainsi que leurs orientations sont déterminants pour obtenir à la fois un de transfert de charges efficace et des chemins de percolation continus jusqu'aux électrodes. Durant ce travail de thèse, nous avons synthétisé plusieurs séries de co-oligomères à blocs donneur-accepteur capables de s’auto-organiser pour former des lamelles alternées D/A à longue distance. Les co-oligomères présentent une architecture moléculaire de type diade (DA) ou triade (DAD ou ADA), et sont constitués d’une longueur de bloc D variable. Les molécules sont toutes composées d'un bloc A à base de perylène diimide et d'un bloc D contenant les motifs thiophène, fluorène et benzothiadiazole. Une attention particulière a été portée sur l'étude des propriétés optiques, électrochimiques, photophysiques, structurales ou encore opto-électroniques de nos matériaux. En particulier, nous nous avons montré que l’organisation lamellaire était très fortement dépendante de l’architecture moléculaire, puisque seuls les systèmes AD et ADA conduisent à une structuration à longue distance. Par ailleurs, en ajustant la densité électronique au sein du bloc D, nous avons montré qu’il était possible de contrôler à la fois le temps de formation et la durée de vie des états à transfert de charges. Enfin,les premiers résultats de caractérisation du transport de charges et des propriétés photovoltaïques démontrent l’intérêt de ces matériaux dans la réalisation de dispositifs photovoltaïques organiques mono-composants. / In the field of organic opto-electronics, the good control of the active layer morphology in devices represents a major objective to improve the stability and the photovoltaic performances. Especially when blends of selforganizing electron donor (D) and acceptor (A) moieties are combined, their mutual orientation and the degree of supramolecular ordering are determinant in controlling the fundamental energy, the electron transfer processes and the existence of continuous percolation pathways for charge carriers. In this work, we have designed and synthesized different series of donor-acceptor block co-oligomers able toself-assemble in a lamellar structure at very long range. The co-oligomers are made of a dyad (AD) or triad (DAD, or ADA) molecular architecture, and have a variable length of the D block. The A block is constituted of a perylene diimide unit, and the D block of benzothiadiazole, thiophene and fluorene segments. A particular attention was paid on the studies of optical, electrochemical, photophysical, structural and opto-electronical properties. In particular, we showed that the lamellar organization was strongly dependent on the molecular architecture, since only the AD and ADA systems lead to long-range organization. Moreover, by tuning the electronic density along the D block, it has been possible to control both the formation and lifetime of the charge transfer states. Finally, the first results on charge transport and photovoltaic properties demonstrate the high interest of these materials for the elaboration of single component organic photovoltaic devices.

Qu’il s’agisse de s’éclairer, de se chauffer, de s’alimenter sainement, de se soigner, de se véhiculer, de s’informer ou encore de se distraire, l’énergie a toujours été au centre des préoccupations et sa conversion en électricité est désormais omniprésente. Le lourd constat environnemental à la suite de l’exploitation intensive de sources fossiles a mené à une indispensable transition vers les énergies renouvelables. Souvent intermittentes, il est nécessaire de les stocker, généralement grâce à des batteries. Parmi les différentes technologies, cette thèse traite des batteries lithium-ion pour le stockage de l’énergie solaire. En effet, cette thèse a pour but l’étude d’un dispositif « tout-en-un » capable de convertir l’énergie solaire et de la stocker. Pour se faire, un semi-conducteur organique photoactif de la famille des pérylènes diimides (PDI) a été emprunté au domaine des cellules solaires organiques et couplé à un matériau phare et durable des batteries lithium-ion : le LiFePO4 (LFP). Cette thèse se décompose en trois parties selon une méthodologie qui vise à la compréhension fondamentale de transferts électroniques photoinduits, en amont du développement d’un dispositif. Pour aboutir à une preuve de concept, une étude de l’extinction de fluorescence du PDI en présence de LFP a d’abord été menée, afin de vérifier l’injection d’électrons en provenance du matériau de batterie dans le semi-conducteur excité. Ce travail a été fait en solution puis à l’état solide, pour la mise au point d’une photoélectrode. Ces deux études ont permis de comprendre les pré-requis du matériau d’électrode positive de batterie pour qu’il soit photoxydé, puis des résultats de spectroscopie Raman ont démontré l’importance des interfaces dans la mise en contact du PDI et du LFP. Finalement, forts d’une première preuve expérimentale de photocharge au sein d’un dispositif « photobatterie », le PDI a été polymérisé et son implémentation dans une photoélectrode de batterie lithium-ion a pu être optimisée. Ses rôles multiples (photoactif, photooxydant, conducteur électronique et liant) ont permis de générer un photocourant sans que cela ne soit au détriment du fonctionnement de la batterie. / Converting energy to electricity is ubiquitous because it plays a vital role in daily life whether for lighting, heating, health, transport, information or entertainment. Societal energy demands are often met with fuel fossils that have had deleterious environmental effects. Transitioning to renewables can mitigate these adverse outcomes. Renewable energy is often intermittent, requiring it to be stored for use during periods when the energy is unavailable. Batteries have become viable means to this end. Among the different technologies, this manuscript examines lithium-ion batteries for solar energy storage. Indeed, this work puts forward an all-in-one device: a device capable of converting and storing solar energy. To this end, a well-known photoactive organic semi-conductor in solar cells (perylene diimide; PDI) was coupled to a conventional and durable electrode material (LiFePO4; LFP) for lithium-ion batteries. This manuscript is divided into three discrete parts following the methodology to demonstrate the fundamental underlying processes of the future all-in-one device before its development: light harvesting and electron transfer. Towards a proof of concept, the thesis systematically studied the light mediated processes in solution, in the solid state, and in an operating device. Initial studies examined the fluorescence quenching of PDI with LFP. This was to validate the injection of electrons from the battery material to the photoexcited semi-conductor indeed occurred. The same emission studies were applied in the solid state for developing a photoelectrode. The two studies generated knowledge about the compositional and architectural requirements of the positive electrode material for it be photoxidized by PDI. Raman spectroscopy further demonstrated the importance of interfaces between the battery material and the organic semiconductor. These enabled a photocharge when the photobattery was illuminated. The PDI was next polymerized and enabled a photocurrent in the battery, courtesy of its collective properties (light harvester, photo-oxidant, electronic conductor, and binder).

The low redox potential of guanines (G 1.29 V vs. NHE) compared to other nucleobases, makes them potentially susceptible to attack by exogenous and endogenous damaging species. This property of guanine has also been utilized for the development of several anticancer agents including the well-known platinum complexes, cisplatin and carboplatin. The two closely related nickel complexes, NiCR and NiCR-2H, exhibit significant differences in cytotoxicity towards MCF-7 cancer cells. In the first part of this work, we explain this difference using biochemical and biophysical approaches to study their interactions with duplex DNA. The nickel complexes were found to selectively oxidize guanines in bulged DNA structures in the presence of oxidant and notably NiCR-2H oxidizes guanines more efficiently than NiCR. According to 1 H NMR studies, NiCR-2H binds strongly to the N7 position of dGMP compared to NiCR and could be an important oxidation product of NiCR under physiological conditions. The second part of this work focuses on the secondary DNA structures known as G-quadruplex formed in the guanine rich telomeric region. G-quadruplex is formed by stacking of G-quartets (a coplanar cyclic array of four Gs) on top of each other. Its formation is known to inhibit the activity of the reverse transcriptase telomerase that is overexpressed in 80-90% cancer cells. The guanines in telomeric DNA are readily oxidized due to their low redox potential and the major oxidation product is 7, 8-dihydro-8-oxoguanine (OxodG). OxodG (0.58 V vs. NHE) can further be oxidized in the presence of one electron oxidants and the resulting product forms adducts with endogenous nucleophiles such as spermine. In light of these findings, we hereby designed and synthesized novel bifunctional perylene derivatives that can selectively bind to the telomeric DNA via G-quadruplex formation and subsequently react with OxodG in close proximity. These compounds have strong binding affinity towards G-quadruplex and can significantly stabilize the OxodG containing G-quadruplex motif by end stacking on the upper G-quartet. The effect of these compounds on telomerase activity and cytotoxicity towards Hep3B cancer cells was also evaluated.