Detailed studies are presented of thin films containing a polycation, a nonlinear optically (NLO) active chromophore, and a synthetic hectorite that self-assemble into the noncentrosymmetric structure required for second order nonlinear optical responses. UV/Vis spectroscopy and ellipsometry were used as probes to monitor film growth for upto 25 deposition cycles. Exceptionally homogeneous films were obtained with regular film growth for up to the 25 cycles deposited. ISAM films self-assemble from polyelectrolyte solutions due to coulombic interactions between a charged substrate and the charged polymer in solution. Charges accumulating at the surface restrict further growth due to charge overcompensation at the surface. The entire process occurs relatively quickly as compared to other competing assembly techniques such as Langmuir-Blodgett assembly and covalent self-assembly. Previous studies indicated that second harmonic signal diminishes after the deposition of the first few bilayers. This is potentially due to adjacent layer interpenetration, which becomes prominent moving further away from the hard substrate interface. Laponite RD, a synthetic hectorite was introduced in the films in an effort to minimize interpenetration of adjacent bilayers and hence maintain chromophore orientation in every bilayer of the ISAM film. The film was deposited in quadlayers that have the following sequence: Polycation–Laponite–Polycation–Chromophore. This study is unique in its approach as it investigates the possible implications of film interpenetration on the NLO-activity of ISAM films that can be easily fabricated. It also shows the effects of different interfaces on the NLO-activities of the films. We have investigated the effect of changing the polycation from poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDDA) and the solution pH to see how these variables affect the growth and NLO properties of ISAM films. At lower pH values (specify relevant range of values), for both polycations, intrachain and interchain repulsion is strong due to little electrostatic screening. This results in polycation deposition in relatively thin, train-like layers. At higher pH levels (specify relevant range of values here) the electrostatic screening is greater due to a higher effective ionic strength. At these conditions, intrachain and interchain repulsion is reduced and so the polymers adsorb to form thicker layers with more loops and tails than for the case at lower pH. This also results in a higher density of the chromophore in the film. Extremely smooth surfaces of Laponite RD in film were obtained as confirmed by AFM imaging on glass. Regular quadlayer growth monitored by UV/Vis spectroscopy and ellipsometry was observed for up to 25 quadlayers. Second harmonic generation (SHG) signal was not conclusively affected by the presence of laponite as the decrease of signal was seen after the first few layers in the laponite containing films. This decrease was however was not as sharp in the films containing laponite as in the films that did not contain laponite. It was also noted that the SHG was not so much affected by the number of layers deposited but more so by the distance of the chromophore layer from the hard glass interface. This study thus brings to light the very important effect of the glass interface on the NLO-activity of these films. / Master of Science

Ionically self-assembled monolayer (ISAM) films are typically an assemblage of oppositely charged polymers built layer by layer through coulombic attraction utilizing an environmentally friendly process to form ordered structures that are uniform, molecularly smooth, and physically robust. ISAM films have been shown to be capable of the noncentrosymmetric order requisite for a second-order nonlinear optical response. However, films fabricated with a nonlinear optical (NLO) polymer result in significant cancellation of the chromophore orientations. This cancellation occurs by two mechanisms: competitive orientation due to the ionic bonding of the polymer chromophore with the subsequent polycation layer, and random orientation of the chromophores within the bulk of each polyanion layer. A reduction in film thickness accompanied by an increase in net polar ordering is one possible avenue to obtain the second-order nonlinear optical susceptibility chi(2) necessary for electro-optic devices. In this thesis, we will discuss the structural characteristics of ISAM films and explore three novel approaches to obtain the desired characteristics for nonlinear optical response. One approach involves the variation of solution parameters of several different cationic polymers separately from the polyanion solution in order to reduce the competitive chromophore orientation at the layer interfaces and to reduce the thickness of the inactive polycation layer. We have found that the complexity of ISAM films does not allow large chi(2) values in polyion-based films, and that the selection of the polymer cation is vital to achieve second harmonic generation (SHG) at all. The second approach involves the incorporation of dianionic molecules into ISAM films in order to eliminate both competitive chromophore orientation and random chromophore orientation inherent with polymer chromophores. We have also studied the effects of complexing dianionic chromophores with beta-cyclodextrin in order to increase solubility and improve chromophore orientation. This approach fails because the outermost monolayer of dianionic chromophore is only tethered to the preceding polycation layer by a single ionic bond for each molecule, so each chromophore can by dissociated during the following immersion into the cation solution. Finally, we have introduced a novel approach of hybrid covalent / ionic self-assembly which overcomes these disadvantages and yields a substantial increase in chi(2) due to the chromophore being locked in place to the preceding polycation layer by a covalent bond. The films fabricated in this manner yield a chi(2) that rival any polymer-polymer films despite the very low first-order molecular hyperpolarizability beta of the incorporated monomer. This suggests that incorporation of high beta molecules may result in significant improvement of chi(2), holding high promise for the hybrid covalent / ionic self-assembly technique. / Master of Science

With a growing demand in industry for cost effective, increased data handling capabilities great attention has been paid to the study of various polymer systems for use in optical telecommunications. Inorganic crystals, currently used in such systems, have high performance, but are more expensive and less obtainable than organic materials. Recent advances in techniques for developing highly efficient and inexpensive organic polymeric electro-optic (EO) devices compatible with current state-of-the-art electronics have created an interest in the commercialization of such electro-optic devices. In light of the many advantages of utilizing organic materials for electro-optic applications, numerous methods have been developed to produce nonlinear optically (NLO)-active polymeric films for such purposes. Ionic self-assembled multilayer (ISAM) films are a recently developed class of materials that allows detailed structural and thickness control at the molecular level, combined with ease of manufacturing and low cost. However, the layer-by-layer deposition technique utilized for this method currently requires lengthy processing times that challenge the feasibility of fabricating a thick film suitable for EO modulator device fabrication. This study focuses on addressing the influence of several pertinent processing variables affecting these challenges for application to electro-optic device fabrication. This study investigated (1) the effect of forced convection, varying deposition time and varying dye concentration on the properties of PAH/Procion Brown films fabricated via the hybrid reactive deposition scheme, (2) the automation and optimization of the fabrication of thick NLO active films and (3) the use of the hybrid covalent-electrostatic deposition scheme to fabricate a polymeric waveguide device with an electro-optic coefficient comparable to that of lithium niobate (LiNbO₃). At fixed deposition time and concentration conditions, the presence of convection had little demonstrated effect on films with deposition times shorter than 2 minutes. For the 5 minute case, the presence of convection correlated with a ~45% increase in Ï (2)zzz values values and a 25% increase in absorbance per bilayer. At a constant dye concentration of 5 mg/ml, the deposition time had little effect on SHG for deposition times less than two minutes. In the presence of convection, the increase in deposition time from 2 minutes to 5 minutes showed a 57% increase in Ï (2)zzz values and a 30% increase in absorbance per bilayer. For a deposition time of 2 minutes in the presence of convection, the dye solution concentration was successfully reduced 5-fold (from 5 mg/ml to 1 mg/ml) with less than a 5% difference in Ï (2)zzz values, less than a 15% decrease in absorbance per bilayer and no detriment to film quality. These results strongly indicate that the deposition conditions remain well outside of the transport-limited regime at a dye concentration of 1 mg/ml. Rather, the surface reaction rate apparently is controlling. Depositing slides at an elevated temperature (~35°C), had an undetermined effect on Ï (2)zzz values, but showed a 15% increase in absorbance per bilayer. An automatic dipper was programmed to replicate the current manual deposition method to fabricate a film suitable for EO modulator devices. Utilizing the optimal conditions for the processing variables, an optically-homogeneous, 100 nm-thick film was fabricated utilizing the automated process, yielding a Ï (2)zzz values~ 23 x 10⁻⁹ esu. A three-layer coplanar electro-optic device was fabricated utilizing the hybrid reactive deposition method. For this device, the presence of added salt was found to increase the electro-optic coefficient r33 by a factor of 3 compared to its value when made with no added salt. The electro-optic coefficient of the added salt case was found to be about 1/2 that of lithium niobate (LiNbO3). / Master of Science

It is of paramount importance to our society that the environment, life style, science and amusement flourish together in a balanced way. Some trends in this direction are the increased utilization of renewable energy, like solar photovoltaics; better health care products, for example advanced biosensors; high definition TV or high resolution cameras; and novel scientific tools for better understanding of scientific observations. Advancement of micro and nanotechnologies has directly and positively impacted our stance in these application domains; one example is that of vertical periodic or aperiodic nano or micro pillar assemblies which have attracted significant research and industrial interest in recent years. In particular, Si pillars are very attractive due to the versatility of silicon. There are many potential applications of Si nanopillar/nanowire assemblies ranging from light emission, solar cells, antireflection, sensing and nonlinear optical effects. Compared to bulk, Si pillars or their assemblies have several unique properties, such as high surface to volume ratios, light localization, efficient light guiding, better light absorption, selective band of light propagation etc.      The focus of the thesis is on the fabrication of Si pillar assemblies and hierarchical ZnO nanowires on Si micro structures in top-down and bottom-up approaches and their optical properties and different applications. Here, we have investigated periodic and aperiodic Si nano and micro structure assemblies and their properties, such as light propagation, localization, and selective guiding and light-matter interaction. These properties are exploited in a few important optoelectronic/photonic applications, such as optical biosensors, broad-band anti-reflection, radial-junction solar cells, second harmonic generation and color filters.         We achieved a low average reflectivity of ~ 2.5 % with the periodic Si micropyramid-ZnO NWs hierarchical arrays. Tenfold enhancement in Raman intensity is also observed in these structures compared to planar Si. These Si microstructure-ZnO NW hierarchical structures can enhance the performance and versatility of photovoltaic devices and optical sensors. A convenient top-down fabrication of radial junction nanopillar solar cell using spin-on doping and rapid thermal annealing process is presented. Broad band suppressed reflection, on average 5%, in 300- 850 nm wavelength range and an un-optimized cell efficiency of 6.2 % are achieved. Our method can lead to a simple and low cost process for high efficiency radial junction nanopillar solar cell fabrication.            Silicon dioxide (SiO2) coated silicon nanopillar (NP) arrays are demonstrated for surface sensitive optical biosensing. Bovine serum albumin (BSA)/anti-BSA model system is used for biosensing trials by photo-spectrometry in reflection mode. Best sensitivity in terms of limit of detection of 5.2 ng/ml is determined for our nanopillar biosensor. These results are promising for surface sensitive biosensors and the technology allows integration in the CMOS platform.         Si pillar arrays used for surface second harmonic generation (SHG) experiments are shown to have a strong dependence of the SHG intensity on the pillar geometry. The surface SHG can be suitable for nonlinear silicon photonics, surface/interface studies and optical sensing.         Aperiodic Si nanopillar assemblies in PDMS matrix are demonstrated for efficient color filtering in transmission mode. These assemblies are designed using the ‘‘molecular dynamics-collision between hard sphere’’ algorithm. The designed structure is modeled in a 3D finite difference time domain (FDTD) simulation tool for optimization of color filtering properties. Transverse localization effect of light in our nanopillar color filter structures is investigated theoretically and the results are very promising to achieve image sensors with high pixel densities (~1 µm) and low crosstalk. The developed color filter is applicable as a stand-alone filter for visible color in its present form and can be adapted for displays, imaging, smart windows and aesthetic applications. / <p>QC 20160407</p>

Thesis (PhD (Physics))--Stellenbosch University, 2008. / The advent of high intensity short pulse lasers has opened the door to investigating buried solid-solid interfaces through the technique of optical second harmonic generation (SHG). This has led to extensive study of technologically important systems such as the Si/SiO2 interface. In this study, SHG is employed to study the interface between highly boron doped p+-type Si and its native oxide layer (SiO2). Previous studies from this laboratory have extensively investigated the photo-induced charge transfer process across the Si/SiO2 interface in the case of undoped natively oxidized Si by means of SHG, with initial SHG measurements being performed on boron doped p+-type Si. The natively oxidized p+-type Si/SiO2 sample was placed on a computer controlled positioning system which allowed for translation of the sample and rotation around the azimuth. The laser system employed was characterized in terms of spectral composition, pulse duration, pulse repetition rate, spatial pro le and pulse energy in order to ensure quantitative measurements. The SHG signal generated from the sample interface was recorded in re ection. Under the applied irradiation conditions, defects are created at the interface by the near infra red (NIR) femtosecond radiation from the laser. These defects are then populated via multi-photon processes by electrons and to a lesser extent holes. The charge transfer across the interface induces an interfacial electric eld. This photo-induced electric eld is in addition to the built-in interfacial electric eld caused by positive ionization of naturally occurring interfacial defects due to the strong doping of the bulk Si. It is this interfacial electric eld, consisting of the built-in doping induced eld and the photo-induced electron and hole elds, that is probed by SHG. The SHG signal is strongly dependent on the magnitude of this interfacial electric eld as the electric eld induced second harmonic (EFISH) signal dominates all other contributions to the observed SHG signal in the case of the Si/SiO2 system. The temporal evolution of the SHG signal is recorded for di erent intensities from virgin as well as the pre-irradiated samples. This yields information about the time scales on which the charge separation occurs as well as the in- uence of existing photo-induced trap sites on the charge separation process, since the strength of the SHG signal is an indirect measure of the interfacial electric eld strength. The angular dependence of the SHG signal (SH rotational anisotropy measurements) for both the initial signal (when the doping induced electric eld dominates) and the saturated signal (when the electron induced electric eld dominates) is measured. Both these measurements show a four fold symmetry but with a relative 45 phase shift between them. This iii is taken as con rmation of the reversal of the interfacial electric eld direction. The initial SHG signal as a function of intensity is also recorded for di erent incident wavelengths. The variation in the non-quadratic dependence of the initial SHG signal on the incident intensity is attributed to a resonant enhancement of two-photon absorption and subsequent screening of the interfacial electric eld by charge carriers. The measurement performed and the results obtained contribute to the understanding of the photo-induced charge separation process across buried solid-solid interfaces, speci cally as it applies to the important Si/SiO2 interface.

Articular cartilage has been imaged using the following multi-photon modalities: Second Harmonic Generation (SHG), Two-photon Fluorescence (TPF) and Coherent Anti-Stokes Raman Scattering (CARS). A simple epi detection microscope was constructed for SHG and TPF imaging in the early stages of this research. Later the imaging was transferred to a new microscope system which allowed simultaneous forwards and epi detection and combined CARS imaging with TPF and SHG. Multiphoton spectroscopic studies were conducted on both intact tissue samples and the major components of the extracellular matrix, in order to identify sources of TPF. Fluorescence was detected from type II collagen, elastin and samples of purified collagen and elastin crosslinks. Age related glycation crosslinks of collagen may be a significant source of TPF. No fluorescence was detected from proteoglycans. In intact, unfixed healthy articular cartilage the cells were observed via CARS, surrounded in their pericellular matrix which is characterised by an increase in TPF. The collagen of the extra cellular matrix showed up clearly in the SHG images. Diseased cartilage was also imaged revealing microscopic lesion at the articular surface in early osteoarthritis and highly fibrous collagen structures and cell clusters in more advanced degeneration. In young healthy cartilage a network of elastin fibres were found lying parallel to the articular surface in the most superficial 50μm of the tissue. Regional variations in these fibres were also investigated. The fibres appeared mainly long and straight suggesting that they may be under tension, further work is needed to identify whether they have a mechanical function. The polarization sensitivity of the SHG from collagen has been investigated for both cartilage and tendon. In the most superficial tissue these measurements can be used directly to determine the collagen fibre orientation. However at increasing depths the effects of biattenuation and birefringence must be considered. Healthy cartilage has a characteristic pattern of polarization sensitivity with depth and this changes at lesions indicating a disruption of the normal collagen architecture. The methods developed in this thesis demonstrate the use of non-linear microscopy to visualise the structure of the extracellular matrix and cells in intact unstained tissue. They should also be appropriate in many areas of cell and matrix biology.

Les phénomènes de diffusion cohérente non-linéaire ont été récemment proposés en alternatives à la fluorescence comme processus de marquage en microscopie multiphotonique. Les matériaux couramment appliqués dans ce contexte buttent toutefois sur une limite inférieure en taille déterminée par le seuil de détection de signaux faibles en optique non-linéaire. Aucun des efforts récents en détection en génération de second-harmonique (GSH), qui est le processus non-linéaire d’ordre le plus bas, n’a permis de descendre à ce jour au-dessous d’une barrière en taille de 40nm même en ayant recours aux techniques de détection les plus sensibles telles que le comptage de photons uniques. Les nanoparticules (NPs) restent ainsi dans la famille des nano-diffuseurs de “grande“ taille. Il apparaît toutefois possible de déplacer de façon significative cette limite inférieure vers les plus petites tailles en substituant aux isolants diélectriques ou aux semi-conducteurs à grands gaps des particules quantiques (PQs) à base de semi-conducteurs à gaps directs.Dans ce travail, un nouveau type de nanosondes hautement non-linéaires a été conçu et développé de façon à franchir cette barrière de taille minimale pour atteindre l’échelle de nanoparticules uniques. Nous considérons ainsi l’excitation résonnante à deux photons de nanoparticules quantiques individuelles à base de CdTe (de la famille des “zinc-blendes”) d’un diamètre d’environ 12.5nm, qui fournissent une émission cohérente efficace par GSH jusqu’à hauteur de 105 comptages de photons par seconde. Elles présentent de plus l’avantage d’une remarquable sensibilité à l’orientation de leur réseau cristallin octupolaire.De plus, il a été démontré que les effets de confinement quantique déterminent fortement les caractéristiques de la susceptibilité non-linéaire du second-ordre χ(2). La caractérisation quantitative du χ(2) des PQs, en particulier leur dispersion spectrale et leur dépendance en taille est menée par spectroscopie de particules uniques ainsi qu’en moyenne d’ensemble par diffusion Hyper-Rayleigh (HRS). Nous fournissons en particulier la preuve que sous certaines conditions, le χ(2) de structures à base de semi-conducteurs en mode de confinement quantique peut très largement dépasser sa valeur en milieu massif. De plus, un nouveau type de PQs hybridant des semi-conducteurs en géométries de type “bâtonnet sur sphère” (BS) a été développé sur la base de composantes cristallines de symétries différentes, afin d’augmenter leur non-linéarité quadratique effective, tout en maintenant leur taille dans un régime proche d’un fort confinement quantique. Le nouveau tenseur hybride complexe χ(2) est analysé en terme d’interférence des susceptibilités constitutives, en prenant en compte les différentes formes et symétries associées aux composantes octupolaires et dipolaires.Il en résulte pour de telles structures une exaltation significative du χ(2), qui excède celle des PQs à constituant unique compte tenu du couplage entre matériaux non-linéaires et d’un temps de décohérence plus long, que nous attribuons à un effet de separation de charge photo-induit. / Nonlinear coherent scattering phenomena from single nanoparticles have been recently proposed as alternative processes for fluorescence in multiphoton microscopy staining. Commonly applied nanoscale materials, however, have reached a certain limit in size dependent detection efficiency of weak nonlinear optical signals. None of the recent efforts in detection of second-harmonic generation (SHG), the lowest order nonlinear process, have been able to cross a ~40 nm size barrier for nanoparticles (NPs), thus remaining at the level of “large” nanoscatterers, even when resorting to the most sensitive detection techniques such as single-photon counting technology. As we realize now, this size limitation can be significantly lowered when replacing dielectric insulators or wide gap semiconductors by direct-gap semiconducting quantum dots (QDs). Herein, a new type of highly nonlinear nanoprobes is engineered in order to surpass above mentioned size barrier at the single nanoparticle scale. We consider two-photon resonant excitation in individual zinc-blende CdTe QDs of about 12.5 nm diameter, which provide efficient coherent SHG radiation, as high as 105 Hz, furthermore exhibiting remarkable sensitivity to spatial orientation of their octupolar crystalline lattice. Moreover, quantum confinement effects have been found to strongly contribute to the second-order nonlinear optical susceptibility χ(2) features. Quantitative characterization of the χ(2) of QDs by way of their spectral dispersion and size dependence is therefore undertaken by single particle spectroscopy and ensemble Hyper-Rayleigh Scattering (HRS) studies. We prove that under appropriate conditions, χ(2) of quantum confined semiconducting structures can significantly exceed that of bulk. Furthermore, a novel type of semiconducting hybrid rod-on-dot (RD) QDs is developed by building up on crystalline moieties of different symmetries, in order to increase their effective quadratic nonlinearity while maintaining their size close to a strong quantum confinement regime. The new complex hybrid χ(2) tensor is analyzed by interfering the susceptibilities from each component, considering different shape and point group symmetries associated to octupolar and dipolar crystalline structures. Significant SHG enhancement is consequently observed, exceeding that of mono-compound QDs, due to a coupling between two nonlinear materials and slower decoherence, which we attribute to the induced spatial charge separation upon photoexcitation.

Optical imaging methods have the potential to detect ovarian cancer at an early, curable stage. Optical imaging has the disadvantage that high resolution techniques require access to the tissue of interest, but miniature endoscopes that traverse the natural orifice of the reproductive tract, or access the ovaries and fallopian tubes through a small incision in the vagina wall, can provide a minimally-invasive solution. We have imaged both rodent and human ovaries and fallopian tubes with a variety of endoscope-compatible modalities. The recent development of fiber-coupled femtosecond lasers will enable endoscopic multiphoton microscopy (MPM). We demonstrated two-and three-photon excited fluorescence (2PEF, 3PEF), and second-and third-harmonic generation microscopy (SHG, THG) in human ovarian and fallopian tube tissue. A study was undertaken to understand the mechanisms of contrast in these images. Six patients (normal, cystadenoma, and ovarian adenocarcinoma) provided ovarian and fallopian tube biopsies. The tissue was imaged with three-dimensional optical coherence tomography, multiphoton microscopy, and frozen for histological sectioning. Tissue sections were stained with hematoxylin and eosin, Masson's trichrome, and Sudan black. Approximately 1 mu m resolution images were obtained with an excitation source at 1550 nm. 2PEF signal was absent. SHG signal was mainly from collagen. 3PEF and THG signal came from a variety of sources, including a strong signal from fatty connective tissue and red blood cells. Adenocarcinoma was characterized by loss of SHG signal, whereas cystic abnormalities showed strong SHG. There was limited overlap of two-and three-photon signals, suggesting that three-photon imaging can provide additional information for early diagnosis of ovarian cancer.

La conception de molécules pour l’optique non linéaires (ONL) est devenue un centre de recherche de pointe pour les télécommunications, les technologies de l'information et le stockage de données optiques. Les molécules dipolaires substituées par des groupes donneur-accepteur ont été les chromophores les plus étudiés pour l’ONL. Cependant les molécules dipolaires diverses limitations telles que leur transparence optique, leur faible stabilité thermique et leur tendance à adopter un alignement antiparallèle à l'état solide. Récemment, une nouvelle classe de matériaux est apparue basé sur des symétries octupolaire qui ne possède pas de dipôle permanent, pour les applications ONL. Au niveau structural, la structure générique idéale pour des molécules tridimensionnelles avec une distribution de charges octupolaire est un cube avec des charges opposées alternées à chaque angle. À ce jour, aucune molécule représentant le cube vrai (déformé) avec huit charges alternées aux sommets et délocalisation des charges complètes entre les plans supérieurs et inférieurs n’a été décrite. Dans le cadre de cette thèse, des complexes de lanthanides III à partir de phthalocyanines de type ABAB présentant en alternance des groupes donneurs et accepteurs d'électrons ont été synthétisés représentant le premier réel octupole. Ces structures ont été caractérisé par UV-NIR, X-Ray et présentent les plus élevés hyperpolarisabilité quadratique jamais enregistré pour des molécules octupolaires. En outre, ce travail a été étendu à divers type de double-decker de lanthanides homoleptiques non-octupolaire basé sur des phthalocyanines AB3, A4, B4, T4. Il a été observé que ces complexes présentent aussi des mesures d’hyperpolarisabilité quadratique élevés, mais inferieur a celles trouvé pour la série de complexes Ln (ABAB)2 octupolaire, comme prévu. / The design of nonlinear optical (NLO) molecules has become a focus of current research in telecommunications, information technologies and optical data storage. Donor-acceptor substituted dipolar molecules have been the most investigated NLO chromophores. Dipolar molecules, however, have several limitations such as low optical transparency, low thermal stability and their strong tendency to adopt anti-parallel packing in the solid state. Recently, a new class of materials based on octupolar symmetries, which lack permanent dipole moments, has been proposed for NLO applications. At a structural level, it can be shown that the basic template for 3D octupolar molecules comes to a cube with alternating charges at the corners such as donor and acceptor substituent. Despite all the various structures reported, it is worth noting that no molecules actually representing the “real” octupolar cube have been obtained so far. In this thesis, we showed that the real octupolar cube can be demonstrated by lanthanide III complexes based on ABAB type phthalocyanine featuring alternating electron donor and electron acceptor groups. These structures are characterized by UV-NIR, X-Ray and exhibit highest quadratic hyperpolarizability ever reported for an octupolar molecule. Moreover, this work was extended to nonoctupolar lanthanide homoleptic double-decker complexes based on AB3, A4, B4, T4 type phthalocyanines. It was observed that these molecules present a quite large quadratic hyperpolarizability too, but smaller than the one obtained for the Ln(ABAB)2 series, as expected. / Doğrusal olmayan optic (NLO) özellik gösteren moleküllerin tasarımı telekomünikasyon, bilgi teknolojileri ve optic very depolama alanlarında güncel bir araştırma konusudur. Alıcı-verici grup bağlı iki kutuplu moleküller en çok araştırılmış NLO malzemeleridirler. Ancak, iki kutuplu moleküllerin düşük optic şeffaflık, düşük termal kararlılık ve katı halde parallel olmayan yığılmaları gibi çeşitli sınırlamaları vardır. Son zamanlarda, kalıcı dipol momentleri olmayan octupolar simetriye dayalı, yeni bir malzeme sınıfı NLO uygulamaları için ileri sürülmüştür. Yapısal olarak bu 3D octupolar moleküller için temel şablon, köşelerinde alıcı verici grupları içeren bir olarak gösterilir. Yapılan tüm çalışmalara ragmen, bugüne kadar gerçek küpü temsil edebilen bir yapı elde edilememiştir. Bu tezde, biz bu octupolar küpün electron alıcı ve verici grupları içeren ABAB tipi halkalı yapıya dayalı lantanid kompleksleri ile ortaya konabilecğini gösterdik. Bu yapılar UV-NIR ve X-Ray ile yapıları aydınlatıldı ve bugüne kadarki en yüksek 2. dereceden NLO değerleri elde edildi. Ayrıca, bu çalışma, çeşitli octupole olmayan AB3, A4, B4 ve T4 tipi lantanit çift katlı ftalosiyaninler sentezlenerek genişletildi. Ve oktupol olmayan moleküllerin 2. Dereceden NLO değerleri oldukça büyük ama beklendiği gibi oktupol Ln(ABAB)2 daha küçük olduğu gözlendi.

Filmes ultrafinos de polímeros que contém azocromóforos são importantes para muitas aplicações como armazenamento óptico, formação de grades de relevo superficiais, alinhamento de camadas de cristal líquido e dispositivos ópticos com propriedades não-lineares. Dentre as muitas técnicas de fabricação de filmes orgânicos ultrafinos, a técnica de Automontagem eletrostática camada a camada (Layer-by-Layer, LBL) é muito atrativa devido a sua simplicidade e versatilidade, permitindo o controle na espessura e na composição dos filmes em escalas nanométricas. Contudo, a completa caracterização estrutural de tais filmes enfrenta dificuldades devido à falta de técnicas experimentais apropriadas. Utilizamos a Geração de Segundo Harmônico (SHG) para estudar a orientação molecular de filmes automontados de um polieletrólito catiônico (PAH - Poli(alilamina hidroclorada)) e um polieletrólito aniônico contendo azocromóforos como grupos laterais (Ma-co-DR13) sobre substrato de vidro. O sinal de SHG é proporcional à susceptibilidade não-linear de segunda ordem do filme, que por sua vez depende da distribuição orientacional dos azocromóforos nesse filme. Os resultados indicam que existem uma orientação preferencial dos azocromóforos, que leva a uma não-linearidade óptica significativa. Entretanto, a intensidade do sinal e a anisotropia não são homogêneas por toda a amostra, indicando a presença de domínios orientacionais, que é verificado por meio da Microscopia a Ângulo de Brewster (BAM). O sinal médio de SHG não aumenta com a espessura do filme, indicando que a ordem orientacional das sucessivas bicamadas são independentes. Analisando o sinal de SHG em função das polarizações de saída e entrada, alguns parâmetros da distribuição orientacional dos azocromóforos podem ser deduzidos. Ajustando as medidas de SHG a uma distribuição modelo concluímos que os cromóforos possuem uma certa distribuição angular com um ângulo médio em relação à superfície do plano de aproximadamente 40° e uma pequena anisotropia ao longo do plano do filme. Utilizamos também o Método da Máxima Entropia (MEM) para determinar a distribuição mais larga possível compatível com nossos dados experimentais e comparar então com a distribuição modelo obtida através dos procedimentos de ajuste. / Ultrathin films of polymers containing azochromophores are important for many applications such as optical data storage, formation of surface relief gratings, liquid crystal alignment layers and non-linear optical devices. Among several techniques for fabricating organic thin films, the Layer-By-Layer electrostatic self-assembly (LBL) is very attractive due to its simplicity and versatility, allowing one to control film thickness and composition in the nanometer scale. However, thorough structural characterization of such films is often difficult due to lack of appropriate experimental techniques. We have used optical second-harmonic generation (SHG) to study the molecular orientation of Layer-by-Layer films of a cationic polyelectrolyte ((PAH - Poly(allylamine hydrochloride)) and a anionic polyelectrolyte containing azochromophores with azo side groups (PAH/Ma-co-DR13) on a glass substrate. The SHG signal is proportional to the second-order nonlinear susceptibility of the film, which in turn depends on the orientational distribution of the azo chromophores in the film. The results indicate that there is a preferential orientation of the azo chromophores in the film, leading to a significant optical nonlinearity. However, both the signal strength and its anisotropy are not homogeneous throughout the sample, indicating the presence of orientational domains. This is verified through Brewster Angle Microscopy (BAM). The average SHG signal does not increase with film thickness, indicating that the orientational order of successive bilayers are independent. Analyzing the SHG signal as a function of the input and output polarizations, a few parameters of the azochromophore orientational distribution can be deduced. Fitting the SHG signal to a simple model distribution, we have concluded that the chromophores have an angular distribution with a mean tilt from the surface plane of approximately 41° and a slight in-plane anisotropy. We have also used the Maximum-Entropy Method (MEM) to determine the widest orientational distribution compatible with our data and compared it to the model distribution obtained by the fitting procedure.