In this work the first observation of new type of liquid crystals is presented. This is ionic self-assembly (ISA) liquid crystals formed by introduction of oppositely charged ions between different low molecular tectonic units. As practically all conventional liquid crystals consist of rigid core and alkyl chains the attention is focused to the simplest case where oppositely charged ions are placed between a rigid core and alkyl tails. The aim of this work is to investigate and understand liquid crystalline and alignment properties of these materials. It was found that ionic interactions within complexes play the main role. Presence of these interactions restricts transition to isotropic phase. In addition, these interactions hold the system (like network) allowing crystallization into a single domain from aligned LC state. Alignment of these simple ISA complexes was spontaneous on a glass substrate. <br><br> In order to show potentials for application perylenediimide and azobenzene containing ISA complexes have been investigated for correlations between phase behavior and their alignment properties. The best results of macroscopic alignment of perylenediimide-based ISA complexes have been obtained by zone-casting method. In the aligned films the columns of the complex align perpendicular to the phase-transition front. The obtained anisotropy (DR = 18) is thermally stable. The investigated photosensitive (azobenzene-based) ISA complexes show formation of columnar LC phases. It was demonstrated that photo alignment of such complexes was very effective (DR = 50 has been obtained). It was shown that photo-reorientation in the photosensitive ISA complexes is cooperative process. The size of domains has direct influence on efficiency of the photo-reorientation process. In the case of small domains the photo-alignment is the most effective. Under irradiation with linearly polarized light domains reorient in the plane of the film leading to macroscopic alignment of columns parallel to the light polarization and joining of small domains into big ones. <br><br> Finally, the additional distinguishable properties of the ISA liquid crystalline complexes should be noted: (I) the complexes do not solve in water but readily solve in organic solvents; (II) the complexes have good film-forming properties when cast or spin-coated from organic solvent; (III) alignment of the complexes depends on their structure and secondary interactions between tectonic units. / In dieser Arbeit wird erstmalig eine neue Klasse von Flüssigkristallen auf Basis ionischer Self-Assembly (ISA) Komplexe beschrieben. Während herkömmliche thermotrope Flüssigkristalle aus steifen, formanisotropen Molekülfragmenten und kovalent gebundenen Flügelgruppen (meist Alkylketten) bestehen, entstehen diese neuartigen supramolekularen Verbindungen durch die Komplexierung gegensätzlich geladener ionischer tektonischer Einheiten und Tenside. <br><br> Ziel der Arbeit war es, die flüssigkristallinen und insbesondere die Orientierungseigenschaften dieser neuen Materialien am Beispiel repräsentativer Modellverbindungen zu untersuchen. Es wurde nachgewiesen, dass die ionischen Wechselwirkungen die thermischen Eigenschaften der Verbindungen entscheidend beeinflussen. So behindern sie den Übergang in die isotrope Phase. Das System wird quasi durch ein Netzwerk ionischer Wechselwirkungen stabilisiert. Makroskopisch orientierte LC Zustände sind offensichtlich Ausgangspunkt für hochgeordnete flüssigkristalline Filme oder gar für die Kristallisation von Monodomänen. In speziellen Fällen erfolgt eine spontane Ausbildung von ISA Monodomänen bereits auf Glassubstraten. <br><br> Mit Hinblick auf potentielle Anwendungen wurden Perylendiimid und Azobenzen enthaltene ISA Komplexe insbesondere hinsichtlich von Zusammenhängen zwischen Phasenverhalten und Orientierungseigenschaften untersucht. Die zone-casting Methode erwies sich als besonders geeignet für die makroskopische Orientierung perylendiimidbasierter ISA Komplexe. In orientierten Filmen richten sich die Kolumnen des Komplexes senkrecht zur Phasenübergangsfront aus. Das dabei erreichte dichroitische Verhältnis (DR=18) ist thermisch stabil. Die untersuchten Azobenzen basierten ISA Komplexe weisen kolumnare LC Phasen auf. Durch Photoalignment mittels linear polarisierten Lichts werden Komplexe sehr effektiv senkrecht bzw. die Columnen der Komplexe parallel zur Polarisation des Lichtes orientiert, wobei sehr hohe DR bis zu 50 erreicht wurden. Weiterhin wurde gezeigt, dass die Photo-Reorientierung photosensitiver ISA Komplexe kooperativ erfolgt. Die Größe der Domänen hat dabei einen entscheidenden Einfluß auf die Effektivität des Photo-Reorientierungsprozesses. So ist der Prozess im Fall kleiner Domänen effektiver. Durch die Bestrahlung mit linear polarisiertem Licht werden die Domänen in der Filmebene reorientiert, was zu einer makroskopischen Ausrichtung der Kolumnen parallel zur Lichtpolarisation und zu einer Vereinigung kleiner Domänen führt.

This dissertation is about fabrication and functionalization of metal nanoparticles for use in plasmonic and nonlinear optical (NLO) applications. In the first two chapters, I describe a series of experiments, where I combined silver nanoparticles fabricated by nanosphere lithography with ionic self-assembled multilayer (ISAM) films, tuning the geometry of the particles to make their plasmonic resonances overlap with the frequency of optical excitation. The designed hybrid metallic/organic nanostructures exhibited large enhancements of the efficiency of second harmonic generation (SHG) compared to conventional ISAM films, causing a modified film with just 3 bilayers to be optically equivalent to a conventional 700-1000 bilayer film. SHG responses from Ag nanoparticle-decorated hybrid-covalent ISAM (HCISAM) films were investigated as the next logical step towards high-Ï ²⁺ ISAM films. I found that the plasmonic enhancement primarily stems from interface SHG. Interface effects were characterized by direct comparison of SHG signals from PAH/PCBS ISAM films and PAH/PB HCISAM films. Though interface &chi²⁺ is substantially smaller in PAH/PCBS than in PAH/PB, plasmonically enhanced PAH/PCBS films exhibit stronger NLO response. I propose that the structure of PAH/PB film makes its interface more susceptible to disruptions in the nanoparticle deposition process, which explains our observations. During the fabrication of monolayer crystals for nanosphere lithography, I developed a variation of the technique of convective self-assembly, where the drying meniscus is restricted by a straight-edge located approximately 100 μM above the substrate adjacent to the drying zone. This technique can yield colloidal crystals at roughly twice the growth rate compared to the standard technique. I attribute this to different evaporation rates in the thin wet films in the two cases. I also found that the crystal growth rate depends strongly on the ambient relative humidity. Finally, dithiocarbamate (DTC)-grafted polymers were synthesized and employed to functionalize surfaces of Au nanopartciles. PAH-DTC shows greater stability in different environments than PEI-DTC. I also investigated the stability of PAH-DTC coated particles in suspensions with UV-Vis spectroscopy and autotitration. The covalently bonded PAH-DTC enhances the colloidal stability of the Au nanoparticles and enables subsequent ISAM film deposition onto the particles. / Ph. D.

The focus of this dissertation research involves surface charge manipulation of functionalized monolayers. Application of potential to acid or base terminated organic films immobilized on electrodes results in the ionization of the terminal groups. The ionization of these groups using applied potential provides conditions favorable the control of polyelectrolyte deposition to the monolayer surface. Research is presented that asserts that the interfacial pH of acid or base terminated monolayers responds to applied potential as a result of the accumulation of phosphate counterions to the monolayer-solution interface. Results obtained from applied potential modulation of surface charge endeavors strongly suggest that manipulation of terminal group ionization with applied potential “turns on“ or “turns off“ the charge of the monolayer. Switching on the surface charge of functionalized monolayers using applied potential yields conditions that make it possible for the promotion or inhibition of electrostatic attachment of polyelectrolyte to the monolayer surface. Electrostatic interactions between immobilized polyelectrolytes and redox probes result in changes in electron transfer that can be monitored with electrochemical impedance measurements. Impedance measurements provide a qualitative assessment of the degree of potential-driven polyelectrolyte self assembly. The electrostatic interactions between the redox probe in solution and the terminal region of monolayers directly affects the extent of charge-transfer between the electrode and the redox probe in solution. For this reason, impedance measurements are able to provide an indication of whether or not potential drives to electrostatic deposition to the terminal region of a functionalized monolayer. Unlike impedance measurements, quartz crystal microbalance measurements provide quantitative mass assessments that confirm polyelectrolyte deposition of inhibition under the direction of applied potential. Application of appropriate potentials is shown to induce variations in the electrostatic interactions between redox probes in solution and terminal groups of monolayers. Variations in the electrostatic interactions between the modified electrode and the redox probe modulate electron transfer that produces varying current. Since scanning electrochemical microscopy (SECM) relies on modulation of feedback current underneath a ten-micrometer platinum tip, SECM provides a means for monitoring of potential-driven surface charge modulation. Experiments presented in this dissertation will show that in addition to monitoring the effect of applied potential on the charge of ionizable surface groups, SECM can also be used to selectively deposit a polyelectrolyte to the surface of a carboxylic acid terminated monolayer. The SECM tip was rastered over the surface of a functionalized monolayer in the form of a simple pattern while the electrode was immersed in a dilute polyelectrolyte solution. As the SECM tip was moved and potential stepped more positive than the PZC, ionization was confined ionization to one spot encouraging localized ionic self assembly. / Ph. D.