The motivation for the current work stems from a unique application, i.e. the photopatterning of optical functionality in a photosensitive material immediately prior to use. In this case, optical devices such as diffraction gratings and optical interconnects are produced in thin films using integrated photonic sources under relatively uncontrolled environmental conditions. The compatibility of the material photoexcitation mechanism with wavelength and fluence levels available from compact solid-state optical sources and the need to understand the impact of local atmospheric composition and temperature on the photosensitive material response are therefore of primary concern. The primary goal of the current study was to investigate photoexcitation mechanisms and photoinduced optical and structural changes in promising candidate material systems for this application: polysilane and polygermane-based molecular hybrid polymers. The work pursued the development of a fundamental understanding of the key photophysical and photostructural responses of thin films composed of both pure, linear-chain polysilanes and of a Ge-Si copolymer. The effects of molecular modifications to the polymers, including polymer backbone catenate structure and side-group identity, on the optical and photosensitive behavior observed in these systems are examined. Through such effort, an understanding of how such structural characteristics influence key photosensitive properties, i.e. the excitation wavelength and the resulting photoinduced optical property changes, was attained. A related objective in the present work was to characterize the thermal stability of these hybrid polymers, specifically in terms of the effect of thermal treatment on as-deposited and photomodified materials. In this case, an evaluation of the similarities and differences in structural modification in response to both thermal and optical fields was pursued. The primary mechanism associated with the photoinduced phenomena observed in both polysilane and polygermane involves backbone chain scissioning and the formation of silane-radicals upon absorption of near-UV (λ ≈ 300 to 400 nm) photons, resonant with the lowest energy, σ - σ* (HOMO-LUMO) transition of the Group IVA backbone. The final photoproducts obtained result from a mixture of different competing processes which occur subsequent to this initial photoscissioning. In aerobic atmospheric environments, the radicals formed capture oxygen and form oxide linkages forming the dominant photoproducts. On the other hand, under anaerobic conditions, photooxidation is suppressed while hydride passivation of the radical dominates the response. The oxidized product, resulting from irradiation under the aerobic environment, exhibited higher refractive index changes than irradiation under anaerobic conditions. Photoexcitation using higher energy photons (typically λ ≈ 230 to 300 nm) are resonant with side-group transitions associated with π-conjugated states of the cyclic moieties. Under these conditions, the excitation accesses both these organic side-groups as well as the Group IVA backbone structure. Such excitation conditions resulted in a larger photoinduced structural modification in the irradiated polymer, as observed both in terms of its electronic structure as well as the resulting refractive index change. Thermally induced structural modification to the backbone and side-group moieties were found to be qualitatively similar those produced under optical irradiation. For example, the primary structural changes were again associated with backbone chain scissioning. Photoinduced structural modifications through resonant optical excitation of the material, however, tended to be more focused on the specific structural moieties accessed.

Stuttgart, Univ., Diss., 2000.

Freiburg, Univ., Diss., 2001.

Universiẗat, Diss., 2001--Freiburg (Breisgau).

No description available.

Polymers incorporating main group elements offer different and interesting properties compared to their all carbon analogues. For example, π-conjugated polymers incorporating phosphorus in the main chain of the polymer have generated interest due to their unique thermal and electronic properties, which primarily result from delocalization of the phosphorous lone pair within aromatic units. Similarly, interest in polysilanes stems from conductivity resulting from σ electron delocalization, though current methods of preparation for both of these types of materials are lacking. In this dissertation, both early and late transition-metal compounds were used to dehydrocouple phosphine and silane substrates. The use of dehydrocoupling catalysis as a method for the synthesis of main group element-linked polymers was explored utilizing substrates designed to engender solubility in their polymeric products. Progress towards the preparation of silane- and phosphine-based conjugated materials via dehydrocoupling catalysis is reported. Catalytic reactions of bisphosphinite pincer-ligated iridium compounds p-XR(POCOP)IrHCl (POCOP) = 2,6-(R2PO)2C6H3, R = iPr, tBu, X = H, COOMe, H, NMe2with primary and secondary silanes have been performed. Compounds featuring the less sterically demanding iPr-substituted ligands facilitate silane redistribution reactions, but dehydrocoupling catalysis is observed for more encumbered silane substrates or with aggressive removal of H2. The bulkier tBu-substituted compounds are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing tBu ligated Ir include low molecular weight oligosilanes with varying degrees of redistribution present or disilanes when employing more sterically demanding substrates. The interplay of steric and electronic effects of the POCOP ligand on the silane product distribution will be presented. In previous work by our group, a triamidoamine-supported zirconium catalyst,[κ5-(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH2]Zr, 1 has been shown to be effective in catalyzing the formation of phosphorus–element bonds via dehydrocoupling. Substrates including 2,5-bisphosphinofuran and 1,4-bisphosphinobenzene were dehydrocoupled to yield hyperbranched polyphosphine products. Efforts to characterize these products have been limited due to poor solubility. Rational substrate design incorporating aliphatic sidechains in primary phosphine linker molecules to engender solubility has been accomplished. Treatment of these second generation substrates with 1 or [Cp*2ZrH3]Li, 2 leads to sluggish reactions reaching moderate conversions to diphosphine products. The working hypothesis is that steric congestion during the bond forming step hinders additional bond-formation. Efforts toward the characterization and utilization of these insoluble materials as metal ion scavengers will be presented.

No description available.

Samples with thin layer of poly[methyl(phenyl)silylene] were prepared for cathodoluminescence measurement. Dependence of cathodoluminescence on temperature was studied on these samples. Spectra of emitted light were measured on the samples when they were gradually heated to 20, 50, 75, 100 and 125°C. Kinetics of the process of poly[methyl(phenyl)silylene] regeneration at higher temperature was observed. Samples of polysilylene were displayed by scanning electron microscopy.

Methylchlorpolysilane/polycarbosilane sind geeignete Vorstufen für Siliciumcarbid. Deren Überführung in den keramischen Zustand erfolgt durch Pyrolyse bis 1500 °C. Eine Steuerung der auf der katalytischen Disproportionierung von Disilanverbindungen basierenden Synthese und das Design der Precursoreigenschaften ist über die Gestaltung des Katalysators und Reaktionsregimes sowie Additive (z. B. borhaltigen Verbindungen) gegeben. Synthetisiert wurden unterschiedliche Polysilane, Polycarbosilane sowie neuartige Polyborocarbosilane. Der präkeramische Strukturwandel der Polymere lässt sich gezielt beeinflussen, insbesondere der Vernetzungsprozess durch thermischen Energie-Input sowie durch Zugabe von reaktiven Komponenten. Der Verlauf der Molekulargewichtsverteilungsfunktionen wurde mittels Gelpermeationschromatographie verfolgt und die ermittelten Molekulargewichte mit unterschiedlichen Standards bewertet. Die Precursoren sind pyrolytisch in mikroporöses SiC-Material überführbar. Eine Skalierung des Porendurchmessers über die Variation der Precursorstruktur gelang im Nanometerbereich. Anwendungsbeispiele wurden aufgezeigt.

Von generellem Interesse für potentielle Anwendungsmöglichkeiten sind Materialien mit speziellen elektrischen bzw. nichtlinearen optischen Eigenschaften. Im Rahmen dieser Arbeit wurden neue dipolare Verbindungen synthetisiert und charakterisiert, welche eine zentrale Organosilanspacereinheit (-SiMex-,-(SiMe2)6-), ein terminales Metallkomplexfragment (potentieller Donor, FcN-) sowie eine terminale organische Akzeptoreinheit (-PhF, -PhBr, -PhCHO) enthalten und gleichzeitig eine große Variationsbreite gewünschter Eigenschaften aufweisen. Aus Photo-EMK-Messungen, UV/VIS-, NMR-Spektroskopie, Mößbauer- und cyclovoltammetrischen Untersuchungen kann auf eine im Festkörper auftretende temperaturabhängig variierende intermolekulare Kopplung zwischen dem Donor und dem organischen Akzeptor geschlossen werden. Photo-EMK- und Einkristallröntgenstrukturanalysen der Salze (Hydrochloride, Pikrate) offenbaren starke intermolekulare Wechselwirkungen (C-H···π, D-C-H···A) mit entscheidendem Einfluß auf Festkörpereigenschaften (supramolekulare MO's).