The influence of the Pt crystalline surface orientation on the glycerol electro-oxidation in acidic media

We investigated the electrochemical oxidation of glycerol on low-index Pt single crystals in acidic media (H2SO4 and HClO4) by cyclic voltammetry and Fourier Transform Infrared (FTIR) spectroscopy and we verified that this is a surface sensitive reaction. Pt(100) and Pt(110) surface structures favor the breaking of the C-C-C bond at low potentials (say 0.05 V), as seen by the formation of CO, one of the adsorbed residues of the glycerol dissociation, which poisons these surfaces even at high potentials. Pt(111) surface structure does not favor the C-C-C bond breaking at potentials as low as 0.05 V. However, Pt(111) is less poisoned by residues of glycerol dissociation and, for this reason, it is more active for glycerol oxidation than Pt(100) and Pt(110) at low potentials. Carbonyl containing compounds and CO2 were detected as reaction products of the glycerol oxidation on all investigated single-crystal Pt surfaces. The ratio between CO2 and carbonyl containing compounds is clearly much higher for Pt(100) and Pt(110) than for Pt(111). (C) 2012 Elsevier Ltd. All rights reserved.

Synthesis and characterization of [Ru(eta(6)-C10H14)(dppf)X][PF6] (X = Cl, Br, I, SnF3) compounds: The X-ray structure of [Ru(eta(6)-C10H14)(dppf)Cl][SnCl3]center dot 0.45CH(2)Cl(2)

The arene-ruthenium complex [Ru(eta(6)-C10H14)(dppf)Cl]PF6 (1) was used as a precursor for the syntheses of the [Ru(eta(6)-C10H14)(dppf)Br]PF6 (2), [Ru(eta(6)-C10H14)(dppf)I]PF6 (3). [Ru(eta(6)-C10H14)(dppf)SnF3]PF6 (4) and [Ru(eta(6)-C10H14)(dppf)Cl][SnCl3]center dot 0.45CH(2)Cl(2) (5) complexes by its reactions with KBr, Kl, SnF2 and SnCl2. respectively. All of the compounds were characterized by NMR, IR, Fe-57 and Sn-119-Mossbauer spectroscopy, and cyclic voltammetry. The single-crystal X-ray structure analysis of the [Ru(eta(6)-C10H14)(dppf)Cl] [SnCl3]center dot 0.45CH(2)Cl(2) complex revealed the expected piano-stool geometry. Cyclic voltammograms of the complexes showed only one quasi-reversible electrochemical process, involving the oxidation of Fe(II) and Ru(II) at the same potential, which was confirmed by exhaustive electrolysis experiments. Fe-57-Mossbauer parameters obtained for the complexes (1-5) were fitted with one doublet corresponding to a site of one iron(II). The Sn-119-Mossbauer parameters of the complex (4) indicate that tin is tetra covalent. (c) 2012 Elsevier Ltd. All rights reserved.

Local electrochemical investigation of copper patina

The patination of copper is known for its complexity and heterogeneous formation. For a deeper investigation, a locally resolved surface analysis was considered. An exact determination of the accessed area and a potentiostatic control in a three-electrode configuration was reached with the use of the electrochemical microcell technique, which enables local electrochemical measurement such as local electrochemical impedance spectroscopy and cyclic voltammetry. Such a technique provides a unique way for performing the investigation of heterogeneities on electrode surfaces. The local electrochemical measurements on the artificially patinated surface have allowed distinguishing areas of different reactivity even when the analysis of the surface revealed a homogenous chemical composition of patina. Local measurements with the electrochemical microcell showed the presence of small defects on the patina layer that can be modelled by considering a hemispherical diffusion process at small active areas surrounded by larger less reactive domains.

Spectroscopic, morphological and electrochromic characterization of layer-by-layer hybrid films of polyaniline and hexaniobate nanoscrolls

The combination of semiconducting oxides and polyaniline in the nanoscale range may result in hybrid materials having enhanced properties, such as electrochromism and charge capacity. This paper reports the spectroscopic, morphological and electrochromic characterization of hybrid films made up of hexaniobate one-dimensional (1D) nanoscrolls and polyaniline prepared by the layer-by-layer assembly technique (LbL). Secondary electron imaging and backscattered electron imaging techniques performed using a scanning electron microscope showed that polyaniline is adsorbed on the hexaniobate nanoscrolls, which confirms the combination of the components in the nanoscale domain. UV-VIS-NIR electronic spectra of the LbL hybrid films showed the absorption tail in the NIR region, assigned to delocalized polarons of the polyaniline. Resonance Raman spectra in the 1000-1700 cm(-1) range indicated that hybrid films present a higher relative intensity of polaron bands at 1337 and 1508 cm(-1) than pristine polyaniline in the emeraldine salt form. These results suggest that hexaniobate nanoscrolls induce a secondary doping of polyaniline. The cyclic voltammetry (CV) data for the hybrid film showed a specific capacity of 870 C cm(-3). According to CV results, the synergistic effect on charge storage properties of the hybrid material is attributed to the enhanced electroactivity of the hexaniobate component in the LbL film. Spectroelectrochemical experiments showed that the electrochromic efficiencies at 420 nm are ca. -41 and 24 cm(2) C-1 as the potential changes from 0.8 to -0.9 V and from -0.9 to -1.8 V, respectively, whereas at 800 nm the efficiencies are ca. -55 and 8 cm(2) C-1 for the same potential ranges. The electrochromic efficiencies and multi-colour character of the LbL film of hexaniobate nanoscrolls and polyaniline indicate that this novel hybrid material is an interesting modified electrode for electrochromic devices.

Development of plurimetallic electrocatalysts prepared by decomposition of polymeric precursors for EtOH/O2 fuel cell

This work aimed to develop plurimetallic electrocatalysts composed of Pt, Ru, Ni, and Sn supported on C by decomposition of polymeric precursors (DPP), at a constant metal:carbon ratio of 40:60 wt.%, for application in direct ethanol fuel cell (DEFC). The obtained nanoparticles were physico-chemically characterized by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). XRD results revealed a face-centered cubic crystalline Pt with evidence that Ni, Ru, and Sn atoms were incorporated into the Pt structure. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry (CA) in slightly acidic medium (0.05 mol L-1 H2SO4), in the absence and presence of ethanol. Addition of Sn to PtRuNi/C catalysts significantly shifted the ethanol and CO onset potentials toward lower values, thus increasing the catalytic activity, especially for the quaternary composition Pt64Sn15Ru13Ni8/C. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed determination of acetaldehyde and acetic acid as the main reaction products. The presence of Ru in alloys promoted formation of acetic acid as the main product of ethanol oxidation. The Pt64Sn15Ru13Ni8/C catalyst displayed the best performance for DEFC.

Electrochemically prepared polypyrrole-2-carboxylic acid films: synthesis protocols and studies on biosensors

The process for obtaining polypyrrole-2-carboxylic acid (PPY-2-COOH) films in acetonitrile was investigated using cyclic voltammetry, electrochemical quartz crystal microgravimetry (EQCM), and infrared spectroscopy (FTIR). Different potential ranges were applied during cyclic voltammetry experiments with the aim of obtaining films without and with the presence of controlled amounts of water added in acetonitrile. The FTIR spectra of the films have evidenced that cations and anions from the electrolyte solution were incorporated into the PPY-2-COOH structure, with a preferential adsorption of cations. After chemically immobilizing polyphenoloxidase (tyrosinase, PPO), PPY-2-COOH/PPO films were build for amperometric detection of catechol, establishing a linear limit of concentrations ranging from 5.0 x 10-4 to 2.5 x 10-2 mol L-1.

Festkörperunterstützte Lipid-Modellmembranen auf Gold zur Rekonstitution von Membranproteinen

Festkörperunterstützte Lipid-Modellmembranen auf Goldzur Rekonstitution von Membranproteinen Ziel der Arbeit war der Aufbau von Lipid-Modellmembranen auf Goldelektroden in welchen die funktionelle Aktivität von rekonstituierten Membranproteinen über elektrochemische Methoden nachgewiesen werden kann.Im Rahmen der Arbeit wurden Lipidbilayer mit und ohne hydrophile Ethylenglykol-Spacer durch Kombination von Selbstorganisation, Langmuir-Blodgett-Kuhn-Techniken und Vesikelfusion aufgebaut. Dabei dienten Thiolipide zur Verankerung der Membranen auf der Goldelektrode und es wurden diverse Wege verfolgt, deren Ankerdichte auf dem Substrat einzustellen.Eine Studie zum Aufbau von festkörperunterstützten Lipidbilayern durch Fusion von Vesikeln auf binäre Alkanthiol-/Hydroxythiol-Monolagen mit definierter Oberflächenenergie zeigte, daß eine minimale Grenzflächenenergie (Monolayer/Wasser) existiert, unterhalb welcher die Fusion nicht mehr zu einer zusätzlichen Monolage, sondern lediglich zur Ausbildung von adsorbierten oder teilgespreiteten Vesikeln führt.Zur Charakterisierung der Membranen wurden Oberflächenplasmonenresonanz, Impedanzspektroskopie, zyklische Voltammetrie, elektrochemische reduktive Desorption, Rasterkraftmikroskopie und Kontaktwinkelmessungen herangezogen.In die Modellmembranen wurden Membranproteine (Porin, Annexin V, H+-ATPase) sowie ganze Membranfragmente (Bande 3 aus roten Blutzellen) rekonstituiert und mittels elektrochemischer Methoden auf ihre funktionelle Aktivität überprüft.

Design and development of new green catalytic methodologies for the synthesis of enantiomerically enriched molecules

The following Ph.D work was mainly focused on catalysis, as a key technology, to achieve the objectives of sustainable (green) chemistry. After introducing the concepts of sustainable (green) chemistry and an assessment of new sustainable chemical technologies, the relationship between catalysis and sustainable (green) chemistry was briefly discussed and illustrated via an analysis of some selected and relevant examples. Afterwards, as a continuation of the ongoing interest in Dr. Marco Bandini’s group on organometallic and organocatalytic processes, I addressed my efforts to the design and development of novel catalytic green methodologies for the synthesis of enantiomerically enriched molecules. In the first two projects the attention was focused on the employment of solid supports to carry out reactions that still remain a prerogative of omogeneous catalysis. Firstly, particular emphasis was addressed to the discovery of catalytic enantioselective variants of nitroaldol condensation (commonly termed Henry reaction), using a complex consisting in a polyethylene supported diamino thiopene (DATx) ligands and copper as active species. In the second project, a new class of electrochemically modified surfaces with DATx palladium complexes was presented. The DATx-graphite system proved to be efficient in promoting the Suzuki reaction. Moreover, in collaboration with Prof. Wolf at the University of British Columbia (Vancouver), cyclic voltammetry studies were reported. This study disclosed new opportunities for carbon–carbon forming processes by using heterogeneous, electrodeposited catalyst films. A straightforward metal-free catalysis allowed the exploration around the world of organocatalysis. In fact, three different and novel methodologies, using Cinchona, Guanidine and Phosphine derivatives, were envisioned in the three following projects. An interesting variant of nitroaldol condensation with simple trifluoromethyl ketones and also their application in a non-conventional activation of indolyl cores by Friedel-Crafts-functionalization, led to two novel synthetic protocols. These approaches allowed the preparation of synthetically useful trifluoromethyl derivatives bearing quaternary stereocenters. Lastly, in the sixth project the first γ-alkylation of allenoates with conjugated carbonyl compounds was envisioned. In the last part of this Ph.D thesis bases on an extra-ordinary collaboration with Prof. Balzani and Prof. Gigli, I was involved in the synthesis and characterization of a new type of heteroleptic cyclometaled-Ir(III) complexes, bearing bis-oxazolines (BOXs) as ancillary ligands. The new heteroleptic complexes were fully characterized and in order to examine the electroluminescent properties of FIrBOX(CH2), an Organic Light Emitting Device was realized.

Hyperverzweigte Polyphenylene und redoxaktive Dendrimere

Die Doktorarbeit gliedert sich in zwei Abschnitte. Das erste Kapitel beschäftigt sich mit den hyperverzweigten Polyphenylenen. Es wurden Untersuchungen des Molekulargewichts in Abhängigkeit von der Monomerkonzentration und der Reaktionszeit durchgeführt. Die synthetisierten Polymere haben große Polydispersitäten, die durch fraktioniertes Fällen herabgesetzt werden können. Die Funktionalisierung der hyperverzweigten Polyphenylene mit unterschiedlichen Methoden führt zu verschiedenen Funktionen auf der Oberfläche der Polymere. Die chlormethylierten hyperverzweigen Polymere können als Makroinitiator für den Aufbau von Kern-Schale-Systemen genutzt werden. Mit Hilfe der ATRP-Polymerisation wurde Methylmethacrylat anpolymerisiert. Als Charakterisierungsmethode zur Bestimmung des freien Volumens findet die Positronenauslöschungsspektroskopie Anwendung. Im zweiten Teil der Arbeit stehen die Synthese und Charakterisierung von redoxaktiven Dendrimeren mit Triphenylamin- bzw. Naphthalinkern im Mittelpunkt. Den Einfluß der Dendrimerhülle auf die Redoxaktivität zeigen cyclovoltammetrische Untersuchungen. Die Zunahme der dendritischen Hülle führt zu einer Abschirmung des Redoxzentrums gegen die Elektrode und damit zu einer Inhibierung des Elektronentransfers. Das spiegelt sich in der Abnahme der Geschwindigkeitskonstanten sowie in der Ausdehnung der cyclovoltammetrischen Kurve wieder. Die Funktionalisierung der Triphenylamin-Dendrimere mit Chromophoren auf der Oberfläche führt zu einer Änderung der optische Eigenschaften, die mit Hilfe von Absorptions- und Emissionsmessungen untersucht wurden.

Azobenzol- und Perylendiimid-funktionalisierte Polyphenylen-Dendrimere

Die Dissertation 'Azobenzol- und Perylendiimid-funktionalisierte Polyphenylen-Dendrimere - Synthese, Charakterisierung und Eigenschaften' gliedert sich in vier Themengebiete. Der erste Abschnitt beschäftigt sich mit der Synthese unterschiedlich dichter Dendrimere um einen Azobenzol-Kern. Einkristallstrukturen und Molekülvisualisierungen verdeutlichen die dreidimensionale Gestalt der Dendrimere. Die Dendrimere zeigen erstmalig eine Abhängigkeit des Isomerisationsverhaltens von der das Chromophor umgebenden Struktur. Der zweite Abschnitt hat Interaktionen von Chromophoren, deren Distanz und Orientierung zueinander gezielt durch einen äußeren Impuls geändert werden können, zum Thema. Die Verbindung von Azobenzol und PMI führt durch deren gegenseitige Beeinflussung zu einem Verlust der charakteristischen Eigenschaften der Chromophore. Eine Oligo-L-Lysinkette, deren Enden mit NMI und PMI funktionalisiert sind, stellt ein FRET-System dar. Distanz und Orientierung der Chromophore zueinander werden durch den mittels TFE induzierten Übergang des Peptids vom Knäuel zur Helix verändert. Der dritte Abschnitt führt die Synthese von PDI-gekernten Dendrimeren durch Substitution in der bay-Region des Chromophors ein. Die Eignenschaften der Verbindungen wurden mittels optischer Methoden und cyclovoltammetrischen Studien untersucht. Weiter wurde die Oberflächenfunktionalisierung mit Aminosäuren und Oligopeptiden zu wasserlöslichen Dendrimeren mit hoher Oberflächenladung verfolgt. Das letzte Kapitel stellt Untersuchungen zur Organisation von Polyphenylen-Dendrimeren auf HOPG vor. Es lassen sich einerseits Nanofasern formieren, andererseits können auch geordnete Mono- und Multilagen erzeugt werden.

Synthese und Strukturierung von Polymeren Halbleitern: Triphenylamine und Triazine

Zusammenfassung In der vorliegenden Arbeit konnte die neuartige Synthese von Triphyenylamin- und Triazin-Monomeren gezeigt werden. Die hergestellten Monomere konnten sowohl frei als auch lebend radikalisch polymerisiert werden, wodurch sich aus beiden Verbindungen Blockcopolymere herstellen ließen. Mittels GPC und DSC Messungen konnte die erhaltene Blockstruktur nachgewiesen werden. In Cyclovoltammetrie Messungen konnten die Elektronen-leitenden und Loch-leitenden Eigenschaften der Homopolymere nachgewiesen werden. Darüber hinaus war es mit diesen Messungen möglich, die Elektronen-leitenden und Loch-leitenden Blöcke dieser Blockcopolymere gezielt anzusprechen.Weiterhin wurden zwei neue Strukturierungsverfahren für Polymere entwickelt. In dem ersten Verfahren wurden dabei harte Siliziumstempel benutzt, so dass Strukturen im Nanometerbereich generiert werden konnten. Der gesamte Strukturierungsprozess konnte bei Raumtemperatur durchgeführt werden, was einen wesentlichen Zeitvorteil gegenüber NIL entspricht. Weiterhin wurden Linienstrukturen durch das Stempeln mit weichen Silikonstempeln hergestellt. Unabhängig ihrer Herstellungsmethode wirken diese Linienstrukturen als Orientierungsschichten für flüssigkristallines Polyfluoren, wobei die bis heute größte Fluoreszens-Anisotropie auf einem Lochleiter von 1:24 erhalten wurde. Somit sind OLEDs die polarisiertes Licht emittieren möglich.Im zweiten neuartigen Strukturierungsverfahren konnten getrennte Polymerstrukturen aus Loch- und Elektronenleitern durch Bestrahlen einer Monomermischung mit Licht erzeugt werden. Dieses Verfahren bietet den Vorteil, dass kein Material entfernt werden muss und die Strukturierung somit in einem Schritt erfolgt.

Liquid crystalline oligofluorenes and their derivatives

Homo-oligofluorenes (OFn), polyfluorenes (PF2/6) and oligofluorenes with one fluorenenone group in the center (OFnK) were synthesized. They were used as model compounds to understand of the structure-property relationships of polyfluorenes and the origin of the green emission in the photoluminescence (after photooxidation of the PFs) and the electroluminescence (EL) spectra. The electronic, electrochemical properties, thermal behavior, supramolecular self-assembly, and photophysical properties of OFn, PF2/6 and OFnK were investigated. Oligofluorenes with 2-ethylhexyl side chain (OF2-OF7) from the dimer up to the heptamer were prepared by a series of stepwise transition metal mediated Suzuki and Yamamoto coupling reactions. Polyfluorene was synthesized by Yamamoto coupling of 2,7-dibromo-9,9-bis(2-ethylhexyl)fluorene. Oligofluorenes with one fluorenone group in the center (OF3K, OF5K, OF7K) were prepared by Suzuki coupling between the monoboronic fluorenyl monomer, dimer, trimer and 2, 7-dibromofluorenone. The electrochemical and electronic properties of homo-oligofluorenes (OFn) were systematically studied by several combined techniques such as cyclic voltammetry, differential pulse voltammetry, UV-vis absorption spectroscopy, steady and time-resolved fluorescence spectroscopy. It was found that the oligofluorenes behave like classical conjugated oligomers, i.e., with the increase of the chain-length, the corresponding oxidation potential, the absorption and emission maximum, ionization potential, electron affinity, band gap and the photoluminescence lifetime displayed a very good linear relation with the reciprocal number of the fluorene units (1/n). The extrapolation of these linear relations to infinite chain length predicted the electrochemical and electronic properties of the corresponding polyfluorenes. The thermal behavior, single-crystal structure and supramolecular packing, alignment properties, and molecular dynamics of the homo-oligofluorenes (OFn) up to the polymer were studied using techniques such as TGA, DSC, WAXS, POM and DS. The OFn from tetramer to heptamer show a smectic liquid crystalline phase with clearly defined isotropization temperature. The oligomers do show a glass transition which exhibits n-1 dependence and allows extrapolation to a hypothetical glass transition of the polymer at around 64 °C. A smectic packing and helix-like conformation for the oligofluorenes from tetramer to heptamer was supported by WAXS experiments, simulation, and single-crystal structure of some oligofluorene derivatives. Oligofluorenes were aligned more easily than the corresponding polymer, and the alignability increased with the molecular length from tetramer to heptamer. The molecular dynamics in a series of oligofluorenes up to the polymer was studied using dielectric spectroscopy. The photophysical properties of OFn and PF2/6 were investigated by the steady-state spectra (UV-vis absorption and fluorescence spectra) and time-resolved fluorescence spectra both in solution and thin film. The time-resolved fluorescence spectra of the oligofluorenes were measured by streak camera and gate detection technique. The lifetime of the oligofluorenes decreased with the extension of the chain-length. No green emission was observed in CW, prompt and delayed fluorescence for oligofluorenes in m-THF and film at RT and 77K. Phosphorescence was observed for oligofluorenes in frozen dilute m-THF solution at 77K and its lifetime increased with length of oligofluorenes. A linear relation was obtained for triplet energy and singlet energy as a function of the reciprocal degree of polymerization, and the singlet-triplet energy gap (S1-T1) was found to decrease with the increase of degree of polymerization. Oligofluorenes with one fluorenone unit at the center were used as model compounds to understand the origin of the low-energy (“green”) emission band in the photoluminescence and electroluminescence spectra of polyfluorenes. Their electrochemical properties were investigated by CV, and the ionization potential (Ip) and electron affinity (Ea) were calculated from the onset of oxidation and reduction of OFnK. The photophysical properties of OFnK were studied in dilute solution and thin film by steady-state spectra and time-resolved fluorescence spectra. A strong green emission accompanied with a weak blue emission were obtained in solution and only green emission was observed on film. The strong green emission of OFnK suggested that rapid energy transfer takes place from higher energy sites (fluorene segments) to lower energy sites (fluorenone unit) prior to the radiative decay of the excited species. The fluorescence spectra of OFnK also showed solvatochromism. Monoexponential decay behaviour was observed by time-resolved fluorescence measurements. In addition, the site-selective excitation and concentration dependence of the fluorescence spectra were investigated. The ratio of green and blue emission band intensities increases with the increase of the concentration. The observed strong concentration dependence of the green emission band in solution suggests that increased interchain interactions among the fluorenone-containing oligofluorene chain enhanced the emission from the fluorenone defects at higher concentration. On the other hand, the mono-exponential decay behaviour and power dependence were not influenced significantly by the concentration. We have ruled out the possibility that the green emission band originates from aggregates or excimer formation. Energy transfer was further investigated using a model system of a polyfluorene doped by OFnK. Förster-type energy transfer took place from PF2/6 to OFnK, and the energy transfer efficiency increased with increasing of the concentration of OFnK. Efficient funneling of excitation energy from the high-energy fluorene segments to the low-energy fluorenone defects results from energy migration by hopping of excitations along a single polymer chain until they are trapped on the fluorenone defects on that chain or transferred onto neighbouring chains by Förster-type interchain energy transfer process. These results imply that the red-shifted emission in polyfluorenes can originate from (usually undesirable) keto groups at the bridging carbon atoms-especially if the samples have been subject to photo- or electro-oxidation or if fluorenone units are present due to an improper purification of the monomers prior to polymerization.

Synthesis and characterization of novel poly(imino ketone)s via palladium-catalyzed aryl amination

The challenge of the present work was to synthesize and to characterize new classes of N-containing polymers via palladium-catalyzed aryl amination. This work was inspired by a desire to combine the properties of high-performance polymers such as PEKs with those of N-containing conductive polymers such as polyaniline (PANI), poly(aromatic amides) (PAAs), and the ready synthesis of N-containing simple aromatic compound by the Buchwald-Hartwig reaction. Careful investigation of a model reaction was carried out to provide insights into the formation of side products which will have a negative effect upon the molecular weight or upon the materials properties of the desired polymers in the polycondensation reaction. In this thesis, five new different polymer classes namely, poly(imino ketone)s (PIKs), poly(imino acridine)s (PIAcs), poly(imino azobenzene)s (PIAzos), poly(imino fluorenone)s (PIFOs), and poly(imino carbazole)s (PICs) were synthesized and fully characterized by means of 1H-NMR, elemental analysis, UV, FT-IR, X-ray, GPC, TGA, DSC, DMA, and dielectric spectroscopy. To optimize the polycondensation process, the influence of the concentration, temperature, ligands and the reactivity of the halogen containing monomers were investigated. A temperature of 100-165 °C and a concentration of 30-36 % were found to be optimal for the palladium-catalyzed polycondensation to produce polymer with high molecular weight (Mn = 85 900, Mw = 474 500, DP = 126). Four different ligands were used successfully in the Pd-catalyzed process, of which the Pd/BINAP system was found to be the most effective catalyst, producing the highest yield and highest molecular weight polymers. It was found that the reactivity decreases strongly with increasing electronegativity of the halogen atoms, for example better yields, and higher molecular weights were obtained by using dibromo compounds than dichloro compounds while difluoro compounds were totally unreactive. Polymer analogous transformations, such as the protonation reaction of the ring nitrogens in PIAcs, or of the azobenzene groups of PIAzos, the photo and thermal cis-trans-isomerization of PIAzos, and of poly(imino alcohol)s were also studied. The values of the dielectric constants of PIKs at 1 MHz were in the range 2.71-3.08. These low values of the dielectric constant are lower than that of "H Film", a polyimide Kapton film which is one of the most preferred high-performance dielectrics in microelectronic applications having a dielectric constant of 3.5. In addition to the low values of the dielectric constants, PIKs have lower and glass transition temperatures (Tgs) than arimides such as Kapton which may make them more easily processable. Cyclic voltammetry showed that PICs exhibited low oxidation and reduction potentials and their values were shifted to low values with increasing degree of polymerization i.e. with increasing of the carbazole content in backbone of PICs (PIC-7, 0.44, 0.33 V, DP= 37, PIC-5, 0.63, 0.46, DP= 16, respectively).

Electronic energy transfer processes in pi-conjugated polymers

Currently pi-conjugated polymers are considered as technologically interesting materials to be used as functional building elements for the development of the new generation of optoelectronic devices. More specifically during the last few years, poly-p-phenylene materials have attracted considerable attention for their blue photoluminescence properties. This Thesis deals with the optical properties of the most representative blue light poly-p-phenylene emitters such as poly(fluorene), oligo(fluorene), poly(indenofluorene) and ladder-type penta(phenylene) derivatives. In the present work, laser induced photoluminescence spectroscopy is used as a major tool for the study of the interdependence between the dynamics of the probed photoluminescence, the molecular structures of the prepared polymeric films and the presence of chemical defects. Complementary results obtained by two-dimensional wide-angle X-ray diffraction are reported. These findings show that the different optical properties observed are influenced by the intermolecular solid-state interactions that in turn are controlled by the pendant groups of the polymer backbone. A significant feedback is delivered regarding the positive impact of a new synthetic route for the preparation of a poly(indenofluorene) derivative on the spectral purity of the compound. The energy transfer mechanisms that operate in the studied systems are addressed by doping experiments. After the evaluation of the structure/property interdependence, a new optical excitation pathway is presented. An efficient photon low-energy up-conversion that sensitises the blue emission of poly(fluorene) is demonstrated. The observed phenomenon takes place in poly(fluorene) derivatives hosts doped with metallated octaethyl porphyrins, after quasi-CW photoexcitation of intensities in the order of kW/cm2. The up-conversion process is parameterised in terms of temperature, wavelength excitation and central metal cation in the porphyrin ring. Additionally the observation of the up-conversion is extended in a broad range of poly-p-phenylene blue light emitting hosts. The dependence of the detected up-conversion intensity on the excitation intensity and doping concentration is reported. Furthermore the dynamics of the up-conversion intensity are monitored as a function of the doping concentration. These experimental results strongly suggest the existence of triplet-triplet annihilation events into the porphyrin molecules that are subsequently followed by energy transfer to the host. After confirming the occurrence of the up-conversion in solutions, cyclic voltammetry is used in order to show that the up-conversion efficiency is partially determined from the energetic alignment between the HOMO levels of the host and the dopant.

Der Einsatz elektrochemischer Methoden für die Untersuchung superschwerer Elemente

Das Hauptziel der vorliegenden Arbeit war die Entwicklung eines Experimentaufbaus für die elektrochemische Abscheidung von Transactiniden mit anschließender Detektion. Zu diesem Zweck wurden Experimente mit den Homologen dieser Elemente durchgeführt. Die Elektrodeposition von Tracermengen an Fremdelektroden führt zu einer Elektrodenbedeckung von weniger als einer Monolage. Die erforderlichen Abscheidepotentiale sind häufig positiver, als nach der Nernst’schen Gleichung zu erwarten ist. Dieses Phänomen nennt man Unterpotentialabscheidung. In zahlreichen Versuchen mit Radiotracern wurde die Abscheideausbeute als Funktion des Elektrodenpotentials bestimmt, wobei abzuscheidendes Ion, Elektrodenmaterial und Elektrolyt variiert wurden. Es wurden kritische Potentiale, bei denen eine nennenswerte Abscheidung gerade begann, ermittelt sowie Potentiale für die Abscheidung von 50 % der in der Lösung befindlichen Atome. Diese Werte wurden mit theoretisch vorhergesagten Potentialen und Werten aus der Literatur verglichen. Die Abscheidung von Pb als Homologem von Element 114 funktionierte sehr gut an Elektroden aus Palladium oder palladinierten Nickelelektroden unter Verwendung von 0,1 M HCl als Elektrolyt. Zur Charakterisierung der Unterpotentialabscheidung wurde neben der Radiotracer-Methode auch die Cyclovoltammetrie eingesetzt. Hier findet die Abscheidung der ersten Monolage auf der Elektrode ebenfalls häufig bei positiveren Potentialen statt, als die der Hauptmenge. Die mit beiden Methoden ermittelten Werte wurden einander gegenübergestellt. Die Elektrodeposition von kurzlebigen Isotopen muss sehr schnell erfolgen. Es konnte gezeigt werden, dass eine hohe Temperatur und damit verbunden eine niedrige Viskosität des Elektrolyten die Abscheidung beschleunigt. Ebenfalls wichtig ist ein gutes Rühren der Lösung, um eine kleine Nernst’sche Diffusionsschichtdicke zu erzielen. Das Verhältnis von Elektrodenfläche zu Elektrolytvolumen muss möglichst groß sein. Auf der Grundlage dieser Ergebnisse wurde eine für schnelle Elektrolysen optimierte Elektrolysezelle entwickelt. Unter Einsatz dieser Zelle wurden die Abscheidegeschwindigkeiten für verschiedene Ionen- und Elektrodenkombinationen gemessen. Es wurden Experimente zur Kopplung von Gasjet und Elektrolysezelle durchgeführt, dabei wurde sowohl mit am Reaktor erzeugten Spaltprodukten, mit Pb-Isotopen aus einer emanierenden Quelle und mit am Beschleuniger erzeugten Isotopen gearbeitet. Mit den dort gewonnenen Erkenntnissen wurde ein Experimentaufbau für die kontinuierliche Abscheidung und Detektion von kurzlebigen Isotopen realisiert. Am Beschleuniger wurden u. a. kurzlebige Hg- und Pb-Isotope erzeugt und mit einem Gasjet aus der Targetkammer zum ALOHA-System transportiert. Dort wurden sie in einem quasi-kontinuierlichen Prozess in die wässrige Phase überführt und zu einer Elektrolyszelle transportiert. In dieser erfolgte die Elektrodeposition auf eine bandförmige Elektrode aus Nickel oder palladiniertem Nickel. Nach der Abscheidung wurde das Band zu einer Detektorphalanx gezogen, wo der -Zerfall der neutronenarmen Isotope registriert wurde. Es wurden charakteristische Größen wie die Abscheidegeschwindigkeit und die Gesamtausbeute der Elektrolyse ermittelt. Das System wurde im Dauerbetrieb getestet. Es konnte gezeigt werden, dass der gewählte Aufbau prinzipiell für die Abscheidung von kurzlebigen, am Beschleuniger erzeugten Isotopen geeignet ist. Damit ist eine wichtige Voraussetzung für den zukünftigen Einsatz der Methode zum Studium der chemischen Eigenschaften der superschweren Elemente geschaffen.