Supramolecular order and dynamics of discotic materials studied by solid-state NMR recoupling methods

The topic of this thesis is the investigation of structure,order and dynamics in discotic mesogens by advancedsolid-state NMR spectroscopy. Most of the discotic mesogensunder investigation are hexa-peri-hexabenzocoronene (HBC)derivatives which are of particular interest for potentialdevice applications due to their high one-dimensional chargecarrier mobilities. The supramolecular stacking arrangement of the discoticcores was investigated by 2D 1H-1H double-quantum (DQ)methods, which were modified by incorporating the WATERGATEsuppression technique into the experiments in order toovercome severe phase problems arising from the strongsignal of the long alkyl sidechains. Molecular dynamics and sample orientation was probed throughthe generation of sideband patterns by reconversion rotorencoding in 2D recoupling experiments. These experimentswere extended by new recoupling schemes to enable thedistinction of motion and orientation effects. The solid-state NMR studies presented in this work aim tothe understanding of structure-property relationships in theinvestigated discotic materials, while the experimentsapplied to these materials include new recoupling schemeswhich make the desired information on molecular orientationand dynamics accessible without isotope labelling.

Optimised polyolefin branch quantification by 13 C NMR spectroscopy

Quantitative branch determination in polyolefins by solid- and melt-state 13C NMR has been investigated. Both methods were optimised toward sensitivity per unit time. While solid-state NMR was shown to give quick albeit only qualitative results, melt-state NMR allowed highly time efficient accurate branch quantification. Comparison of spectra obtained using spectrometers operating at 300, 500 and 700 MHz 1H Larmor frequency, with 4 and 7~mm MAS probeheads, showed that the best sensitivity was achieved at 500 MHz using a 7 mm 13C-1H optimised high temperature probehead. For materials available in large quantities, static melt-state NMR, using large diameter detection coils and high coil filling at 300 MHz, was shown to produce comparable results to melt-state MAS measurements in less time. While the use of J-coupling mediated polarisation transfer techniques was shown to be possible, direct polarisation via single-pulse excitation proved to be more suitable for branch quantification in the melt-state. Artificial line broadening, introduced by FID truncation, was able to be reduced by the use of π pulse-train heteronuclear dipolar decoupling. This decoupling method, when combined with an extended duty-cycle, allowed for significant improvement in resolution. Standard setup, processing and analysis techniques were developed to minimise systematic errors contributing to the measured branch contents. The final optimised melt-state MAS NMR method was shown to allow time efficient quantification of comonomer content and distribution in both polyethylene- and polypropylene-co-α-olefins. The sensitivity of the technique was demonstrated by quantifying branch concentrations of 8 branches per 100,000 CH2 for an industrial ‘linear’ polyethylene in only 13 hours. Even lower degrees of 3–8 long-chain branches per 100,000 carbons were able to be estimated in just 24 hours for a series of γ-irradiated polypropylene homopolymers.

NMR spectroscopy and imaging of hyperpolarized gases

Since the discovery of the nuclear magnetic resonance (NMR) phenomenon, countless NMR techniques have been developed that are today indispensable tools in physics, chemistry, biology, and medicine. As one of the main obstacles in NMR is its notorious lack of sensitivity, different hyperpolarization (HP) methods have been established to increase signals up to several orders of magnitude. In this work, different aspects of magnetic resonance, using HP noble gases, are studied, hereby combining different disciplines of research. The first part examines new fundamental effects in NMR of HP gases, in theory and experiment. The spin echo phenomenon, which provides the basis of numerous modern experiments, is studied in detail in the gas phase. The changes of the echo signal in terms of amplitude, shape, and position, due to the fast translational motion, are described by an extension of the existing theory and computer simulations. With this knowledge as a prerequisite, the detection of intermolecular double-quantum coherences was accomplished for the first time in the gas phase. The second part of this thesis focuses on the development of a practical method to enhance the dissolution process of HP 129Xe, without loss of polarization or shortening of T1. Two different setups for application in NMR spectroscopy and magnetic resonance imaging (MRI) are presented. The continuous operation allows biological and multidimensional spectroscopy in solutions. Also, first in vitro MRI images with dissolved HP 129Xe as contrast agent were obtained at a clinical scanner.

Influence of spatial constraints in non-crystalline regions on the polymer dynamics in semi-crystalline polyethylene: a solid state NMR study

A broad variety of solid state NMR techniques were used to investigate the chain dynamics in several polyethylene (PE) samples, including ultrahigh molecular weight PEs (UHMW-PEs) and low molecular weight PEs (LMW-PEs). Via changing the processing history, i.e. melt/solution crystallization and drawing processes, these samples gain different morphologies, leading to different molecular dynamics. Due to the long chain nature, the molecular dynamics of polyethylene can be distinguished in local fluctuation and long range motion. With the help of NMR these different kinds of molecular dynamics can be monitored separately. In this work the local chain dynamics in non-crystalline regions of polyethylene samples was investigated via measuring 1H-13C heteronuclear dipolar coupling and 13C chemical shift anisotropy (CSA). By analyzing the motionally averaged 1H-13C heteronuclear dipolar coupling and 13C CSA, the information about the local anisotropy and geometry of motion was obtained. Taking advantage of the big difference of the 13C T1 relaxation time in crystalline and non-crystalline regions of PEs, the 1D 13C MAS exchange experiment was used to investigate the cooperative chain motion between these regions. The different chain organizations in non-crystalline regions were used to explain the relationship between the local fluctuation and the long range motion of the samples. In a simple manner the cooperative chain motion between crystalline and non-crystalline regions of PE results in the experimentally observed diffusive behavior of PE chain. The morphological influences on the diffusion motion have been discussed. The morphological factors include lamellar thickness, chain organization in non-crystalline regions and chain entanglements. Thermodynamics of the diffusion motion in melt and solution crystallized UHMW-PEs is discussed, revealing entropy-controlled features of the chain diffusion in PE. This thermodynamic consideration explains the counterintuitive relationship between the local fluctuation and the long range motion of the samples. Using the chain diffusion coefficient, the rates of jump motion in crystals of the melt crystallized PE have been calculated. A concept of "effective" jump motion has been proposed to explain the difference between the values derived from the chain diffusion coefficients and those in literatures. The observations of this thesis give a clear demonstration of the strong relationship between the sample morphology and chain dynamics. The sample morphologies governed by the processing history lead to different spatial constraints for the molecular chains, leading to different features of the local and long range chain dynamics. The knowledge of the morphological influence on the microscopic chain motion has many implications in our understanding of the alpha-relaxation process in PE and the related phenomena such as crystal thickening, drawability of PE, the easy creep of PE fiber, etc.

Supramolecular order and dynamics of functional materials studied by solid state NMR

The goal of this thesis was the investigation of the structure, conformation, supramolecular order and molecular dynamics of different classes of functional materials (phthalocyanine, perylene and hexa-peri-hexabenzocoronene derivatives and mixtures of those), all having planar aromatic cores modified with various types of alkyl chains. The planar aromatic systems are known to stack in the solid and the liquid-crystalline state due to p-p interactions forming columnar superstructures with high one-dimensional charge carrier mobility and potential application in photovoltaic devices. The different functionalities attached to the aromatic cores significantly influence the behavior of these systems allowing the experimentalists to modify the structures to fine-tune the desired thermotropic properties or charge carrier mobility. The aim of the presented studies was to understand the interplay between the driving forces causing self-assembly by relating the structural and dynamic information about the investigated systems. The supramolecular organization is investigated by applying 1H solid state NMR recoupling techniques. The results are related with DSC and X-ray scattering data. Detailed information about the site-specific molecular dynamics is gained by recording spinning sideband patterns using 1H-1H and 13C-1H solid state NMR recoupling techniques. The determined dipole-dipole coupling constants are then related with the coupling constants of the respective rigid pairs, thus providing local dynamic order parameters for the respective moieties. The investigations presented reveal that in the crystalline state the preferred arrangement in the columnar stack of discotic molecules modified with alkyl chains is tilted. This leads to characteristic differences in the 1H chemical shifts of otherwise chemically equivalent protons. Introducing branches and increasing the length of the alkyl chains results in lower mesophase transitions and disordered columnar stacks. In the liquid-crystalline state some of the discs lose the tilted orientation, others do not, but all start a rapid rotation about the columnar axis.

NMR studies on supramolecular aggregates in solution and the solid state

The aim of this work presented here is the characterization of structure and dynamics of different types of supramolecular systems by advanced NMR spectroscopy. One of the characteristic features of NMR spectroscopy is based on its high selectivity. Thus, it is desirable to exploit this technique for studying structure and dynamics of large supramolecular systems without isotopic enrichment. The observed resonance frequencies are not only isotope specific but also influenced by local fields, in particular by the distribution of electron density around the investigated nucleus. Barbituric acid are well known for forming strongly hydrogen-bonded complexes with variety of adenine derivatives. The prototropic tautomerism of this material facilitates an adjustment to complementary bases containing a DDA(A = hydrogen bond acceptor site, D = hydrogen bond donor site) or ADA sequences, thereby yielding strongly hydrogen-bonded complexes. In this contribution solid-state structures of the enolizable chromophor "1-n-butyl-5-(4-nitrophenyl)-barbituric acid" that features adjustable hydrogen-bonding properties and the molecular assemblies with three different strength of bases (Proton sponge, adenine mimetic 2,6-diaminopyridine (DAP) and 2,6-diacetamidopyridine (DAC)) are studied. Diffusion NMR spectroscopy gives information over such interactions and has become the method of choice for measuring the diffusion coefficient, thereby reflecting the effective size and shape of a molecular species. In this work the investigation of supramolecular aggregates in solution state by means of DOSY NMR techniques are performed. The underlying principles of DOSY NMR experiment are discussed briefly and more importantly two applications demonstrating the potential of this method are focused on. Calix[n]arenes have gained a rather prominent position, both as host materials and as platforms to design specific receptors. In this respect, several different capsular contents of tetra urea calix[4]arenes (benzene, benzene-d6, 1-fluorobenzene, 1-fluorobenzene-d5, 1,4-difluorobenzene, and cobaltocenium) are studied by solid state NMR spectroscopy. In the solid state, the study of the interaction between tetra urea calix[4]arenes and guest is simplified by the fact that the guests molecule remains complexed and positioned within the cavity, thus allowing a more direct investigation of the host-guest interactions.

Assemblaggio e caratterizzazione delle prestazioni di un nuovo rilassometro nmr con bobina a radiofrequenza di 8 cm di diametro

Lo scopo di questa tesi è l'installazione di un Rilassometro ottenuto a partire da un magnete permanente situato nel Dipartimento di Fisica e Astronomia (DIFA - via Irnerio, 46), al fine di eseguire misure attendibili di Rilassometria in mezzi porosi su campioni del diametro di alcuni centimetri. Attualmente nel Dipartimento è gia presente un elettromagnete adibito a misure di questo tipo; tuttavia, questo strumento permette lo studio di campioni di piccole dimensioni (circa 220mm3) e si rivela insuffciente per lo studio di rocce, coralli e altre strutture porose di più grande dimensione senza la frantumazione del campione stesso; per questa ragione si è presentata la necessità dell'istallazione di una nuova strumentazione. Parte della strumentazione utilizzata è in disuso da parecchi anni e le caratteristiche devono essere verificate. Dopo l'assemblaggio della strumentazione (magnete, console, probe), sono state determinate le migliori condizioni in cui effettuare le misure, ovvero i parametri fondamentali dell'elettronica (frequenza di risonanza, TATT, tempo morto del probe, tempo di applicazione dell'impulso 90°) e la zona di maggiore uniformità del campo magnetico. Quindi, sono state effettuate misure di T1 e T2 su campioni bulk e su un campione di roccia saturata d'acqua, confrontando i risultati con valori di riferimento ottenuti tramite elettromagnete. I risultati ottenuti risultano consistenti con i valori attesi, con scarti - inevitabili a causa della grande differenza di volume dei campioni - molto ridotti, pertanto l'installazione del nuovo Rilassometro risulta essere completata con successo.

13C NMR of a single molecule magnet: analysis of pseudocontact shifts and residual dipolar couplings

Paramagnetic triple decker complexes of lanthanides are promising Single Molecule Magnets (SMMs), with many potential uses. Some of them show preferable relaxation behavior, which enables the recording of well resolved NMR spectra. These axially symmetric complexes are also strongly magnetically anisotropic, and this property can be described with the axial component of the magnetic susceptibility tensor, χa. For triple decker complexes with phthalocyanine based ligands, the Fermi˗contact contribution is small. Hence, together with the axial symmetry, the experimental chemical shifts in 1H and 13C NMR spectra can be modeled easily by considering pseudocontact and orbital shifts alone. This results in the determination of the χa value, which is also responsible for molecular alignment and consequently for the observation of residual dipolar couplings (RDCs). A detailed analysis of the experimental 1H-13C and 1H-1H couplings revealed that contributions from RDCs (positive and negative) and from dynamic frequency shifts (negative for all observed couplings) have to be considered. Whilst the pseudocontact shifts depend on the average positions of 1H and 13C nuclei relative to the lanthanide ions, the RDCs are related to the mobility of nuclei they correspond to. This phenomenon allows for the measurement of the internal mobility of the various groups in the SMMs.

Structural transformations related to organic solid-state reactions: correlation studies of NMR and X-ray analysis

Eine zielgerichtete Steuerung und Durchführung von organischen Festkörperreaktionen wird unter anderem durch genaue Kenntnis von Packungseffekten ermöglicht. Im Rahmen dieser Arbeit konnte durch den kombinierten Einsatz von Einkristallröntgenanalyse und hochauf-lösender Festkörper-NMR an ausgewählten Beispielen ein tieferes Verständnis und Einblicke in die Reaktionsmechanismen von organischen Festkörperreaktionen auf molekularer Ebene gewonnen werden. So konnten bei der topotaktischen [2+2] Photodimerisierung von Zimt-säure Intermediate isoliert und strukturell charakterisiert werden. Insbesondere anhand statischer Deuteronen- und 13C-CPMAS NMR Spektren konnten eindeutig dynamische Wasserstoffbrücken nachgewiesen werden, die transient die Zentrosymmetrie des Reaktions-produkts aufheben. Ein weiterer Nachweis gelang daraufhin mittels Hochtemperatur-Röntgen-untersuchung, sodass der scheinbare Widerspruch von NMR- und Röntgenuntersuchungen gelöst werden konnte. Eine Veresterung der Zimtsäure entfernt diese Wasserstoffbrücken und erhält somit die Zentrosymmetrie des Photodimers. Weiterhin werden Ansätze zur Strukturkontrolle in Festkörpern basierend auf der molekularen Erkennung des Hydroxyl-Pyridin (OH-N) Heterosynthon in Co-Kristallen beschrieben, wobei vor allem die Stabilität des Synthons in Gegenwart funktioneller Gruppen mit Möglichkeit zu kompetetiver Wasserstoffbrückenbildung festgestellt wurde. Durch Erweiterung dieses Ansatzes wurde die molekulare Spezifität des Hydroxyl-Pyridin (OH-N) Heterosynthons bei gleichzeitiger Co-Kristallisation mit mehreren Komponenten erfolgreich aufgezeigt. Am Beispiel der Co-Kristallisation von trans--1,2-bis(4-pyridyl)ethylen (bpe) mit Resorcinol (res) in Gegenwart von trans-1,2-bis(4-pyridyl)ethan (bpet) konnten Zwischenprodukte der Fest-körperreaktionen und neuartige Polymorphe isoliert werden, wobei eine lückenlose Aufklärung des Reaktionswegs mittels Röntgenanalyse gelang. Dabei zeigte sich, dass das Templat Resorcinol aus den Zielverbindungen entfernbar ist. Ferner gelang die Durchführung einer seltenen, nicht-idealen Einkristall-Einkristall-Umlagerung von trans--1,2-bis(4-pyridyl)ethylen (bpe) mit Resorcinol (res). In allen Fällen konnten die Fragen zur Struktur und Dynamik der untersuchten Verbindungen nur durch gemeinsame Nutzung von Röntgenanalyse und NMR-Spektroskopie bei vergleichbaren Temperaturen eindeutig und umfassend geklärt werden.

Structure, organization and dynamics of functional supramolecular materials studied by solid-state NMR

Functional materials have great importance due to their many important applications. The characterization of supramolecular architectures which are held together by non-covalent interactions is of most importance to understand their properties. Solid-state NMR methods have recently been proven to be able to unravel such structure-property relations with the help of fast magic-angle spinning and advanced pulse sequences. The aim of the current work is to understand the structure and dynamics of functional supramolecular materials which are potentially important for fuel-cell (proton conducting membrane materials) and solar-cell or plastic-electronic applications (photo-reactive aromatic materials). In particular, hydrogen-bonding networks, local proton mobility, molecular packing arrangements, and local dynamics will be studied by the use of advanced solid-state NMR methods. The first class of materials studied in this work is proton conducting polymers which also form hydrogen-bonding network. Different materials, which are prepared for high 1H conduction by different approaches are studied: PAA-P4VP, PVPA-ABPBI, Tz5Si, and Triazole-functional systems. The materials are examples of the following major groups; - Homopolymers with specific functional groups (Triazole functional polysiloxanes). - Acid-base polymer blends approach (PAA-P4VP, PVPA-ABPBI). - Acid-base copolymer approach (Triazole-PVPA). - Acid doped polymers (Triazole functional polymer doped with H3PO4). Perylenebisimide (PBI) derivatives, a second type of important functional supramolecular materials with potent applications in plastic electronics, were also investigated by means of solid-state NMR. The preparation of conducting nanoscopic fibers based on the self-assembling functional units is an appealing aim as they may be incorporated in molecular electronic devices. In this category, perylene derivatives have attracted great attention due to their high charge carrier mobility. A detailed knowledge about their supramolecular structure and molecular dynamics is crucial for the understanding of their electronic properties. The aim is to understand the structure, dynamics and packing arrangements which lead to high electron conductivity in PBI derivatives.

Solid-state NMR investigation of phosphonic acid based proton conducting materials

In this work, new promising proton conducting fuel cell membrane materials were characterized in terms of their structure and dynamic properties using solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction. Structurally different, phosphonic acid (PA) containing materials were systematically evaluated for possible high-temperature operation (e.g. at T>100°C). Notably, 1H, 2H and 31P magic angle spinning (MAS) NMR provided insight into local connectivities and dynamics of the hydrogen bonded network, while packing arrangements were identified by means of heteronuclear dipolar recoupling techniques.rnThe first part of this work introduced rather crystalline, low molecular weight ionomers for proton conducting membranes, where six different geometries such as line, triangle, screw, tetrahedron, square and hexagon, were investigated. The hexagon was identified as the most promising geometry with high-temperature bulk proton conductivities in the range of 10-3 Scm-1 at a relative humidity of 50%. However, 2H NMR and TGA-MS data suggest that the bulk proton transport is mainly due to the presence of crystal water. Single crystal X-ray data revealed that in the tetrahedron phosphonic acids form tetrameric clusters isolating the mobile protons while the phosphonic acids in the hexagon form zigzag-type pathways through the sample.rnThe second part of this work demonstrates how acid-base pairing and the choice of appropriate spacers may influence proton conduction. Different ratios of statistical copolymers of poly (vinylphosphonic acid) and poly (4-vinylpyridine) were measured to derive information about the local structure and chemical changes. Though anhydrous proton conductivities of all statistical copolymers are rather poor, the conductivity increases to 10-2 S cm-1 when exposing the sample to relative humidity of 80%. In contrast to PVPA, anhydride formation of phosphonic acids in the copolymer is not reversible even when exposing the sample to a relative humidity of 100%.rnIn addition, the influence of both spacers and degree of backbone crystallinity on bulk proton conductivity was investigated. Unlike in systems such as poly benzimidazole (PBI), spacers were inserted between the protogenic groups along the backbone. It was found that dilution of the protogenic groups decreases the conductivity, but compared to PVPA, similar apparent activation energies for local motions were obtained from both variable temperature 1H NMR and impedance spectroscopy data. These observations suggest the formation of phosphonic acid clusters with high degrees of local proton motion, where only a fraction of motions contribute to the observable bulk proton conductivity. Additionally, it was shown that gradual changes of the spacer length lead to different morphologies.rnIn summary, applying advanced solid-state NMR and X-ray analysis, structural and dynamic phenomena in proton conducting materials were identified on a molecular level. The results were discussed with respect to different proton conduction mechanisms and may contribute to a more rational design or improvement of proton conducting membranes.rn

Solid-state NMR on columnar supramolecular structures

The present work deals with the characterisation of three columnar self-assembled systems, that is, benzene-1,3,5-tricarboxamides, a peripherally thioalkyl-substituted phthalocyanine, and several oligo-(p-phenylenevinylene)s. In order to probe the supramolecular organisation solid-state NMR has been used as the main technique, supported by X-ray measurements, theoretical methods, and thermal analysis. rnrnBenzene-1,3,5-tricarboxamides (BTAs) turned out to be well suited model compounds to study various fundamental supramolecular interactions, such as π-π-interactions, hydrogen bonding, as well as dynamic and steric effects of attached side chains. Six BTAs have been investigated in total, five with a CO-centred amide group bearing different side chains and one with an inverted N-centred amide group. The physical properties of these BTAs have been investigated as a function of temperature. The results indicated that in case of the CO-centred BTAs the stability of the columnar mesophase depends strongly on the nature of the side chains. Further experiments revealed a coplanar orientation of adjacent BTA molecules in the columnar assembly of CO-centred BTAs, whereas the N-centred BTA, showed a deviating not fully coplanar arrangement. These differences were ascribed to distinct hydrogen bonding schemes, involving a parallel alignment of hydrogen bonds in case of CO-centred BTAs and an antiparallel alignment in case of the N-centred counterpart.rnrn The fundamental insights of the supramolecular organisation of BTAs could be partially adapted to an octa-substituted phthalocyanine with thiododecyl moieties. Solid-state NMR in combination with chemical shift calculations determined a tilted herringbone arrangement of phthalocyanine rings in the crystalline phase as well as in the mesophase. Moreover, 1H NMR measurements in the mesophase of this compound suggested an axial rotation of molecules, which is inhibited in the crystalline phase.rnrnAs a third task, the supramolecular assembly of oligo-(p-phenylenevinylene)s of varying length and with different polar head groups have been investigated by a combined X-ray and solid-state NMR study. The results revealed a columnar structure formation of these compounds, being promoted by phase separation of alkyl side chains and aromatic rigid rods. In this system solid-state NMR yielded meaningful insight into the isotropisation process of butoxy and 2-S-methylbutoxy substituted oligo-(p-phenylenevinylene) rods.rn

Sensitivity enhancement in NMR by using parahydrogen induced polarization

Enhancing the sensitivity of nuclear magnetic resonance measurements via hyperpolarization techniques like parahydrogen induced polarization (PHIP) is of high interest for spectroscopic investigations. Parahydrogen induced polarization is a chemical method, which makes use of the correlation between nuclear spins in parahydrogen to create hyperpolarized molecules. The key feature of this technique is the pairwise and simultaneous transfer of the two hydrogen atoms of parahydrogen to a double or triple bond resulting in a population of the Zeeman energy levels different from the Boltzmann equation. The obtained hyperpolarization results in antiphase peaks in the NMR spectrum with high intensities. Due to these strong NMR signals, this method finds arnlot of applications in chemistry e.g. the characterization of short-lived reaction intermediates. Also in medicine it opens up the possibility to boost the sensitivity of medical diagnostics via magnetic labeling of active contrast agents. Thus, further examination and optimization of the PHIP technique is of significant importance in order to achieve the highest possible sensitivity gain.rnrnIn this work, different aspects concerning PHIP were studied with respect to its chemical and spectroscopic background. The first part of this work mainly focused on optimizing the PHIP technique by investigating different catalyst systems and developing new setups for the parahydrogenation. Further examinations facilitated the transfer of the generated polarization from the protons to heteronuclei like 13C. The second part of this thesis examined the possibility to transfer these results to different biologically active compounds to enable their later application in medical diagnostics. Onerngroup of interesting substances is represented by metabolites or neurotransmitters in mammalian cells. Other interesting substances are clinically relevant drugs like a barbituric acid derivative or antidepressant drugs like citalopram which were investigated with regard to their applicability for the PHIP technique and the possibility to achievernpolarization transfer to 13C nuclei. The last investigated substrate is a polymerizable monomer whose polymer was used as a blood plasma expander for trauma victims after the first half of the 20th century. In this case, the utility of the monomer for the PHIP technique as a basis for later investigations of a polymerization reaction using hyperpolarized monomers was examined.rnrnHence, this thesis covers the optimization of the PHIP technology, hereby combining different fields of research like chemical and spectroscopical aspects, and transfers the results to applications of real biologally acitve compounds.

Interplay of pi–pi stacking and hydrogen bonding in conjugated supramolecular systems studied by solid-state NMR

In this work supramolecular organic systems based on rigid pi-conjugated building blocks and flexible side chains were studied via solid-state NMR spectroscopy. Specifically, these studies focussed on phenylene ethynylene based macrocycles, polymer systems including polythiophenes, and rod-coil copolymers of oligo(p-benzamide) and poly(ethylene glycol). All systems were studied in terms of the local order and mobility. The central topic of this dissertation was to elucidate the role of the flexible side chains in interplay of different non-covalent interactions, like pi-pi-stacking and hydrogen bonding.Combining the results of this work, it can be concluded that the ratio of the rigid block and the attached alkyl side chains can be crucial for the design of an ordered pi-conjugated supramolecular system. Through alkyl side chains, it is also possible to introduce liquid-crystalline phases in the system, which can foster the local order of the system. Moreover in the studied system longer, unbranched alkyl side chains are better suited to stabilize the corresponding aggregation than shorter, branched ones.The combination of non-covalent interactions such as pi-pi-stacking and hydrogen bonding play an important role for structure formation. However, the effect of pi-pi-stacking interaction is much weaker than the effect of hydrogen bonding and is only observed in systems with a suitable local order. Hence, they are often not strong enough to control the local order. In contrast, hydrogen bonds predominantly influence the structural organization and packing. In comparison the size of the alkyl side chains is only of minor importance. The suppression of certain hydrogen bonds can lead to completely different structures and can induce a specific aggregation behavior. Thus, for the design of a supramolecular ordered system the presence of hydrogen bonding efficiently stabilizes the corresponding structure, but the ratio of hydrogen bond forming groups should be kept low to be able to influence the structure selectively.

Investigation of the lithium ion mobility in cyclic model compounds and their ion conducting properties

Efficient energy storage and conversion is playing a key role in overcoming the present and future challenges in energy supply. Batteries provide portable, electrochemical storage of green energy sources and potentially allow for a reduction of the dependence on fossil fuels, which is of great importance with respect to the issue of global warming. In view of both, energy density and energy drain, rechargeable lithium ion batteries outperform other present accumulator systems. However, despite great efforts over the last decades, the ideal electrolyte in terms of key characteristics such as capacity, cycle life, and most important reliable safety, has not yet been identified. rnrnSteps ahead in lithium ion battery technology require a fundamental understanding of lithium ion transport, salt association, and ion solvation within the electrolyte. Indeed, well-defined model compounds allow for systematic studies of molecular ion transport. Thus, in the present work, based on the concept of ‘immobilizing’ ion solvents, three main series with a cyclotriphosphazene (CTP), hexaphenylbenzene (HBP), and tetramethylcyclotetrasiloxane (TMS) scaffold were prepared. Lithium ion solvents, among others ethylene carbonate (EC), which has proven to fulfill together with pro-pylene carbonate safety and market concerns in commercial lithium ion batteries, were attached to the different cores via alkyl spacers of variable length.rnrnAll model compounds were fully characterized, pure and thermally stable up to at least 235 °C, covering the requested broad range of glass transition temperatures from -78.1 °C up to +6.2 °C. While the CTP models tend to rearrange at elevated temperatures over time, which questions the general stability of alkoxide related (poly)phosphazenes, both, the HPB and CTP based models show no evidence of core stacking. In particular the CTP derivatives represent good solvents for various lithium salts, exhibiting no significant differences in the ionic conductivity σ_dc and thus indicating comparable salt dissociation and rather independent motion of cations and ions.rnrnIn general, temperature-dependent bulk ionic conductivities investigated via impedance spectroscopy follow a William-Landel-Ferry (WLF) type behavior. Modifications of the alkyl spacer length were shown to influence ionic conductivities only in combination to changes in glass transition temperatures. Though the glass transition temperatures of the blends are low, their conductivities are only in the range of typical polymer electrolytes. The highest σ_dc obtained at ambient temperatures was 6.0 x 10-6 S•cm-1, strongly suggesting a rather tight coordination of the lithium ions to the solvating 2-oxo-1,3-dioxolane moieties, supported by the increased σ_dc values for the oligo(ethylene oxide) based analogues.rnrnFurther insights into the mechanism of lithium ion dynamics were derived from 7Li and 13C Solid- State NMR investigations. While localized ion motion was probed by i.e. 7Li spin-lattice relaxation measurements with apparent activation energies E_a of 20 to 40 kJ/mol, long-range macroscopic transport was monitored by Pulsed-Field Gradient (PFG) NMR, providing an E_a of 61 kJ/mol. The latter is in good agreement with the values determined from bulk conductivity data, indicating the major contribution of ion transport was only detected by PFG NMR. However, the μm-diffusion is rather slow, emphasizing the strong lithium coordination to the carbonyl oxygens, which hampers sufficient ion conductivities and suggests exploring ‘softer’ solvating moieties in future electrolytes.rn