Dipodal Ferrocene Derivatives for Nanostructured Redox-Functionalised Surfaces

Self-assembled monolayers (SAMs) on solid surfaces are of great current interest in science and nanotechnology. This thesis describes the preparation of several symmetrically 1,1’-substituted ferrocene derivatives that contain anchoring groups suitable for chemisorption on gold and may give rise to SAMs with electrochemically switchable properties. The binding groups are isocyano (-NC), isothiocyanato (-NCS), phosphanyl (-PPh2), thioether (-SR) and thienyl. In the context of SAM fabrication, isothiocyanates and phosphanes are adsorbate systems which, surprisingly, have remained essentially unexplored. SAMs on gold have been fabricated with the adsorbates from solution and investigated primarily by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results of these analytical investigations are presented and discussed in matters of the film quality and possible binding modes. The quality of self-assembled monolayers fabricated from 1,1’-diisocyanoferrocene and 1,1’-diisothiocyanatoferrocene turned out to be superior to that of films based on the other adsorbate species investigated. Films of those absorbates as well as of dppf afforded well-defined SAMs of good quality. All other films of this study based on sulfur containing anchoring groups exhibit chemical inhomogeneity and low orientational order of the film constituents and therefore failed to give rise to well-defined SAMs. Surface coordination chemistry is naturally related to molecular coordination chemistry. Since all SAMs described in this thesis were prepared on gold (111) surfaces, the ferrocene-based ligands of this study have been investigated in their ability for complexation towards gold(I). The sulfur-based ferrocene ligands [fc(SR)2] failed to give stable gold(I) complexes. In contrast, 1,1’-diisocyanoferrocene (1) proved to be an excellent ligand for the complexation of gold(I). Several complexes were prepared and characterised utilising a series of gold(I) acetylides. These complexes show interesting structural motifs in the solid state, since intramolecular aurophilic interactions lead to a parallel orientation of the isocyano moieties, combined with an antiparallel alignment of neighbouring units. The reaction of 1 with the gold(I) acetylide [Au(C≡C–Fc)]n turned out to be very unusual, since the two chemically equivalent isocyano groups undergo a different reaction. One group shows an ordinary coordination and the other one undergoes an extraordinary 1,1-insertion into the Au-C bond. As a sideline of the research of this thesis several ferrocene derivatives have been tested for their suitability for potential surface reactions. Copper(I) mediated 1,3-dipolar cycloadditions of azidoferrocene derivatives with terminal alkynes appeared very promising in this context, but failed to a certain extent in terms of ‘click’ chemistry, since the formation of the triazoles depended on the strict exclusion of oxygen and moisture and yields were only moderate. Staudinger reactions between dppf and azidoferrocene derivatives were also tested. The nucleophilic additions of secondary amines to 1,1’-diisothiocyanatoferrocene led to the respective thiourea derivatives in quantitative yields.

Dye-sensitized solar cells based on perylene derivatives

The oil price rises more and more, and the world energy consumption is projected to expand by 50 percent from 2005 to 2030. Nowadays intensive research is focused on the development of alternative energies. Among them, there are dye-sensitized nanocrystalline solar cells (DSSCs) “the third generation solar cells”. The latter have gained attention during the last decade and are currently subject of intense research in the framework of renewable energies as a low-cost photovoltaic. At present DSSCs with ruthenium based dyes exhibit highest efficiencies (ca 11%). The objective of the present work is to fabricate, characterize and improve the performance of DSSCs based on metal free dyes as sensitizers, especially on perylene derivatives. The work begins by a general introduction to the photovoltaics and dye-sensitized solar cells, such as the operating principles and the characteristics of the DSSCs. Chapter 2 and 3 discuss the state of the art of sensitizers used in DSSCs, present the compounds used as sensitizer in the present work and illustrate practical issues of experimental techniques and device preparation. A comparative study of electrolyte-DSSCs based on P1, P4, P7, P8, P9, and P10 are presented in chapter 4. Experimental results show that the dye structure plays a crucial role in the performance of the devices. The dye based on the spiro-concept (bipolar spiro compound) exhibited a higher efficiency than the non-spiro compounds. The presence of tert-butylpyridine as additive in the electrolyte was found to increase the open circuit voltage and simultaneously decrease the efficiency. The presence of lithium ions in the electrolyte increases both output current and the efficiency. The sensitivity of the dye to cations contained in the electrolyte was investigated in the chapter 5. FT-IR and UV-Vis were used to investigate the in-situ coordination of the cation to the adsorbed dye in the working devices. The open-circuit voltage was found to depend on the number of coordination sites in the dye. P1 with most coordination sites has shown the lowest potential drop, opposite to P7, which is less sensitive to cations in the working cells. A strategy to improve the dye adsorption onto the TiO2 surface, and thus the light harvesting efficiency of the photoanode by UV treatment, is presented in chapter 6. The treatment of the TiO2 film with UV light generates hydroxyl groups and renders the TiO2 surface more and more hydrophilic. The treated TiO2 surface reacts readily with the acid anhydride group of the dye that acts as an anchoring group and improves the dye adsorption. The short-circuit current density and the efficiency of the electrolyte-based dye cells was considerably improved by the UV treatment of the TiO2 film. Solid-state dye-sensitized solar cells (SSDs) based on spiro-MeOTAD (used as hole transport material) are studied in chapter 7. The efficiency of SSDs was globally found to be lower than that of electrolyte-based solar cells. That was due to poor pore filling of the dye-loaded TiO2 film by the spin-coated spiro-MeOTAD and to the significantly slower charge transport in the spiro-MeOTAD compared to the electrolyte redox mediator. However, the presence of the donor moieties in P1 that are structurally similar to spiro-MeOTAD was found to improve the wettability of the P1-loaded TiO2 film. As a consequence the performance of the P1-based solid-state cells is better compared to the cells based on non-spiro compounds.

Synthesis and characterisation of novel nitrogen and fluorine containing spirobifluorene derivatives for electronic applications and crystal engineering

Among organic materials, spirobifluorene derivatives represent a very attractive class of materials for electronic devices. These compounds have high melting points, glass transitions temperatures and morphological stability, which makes these materials suitable for organic electronic applications. In addition, some of spirobifluorenes can form porous supramolecular associations with significant volumes available for the inclusion of guests. These molecular associations based on the spirobifluorenes are noteworthy because they are purely molecular analogues of zeolites and other microporous solids, with potential applications in separation, catalysis, sensing and other areas.

Individual Decision-Making and Inflation Persistence

The traditional task of a central bank is to preserve price stability and, in doing so, not to impair the real economy more than necessary. To meet this challenge, it is of great relevance whether inflation is only driven by inflation expectations and the current output gap or whether it is, in addition, influenced by past inflation. In the former case, as described by the New Keynesian Phillips curve, the central bank can immediately and simultaneously achieve price stability and equilibrium output, the so-called ‘divine coincidence’ (Blanchard and Galí 2007). In the latter case, the achievement of price stability is costly in terms of output and will be pursued over several periods. Similarly, it is important to distinguish this latter case, which describes ‘intrinsic’ inflation persistence, from that of ‘extrinsic’ inflation persistence, where the sluggishness of inflation is not a ‘structural’ feature of the economy but merely ‘inherited’ from the sluggishness of the other driving forces, inflation expectations and output. ‘Extrinsic’ inflation persistence is usually considered to be the less challenging case, as policy-makers are supposed to fight against the persistence in the driving forces, especially to reduce the stickiness of inflation expectations by a credible monetary policy, in order to reestablish the ‘divine coincidence’. The scope of this dissertation is to contribute to the vast literature and ongoing discussion on inflation persistence: Chapter 1 describes the policy consequences of inflation persistence and summarizes the empirical and theoretical literature. Chapter 2 compares two models of staggered price setting, one with a fixed two-period duration and the other with a stochastic duration of prices. I show that in an economy with a timeless optimizing central bank the model with the two-period alternating price-setting (for most parameter values) leads to more persistent inflation than the model with stochastic price duration. This result amends earlier work by Kiley (2002) who found that the model with stochastic price duration generates more persistent inflation in response to an exogenous monetary shock. Chapter 3 extends the two-period alternating price-setting model to the case of 3- and 4-period price durations. This results in a more complex Phillips curve with a negative impact of past inflation on current inflation. As simulations show, this multi-period Phillips curve generates a too low degree of autocorrelation and too early turnings points of inflation and is outperformed by a simple Hybrid Phillips curve. Chapter 4 starts from the critique of Driscoll and Holden (2003) on the relative real-wage model of Fuhrer and Moore (1995). While taking the critique seriously that Fuhrer and Moore’s model will collapse to a much simpler one without intrinsic inflation persistence if one takes their arguments literally, I extend the model by a term for inequality aversion. This model extension is not only in line with experimental evidence but results in a Hybrid Phillips curve with inflation persistence that is observably equivalent to that presented by Fuhrer and Moore (1995). In chapter 5, I present a model that especially allows to study the relationship between fairness attitudes and time preference (impatience). In the model, two individuals take decisions in two subsequent periods. In period 1, both individuals are endowed with resources and are able to donate a share of their resources to the other individual. In period 2, the two individuals might join in a common production after having bargained on the split of its output. The size of the production output depends on the relative share of resources at the end of period 1 as the human capital of the individuals, which is built by means of their resources, cannot fully be substituted one against each other. Therefore, it might be rational for a well-endowed individual in period 1 to act in a seemingly ‘fair’ manner and to donate own resources to its poorer counterpart. This decision also depends on the individuals’ impatience which is induced by the small but positive probability that production is not possible in period 2. As a general result, the individuals in the model economy are more likely to behave in a ‘fair’ manner, i.e., to donate resources to the other individual, the lower their own impatience and the higher the productivity of the other individual. As the (seemingly) ‘fair’ behavior is modelled as an endogenous outcome and as it is related to the aspect of time preference, the presented framework might help to further integrate behavioral economics and macroeconomics.

Adsorption kinetic investigations of phthalocyanine derivatives self assembled monolayers (SAMs) on gold: Temperature influence on the SAM formation process and quality

The ordered nano-structured surfaces, like self-assembled monolayers (SAMs) are of a great scientific interest, due to the low cost, simplicity, and versatility of this method. SAMs found numerous of applications in molecular electronics, biochemistry and optical devices. Phthalocyanine (Pc) complexes are of particular interest for the SAM preparation. These molecules exhibit fascinating physical properties and are chemically and thermally stable. Moreover their complex structure is advantageous for the fabrication of switchable surfaces. In this work the adsorption process of Pcs derivatives, namely, subphthalocyanines (SubPcB) and terbium (2TbPc) sandwich complexes on gold has been investigated. The influence of the molecular concentration, chain length of peripheral groups, and temperature on the film formation process has been examined using a number of techniques. The SAMs formation process has been followed in situ and in real time by means of second harmonic generation (SHG) and surface plasmon resonance (SPR) spectroscopy. To investigate the quality of the SAMs prepared at different temperatures atomic force microscopy (AFM) and X-Ray photoelectron spectroscopy (XPS)measurements were performed. Valuable information about SubPcB and 2TbPc adsorbtion process has been obtained in the frame of this work. The kinetic data, obtained with SHG and SPR, shows the best conformance with the first order Langmuir kinetic model. Comparing SHG and SPR results, it has been found, that the film formation occurs faster than the formation of chemical bonds. Such, the maximum amount of molecules on the surface is reached after 6 min for SubPcB and 30 min for 2TbPc. However, at this time the amount of formed chemicals bonds is only 10% and 40% for SubPcB and 2TbPc, respectively. The most intriguing result, among others, was obtained at T = 2 °C, where the formation of the less dense SAMs have been detected with SHG.However, analyzing XPS and AFM data, it has been revealed, that there is the same amount of molecules on the surface at both temperature T = 2 °C, and T = 21 °C, but the amount of formed chemicals bond is different. At T = 2 °C molecules form aggregates, therefore many of available anchor groups stay unattached.