<p>To optimize contrast agent in MRI scan region, e.g. to enhance paramagnetic relaxation in the MRI scan fields(0.1T-3T), one possible way is to slow down the tumbling of the paramagnetic complex. The effect of slowing down the reorientational motion of the complex to increase relaxivity is obvious and this strategy has already been employed in producing MRI contrast agent that can bind to specific proteins. An example is MS-325 binds to human serum albumin(HSA). The slow down effects on the ligands around paramagnetic ion, and on the zero field splitting(ZFS) interaction are under studies and the physics behind is still not clear. In this thesis, a generalized Solomon-Bloembergen-Morgan(GSBM) theory together with stochastic Liouville approach(SLA), is applied to investigate the mechanism behind the slow down effects. Two gadolinium complexes, MS-325+HSA and Gd(H₂O)₈³⁺+glycerol are studied by means of NMRD and ESR experiments.</p><p>GSBM is a second order perturbation theory with closed analytical form. The computation based on this theory is fast, but it has its limitation and in the case of Gd(S=7/2) the ZFS strength times its correlation time(Δ<i>t</i>.<i>τ</i>_ƒ) should be less than 0.1. In comparison, the SLA is an "exact" theory that can evaluate the validity of GSBM calculation. However, the calculation in SLA is time consuming due to the large matrix it constructed. The major model used in GSBM is a two dynamic model, characterized by transient ZFS Δ<i>t</i> and static ZFS Δ<i>s</i> and their corresponding correlation time <i>τ</i>_ƒ and <i>τR</i>, while in SLA the model is only described by Δ<i>t</i> and <i>τ</i>_ƒ. A combined NMRD and ESR analysis is used to understand the details of ZFS interaction. Both models can reproduce experimental NMRD profiles and model parameters are similar; for ESR linewidths the model parameters are quite different. The fitting results indicate the NMRD profiles are less sensitive to the detail expression of ZFS correlation function. In order to interpret both NMRD and ESR experiments with identical parameters, a more complex ZFS interaction model should be developed.</p>

<p>This thesis describes water proton and deuterium relaxation processes, as seen by Nuclear Magnetic Resonance (NMR) spectroscopy, using Brownian Dynamics (BD) or Molecular Dynamics (MD) simulations. The MD simulations reveal new detailed information about the dynamics and order of water molecules outside of a lipid bilayer. This is very important information in order to fully understand deuterium NMR measurements in lipid bilayer systems, which require an advanced analysis, because of the complicated water motion (such as tumbling and self-diffusion). The BD simulation methods are combined with the powerful Stochastic Liouville Equation (SLE) in its Langevin form (SLEL) to give new insight into both ¹H₂O and ²H₂O relaxation. The new simulation techniques which combine BD and SLEL can give important new information in cases where other methods do not apply. The deuterium relaxation is described in the context of a water/lipid interface and is in a very elegant way combined with the simulation of diffusion on curved surfaces developed by our research group. ¹H₂O spin-lattice relaxation is described for paramagneticsystems. With this we mean systems with paramagnetic transition metal ions or complexes, that are dissolved into a water solvent. The theoretical description of such systems are quite well investigated but such systems are not yet fully understood. An important consequence of the Paramagnetic Relaxation Enhancement (PRE) calculations when using the SLEL approach combined with BD simulations is that we obtain the electron correlation functions, which describe the relaxation of the paramagnetic electron spins. This means for example that it is also straight forward to generate Electron Spin Resonance (ESR) lineshapes.</p>

<p>The interactions between the molecular constituents in dye-sensitized solar cells were studied with UV-VIS and IR spectroscopy, Raman scattering, conductivity and electron accumulation measurements.</p><p>From stability studies of the dye, bis(tetrabutylammonium)cis-bis(thiocyanato) bis(2,2’-bipyridine-4-carboxylic acid, 4’-carboxylate) ruthenium(II), in the complete solar cell, the thiocyanate ion ligand was found to be lost from the dye. A method was developed to study mechanisms in a sealed dye-sensitized solar cell using resonance Raman scattering (RRS). RRS studies of a complete dye-sensitized solar cell including iodine and lithium iodide in the electrolyte indicate that triiodide exchange the SCN^- ligand of the dye. It was proposed that an ion pair Li⁺…I₃^- formation occurred, which, by a reduced electrostatic repulsion between I₃^- and SCN^- facilitated the exchange of these anions at Ru(II) of the dye. The additive 1-methylbenzimidazole suppressed the SCN^-/I₃^- ligand exchange by forming a complex with Li⁺.</p><p>In order to study charge transport in nanostructured TiO₂ films permeated with electrolyte, a technique was developed for determining activation energies of conduction, electron accumulation and effective mobility. Two regions were distinguished from the relation between conductivity and electron concentration. In the first region (~1-20 electrons per TiO₂ particle), which resembles best the region where the nanostructured dye-sensitized solar cell operates, the results can be fitted to some extent with a trapping/detrapping or a hopping model for charge transport, but not with a conduction band model. For the second region (> 20 electrons per TiO₂ particle), charge transport by electrons in the conduction band seems to be the most applicable model.</p><p>Through this work many effects from the interplay between the solar cell components were observed. These observations emphasize the importance of well-balanced interactions in dye-sensitized solar cells.</p>

<p>Conjugated polymers that exhibit high electronic conductivities play key roles in the emerging field of molecular electronics. In particular, linking metal centres with useful electrochemical, photophysical, or catalytic properties to the backbone, or within the polymer chain itself, is a topic which has attracted a significant amount of interest lately. Structurally rigid monomers that can be electropolymerised to form highly conducting molecular wires may provide new insights into conduction mechanisms, e.g., exploiting resonant superexchange (electron-hopping) by tuning the energies of redox centre and bridge states. The focus of this thesis lies on the electrochemical investigation of preparation, growth dynamics, and charge transport dynamics of oligothiophene/transition metal hybrid materials. The incorporation of ruthenium(II) and osmium(II) terpyridine complexes into such polymeric assemblies was accomplished by an electropolymerisation procedure, to produce rod-like oligothienyl-bridged metallopolymers. The properties of the monomers used were characterised by optical spectroscopy and electrochemical techniques. Charge transport was studied in detail for some of the materials created, and it was found that the electron transport rate and dc conductivity was enhanced by up to two orders of magnitude compared to relevant non-conjugated polymers, demonstrating the usefulness of this approach for optimization of charge transport in metallopolymers. The charge transport diffusion coefficent was determined to (2.6 ± 0.5) x 10^-6 cm² s^-1 for a quaterthienyl-bridged {Os(tpy)₂} polymer by use of an electrochemical steady-state method carried out using a transistor-like experimental geometry. It was found that charge transport in these materials is concentration-gradient driven. The rate limiting step of the charge transport process was investigated using electrochemical impedance spectroscopy. The electropolymerisation dynamics of one of the monomers was studied using microelectrodes, and the results obtained shows that electropolymerisation is highly efficient, and indicate that mass transport controls this process. Through a combination of controlled potential deposition and SEM imaging it was demonstrated that it is possible to exploit the edge effect of microelectrodes to promote film growth in a direction co-planar with the electrode surface.</p>

<p>In this thesis electron transfer reactions and diffusion of redox molecules in three different types of self-aggregated structures are investigated. Electrochemistry was used to investigate the redox potential and diffusion coefficients for redox active molecules with different polarity. The first aggregate system studied was the micellar phase. The role of electrostatic interactions in the stability of an amphiphilic viologen was investigated for differently charged micelles. It was concluded that the electrostatic environment changed the redox potential of the viologen. In differently charged micelles the redox potential was more negative compared to when the viologen was situated in micelles with the same charge.</p><p>The second structure investigated is a very fascinating phase, the bicontinuous cubic phase, with its continuous channels of water and an apolar bilayer. Its domains with different polarity made it possible to solvate both hydrophilic and hydrophobic molecules. An amphiphilic molecule will have its head-group at the interface between the apolar and polar part, and can move lateral within the bilayer. All molecules investigated made contact with and reacted at the surface of the electrode. The diffusion of water bound species diffusing in the water channels was 3-4 times slower than in water. Hydrophobic and amphiphilic molecules were much more hindered, probably because the cubic phase was not defect free.</p><p>The third kind of structure studied was a lamellar system. This phase is built up from planar bilayers that are stacked with a repeating distance and with water in between. A hydrophilic molecule was severely hindered to move in the direction perpendicular to the bilayer plane. Upon addition of the peptide melittin the current increased, due to pore formation in the bilayer.</p>

The interactions between the molecular constituents in dye-sensitized solar cells were studied with UV-VIS and IR spectroscopy, Raman scattering, conductivity and electron accumulation measurements. From stability studies of the dye, bis(tetrabutylammonium)cis-bis(thiocyanato) bis(2,2’-bipyridine-4-carboxylic acid, 4’-carboxylate) ruthenium(II), in the complete solar cell, the thiocyanate ion ligand was found to be lost from the dye. A method was developed to study mechanisms in a sealed dye-sensitized solar cell using resonance Raman scattering (RRS). RRS studies of a complete dye-sensitized solar cell including iodine and lithium iodide in the electrolyte indicate that triiodide exchange the SCN- ligand of the dye. It was proposed that an ion pair Li+…I3- formation occurred, which, by a reduced electrostatic repulsion between I3- and SCN- facilitated the exchange of these anions at Ru(II) of the dye. The additive 1-methylbenzimidazole suppressed the SCN-/I3- ligand exchange by forming a complex with Li+. In order to study charge transport in nanostructured TiO2 films permeated with electrolyte, a technique was developed for determining activation energies of conduction, electron accumulation and effective mobility. Two regions were distinguished from the relation between conductivity and electron concentration. In the first region (~1-20 electrons per TiO2 particle), which resembles best the region where the nanostructured dye-sensitized solar cell operates, the results can be fitted to some extent with a trapping/detrapping or a hopping model for charge transport, but not with a conduction band model. For the second region (&gt; 20 electrons per TiO2 particle), charge transport by electrons in the conduction band seems to be the most applicable model. Through this work many effects from the interplay between the solar cell components were observed. These observations emphasize the importance of well-balanced interactions in dye-sensitized solar cells.

Conjugated polymers that exhibit high electronic conductivities play key roles in the emerging field of molecular electronics. In particular, linking metal centres with useful electrochemical, photophysical, or catalytic properties to the backbone, or within the polymer chain itself, is a topic which has attracted a significant amount of interest lately. Structurally rigid monomers that can be electropolymerised to form highly conducting molecular wires may provide new insights into conduction mechanisms, e.g., exploiting resonant superexchange (electron-hopping) by tuning the energies of redox centre and bridge states. The focus of this thesis lies on the electrochemical investigation of preparation, growth dynamics, and charge transport dynamics of oligothiophene/transition metal hybrid materials. The incorporation of ruthenium(II) and osmium(II) terpyridine complexes into such polymeric assemblies was accomplished by an electropolymerisation procedure, to produce rod-like oligothienyl-bridged metallopolymers. The properties of the monomers used were characterised by optical spectroscopy and electrochemical techniques. Charge transport was studied in detail for some of the materials created, and it was found that the electron transport rate and dc conductivity was enhanced by up to two orders of magnitude compared to relevant non-conjugated polymers, demonstrating the usefulness of this approach for optimization of charge transport in metallopolymers. The charge transport diffusion coefficent was determined to (2.6 ± 0.5) x 10-6 cm2 s-1 for a quaterthienyl-bridged {Os(tpy)2} polymer by use of an electrochemical steady-state method carried out using a transistor-like experimental geometry. It was found that charge transport in these materials is concentration-gradient driven. The rate limiting step of the charge transport process was investigated using electrochemical impedance spectroscopy. The electropolymerisation dynamics of one of the monomers was studied using microelectrodes, and the results obtained shows that electropolymerisation is highly efficient, and indicate that mass transport controls this process. Through a combination of controlled potential deposition and SEM imaging it was demonstrated that it is possible to exploit the edge effect of microelectrodes to promote film growth in a direction co-planar with the electrode surface.

In this thesis electron transfer reactions and diffusion of redox molecules in three different types of self-aggregated structures are investigated. Electrochemistry was used to investigate the redox potential and diffusion coefficients for redox active molecules with different polarity. The first aggregate system studied was the micellar phase. The role of electrostatic interactions in the stability of an amphiphilic viologen was investigated for differently charged micelles. It was concluded that the electrostatic environment changed the redox potential of the viologen. In differently charged micelles the redox potential was more negative compared to when the viologen was situated in micelles with the same charge. The second structure investigated is a very fascinating phase, the bicontinuous cubic phase, with its continuous channels of water and an apolar bilayer. Its domains with different polarity made it possible to solvate both hydrophilic and hydrophobic molecules. An amphiphilic molecule will have its head-group at the interface between the apolar and polar part, and can move lateral within the bilayer. All molecules investigated made contact with and reacted at the surface of the electrode. The diffusion of water bound species diffusing in the water channels was 3-4 times slower than in water. Hydrophobic and amphiphilic molecules were much more hindered, probably because the cubic phase was not defect free. The third kind of structure studied was a lamellar system. This phase is built up from planar bilayers that are stacked with a repeating distance and with water in between. A hydrophilic molecule was severely hindered to move in the direction perpendicular to the bilayer plane. Upon addition of the peptide melittin the current increased, due to pore formation in the bilayer.

This thesis describes water proton and deuterium relaxation processes, as seen by Nuclear Magnetic Resonance (NMR) spectroscopy, using Brownian Dynamics (BD) or Molecular Dynamics (MD) simulations. The MD simulations reveal new detailed information about the dynamics and order of water molecules outside of a lipid bilayer. This is very important information in order to fully understand deuterium NMR measurements in lipid bilayer systems, which require an advanced analysis, because of the complicated water motion (such as tumbling and self-diffusion). The BD simulation methods are combined with the powerful Stochastic Liouville Equation (SLE) in its Langevin form (SLEL) to give new insight into both 1H2O and 2H2O relaxation. The new simulation techniques which combine BD and SLEL can give important new information in cases where other methods do not apply. The deuterium relaxation is described in the context of a water/lipid interface and is in a very elegant way combined with the simulation of diffusion on curved surfaces developed by our research group. 1H2O spin-lattice relaxation is described for paramagneticsystems. With this we mean systems with paramagnetic transition metal ions or complexes, that are dissolved into a water solvent. The theoretical description of such systems are quite well investigated but such systems are not yet fully understood. An important consequence of the Paramagnetic Relaxation Enhancement (PRE) calculations when using the SLEL approach combined with BD simulations is that we obtain the electron correlation functions, which describe the relaxation of the paramagnetic electron spins. This means for example that it is also straight forward to generate Electron Spin Resonance (ESR) lineshapes.

Relaxation models are developed using numerical solutions of the Stochastic Liouville Equation of motion. Simplified descriptions such as the stochastic master equation is described in the context of fluorescence depolarisation experiments. Redfield theory is used in order to describe NMR relaxation in bicontinuous phases. The stochastic fluctuations in the relaxation models are accounted for using Brownian Dynamics simulation technique. A novel approach to quantitatively analyse fluorescence depolarisation experiments and to determine intramolecular distances is presented. A new Brownian Dynamics simulation technique is developed in order to characterize translational diffusion along the water lipid interface of bicontinuous cubic phases.