Dye-sensitized solar cells (DSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Although efficiencies exceeding 10% in full sunlight have been presented, major improvements of the system are however limited. Electron transport is one of the processes in the cell and is of major importance for the overall performance. It is further a complex process because the transport medium is a mesoporous film and the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, present models describing electron transport include simplifications, which limit the practical use, in terms of improving the DSC, because the included model parameters usually have an effective nature. This thesis focuses in particular on the influence of the mesoporous film on electron transport and also on the influence of electron-ion interactions. In order to model diffusion, which is assumed to be the transport process for electrons in the DSC, Brownian motion simulations were performed and spatial restrictions, representing the influence of the mesoporous film, were introduced by using representative models for the structure. The simulations revealed that the diffusion coefficient is approximately half the value for electrons and ions in mesoporous systems. To study the influence of ions, a simulation model was constructed in where electric fields were calculated with respect to the net charge densities, resulting from the different charge carrier distributions. The simulations showed that electron transport is highly dependent on the nature of the ions, supporting an ambipolar diffusion transport model. Experimentally, it was found that the transport process is dependent on the wavelength of the incident light; we found that the extracted current was composed of two components for green light illumination, one fast and one slow. The slow component showed similar trends as the normal current. Also we found that the transport coefficient scaled linearly with film thickness for a fixed current, which questions diffusion as transport process. Other experiments, investigating various effects in the DSC, such as the effect of different cations in the electrolyte, are also presented. / QC 20100708

During the last decade, the dye sensitised solar cell (DSC) has attracted much attention. The technology has a potential to act as a new generation of photovoltaic device, it has also increased our knowledge within the field of photoelectrochemistry. The materials used in the DSC have been used in other technologies, such as electrochromic displays. This thesis examines how such systems can be analysed to understand their properties from their components. Both of the considered device technologies consist of a thin mesoporous semiconductor film immersed in an electrolyte. The study starts by investigating some of the fundamental properties of the mesoporous semiconductor and its interface with the electrolyte. This gives rise to the charge-voltage relationship for the devices, which is related to the chemical capacitance and electronic energy levels for the materials. In particular,special attention is given to the DSC and the properties of the charge carriers in the semiconductor. For the DSC, several techniques have been developed in order to understand the processes of transport and recombination for the charge carriers in the semiconductor film, which are vitally important for performance. In this thesis, particular focus is given to light modulation techniques and electrical analysis with impedance spectroscopy. The transportproperties show for both techniques a nonlinear behaviour, which is explained with the trapping model. The DSC solar cell is analysed in order to interpret the transport measurements for film thickness optimisation. DSC cells with new semiconductor materials, such as ZnO, were analysed with impedance measurements to provide new insights into the optimisation of the performance of the photoelectrochemical solar cell technology. / QC 20100804

The photophysical properties of a series of Zn (II) porphyrins adsorbed onto a semiconductor were investigated using steady-state absorbance and emission measurements. The ability of the porphyrins to undergo triplet-triplet annihilation (TTA), a photophysical process through which photons in the red and near-infrared (NIR) regions of the optical spectrum can be converted into higher energy photons (upconversion), was explored. Aggregation capabilities were determined to verify possibility of these molecules to undergo triplet-triplet annihilation (TTA). TTA has significant potential for increasing the efficiency of dye-sensitized solar cells (DSSCs) by upconverting photons in the energy rich NIR region of the solar spectrum. A key requirement for efficient TTA is aggregation of the sensitizer dye, and in this thesis, we have examined the aggregation of porphyrins in TiO2-based sol-gel films. Solution phase absorption and emission studies were conducted using zinc (II) tetraphenylporphyrin and three of its functionalized derivatives, tetra(4-aminophenyl)porphyrin Zn(II), tetra(4-carboxyphenyl)porphyrin Zn(II), and tetra(4-sulfonatophenyl)porphyrin Zn(II), to evaluate their potential as DSSC sensitizers on TiO2 thin films. Mesoporous TiO2 thin films were synthesized, using a polymer-templating sol-gel route, and characterized with tunneling electron microscopy (TEM), atomic force microscopy (AFM), and UV-Vis absorbance measurements. Spectroscopy measurements were also carried out on porphyrin-sensitized TiO2 thin films and compared to solution-based results. A simple DSSC was constructed and used to further explore the application of zinc (II) porphyrin sensitizers in photovoltaic applications.

Carbocyanine dyes are organic compounds containing chains of conjugated methine groups with electron-donating and electron-withdrawing substituents at the terminal heterocycles of the general formula [R1-(CH)n-R2]+X-. The synthetic methodology and optical properties of carbocyanines will be discussed. This thesis consists of two parts: (A) synthesis and optical properties of novel carbocyanine dyes substituted with various amines and the synthesis of unsymmetrical carbocyanine dyes containing monofunctional groups for bioconjugation. (B) synthesis of heptamethine carbocyanine dyes to be used for image-guided surgery. In part A, the synthesis of carbocyanine dyes functionalized with various amines and studies of their optical properties with respect to absorbance, fluorescence, quantum yield and extinction coefficient will be presented. These property studies will aid in designing efficient dyes for future biomedical applications. Part A will also include a one pot synthesis of unsymmetrical carbocyanine dyes functionalized with mono carboxylic acid chains, useful for biomolecule (i.e. proteins, amino acids, etc.) conjugation. Part B will describe the synthesis of novel carbocyanine dyes to be used for cancer image-guided surgery. Cancers are thus far incurable diseases, i.e. there are no drugs currently available to cure cancer; however, by designing a dye to visualize tumor cells will greatly increase the efficiency of cancer removal and hopefully increase the survival rate of cancer patients. The dyes reported in this thesis are superior to commercially available dyes used to visualize and identify various tumors invisible to the naked eye of surgeons with regards to biodistribution and clearance through kidney filtration.

Nanofluids, a new class of fluids engineered by suspending nanometer-sized particles in a host liquid, are offered as a new strategy in order to improve heat and mass transfer efficiency. My research was motivated by previous exciting studies on enhanced mass diffusion and the possibility of tailoring mass transport by direct manipulation of molecular diffusion. Therefore, a microfluidic approach capable of directly probing tracer diffusion between nanoparticle-laden fluid streams was developed. Under conditions matching previously reported studies, strong complexation interactions between the dye and nanoparticles at the interface between fluid streams was observed. When the tracer dye and surfactant were carefully chosen to minimize the collective effects of the interactions, no significant change in tracer dye diffusivity was observed in the presence of nanoparticles. Next, adapting tracer dyes for studies involving colloidal nanomaterials was explored. Addition of these charged tracers poses a myriad of challenges because of their propensity to disrupt the delicate balance among physicochemical interactions governing suspension stability. Here it was shown how important it is to select the compatible combinations of dye, nanoparticle, and stabilizing surfactant to overcome these limitations in low volume fraction (< 1 vol%) aqueous suspensions of Al2O3 nanoparticles. A microfluidic system was applied as a stability probe that unexpectedly revealed how rapid aggregation could be readily triggered in the presence of local chemical gradients. Suspension stability was also assessed in conjunction with coordinated measurements of zeta potential, steady shear viscosity and bulk thermal conductivity. These studies also guided our efforts to prepare new refrigerant formulations containing dispersed nanomaterials, including graphene nanosheets, carbon nanotubes and metal oxide and nitride. The influence of key parameters such as particle type, size and volume fraction on the suspension's thermal conductivity was investigated using a standard protocol. Our findings showed that thermal conductivity values of carbon nanotube and graphene nanosheet suspensions were higher than TiO2 nanoparticles, despite some nanoparticles with large particle sizes provided noticeable thermal conductivity enhancements. Significantly, the graphene containing suspensions uniquely matched the thermal conductivity enhancements attained in nanotube suspensions without accompanying viscosity, thus making them an attractive new coolant for demanding applications such as electronics and reactor cooling.

A molecular nitrogen laser was constructed and preliminary tests were performed to establish the fact that lasing action was taking place. The purpose was to show that a high energy pump source of ultraviolet radiation could be constucted, given a limited budget and expertise, which would be of the quality required to perform spectrographic research.Ball State UniversityMuncie, IN 57406

El processament convencional de materials d'òxid de titani (TiO2) inherentment implica un consum energètic important i ha esdevingut una limitació tecnològica per a la fabricació de dispositius emprant substrats termolàbils així com per a la preparació de materials híbrids orgànic/TiO2. Aquesta tesi doctoral tracta del desenvolupament de processos químics per a la preparació de capes i pols de TiO2 d'acord amb principis de Química Verda, posant especial èmfasi en el processament a baixa temperatura. Plantejaments simples, benignes amb el medi ambient i de baix cost són els desitjats sota aquestes directrius. A més a més, els mètodes a baixa temperatura (idealment fins a un màxim proper a 100ºC) haurien de donar lloc a materials que exhibeixin propietats similars a aquells processats a alta temperatura o tractats solvotermalment. S'ha focalitzat especial interès en la recerca d'aplicacions pràctiques dels materials produïts en camps com la conversió d'energia solar i materials actuadors. / El procesamiento convencional de materiales de óxido de titanio (TiO2) inherentemente implica un consumo energético importante y ha resultado una limitación tecnológica para la fabricación de dispositivos utilizando substratos termolábiles así como para la preparación de materiales híbridos orgánico/TiO2. Esta tesis doctoral trata el desarrollo de procesos químicos suaves para la preparación de capas y polvos de TiO2 de acuerdo con principios de Química Verde, poniendo especial énfasis en el procesamiento a baja temperatura. Planteamientos simples, benignos con el medioambiente y de bajo conste son los deseados bajo estas directrices. Además, los métodos a baja temperatura (idealmente hasta un máximo próximo a 100ºC) deberían dar lugar a materiales que exhiban propiedades similares a aquellos procesados a alta temperatura o tratados solvotermalmente. Se ha centrado especial interés en la búsqueda de aplicaciones prácticas de los materiales producidos en campos como la conversión de energía solar y materiales actuadores. / Conventional high-temperature processing of titanium dioxide (TiO2) materials inherently implies important energy consumption and has became a technological limitation for fabricating devices employing thermolabile substrates as well as preparing hybrid organic/TiO2 materials. This PhD thesis deals with the development of chemical processes for preparing TiO2 films and powders fitting Green Chemistry principles, putting special emphasis on low-temperature processing. Simple, environmentally benign and low-cost approaches are desired upon these guidelines. Moreover, low-temperature methods (ideally up to a maximum closer to 100ºC) should give rise to materials exhibiting properties similar than those processed at high temperature or solvothermally treated. Special interest has been focused on finding practical applications of the as-prepared materials in fields such as solar energy conversion and actuating materials.

<p>The visual system is thought to represent the trajectory of moving objects in the activity of large populations of cortical neurons that respond preferentially to the direction of stimulus motion. Here I employed in vivo voltage sensitive dye (VSD) imaging to explore how abrupt changes in the trajectory of a moving stimulus impact the population coding of motion direction in ferret primary visual cortex (V1). For motion in a constant direction, the peak of the cortical population response reliably signaled the stimulus trajectory; but for abrupt changes in motion direction, the peak of the population response departed significantly from the stimulus trajectory in a fashion that depended on the size of the direction deviation. For small direction deviation angles, the peak of the active population shifted from values consistent with the initial direction of motion to those consistent with the final direction of motion by progressing smoothly through intermediate directions not present in the stimulus. In contrast, for large direction deviation angles, peak values consistent with the initial motion direction were followed by: a small deviation away from the final motion direction, a rapid 180° jump, and a gradual shift to the final direction. These departures of the population response from the actual trajectory of the stimulus predict specific misperceptions of motion direction that were confirmed by human psychophysical experiments. I conclude that cortical dynamics and population coding mechanisms combine to place constraints on the accuracy with which abrupt changes in direction of motion can be represented by cortical circuits.</p> / Dissertation

Supramolecular chemistry covers intermolecular interactions where non-covalent bonds are involved, and many of them are based on host-guest interactions. Cyclodextrins (CDs) are cyclic oligosaccharides consisting of 6-, 7- or 8-glucose units, which are called alpha-, beta- or gamma-CDs, respectively. They have hydrophobic interior and hydrophilic exterior, and are widely being used as hosts for various organic molecules. The formation of CD inclusion complexes with a variety of dyes has continuously drawn our interests, since CDs are readily available and have ability to include dye molecules altering their properties. The present thesis covers the study of inclusion complexes of CDs and chromophore dyes, largely in two ways; rotaxane and pseudorotaxane. The stable rotaxane structure is achieved with the synthesis of dye rotaxane. The introduction of CD ring around azo chromophore provides a simple way to improve the solubility and stability of azo dye. We have shown that by incorporating proper compounds as a coupler, azo dye rotaxanes can be used as pH indicators and metal ion sensors. We have described the synthesis of novel acetylene dye rotaxane using the Pd-catalyzed reaction of Heck-Cassar-Sonogashira-Hagihara type. Its fluorescence properties in the solid state as well as in solutions are examined and compared with those of free dye. Free dye, which has tetra-carboxylic groups, is found to be highly sensitive to various metal ions, exhibiting high Stern-Volmer constants, K(SV). On the contrary, acetylene dye rotaxane exhibits much less quenching against various quenchers. The appearance of fluorescent anisotropic structure has been observed by the formation of inclusion complex between acetylene dye and gamma-CD. Its structural nature is studied by various techniques, including fluorescence, fluorescence anisotropy, wide angle X-ray scattering (WAXD) and differential scanning calorimetry (DSC) measurements. Methyl orange, an acid azo dye, forms a dimeric inclusion complex with gamma-CD, resulting in the formation stable anisotropic aggregates. Several other azo dyes are found to form anisotropic supramolecule in the presence of gamma-CD, and their structural characteristic has been discussed in terms of the number and position of solubilizing groups.

The dual-writing process of holographic technique was applied to fabricate the two-dimensional surface relief gratings on azo-dye doped polymer film in this study. The structure of two-dimensional grooves was investigated under the various polarization state of writing beam, the various angle between two stages of writing, and the adoption of nematic liquid crystals as the interface. The results revealed that the depth of two-dimensional surface relief gratings produced by the writing beams with P-polarization and the interface of nematic liquid crystals in contact with azo-dye polymer film was about 2~3 times of that without nematic liquid crystals as the interface. As the angle between two stages of writing increases, the first order diffraction efficiency and the depth of surface relief structure in the second writing becomes smaller for the writing beam with S polarization; while the first order diffraction efficiency and the depth of surface relief structure becomes larger for the writing beam with P polarization.