No description available.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 159-168).

No description available.

Three-dimensional (3D) optical data storage based on two-photon processes provides highly confined excitation in a recording medium and a mechanism for writing and reading data with less cross talk between multiple memory layers, due to the quadratic dependence of two photon absorption (2PA) on the incident light intensity. The capacity for highly confined excitation and intrinsic 3D resolution affords immense information storage capacity (up to 1012 bits/cm3). Recently, the use of photochromic materials for 3D memory has received intense interest because of several major advantages over current optical systems, including their erasable/rewritable capability, high resolution, and high sensitivity. This work demonstrates a novel two-photon 3D optical storage system based on the modulation of the fluorescence emission of a highly efficient two-photon absorbing fluorescent dye (fluorene derivative) and a photochromic compound (diarylethene). The feasibility of using efficient intermolecular Förster Resonance Energy Transfer (RET) from the non-covalently linked two-photon absorbing fluorescent fluorene derivative to the photochromic diarylethene as a novel read-out method in a two-photon optical data storage system was explored. For the purpose of the development of this novel two-photon 3D optical storage system, linear and two-photon spectroscopic characterization of commercial diarylethenes in solution and in a polymer film and evidence of their cyclization (O→C) and cycloreversion (C→O) reactions induced by two-photon excitation were undertaken. For the development of a readout method, Resonance Energy Transfer (RET) from twophoton absorbing fluorene derivatives to photochromic compounds was investigated under one and two-photon excitation. The Förster's distances and critical acceptor concentrations were determined for non-bound donor-acceptor pairs in homogeneous molecular ensembles. To the best of my knowledge, modulation of the two-photon fluorescence emission of a dye by a photochromic diarylethene has not been reported as a mechanism to read the recorded information in a 3D optical data storage system. This system was demonstrated to be highly stable and suitable for recording data in thick storage media. The proposed RET-based readout method proved to be non-destructive (exhibiting a loss of the initial fluorescence emission less than 20% of the initial emission after 10,000 readout cycles). Potential application of this system in a rewritable-erasable optical data storage system was proved. As part of the strategy for the development of diarylethenes optimized for 3D optical data storage, derivatives containing Ï€-conjugated fluorene molecules were synthesized and characterized. The final part of this reasearch demonstrated the photostability of fluorine derivatives showing strong molecular polarizability and high fluorescence quantum yields. These compounds are quite promising for application in RET-based two-photon 3D optical data storage. Hence, the photostability of these fluorene derivatives is a key parameter to establish, and facilitates their full utility in critical applications.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The use of various ‘smart materials’ (briefly meaning materials that respond to a change in their environment) is currently of interest to both academics and industry. The primary aim of the current study was to entrap photochromic (PC) dyes in miniemulsions, as a means to improve their fatigue resistance, thus synthesizing smart nanoparticles. In the coatings industry the use of aqueous systems is becoming a common requirement for health and environmental reasons. Miniemulsion entrapment allows the direct dispersion of PC dyes into aqueous systems while allowing for the opportunity to tailor-make the host matrix in order to obtain a suitable PC response and improved fatigue resistance. The optimal instrument set-up required to establish the PC response of films of the so-called smart nanoparticles (i.e. PC miniemulsions) was determined. A UV-Vis instrument with a chip-type UV LED mounted inside for activation of the samples provided PC response results. A tungsten lamp with filter provided deactivation of the samples. A stable butyl methacrylate (BMA) miniemulsion formulation was established by conducting a design of experiments. A chromene and spironapthoxazine (SNO) PC dye were entrapped in the BMA miniemulsion. A hindered amine light stabiliser (HALS) was also entrapped with the SNO dye in the BMA miniemulsion to further improve the fatigue resistance. The following PC properties of the smart nanoparticles films were evaluated: colourability, thermal decay rate, half-life and fatigue resistance. To compare results with conventional systems, a BMA solution polymer was prepared. The SNO dye and different concentrations of the HALS were mixed with the BMA solution polymer. In comparison to the SNO smart nanoparticles the chromene smart nanoparticles films had lower colourability, but better fatigue resistance. Incorporating HALS at levels of 0.5–2% in the BMA miniemulsion with PC dye did not lead to any significant improvement in fatigue resistance, yet films of the BMA solution polymer showed some improvement. SNO dye incorporated at 1% gave similar colourability in both miniemulsion and in solution polymer, yet the fatigue resistance of the films of the PC miniemulsions was much better. / AFRIKAANSE OPSOMMING: Die gebruik van verskeie “slim materiale’ (kortliks beskryf as materiale wat reageer op `n verandering in hul omgewing) is tans van belang vir beide akademici en die industrie. Die hoofdoel van hierdie studie was om miniemulsietegnologie te gebruik om fotochromiese (FC) kleurstowwe vas te vang, vir die sintese van slim nanopartikels, om sodoende die weerstand teen afgematheid te verbeter. In die verfindustrie word die gebruik van waterbasissisteme meer algemeen weens gesondheids- en omgewingsredes. Die gebruik van miniemulsie sisteme om materiale vas te vang maak dit moontlik om FC kleurstowwe direk in waterbasissisteme te meng. Die sintese van `n unieke gasheer matriks word benodig om die optimum FC verandering te toon en weerstand teen afgematheid te verbeter. Om die FC verandering van die sogenaamde slim nanopartikel films (d.w.s. FC miniemulsies) te ondersoek was `n gepaste instrumentele opstelling nodig. Dit is vasgestel dat `n UV-Vis instrument waarin `n skyfie-tipe UV LED gemonteer is vir aktivering van die monsters, reproduseerbare resultate gegee het. Die monsters is gedeaktiveer deur gebruik te maak van `n tungsten lig met ‘n filter. `n Eksperimentele ontwerp is toegepas om `n stabiele butielmetakrielaat (BMA) miniemulsie formulasie te verkry. `n ‘Chromene’ en ‘spironapthoxazine’ (SNO) FC kleurstof is in die BMA miniemulsie vasgevang tesame met `n verhinderde amien ligstabiliseerder (VALS) om die weerstand teen afgematheid verder te verbeter. Die volgende FC eienskappe van die slim nanopartikels is gemeet: kleurintensiteit, tempo van termiese verwering, half-lewe en weerstand teen afgematheid. `n BMA polimeeroplossing is berei om resultate mee te vergelyk. Die SNO kleurstof en verskillende konsentrasies van die VALS is met die BMA polimeeroplossing gemeng. In vergelyking met die slim SNO nanopartikels het die intelligente chromene nanopartikelfilms `n swakker kleurintensiteit gehad, maar `n hoër weerstand teen afgematheid. Die gebruik van 0.5–2% VALS in die BMA miniemulsie met FC kleurstof het minimale verbetering in weerstand teen afgematheid getoon, maar daar was wel `n beduidende verbetering in die geval van films met FC kleurstof in `n BMA polimeeroplossing. Byvoeging van 1% SNO kleurstof in `n BMA miniemulsie of polimeeroplossing het dieselfde kleurintensiteit gelewer, maar die weerstand teen afgematheid van die FC miniemulsie was baie beter.

Rewritable photochrome-based 3D optical data storage requires photochromic molecules with high two-photon absorption (2PA) cross sections. Currently, the low value of two-photon absorption cross sections of existing photochromes makes them unsuitable for practical application in 3D data storage. Worldwide attempts to increase the cross section of photochromic molecules by altering the chemical structure have yielded poor results. In this work, two ways to increase the two-photon absorption cross sections of photochromes were investigated. In the first method, partial success demonstrated by extending the conjugation of a photochromic molecule, a high two-photon absorption cross section of the closed form isomer and high photoconversion to the closed form were realized. At the same time, a decrease in photoswitching quantum yield and low photoconversion to open form was observed. A discussion is provided to explain the results, suggesting that the proposed method of extending the conjugation may not solve the problem. For this reason a new method for effective two-photon absorption cross section enhancement of photochromes was proposed. As a proof of principle, a new two-photon absorbing dye with a hydrogen bonding moiety was synthesized and used for the formation of supramolecular structures with a photochromic compound. Theoretical reasoning and experimental demonstration of energy transfer from the dye to the photochrome under one and two-photon excitation confirmed the practical value of the method. The effects of a 2PA dye on the photochromic properties of a diarylethene were investigated using a model compound to simplify data analysis. Formation of supramolecular structures was revealed using ¹H NMR spectroscopic methods. The model compound, having the same hydrogen bonding moiety as 2PA dye, has been demonstrated to bind with photochrome molecules at very low concentrations. Photochromic properties of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleimide, including conversions at the photostationary state, extinction coefficients, photoisomerization reaction rates and quantum yields, were shown to be affected by hydrogen bonding with the model compound - 2,6-bis-(acetamido)pyridine. The extent of this change was determined and discussed, demonstrating a balanced supramolecular strategy to modulate photochemical and photophysical properties of this important class of photochromic material.

Scientists have recently discovered simultaneous photoconductivity and photochromism (i.e., optical switching upon light exposure) of oxygen-containing rare-earth metal hydrides (REMHO). A deep understanding of these extraordinary optical and electrical properties can open the door to advanced technological uses such as smart windows. This thesis work is to establish a correlation between the photochromism of these materials with their photoconductive response and comprehend the underlying physics behind them. The samples were grown by reactive magnetron sputtering. The dynamics of the photochromic effect were observed by recording the time-resolved relative transmittance of the films during photodarkening and bleaching using a UV-vis spectrometer. The samples were characterized electrically by employing the two-point probe resistance measurement. The depth profiles of the concentration of chemical elements were extracted from Ion Beam Analysis. A systematic study was performed to see how the photoconductive and photochromic responses of the REMHO thin films depend on the wavelength and intensity of the illuminating light as well as the chemical composition of the films. Both effects showed i) higher response for shorter wavelength, ii) a cut-off near a similar wavelength, iii) saturation near UV region, and iv) similar relaxation time but with different kinetics. Multiple measurements performed on the same sample showed that the previous measurement affects the next measurement indicating a memory effect. Finally, the photoconductive response showed an increase with increasing oxygen concentration.

The synthesis of benzo[e]dimethyldihydropyrene (BDHP) photoswitches with ter-27, quarter-36, and quinque-28 thiophene oligomers attached on the same side of the switch was achieved using Stille coupling reactions. BDHP photoswitches with bi-75, ter-76 and quinque-77 thiophene oligomers attached directly to the switch on one side, and via a carbonyl spacer on the opposite side of the switch were also synthesized. Dimethyldihydropyrene (DHP) photoswitches with a naphthoyl functional group in the 2 position were synthesized using a Friedel Crafts reaction, and ter-96, quinque-97 and septi-98 thiophene oligomers were attached on opposite sides of the switch using Stille coupling reactions. All compounds were characterized by NMR, IR UV-vis spectroscopy and mass spectrometry. The relative rates of the photo-opening reactions under excess light conditions and the UV closing reactions versus BDHP were measured. Improvements in the photo-opening properties of the oligothiophene functionalized switches compared to BDHP were observed. The most dramatic photo-opening improvement was found for the quinquethienyl substituted DHP switch 97 which photo-opened when irradiated with visible light over 100 times faster than BDHP. UV closing rates were virtually the same as that of BDHP. However the addition of oligothiophenes led to an increase in the thermal closing reaction rates. Compounds with the naphthoyl functional group in the 2 position of DHP were found to have dramatically increased thermal closing rates. The electrochemical properties of oligothiophene functionalized BDHP and naphthoyl functionalized DHP switches in the closed form were studied by cyclic voltammetry and spectroelectrochemistry. During the oxidation cycle, a closing reaction from the cyclophanediene (CPD) form to the DHP form of the switches occurred which prevented the study of the electrochemical properties of the switches in the open form. Conductivity testing was performed on the quinquethienyl substituted DHP switch 97 using a gold interdigitated micro electrode array. The conductivity of undoped 97 was greater in the closed DHP isomer than in the open CPD isomer. Irradiation with red or blue light allowed for repetitive switching between the more highly conducting closed form and the less conducting open form. When electrochemically doped, 97 showed improved conductivity over the undoped form but only the conductivity of the closed doped form could be measured due to electrochemically induced closing.

Les systèmes micro-opto-électro-mécaniques (MOEMS) représentent un atout considérable pour les technologies de demain et démontrent régulièrement leur capacité d'innovation dans tous les domaines de recherches. L'astronomie en profite déjà à travers l'optique adaptative et leur versatilité a récemment permis de développer un nouveau spectro-imageur BATMAN qui verra sa première lumière au Telescopio Nazionale Galileo (TNG) à La Palma (Iles Canaries). Le code de contrôle du MOEMS permettant l'automatisation de l'acquisition des spectres a été le point de départ de mon travail au LAM.La partie principale de ce manuscrit traite d'une seconde application imaginée en associant les MOEMS à un matériau photochromique développé à Polytecnico di Milano (Italie) qui peut prendre deux états différenciés par leur transparence. Le MOEMS, initialement utilisé pour la projection d'image, permet de moduler la dose d'énergie lumineuse projeté sur la plaque photochromique qui répond en s'éclaircissant progressivement. Ce procédé permet donc d'enregistrer des images en niveau de gris sur la plaque et notamment des hologrammes générés par ordinateur (CGH) utilisés en métrologie optique. Actuellement, les CGHs utilisés sont binaires, mais notre procédure permet d'enregistrer des CGHs quantifiés en amplitude avec une résolution de 13,68 µm et une précision inférieure à 1% en terme de transparence malgré un éclairage peu homogène. La quantification des CGHs de type Fresnel et Fourier ont été calculés, réalisés et testés avec succès. Deux nouveaux algorithmes de Fourier ont étaient imaginés, réalisés et ont montrés des performances très supérieurs au code usuel de Lee qui est un codage binaire. / Micro-opto-electro-mecanical systems (MOEMS) are primordial tools for future applications in several scientific fields as telecommunications or image display. Astronomy takes also advantage of their great adaptatbility thanks to the development of adaptative optics; a new spectro-imager called BATMAN has recently been develloped to be installed at Telescopio Nazionale Galileo (TNG) in the Canaries Islands. The control of the MOEMS allowing computerizing this processus has been the starting point of my work at the LAM.The main part of this manuscript deals with another application conceived thanks to the association of the characteristics of MOEMS and photosensitive materials developed at Politecnico di Milano (Italy). These materials can be put in two states differentiated by their transparency. The MOEMS, initially used to display images, allows controlling the dose of light projected on the photocrhomic plate which reacts by becoming more and more transparent. This process permit to record Computer Generated Holograms (CGHs) in grayscale which are used in optical metrology. Today, binary CGHs are used but our process allows to record amplitude quantified CGHs with a resolution of 13.68 µm and a precision better than 1% in term of transparency, even with a non homogeneous illumination beam. Comparative studies have shown advantages of quantified CGHs of Fresnel and Fourier families. Two new Fourier algorithms have been conceived thanks to use of the third dimension offered by the control of the transparency. They have been realized and tested succesfully, and have shown much better performances than the current binary coding, so called Lee algorithm.