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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.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Polymeric nanofibrous membranes that act as surfaces offer two compelling properties; they have extremely large surface areas that can be modified and they can offer multiple reactive sites depending on which polymer they were electrospun from. Combining nanofibrous surfaces such as these with photochromic dyes can give remarkable, light responsive materials. In this study, a terpolymer was electrospun and crosslinked (to impart insolubility to the material) to produce a nanofibrous mat that contained surface secondary-hydroxyl units and benzyl chloride units, from which monomers could grow using surface-initiated atom transfer polymerization (SI-ATRP). The surface was further fluorinated though the secondary-hydroxyl moieties to produce a hydrophobic crosslinked nanofibrous surface. n-Butyl acrylate and a photochromic spiropyran dye were copolymerized from the surface using SIATRP, in order to produce a surface that exhibited reversible adhesion towards a water droplet using ultraviolet and visible light as a stimulus to change between the two states. This in principle would allow the droplet to roll off and stick to the surface respectively. Although the surface displayed a colour change when switched, proving that the SI-ATRP had taken place, the droplet of water remained attached to the surface in both states. / AFRIKAANSE OPSOMMING: Polimeriese nanovesel membrane wat dien as oppervlaktes bied twee aantreklike eienskappe; hulle het baie groot oppervlakareas wat gemodifiseer kan word en hulle bied veelvuldige reaktiewe punte, afhangende van die polimeer waarvan hulle ge-elektrospin is. Deur sulke nanovesel oppervlaktes met fotochromiese kleurstowwe te kombineer, kan uitstekende lig reagerende materiale verkry word. In hierdie studie is ‘n terpolimeer ge-elektrospin en daarna gekruisbind (om die materiaal onoplosbaar te maak) om ‘n nanovesel web te kry wat oppervlak sekondêre-hidroksiel en benzielchloried eenhede bevat. Monomere kan dan vanaf hierdie eenhede groei deur middel van oppervlak-geïnisieerde atoomoordrag polimerisasie (OI-AOPR). Die oppervlak was verder gefluorineer via die sekondêre-hidroksiel eenhede om ‘n hidrofobiese, gekruisbinde nanovesel oppervlak te vorm. n-Butielakrilaat en ‘n fotochromiese spiropiraan kleurstof is gekopolimeriseer vanaf die oppervlak deur middel van OI-AORP om sodoende ‘n oppervlak te skep wat omkeerbare adhesie van ‘n water druppel gee as ultraviolet en sigbare lig as stimulus gebruik word om tussen die twee toestande te wissel. In beginsel sal die water druppel vanaf die oppervlak kan afrol én daaraan vassit, afhangende van die toestand van die oppervlak. Alhoewel die oppervlak van kleur verander het met die wisseling tussen die twee toestande, wat as bewys dien dat OI-AORP wel plaasgevind het, het die druppel water bly vassit aan die oppervlak in beide toestande.

De nos jours, des fibres et films photochromiques sont tournés vers le développement des matériaux intelligent qui sont appliqués pour évaluer, signaliser et réagir à un changement de couleur et de spectre d’absorbance. Dans ce travail, l’activité photochromique de six différents types commerciaux de polyuréthane contenant de petites quantités de spiropyrane [1-hexyle-3,3-diméthyle-6'-nitrospiro (indoline-2',2'-benzopyrane)] a été étudiée. Les effets d'épaisseur du film, du temps d'irradiation, et de la concentration en SP sur la réponse photochromique des films de PU/SP ont été étudiés et également leurs interactions. En outre, le comportement photochromique de ces films sous étirement et leurs cinétiques de décoloration ont été abordés. La cinétique et la caractérisation des systèmes photochromiques de spiropyrane incorporé dans le polyuréthane et irradié avec la lumière monochromatique ont été modélisées. Les modèles obtenus peuvent être correctement appliqués dans tous les cas (avec et sans irradiation, avec et sans étirement), en particulier pour tous les rapports massique de SP et pour toute l’épaisseur de film. Le comportement mécanique des polyuréthanes et sa relation avec leurs propriétés photochromiques ont été étudiés et modélisées. Ce modèle est capable de déterminer le taux d’étirement qui peut être traduit en compression locale à partir de quatre mesures photochromiques, et ceci ouvre la porte à des applications potentielles. Un intérêt particulier dans ce contexte, peut être porté aux textiles utilisés pour des applications biomédicales, y compris les bas de contention destinés à empêcher ou traiter la thrombose profonde des veines. Une autre application possible est le développement récent de l'habillement sportif pour améliorer la récupération après des efforts violents / Nowadays, photochromic fibers and films are turned towards the development of intelligent “smart” materials which are applied to evaluate, signalize and react to a change in color and absorbance spectra. In this work, the photochromic activity of six commercial grades of polyurethane that contains small quantities of spiropyran [1-hexyle-3,3-diméthyle-6'-nitrospiro (indoline-2',2'-benzopyran)] has been studied. The effects of film thickness, irradiation time, and SP concentration on the photochromic response of PU/SP films have been studied and also their couplings. Furthermore, the photochromic behaviors of these films under stretching and their decoloration kinetics have been investigated. The kinetics and characterization of the photochromic system of spiropyran incorporated into polyurethane and irradiated with monochromatic light was modeled. The obtained models can be correctly applied in all cases (with and without irradiation, with and without stretching), in particular for all SP mass ratios and for all film thickness. The mechanical behavior of polyurethanes and its relation with the photochromic properties is studied and modeled. This model has the capability to determine the stretching ratio which can be translate to the local compression by employing only four photochromic measurements and this open the way for a wide range of potential applications. Of particular interest in this context are the textiles used for biomedical applications, including graduated compression stockings for preventing or treating deep vein thrombosis. Another related application is the recent development of special sport clothing for improving recovery after strong efforts

Since the discovery of conducting polymers three decades ago the field of organic electronics has evolved rapidly. Organic light emitting diodes have already reached the consumer market, while organic solar cells and transistors are rapidly maturing. One of the great benefits with this class of materials is that they can be processed from solution. This enables several very cheap production methods, such as printing and spin coating, and opens up the possibility to use unconventional substrates, such as flexible plastic foils and paper. Another great benefit is the possibility of tailoring the molecules through carefully controlled synthesis, resulting in a multitude of different functionalities. This thesis reports how charge transport can be altered in solid-state organic electronic devices, with specific focus on memory applications. The first six chapters give a brief review of the field of solid-state organic electronics, with focus on electronic properties, resistance switch mechanisms and systems. Paper 1 and 3 treat Rose Bengal switch devices in detail – how to improve these devices for use in cross-point arrays as well as the origin of the switch effect. Paper 2 investigates how the work function of a conducting polymer can be modified to allow for better electron injection into an organic light emitting diode. The aim of the work in papers 4 and 5 is to understand the behavior of switchable charge trap devices based on blends of photochromic molecules and organic semiconductors. With this in mind, charge transport in the presence of traps is investigated in paper 4 and photochromic molecules is investigated using quantum chemical methods in paper 5. / Elektroniska komponenter har traditionellt sett tillverkats av kisel ellerandra liknande inorganiska material. Denna teknologi har förfinats intillperfektion sedan mitten av 1900-talet och idag har kiselkretsar mycket högprestanda. Tillverkningen av dessas kretsar är dock komplicerad och är därförkostsam. Under 1970-talet upptäcktes att organiska polymerer (dvs plast) kanleda ström under vissa förutsättningar. Genom att välja lämplig polymer ochbehandla den med vissa kemikalier (så kallad dopning) kan man varieraledningsförmågan från isolerande till nästintill metallisk. Det öppnarmöjligheten för att skapa elektroniska komponenter där dessa organiskamaterial utgör den aktiva delen istället för kisel. En av de stora fördelarna medorganiska material är att de vanligtvis är lösliga i vanliga lösningsmedel. Det göratt komponenter kan tillverkas mycket enkelt och billigt genom att användakonventionell tryckteknik, där bläcket har ersatts med lösningen av detorganiska materialet. Det gör också att komponenterna kan tillverkas påokonventionella ytor såsom papper, plast eller textil. En annan spännandemöjlighet med organiska material är att dess funktioner kan skräddarsys genomvälkontrollerad kemisk syntes på molekylär nivå. Inom forskningsområdetOrganisk Elektronik studerar man de elektroniska egenskaperna i de organiskamaterialen och hur man kan använda dessa material i elektroniskakomponenter. Vi omges idag av apparater och applikationer som kräver att data sparas,som till exempel digitala kameror, datorer och mobiltelefoner. Eftersom det finnsett stort intresse från konsumenter för nya smarta produkter ökar behovet avmobila lagringsmedia med stor lagringskapacitet i rasande fart. Detta harsporrat en intensiv utveckling av större och billigare fickminnen, hårddiskar ochminneskort. Många olika typer av minneskomponenter baserade på organiskamaterial har föreslagits de senaste åren. I vissa fall har dessa påståtts kunna erbjuda både billigare och större minnen än vad dagens kiselteknologi tillåter.En typ av organiska elektroniska minnen baseras på en reversibel ochkontrollerbar förändring av ledningsförmågan i komponenten. En informationsenhet – en så kallad bit – kan då lagras genom att till exempel koda en högledningsförmåga som en ”1” och en låg ledningsförmåga som en ”0”. Den härdoktorsavhandlingen är ett försök till att öka förståelsen för sådanaminneskomponenter. Minneskomponenter bestående av det organiska materialet Rose Bengalmellan metallelektroder har undersökts. Egenskaper för system bestående avmånga sådana komponenter har beräknats. Vidare visas att minnesfenomenetinte härstammar i det organiska materialet utan i metallelektroderna.Tillsammans med studier av andra forskargrupper har det här resultatetbidragit till en debatt om huruvida minnesmekanismerna i andra typer avkomponenter verkligen beror på det organiska materialet.Olika sätt att ändra transporten av laddningar i organiska elektroniskasystem har undersökts. Det visas experimentellt hur överföringen av laddningarmellan metallelektroder och det organiska materialet kan förbättras genom attmodifiera metallelektroderna på molekylär nivå. Vidare har det studeratsteoretiskt hur laddningar kan fastna (så kallad trapping) i organiska materialoch därmed påverka ledningsförmågan i materialet.En speciell typ av organiska molekyler ändrar sin struktur, och därmedegenskaper, reversibelt när de belyses av ljus av en viss våglängd, så kalladefotokroma molekyler. Denna förändring kan användas till att ändraledningsförmågan genom en komponent och därmed skulle man kunna användamolekylerna i en minneskomponent. I den sista delen av avhandlingen användskvantkemiska metoder för att beräkna egenskaperna hos dessa molekyler för attöka förståelsen för hur de kan användas i minneskomponenter.

Doctor of Philosophy / Department of Chemistry / Stefan H. Bossmann / The photochromic spirodihydroindolizine/betaine (DHI/B) system has been reinvestigated applying picosecond, microsecond, stationary absorption measurements, and NMR-kinetics. The first surprise was that the electronic structure of the betaines is quite different than commonly assumed. The photochemical ring-opening of DHIs to betaines is a conrotatory 1,5 electrocyclic reaction, as picosecond absorption spectroscopy confirms. The (disrotatory) thermal ring-closing occurs from the cisoid betaine. The lifetime of the transoid betaine is 60 s at 300 K, whereas the lifetime of the cisoid isomer is of the order of 250 microseconds. According to these results, the electrocyclic back reaction of the betaines to the DHI is NOT rate determining, as previously thought, but the cisoid-transoid-isomerization of the betaine. Although the presence of a second nitrogen atom increases the photostability of the spirodihydroindolizine-pyridazine/betaine-system remarkably, the photochemical reaction mechanism appears to be exactly the same for spirodihydroindolizine-pyridazine/betaine-system. A nondestructive photoswitch or an information recording systems has been explored using styryl-quinolyldihydroindolizines. Both isomers DHI and betaine are fluorescent. When the blue betaine is stabilized in a thin polymethyl methacrylate (PMMA) matrix, it is stable for several hours even in room temperature and very stable at 77K. Although irradiation of visible light = 532 nm allows the photo-induced reaction of the Betaine back to the DHI, a nondestructive read-out can be performed at λ = 645 nm upon excitation with λ = 580 nm. Image recording (write) and read-out, as well as information storage (at 77K) have been demonstrated. Charged and maleimide-functionalized DHI/B systems have beed synthesized for use as photochemical gates of the mycobacterial channel porin MspA. Positively charged and maleimide functionalized DHI groups that were attached to the DHI/B-system permit the binding of the photoswitch to selective positions in the channel proteins due to the presence of a cysteine moiety. An inexpensive new method for the large scale synthesis of coelenterazine is developed. A modified Negishi coupling reaction is used to make pyrazine intermediates from aminopyrazine as an economical starting material. This method permits the use of up to 1g coelenterazine per kg body weight and day, which turns the renilla transfected stem cells into powerful light sources.