Ormosils (Organically Modified Silicates) have been used in the past as hosts for various organic molecules. In this work, seven different photochromic dyes most of which belong to the spirooxazine / merocyanine family were doped into thin films that were prepared using several increasingly inorganic Ormosil formulations. These dyes were either physically incorporated into the pores of the film or covalently bound to the matrix via a siloxane substituent. The dyes, which undergo a reversible color change upon irradiation, are relatively stable, although they will ultimately degrade after prolonged exposure to ultraviolet irradiation. This work focuses on identifying the variables that influence the rate of dye degradation, including rigidity of the Ormosil matrix, wavelength of irradiation, and the presence of oxygen. The silylated dyes, which are generally regarded as having reduced mobility within the pores of the Ormosil, degraded more slowly, suggesting a link between stability and rotational and translational freedom. Irradiation wavelength also affected dye stability in that limiting exposure to wavelengths in the near UV (and eliminating visible light) causes the least degradation. This is attributed to the photostability of the photomerocyanine isomer. Finally, the presence of oxygen was shown to cause dramatic enhancement in degradation. The mechanisms of each of these effects are discussed.

Les diaryléthènes et leurs dérivés terrylènes sont prometteurs pour la prochaine génération de dispositifs optoélectroniques en raison de leurs excellentes propriétés photochimiques. Pour les rendre viables pour les appareils électroniques miniaturisés, il est nécessaire d'étudier cette classe de molécules au niveau unimoléculaire avec le microscope à tunnel sous vide ultra-élevé (UHV STM). Cette thèse comporte trois parties: 1) développement de terarylènes hautement sensibles à la commutation; (2) leur modification pour les études STM; et 3) les résultats de ces études STM. Pour être étudié à l'échelle de la molécule unique par STM, des terarylènes ayant une sensibilité de commutation élevée ont été sélectionnés. Ces composés présentent des rendements quantiques élevés allant jusqu'à 100%. Cependant, la réaction de cycloréversion reste faible, de sorte qu'une voie alternative, grâce à un mécanisme oxydatif à réaction en chaîne, a été recherchée. Dans une première partie, nous montrons que l'efficacité et la vitesse de cette réaction peuvent être contrôlées par la fixation de groupes aromatiques sur les carbones réactifs. Dans la deuxième partie, nous avons fonctionnalisé ces molécules afin de les étudier par STM en introduisant des groupes tert-butyle et chlorure. Tout en préservant leurs excellentes propriétés photochimiques, les groupes tert-butyle présentent un excellent contraste lumineux dans les images STM, ils minimisent aussi l'agrégation de ces molécules sur la surface et découplent légèrement les molécules de la surface. Les atomes de chlore permettent de contrôler les assemblages moléculaires sur des substrats isolants de type bicouche de NaCl cristalline précédemment déposés sur un substrat métallique. Dans la troisième partie, les résultats de STM sont présentés. Nous avons développé une nouvelle approche ascendante pour la formation reproductible de nano-assemblages du terarylène non modifié à 77 K. Quant au terarylène modifié par les groupes tert-butyle, il présente à 5 K sur une surface d'Ag (111) différentes formes qui, grâce à la position des groupes tert­butyles à contraste élevé et à l'aide de calculs DFT, ont pu être assignées comme étant différentes conformations de surface de la molécule. Sur NaCl / Ag (111), il a été possible de visualiser les états occupés et inoccupés de la molécule. Cela illustre que, pour ces applications, des molécules avec des propriétés appropriées peuvent être des candidates intéressantes pour des études STM afin d'obtenir des informations sur leurs propriétés à l'échelle de la molécule unique. De telles molécules peuvent être optimisées pour tenir compte de la surface, car sa simple présence peut induire un comportement bien différent de celui obtenu en solution. Cette thèse ouvre les terarylènes à des applications futures nécessitant une surface solide. / Photoswitching diarylethenes, and their terarylene derivatives, are promising for the next generation optoelectronic devices because of their excellent photochemical properties. To make them viable for miniaturized electronic devices, it is necessary to study this class of molecules at the single molecular level by scanning tunneling microscopy under ultra-high vacuum (UHV STM). This thesis has three parts: 1) development of terarylenes highly sensitive to switching; (2) their modification for STM studies; and 3) results of STM investigations. To be studied at the single molecular level by STM, terarylenes with high switching sensitivity have been selected. These compounds display high quantum yields of up to 100 %. However, the cycloreversion reaction remains low so an alternative route, through a chain-reaction oxidative mechanism, has been sought. In the first part, we show that the efficiency and speed of this reaction may be controlled by attachment of aromatic groups on the reactive carbons. In the second part, we functionalized these molecules for STM studies by attaching tert-butyl and chloride groups. These substituents preserve their excellent photochemical and switching properties while tert-butyl groups show bright contrast in STM images, minimize aggregation of these molecules on the surface, and slightly decouple the molecule from the surface. The chlorine group has been introduced to direct their surface assembly on insulating substrates composed of crystalline NaCl bilayer previously grown over a metallic substrate. In the third part, results of STM are presented. We developed a new bottom-up approach for forming reproducible nanoassemblies of the unmodified terarylene at 77 K. Meanwhile, at 5 K, the terarylene functionalized with tert-butyl groups present different forms on the Ag(111) surface. From the positioning of the high-contrast tert-butyl groups and with the aid of DFT calculations, we assign different conformations of the molecule on the surface. On NaCl/Ag(111), direct visualization of the occupied and unoccupied states could be achieved. This illustrates that for these applications, molecules with appropriate properties can be interesting candidates for STM studies to obtain information at the single molecular level. Such molecules may be redesigned with a consideration of the surface as its mere presence may induce behavior previously unobserved or neglected if they were studied in solution. This thesis opens terarylenes to future applications which require a solid surface.

Neste trabalho, é analisada a estrutura de materiais híbridos contendo poliânions de ácido 12-tungstofosfórico (H3PW12O40, HPW) inseridos em uma matriz de silicatos orgânico-inorgânica (ormosil). Estes materiais apresentam propriedade reversível de fotocromismo na faixa do UV (200-400nm), sendo cogitados como possíveis candidatos para aplicação como dosímetros pessoais UV. A metodologia sol-gel possibilita a obtenção destes compostos por vias relativamente simples e de baixo custo para a combinação dos componentes orgânicos e inorgânicos formadores da matriz ormosil. As propriedades do efeito fotocrômico, como intensidade e tempo de vida, ser alteradas variando-se a concentração e a natureza dos grupos presentes na matriz ormosil. Outras propriedades também podem ser ajustadas, como porosidade, adesão dos filmes, resistência mecânica, homogeneidade e transparência. No entanto uma correlação clara entre o processo de fotocromismo e a estrutura local ao redor do poliânion ainda não foi estabelecida. O objetivo geral da pesquisa é a caracterização estrutural e dinâmica destes compostos, a fim de se avançar no entendimento do processo fotocrômico e na otimização de métodos de preparação para o controle das propriedades fotocrômicas. Resultados preliminares mostram que o ambiente de coordenação do HPW nos ormosils é complexo, envolvendo diversas espécies de prótons, e os níveis de hidratação parecem desempenhar importante papel estrutural. Portanto, o objetivo específico deste trabalho é obter uma descrição da estrutura/dinâmica das espécies no ambiente de coordenação do poliânion, como espécies de hidratação e/ou grupos da matriz ormosil, e da interação entre estas espécies e o HPW. Para tal, foram utilizadas técnicas de ressonância magnética nuclear (RMN) para analisar amostras de composição simplificada, como uma amostra modelo HPW n6H2O e xerogeis contendo tetraetilortosilicato (TEOS) e no máximo dois organosilanos na composição, dentro do conjunto: 3-aminopropiltrietóxisilano (APTS), butironitrilatrietoxisilano (BUT) e 3 glicidoxipropilltrimetóxisilano (GLYMO). Embora a estrutura do HPW n6H2O seja extensamente discutida na literatura, ainda existem questões estruturais a serem discutidas, para as quais as técnicas de RMN podem fornecer importante contribuição. Diferentes tratamentos térmicos sobre o HPW nH2O foram testados para a obtenção do HPW n6H2O, e os resultados de RMN mostram que o controle de atmosfera durante o processo de secagem é determinante para a estrutura final das espécies de hidratação. No caso dos xerogeis, diferentes atmosferas foram testadas durante o preparo, estudando-se o efeito desta variável sobre a estrutura das espécies no ambiente de coordenação do HPW. Adicionalmente, tratamentos térmicos para a secagem das amostras também foram realizados. Após a irradiação das amostras com luz UV é formado um centro paramagnético WV no poliânion, que foi estudado por ressonância paramagnética eletrônica (RPE). A técnica de 31P permitiu avaliar a estrutura no ambiente mais local da molécula de HPW. Utilizando técnicas de 1H RMN, polarização cruzada (CP) {1H}-31P, correlação heteronuclear (HETCOR) {1H}-31P, {1H}-29Si e {1H}-13C, e medidas de tempos de relaxação spin-rede de 1H no sistema rotante (T1&rho;), foi constatado que o ambiente de coordenação do HPW nos xerogeis é basicamente constituído de espécies de hidratação, como H2O, H3O+, H5O2+ e H+(H2O)n, e espécies OH, que provavelmente pertencem a grupos na matriz de ormosil. Os experimentos de RPE permitiram identificar a existência de uma processo termicamente ativado, em que o elétron excitado realiza saltos entre os diferentes sítios WO6. Dois tipos de centros paramagnéticos WO6, ambos com simetria ortorrômbica, foram resolvidos em 20K. Um deles pôde ser atribuído a sítios WO6 interagindo fortemente com H2O, com a elongação da ligação W=O em WO6. Este sítio é dominante para amostras mais hidratadas. Além deste, outro sítio é observado em amostras mais secas, atribuído a centros WO6 interagindo mais fracamente com os H no ambiente do HPW. Estes resultados mostram que as espécies de hidratação desempenham um importante papel no processo de fotocromismo. / The local structure of hybrid organic-inorganic (ormosils) materials based on 12-phosphotungstic acid (H3PW12O40, HPW) was analyzed. These materials have reversible photochromic response in the range of ultraviolet (200 - 400 nm), and may found application in personal UV dosimeters. These ormosils can be prepared in a simple way using the sol-gel method, allowing the possibility of film depositions. It is known that properties such as the intensity of the photochromic response and the life-time in this state can be controlled changing the organic functional groups in the silane precursors. Other general properties can be also adjusted with these organic functionalities, such as film adhesion, mechanical response, homogeneity and transparency. However, the relation between the photochromic response, the chemical species (including water molecules) around the polyanion, and the local structure is still an open problem. The objective of this work was to analyze the effect of the preparation conditions of the ormosils (composition, atmosphere and thermal treatments) on the chemical environment around the polyanion and their possible influence in the photochromic response. The analysis of the interaction between the polyanion and the chemical species in the ormosil network and hydration species was carried out using nuclear magnetic resonance spectroscopy (NMR) in the solid-state for 1H, 31P, 13C, and 29Si. A set of simple photochromic ormosils were considered in this study, prepared with tetraethilorthosilicate (TEOS) and a maximum of two organosilane precursors from the set aminopropyltriethoxysilane (APTS), butyronitriletriethoxysilane (BUT) and 3-Glycidoxypropyltrimethoxysilane (GLYMO). Also, the HPW hexahydrate (HPW 6H2O) was analyzed as a model system to test the response of the NMR technique to the structural and dynamical process known in this crystal. The effects of thermal treatments and atmosphere in the preparation of the hexahydrate were analyzed. New information concerning the H dynamics and the thermal transformations observed in this system was gathered in this study. For the photochromic ormosils, preparations under three different atmospheres (uncontrolled ambient, N2 flow, and Ar glove-box) were carried out, as well thermal treatments to remove loosely bound water. Electronic paramagnetic resonance (EPR) experiments were carried out in UV-irradiated ormosils, were paramagnetic centers in WV, related with the photochromic process, were observed. The chemical environment around the polyanion was probed using the techniques of 1H-NMR, {1H}-31P cross-polarization, heteronuclear correlations {1H}-31P, {1H}-29Sie {1H}-13C, and the measurement of the proton spin-lattice relaxation in the rotating frame (T1&rho;). The results revealed the presence of close hydration species such as H2O, H3O+</sup), H5O2+ and H+(H2O)n, and OH groups from the ormosil network. No evidence of interaction between the polyanion and the organic functionalities was found. In the irradiated samples, the EPR experiments revealed a thermally activated hopping process for the excited unpaired electron between WO6 octahedra. Two kinds of paramagnetic sites at the WO6 octahedra, both with orthorrombic symmetry, were resolved at 20K. One of them corresponds to WO6 strongly interacting with water species, with an elongated W=O bond length. This site is dominant for higher hydrated samples. The other site corresponds to WO6 with a weak interaction with protons in the polyanion environment and is observed in higher amounts in less hydrated samples. These results show that the hydrate species in the polyanion coordination environment plays an important role in the photochromic process.

Neste trabalho, é analisada a estrutura de materiais híbridos contendo poliânions de ácido 12-tungstofosfórico (H3PW12O40, HPW) inseridos em uma matriz de silicatos orgânico-inorgânica (ormosil). Estes materiais apresentam propriedade reversível de fotocromismo na faixa do UV (200-400nm), sendo cogitados como possíveis candidatos para aplicação como dosímetros pessoais UV. A metodologia sol-gel possibilita a obtenção destes compostos por vias relativamente simples e de baixo custo para a combinação dos componentes orgânicos e inorgânicos formadores da matriz ormosil. As propriedades do efeito fotocrômico, como intensidade e tempo de vida, ser alteradas variando-se a concentração e a natureza dos grupos presentes na matriz ormosil. Outras propriedades também podem ser ajustadas, como porosidade, adesão dos filmes, resistência mecânica, homogeneidade e transparência. No entanto uma correlação clara entre o processo de fotocromismo e a estrutura local ao redor do poliânion ainda não foi estabelecida. O objetivo geral da pesquisa é a caracterização estrutural e dinâmica destes compostos, a fim de se avançar no entendimento do processo fotocrômico e na otimização de métodos de preparação para o controle das propriedades fotocrômicas. Resultados preliminares mostram que o ambiente de coordenação do HPW nos ormosils é complexo, envolvendo diversas espécies de prótons, e os níveis de hidratação parecem desempenhar importante papel estrutural. Portanto, o objetivo específico deste trabalho é obter uma descrição da estrutura/dinâmica das espécies no ambiente de coordenação do poliânion, como espécies de hidratação e/ou grupos da matriz ormosil, e da interação entre estas espécies e o HPW. Para tal, foram utilizadas técnicas de ressonância magnética nuclear (RMN) para analisar amostras de composição simplificada, como uma amostra modelo HPW n6H2O e xerogeis contendo tetraetilortosilicato (TEOS) e no máximo dois organosilanos na composição, dentro do conjunto: 3-aminopropiltrietóxisilano (APTS), butironitrilatrietoxisilano (BUT) e 3 glicidoxipropilltrimetóxisilano (GLYMO). Embora a estrutura do HPW n6H2O seja extensamente discutida na literatura, ainda existem questões estruturais a serem discutidas, para as quais as técnicas de RMN podem fornecer importante contribuição. Diferentes tratamentos térmicos sobre o HPW nH2O foram testados para a obtenção do HPW n6H2O, e os resultados de RMN mostram que o controle de atmosfera durante o processo de secagem é determinante para a estrutura final das espécies de hidratação. No caso dos xerogeis, diferentes atmosferas foram testadas durante o preparo, estudando-se o efeito desta variável sobre a estrutura das espécies no ambiente de coordenação do HPW. Adicionalmente, tratamentos térmicos para a secagem das amostras também foram realizados. Após a irradiação das amostras com luz UV é formado um centro paramagnético WV no poliânion, que foi estudado por ressonância paramagnética eletrônica (RPE). A técnica de 31P permitiu avaliar a estrutura no ambiente mais local da molécula de HPW. Utilizando técnicas de 1H RMN, polarização cruzada (CP) {1H}-31P, correlação heteronuclear (HETCOR) {1H}-31P, {1H}-29Si e {1H}-13C, e medidas de tempos de relaxação spin-rede de 1H no sistema rotante (T1&rho;), foi constatado que o ambiente de coordenação do HPW nos xerogeis é basicamente constituído de espécies de hidratação, como H2O, H3O+, H5O2+ e H+(H2O)n, e espécies OH, que provavelmente pertencem a grupos na matriz de ormosil. Os experimentos de RPE permitiram identificar a existência de uma processo termicamente ativado, em que o elétron excitado realiza saltos entre os diferentes sítios WO6. Dois tipos de centros paramagnéticos WO6, ambos com simetria ortorrômbica, foram resolvidos em 20K. Um deles pôde ser atribuído a sítios WO6 interagindo fortemente com H2O, com a elongação da ligação W=O em WO6. Este sítio é dominante para amostras mais hidratadas. Além deste, outro sítio é observado em amostras mais secas, atribuído a centros WO6 interagindo mais fracamente com os H no ambiente do HPW. Estes resultados mostram que as espécies de hidratação desempenham um importante papel no processo de fotocromismo. / The local structure of hybrid organic-inorganic (ormosils) materials based on 12-phosphotungstic acid (H3PW12O40, HPW) was analyzed. These materials have reversible photochromic response in the range of ultraviolet (200 - 400 nm), and may found application in personal UV dosimeters. These ormosils can be prepared in a simple way using the sol-gel method, allowing the possibility of film depositions. It is known that properties such as the intensity of the photochromic response and the life-time in this state can be controlled changing the organic functional groups in the silane precursors. Other general properties can be also adjusted with these organic functionalities, such as film adhesion, mechanical response, homogeneity and transparency. However, the relation between the photochromic response, the chemical species (including water molecules) around the polyanion, and the local structure is still an open problem. The objective of this work was to analyze the effect of the preparation conditions of the ormosils (composition, atmosphere and thermal treatments) on the chemical environment around the polyanion and their possible influence in the photochromic response. The analysis of the interaction between the polyanion and the chemical species in the ormosil network and hydration species was carried out using nuclear magnetic resonance spectroscopy (NMR) in the solid-state for 1H, 31P, 13C, and 29Si. A set of simple photochromic ormosils were considered in this study, prepared with tetraethilorthosilicate (TEOS) and a maximum of two organosilane precursors from the set aminopropyltriethoxysilane (APTS), butyronitriletriethoxysilane (BUT) and 3-Glycidoxypropyltrimethoxysilane (GLYMO). Also, the HPW hexahydrate (HPW 6H2O) was analyzed as a model system to test the response of the NMR technique to the structural and dynamical process known in this crystal. The effects of thermal treatments and atmosphere in the preparation of the hexahydrate were analyzed. New information concerning the H dynamics and the thermal transformations observed in this system was gathered in this study. For the photochromic ormosils, preparations under three different atmospheres (uncontrolled ambient, N2 flow, and Ar glove-box) were carried out, as well thermal treatments to remove loosely bound water. Electronic paramagnetic resonance (EPR) experiments were carried out in UV-irradiated ormosils, were paramagnetic centers in WV, related with the photochromic process, were observed. The chemical environment around the polyanion was probed using the techniques of 1H-NMR, {1H}-31P cross-polarization, heteronuclear correlations {1H}-31P, {1H}-29Sie {1H}-13C, and the measurement of the proton spin-lattice relaxation in the rotating frame (T1&rho;). The results revealed the presence of close hydration species such as H2O, H3O+</sup), H5O2+ and H+(H2O)n, and OH groups from the ormosil network. No evidence of interaction between the polyanion and the organic functionalities was found. In the irradiated samples, the EPR experiments revealed a thermally activated hopping process for the excited unpaired electron between WO6 octahedra. Two kinds of paramagnetic sites at the WO6 octahedra, both with orthorrombic symmetry, were resolved at 20K. One of them corresponds to WO6 strongly interacting with water species, with an elongated W=O bond length. This site is dominant for higher hydrated samples. The other site corresponds to WO6 with a weak interaction with protons in the polyanion environment and is observed in higher amounts in less hydrated samples. These results show that the hydrate species in the polyanion coordination environment plays an important role in the photochromic process.

A series of photochromic bisthienylethenes (BTE) chromophores with different central ethene bridges were synthesized. Up to date, the rational design of BTE have been mainly carried out on the side aryl groups. In our work, the influence of the aromaticity of the central ethene bridge on the photochromic properties was studied. Moreover, unlike in the literature where most of BTE have a five-membered ring bridge, six-membered ring bridges were used. In Chapter 1, examples of photochromes are given, along with the main definitions. Chapter 2 deals with BTTE, a BTE with a benzobisthiadiazole bridge and with excellent photochromic properties. c-BTTE, the closed isomer, exhibits excellent thermal stability in various solvents and in the solid state. Its fluorescence can be modulated by solvato- and photochromism. It eliminates the usual bias of thermal back reaction, typical of BTE with a six-membered ring ethene bridge. Chapter 3 is devoted to compounds with bridges having different aromaticities (BTE-NA, BTA and BTTA). Their fluorescence can be modulated by solvato- and photochromism. The relation between aromaticity and thermal stability was established: the low aromaticity of the central ethene bridge with benzobisthiadiazole unit leads to a thermal irreversibility for BTTA, and the small energy barrier between the parallel and anti-parallel conformers and the great difference in absorption between BTTA and c-BTTA allow the full conversion from BTTA to c-BTTA. Molecules with a benzothiadiazole bridge, designed for complexation and for switchable nonlinear optical properties were prepared (Chapters 4 and 5). However, the targeted properties were not evidenced up to now.

The synthesis of the cyclopentadiene-fused dimethyldihydropyrene, CpDI-IP(H) 44, from DHP 31 was achieved in a seven-step synthesis in an overall yield of 7%. Deprotonation of 44 gave the Cp anion fused CpDHP anion 28. The photochromic properties of 28 were studied. It is found that 28 is photochromic and its behavior is intermediate between the parent DHP 31 and the benzannelated DHP 36. The 1H-NMR data of 28 were also analyzed and showed that the Cp anion has similar bond fixing effect on the DHP ring as benzene does, but to a lesser extent. The complexation of anion 28 to various metal centers has been investigated. While the reactions of 28 with Re(CO)5Br, (Cp*RuCl2)„ and FeC12 yielded (CpDHP)Re(CO)3 51. Cp*Ru(CpDHP) 52 and (CpDHP)2Fe 54 respectively, the reactions with Mn. Y. Yb(III) or Zr precursors either gave the starting materials back or resulted in the decomposition of 28 to unidentified products. Reaction of the protonated form CpDHP(H) 44 with Yb[N(SiMe3)2I(thf)2 afforded Yb(CpDHP)2(thf)2 57.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 263-287) Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 263-287) Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 303-328). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 303-328). Also available online.