Thirty four silver(I) complexes of azobenzene and derivatives have been synthesised, only two of which have been previously published. The azobenzene derivatives used are 2-bromo, 3-bromo, 4-bromo, 3,4’-dibromo, 2,4’-dibromo, 3-nitro, 4-dimethylamino, 4-methoxy, 2,6-dimethyl-4’-chloro, 2,6,2’,6’-tetramethyl and 2,2’-ethyleneazobenzene. 2,2’- and 4,4’-azobispyridine were also used along with diphenyltriazine. Six different silver(I) salts were used to make the complexes; they are tetrafluoroborate, hexafluorophosphate, perchlorate, nitrate, triflate and trifluoroacetate. All of the complexes were analysed using X-ray crystallography. In the complexes with azobenzene the anion was the most crucial factor in determining the resulting structure, as five different molecular topologies were seen with each change of anion. The 2-bromoazobenzene containing complexes continue this trend giving similar topologies to the azobenzene containing complexes. Once we come to the 3-bromo and 4-bromoazobenzene, we get a different molecular topology for the hexafluorophosphate containing complexes when compared to the original azobenzene containing complex, but we see a very similar structure for the perchlorate containing complexes. This would suggest that the coordinating anions give more predictable structures than the non-coordinating anions. The trend continues with both the 3,4’-dibromo and 2,4’-dibromoazobenzene complexes with triflate being structurally similar to the previous triflate containing complexes. The trend is reinforced further with 3-nitro and 4-methoxyazobenzene showing similar structures to the previously discussed complexes. The complex containing 4-dimethylaminoazobenzene can be disregarded, as the ligand has become protonated and therefore is unlike all the previously described results. When we come to the sterically hindered ligands 2,6-dimethyl-4’-chloroazobenzene the first three complexes show the same molecular topology of a silver atom bound to two ligands with a coordinating anion, however once we come to a tridentate coordinating anion triflate a 1-D metallopolymer is observed. This breaks the trend, as the structures are similar regardless of the change in anion. A similar effect is seen in 2,6,2’,6’-tetramethylazobenzene with both structures standing alone as no complexes with a similar molecular topology were observed. This effect is again noted in the complexes containing 2,2’-ethyleneazobenzene. The complexes all form a similar structure regardless of the anion used. As expected the 2,2’- and 4,4’-azobispyridine along with diphenyltriazine do not follow the trend observed earlier with the non-sterically hindered ligands as they can coordinate through additional nitrogen atoms in the aromatic ring or in the case of diphenyltriazine an additional nitrogen atom in the triazine group.

No description available.

NMR spectroscopy with in situ laser irradiation has been used to investigate the photo- and thermal isomerisation of eight azobenzene derivatives; diphenyldiazene (azobenzene), p-phenylazoaniline (p-aminoazobenzene), 4-(dimethylamino)azobenzene (Methyl Yellow), 4-dimethylamino-2-methylazobenzene (o-Methyl-Methyl Yellow), p-nitroazobenzene, 4-nitro-4’-dimethylaminoazobeneze (Dimethyl-nitroazobenzene), 4-(4-nitrophenylazo)aniline (Disperse Orange 3) and N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) (Disperse Red 1). The rate constants and activation parameters of the thermal cis-to-trans isomerisation have been measured experimentally and correlated to the mechanism of isomerisation in two solvents. The experimental data show that the values of the activation energy (related to the enthalpy of activation) and the entropy of activation (related to the Arrhenius pre-exponential factor) vary significantly from molecule to molecule and thus both of these parameters influence the inter-molecule variation of the rate constant. Similarly, both of these parameters influence the solvent-dependence of the rate constant. Complementary computational studies have been carried out in the gas phase and in solution using density functional theory (DFT) to predict the structures of the cis and trans isomers and the transition state, and to explore the reaction coordinate. The theoretically predicted activation parameters are compared with those determined experimentally, and the utility of DFT calculations in predicting the effects of molecular structure and solvation on the kinetics of cis-to-trans isomerisation assessed. The DFT-predicted values of the activation energy and Gibbs free energy of activation in DMSO are in good agreement with the experimental values, while the values in benzene tend to be in less good agreement. The DFT calculations are unsuccessful at predicting the entropy of activation, where in all cases there is a large discrepancy between the theoretical and experimental values. The DFT- calculated energy differences between the activation energies of the two inversion pathways for the asymmetric azobenzenes suggests the favourable phenyl ring for inversion. The formation of a linear transition state from a dihedral rotation potential energy curve is explained in terms of the lower activation barrier of the more favourable inversion route (α-inversion) than that of the dihedral rotation pathway, and suggests the inversion through the α-phenyl ring to be the favoured pathway for substituted azobenzene. DFT calculations are able to obtain a transition state corresponding to pure rotation pathway for two azobenzene derivatives. The higher activation barrier for the formation of the transition state corresponding to this pathway compared to that of the formation of the α-transition state confirmed the previous conclusion. DFT predictions of the effect of protonation on the thermal rates of isomerisation of azobenzenes substituted with electron-donating group were in good agreement with the experimental results; both conclude faster isomerisation and lower activation barriers on protonation. However, DFT calculations could not confirm the postulation of rotational transition state for the isomerisation of the protonated molecule, as a result of weakening of the N=N bond by protonation.

Abstract: Owing to the light-induced switching between their trans- and cis-isomers, azobenzenes display a wide range of applications including stimuli-responsive polymers, acid-base indicators, colorful systems, liquid crystals, and bio-medicals. In the past decades, much research on azobenzenes has been carried out and they have become a growing research topic. Particularly, the synthetic methodology of azobenzene derivatives has become mature. However, a general synthetic method of furnishing the bis- and tris-azobenzene compounds in one step is still lacking, and the study of bis-azobenzene is nearly blank including the solution properties and applications. In this thesis, we focus on the design, and preparation of bis-, tris- and small cyclic azobenzene derivatives; followed by a further investigation of their properties in solution. We also explore the preparation and applications of azobenzene-based stimuli-responsive polymeric materials. The first chapter describes an efficient strategy for the synthesis of bis- and tris-azobenzene derivatives. In this synthetic pathway, the bis- and tris-azobenzenes could be obtained in one pot, together with mono-azobenzene side products. By modifying the reaction conditions, the yields of the azobenzene compounds were mainly dependent on the substituents on the phenols and diazonium salts, and the molar ratio of starting materials. Compared with the unsubstituted aniline, the use of anilines with electron-withdrawing groups, leading to electron-deficient diazonium salts, favors the formation of mono-azobenzenes, rather than bis-azobenzenes. Whereas, anilines with electron-donating groups are not efficient during the first step leading to the formation of mono-azobenzene and thus favor the generation of bis-azobenzenes. Large amounts of anilines (over two-fold and three-fold excess), are the best choice to obtain bis- and tris-azobenzenes in good yields. In Chapter 2, we describe a novel method for the cyclization of mono- and bis-azobenzenes without ultraviolet light to form seven-membered heterocycles. The starting materials contain ortho-fluoro atom and ortho-phenol groups on the phenyl rings of the azobenzene systems. The role of the fluoro substituent is twofold. It promotes the stability of the cis-form of the azobenzene and it acts as a leaving group when its carbon atom neighbor is attacked by the phenolate. The nature of solvents was found to have a pronounced effect on the spontaneous cyclization reaction by stabilizing the  intermediate complex. The cyclization rate could be accelerated under the UV irradiation and by using more polar solvents. Due to the competing keto-enol tautomerizations and cyclizations, we observed complicated changes in UV-vis absorption and color of solutions over time. It was revealed that, for ortho-hydroxyl azobenzenes with ortho-fluorine atom in polar solvents, the trans-to-cis isomerization and cyclization happened under daylight, and keto-enol tautomerization occurred in the dark. In Chapter 3, we studied a class of novel dual-responsive (photo- and thermo-) copolymers by modifying Poly(N-isopropylacrylamide) (PNIPAM) with bis-azobenzene moieties. The copolymers were prepared from a free radical copolymerization of N-isopropylacrylamide (NIPAM) and bis-azobenzenes bearing electron-donating or electron-accepting substituents. It was found that bis-azobenzene moieties could influence the cloud point of aqueous copolymer solution due to the photoisomerization of bis-azobenzenes and the conformation of polymer chain upon the photoreactions. Varying substituents on bis-azobenzene moieties, the copolymer solutions displayed an opposite cloud point shift after the photoreactions of the chromophores. When the substituents on azobenzene have push-pull feature, the polymer chains prefer aggregation after UV irradiation, which decreases the cloud point. By contrast, the cloud point shifts to higher temperature upon UV light irradiation when the bis-azobenzenes bears the donors, which is caused by cis-isomer being more hydrophilic than the trans-isomer. However, the effect of photoisomerization of azobenzene on the cloud point shift appears to be greater on PNIPAM containing mono-azobenzene pendent groups. / En raison de la commutation induite par la lumière entre leurs isomères trans et cis, les azobenzènes affichent une gamme étendue d'applications. On y retrouve des polymères sensibles aux stimuli, des indicateurs acido-basiques, des systèmes colorés, des cristaux liquides et des matériaux aux applications biomédicales. Dans les dernières décennies, de nombreuses recherches sur les azobenzènes ont été menées et ils sont devenues un sujet de plus en plus important. En particulier, la méthodologie de synthèse des dérivés d'azobenzène est devenue mature. Cependant, une méthode synthétique générale pour l’obtention des composés bis- et tris-azobenzène en une seule étape est encore manquante, et l'étude du bis-azobenzène est presque vierge, y compris les propriétés et les applications en solution. Dans cette thèse, nous nous concentrons sur la conception et la préparation de bis-, tris- et de petits dérivés cycliques de l'azobenzène. Ce premier volet est suivi d'une étude plus poussée de leurs propriétés en solution. Nous explorons également la préparation et l'application de matériaux polymères d'azobenzène, réagissant à plusieurs stimulations. Le premier chapitre décrit une stratégie efficace pour la synthèse des dérivés bis- et tris-azobenzène. Dans cette voie de synthèse, les bis- et tris-azobenzènes peuvent être obtenus dans un pot réactionnel, avec des produits secondaires mono-azobenzène. En modifiant les conditions de réaction, les rendements des composés azobenzène dépendent principalement des substituants sur les phénols et les sels de diazonium, et du rapport molaire des produits de départ. Par rapport à l'aniline non substituée, l'utilisation d'anilines avec des groupes électroattracteurs, conduisant à des sels de diazonium déficients en électrons, favorise la formation de monoazobenzènes plutôt que de bis-azobenzènes. En revanche, les anilines à groupements donneurs d'électrons ne sont pas efficaces au cours de la première étape conduisant à la formation de monoazobenzènes et favorisent ainsi la génération de bis-azobenzènes. De grandes quantités d'anilines (excès de plus de deux et trois fois) sont le meilleur choix pour obtenir des bis- et tris-azobenzènes avec de bons rendements. Dans le chapitre 2, nous décrivons une nouvelle méthode de cyclisation des mono- et bis-azobenzènes, sans lumière ultraviolette, pour former des hétérocycles à sept chaînons. Les produits de départ contiennent des groupes ortho-fluoro et orthophénol sur les cycles phényle des systèmes azobenzène. Le rôle du substituant fluoro est double. Il favorise la stabilité de la forme cis de l'azobenzène et agit comme un groupe partant lorsque son atome de carbone voisin est attaqué par le phénolate. La nature des solvants s'est avérée avoir un effet prononcé sur la réaction de cyclisation spontanée en stabilisant le complexe intermédiaire . La vitesse de cyclisation peut être accélérée sous l'irradiation UV et en utilisant des solvants plus polaires. En raison des tautomérisations céto-énol et des cyclisations en compétition, nous avons observé que l’évolution des spectres d'absorption UV-vis et de la couleur des solutions au fil du temps était compliqué. Il a été révélé que, pour les ortho-hydroxyl azobenzènes avec un atome d'ortho-fluor dans les solvants polaires, l'isomérisation et la cyclisation trans-cis se produisaient à la lumière du jour et que la tautomérisation céto-énol se produisait dans l'obscurité. Dans le chapitre 3, nous avons étudié une classe de nouveaux copolymères biosensibles (photo- et thermo-) en modifiant le poly(N-isopropylacrylamide) (PNIPAM) avec des portions bis-azobenzène. Les copolymères ont été préparés à partir d'une copolymérisation radicalaire de N-isopropylacrylamide (NIPAM) et de bis-azobenzènes portant des substituants donneurs ou accepteurs d'électrons. Il a été constaté que les fragments bis-azobenzène pouvaient influencer le point de trouble de la solution aqueuse de copolymère en raison de la photoisomérisation des bis-azobenzènes et de la conformation de la chaîne polymère lors des photoréactions. En changeant les substituants sur les fragments bis-azobenzène, les solutions de copolymères présentaient un décalage du point de trouble opposé après les photoréactions des chromophores. Lorsque les substituants sur l'azobenzène ont une influence «push-pull», les chaînes polymères préfèrent l'agrégation après l'irradiation UV, ce qui diminue le point de trouble. En revanche, le point de trouble passe à une température plus élevée lors de l'irradiation par la lumière UV lorsque les bis-azobenzènes portent des donneurs, ce qui est dû au fait que l'isomère cis est plus hydrophile que l'isomère trans. Cependant, l'effet de la photo-isomérisation de l'azobenzène sur le décalage du point de trouble semble être plus important sur les groupes pendants mono-azobenzène contenant du PNIPAM.

Nesta tese foram investigadas as propriedades foto-switch de novas tríades constituídas por uma unidade central de Si(IV)-Ftalocianina e dois ligantes axiais azobenzênicos. A posição 4\' dos ligantes azobenzênicos apresenta substituintes (X) com diferentes propriedades eletrônicas e estéricas, a saber: -H; -CH3; -C(CH3)3; -OCH3; e -I. A tríade com substituinte -NO2 foi novamente investigada e incluída como tríade de maior caráter push-pull da série. Para efeito de comparação, também foram investigados hidróxiazobenzenos (HO-Azo-X) com os mesmos substituintes (X) na posição 4\' que os presentes nas tríades. Os HO-Azo-X apresentam propriedades espectroscópicas, fotoquímicas (fotoisomerização E→Z e Z→E) como também retorno térmico Z→E com características intermediárias entre a classe dos azobenzenos e dos amino-azobenzenos. Estas propriedades podem ser atribuídas à presença comum do substituinte hidróxi que apresenta um caráter doador, porém menos acentuado que a do grupo amino. Os espectros de absorção eletrônica das tríades apresentam uma banda B no UV e um conjunto de bandas Q na região visível do espectro eletromagnético. Observou-se a existência de um processo de agregação dos complexos dependente do substituinte 4\'. As tríades apresentam emissão de fluorescência quando excitadas tanto na banda B como na banda Q, com pequenos deslocamentos Stokes. Os rendimentos quânticos de fluorescência obedecem à regra de Kasha. Isto foi confirmado para os rendimentos quânticos corrigidos da banda B, os quais excluem a fração de luz absorvida pelos ligantes axiais nesta região de excitação. A excitação das tríades em THF resulta em photobleaching, que ocorre tanto na presença como na ausência de oxigênio, sendo mais efetivo neste último caso; temos que: a) na ausência de oxigênio provavelmente existe a formação de radicais acíclicos de THF que destroem a ftalocianina; b) na presença de oxigênio peróxidos estão envolvidos na degradação, tendo sido detectados e quantificados nas soluções das tríades após irradiação. Nos dois casos o estado excitado triplete é responsável pelo início do processo. Em benzeno puderam ser investigados a fotoisomerização E→Z, a isomerização fotossensibilizada Z→E, assim como a isomerização térmica (retorno térmico) Z→E. Os resultados mostram que a coordenação não altera as propriedades do estado excitado dos ligantes azobenzênicos evidenciado pela similaridade dos rendimentos quânticos e constantes de velocidade E→Z comparativamente aos HO-Azo-X. Entretanto, o retorno térmico Z→E, é muito mais lento comparativamente aos HO-Azo-X. A ligação Si-O nos complexos comparativamente a H-O nos HO-Azo-X e os momento de dipolo resultante devem ser os responsáveis por esse fenômeno. As isomerizações fotossensibilizadas Z→E são muito mais rápidas que as respectivas térmicas existindo diferenças de até 30 vezes nos valores das respectivas constantes. Todas as tríades apresentam o comportamento foto-switch de emissão que é controlado pelo estado E ou Z do ligante axial. Ao longo da série as variações de intensidade de emissão se situam entre 19 - 27% da intensidade inicial. O fato do processo Z→E nas tríades ocorrer através do processo térmico ou fotossensibilizado que é consideravelmente mais rápido faz destas tríades sistemas switches quase-biestáveis. Este controle cinético também potencializa a utilização destas tríades em sistemas de informação molecular binário. / In this work have been studied the photoswitch properties of new triads with one central Si(IV)-phthalocyanine and two axially coordinated azobenzenes. The 4\' position of the azobenzene ligands has substituents (X) presenting different electronic/steric contributions: -H; -CH3; -C(CH3)3; -OCH3; and -I. The triad with -NO2 substituent was reinvestigated and included as the triad with the major push-pull effect in the series. For comparative purposes have been investigated hydroxyazobenzenes (HO-Azo-X) with the same substituents (X) at the 4\' position of the triads. The HO-Azo-X compounds show spectroscopic, photochemical (photoisomerization E→Z and Z→E) and thermal Z→E reaction with intermediate properties that which shown by the class of azobenzene and aminoazobenzene compounds. These characteristics can be attributed to the hydroxyl-substituent present in all compounds, which has donor character, but less pronounced than the amino group. The electronic absorption spectra of the triads show a B band in the UV and a set of Q bands in the visible region of the electromagnetic spectrum. Could be noticed an aggregation behavior for these triads dependent on the 4\' substituent. The triads show fluorescence emission when excited at B or Q bands, presenting small Stokes shift. Fluorescence quantum yields are in accordance with Kasha\'s rule. Photobleaching is observed when THF solutions of the triads are irradiated. This photobleching occurs in presence or absence of oxygen, been most effective in this last case. Concerning the photobleaching process and presence/absence of oxygen: a) in absence of oxygen probably are formed THF acyclic radicals which lead to the destruction of the phthalocyanine; b) in the presence of oxygen, peroxides are involved in the degradation and peroxides were detected and quantified in THF solutions of the triads after irradiation. In both cases the excited triplet state is responsible for starting the steps that result in the observed bleaching. In benzene solutions could be investigated the E→Z photoisomerization, the Z→E photosensitized isomerization and Z→E thermal isomerization. The results show that coordination does not alter the excited state properties of the azobenzene ligands. This conclusion can be made by the similarity between the quantum yields and the E→Z rate constants values for the triads and HO-Azo-X compounds. Otherwise, the Z→E thermal isomerization is much slower for the triads comparatively to the HO-Azo-X compounds. The Si-O bound in the complexes compared to the H-O bond in the HO-Azo-X and the resulting dipole moments must be responsible for this phenomenon. The Z→E photosensitized isomerization reactions are much faster than the corresponding thermal ones existing up to 30 times differences on the respective constants. The investigated triads show photoswitch behavior concerning fluorescence emission which is controlled by the axial ligand E or Z state. The emission intensity variations along the series are found to be between 19 - 27% of the initial intensity. These triads can be classified as \"quasi\" bistable switches considering the Z→E process can be carried out by means a slow thermal or a fast photosensitized process. This kinetic control enable too the utilization of these triads in molecular binary information systems.

Nesta tese foram investigadas as propriedades foto-switch de novas tríades constituídas por uma unidade central de Si(IV)-Ftalocianina e dois ligantes axiais azobenzênicos. A posição 4\' dos ligantes azobenzênicos apresenta substituintes (X) com diferentes propriedades eletrônicas e estéricas, a saber: -H; -CH3; -C(CH3)3; -OCH3; e -I. A tríade com substituinte -NO2 foi novamente investigada e incluída como tríade de maior caráter push-pull da série. Para efeito de comparação, também foram investigados hidróxiazobenzenos (HO-Azo-X) com os mesmos substituintes (X) na posição 4\' que os presentes nas tríades. Os HO-Azo-X apresentam propriedades espectroscópicas, fotoquímicas (fotoisomerização E→Z e Z→E) como também retorno térmico Z→E com características intermediárias entre a classe dos azobenzenos e dos amino-azobenzenos. Estas propriedades podem ser atribuídas à presença comum do substituinte hidróxi que apresenta um caráter doador, porém menos acentuado que a do grupo amino. Os espectros de absorção eletrônica das tríades apresentam uma banda B no UV e um conjunto de bandas Q na região visível do espectro eletromagnético. Observou-se a existência de um processo de agregação dos complexos dependente do substituinte 4\'. As tríades apresentam emissão de fluorescência quando excitadas tanto na banda B como na banda Q, com pequenos deslocamentos Stokes. Os rendimentos quânticos de fluorescência obedecem à regra de Kasha. Isto foi confirmado para os rendimentos quânticos corrigidos da banda B, os quais excluem a fração de luz absorvida pelos ligantes axiais nesta região de excitação. A excitação das tríades em THF resulta em photobleaching, que ocorre tanto na presença como na ausência de oxigênio, sendo mais efetivo neste último caso; temos que: a) na ausência de oxigênio provavelmente existe a formação de radicais acíclicos de THF que destroem a ftalocianina; b) na presença de oxigênio peróxidos estão envolvidos na degradação, tendo sido detectados e quantificados nas soluções das tríades após irradiação. Nos dois casos o estado excitado triplete é responsável pelo início do processo. Em benzeno puderam ser investigados a fotoisomerização E→Z, a isomerização fotossensibilizada Z→E, assim como a isomerização térmica (retorno térmico) Z→E. Os resultados mostram que a coordenação não altera as propriedades do estado excitado dos ligantes azobenzênicos evidenciado pela similaridade dos rendimentos quânticos e constantes de velocidade E→Z comparativamente aos HO-Azo-X. Entretanto, o retorno térmico Z→E, é muito mais lento comparativamente aos HO-Azo-X. A ligação Si-O nos complexos comparativamente a H-O nos HO-Azo-X e os momento de dipolo resultante devem ser os responsáveis por esse fenômeno. As isomerizações fotossensibilizadas Z→E são muito mais rápidas que as respectivas térmicas existindo diferenças de até 30 vezes nos valores das respectivas constantes. Todas as tríades apresentam o comportamento foto-switch de emissão que é controlado pelo estado E ou Z do ligante axial. Ao longo da série as variações de intensidade de emissão se situam entre 19 - 27% da intensidade inicial. O fato do processo Z→E nas tríades ocorrer através do processo térmico ou fotossensibilizado que é consideravelmente mais rápido faz destas tríades sistemas switches quase-biestáveis. Este controle cinético também potencializa a utilização destas tríades em sistemas de informação molecular binário. / In this work have been studied the photoswitch properties of new triads with one central Si(IV)-phthalocyanine and two axially coordinated azobenzenes. The 4\' position of the azobenzene ligands has substituents (X) presenting different electronic/steric contributions: -H; -CH3; -C(CH3)3; -OCH3; and -I. The triad with -NO2 substituent was reinvestigated and included as the triad with the major push-pull effect in the series. For comparative purposes have been investigated hydroxyazobenzenes (HO-Azo-X) with the same substituents (X) at the 4\' position of the triads. The HO-Azo-X compounds show spectroscopic, photochemical (photoisomerization E→Z and Z→E) and thermal Z→E reaction with intermediate properties that which shown by the class of azobenzene and aminoazobenzene compounds. These characteristics can be attributed to the hydroxyl-substituent present in all compounds, which has donor character, but less pronounced than the amino group. The electronic absorption spectra of the triads show a B band in the UV and a set of Q bands in the visible region of the electromagnetic spectrum. Could be noticed an aggregation behavior for these triads dependent on the 4\' substituent. The triads show fluorescence emission when excited at B or Q bands, presenting small Stokes shift. Fluorescence quantum yields are in accordance with Kasha\'s rule. Photobleaching is observed when THF solutions of the triads are irradiated. This photobleching occurs in presence or absence of oxygen, been most effective in this last case. Concerning the photobleaching process and presence/absence of oxygen: a) in absence of oxygen probably are formed THF acyclic radicals which lead to the destruction of the phthalocyanine; b) in the presence of oxygen, peroxides are involved in the degradation and peroxides were detected and quantified in THF solutions of the triads after irradiation. In both cases the excited triplet state is responsible for starting the steps that result in the observed bleaching. In benzene solutions could be investigated the E→Z photoisomerization, the Z→E photosensitized isomerization and Z→E thermal isomerization. The results show that coordination does not alter the excited state properties of the azobenzene ligands. This conclusion can be made by the similarity between the quantum yields and the E→Z rate constants values for the triads and HO-Azo-X compounds. Otherwise, the Z→E thermal isomerization is much slower for the triads comparatively to the HO-Azo-X compounds. The Si-O bound in the complexes compared to the H-O bond in the HO-Azo-X and the resulting dipole moments must be responsible for this phenomenon. The Z→E photosensitized isomerization reactions are much faster than the corresponding thermal ones existing up to 30 times differences on the respective constants. The investigated triads show photoswitch behavior concerning fluorescence emission which is controlled by the axial ligand E or Z state. The emission intensity variations along the series are found to be between 19 - 27% of the initial intensity. These triads can be classified as \"quasi\" bistable switches considering the Z→E process can be carried out by means a slow thermal or a fast photosensitized process. This kinetic control enable too the utilization of these triads in molecular binary information systems.

Die andauernden Entwicklungen auf dem Gebiet der kontrollierten Polymerisation haben zu zahlreichen neuen Methoden geführt, um klar definierte Polymere zu synthetisieren. Die dabei entstehenden molekularen Strukturen haben einen großen Einfluss auf die makroskopischen Eigenschaften. Hier werden Ansätze beschrieben um Polymerisation in situ zu steuern, was zur besseren Kontrolle von Polymereigenschaften führen soll. Zu diesem Zweck wurden etablierte organometallische Katalysatoren mit Azobenzolen funktionalisiert, um die Geometrie des Katalysators in situ zu ändern. Zuerst wurde ein Salen-Katalysator synthetisiert, der ein Azobenzol in der Nähe des aktiven Zentrums besitzt. Dieser zeigte vielversprechende photochemische Eigenschaften. Es wurde aber festgestellt, dass die Bestrahlung die LMCT Bande des Metalls anregt, was die Bindung des Polymers zum Katalysator beeinträchtigt. Um dieses Problem zu umgehen wurde ein dinuklearer Salen-Katalysator, mit einer besseren Bandentrennung, synthetisiert. Dieser Katalysator zeigte eine trans-cis-Isomerisierung, konnte photochemisch aber nicht zurück geschaltet werden, da die Absorptionsbanden des Azobenzols mit denen des Metalls überlappten. Daher wurde das Absorptionsverhalten des katalytischen Zentrums durch die Einführung eines rigiden durchkonjugierten Salphen Liganden geändert. Drei Systeme wurden synthetisiert, wobei der Katalysator mit einer Ethylenbrücke zwischen dem Azobenzol und dem Metallzentrum die besten Ergebnisse zeigte. Dieser Katalysator konnte reversibel geschaltet werden und zeigte auch einen Aktivitätsunterschied in der Polymerisation von b-Butyrolacton. Es konnte gezeigt werden, dass die Aktivität des Katalysators um einen Faktor von 2,4 zwischen dem trans-Isomer und dem bestrahlten Reaktionsgesmisch erhöht werden konnte. Das gleiche Ergebnis wurde auch bei in situ Experimenten beobachtet. / Rapid developments in the field of controlled polymerization have led to numerous ways to produce well defined polymeric structures. This influence on the polymeric microstructure allowed a more efficient control over the macroscopic properties as well. Here, approaches are described to in situ control the polymerization outcome, which will eventually lead to a more defined manipulation of polymeric properties. For this purpose well established organometallic catalyst were functionalized with azobenzene moieties to alter the catalysts geometry in situ. First a salen catalyst with an azobenzene in close proximity to the active site was synthesized. The catalyst showed promising photochemical behavior, but irradiation of the catalyst would interfere with the binding of the polymeric chain, due to excitation of the metal’s LMCT band. To overcome this challenge a dinuclear salen catalysts with a better separation of the bands was synthesized that would allow control over cooperative effects. This catalysts showed trans-cis-isomerization but no photochemical back-reaction, due to an overlap of the absorption bands of the cis-azobenzene with the metal moiety. Therefore, the absorption of the catalytically active moiety was altered by introducing a rigid fully conjugated salphen system as the ligand. Three systems were synthesized, of which an ethylene bridged ligand showed the best results. It allowed reversible switching between both states and showed an activity change in the polymerization of b-butyrolactone. The catalyst showed an increased activity by a factor of 2.4 in the trans-isomer compared to the photostationary state and it also allowed for an in-situ switching between both states without affecting the efficiency of the system.

Die fortschreitende Entwicklung auf dem Gebiet der kontrollierten Polymerisationstechniken ermöglicht heutzutage die Synthese definierter Makromoleküle. Durch das Design der Primärstruktur dieser Makromoleküle kann ein starker Einfluss auf die sich bildende Sekundärstruktur ausgeübt werden. Um den Grad der Kontrolle über den Polymerisationsprozess zu erhöhen sollten in dieser Arbeit photoschaltbare Azobenzolfunktionalitäten in Guanidin- und Thioharnstoffmotive integriert werden, so dass durch die reversibel photoschaltbare Ausbildung von Wasserstoffbrücken die vorliegenden Polymerisationsprozesse beeinflusst werden können. In einem Ansatz wurden dazu neuartige azobenzolverknüpfte Guanidin- und Thioharnstoffkatalysatoren für die Ringöffnungspolymerisation (ROP) von Lactid (LA) synthetisiert. Im Fall der photoschaltbaren Guanidinkatalysatoren wurde eine Synthesemethode entwickelt, welche die zu Beginn langwierige Aufreinigung der Katalysatoren bedeutend vereinfacht und somit die Darstellung mehrerer Katalysatorgenerationen ermöglichte. Die erste Guanidinkatalysatorgeneration zeigte keine katalytische Aktivität. Durch die Synthese von verschiedenen Referenzguanidinen und deren Einsatz in der ROP von LA konnten die aromatischen Substituenten der Guanidinfunktionalität als Ursache der katalytischen Inaktivität identifiziert werden. Daraufhin wurde eine mit zwei Alkylsubstituenten versehene zweite Generation synthetisiert und erfolgreich in der ROP von Lactid eingesetzt. In einem anderen Ansatz wurde versucht ein azobenzolverknüpftes Guanidinium-Carboxylat-Zwitterion so zu gestalten, dass es als photoschaltbares Monomer zur Bildung supramolekularer Polymere verwendet werden kann. Hierzu wurden zwei Generationen photoschaltbarer Zwitterionen synthetisiert. Die Eigenschaften der zweiten Generation wurden mit verschiedenen spektroskopischen Methoden untersucht. Dabei wurden Hinweise auf die Bildung eines supramolekualren Polymers gefunden. / Following the progressive development in the field of controlled polymerizations, it is now possible to synthesize well defined macromolecular structures. Controlling the primary structure in these macromolecules significantly influences the secondary structure, allowing the preparation of smart materials. In order to improve the achievable degree of control, this work aims to incorporate azobenzene functionalities into guanidine and thiourea moieties and, through the photo triggered reversible formation of hydrogen bridges, influence polymerization processes. Novel azobenzene substituted guanidine and thiourea catalysts for the ring opening polymerization (ROP) of lactide were synthesized. In the case of the photoswitchable guanidine catalysts, a new synthetic protocol was developed to overcome the difficult purification of the catalysts, allowing the facile preparation of multiple catalyst generations. The first generation of photoswitchable guanidines showed catalytic activity. Synthesis of reference guanidine catalysts demonstrated a negative effect between aromatic guanidine substituents and the catalytic performance. Following this observation, a second generation of alkyl substituted guanidine catalysts was synthesized and applied successfully in the ROP of lactide. In a concurrent approach, a guanidinium carboxylate zwitterion was rendered photoswitchable by the incorporation of an azobenzene functionality and used as a monomer in supramolecular polymerization processes. The first generation of photoswitchable zwitterions showed promising photochemical properties, but its poor solubility in apolar, aprotic solvents prevented a final proof of the concept. To achieve this, a second generation of photoswitchable zwitterions was synthesized, incorporating solubilizing functionalities into the molecular design. The properties of the second generation zwitterion were examined by various spectroscopical methods, indicating the formation of supramolecular polymers.

Cette thèse comporte deux parties indépendantes. La première étude présente les premiers exemples de métallation de la structure azobenzène par les réactifs organométalliques polaires. Largement utilisés en tant que colorants, les azobenzènes trouvent actuellement de nombreuses applications dans le domaine des matériaux en raison de leur facile photoisomerisation E/Z. Il est montré que les bases organométalliques polaires classiques (n-BuLi, n-BuLi/TMEDA, n-BuLi/t-BuOK, TMPMgCl.LiCl, LDA) ne métallent pas l’azobenzène parent mais réduisent plutôt la liaison N=N. Cependant la métallation est possible avec le tétraméthylpipéridure de lithium si un groupement directeur de métallation tel que le méthoxy (OMe), diéthylamide (CONEt2) ou fluoro (F) est présent sur l’azobenzène. La réaction permet un accès original et direct à de nouveaux azobenzènes substitués. L’objectif de la deuxième partie est la synthèse de dérivés biaryliques chiraux en l’absence de métaux de transition (Pd, Ni…). Les biaryles chiraux sont présents dans de nombreuses molécules biologiquement actives et peuvent être utilisés comme ligands pour la catalyse asymétrique. La substitution nucléophile aromatique des acides naphtoïques en présence de ligands chiraux a été étudiée. Une optimisation fine des conditions réactionnelles (choix du solvant, température, structure du ligand…) a permis de préparer des 1,1’-binaphtalènes, 1,2’-binaphtalènes et phénylnaphtalènes avec de bons rendements et excès énantiomériques (jusqu’à 89% ee). La substitution nucléophile aromatique atroposélective de dérivés d’acides naphtoïques de type naphtyloxazolines et naphtoates est également décrite. / This thesis is divided into two independant parts. The first part describes for the first time the chemoselective lithiation of azobenzenes. Azobenzenes derivatives are widely used as dyes and more recently have been applied to the preparation of photoresponsive molecular switches and materials by taking advantage of the N=N bond E/Z photoisomerization. Whereas standard polar organometallics (n-BuLi, n-BuLi/TMEDA, n-BuLi/t-BuOK, TMPMgCl.LiCl, LDA) reduce the N=N bond of the parent compound, aromatic HLi permutation occurs with LTMP when a suitable director of lithiation (OMe, CONEt2, F) is present in the benzene residue of the azo compound. The method allows a direct access to new substituted azobenzenes.Axially chiral biaryls, which are found in many biologically active natural products, are conventionally used as ligands for asymmetric catalysis. The purpose of the second part is to develop a new method for the preparation of axially chiral biaryls in the absence of transition metals (Pd, Ni…). To tackle that goal, nucleophilic aromatic substitution reactions on unprotected naphthoic acids were performed in the presence of chiral ligands. A careful optimization of the reaction parameters (choice of the solvent, temperature, structure of the ligand…) allowed to prepare chiral 1,1’- binaphthalenes 1,2’- binaphthalenes and phenylnaphthalenes in good yields and enantiomeric excesses (up to 89% ee). The atroposelective SNAr reaction of naphthyloxazoline and naphthoate derivatives was also reported.