Nitrate esters of aromatic alcohols were synthesized by esterification which involved competition between 0-nitration and aromatic C-nitration. TLC analysis gave a pattern of adsorption affinities for the nitroxy group and other substituents consistent with the molecular conformations. The NMR frequency of the α-protons showed a linear correlation with the accepted group electronegativities of the substituents in molecules with rigid carbon skeletons and gave a value of 4.18 kcal/mole for the nitroxy group. The symmetric and asymmetric IR stretching frequencies of nitroxy groups in dilute cyclohexane solution were shifted to higher values by steric interaction between contiguous groups when the C-ONO₂ bonds were constrained to coplanarity. The UV spectra showed benzenoid, π→π*, and n→π* bands and a solvent perturbation effect assigned to a solvent → solute charge-transfer interaction. The nitrate esters reacted with the solvent when irradiated in solution in the wavelength range of the n→π* excitation. Product analysis indicated that C-C bond cleavage occurred via intermediate alkoxyl radicals. Rate studies showed the following order of reactivity: benzyl nitrate < dl-hydrobenzoin dinitrate < meso-hydrobenzoin dinitrate, < trans-1, 2-acenaphthenediol nitrate < cis-1, 2-acenaphthenediol dinitrate. The rate measurements and ESR spectra gave evidence of intramolecular energy transfer from the naphthalene moiety to the nitroxy groups in the 1, 2-acenaphthenediol dinitrates assigned as a singlet→singlet transfer. Calculations from the apparent first-order rate constants and spectra showed that benzyl nitrate, and meso- and dl-hydrobenzoin dinitrates photolysed with a quantum yield of about 2 in benzene solution. A solvent effect caused k[subscript Et₂O] > k[subscript EtOH] >k[subscript PhH]. On the basis of product analysis, rate measurements, estimated quantum yields and ESR spectra a mechanism for the nitrate ester photolysis was proposed. / Science, Faculty of / Chemistry, Department of / Graduate

L’objectif principal de ce travail de thèse était de mettre en évidence et de mesurer l’effet co-catalytique de complexes moléculaires organo-métalliques à base de métaux de transition adsorbés sur des semi-conducteurs dopés photo-actifs vis-à-vis des réactions de photo-dissociation de l’eau et de photo-réduction du dioxyde de carbone, en en vue d’applications dans des cellules photochimiques et photo-électrochimiques. Nous avons tout d’abord identifié et sélectionné les matériaux (deux semi-conducteurs photo-actifs et deux co-catalyseurs moléculaires électroactifs) les plus adaptés (les résultats sont présentés dans le chapitre I). Nous avons ensuite conçu, développé et mis au point un bâti expérimental permettant la détection et le dosage en continu des produits de réaction lors des réactions d’intérêt (les résultats sont présentés dans le chapitre II). La détection des produits de réaction se fait à l’aide d’un chromatographe en phase gazeuse couplé au réacteur. Nous avons ensuite élaboré/synthétisé et mesuré les propriétés intrinsèques des matériaux sélectionnés (les résultats sont présentés dans le chapitre III). Finalement, nous avons mis en évidence l’activité co-catalytique des complexes utilisés et mesuré un ensemble d’indicateurs de performance tels que les cinétiques de réaction et les fréquences de « turn-over » (les résultats sont présentés dans le chapitre IV). / The main objective of this research work was to put into evidence the co-catalytic effect of organo-metallic molecular complexes containing transition metals as reactive centers, adsorbed at the surface of doped semiconductors with photo-activity with regard to water photo-dissociation and carbon dioxide photo-reduction, in view of practical applications in photochemistry and photo-electrochemistry. First, appropriate materials (two photoactive semiconductors and two molecular co-catalysts) have been identified and selected (results are presented in chapter I). Then, we have designed, constructed and optimized a specific test bench that can be used for the continuous detection and titration of reaction products (results are presented in chapter II). Product analysis was achieved by coupling a gas-phase chromatograph to the photo-electrochemical reactor. Then, photoactive semiconductors and molecular co-catalysts have been elaborated/synthesized and their intrinsic properties have been measured (results are presented in chapter III). Finally, the co-catalytic activity of molecular complexes has been put into evidence and several performance indicators such as reaction kinetics and turn-over frequency have been measured (results are presented in chapter IV).

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