Le concept de la DOS (Diversity-Oriented Synthesis) est une nouvelle approche qui vise à générer des collections de petites molécules avec des hauts degrés de diversité et de complexité structurale. Diverses stratégies ont été mises en place pour y parvenir de manière la plus efficace possible à partir de simples substrats de départ.Dans ce contexte, ce travail de thèse a permis de montrer comment un processus domino avait tout le potentiel à être exploité en tant que formidable outil dans le cadre d’une approche DOS, générateur à la fois de complexité mais également de diversité structurale. Un précurseur connu et largement étudié pour son caractère exceptionnellement versatile a été valorisé dans ce contexte : la 3-formylchromone. Dans ce manuscrit, nous montrerons comment il est possible de moduler le cours d’un processus domino pour atteindre de hauts degrés de diversité structurale, à partir des chromones accepteurs de Michael-1,6 et d’amines primaires. Nous verrons en particulier comment le contrôle d'une ou de plusieurs étapes clefs des séquences réactionnelles impliquées peut être réalisé selon :(I) la modulation pertinente d’une ou plusieurs unité(s) de structure au sein des substrats de départ, (II) la modulation des paramètres réactionnels (solvants, température, additifs), et(III) l’induction d’un changement de réactivité au sein d’un intermédiaire réactionnel par addition d’un agent externe. / In the early 2000s a general consensus has emerged in which the molecular diversity within a given library of small molecules, rather than its size, has been recognized as a crucial requirement. Diversity-oriented synthesis (DOS) has emerged from this new paradigm. This novel approach aims to generate collections of small molecules with high degrees of structural diversity, in the most efficient way, starting from simple building-blocks. Since the generation of collections of structurally diverse small molecules in a DOS-driven approach constitutes a real challenge, diverse strategies have been set up for this purpose.In this line, this work has shed light on the great potential of a domino process as a valuable tool in a DOS-driven strategy, capable of generating both molecular diversity and architectural complexity. This study has been focused on the 3-formylchromone building block, a particular framework which has already proven being an exceptionally versatile precursor of molecular diversity. In this manuscript, we will highlight how it is possible to modulate the course of a domino process to achieve high degrees of molecular diversity, starting from the chromone based 1,6-Michael acceptors platform and primary amines as reaction partners. In particular we will show how it is feasible to control the course of particular steps involved in the domino process through: (I) the pertinent modulation of the Michael acceptors and the primary amines structures, (II) the modulation of the reaction parameters (solvent, temperature, additives), and (III) the tuning of the reactivity within a key reaction intermediate induced by the introduction of an external agent.

O comportamento eletroquímico do Nitrofural (NFZ) foi estudado em eletrodos de pasta de carbono, carbono vítreo e diamante altamente dopado com boro (EDADB) em tampão Britton-Robinson (BR) usando a voltametria cíclica. Os melhores resultados foram obtidos em EDADB, no qual foi possível estabilizar o radical aniônico (R-NO2•&#8254) em meio predominantemente aquoso, como também estudar a interação entre o R-NO2•‾ a glutationa (GSH), a L-cisteína (Cis) e o O2. Somente na superfície do EDADB, o NFZ foi diretamente reduzido à amina derivada (R-NH2) no intervalo de 2,02 ≤ pH ≤ 4,03 num processo envolvendo seis (6,0 ± 0,4) elétrons e seis prótons. Na faixa de 7,04 &#8804 pH ≤ 12 e meio predominantemente aquoso, a etapa de redução desmembrou-se em seus dois componentes: a redução do NFZ ao nitro radical aniônico (R-NO2•‾) e posterior redução deste ao derivado hidroxilamínico (R-NHOH) em processos envolvendo um e três (3,1 ± 0,1) elétrons respectivamente. No sentido anódico da varredura dos voltamogramas cíclicos registrados em pH 8,06, observou-se a oxidação da hidroxilamina ao derivado nitroso (R-NO), num processo envolvendo 2 (1,7 ± 0,2) elétrons e 2 prótons. Além disto, um novo pico de oxidação não relatado na literatura em qualquer material de eletrodo foi detectado em pH ≤ 8,06, que foi observado não importando se o NFZ havia sido previamente reduzido ou não. O cálculo do número de elétrons, n, envolvido em cada etapa eletroquímica foi satisfatoriamente estimado usando-se a equação de Randles-Sevcik. Na presença de [Tiol] ≤ 3,7 x 10-2 mol L-1, o NFZ é reduzido ao aduto R-NO-Tiol em um processo eletroquímico envolvendo dois elétrons e dois prótons. Por outro lado, o O2 atua como um aceptor de R-NO2•‾ e a constante de equilíbrio para a transferência monoeletrônica do R-NO2•‾ para o oxigênio, kO2, é 60. O processo é catalítico e pode ser utilizado para a determinação analítica de NFZ na faixa de 9,9 x 10-7 ≤ [NFZ] ≤ 1,1 x 10-5 mol L-1 em pH 8,06, com sensibilidade amperométrica de 2,2 x 104 µA L mol-1 cm-2 e limite de detecção de 3,4 x 10-7 mol L-1. Os parâmetros analíticos foram similares aqueles obtidos em pH 4,0 usando a redução direta do NFZ à respectiva amina derivada em um processo envolvendo seis elétrons e seis prótons. A caracterização do processo de redução total do NFZ em meio aquoso e velocidades de varredura relativamente baixas, 100 mV s-1, somente foi possível devido às características superficiais intrínsecas do EDADB, o qual estabiliza o radical livre, R-NO2•‾, permitindo trabalhar numa ampla janela de potencial, sem haver perda do sinal de oxidação do R-NO2•‾. / The electrochemical behaviour of nitrofural (NFZ) at carbon paste, glassy carbon and highly boron doped diamond (HBDD) electrodes was studied in Britton- Robinson (BR) buffer using cyclic voltammetry. The best results were obtained at HBDD electrodes, in which it was possible to stabilize the radical anion (R-NO2•‾) in predominantly aqueous medium as well as to study the interaction between the radical anion and glutathione (GSH), L-cysteine (Cys), and O2. Only at HBDD surface, NFZ was directly reduced to the amine derivative (R-NH2) in the pH range of 2.02 to 4.03 in a process involving six (6.0 ± 0.4) electrons and six protons. In the range of pH 7.04 to 12 and, predominantly aqueous medium, the reduction step split into its two components: the reduction of NFZ to the nitro radical anion (R-NO2•‾) and reduction of R-NO2•‾ to hydroxylamine derivative (R--NHOH) in processes involving one and three (3.1 ± 0.1) electrons respectively. On the anodic scan of the cyclic voltammograms and at pH 8.06, it was observed the oxidation of the hydroxylamine to the nitroso derivative (R-NO), in a process involving 2 (1.7 ± 0.2) electrons and 2 protons. In addition and unreported in the literature on any electrode material, was the detection of a new oxidation peak at pH > 8.06, which was observed regardless of whether NFZ had been previously reduced or not. The calculation of n, number of electrons, involved in each electrochemical step was satisfactorily accomplished using the Randles-Sevcik equation. In presence of [Thiol] ≤ 3.7 x 10-2 mol L-1 NFZ is directly reduced to R-NO---Thiol adducts in an electrochemical process involving two electrons and two protons. On the other side, O2 acts as a R-NO2•‾ scavenger and the equilibrium constant for the electron transfer from nitro radical to oxygen, kO2, is 60. The process is catalytic and can be used to the analytical determination of NFZ in the range of 9.9 x 10-7 ≤ [NFZ] ≤ 1.1 x 10-5 mol L-1 at pH 8.0, with amperometric sensitivity of 2.2 x 104 µA L mol-1 cm-2 and detection limit of 3.4 x 10-7 mol L-1. The analytical parameters were similar to those obtained at pH 4.03 using the direct reduction of NFZ to the respective amine derivative in a process involving six electrons and six protons. The characterization of NFZ global reduction process in aqueous medium and at relative low scan rate, 100 mVs-1, was only possible due the intrinsic superficial characteristics of the HBDD electrode, which stabilize the R-NO2•‾ free radical, allowing to work in a large potential window, without losing the R-NO2•‾ oxidation signal.

Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.

The electrical properties of ZnO and contacts to ZnO have been investigated using different techniques. Temperature dependent Hall (TDH) effect measurements have been used to characterize the as-received melt grown ZnO samples in the 20 – 330 K temperature range. The effect of argon annealing on hydrogen peroxide treated ZnO samples has been investigated in the 200 – 800oC temperature range by the TDH effect measurement technique. The experimental data has been analysed by fitting a theoretical model written in Matlab to the data. Donor concentrations and acceptor concentrations together with the associated energy levels have been extracted by fitting the models to the experimentally obtained carrier concentration data by assuming a multi-donor and single charged acceptor in solving the charge balance equation. TDH measurements have revealed the dominance of surface conduction in melt grown ZnO in the 20 – 40 K temperature range. Surface conduction effects have proved to increase with the increase in annealing temperature. Surface donor volume concentrations have been determined in the 200 – 800oC by use of theory developed by D. C. Look. Good rectifying Schottky contacts have been fabricated on ZnO after treating the samples with boiling hydrogen peroxide. Electrical properties of these Schottky contacts have been investigated using current-voltage (IV) and capacitance-voltage (CV) measurements in the 60 – 300 K temperature range. The Schottky contacts have revealed the dominance of predominantly thermionic emission at room temperature and the existence of other current transport mechanisms at temperatures below room temperature. Polarity effects on the Schottky contacts deposited on the O-polar and Zn-polar faces of ZnO have been demonstrated by the IV technique on the Pd and Au Schottky contacts at room temperature. Results obtained indicate a strong dependence of the Schottky contact quality on the polarity of the samples at room temperature. The quality of the Schottky contacts have also indicated their dependence on the type of metal used with the Pd producing contacts with the better quality as compared to the Au. Schottky barrier heights determined using temperature dependent IV measurements have been observed to increase with increasing temperature and this has been explained as an effect of barrier inhomogeneities, while the ones obtained from CV measurements have proved to follow the negative temperature coefficient of the II – VI semiconductor material, i.e. a decrease in barrier height with increasing temperature. However, the values have proved to be larger than the energy gap of ZnO, an effect that has been explained as caused by an inversion layer. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Physics / unrestricted

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