Earths most abundant biomolecules, carbohydrates, offer tremendous potential forelectricity production. Carbohydrate fuel cells are electrical fuel cells that can harvest the stored electrons in carbohydrates and offer a cheap and efficient method that could help solve growing energy demands, while providing a renewable green energy source. Viologen-mediated carbohydrate fuel cells have demonstrated the ability to accelerate carbohydrate oxidation while decreasing partial or incomplete oxidation products reducing the electricity production. Subsequent studies suggested polymeric viologen compounds could improve the efficiency by increasing the local concentration of viologen. This thesis presents the utility of surface-immobilized viologen mediators for the oxidation of simple carbohydrates. Methyl viologen formed a self-assembled monolayer on a gold electrode surface to enhance its electrocatalytic oxidation of dihydroxyacetone, fructose, and glucose. The thiolated viologen formed surface adsorbed films on the gold electrodes that where consistent with monolayers and were characterized by quartz crystal microbalance and cyclic voltammetry. Cyclic voltammetry indicated that carbohydrates can generate electricity when combined with methyl viologen. Monolayer formation of methyl viologen indicates that immobilized mediators can be used to enhance oxidation of simple carbohydrates to generate electricity. This same tethered mediator strategy could be used for other mediators to increase their electrochemical efficiency in carbohydrate fuel cells.

Glucose and other carbohydrates are some of the most abundant renewable energy sources in the world. The oxidation of carbohydrates in a fuel cell allows their chemical energy to be converted directly into electrical energy. Viologen has been indentified and shows promising ability as an electron-transfer catalyst or mediator for carbohydrate oxidation in an alkaline carbohydrate fuel cell. Building on the previous results, the objective of this work was to develop an immobilization chemistry of viologen onto an electrode and to investigate the catalytic activity for carbohydrate oxidation in direct carbohydrate fuel cells.The immobilization was achieved by electropolymerizing a novel viologen monomer onto an electrode surface. The novel viologen monomer, which functions as a monosubstituted viologen, was synthesized and isolated in-house. Gold-plated nickel wire and graphite disks were used as the substrates for the electropolymerization. SEM, EDAX, XPS and water-contact-angle measurement were used to verify the formation of the coating on the gold and graphite surfaces. The catalytic activity of the immobilized viologen on graphite disk surface was examined using a fuel-cell-like device. The test was operated within the desired pH range for an operating fuel cell; it was found that the immobilized viologen polymer has a low catalytic activity toward oxidizing carbohydrates. In addition, the electrochemical properties of the novel viologen monomer were investigated by the method of cyclic voltammetry, as well as for that of two aminoviologens synthesized in-house. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants were determined.

Energy usage is continually on the rise and significant efforts are being extended to provide more renewable energy. One area of exploration is the development of fuel cells, which includes biofuel cells that can extract energy from carbohydrates obtained from biomass. Recently, viologen catalysts have been shown to enhance reaction rates of energy extraction and improve carbohydrate conversion efficiencies. However, characterizing the effects of process parameters such as pH, reactant concentrations, and carbohydrate exposure time to buffer solutions with a rigorous model is lacking. This thesis characterizes the homogeneous reaction between carbohydrates and a methyl viologen catalyst to provide insights on ways to enhance the reaction rates to produce more energy. Specifically, the rate of formation of reduced methyl viologen (MV+) in the presence of carbohydrates was measured based on changes in the MV2+ concentration, carbohydrate concentration, pH, and carbohydrate exposure time. A rigorous mechanistic model of the reaction rate was developed and showed a first-order dependence on OH- concentration, a zero-order dependence when the MV2+ concentration was >> 0.5 mM, and a 3-fold increase in the reaction rate when glucose was pre-incubated in a pH 12 buffer solution for 100 minutes. The pre-incubation effect had a strong dependence on pH. The mechanistic model agreed well with experimental data. This thesis also addresses the decomposition of viologen catalysts. MV2+ decomposition experiments showed a trend seen previously in literature that the rate of decomposition increases with an increase in MV2+ concentration, OH- concentration, and temperature. The data and mechanistic model suggest second order dependence of both MV2+ and OH- concentrations under conditions in this thesis (MV2+ concentrations of 100-300 mM and OH- concentrations of 0.001 M and 0.01 M). An activation energy was found from MV2+ decomposition to be 145 kJ/mol. MMV+ decomposition was shown to decompose anywhere from 6.2 – 16.1 times slower than MV2+. Therefore, MMV+ decomposes slower and is more stable than MV2+. It was also found that MV2+ is more stable than IPV-Cl and IPV-Br. An analysis was performed to find the recommended operating range for MV2+/glucose biofuel cells under different conditions while ensuring that at least a viable amount of energy could be produced.

This dissertation describes the effective encapsulation of redox active compounds inside deep-cavity cavitands: Gibb's octaacid40 and Rebek's 41 tetracarboxylate cavitand. Gibb's octaacid is a water-soluble, deep-cavity cavitand that forms well-characterized dimeric molecular capsules around hydrophobic guests. Both 1H NMR spectroscopic and voltammetric experiments clearly reveal that ferrocene plays the role of hydrophobic guest effectively. Ferrocene derivatives (ferrocenylmethyltrimethylammonium (FcNMe3+), ferrocenemethanol (FcOH), and ferrocene carboxylic acid (FcCOOH)) were also found to form inclusion complexes with octaacid cavitand however, in this case 1:1 (host to guest) ratio complexes are formed. This is in strong contrast with the dimeric capsule formed around ferrocene. Under the surveyed experimental conditions encapsulated ferrocene is electrochemically silent. We have also found that the negative charges around this dimeric molecular capsule play a very important role. For instance, hydrophobic cations, such as viologens,60 bind to the outer surface of the capsule. This opened a possibility of mediated electron transfer reactions between molecules bound inside the octaacid capsule and tightly attached to its outer surface in purely synthetic system. The cationic ferrocene derivative, ferrocenylmethyltrimethylammonium (FcNMe3+), was used as a mediator since its electrochemical potential range makes it suitable as a mediator molecule. In fact, our data clearly support that FcNMe3+ mediates electron transfer between encapsulated ferrocene and the electrode surface. Ferrocene, its derivatives (FcNMe3+ and FcOH), and cobaltocenium (Cob+) also form 1:1 inclusion complexes with Rebek's tetracarboxylate cavitand, which surprisingly are all voltammetrically silent. The formation of these inclusion complexes seems to be driven by hydrophobic interactions between the host and the guest. The lack of voltammetric response observed in this work is a very intriguing finding.

Reversible changes in the self-organization of polysoaps may be induced by controlling their charge numbers via covalently bound redox moieties. This is illustrated with two viologen polysoaps, which in response to an electrochemical stimulus, change their solubility and aggregation in water, leading from homogeneously dissolved and aggregated molecules to collapsed ones and vice verse. Using the electrochemical quartz crystal microbalance (EQCM), it could be shown that the reversibility of this process is better than 95% in 16 cycles. /

The emergence of complex, carefully designed, molecular architectures incorporating either a lanthanide ion or the porphyrinic macrocycle have stimulated significant interest of late, particularly in the fields of molecular switches, molecular machines and data storage systems. The integration of these emissive species has been shown to permit the analysis of conformational, coordinative, or electronic change, and employed, in the case of the porphyrinic macrocycle, to acquire a deeper understanding of the natural process of photosynthesis, thus opening up the possibility of developing more efficient and inexpensive photovoltaic cells. This thesis begins by providing insight into the generation of cathodic photocurrent density within both monophasic and biphasic self-assembled monolayers, before documenting how the magnitude of such photoelectochemical output can be gated upon the integration of an electron relay moiety, both at the interface and into solution. The introduction of an electron relay moiety into solution has been shown to bring about increases of up to 283 % in the magnitude of the cathodic photocurrent density acquired, whilst optimisation of the distances between the metallic interface, the electron relay moiety and the porphyrinic macrocycle has also proven beneficial. Greatest photoelectrochemical output (5.1 x 1014 nA mol-1 cm-2) is realised when the porphyrinic macrocycle is covalently tethered at a distance of 4.6 nm from the quenching, metallic interface, and the relay moiety integrated at a distance of 1.7 nm from the interface and 2.9 nm from the porphyrinic macrocycle, respectively. However, greatest variation (94 %) in the magnitude of the cathodic photocurrent densities acquired is observed when the distance between the porphyrinic macrocycle and the gold surface is kept at 3.3 nm, and the relay moiety situated at either 1.2 nm or 1.7 nm from the interface, respectively. Research then moved towards trying to integrate this established conformational ruler within a porphyrin-appended, bistable [2]rotaxane. Its implementation served to try to ensure that photoelectrochemical differentiation of the ground state coconformation (GSCC) and the metastable state co-conformations (MSCC) was viable, thus enabling the efficient resolution of anion-induced molecular motion within a dynamic supramolecular architecture by means of a novel approach. The focus of this thesis then shifts to the assembly of novel, optically switchable, ternary complexes exhibiting charge-transfer based on the donor-acceptor interaction between an electron-rich naphthalene derivative (EuNap) and MV2+, an electron-poor, redox-addressable moiety. Prior to the deposition of (MV, EuNap)-CB[8] at the interface, the homoternary analogue ((MV+.)2-CB[8]) was acquired upon one electron reduction of (MV, EuNap)-CB[8] in the presence of excess MV2+. This process was revealed to be reversible upon the application of a stream of oxygen, and the relative concentration of each complex present in solution quantified upon mathematical manipulation of the biexponential decay curve acquired; upon the addition of sodium thiosulfate (Na2S2O3), the percentage of uncomplexed EuNap (τ = 0.60 ms cf. τ = 0.1 ms (MV, EuNap)-CB[8]) present in solution increased in accordance with the generation of ((MV+.)2-CB[8]) and loss of the charge-transfer interaction (λmax = 390, 490 nm), of which has been shown to quench lanthanide luminescence (Eu3+, Yb3+, Nd3+). Thus, the assembly of a molecular switch is documented which may be followed qualitatively at higher concentration by a visible colour change, and at low concentrations quantitatively by virtue of luminescence spectroscopy. No optical output (λex = 227 nm, λem = 616 nm) was acquired upon the deposition of (MV, EuNap)CB[8]) due to the occurrence of surface energy transfer (SET). As a result, 1-(10-mercaptodecyl)-1'methyl-[4,4'-bipyridine]-diium bromide and 1-methyl-1'-(10-(naphthalen-2yloxy)decyl)-[4,4'bipyridine]-1,1'-diium bromide iodide were synthesised and the assembly of a molecular film envisaged in which the molecular recognition properties of CB[n] were maintained and significant optical output from the lanthanide ion (Eu3+, λem 616 nm) detected; the assembly of such a film centred on the formation of 1:2 intermolecular heteroternary complexes and the recruitment of EuNap at a distance ≥ 3.2 nm from the gold substrate. It was envisaged that the modulation of any emissive output would be brought about upon manipulating the oxidation state of a surface-confined metallocene. This thesis ends by summarising the research conducted and assessing how the inclusion chemistry of cucurbit[8]uril and the photophysical properties of the porphyrinic macrocycle can be combined in order to fabricate a dynamic, photoresponsive molecular assembly. The electrical energy generated from the efficient harvesting of light energy could be used in a multitude of applications, most notably as a nanoscale power supply to drive and control molecular and supramolecular actuations.

Deriving electrical energy from glucose and other carbohydrates under mild conditions is an important research objective because these biomolecules are abundant, renewable, and can provide 12 to 24 electrons per molecule, yielding substantial electrical power. It was previously observed that disubstituted viologens, salts of N,N'-disubstituted 4,4'-bipyridine, are able to oxidize glucose under alkaline conditions. Building on that initial result, the objective of this work was to understand and quantify the effectiveness and utility of viologens as catalysts for use in direct carbohydrate fuel cells.The extent that viologens oxidize carbohydrates, the conditions under which that oxidation occurs, and the mechanism for the oxidation were examined using oxygen-uptake and other methods. Viologens were found to catalytically oxidize carbohydrates extensively in alkaline solution. Viologens were also found to react with the enediol form of the carbohydrate, initiating carbohydrate oxidation with subsequent reduction of the viologen. If the viologen/carbohydrate ratio is low, electron transfer from the carbohydrate to the viologen becomes limiting and the carbohydrates undergoing oxidation rearrange into unreactive intermediates such as carboxylic acids and alcohols. At high catalyst ratios, excess viologen more rapidly oxidizes the carbohydrate and minimizes formation of unreactive intermediates. We also found that viologen polymers were more efficient than an equivalent concentration of monomers, suggesting that the higher localized concentration in polymeric viologen acts to efficiently oxidize carbohydrates and simulates high viologen/carbohydrate ratios.Monoalkyl viologens, aminoviologens, indigo carmine, and methylene blue were investigated by the method of cyclic voltammetry to inform their use as catalysts in the oxidation of carbohydrates. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants were determined. Stability in alkaline solution and aqueous solubility were also examined in a semi-quantitative fashion. A comparison between the catalysts was made and viologens were found to be superior based on the examined parameters.The catalytic oxidation of carbohydrates by viologen was also examined using a fuel cell-like device. For the conditions in which a test cell was operated, oxidation efficiencies of up to 33% were observed, compared to previously reported values from about 2.5% to 80%. Anode polarization curves were obtained and used to determine the behavior of the viologen-controlled anode as a function of pH, viologen and carbohydrate concentration, and carbohydrate identity. pH was found to have a stronger effect on the performance at the anode for carbohydrates with a higher number of carbons than those with a lower number.

Methyl Viologen (MV) is an electron mediator that has great possibilities to be used with an electrode system in which the electrode system provides electrons towards reducing MV species. MV has three redox states and they can be converted to each other via redox reactions on the surface of the electrode. The concentration of the three species of MV was related to the voltage potential applied to the system through a thermodynamic model. With the thermodynamic model the concentration of the three species can be predicted with different applied voltage potentials towards providing guidance for controlling the redox state of MV in a system. The kinetic rates of MV reduction were also assessed using a preliminary kinetic model. The kinetic model predicted all three species concentration changes with time although only the MV+ concentration was measured with time. Analysis revealed that the rate of MV reduction was three orders of magnitude slower than the rate of electrons required for bioethanol production. However, increasing the affinity of MV+ on the surface and blocking the H+ on the surface potentially can increase the reduction rate of MV by up to three orders of magnitude and can potentially enable MV to be used in commercial applications. As for the efficiency study, the coloumbic efficiency was less than 22% which was much lower than the efficiency of more than 85% observed in other studies for the direct electron transfer between electrode and bio organism. The efficiency was lowered mainly by the reduction of H+ and minimizing H+ on the electrode can largely increase the efficiency. Medium used for cell growth can also affect the efficiency through medium species consuming electrons provided by the electrode. Electron mediators, such as MV, have potential promise in applications such as microbial fuel cells, biofuel formation, and waste water treatment. However, engineering analysis of electron mediators is critical to provide better engineering control, design, and economic analysis for future applications.

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-07-21T16:17:26Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ATUALIZADA DISSERTAÇÃO_ARTHUR_UFPE_.pdf: 6640779 bytes, checksum: 54162674f1fcaee2b4fef8836f21cd72 (MD5) / Made available in DSpace on 2016-07-21T16:17:26Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ATUALIZADA DISSERTAÇÃO_ARTHUR_UFPE_.pdf: 6640779 bytes, checksum: 54162674f1fcaee2b4fef8836f21cd72 (MD5) Previous issue date: 2016-03-30 / CNPQ / O estudo das propriedades de materiais orgânicos tem chamado atenção devido sua versatilidade estrutural e de composição que podem moldar suas propriedades físicas e químicas. Neste trabalho preparamos seis cromóforos rígidos contendo o heterociclo tiazolo[5,4-d]tiazol (Thz) como espaçador aromático, e grupos terminais piridínicos ou carboxílicos. Desta forma trabalhamos com duas linhas de pesquisa: foto-eletroquímica para os derivados piridínicos e síntese e caracterização de cristais líquidos (CLs). Investigamos as propriedades fotoquímicas e processos redox das bipiridinas X,X'-(tiazolo[5,4-d]tiazol-2,5- dil)bis(piridil) (X,X’ = 2,2’; 3,3’ ou 4,4’). Em solução, apresentaram propriedades acidocrômica via foto- e eletrodissociação de solventes clorados. A seguir, preparamos sais de trifluoracetato dos bipiridínio (viologens), que apresentaram propriedades fotocromáticas via transferência de elétron quando expostos à radiação UVB. Utilizamos os derivados carboxílicos como centros rígidos para a preparação de cristais líquidos. Escolhemos o grupo carboxilato como precursor sintético dos conectores orgânicos: éster, amida e 1,3,4-oxadiazol. Planejamos os cristais líquidos contendo tais conectores e cadeias alquílicas dodeciloxi (-OC12H25), obtendo materiais com estrutura geral: centro rígido + conectores + cadeias alcóxi. De acordo com a estrutura dos centros rígidos, preparamos treze mesógenos calamíticos (ácido tiazolo[5,4- d]tiazol-2,5-dicarboxílico), das quais seis apresentaram mesofases calamítica (comportamento esperados) e três apresentaram mesofases discóticas. O fotocromismo apresentado pelos sais de bipiridinas frente à radiação UVB nos permite sugerir aplicações como dosimetria desta radiação, presente na luz solar. As propriedades mesomórficas ainda estão em estudo. No entanto, conseguimos obter CL’s discóticos a temperatura ambiente e uma mesofase discótica nemática, bastante rara. / The study properties of organic materials has drawn attention due to its structural versatility and composition versatility, which can shape their physical and chemical properties. In this work, we prepared six rigid chromophores containing the heterocycle thiazolo[5,4-d] thiazole (Thz) as aromatic spacers, and pyridyl or carboxylic terminal groups. Hence, we have worked with two research lines: photo-electrochemistry for the pyridine derivatives and synthesis and characterization of liquid crystals (LCs). We investigated the photochemical properties and redox processes of the bipyridines X,X'-(thiazolo[5,4-d] thiazole-2,5-diyl)bis(pyridyl) (X,X' = 2,2 '; 3,3' or 4,4 '). In solution, these compounds showed acidochromic properties via photonand electrodissociantion of chlorinated solvents. Next, we prepare bipyridinium trifluoroacetate salts (viologens), which exhibited photochromic properties through electron transfer when exposed to UVB radiation. We used the carboxylic derivatives as rigid centers for the preparation of liquid crystals. We chose the carboxylate group as a synthetic precursor of organic connectors: esther, amide, and 1,3,5-oxadiazole. We plannned the liquid crystal containing these connectors and the alkoxy chains dodecyloxy (-OC12H25), obtaining materials with general structure: rigid center + connectors + alkoxy chains. According to the rigid center structure, we obtained thirteen calamitic (acid thiazolo [5,4-d] thiazole-2,5-dicarboxylic acid), six of which had mesophases calamítica (expected behavior) and three had discóticas mesophases. The photochromic presented by bipyridinium salts when exposed of UVB radiation allows suggest applications such as dosimetry of sunlight radiation. The mesomorphic properties are still under study. However, we obtained room temperatures discóticos LCs, as well as a nematic discótica mesophase which are quite rare.

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