The roles of hydrogen induced defects in pure ZnO has been studied extensively. However, in a transition metal, such as Co, doped ZnO thin films the effect of hydrogen in electric conduction and magnetic coupling is still unclear and needs further study. Recently model predicts that hydrogen can be a shallow donor as well as an agent to induce ferromagnetism coupling between two adjacent Co ions which substitute the Zn sites at room temperature in a ZnO sample with a high Co doping ratio. However, the experimental supports is rare. In this study, Co-doped(5%) ZnO films are grown by a RF-magnetron sputtering system on glass substrate at room temperature. The growth condition is fixed for RF power in 200W, working press of 70 mtorr and various mixing ratio of H2/Ar+H2 gas. The crystal structure, electric and optical properties and the influence of vacuum annealing on the samples are studied. In this research, we found that the doping of hydrogen in Co-doped ZnO thin films truly increases the electric conductivity which is proportional to the H2/(Ar+H2) ratio. When the ratio of hydrogen is low, the (002) peak taken by a Glazing Angle X-ray Diffractometer dominates, while increasing hydrogen ratio other diffraction peaks appear, indicating an enhancement of crystal structure in all directions, and grain sizes and unit cell volume decrease. From the optical transmittance measurement, it is found that the color of films turned into metallic like and the optical band gap increases linearly with H2 ratio which can be attributed to the Burstein-Moss effect that corresponds to the increasing of carriers in the conduction band by doping of H2. The transmittance data provides the information of the ratio of crystalline and amorphous, which can also be correlated to the AFM results. When the H2 ratio is higher than 30%, more crystals and larger sizes of grains were formed in the films, such that carriers did not need to pass grain boundaries so frequently and experienced less scattering that was actually improve the electric conductivity. The electric conductivity can be even improved by post annealing in H2 environment. Moreover, the Magnetic circular dichroism (MCD) measurement shows that the Co2+ ions does truly substitute on Zn sited in Td symmetry during thin film deposition. The resistance measurement as a function of temperature found the hydrogenated Co-doped thin films are semiconductor conductive. More works are needed to determine the magnetization, identify second phases and Vo by SQUID and X-ray photoelectron spectroscopy.

ABSTRACT Structural evolution and its effect on optical absorption/emission behavior of derivative of PPVs upon isothermal heat treatment at elevated temperatures were studied by means of a combination of polarized light microscopy, x-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, and photoluminescence spectroscopy. The main physical picture drawn from results of this study over a series of PPVs with flexible side-chains may be summarized as the following: (1) They are generally liquid-crystalline in nature, typically biaxially nematic in optical texture but morphologically characterized as of lamellar or hexagonal columnar structure. This is consistent with the nematogenic nature one would expect from the rigid backbone as well as the smectogenic nature one would expect from the aliphatic side-chains. (2) The aggregates formed in solutions and the supramolecular assemblies formed in the bulk state are structurally similar (in terms of the similar level of conjugation), and hence possibly of the same thermodynamic origin. This surfactant-like self-ordering behavior is consistent with the tendency towards segregation between the aromatic, rigid backbone and the aliphatic, flexible side-chains. (3) The collapse of these conjugated polymers with flexible side-chains into aggregates appears to be a general phenomenon upon slow to moderate solvent removal and not limited to the present case of poor solvency power. This is consistent with the strong tendency toward phase separation in rigid rod solutions delineated by Flory some 30 years ago. (4) All the above observations may be explained in terms of lyotropic or thermotropic self-assembly of hairy-rod chains into coiled helical conformation with ellipsoidal cross section for the conjugated backbone as shown schematically in Figure 4-42 and 4-43. The flexible side-chains generally tend to fill the space within the ellipsoidal cylindrical structure. As the side-chain length is increased, the increased Van der Waals attraction among side-chains results in more extended period of helical twist or more straighten backbone conformation, rendering preference of lamellar structure over hexagonal helical structure. (5) As a consequence, supramolecular aggregation is basically enhanced by increased side-chain length or backbone rigidity. This in turn results in more extended conjugation length or more fully developed

Neste trabalho estudamos as propriedades estruturais e eletrônicas do CO2 supercrítico, iniciando com a avaliação de campos de força balizados por aplicações anteriores de simulação quântica do tipo Dinâmica Molecular de Born-Oppenheimer (BOMD). A aplicação principal é a descrição do espectro de absorção da paranitroanilina (pNA) em CO2 supercrítico. O CO2 supercrítico pode ser considerado como uma ``alternativa verde para os solventes orgânicos convencionais e a busca por solventes mais seguros, juntamente com a crescente consciência sobre a questão ambiental, tem levado a uma ``química verde com o intuito de se buscar soluções sustentáveis. A princípio estudamos três campos de força tradicionais para o CO2, aplicados na região supercrítica. Estes campos de força podem ser validados por meio de simulação de primeiros principios. Iniciamos considerando a condição supercrítica para o CO2 como T = 315 K, = 0.81 g/cm³ e o campo de força clássico de Zhang e Duan. Depois fizemos uma análise consistindo de uma alteração de cargas e também da geometria do CO2, que seria um caso não linear no qual foi considerado um ângulo (O-C-O) = 176° . O estudo do solvatocromismo da pNA em CO2 supercrítico foi feito considerando todas estas situações descritas para o campo de força, avaliando os resultados experimentais e teóricos já existentes. A simulação gera estruturas usando Monte Carlo e são usadas em cálculos de Mecânica Quântica do tipo DFT (CAM-B3LYP). Por fim, para verificar a importância da geometria do sistema, ou seja, a propriedade estrutural, consideramos uma outra geometria para a pNA, diferente da geometria que utilizamos a princípio nas simulações com o CO2 supercrítico. Essa ``geometria modificada\" da pNA foi obtida de uma simulação existente de Born-Oppenheimer e a utilizamos numa simulação Monte Carlo com o caso não linear para o CO2 supercrítico. Os resultados de todas essas simulações nos indicaram que a alteração das cargas e por consequência a alteração da polarização do solvente, não possui muita importância na mudança do espectro de absorção da pNA. Ao se considerar o CO2 não linear, obtivemos resultados um pouco melhor, mas não muito, comparados com a previsão teórica. Mas os resultados mais significativos são os obtidos para a situação em que utilizamos a geometria modificada da pNA. Uma parte do deslocamento do máximo da banda de absorção no espectro da pNA vem com a contribuição eletrostática da interação soluto-solvente e a outra parte vem da mudança estrutural. / In this work we study the structural and electronic properties of CO2 supercritical starting with the evaluation of force fields based on previous ab initio Born-Oppenheimer molecular dynamics (BOMD). The main application is the description of the absorption spectrum of paranitroanilina (pNA) in supercritical CO2. The supercritical CO2 is considered a ``green alternative\" to conventional organic solvents and the search for safer solvents, along with the increasing awareness of environmental issues has led to the interest in ``green chemistry\", seeking sustainable solutions. At first we studied three traditional force fields for CO2, applied in the supercritical region. These force fields can be validated by first principles simulation. We considered the supercritical condition for CO2 as T=315K, =0.81g/cm³ and the classical force field of Zhang and Duan. We also did an analysis consisting of a change of the atomic point charges and the geometry of CO2, including a non-linear case in which an angle (O-C-O)=176° was considered. The study of the solvatochromism of pNA in supercritical CO2 was made considering all these situations, evaluating the theoretical outcome and the experimental results. The simulation generates structures using Monte Carlo and are used in quantum mechanics calculations of DFT (CAM-B3LYP). To verify the importance of geometry in the system, that is, the structural property, we considered another geometry for the pNA geometry different from that we used initially in the simulations with supercritical CO2. This ``modified geometry\" of pNA was obtained from a previous Born-Oppenheimer simulation and was used in a Monte Carlo simulation with the non-linear case for supercritical CO2. The results of all these simulations indicated that the alterations of charge and thus the change in the polarization of the solvent, has no great importance in the change of the absorption spectrum of the pNA. When considering the nonlinear CO2, we obtained slightly better results. But the most significant results are obtained for the situation in which we use the modified geometry of pNA. Part of the shift in the absorption spectrum of the pNA comes with the electrostatic contribution of solute-solvent interaction and the other part comes from the structural change.

O complexo formado pela molécula de tetraciclina com o íon de magnésio é capaz de impedir a replicação do material genético no ribossomo bacteriano, tornando a tetraciclina um excelente antibiótico. Outra aplicação da tetraciclina, ligada ao íon európio, consiste em estimar a concentração de colesterol no sangue a partir das mudanças do espectro de emissão. Tal técnica apresenta uma resposta imediata e confiável, comparada às técnicas atuais. Emgeral, o espectro de absorção e emissão da tetraciclina é bastante sensível aos íons alojados e ao pH do solvente que o conjunto está imerso. Entretanto, o espectro de absorção teórico em solvente foi obtido com simples modelos contínuos que não consideram interações específicas impostas pelo ambiente no líquido, além da escassez de estudos teóricos para os complexos. Nossa proposta é obter o espectro de absorção eletrônica da tetraciclina e dos complexos formados com os íons Mg e Eu. Além disso, analisamos as mudanças de intensidade e deslocamentos dos máximos das bandas nos sistemas mencionados, em função do pH do solvente e do posicionamento do íon, estimando seu correto posicionamento. Realizamos a simulação clássica usando a técnica de Monte Carlo aplicando o potencial de Lennard-Jones mais Coulomb para cada átomo da molécula de tetraciclina e dos complexos em água. O espectro de absorção eletrônica foi obtido a partir da teoria funcional da densidade dependente do tempo considerando diversos modelos para descrição do solvente e do íon. Em geral, obtivemos uma boa descrição qualitativa dos espectros, quando comparado com os resultados experimentais. Os deslocamentos das bandas e mudanças de intensidades foram bem descritos pelos modelos que utilizaram a simulação clássica para gerar as configurações. Porém cada modelo privilegiou uma propriedade de um determinado sistema, tanto para as diferentes formas da tetraciclina quanto para a presença de íons. Palavras-chaves: tetraciclina, magnésio-tetraciclina, európio-tetraciclina, espectro de absorção, teoria do funcional da densidade dependente do tempo, simulação por Monte Carlo / The complex formed by the tetracycline molecule with the magnesium ion is able to avoid the replication of the genetic material in bacterial ribosome, making tetracycline an excellent antibiotic. Another application of tetracycline attached to the europium ion, is to evaluate the concentration of cholesterol in the blood from the changes in the emission spectrum. This technique presents an immediate and reliable response compared to current techniques. In general, the absorption and emission spectrum of tetracycline is sensitive to ions coupled and the pH of the solvent that the complex is immersed. However, the theoretical absorption spectrum in solvent was obtained with simple continuum models that do not consider specific interactions imposed by the liquid environment, and also the lack of theoretical studies for the complexes. Our proposal is to obtain the electronic absorption spectrum of tetracycline and complexes formed with the ions Mg and Eu. In addition, we analyze the changes in intensity and peak shifts of the bands in the systems mentioned as the function of pH of the solvent and the position of the ion, and estimating the correct position of the ion. We performed a simulation using the classical Monte Carlo technique applying the Lennard-Jones plus Coulomb potential for each atom of the molecule tetracycline and complexes in water. The electronic absorption spectrum was obtained with the time dependent density functional theory considering several models to describe the solvent and ion. In general, we obtained a good qualitative description of the spectra when compared to the experimental results. The shift of the bands and intensity changes were well described by the used models on classical simulation. However, each model favored one property of the system, both for the different forms of tetracycline and for the presence of ions. Keywords: tetracycline, magnesium-tetracycline, europium-tetracycline, absorption spectrum, time dependent density functional theory, Monte Carlo simulation

O estudo da penetração da radiação solar no meio aquático foi desenvolvido em quatro partes. Na primeira delas, voltada para a atenuação da radiação solar na coluna d’água, foram discutidos fatores de interferência e suas inter-relações. Neste sentido, foi feita uma comparação da penetração da radiação solar em ecossistemas continentais naturais e artificiais, analisando as diferenças e similaridades. O estudo comparativo da atenuação da radiação solar subaquática em toda extensão de reservatórios constituiu a segunda parte deste trabalho. A comparação foi feita entre reservatórios que apresentam proximidades de localização, mas com diferenças marcantes nos usos e ocupações nas regiões em que os mesmos estão inseridos. Na terceira parte foram apresentados dois recursos de grande utilização na obtenção das respostas imediatas do ambiente aquático, do ponto de vista óptico, diante dos impactos sofridos. O primeiro recurso foi a determinação do espectrograma da radiação solar, indicando a atenuação da radiação solar subaquática na faixa fotossinteticamente ativa (400 nm - 700 nm). O outro recurso foi a obtenção do espectro de absorção da água superficial, que permitiu o estabelecimento do “Índice de Absorção Espectral da Água", I.A.E.A., que facilmente possibilita a detecção de fontes pontuais de poluição e contaminação. Como quarta e última parte foi proposto o desenvolvimento de um aparelho a partir da reconstrução do hidrofotômetro (Modelo Nº 268 WA 310 GM MFG & Instrument Corp. Bronx. N.Y. 10 451), onde foi introduzido e adaptado o detector fotocondutivo (PIN - 250DP) em substituição às fotocélulas anteriormente danificadas. Durante o trabalho de campo, este aparelho foi testado e foi feita a comparação com os obtidos do Quanta-meter LI-COR (LI - 185A) também utilizado neste trabalho. / The study of solar radiation penetration in aquatic environment was developed in four parts. The first one, directed to solar radiation attenuation in the water column, interference factors and their inter-relations were discussed. In this sense, a penetration comparison of the solar radiation in natural and artificial continental ecosystems was carried out, analyzing differences and similarities. The second part of this work consisted of a comparative study of underwater solar radiation in the entire reservoir. The comparison was done between reservoirs that are near to one another, but with marked differences in use and occupation within the regions where they are located. In the third part, two resources of great utilization in obtaining immediate response from the aquatic environment, from an optical point of view of the impacts experienced, were presented. The first resort was the spectrogram determination of solar radiation, which indicated the underwater solar radiation attenuation in the active photosynthetic range (400 nm - 700 nm). The other resort was the superficial water absorption spectrum, which allowed establishing the “Water Spectral Absorption Index", I.A.E.A. that easily makes possible detection of accurate sources of pollution and contamination. The fourth and last part proposed to develop an apparatus from the construction of an underwater hydrophotometer (Model 268 WA 310 GM MFG & Instrument Corp. Bronx N.Y. 10451), where the photoconductor detector was adapted and introduced (PIN - 250DP) substituting the previously damaged photocells. During field work, this apparatus was tested and comparison was performed with data obtained from Quanta-meter LI-COR (LI - 185A), also used in this work.

In this thesis, we have performed systematical study of anomalous electric and magnetic behaviors of the 3d transition metal oxides; colossal magnetoresistance (La1−xRxMnO3 where R is a divalent alkaline earth ion) and Multiferroic (Ho1-xLaxMn2O5) systems by X-ray and Neutron scattering techniques. In our study, the enhancement of the transfer temperature for La0.8Ba0.2MnO3 under strain effect from the SrTiO3 substrate could be possible due to two reasons which one is Sr diffusion from SrTiO3 substructure, and other one is the octahedral MnO6 high symmetry are increasing. We focus the intrinsic strain effect on La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 films, and findings show that due to the different ionic sizes of doped Ca or Ba ions, the strain effect acts differently in the way it deforms. The interfacial strain effect produces opposite influences on the lattice symmetry, the average Mn¡VO bond lengths, the average oxygen disorders, the coupling symmetries inside and in the vicinity of the MnO6 octahedrons, as well as producing an opposing trend in metal-insulator and magnetic transition temperatures of the strained La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 films. The strain effects on the electronic structures of La0.67Ca0.33MnO3 and La0.8Ba0.2MnO3 thin films have been studied by O K-edge x-ray absorption near edge structure (XANES) spectroscopy. For La0.67Ca0.33MnO3, the first-principles calculations reveal that the features in the XANES spectra are associated with hybridized states between O 2p and Mn minority-spin 3d t2g and eg, La 5d/Ca 3d, and Mn 4s/Ca 4p states. An analysis of these features shows that the tensile strain decreases substantially La¡VO and Ca¡VO hybridization and TC for La0.67Ca0.33MnO3. For La0.8Ba0.2MnO3, the small compressive strain enhances slightly La¡VO and Ba¡VO hybridization and TC. In this thesis, the influence of the local structure distortion on the magnetic transition in La doped HoMn2O5 Multiferroics has been investigated systematically. The orthorhombic crystal structure of Ho1−xLaxMn2O5 is maintained up to x¡Ø0.2 but decomposed into multiphase for x¡Ù0.25. By doping La ions to a concentration of 0.1¡Øx¡Ø0.2, the formation of the RMnO3 1(13) phase can be suppressed and single-phase Ho1−xLaxMn2O5 (0.1¡Øx¡Ø0.2) compounds can be formed under 1 atm flowing oxygen. For x=0.2, a ferromagnetic FM transition at 150 K is superimposed on the paramagnetic background, which implies that the compound undergoes a ferromagnetic to antiferromagnetic (AFM) transition. This unique FM to AFM transition is observed for the first time. The FM transition is attributed to the formation of magnetic clusters in a host paramagnetic matrix. The anomalous magnetic clusters phenomena observed in Ho0.8La0.2Mn2O5 can be directly attributed to the different properties between Ho and La ions, and the differences of Ho and La ions are not only in the ionic radius but also in the electron negativity. During 90~150K, X-ray scattering diffraction presented the new addition peaks indicates the new electric density distribution, and the Neutron powder scattering diffraction (NPD) refining results show that the local structure of R-O (R: La, Ho) is un-symmetry which is conflict to the La Extended X-ray absorption fine structure (EXAFS) (which shows that the local structure of La-O becomes more symmetry than H-O. Since the refining values of the NPD are an average of entire crystal, such that it cannot tell the local changes. X-ray absorption spectrum (XAS) and EXAFS, in contrarily, can provide the local information. They implies that the temperature evolutions of the coupling strength with O 2p or unoccupied density state are opposite for the Ho and La ions in our Ho0.8La0.2Mn2O5 sample. Therefore, local change of ions position and charge redistribution happens in this specific temperature range.

O estudo da penetração da radiação solar no meio aquático foi desenvolvido em quatro partes. Na primeira delas, voltada para a atenuação da radiação solar na coluna d’água, foram discutidos fatores de interferência e suas inter-relações. Neste sentido, foi feita uma comparação da penetração da radiação solar em ecossistemas continentais naturais e artificiais, analisando as diferenças e similaridades. O estudo comparativo da atenuação da radiação solar subaquática em toda extensão de reservatórios constituiu a segunda parte deste trabalho. A comparação foi feita entre reservatórios que apresentam proximidades de localização, mas com diferenças marcantes nos usos e ocupações nas regiões em que os mesmos estão inseridos. Na terceira parte foram apresentados dois recursos de grande utilização na obtenção das respostas imediatas do ambiente aquático, do ponto de vista óptico, diante dos impactos sofridos. O primeiro recurso foi a determinação do espectrograma da radiação solar, indicando a atenuação da radiação solar subaquática na faixa fotossinteticamente ativa (400 nm - 700 nm). O outro recurso foi a obtenção do espectro de absorção da água superficial, que permitiu o estabelecimento do “Índice de Absorção Espectral da Água”, I.A.E.A., que facilmente possibilita a detecção de fontes pontuais de poluição e contaminação. Como quarta e última parte foi proposto o desenvolvimento de um aparelho a partir da reconstrução do hidrofotômetro (Modelo Nº 268 WA 310 GM MFG & Instrument Corp. Bronx. N.Y. 10 451), onde foi introduzido e adaptado o detector fotocondutivo (PIN - 250DP) em substituição às fotocélulas anteriormente danificadas. Durante o trabalho de campo, este aparelho foi testado e foi feita a comparação com os obtidos do Quanta-meter LI-COR (LI - 185A) também utilizado neste trabalho. / The study of solar radiation penetration in aquatic environment was developed in four parts. The first one, directed to solar radiation attenuation in the water column, interference factors and their inter-relations were discussed. In this sense, a penetration comparison of the solar radiation in natural and artificial continental ecosystems was carried out, analyzing differences and similarities. The second part of this work consisted of a comparative study of underwater solar radiation in the entire reservoir. The comparison was done between reservoirs that are near to one another, but with marked differences in use and occupation within the regions where they are located. In the third part, two resources of great utilization in obtaining immediate response from the aquatic environment, from an optical point of view of the impacts experienced, were presented. The first resort was the spectrogram determination of solar radiation, which indicated the underwater solar radiation attenuation in the active photosynthetic range (400 nm - 700 nm). The other resort was the superficial water absorption spectrum, which allowed establishing the “Water Spectral Absorption Index”, I.A.E.A. that easily makes possible detection of accurate sources of pollution and contamination. The fourth and last part proposed to develop an apparatus from the construction of an underwater hydrophotometer (Model 268 WA 310 GM MFG & Instrument Corp. Bronx N.Y. 10451), where the photoconductor detector was adapted and introduced (PIN - 250DP) substituting the previously damaged photocells. During field work, this apparatus was tested and comparison was performed with data obtained from Quanta-meter LI-COR (LI - 185A), also used in this work.

Solar cells are designed to transform the optical energy into electrical energy. Using solar energy is the best way for humans to solve the energy shortage problem. Dye sensitized solar cell(DSSC) has a low cost and helps people to obtain the solar energy expediently. The DSSC is based on nano structured TiO2 ; and dye molecules help the particles of TiO2 to absorb more photons. Hence DSSC has higher efficiency than SC(solar cell without dye). This thesis elaborates and analyzes the dye which is sensitized to TiO2. The absorption spectrum of the dye was achieved. Two kinds of dye sample were made on the basis of their places in structure of TiO2. One dye sample is solution, nanopowder of the dye in aceton. The other dye sample is film, thin film on a quartz plate. The absorption spectrums of the samples have been measured in laboratory. The measurement suggests that the dye works improves the absorption of solar energy in DSSC. This thesis mainly contains the following sections: Chapter I reviews the solar energy technology development, the research purposes, and the principles of DSSC. Chapter II introduces the theory of optical spectroscopy. Chapter III and Chapter IV describe the apparatus employed in this experimental system, the experimental method, and the testing results. Chapter V gives the conclusions drawn from the experiments.

Um procedimento baseado no uso sequencial de simulação Monte Carlo e cálculos de Mecânica Quântica é proposto e usado para o tratamento de efeitos de solvente, com especial atenção parao sovatocromismo no espectro de absorção molecular. A ideia básica é realizar simulações clássicas com o método Monte Carlo para gerar estruturas supermoleculares do sistema em solução e em seguida tratar estas supermoléculas (soluto, solvente e suas interações) com cálculos quânticos. Um modelo totalmente discreto do solvente é utilizado e, portanto, o uso de meios dielétricos contínuos é dispensado. Neste procedimento, as supermoléculas são compostas por uma molécula do soluto rodeada pela primeira camada de solvatação definida através da função distribuição. Os efeitos de solvente são calculados usando médias configuracionais sobre estruturas supermoleculares descorrelacionadas obtidas através de análises estatísticas das simulações. Como aplicação, os deslocamentos espectrais da primeira banda de absorção do benzeno 1B2u(- *), devido a presença de diversos solventes, foram analisados e calculados. Boa concordância com os resultados experimentais foram obtidos. / A approach based on the sequential use of Monte Carlo simulation and Quantum Mechanics is proposed and use for the treatment of solvent effects with special attention to solvatochromic shifts. The basic Idea is to perform a classical Monte Carlo simulation to generate supermolecular structures of the system, then to treat these supermolecules (solute, solvent and all its interaction) by quantum mechanics. This is a totally discrete modelo f the solvent that avoids the use of a dielectric continuum. In this approach, the supermolecules are composed by the solute molecule surrounded by the first solvation Shell as determined by the distribution function. The solvent effects are calculated using ensemble average over uncorrelated supermolecular structures obtained by statistical analysis. As na application, the spectral shifts of the 1B2u(- *) trnsition of benzene in different solvents are investigated. Good agreement with the experimental results are obtained.

Estudamos as propriedades estruturais e eletrônicas da molécula emodina (EM), em diferentes condições, do ponto de vista experimental e teórico. Numa primeira parte, realizamos medidas do espectro eletrônico de absorção da EM, em meio solvente (água, clorofórmio e metanol). Nessa parte, obtivemos que o solvente provoca pouco efeito nos deslocamentos das bandas. Numa segunda parte, estudamos a EM, isoladamente e nos três solventes, através de cálculos quânticos com funcional de densidade (B3LYP), conjunto de função base de Pople (6-31G*) e modelo contínuo polariz ável (PCM). Como principais resultados obtivemos que a EM é rígida a menos da orientação relativa das 3 hidroxilas. A mudança orientacional nessas hidroxilas pode provocar formação de até 2 ligações de hidrogênio intramolecular (o que estabiliza sua geometria) e conseqüente uma diminuição no momento dipolo de 5.5 a 1.7D (o que desestabiliza sua interação com a água). Numa terceira parte, realizamos simulações com método Monte Carlo e Dinâmica Molecular em solução. Nessa parte, obtivemos que as ligações de hidrogênio intramoleculares são raramente quebradas devido as interações com o solvente e isso atribui a EM um caráter hidrofóbico. Adicionalmente, utilizando Teoria de Perturbação Termodinâmica nas simulações, calculamos a variação de energia livre de solvatação da EM em partição água/clorofórmio e água/- metanol e obtivemos -2.6 e -4.9 kcal/mol, respectivamente. Esse resultado está em boa concordância com o resultado experimental de -5.6 kcal/mol para partição de água/octanol. Por último, realizamos cálculos do espectro eletrônico de absorção da EM, isoladamente e nos três solventes, considerando as moléculas através do modelo, contínuo de solvente (SCRF) e explícito de solvente, com o método INDO/CIS. Nessa parte, obtivemos que o efeito do solvente é bem descrito teoricamente. / We study the structural and electronic properties of the emodin (EM) in different solvents of experimental and theoretical the point of view. We started performing measurements of the UV-Vis absorption spectrum of the EM in solution (water, chloroform and methanol). Our main result is that the solvent causes little effect on shifts the bands. In the second part of this work, we performing quantum calculations of isolated EM and in the three solutions using density functional (B3LYP), a set of Pople basis function (6-31G*) and the polarizable continuum model (PCM). In this part, our result is that EM presents a rigid conformation unless the orientation of its 3 hydroxyls. The change in these hydroxyls orientation can form up to 2 intramolecular H-bonds (which stabilizes its geometry) and causes a decrease in the dipole moment from 5.5 to 1.7D (which destabilizes its interaction with water). In the third part of this work, we performing Monte Carlo and Molecular Dynamics simulations in solution. Our main result is that the intramolecular H-bonds are rarely broken, even in aqueous solution, and these give to EM a hydrophobic character. Additionally, using Thermodynamics Perturbation Theory in the simulations, we calculate variations of free energy of solvation of EM in partition of water/chloroform and water/methanol and obtained -2.6 and -4.9kcal/mol, respectively. This last result is in good agreement with the experimental result[3] of -5.6kcal/mol for partition of water/octanol. Finally, we performing calculations of UV-Vis absorption spectrum of isolated EM and in the three solutions. In this calculations, we considering the molecules through the continuum solvent (SCRF) and explicit solvent model with the method INDO/CIS. In this part, we obtaining that effect of solvent is well described theoretically.