Na primeira parte deste trabalho foi estudada a interação da porfirina catiônica meso-tetrakis N-metil-4-piridil (TMPyP) e a porfirina aniônica meso-tetrakis 4-fenilsulfonato (TPPS4) nas formas de base livre com sistemas modelos de membrana biológica (micelas iônicas, micelas mistas e vesículas de fosfolipídios) em soluções aquosas, através das técnicas de absorção ótica, espalhamento de luz ressonante (RLS do inglês \"resonante light scattering), fluorescência e SAXS, do inglês \"Small Angle X-Ray Scattering\". As curvas de SAXS das micelas catiônicas de CTAC (cloreto de cetiltrimetilamônio) foram ajustadas como um elipsóide prolato na ausência e na presença de 2-10 mM de TPPS4. Os dados de SAXS mostraram que a presença da porfirina TPPS4 modifica o centro hidrofóbico micelar, levando a formação de micelas menores. Através das análises dos dados de SAXS das micelas de SDS (dodecilsulfato de sódio) observamos que a forma da micela na ausência e na presença de 2-10 mM TMPyP apresenta a forma de um elipsóide prolato sem mudanças. Entretanto, o coeficiente de ionização, diminuiu com o aumento da concentração de porfirina, sugerindo a \"blindagem\" da carga aniônica do SDS pela porfirina catiônica. A supressão de fluorescência da TPPS4 e TMPyP foi estudada na ausência e na presença de diferentes micelas de surfactantes, tais como as de SDS, CTAC, HPS (N-hexadecil-N,N,dimetil-3-amônio-1-propano sulfato) e TX-100 (t-octil-fenoxi-polietoxi-etanol). O iodeto de potássio (KI) foi utilizado como supressor. Os gráficos de Stern-Volmer dos dados de fluorescência no estado estacionário foram ajustados pela equação quadrática, incluindo a supressão dinâmica (KD) e estática (KS). Os valores de KS são muito menores do que os valores de KD. Os resultados da TMPyP são consistentes com as constantes de ligação reportadas na literatura: uma redução significativa de supressão acontece para a TMPyP na presença de SDS, e uma redução moderada é observada para o sistema TMPyP-HPS e quase nenhuma mudança é vista para a TMPyP na presença de TX-100. Para o sistema CTAC-TPPS4 um aumento na supressão foi observado quando comparada com a TPPS4 em tampão puro. Isto provavelmente é associado ao acúmulo de iodeto na interface da micela catiônica. A atração entre a cabeça polar do CTAC e I-, e a repulsão entre SDS e I-, aumenta e reduz a supressão de fluorescência, respectivamente, das porfirinas que se localizam na interface micelar. A pequena supressão da TPPS4 em TX-100 é coerente com a forte ligação entre a TPPS4-TX-100 reportada na literatura. A TPPS4 e a TMPyP na presença de concentrações baixas dos surfactantes CTAC e SDS, respectivamente, apresentaram formação de agregados pré-micelares. A adição de surfactante neutro, TX-100, reduziu o efeito de agregação, acompanhada pelas várias técnicas espectroscópicas utilizadas neste trabalho. Portanto, sob condições onde temos a máxima formação de agregados (porfirina-surfactante), a titulação da TPPS4 com micelas de 40%CTAC-60%TX-100 e a TMPyP com micelas de 80%SDS-20%TX-100 não foi suficiente para eliminar a agregação, apesar da diminuição significativa do efeito de supressão de fluorescência e da intensidade de luz espalhada. A interação da TMPyP com 1-Palmitoil-2-Oleoil-sn-Glicero-3-fosfocolina (POPC), 1-Palmitoil-2-Oleoil-sn-Glicero-3-[Fosfo-rac-(1-glicero)] (POPG) e a mistura POPC + POPG é predominantemente devido à contribuição de eletrostática. O aumento da carga negativa, devido à adição de POPG, favorece a interação das vesículas com a porfirina catiônica. Na segunda parte deste trabalho foram estudados os efeitos de três surfactantes na estrutura oligomérica da hemoglobina extracelular gigante de Glossoscolex paulistus (HbGp) na sua forma oxi. O estudo com o SDS, CTAC e HPS permitiu diferenciar os efeitos de cargas opostas da cabeça polar dos surfactantes na dissociação da estrutura oligomérica e na autoxidação da hemoglobina. A interação do HPS com HbGp foi claramente menos intensa que a interação desta hemoglobina com os surfactantes catiônico (CTAC) e aniônico (SDS). Provavelmente, esta menor interação da HbGp com HPS, quando comparada com o SDS e o CTAC, é devido a menor atração eletrostática entre o HPS e os sítios iônicos da proteina. Dados espectroscópicos foram discutidos e comparados com os da literatura, afim de compreender a interação hemoglobina-surfactante, e como o ponto isoelétrico ácido (pI) pode influenciar na relação da estrutura-atividade das hemoglobinas gigantes extracelulares. As amostras de HbGp foram estudadas por espalhamento de luz dinâmico (DLS do inglês \"Dynamic light scattering\"). Na faixa de pH 6.0 a 8.0, HbGp é bastante estável e a distribuição de tamanho das partículas é monodispersa com um diâmetro hidrodinâmico médio (Dh) de 27 nm. O aumento dos valores de pH (pH>9.0) induziu um processo de dissociação irreversível, resultando num valor do Dh menor (10 nm). A diminuição do Dh sugere uma dissociação completa da hemoglobina. Em pH>9,0 a cinética de dissociação é lenta, com um mínimo 24 h para ser completada. As constantes cinéticas de dissociação aumentam progressivamente, com o aumento do valor do pH. As curvas de melting point para HbGp apresentaram dissociação oligomérica e desnaturação da proteina em função do pH. Os processos de autoxidação e dissociação estão intimamente relacionados, de modo que a dissociação da proteina oligomérica promove um aumento na velocidade de autoxidação e vice-versa. / In the first part of this work interactions of the cationic meso tetrakis (4-N-methilpyridil) porphyrin (TMPyP) and meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) in the free base forms with membrane model systems (ionic micelles, mixed micelles and phospholipids vesicles) in aqueous solutions, have been investigated by optical absorption, resonance light scattering (RLS), fluorescence and SAXS (Small Angle X-Ray Scattering). The best-fit SAXS curves were obtained assuming for cetyltrimethylammonium chloride (CTAC) micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS4. SAXS results show that the presence of TPPS4 impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. SAXS data analysis demonstrated a prolate ellipsoidal shape for sodium dodecyl sulfate (SDS) micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, α, decreases with the increase of the porphyrin concentration, suggesting the \"screening\" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with ionic surfactants. Fluorescence quenching of TPPS4 and TMPyP is studied in aqueous solution and upon addition of micelles of SDS, CTAC, N-hexadecyl-N,N-dimethyl-3-ammonio-1- propanesulfonate (HPS) and t-octylphenoxypolyethoxyethanol (Triton X-100). Potassium iodide (KI) was used as quencher. Steady-state Stern-Volmer plots were best fitted by a quadratic equation, including dynamic (KD) and static (KS) quenching. KS was significantly smaller than KD. For TMPyP quenching results are consistent with reported binding constants: a significant reduction of quenching takes place for SDS, a moderate reduction is observed for HPS and almost no change is seen for Triton X-100. For CTAC-TPPS4 system an enhancement of quenching was observed as compared to pure buffer. This is probably associated to accumulation of iodide at the cationic micellar interface. The attraction between CTAC headgroups and I-, and repulsion between SDS and I-, enhances and reduces the fluorescence quenching, respectively, of porphyrins located at the micellar interface. The small quenching of TPPS4 in Triton X-100 is consistent with strong binding as reported in the literature. Anionic TPPS4 and cationic TMPyP in the presence of low concentrations of the surfactants CTAC and SDS, respectively, showed formation of aggregates, monitored by optical absorption, fluorescence and resonance light scattering intensity (RLS). The addition of nonionic surfactant, Triton X-100, reduced the effect of aggregation monitored by the various techniques used in the present work. Therefore, under conditions for the maximum of aggregate formation (porphyrin-surfactant), apparently, the CTAC: TX-100 ratio equal to 40:60 and SDS:TX-100 ratio equal to 80:20 are not sufficient to eliminate aggregation, despite the significant decrease of the quenching effect of fluorescence and of the light scattering intensity. The interaction of TMPyP with 1-Palmitoyl-2-Oleoyl-sn- Glycero-3-Phosphocholine (POPC), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-rac-(1- glycerol)] (POPG) and the mixture POPC+POPG is predominantly due to the electrostatic contribution. The increase of the negative charge, due to addition of POPG, favors the interaction of vesicles with the cationic porphyrin. On the second part of this work the effects of three surfactants upon the oligomeric structure of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy - form was studied. The use of SDS, CTAC and HPS has allowed to differentiate the effects of opposite headgroup charges on the oligomeric structure dissociation and hemoglobin autoxidation. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin-surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on its structure-activity relationship. HbGp samples were studied by dynamic light scattering (DLS). In the pH from range 6.0 to 8.0, HbGp is stable and a monodisperse size distribution with a z-average hydrodynamic diameter (Dh) of 27±1 nm is observed. More alkaline pH (pH>9.0) induced an irreversible dissociation process, resulting in smaller Dh of 10±1 nm. Dh decrease suggests a complete hemoglobin dissociation. At pH 9.0 the dissociation kinetics is slow, taking a minimum of 24 h to be completed. Dissociation rate constants progressively increase at higher pH. Melting curves for HbGp showed oligomeric dissociation and protein denaturation as a function of pH. Autoxidation and dissociation processes are intimately related, so that oligomeric protein dissociation promotes the increase of autoxidation rate and vice-versa.

Magnetorheological fluids (MRFs) are non-colloidal stable suspensions of polarizable mesoscale soft magnetic particles, usually metallic Fe-particles, in a carrier liquid such as oil or water; the solidity of which can be tuned by varying the applied magnetic field strength. Magnetorheological fluids are agile candidates for impact mitigation due to their tunable “solidity”, quick and complete reversibility of physical states, durability and reusability in comparison to their mechanical counterparts. The highly desirable property of an MRF is its yield strength and hence the conventional MRFs are Fe-based. However, uncoated Fe-particles suffer from poor chemical and thermo-oxidative stabilities, poor sedimentation stability and redispersibilities necessitating the coatings / additives; which always lead to compromised performance when used in MRFs. An alternative (to Fe) magnetic filler phase is the use of magnetic oxide particles. Soft magnetic spinel ferrites and garnets (though with moderate yield strength in an MRF) with their excellent chemical, thermo-oxidative and sedimentation stabilities, ready-redispersibility, less stringent synthesis and preservation conditions, lower cost, need no stabilizers and additives make them potential contenders for use in MRFs which can provide reliable MR performance. As the microstructure and magnetic nature of particles have direct influence on the MR property, the effects of these were studied by preparing MRFs with magnetic oxide particles of different sizes and shapes. These MRFs were simple bi-phasic as magnetic oxide particles were dispersed in versatile carrier fluid (silicone oil) without any additives; where the magnetic fill fraction was decided based on off state viscosity and the wettability criteria. As the MRFs in a device can undergo different stress / strain conditions of varying amplitudes and frequencies during their service, such a response was studied in laboratory using magnetorheometer via different modes of operation which mimic the service conditions. By varying the applied magnetic field strength and applied shear conditions, the performance of MRFs was evaluated and correlated to the physical and magnetic properties of the particles. Such a study provides a basis for the choice of magnetic phase in MRFs and their required concentration in the base fluid to provide highest efficiency. The dynamic yield strengths (field dependent yield stress) of MRFs extracted from steady shear measurements showed that the yield strength was strongly dependent on the saturation magnetization as well as on the microstructure of the particles used in MRF. The yield strength scaled with the saturation magnetization, magnetic fill fraction and applied magnetic field strength due to stronger magnetic column formation. The stability of MRFs (via the absence of wall slip) was found to depend predominantly on the microstructure of magnetic particles in the fluid such that MRFs containing structured particles showed the absence of wall slip while the MRFs containing irregular shaped powder particles showed poor stability via the occurrence of wall slip. The steady shear tests highlight the importance of using particles of definite shape with superior magnetic properties at a certain magnetic fill fraction for an efficient and reliable MR performance. The MRFs subjected to different oscillatory shear conditions showed that sturdier structures form in-field (exhibited via high gain modulus or low loss factor) when the particles have certain shapes (and size distribution) which result in high surface contact and are highly magnetic. Hence, the MRF containing Fe3O4 micro-octahedrons with high magnetization and large surface area for contact with other octahedron showed the large value of gain modulus and low loss factor compared to all other MRF samples. Poly-dispersity in spheres was found to be advantageous over monodisperse spherical magnetic particles due to void-bridging effects that strengthen the magnetic structuration. The irregular shaped particles based MRFs showed lower gain (higher loss factor) due to weak structuration. Anomalously high loss factor observed for rod shaped LZFP particles based MRF at medium strains and low field strengths is attributed to the rotation hindrance and low density of particles. The polydisperse particles based MRFs showed need for higher applied field strengths to decrease the loss and irregular particles based MRFs showed noisy response. The magnetosweep results showed that shape anisotropic particles based MRFs respond faster to applied field manifested as a faster decrease in loss factor with field. With magnetorheological parameters showing high dependence on the physical and magnetic nature of particles, oscillatory shear tests can serve as a means to select and assess the suitability of these particles for magnetorheological fluid for specific applications. The time dependent magneto-mechanical behaviour such as creep-recovery in MRFs showed that the strain recovery was dependent on the microstructure and magnetic nature of the particles such that fluids containing structured particles with high saturation magnetization showed higher recovery (due to better in-field structuration) compared to the irregular shaped and lower magnetization particles based MRF counterparts. The endurance of the MRFs (sustenance of strength of the MRF) under sustained stress conditions were estimated by a novel method which showed that MRFs containing ‘structured’ particles with high saturation magnetization showed high creep strength. In case of spherical particles based MRFs, the polydispersity of particles was found to aid in better column strength due to void-filling. The high surface contact between rod-shaped particles in the fluid resulted in good creep-strength among all MRFs. Among all the particles, the octahedron shaped Fe3O4 particles with large surface contact coupled with high saturation magnetization makes the Fe3O4 micro-octahedron particles based MRF the best amongst all the MRFs studied in this work. In case of irregular shaped particles based MRFs, the creep strength lagged behind the yield strength suggesting that such MRFs are not suitable for applications which demand sustained strength over prolonged action of stresses. Thus, the present work highlights the importance of considering the physical and magnetic properties of magnetic particles while selecting them for application specific MRFs where high endurance is sought. The stress relaxation behaviour of MRFs showed an overall high strength (via relaxation moduli) for MRFs containing particles with definite shape and high magnetization values (increased structure strength). However, the rod shaped particles based MRF did not witness increased strain limit with increased field strength, probably due to the mass flow in fluid due to higher inter-particle interaction than the interaction with applied field. The observation of increase in critical strain with increase in field for MRFs containing irregular shaped particles is only due to the higher number of particles resulting in overall increase in viscosity with field. Among all the MRFs, octahedron Fe3O4 particles with superior magnetic properties and large surface contact between facets showed highest critical strain for flow, which is in corroboration with other magnetorheological studies discussed so far. The creep-recovery and stress relaxation behaviours of MRFs are rarely studied, yet very important when selecting an MRF for an application which seeks high retention of MR strength over prolonged action of stress or strains. A comparison of particle shapes used in the MRFs suggests that although both octahedron shaped and rod shaped particles make high surface contact during structuration, the former is better due to lack of rotation hindrance, thus useful for preparing quickly responding MRFs. The inadequacies in th e conventio nal FOMs are address ed by a new FOM which is based o n a wholistic approach formulated consideri ng all relev ant physical and magnetic paramete rs of the particles. Also, the individ ual terms of this FOM help in selecting a particular MRF for a specific application. The FOM is as follows: λ – sedimentation constant (time taken by the MRF to sediment to about 1/eth of its total volume) With the MRFs containing octahedron shape d Fe3O4 pa rticles showing the highest FOM followed by s pheres (mod erate value ) which are succeeded by irregular powder samples based MRFs, the FO M observed in all MRF cases follow the same trend as observed by results from different magnetorheologi cal studies. Hence, the highest F4 (or FAB) observed for Fe3O4 octahedron particles based MR F in comparison to a ll other MR Fs (including Fe-based) is justified by the o Mbserved large yield strength, creep-resistance, low density and ready-redispersibilities, validating the FOM. The entire thesis is organized as follows. Chapter 1 details the motivation for the present research work, introduction to the material of interest (Magnetorheological fluid) with overview of different areas of potential applications, important properties of MRF, the current status of MRF, the challenges / issues needed to be addressed followed by choice of alternate materials for addressal of these drawbacks faced by conventional (Fe based) MRFs. Chapter 2 explains the synthesis of magnetic-oxide particles of different sizes and shapes by following different synthesis techniques. This is followed by the structural, microstructural and magnetic properties characterizations carried out by employing different, standard characterization techniques. The procedure for preparation of MRFs from the synthesized magnetic oxide particles is discussed. The basis of carrier fluid selection and magnetic particle concentration in MRF is explained. Chapter 3 gives a background to magnetorheology, in terms of the instrumentation (magnetorheometer), the relation between the magnetorheological parameters and the instrumental parameters (conversion factors), the different operating modes and the relevance of characterization modes in terms of practical applications, the procedure of different characterizations and the standard response behavior of MRFs to the characterizations. Chapter 4 is comprehensive characterization of all the MRFs subjected to steady shear conditions at various applied fields. The detailed analyses in terms of MR response are given with respect to the structure, microstructure, magnetic nature, and magnetic fill fraction of the magnetic particle in the fluid. Chapter 5 is extensive study of all the MRFs subjected to dynamical shear conditions at various applied fields. The magnetorheological responses of MRFs under different dynamical conditions (amplitude sweep, frequency sweep and magnetosweep) are analyzed in regard to role of microstructure, magnetic nature and magnetic fill fraction of the magnetic particle in the fluid. Chapter 6 explains the creep-recovery response of MRFs for the best magnetic fill fraction, decided from the steady and dynamical shear responses for all concentrations of MRFs. The recovered strain is analyzed with respect to a range of applied field strength and stress values. The creep strength determined from this study is correlated to the microstructure and magnetic nature of particles constituting the MRFs. Chapter 7 elaborates the stress relaxation behaviour of MRFs for the best magnetic fill fraction, decided from the steady and dynamical shear responses for all concentrations of MRFs. The stress relaxation (plateau values) moduli for the MRFs extracted at various applied field strength and strain values are analyzed to estimate the critical stress for flow in MRFs. This relationship between the critical stress that an MRF can withstand and the microstructure and magnetic nature of the particles in the fluid are investigated. Chapter 8 is about the study of sedimentation stability (and the redispersibility) of magnetic oxide particles based MRFs and the comparison of these properties with Fe- based MRFs. The role of mass-density and microstructure of particles in the fluid on sedimentation rate is briefly explained. Chapter 9 compares the important outcome of all the magnetorheological characterizations for all the studied MRFs in terms of extent and speed of response, the sedimentation stability and eases of redispersibility, and relates the observations to the physical and magnetic properties of the magnetic particles. The method of developing a new figure of merit based on a wholistic approach for assessing the efficiency and reliability of MRF is discussed which overcomes the shortcomings of conventional figures of merit. Chapter 10 summarizes the important findings of research work and highlights the validity of the new figure of merit in assessing ‘reliability and performance’ of MRFs.

Na primeira parte deste trabalho foi estudada a interação da porfirina catiônica meso-tetrakis N-metil-4-piridil (TMPyP) e a porfirina aniônica meso-tetrakis 4-fenilsulfonato (TPPS4) nas formas de base livre com sistemas modelos de membrana biológica (micelas iônicas, micelas mistas e vesículas de fosfolipídios) em soluções aquosas, através das técnicas de absorção ótica, espalhamento de luz ressonante (RLS do inglês \"resonante light scattering), fluorescência e SAXS, do inglês \"Small Angle X-Ray Scattering\". As curvas de SAXS das micelas catiônicas de CTAC (cloreto de cetiltrimetilamônio) foram ajustadas como um elipsóide prolato na ausência e na presença de 2-10 mM de TPPS4. Os dados de SAXS mostraram que a presença da porfirina TPPS4 modifica o centro hidrofóbico micelar, levando a formação de micelas menores. Através das análises dos dados de SAXS das micelas de SDS (dodecilsulfato de sódio) observamos que a forma da micela na ausência e na presença de 2-10 mM TMPyP apresenta a forma de um elipsóide prolato sem mudanças. Entretanto, o coeficiente de ionização, diminuiu com o aumento da concentração de porfirina, sugerindo a \"blindagem\" da carga aniônica do SDS pela porfirina catiônica. A supressão de fluorescência da TPPS4 e TMPyP foi estudada na ausência e na presença de diferentes micelas de surfactantes, tais como as de SDS, CTAC, HPS (N-hexadecil-N,N,dimetil-3-amônio-1-propano sulfato) e TX-100 (t-octil-fenoxi-polietoxi-etanol). O iodeto de potássio (KI) foi utilizado como supressor. Os gráficos de Stern-Volmer dos dados de fluorescência no estado estacionário foram ajustados pela equação quadrática, incluindo a supressão dinâmica (KD) e estática (KS). Os valores de KS são muito menores do que os valores de KD. Os resultados da TMPyP são consistentes com as constantes de ligação reportadas na literatura: uma redução significativa de supressão acontece para a TMPyP na presença de SDS, e uma redução moderada é observada para o sistema TMPyP-HPS e quase nenhuma mudança é vista para a TMPyP na presença de TX-100. Para o sistema CTAC-TPPS4 um aumento na supressão foi observado quando comparada com a TPPS4 em tampão puro. Isto provavelmente é associado ao acúmulo de iodeto na interface da micela catiônica. A atração entre a cabeça polar do CTAC e I-, e a repulsão entre SDS e I-, aumenta e reduz a supressão de fluorescência, respectivamente, das porfirinas que se localizam na interface micelar. A pequena supressão da TPPS4 em TX-100 é coerente com a forte ligação entre a TPPS4-TX-100 reportada na literatura. A TPPS4 e a TMPyP na presença de concentrações baixas dos surfactantes CTAC e SDS, respectivamente, apresentaram formação de agregados pré-micelares. A adição de surfactante neutro, TX-100, reduziu o efeito de agregação, acompanhada pelas várias técnicas espectroscópicas utilizadas neste trabalho. Portanto, sob condições onde temos a máxima formação de agregados (porfirina-surfactante), a titulação da TPPS4 com micelas de 40%CTAC-60%TX-100 e a TMPyP com micelas de 80%SDS-20%TX-100 não foi suficiente para eliminar a agregação, apesar da diminuição significativa do efeito de supressão de fluorescência e da intensidade de luz espalhada. A interação da TMPyP com 1-Palmitoil-2-Oleoil-sn-Glicero-3-fosfocolina (POPC), 1-Palmitoil-2-Oleoil-sn-Glicero-3-[Fosfo-rac-(1-glicero)] (POPG) e a mistura POPC + POPG é predominantemente devido à contribuição de eletrostática. O aumento da carga negativa, devido à adição de POPG, favorece a interação das vesículas com a porfirina catiônica. Na segunda parte deste trabalho foram estudados os efeitos de três surfactantes na estrutura oligomérica da hemoglobina extracelular gigante de Glossoscolex paulistus (HbGp) na sua forma oxi. O estudo com o SDS, CTAC e HPS permitiu diferenciar os efeitos de cargas opostas da cabeça polar dos surfactantes na dissociação da estrutura oligomérica e na autoxidação da hemoglobina. A interação do HPS com HbGp foi claramente menos intensa que a interação desta hemoglobina com os surfactantes catiônico (CTAC) e aniônico (SDS). Provavelmente, esta menor interação da HbGp com HPS, quando comparada com o SDS e o CTAC, é devido a menor atração eletrostática entre o HPS e os sítios iônicos da proteina. Dados espectroscópicos foram discutidos e comparados com os da literatura, afim de compreender a interação hemoglobina-surfactante, e como o ponto isoelétrico ácido (pI) pode influenciar na relação da estrutura-atividade das hemoglobinas gigantes extracelulares. As amostras de HbGp foram estudadas por espalhamento de luz dinâmico (DLS do inglês \"Dynamic light scattering\"). Na faixa de pH 6.0 a 8.0, HbGp é bastante estável e a distribuição de tamanho das partículas é monodispersa com um diâmetro hidrodinâmico médio (Dh) de 27 nm. O aumento dos valores de pH (pH>9.0) induziu um processo de dissociação irreversível, resultando num valor do Dh menor (10 nm). A diminuição do Dh sugere uma dissociação completa da hemoglobina. Em pH>9,0 a cinética de dissociação é lenta, com um mínimo 24 h para ser completada. As constantes cinéticas de dissociação aumentam progressivamente, com o aumento do valor do pH. As curvas de melting point para HbGp apresentaram dissociação oligomérica e desnaturação da proteina em função do pH. Os processos de autoxidação e dissociação estão intimamente relacionados, de modo que a dissociação da proteina oligomérica promove um aumento na velocidade de autoxidação e vice-versa. / In the first part of this work interactions of the cationic meso tetrakis (4-N-methilpyridil) porphyrin (TMPyP) and meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) in the free base forms with membrane model systems (ionic micelles, mixed micelles and phospholipids vesicles) in aqueous solutions, have been investigated by optical absorption, resonance light scattering (RLS), fluorescence and SAXS (Small Angle X-Ray Scattering). The best-fit SAXS curves were obtained assuming for cetyltrimethylammonium chloride (CTAC) micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS4. SAXS results show that the presence of TPPS4 impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. SAXS data analysis demonstrated a prolate ellipsoidal shape for sodium dodecyl sulfate (SDS) micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, α, decreases with the increase of the porphyrin concentration, suggesting the \"screening\" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with ionic surfactants. Fluorescence quenching of TPPS4 and TMPyP is studied in aqueous solution and upon addition of micelles of SDS, CTAC, N-hexadecyl-N,N-dimethyl-3-ammonio-1- propanesulfonate (HPS) and t-octylphenoxypolyethoxyethanol (Triton X-100). Potassium iodide (KI) was used as quencher. Steady-state Stern-Volmer plots were best fitted by a quadratic equation, including dynamic (KD) and static (KS) quenching. KS was significantly smaller than KD. For TMPyP quenching results are consistent with reported binding constants: a significant reduction of quenching takes place for SDS, a moderate reduction is observed for HPS and almost no change is seen for Triton X-100. For CTAC-TPPS4 system an enhancement of quenching was observed as compared to pure buffer. This is probably associated to accumulation of iodide at the cationic micellar interface. The attraction between CTAC headgroups and I-, and repulsion between SDS and I-, enhances and reduces the fluorescence quenching, respectively, of porphyrins located at the micellar interface. The small quenching of TPPS4 in Triton X-100 is consistent with strong binding as reported in the literature. Anionic TPPS4 and cationic TMPyP in the presence of low concentrations of the surfactants CTAC and SDS, respectively, showed formation of aggregates, monitored by optical absorption, fluorescence and resonance light scattering intensity (RLS). The addition of nonionic surfactant, Triton X-100, reduced the effect of aggregation monitored by the various techniques used in the present work. Therefore, under conditions for the maximum of aggregate formation (porphyrin-surfactant), apparently, the CTAC: TX-100 ratio equal to 40:60 and SDS:TX-100 ratio equal to 80:20 are not sufficient to eliminate aggregation, despite the significant decrease of the quenching effect of fluorescence and of the light scattering intensity. The interaction of TMPyP with 1-Palmitoyl-2-Oleoyl-sn- Glycero-3-Phosphocholine (POPC), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-rac-(1- glycerol)] (POPG) and the mixture POPC+POPG is predominantly due to the electrostatic contribution. The increase of the negative charge, due to addition of POPG, favors the interaction of vesicles with the cationic porphyrin. On the second part of this work the effects of three surfactants upon the oligomeric structure of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy - form was studied. The use of SDS, CTAC and HPS has allowed to differentiate the effects of opposite headgroup charges on the oligomeric structure dissociation and hemoglobin autoxidation. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin-surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on its structure-activity relationship. HbGp samples were studied by dynamic light scattering (DLS). In the pH from range 6.0 to 8.0, HbGp is stable and a monodisperse size distribution with a z-average hydrodynamic diameter (Dh) of 27±1 nm is observed. More alkaline pH (pH>9.0) induced an irreversible dissociation process, resulting in smaller Dh of 10±1 nm. Dh decrease suggests a complete hemoglobin dissociation. At pH 9.0 the dissociation kinetics is slow, taking a minimum of 24 h to be completed. Dissociation rate constants progressively increase at higher pH. Melting curves for HbGp showed oligomeric dissociation and protein denaturation as a function of pH. Autoxidation and dissociation processes are intimately related, so that oligomeric protein dissociation promotes the increase of autoxidation rate and vice-versa.

Dans cette thèse, nous avons étudié les propriétés photoniques et vibrationnelles de monocouches moléculaires auto-assemblées sur graphène et la possibilité d'utiliser des multicouches auto-assemblées de pérylène comme milieu à gain pour l'amplification de plasmons. Le graphène, en tant que matériau transparent et conducteur, a permis pour la première fois de corréler la géométrie du réseau de l’auto-assemblage supramoléculaire avec ses propriétés optiques, grâce à la microscopie à effet tunnel et à des mesures de spectroscopiques optiques et Raman. En comparant plusieurs colorants autoassemblés sur le graphène, nous avons mis en lumière les effets des interactions intermoléculaires et des interactions colorant-graphène sur le spectre d'absorption du colorant adsorbé. Le transfert d'énergie rapide des colorants vers la couche degraphène par les mécanismes de Förster et de Dexter empêche toute relaxation radiative du colorant..Néanmoins, nous avons démontré la première fonctionnalisation fluorescente non-covalente du graphène par une monocouche de colorants autoassemblée en mettant en place une stratégie à base d’espaceurs. Nous avons exploité l’extinction rapide de la fluorescence des colorants par le graphène pour étudier les spectres Raman des auto-assemblages moléculaires sur graphène, et nous avons révélé l'apparition d'un mode vibrationnel couplé entre les molécules adsorbées et le substrat de graphène. Nous avons démontré le régime de couplage fort entre un auto-assemblage tri-dimensionnel de pérylène et un plasmon polariton de surface en optimisant l'orientation et l'organisation des molécules de colorant par rapport au champ électrique du mode de plasmon. Nous avons prouvé que les milieux de gain auto-assemblés en agrégats-J peuvent théoriquement conduire à des milieux de gain efficaces pour l'amplification de plasmons. Cependant, nous avons révélé expérimentalement que les recombinaisons exciton-exciton limitent le taux de pompage à des fluences élevées dans ces milieux denses. / In this work, we have studied thephotonic and vibrational properties of selfassembled molecular monolayers on graphene and the possibility to use perylene self-assembled multilayers as a gain medium for plasmon amplification. Graphene, as a transparent and conductive material, has offered for the first time to correlate the self-assembly structure as deduced from scanning tunneling microscopy to photonic properties as analyzed by optical and Raman spectroscopy measurements. By comparing several self-assembled dyes on graphene we have shed lighton how intermolecular and dye-graphene interactions modify the absorption spectrum of the adsorbed dye.Fast Förster and Dexter energy transfer from the adsorbed dyes to the graphene layer prevent any radiative decay of the dye.Nevertheless, we have demonstrated the first fluorescent non-covalent functionalization of graphene by a supramolecular self-assembled monolayer using a spacer approach.We have exploited the fast dye fluorescence quenching by graphene to study Raman spectra of self-assembled dye on graphene, and we have shown the appearance of a coupled vibrational mode between the adsorbed molecules and the graphene substrate. We have demonstrated the strong couplingregime between a three-dimensional perylene self-assembly and a propagating plasmon polariton by optimizing the orientation and the organisation of the dye molecules compared to the electric field of the plasmon mode. We have shown that J-aggregated self-assembled gain media may theoretically lead to efficient gain media for plasmon amplification. However, we experimentally demonstrated that exciton-exciton recombination limits the achievable pumping rate at high fluences in such dense media.

Ce travail, qui concerne l’étude des nanotubes de carbone mono- et double parois, comporte deux volets distincts: (i) une compréhension des propriétés optiques et phononiques intrinsèques des nanotubes de carbone individuels, (ii) une approche expérimentale originale des propriétés des nanotubes de carbone double-parois fonctionnalisés de manières covalente et non-covalente. Concernant l’étude des propriétés intrinsèques des nanotubes de carbone individuels, des informations originales ont été obtenues en couplant des résultats de spectroscopie Raman, incluant la mesure des profils d’excitation des différents modes, avec des données d’absorption optique et de diffraction électronique. De manière générale, l’approche que nous avons développée a mis en avant la complémentarité de la spectroscopie Raman et de la diffraction électronique pour l’identification « la plus probable » de la structure de chaque tube. Parmi les résultats obtenus sur les tubes mono-paroi (SWNTs) individuels, on peut souligner la confirmation originale du caractère excitonique des transitions optiques obtenue en combinant des données d’absorption et de profils d’excitation Raman, ainsi que la mise en évidence d’un comportement inattendu des rapports d’intensité des composantes LO et TO des modes G. L’étude des nanotubes de carbone double-parois (DWNTs) individuels de structures clairement identifiées a permis de comprendre le rôle de la distance inter-tubes dans les déplacements en fréquence des modes Raman (modes de respiration (RBLM) et modes G), en associant à une distance inter-tube donnée une pression interne négative (positive) quand cette distance est supérieure (inférieure) à 0.34 nm. D’autre part, le rôle des effets d’interférences quantiques dans l’évolution avec l’énergie d’excitation des intensités des composantes LO et TO des modes G a été clairement identifié. Enfin, une attribution de l’origine des transitions optiques, mesurées par spectroscopie d’absorption, de différents DWNTs a été proposée.L’étude des propriétés de DWNTs fonctionnalisés a été réalisée en couplant des expériences de spectroscopie Raman, d’absorption UV-visible-NIR et de photoluminescence (PL), incluant les cartes d’excitation de la photoluminescence (PLE), sur des suspensions de DWNTs avant et après fonctionnalisation, (i) covalente via un groupement diazonium, (ii) covalente et non-covalente (pi-stacking) par un colorant. Ce travail présente une contribution au débat sur une question essentielle pour l’utilisation des DWNTs dans des dispositifs opto-électroniques, à savoir : « les DWNTs luminescent-ils ? Et si oui, quelle est l’origine de la luminescence ? ». La présence de photoluminescence dans nos échantillons de DWNTs est établie, et l’étude de son évolution avec différents types et degrés de fonctionnalisation démontre qu’elle ne peut provenir que des tubes internes des DWNTs (PL intrinsèque aux DWNTs), ou de SWNTs générés par l’extrusion des tubes internes de DWNTs durant la préparation des suspensions. D’autre part, on peut souligner la mise en évidence d’un transfert d’énergie du colorant vers le tube interne quand le colorant est greffé de manière covalente sur la tube externe. / This work concerns the study of mono- and double-walled carbon nanotubes. It contains two distinct parts: (i) the first part is devoted to the understanding of the intrinsic optical and phonon properties of individual carbon nanotubes; (ii) the second part reports an experimental investigation of the properties of covalently and non-covalently functionalized double-walled carbon nanotubes. Concerning the study of the intrinsic properties of the individual carbon nanotubes, new information was obtained by coupling Raman spectroscopy data, including the measurement of the excitation profiles of different Raman-active modes, with optical absorption and electronic diffraction data. From a general point of view, our approach put in evidence the complementarity of the Raman spectroscopy and electronic diffraction for “the most probable” assignment of the structure of the nanotubes.Among the results obtained on individual single-walled carbon nanotubes (SWNTs), one can underline the confirmation of the excitonic character of the optical transitions by combining optical absorption and Raman excitation profiles on the same nanotubes, and the evidence of an unexpected behavior of the relative intensities of the LO and TO components of the G-modes. The study of the index-identified individual double-walled carbon nanotubes has permitted to understand the role of the inter-walls distance in the frequency shifts of the radial breathing-like modes (RBLM) and G-modes, by associating a given inter-walls distance to a negative (positive) internal pressure when this distance is larger (smaller) than 0.34 nm. On the other hand, the role of quantum interferences in the evolution with the excitation energy of the intensities of the LO and TO components of the G-modes was clearly identified. Finally, the assignment of the optical transitions, measured by absorption spectroscopy, of index-identified DWNTs was proposed.The study of the properties of functionalized DWNTs was performed by combining Raman spectroscopy, UV-visible-NIR absorption and photoluminescence (PL), including maps of photoluminescence excitation (PLE), on suspensions of DWNTs before and after functionalization: (i) covalently by using diazonium, (ii) covalently and non-covalently (pi-stacking) by using dye molecules. This work is a contribution to the debate on an essential question for the use of the DWNTs in opto-electronic devices, namely: “Do the DWNTs they luminesce? And if yes, what is the origin of the luminescence?". The presence of photoluminescence in our samples of DWNTs was established, and the study of its evolution with various kinds and degrees of functionalization states that PL can only result from inner tubes (intrinsic PL of DWNTs), or from SWNTs generated by the extrusion of the internal tubes of DWNTs during the preparation of the suspensions. On the other hand, one must emphasize the evidence of an energy transfer from the dye molecules towards the internal tube when such molecules are covalently grafted on the outer tube.

La focalisation de lasers à impulsions ultra-brèves dans les verres a montré des potentialités importantes pour la structuration des matériaux transparents, permettant d’envisager la réalisation de dispositifs tout-optique en une seule étape. Le développement de nouveaux matériaux vitreux de composition 40P2O5-55ZnO-xAg2O-(5-x)Ga2O3 permet de tirer avantage de la photosensibilité de l’ion Ag+ pour la structuration de propriétés optiques au cœur du matériau. L’augmentation du taux d’oxyde de gallium provoque la dépolymérisation des chaînes phosphates et s’accompagne de la réticulation du réseau vitreux par des polyèdres GaOx (4 ≤ x ≤ 6). La formation de des derniers n’affecte pas les propriétés d’émission lumineuses, qui proviennent des ions Ag+ isolés dans différents sites cristallographiques. L’exposition des verres sous faisceau laser intense provoque la formation de centres-trous Ag2+, responsables d’une luminescence intense, et de pièges d'électrons Ag0. Un traitement thermique consécutif ou simultané à l’irradiation provoque la dissociation de ces espèces, et s’accompagne de la formation d’agrégats moléculaires de la forme Agmx+. L’utilisation d’un laser femtoseconde à haute cadence permet, en combinant création de paires électron-trou et élévation locale de la température, de réaliser des architectures complexes conduisant à la structuration de propriétés optiques. / The development of new vitreous materials in the 40P2O5-55ZnO-xAg2O-(5-x)Ga2O3 diagram permits to take advantage of the Ag+ ion photosensitivity for structuring optical properties within the material. Increasing the gallium oxide content leads to the depolymerisation of the phosphate chains and the reticulation of the glass network by GaOx polyhedra (4 ≤ x ≤ 6). The formation of the latters does not affect the luminescence properties which are related to silver ions in various crystallographic environments. The intense laser exposure of the glasses leads to the formation of Ag2+ hole centers responsible for an intense luminescence and electron traps Ag0. A subsequent or simultaneous heat treatment provokes the dissociation of the hole centers and is accompanied by the formation of Agmx+ molecular-like clusters. The use of a high repetition rate femtosecond laser combining electrons and hole traps and temperature rising permits to obtain complex features leading to the structuring of optical properties.

Le but de cette thèse était de comprendre l'organisation supramoléculaire et le possible réarrangement dynamique de copolymères supramoléculaires multifonctionnels. Ainsi, nous avons synthétisé diverses molécules présentant un coeur urée ou pérylène fonctionalisé par différentes chaines latérales afin de combiner des propriétés de structuration, de fluorescence et de bioreconnaissance dans une même chaine de polymère supramoléculaire. En combinant différentes techniques de spectroscopie, de diffusion du rayonnement et de microscopie, nous avons montré que des molécules avec un même coeur mais des chaines latérales différentes conduisaient à des nanostructures différentes comme des rubans vrillés, des plaques 20 ou encore des fibres branchées. Enfin, plusieurs unités monomériques avec un même coeur mais des chaines latérales différentes ont été mélangées pour former des copolymères supramoléculaires multifonctionnels. La formation préférentielle d'une nanostructure unique dictée par un des monomères a été démontrée selon un mécanisme de tri dit social ( « social self-sorting » ). / The goal of this thesis was to understand the supramolecular organization and the possible dynamic rearrangement of multifunctional supramolecular copolymers. To this end, we havedeveloped a series of building blocks based on urea or perylene cores with various lateral side chains for combining structuring, fluorescence, and biorecognition properties in a singlesupramolecular polymer chain. Using a combination of spectroscopy, scattering, and microscopy techniques, we have shown that molecules with a same core but different lateral chains can lead to the formation of various nanostructures su ch as twisted ribbons, 20 plates, or branched fibers. Ultimately, by combining monomeric units with different functional side chains, multifunctional supramolecular copolymers have been obtained. Whereas radiation scattering and imaging techniques were used to demonstrate that one of the monomer can dictate the formation of a preferential nanostructure, optical spectroscopies revealed that the polymerization process of our systems indeed occurs via social self-sorting.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-04-27T13:00:02Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Euclides_Almeida_Fisica.pdf: 5907240 bytes, checksum: 503a5b57e757a03f24206d4d3d26032c (MD5) / Made available in DSpace on 2017-04-27T13:00:02Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Euclides_Almeida_Fisica.pdf: 5907240 bytes, checksum: 503a5b57e757a03f24206d4d3d26032c (MD5) Previous issue date: 2012-07-30 / CNPQ / O principal objetivo deste trabalho foi investigar fenômenos ópticos ultrarrápidos em sistemas nanoestruturados empregando diferentes técnicas espectroscópicas não lineares, tanto no domínio do tempo quanto no domínio da frequência. Para fornecer uma base adequada que permita entender os experimentos feitos nessa tese, os princípios físicos das espectroscopias ópticas não lineares são apresentados. Inicialmente é apresentada uma descrição da função resposta não linear no domínio do tempo. A evolução temporal da polarização óptica, que gera o sinal espectroscópico, é descrita em detalhes usando uma teoria de perturbação diagramática. Técnicas ópticas não lineares são apresentadas, tais como eco de fótons, bombeamento-e-sonda e hole burning, assim como o comportamento dinâmico de um material pode ser interpretado a partir do sinal gerado. A técnica de mistura degenerada de quatro ondas com luz incoerente foi usada para investigar, pela primeira vez, o defasamento ultrarrápido de éxcitons em uma vitrocerâmica contendo nanocristais de niobato de sódio. O tempo de defasamento medido (T2 = 20 fs) indica qu empregada para investigar processos de transferência de carga em colóides com nanopartículas de TiO2 e rodamina 6G. O comportamento do sinal de depleção transiente é comparado com o observado para a rodamina livre suspensa em etanol. A análise dos resultados permitiu atribuir o comportamento de depleção à transferência de carga de estados excitados termalizados das moléculas de corante para a banda de condução do semicondutor e a transferência no sentido inverso do semicondutor para as moléculas. / The main objective of this work was the investigation of ultrafast optical phenomena in selected nanostructured systems employing different nonlinear spectroscopic techniques, either in the time or the frequency domain. To provide an appropriate background to understand the performed experiments the principles of nonlinear optical spectroscopies are presented. Initially a description of the nonlinear optical response function in the time domain is given. The time evolution of the optical polarization, that gives rise to the spectroscopic signal, is described in detail using a diagrammatic perturbation theory. Nonlinear optical techniques are discussed such as photon echoes, pump-and-probe and hole-burning, as well as how the dynamical behavior of a material can be interpreted from the generated signals. The degenerate four-wave mixing technique with incoherent light was used to investigate for the first time the ultrafast dephasing of excitons in a glass-ceramic containing sodium niobate nanocrystals. The short dephasing time measured (T2 = 20 fs) indicates that different dephasing channels contribute for the excitonic dephasing, namely: electron-electron scattering, electron-phonon coupling and fast trapping of electrons in defects on the nanocrystals interface. Low-temperature luminescence experiments were also performed to measure excitonic and trap states lifetimes. The persistent spectral holeburning technique was applied to measure localized surface plasmons dephasing times in colloidal silver nanoparticles capped with different stabilizing molecules. The dependence of T2 with three different stabilizers was demonstrated and theoretically analyzed. The results show that the dephasing times are shorter than the theoretically calculated T2 using the bulk dielectric functions of the metal. This discrepancy is attributed to changes in the electronic density of states at the nanoparticles interface caused by the presence of the stabilizers. Ab-initio calculations based on the Density Functional Theory were performed to further understand the interaction between the nanoparticles and stabilizing agents. The femtosecond transient absorption technique was employed to study the ultrafast dynamics of in-gap states in a glassceramics containing sodium niobate nanocrystals. Two main temporal components were found for the excited state absorption signal: a fast component, with decay time of ≈ 1 ps, and a slower component which is attributed to deep trap states. This slower component is responsible for the excited state absorption contribution in optical limiting experiments previously reported in the literature. The dynamics of the optical limiting in this sample was also studied, in the millisecond range, exciting the sample with a train of femtosecond pulses. The optical limiting behavior reflects the dynamics of population in the excited and trap states and this dynamics was modeled using rate equations for the electronic states’ populations. Finally, the pump-andprobe transient absorption technique was employed to investigate charge-transfer processes in colloids with rhodamine 6G and TiO2 nanoparticles. The transient bleaching signal behavior is compared with the one observed for unlinked rhodamine 6G dissolved in ethanol. The analysis of the results allowed the attribution of the bleaching behavior to charge-transfer from thermalized excited states of the dye molecules to the semiconductor conduction band and to the back charge-transfer from the semiconductor to the molecules.

In this work the transient non-instantaneous polarization, i.e., laser-pulse injected small polarons and self-trapped excitons, is studied in the perovskite-like ferroelectric lithium niobate. The investigations span a time scale from femtoseconds to several hours. It is shown that the established small polaron picture is not able to describe transient absorption and photoluminescence of lithium niobate consistently. Several strong indications are presented demonstrating that the photoluminescence cannot be caused by geminate small polaron annihilation. Instead, the idea of radiatively decaying self-trapped excitons at the origin of the blue-green photoluminescence is revived. Excitons pinned on defect sites are proposed to lead to the already observed long-lived transient absorption in the blue spectral range in Mg- and Fe-doped crystals. Excitons pinned on iron-defects are studied in more detail. Their spectral fingerprint and absorption cross section is determined. Furthermore, it is shown that the occurrence of these pinned STEs can be tailored by chemical treatment of the samples and the experimental parameters such as the pump pulse intensity and photon energy. Based on the new experimental results and reviewing data published in literature, an atomistic picture of hopping and pinning of self-trapped excitons in lithium niobate is proposed. The question is addressed whether small polarons and self-trapped excitons in lithium niobate are coupled species in the sense that oppositely-charged polarons may merge into self-trapped excitons or STEs break into small polaron pairs. Decay kinetics of transient absorption and luminescence assigned to free small polarons and STEs indicate that this is not the case. For a more complete picture the ultrafast time scale is investigated as well. The formation times of small polarons and STEs are determined, which both lie in the range of 200 fs. No indications are found on the (sub)picosecond time scale indicating a coupling of both quasi-particle species either. In order to gain access to the formation of self-trapped excitons a custom-built femtosecond broadband fluorescence upconversion spectrometer is installed. Based on an already existing scheme, it is adapted to the inspection of weakly luminescent solid samples by changing to an all reflective geometry for luminescence collection. To avoid the necessity for an experimentally determined photometric correction of the used setup, an already established calculation method is extended considering the finite spectral bandwidth of the gate pulses. The findings presented here are important not only as fundamental research, but also regarding the technical application of lithium niobate and other similar nonlinear optical crystals. The simultaneous occurrence of both small polarons and self-trapped excitons is a rather rarely described phenomenon. Usually, the optical response of wide band gap oxide dielectrics is associated with only one of these quasi-particle species. This work may therefore be a stimulus to review the existing microscopic models for transient phenomena in other oxide dielectrics, which may help to improve their application in nonlinear optical and electro-optical devices. In this context the ultrafast transient photoluminescence spectroscopy established here for weakly luminescing solid samples may again provide valuable insight. With respect to lithium niobate, the results do not only resolve inconsistencies between the microscopic pictures described in literature, but also provide information regarding the extends to which the propagation of ultrashort laser pulses may be affected by (pinned-)STE absorption. It is shown that tailoring of the long-lived absorption center in the blue spectral range is possible, which may be used to avoid optical damage when high repetition rates are applied. It is important to emphasize that the microscopic model proposed in this work is mainly based on experimental indications. It is the task of further detailed theoretical investigations, e.g., via time-dependent density functional theory, to test whether the proposed model is justified. From an experimental perspective the important question remains whether (pinned-)STEs contribute to a photorefractive effect. In the experimentally easily accessible spectral range no absorption feature of mobile STEs is observed. As a complementary experimental technique, ultrafast holographic spectroscopy may reveal an excitonic contribution to photorefraction and provide further insight to STE transport and pinning phenomena.