O presente trabalho apresenta a síntese e a caracterização de um derivado de quitosana anfifílica preparado a partir da reação de despolimerização parcial da quitosana comercial, bem como a influência de ambos os polímeros (quitosana anfifílica e quitosana comercial) sobre as propriedades espectroscópicas da curcumina (CUR). Na etapa inicial, a quitosana comercial foi caracterizada e despolimerizada. Em seguida, foram realizadas reações de substituições para a inserção de grupos hidrofílicos (cloreto de 2-cloro-N,N-dietiletilamina - DEAE) e grupos hidrofóbicos (dodecil - DD) no polímero. O grau médio de substituição por grupos DEAE e DD foram determinados por Espectroscopia de Ressonância Magnética Nuclear de Hidrogênio (RMN de 1H). A Concentração de Agregação Crítica (CAC) da quitosana anfifílica foi determinada (0,011 g L-1) utilizando pireno como sonda fluorescente. As propriedades fotofísicas da CUR na presença das quitosanas comercial e anfifílica foram estudadas por meio de técnicas de Espectroscopia de UV-Visível e de Fluorescência. Os espectros de absorção da desse corante na presença da quitosana modificada, em concentrações acima da CAC, apresentaram deslocamento para o azul, formação da banda em 360 nm e redução da absorbância em 420-425 nm, indicando que a quitosana modificada estabilizou as moléculas da CUR na forma ceto. Nos espectros de fluorescência também foi observado deslocamento para o azul, em contrapartida, a intensidade de emissão aumentou com o aumento da concentração do polímero modificado. Resultados similares foram obtidos para CUR em diferentes solventes, onde foi observado maior intensidade de emissão e deslocamento da banda para menores comprimentos de onda com a diminuição da polaridade do solvente. O equilíbrio tautomérico da CUR é deslocado para a forma ceto em solventes apolares. O valor de rendimento quântico obtido foi maior para o cromóforo em quitosana modificada (QM= 0,05 g/L, acima da CAC) do que nos outros ambientes poliméricos estudados. A porcentagem de degradação da CUR em QM 0,05 g L-1 foi menor em comparação a degradação nos outros meios. Essa concentração de QM está associada à sua forma agregada, onde estão presentes ambientes hidrofóbicos. A presença dos grupamentos DD na QM promove a formação de ambientes apolares que podem envolver as moléculas do corante, proporcionando maior estabilidade. / This work presents the synthesis and characterization of an amphiphilic chitosan derivative prepared from deacetylation of commercial chitosan, as well as both polymers influence (amphiphilic and commercial chitosan) regarding the spectroscopic properties of curcumin. Firstly, the commercial chitosan was characterized and depolymerized. Then, the substitution reactions were carried out to insert hydrophilic groups (DEAE) and hydrophobic groups (dodecyl), being the average degree of substitution by DEAE and dodecyl groups determined by Hydrogen Nuclear Magnetic Resonance Spectroscopy <br /> (1H NMR). The Critical Aggregation Concentration (CAC) of amphiphilic chitosan was determined (0,011 g L-1) using pyrene as a fluorescent probe. The photophysical properties of curcumin in the presence of commercial and amphiphilic chitosan were studied by UV-visible Spectroscopy and Fluorescence techniques. The absorption spectra of curcumin in the presence of amphiphilic chitosan, at concentrations above CAC presented a blue shifted, band formation at 360 nm and absorbance reduction at <br /> 420-425 nm, indicating that modified chitosan stabilized curcumin molecules in the keto form. The fluorescence spectra also presented a blue shifted, however, the emission intensity was raised with an increasing of modified polymer concentration. Similar results were obtained to curcumin in different solvents, it was observed the increasing of emission intensity and a band shift to smaller wavelengths due to a decreased of solvent polarity. The tautomeric equilibrium of curcumin is shifted to keto form in non-polar solvents. The fluorescence quantum yield obtained for curcumin in modified chitosan presence (QM= 0,05 g/L, above CAC) was higher than other studied polymer environments. The degradation percentage of curcumin in QM 0,05 g L-1 was smaller in comparison to degradation in other environments. This QM concentration is associated to their aggregated form, wherein presents hydrophobic environments for curcumin. DD groups in the QM promote the hydrophobic environments formation and it can involve the dye molecules, promoting more stability.

This thesis aims to study external field induced alignment of semiconductor quantum dot by utilizing single molecule spectroscopy. Wurtzite structure semiconductors, such as CdSe, exhibit strong electric dipole moment along its c-axis. It is proposed that quantum dot can be aligned along the applied field with sufficient strength. Experiments with two kind of matrix: PMMA mixing with wax, and liquid crystal thin film, were performed for that quantum dots are able to rotate freely in the matrix. Experiments with PMMA matrix were also performed as its rigid matrix for comparison. Interdigitated structure electrodes was deposited on the cover glass for the electric field experiments. The topical transition (absorption and emission) of CdSe quantum dots has a bright plane perpendicular to its c-axis, and a dark axis along the c-axis. It thus used for characterizing the field alignment. For each observing quantum dot, we record the fluorescence intensity, anti-bunching, polarization anisotropy, and fluorescence lifetime information. In addition, we also analyze the fluorescence correlation spectroscopy to probe the small modulation signal from the fluctuating fluorescence intensity. However, the results indicate that we didn¡¦t observe the field induced change with the field up to 1E7(v/m).

Orientador: Teresa Dib Zambon Atvars / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-16T13:58:18Z (GMT). No. of bitstreams: 1 Zalloum_NeifeLilian_D.pdf: 6371493 bytes, checksum: 34b58b4e3f06b8bb42b89ffa183838c1 (MD5) Previous issue date: 2007 / Resumo: Desenvolveu-se, neste trabalho, uma metodologia que permitiu conhecer detalhes intermoleculares da microencapsulação, fundamentais na definição de parâmetros que controlam este processo. Foram preparadas microesferas biodegradáveis de poli(hidroxibutirato-hidroxivalerato) (P(HB-HV)), por meio de emulsificação o/w com evaporação de solvente, de interação controlada com os marcadores fluorescentes. Os estudos foram conduzidos de forma a se avaliar como o polímero e alguns parâmetros afetam as propriedades finais das microesferas, tais como concentração de PVA, velocidade de agitação da emulsão, número de ciclos de lavagem durante a centrifugação, presença do ativo a ser encapsulado (cumarina, cumarina-6 e pireno), e massa molar do polímero (130 e 450 kg mol). As microesferas poliméricas foram submetidas à análise de microscopia eletrônica de varredura para análise morfológica e de distribuição de tamanho de partículas; de potencial-zeta para análise da carga superficial; de microscopia de fluorescência confocal para confirmar a encapsulação; estudos fotofísicos e de liberação. Os parâmetros que mais afetaram o diâmetro médio e a distribuição de tamanhos das microesferas foram a concentração de PVA e a velocidade de agitação durante a emulsificação. Medidas de potencial-zeta permitiram colocar as intensidades de carga superficial na ordem microesferas+pireno < micropartículas vazias < microesferas+cumarina-6. As eficiências de encapsulação (de 95% e 17% para as microesferas contendo cumarina-6 e pireno, respectivamente) indicaram a ocorrência de diferentes tipos de interações polímero-fluoróforo. Imagens de microscopia de fluorescência confocal confirmaram a formação de agregados de cumarina-6 no interior das microesferas, ao contrário do pireno, que formou excímeros nas camadas mais externas das partículas. Estudos de liberação mostraram que as microesferas de P(HB-HV) são polares e que a difusão da cumarina-6 depende do tamanho das micropartículas e das interações eletrostáticas entre polímerofluoróforo. A difusão do pireno depende somente das interações hidrofóbicas com o polímero / Abstract: In this research was developed a methodology, which allowed microencapsulation intermolecular details knowledge, essential in the definition of the parameters that controls the process. The work aimed to prepare biodegradable poly(hydroxybutyrate-hydroxyvalerate) (P(HB-HV)) microspheres through oil-in-water emulsion solvent evaporation technique, having controlled interaction with fluorescent probes. The study was conducted to evaluate how the polymer and some process parameters affect the final microspheres properties, such as polyvinyl alcohol (PVA) concentration, stirring speed emulsification, number of washing cycles during centrifugation, presence of the active compound to be encapsulated (coumarin, coumarin-6 and pyrene) and polymer molecular weight. The polymeric microspheres were evaluated by scanning electronic microscopy for their morphology analysis and size distribution; zeta-potential for their surface charge; confocal laser scanning microscopy for their encapsulation confirmation through coumarin-6 and pyrene localization; photophysics and release studies. From the results, it was found that the parameters most affected microsphere size were surfactant concentration (PVA) in the emulsion water phase, and the stirring speed of emulsification. Zeta-potential results were microsphere+pyrene< unloaded microsphere< microspheres+coumarin 6 in surface charge. Drug loadings (95% and 17%, m/m, to coumarin 6 and pyrene microparticles, respectively) indicated the occurrence of different interactions between polymer and fluorophore. Confocal fluorescence microscopy images confirmed the coumarin-6 aggregate formation inside the microsphere, while pyrene appeared as excimers in more external layers of the microparticles. Release behavior showed that the polymeric microspheres are polar and the coumarin-6 diffusion depends on the microparticles radius and the electrostatics interactions between polymer and fluorophore. Pyrene diffusion depends, only, on the hydrophobic interactions with the polymer / Doutorado / Físico-Química / Doutor em Quimica

Copper(I) complexes have been studied through both experimental and computational means in the presented work. Overall, the work focuses on photophysical and photochemical properties of copper(I) complexes. Photophysical and photochemical properties are found to be dependent on the geometries of the copper(I) complexes. One of the geometric properties that are important for both photochemical and photophysical properties is coordination number. Coordination numbers have been observed to be dependent on both ligand size and recrystallization conditions. The complexes geometric structure, as well as the electronic effects of the coordination ligands, is shown both computationally as well as experimentally to affect the emission energies. Two-coordinate complexes are seen to have only weak emission at liquid nitrogen temperature (77 K), while at room temperature (298 K) the two-coordinate complexes are not observed to be luminescent. Three-coordinate complexes are observed to be luminescent at liquid nitrogen temperature as well as at room temperature. The three-coordinate complexes have a Y-shaped ground (S0) state that distorts towards a T-shape upon photoexcitation to the lowest lying phosphorescent state (T1). The geometric distortion is tunable by size of the coordinating ligand. Luminescence is controllable by limiting the amount of non-radiative emission. One manner by which non-radiative emission is controlled is the amount of geometric distortion that occurs as the complex undergoes photoexcitation. Bulky ligands allow for less distortion than smaller ligands, leading to higher emission energies (blue shifted energies) with higher quantum efficiency. Tuning emission and increasing quantum efficiencies can be used to create highly efficient, white emitting materials for use in white OLEDS.

DNA provides the genetic code which is almost universal in all living organisms. When DNA is exposed to ultra-violet light it can cause cell degradation and mutation which are two of the major causes which lead to cancer. The nature of decay in DNA oligomers is a widely studied topic. Fluorescence and Transient Absorption (TA) experiments on polynucleotides which compare the behavior of the decay to the monomer bases have revealed the presence of longer-lived components in the multimeric systems. There has been heated debate over the character of the excited states responsible for the long-lived signals. Theoretical methods are well suited to compliment experiment by providing a description of processes and physical properties on the molecular level. We have studied π-stacked adenines in the gas-phase with Quantum Mechanical (QM) methods, but also in the helical environment using high-level ab initio methods, classical simulations and the combination of the two (QM/MM). Inclusion of the environmental interactions dramatically alters the shape of the potential energy surfaces due to steric interactions from the backbone and interactions with the surrounding bases and environment. This work examines the complete picture of photophysical processes occurring in adenine oligonucleotides within the helical environment after the absorption of a photon: the nature of initial absorption and the subsequent radiative and non-radiative decay pathways. It contributes key discoveries inherent to the mechanisms which govern photo-initiated processes in DNA, and also contributes to our fundamental knowledge of the photophysical behavior of π-stacked chromophores. The work reveals the effects of π-stacking interactions and the environment on photo-initiated processes in oligonucleotides. It reveals that excitonic coupling is responsible for the key differences in features in the absorption spectrum of adenine oligomers compared to the isolated bases, illustrates the role of charge transfer (CT) mixing in both absorption and decay processes, and the importance of bonded excimers in deactivation. The work also illustrates that CT excimers are responsible for the long-lived signals evidenced in Transient Absorption and Fluorescence experiments and that neutral excimers can exist within the DNA helical environment. It also adds to the discussion in the field on the nature of photodecay mechanisms occurring within the DNA helix. / Chemistry

Metal-organic frameworks (MOFs) are crystalline materials composed of metal clusters and organic ligands. MOFs that exhibit photoluminescence are promising materials for a broad range of applications. Due to their structural tunability and crystalline nature, luminescent MOFs also provide an excellent platform for studying structure–property relationships of materials. The photophysical properties of three anthracene-dicarboxylic acids – 1,4-anthracene dicarboxylic acid (1,4-ADCA), 2,6-anthracene dicarboxylic acid (2,6-ADCA) and 9,10-anthracene dicarboxylic acid (9,10-ADCA) – were studied in a series of polar aprotic solvents using steady-state absorption, steady-state emission spectroscopy and time-correlated single photon counting (TCSPC) emission lifetime spectroscopy. The addition of carboxylic acid functional groups on the anthracene ring alters photophysical properties to varying degrees depending on the location and protonation state. Density functional theory (DFT) calculations reveal that the lowest-energy ground-state structures of both 2,6-ADCA and 1,4-ADCA have dihedral angles between the carboxylic acids and aromatic planes of θ = 0°, while the same dihedral angle increases to θ = 56.6° for 9,10-ADCA. Time-dependent DFT calculations suggest that the carboxyl groups of 1,4-ADCA and 2,6-ADCA remain coplanar with the anthracene ring system in the excited state. In contrast, the calculations reveal significant changes between the ground and excited geometries for 9,10-ADCA and puckering of the anthracene moiety of is observed. The three anthracene dicarboxylic acids were then incorporated into zirconium-based MOFs. The MOF structures were characterized using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The steady-state absorption and emission spectra as well as the fluorescence lifetimes of the MOFs were compared to that of the corresponding ligand in solution. The MOFs comprising 9,10-ADCA and 2,6-ADCA formed highly crystalline octahedral shaped crystals and were found to be isostructural with the well-known UiO-66 and UiO-67 frameworks. However, incorporation of the 1,4-ADCA ligand resulted in large rod-shaped crystals. The absorption spectra of the MOFs are broadened and redshifted compared with that of the corresponding free ligands. The emission spectra of the MOFs constructed from 9,10-ADCA and 1,4-ADCA display emission bands that resemble that of the free ligand in acidic solutions, but are slightly broadened and redshifted in the MOF. Little difference is observed between that of 2,6-ADCA within the MOF and in acidic solution. The broadening and redshift observed in the absorption and emission is indicative of intermolecular interactions between anthracene units and/or with the Zr4+ clusters. The fluorescence lifetimes measured for the anthracene-based MOFs show a long component, comparable to the lifetime of the free ligand, along with shorter component. This may also suggest intermolecular interactions between chromophores in the MOFs. Altogether, derivatization of anthracene was shown to have specific effects on the photophysical properties of the parent anthracene molecule. These properties are further altered when the ligand is incorporated into a metal organic framework. Such systematic studies can provide a guide in designing luminescent MOFs with the excited-state properties desired for a given application. / Master of Science

This dissertation addresses the following issues. Firstly, to reduce the efficiency roll-off at high current densities or brightness, of green, fluorescent organic light-emitting (OLEDs), we introduced a double-doped structure into the emissive layer. It includes two thin buffer layers and a broad emissive region stacked with two doped layers. This modification better controls charge injection/transport and recombination, boosting EL and PL efficiency. Secondly, aiming for highly efficient phosphorescent OLEDs surpassing the theoretical EQE limit of ~20%, a new class of platinum(II)-based phosphorescent complexes have been designed and synthesized serving as both emitters and electron transporters in straightforward undoped bi-/tri-layered devices. Achieving this without costly doping techniques, these OLEDs boast a relatively low turn-on voltage, extremely high power efficiency, and stable emission color dependent on applied voltages. This design anticipates reduced or no efficiency roll-off even at brightness levels exceeding 20,000 cd/m2, far surpassing DOE technology requirements (only 500-1500 cd/m2). This work sheds light on the influence of molecular design on crystalline packing and optoelectronic device performance and accelerates the development of efficient and stable Pt-based emitters.

This thesis describes the synthesis of polyyne rotaxanes and an investigation of their excited state photophysical properties. The threading of dumbbell-shaped carbon chains with macrocyclic components is a way to mechanically insulate and control the environment around the carbon chains. The resulting polyyne rotaxanes can serve as model compounds for insulated carbyne. Different strategies have been tested for the synthesis of polyyne rotaxanes with different topologies and structures. Study of rotaxanes in the excited states reveals strong electronic communication between an acetylenic thread and a macrocycle. Chapter 1 summarizes the field of acetylene scaffolding, introducing some recent achievements in acetylene chemistry. General synthetic methods for polyynes are discussed, and an introduction to active metal template synthesis of rotaxanes is given. Chapter 2 describes the synthesis of a family of polyyne rotaxanes with different axle lengths and macrocycles, prepared by homocoupling of terminal alkynes. Synthesis of hexayne rotaxane with functional pyridine end-group is presented and a number of crystal structures of polyyne rotaxanes are analyzed. Chapter 3 demonstrates the use of acetylene cross-coupling in the synthesis of rotaxanes. Synthesis of rotaxanes with different topological structure is provided. Chapter 4 details the excited state properties of polyynes studied by time -resolved spectroscopy. The complexes of rhenium(I) carbonyls with rotaxanes is presented and the excited state energy transfer in rotaxanes is studied. Chapter 5 explores new synthetic strategies for polyyne rotaxanes, using "masked" precursors. It also highlights the potential of carbenoid rearrangement of alkyliden es for the construction of linear and cyclic architectures. Chapter 6 is the summary of the project and general discussion of future directions. There are two appendices in the end of thesis: Appendix A covers the photophysics of rhenium tricarbonyl complex of the hexayne rotaxane with a small macrocycle and Appendix B reports work towards the synthesis of rotaxanes with platinum(II)-alkyne complexes.

Thesis advisor: Torsten Fiebig / Thesis advisor: Mary Roberts / Understanding the electronic nature of DNA is profound and has been attempted for decades. Photoexcitation of DNA with UV light deposits electronic energy in the base stack and prepares highly reactive excited states. These states are precursors for photoinduced damage reactions which can lead to mutations and ultimately to cell death. While many DNA photo products have been isolated and characterized, the primary events immediately after photon absorption are not yet understood. Recent studies with ultrafast lasers have revealed that the majority of excess energy gained by DNA with light absorbance is dissipated on the femtosecond and picosecond time scales. In this study double-stranded oligonucleotides with different base sequences, content and lengths were systematically examined using femtosecond pump-probe spectroscopy. The results indicate that excitations in DNA are delocalized over more than two bases and the extent of the delocalization depends strongly on the structure of the investigated systems. Exciton delocalization domains in the longer duplexes are larger than in the shorter ones. Also, single-stranded oligonucleotides show smaller extent of exciton delocalization than duplexes with the same length. In addition to the fundamental studies on DNA photophysics, the properties and the structure of new molecular beacons based on thiazole orange dimers were studied. A full account of the optical and structural properties of the dimers in different base environments and orientations is presented here. Currently, the development of efficient ways to utilizing solar energy is at the forefront of the scientific community due to the ever rising demand for energy. Both, colloidal semiconductor nanocrystals and single-walled carbon nanotubes are potential alternatives to conventional inorganic and organic materials in photovoltaic devices Thorough understanding of the charge transfer and related photophysical phenomena in these systems will answer the question whether these nanomaterials can be applied in future generations of solar cells. The photoinduced electron transfer in donor-acceptor CdSe/CdTe heterostructured nanorods, in which CdTe is grown on top of CdSe in a single rod structure, was studied. The electron transfer between the two nanocrystals occurs on the subpicosecond time scale, competing with the ultrafast relaxation mechanisms in the quantum confined nanocrystals. Furthermore, investigations on how quantum confinement influences the phonon wavepackets in semiconductor nanocrystals were carried out. Quantum beats corresponding to longitudinal optical phonon modes were observed in the femtosecond pump-probe spectra of colloidal CdTe nanocrystals. Size-dependent experiments revealed that the optical phonon frequencies and the exciton-phonon coupling strength do not depend on the crystal's size. Only the wavepacket dephasing time was influenced by the diameter of the particles which was correlated with the hole relaxation to the exciton band edge. Electron donor-acceptor constructs, based on single-walled carbon nanotubes (SWNT), can be attained by noncovalent functionalization of the nanotubes with pyrene derivatives. However, charge transfer does not take place in the simplest pyrene-SWNT constructs. For the first time the pure SWNT-pyrene construct was isolated and investigated. Our results revealed that the optical properties of pyrene are drastically altered due to strong electronic interactions with the SWNT surface. In other words, aromatic molecules lose their electronic (and chemical) signature when non-covalently attached to carbon nanotubes. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Neste trabalho foi realizada a síntese e caracterização de um derivado de S,S-dioxidotioxantona, 7,8-benzotioxanton-9-ona-10,10-dióxido (TX-Np-SO2). A TX-Np-SO2 foi caracterizada estruturalmente por espectros eletrônico e vibracional (UV-vis e fluorescência, Infravermelho) e também por ressonância magnética nuclear (RMN) de 1H e 13C. As propriedades fotofísicas, espectros de emissão de fluorescência e fosforescência e o rendimento quântico de fluorescência da TX-Np-SO2 foram determinadas, assim como os tempos de vida de fluorescência (&tau;F = 3,62 ns) e fosforescência (&tau;Ph = 800 ms). Os espectros de absorção triplete-triplete dos transientes da TX-Np-SO2, em soluções desoxigenadas de metanol, acetonitrila e metilciclohexano, foram determinados por Fotólise por Pulso de Laser, bem como as constantes de velocidade de supressão bimoleculares do derivado pelos supressores trans-estilbeno, trietilamina, p-dimetilamina benzoato de etila e 2-propanol. A fotopolimerização do metacrilato de metila (MMA) iniciada por TX-Np-SO2 foi estudada por dilatometria. A reação de polimerização do iniciador (TX-Np-SO2) na presença de amina e o monômero MMA foi estudada de modo a determinar a taxa de polimerização (Rp) a diferentes concentrações de trietilamina (TEA) e p-dimetilamina benzoato de etila (EDB). / The aim of this work was the synthesis and characterization of a S,S-dioxidethioxanthone derivative, 7,8-benzo-thioxanthen-9-one-10,10-dioxide (TX-Np-SO2). The TX-Np-SO2 was structurally characterized by its electronic and vibrational spectra (UV-vis and fluorescence, IR) and also by 1H and 13C RMN methods. The photophysical properties, fluorescence and phosphorescence emission spectra, and fluorescence quantum yield of TX-Np-SO2 were determined, as well as the fluorescence lifetime (&tau;F = 3,62 ns) and the phosphorescence lifetime (&tau;Ph = 800 ms). The transient absorption spectra of TX-Np-SO2 in degassed solutions of methanol, acetonitrile and methylcyclohexane were determined by Laser Flash Photolysis, as well as the bimolecular triplet quenching rate constants for of the derivative by various compounds. The photopolymerization of methyl methacrylate (MMA) initiated by TX-Np-SO2 was studied by dilatometry. The polymerization reaction of the initiator (TX-Np-SO2) in the presence of amine and MMA monomer was studied in order to determine the polymerization rate (Rp) at different loadings of triethylamine (TEA) and ethyl-4-dimethylaminobenzoate (EDB).