Nous proposons de développer une méthodologie théorique pour étudier l’influence de stimuli externes sur les cristaux organiques. On s’intéresse en particulier au mécanochromisme, aggregation-induced emission, et le transfet des protons. Ces phénomènes, récemment observés expérimentalement, sont encore mal compris et il n’existe pas à l’heure actuelle de méthodologie bien définie pour les comprendre. Cette thèse développera les outils de modélisation des couplages des propriétés optiques aux phénomènes d’aggregation, réactivité et de déformation á l'etat solide. / To develop a theoretical methodology to study the influence of external stimuli on fluorescent crystals. We are particularly interested in excited state reactivity, aggregation-enhanced fluorescence and responses to mechanical stimuli. Such phenomena are often not yet understood at a molecular level, a problem exacerbated by the absence of adequate and cost-efficient computational models. This thesis counters this problem by developing a method capable of describing the solid state environment in the context of excited-state calculations at the quantum level.

Limitadores ópticos são dispositivos que apresentam alta transmitância para baixas intensidades de luz incidente e, inversamente, baixa transmitância para altas intensidades, sendo usados como protetores contra danos em sensores ópticos e olhos humanos. Com o objetivo de estudarmos novos materiais com mecanismos não lineares eficientes para o processo de limitação, bem como novas geometrias ópticas, apresentamos neste trabalho o desenvolvimento de um limitador óptico baseado na absorção saturada reversa de porfirinas e metaloporfirinas. Construímos também um dispositivo baseado na configuração óptica bifocal, usando porfirina como absorvedor saturável reverso. Além disso, obtivemos parâmetros espectroscópicos do estado excitado pelos ajustes teóricos das curvas de transmitância, através da resolução de equações de taxa. / Optical limiters are devices with a high transmittance in the presence of low intensity light, and a considerable lower transmittance otherwise, been used as protectors against damage in optical sensors and human eyes. Aiming at searching for new materials and optical geometries efficient for optical limiting. We report on the development of an optical limiter based on the reverse saturable absorption in porphyrin and metalioporphyrins. We also built a device-based .on a cascade focus configuration, using free base porphyrin as the absorber. Besides, we obtain the excited state spectroscopy parameters by the theoretical fitting of transmittance curves, by solving a set of rate equations.

"Hydroxyl ions are a common contaminant in optical fibers, and are responsible for strong absorption centered at 1380 nm that becomes significant over long optical path lengths. Recently, however, special fabrication methods have been developed that minimize the hydroxyl ion contamination, permitting use of the entire 1300-1700 nm spectral region for telecommunications. There is therefore interest in examining the Nd 4F3/2 to 4I13/2 transition for a potential optical amplifier at 1400 nm. In this thesis, the excited state absorption cross section and the overall gain/loss spectrum of neodymium in a silica glass fiber were determined for the 1200-1500 nm wavelength region using the pump-probe method. The ground state absorption cross section was also determined from transmission measurements, and the stimulated emission cross section was calculated using the fluorescence spectrum and the McCumber relation. Oscillator strengths for absorption and emission transitions were calculated in the 800-1600 nm wavelength range using the Judd-Ofelt method. The above procedures were followed for both the Nd-doped fiber, as well as an erbium-doped silica fiber. The shape of the Nd emission spectrum is also noteworthy, since the characteristic Nd peak at 1064 nm is not observed, although there is strong emission at 1092 nm. The pump-probe measurements revealed significant excited state absorption loss between 1200 and 1350 nm, due to excitation from the 4F3/2 to the higher 4G9/2 and 4G7/2 states. Between 1350 and 1475 nm, there was no net gain or loss that could be observed beyond the level of the noise. For the glass fibers studied, it appears that in the spectral region of interest for an optical amplifier, the stimulated emission and excited state absorption cancel one another out."

Neste trabalho, métodos ab initio multiconfiguracionais de alto nível com extenso conjunto base e inclusão de correções relativísticas foram empregados para estudar vários sistemas diatômicos contendo metais de transição. As abordagens de Teoria de Pertur- bação de Segunda Ordem Multiconfiguracional (CASPT2) ou sua versão Multi-State (MS-CASPT2), baseadas em funções de onda do tipo Complete-Active-Space Self- Consistent-Field (CASSCF) foram utilizadas, com o conjunto base do tipo Orbitais Naturais contraídas em ambiente relativístico (ANO - RCC) com qualidade quádrupla- , para se estudar esses sistemas. Em relação aos dímeros de metais de transição homonucleares (Re2, Tc2, Ta2, Mo2 e W2), caracterizamos seu estado fundamental e diversos estados excitados através das curvas de energia potencial, constantes espectroscópicas e ordens de ligação efetiva. Todos os dímeros estudados por nós apresentam multiplicidades de ligação acima de quatro. Para esses sistemas também estudamos os efeitos do desdobramento causado pelo acoplamento spin-órbita com o intuito de determinar inequivocadamente a simetria do estado fundamental e, também, de auxiliar na interpretação dos espectros experimentais, quando existentes. Sobre as diatômicas formadas pela junção de um átomo de metal de transição e um elemento do grupo principal, enfocamos principalmente os nitretos e os boretos de metais de transição (CoN, MnN, TcN e RhB). Da mesma maneira, os sistemas foram descritos em termos de suas curvas de energia potencial e constantes espectroscópicas e foram comparadas com outros resultados teóricos e experimentais. Todas as moléculas estudadas nessa parte são caracterizadas por ligações triplas, com um par de elétrons sobre o átomo não metálico e os elétrons restantes localizados sobre o metal, acoplados de diferentes formas / In this work, high level ab initio multiconfigurational methods with extensive basis set and inclusion of relativistic e¤ects were employed to study several diatomic systems containing transition metals. The Multiconfiguration Second Order Perturbation Theory (CASPT2) or its Multi-State version (MS-CASPT2) approaches, based on Complete- Active-Space Self-Consistent-Field (CASSCF), were employed, with the Atomic Natural Orbital contracted in a relativistic environment (ANO-RCC) with quadruple- quality, in order to study these systems. In relation to the homonuclear dimers of transition metals atoms (Re2, Tc2, Ta2, Mo2, and W2), we have characterized their ground state and several excited states through potential energy curves, spectroscopic constants and e¤ective bond orders. All dimers we studied have the multiplicity of the chemical bond above four. To these kind of systems, we have also studied the splitting caused by spin-orbit coupling with the the aim of determine the symmetry of the ground state and help in the interpretation of the experimental spectras. About the diatomic formed by joining of a transition metal atom and an atom of the main group, we have focused, mainly, the transition metal nitrites and borides (CoN, MnN, TcN, and RhB) In the same way, these systems were described in terms of their potential energy curves, spectroscopic constants and wavefunctions and we have com- pared to other theoretical and experimental results. All molecules studied in this part were characterized as triple bonded, with a pair of electrons on the non–metalic center and the remaining electrons localized on the metal, coupled on di¤erent forms

Electron transfer is one of the fundamental process occurring in many chemical reactions. Electron transfer process has been under intensive study for many applications, for example artificial photosynthesis, where electrons from photo-excited chromophore molecules are harnessed to produce solar fuels in various forms. Transition metal complexes, such as ruthenium and rhenium complexes, play an important role in the continuing development of artificial photosynthetic devices. The electron transfer process in chromophores involving transition metal complexes often occurs on an ultrafast time scale from sub-ps to ns. To resolve such dynamics, ultrafast spectroscopic techniques are required. A variety of ultrafast techniques, such as time-resolved infrared spectroscopy and multi-pulse transient absorption spectroscopy, were used in this study to unravel the excited state electron transfer dynamics in a series of Re(I) complexes. Transition metal complexes often feature excited states that involve only partial electron transfer between the electron donating and accepting ligands, even for ligands with strong electron donating and accepting properties. It is often difficult to design a compact complex feature a full electron transfer excited state. Therefore, part of the work presented in this thesis was dedicated to the study of the electron transfer extent in the excited states of a series of [Re(N,N)(CO)3L]+ compounds, where N,N stands for electron accepting and L stands for electron donating ligands. By carefully designing the structure and redox properties of both the electron donor and acceptor, we demonstrated that essentially a full-electron charge transfer excited state can be prepared, while the designed Re(I) complex is still compact. To further extend the understanding of the electron transfer in transition metal complexes, modulation of the electron transfer rate in a compact Re(I) complex was studied. By perturbing the electron transfer process with a femtosecond mid-IR pulse, we showed that a 28% increase of the electron transfer rate was achieved. This study demonstrated the possibility of using a small energy mid-IR quanta to change the energy conversion process in a chromophore. Vibrational energy transfer in molecules is another important process in nature. Detailed understanding of the vibrational energy transfer on a molecule level is fundamentally important and essential for the development of molecular optical devices. It was recently discovered that the transport of vibrational energy in molecules can be fast and efficient due to its ballistic character. To understand the mechanism of the ballistic energy transport, experiments with several series of oligomers were performed using a relaxation-assisted two-dimensional infrared method. The energy transport speed was found to be dependent on transport initiation method and the transport pathways for different cases of initiation were identified. Detailed analysis on the chain band structure, group velocity and vibrational relaxation dynamics is presented. / acase@tulane.edu

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 21, 2007). Includes bibliographical references.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 21, 2007). Includes bibliographical references.

This thesis discusses developing new tools to probe DNA damage resulting from photoinduced chemical processes and probing the initial excited-state structural dynamics of nucleic acids and sunscreen agents. The results of this thesis show that UV resonance Raman spectroscopy (UVRRS) is an information-rich probe of chemical compositions in in situ analysis of sunscreen formulations. The results indicate that 244-nm excited UV resonance Raman spectra can provide a limit of detection of 0.23% w/w of sunscreen active ingredients (AIs), far below typical active ingredient (AI) concentrations in sunscreen formulations. UVRRS was used to probe the photostability of sunscreens, by determining the initial excited-state structural dynamics of Benzophenone-3 (BZ3), a common sunscreen active ingredient. Only minor excited-state structural distortions were obtained, based on the low displacement values, suggesting an inherently stable molecule. The largest structural change occurs along the carbonyl stretch, suggesting a strong interaction with the methanol solvent and a dissipative decay path for the molecule. Similarly, to gain an insight into how the structure of nucleic acids determine their photochemistry, UVRRS was used to probe the initial excited-state structural dynamics of 9-methyladenine (9-MeA). As for BZ3, the initial excited-state structural dynamics obtained for 9-MeA, are low, and much lower than for pyrimidine bases, providing a strong evidence for the photochemical stability of this purine base analog, compared to pyrimidines. Since DNA does not exist in isolation in cells, the role of a UV-absorbing amino acid, tryptophan, in UV-induced DNA photodamage was explored using molecular beacons (MBs) to detect the damage. The results indicate that tryptophan protective effects on DNA far outweighs their photodamage potential. However, MBs are expensive and they have some technical limitations, despite their exquisite sensitivity. Therefore, a new DNA damage detection method was developed based on smart probes (SPs). These probes are shown to be sensitive and sequence specific for detecting DNA photodamage.

The vibrational potential energy surfaces in electronic ground and excited states of several ring molecules were investigated using several different spectroscopic methods, including far-infrared (IR), Raman, ultraviolet (UV) absorption, fluorescence excitation (FES), and single vibronic level fluorescence (SVLF) spectroscopies. Based on new information obtained from SVLF and millimeter wave spectra, the far-IR spectra of coumaran were reassigned and the one-dimensional ring-puckering potential energy functions for several vibrational states in the S0 ground state were determined. The barrier was found to be 154 cm-1 and the puckering angles to be ± 25°, in good agreement with the millimeter wave barrier of 152 cm-1 and puckering angles of ± 23°. Moreover, the UV absorption and FES spectra of coumaran allowed the one-dimensional ring-puckering potential energy functions in the S1 excited state to be determined. The puckering barrier is 34 cm-1 for the excited state and the puckering angles are ± 14°. Several calculations with different basis sets have been carried out to better understand the unusual vibrational frequencies of cyclopropenone. It was shown that there is strong interaction between the C=O and symmetric C-C stretching vibrations. These results differ quantitatively from a previous normal coordinate calculation and interpretation. The vapor-phase Raman spectrum of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene was analyzed and compared to the predicted spectrum from DFT calculations. The spectrum further shows it has D2h symmetry, in which the skeletons of both rings are planar. The infrared and Raman spectra of vapor-phase and liquid-phase 1,4-benzodioxan and 1,2,3,4-tetrahydronaphthalene were collected and the complete vibrational assignments for both molecules were made. Theoretical calculations predicted the barriers to planarity to be 4809 cm-1 for 1,2,3,4-tetrahydonaphthalene and 4095 cm-1 for 1,4-benzodioxan. The UV absorption, FES, and SVLF spectra of both molecules were recorded and assigned. Both one and two-dimensional potential energy functions of 1,4-benzodioxan for the ring-twisting and ring-bending vibrations were carried out for the S0 and S1(π,π*) states, and these were consistent with the high barriers calculated for both states. The low-frequency spectra of 1,2,3,4-tetrahydronaphthalene in both S0 and S1(π,π*) states were also analyzed.

In this study, we study the polarization dependence, gain property, and amplified spontaneous emission in Cr4+: YAG crystal fibers. Cr4+: YAG crystal has an ultra-wide bandwidth of 300 nm. Cr4+: YAG crystal fibers fabricated through laser heated pedestal growth technique are suitable for the applications of fiber amplifiers, fiber lasers, and broadband light sources. The experiment results showed that the polarization-dependent loss has a severe variation as the optical wavelength change. The maximum polarization-dependent loss was up to 18 dB. The main reason of such a large polarization-dependent loss is the combination of multimode interference and the birefringence induced by the non-uniformity of optical waveguide structure and residue strain in Cr4+: YAG crystal fibers. Thus, the results of polarization-dependent loss can be used as a feedback parameter to improve the fabrication process. In the experiment of gain property, bi-directional pump and double-pass transmission scheme was adopted and a 0.2 dB net gain was obtained for the first time at signal wavelength of 1400 nm, pumping wavelength of 1060 nm, and total pumping power of 2.8 W. It shows that Cr4+: YAG crystal fiber has potential to be developed as a broadband fiber amplifier. In the measurement of amplified spontaneous emission spectrum, a wide bandwidth of amplified spontaneous emission of 300 nm with total power of 50 £gWwas obtained at 0.2W pumping power condition. The coupling efficiencies from amplified spontaneous emission to single mode fibers and multimode fibers were 1.5 % and 9.9 %, respectively. This result reveals that it has potential to be developed as a broadband light source. To improve the optical properties of Cr4+: YAG crystal fiber in the future, improving the uniformity of optical fiber waveguide and reducing the residue strain in Cr4+: YAG crystal fiber may suppress the polarization-dependent loss; increasing the fiber length, decreasing the mode number, and employing a cladding pump technique with a well-distributed pump power in the crystal fiber to alleviate the excited state absorption may raise the gain performance and the amplified spontaneous emission power.