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Graduation date: 2000

The photophysics of highly electronically excited states of a set of d0 and d10 metallated tetrapyrroles, which have different peripheral substituents and central metal atoms, macrocycle substitution patterns and macrocycle conformations, have been investigated both theoretically and experimentally. Theoretically, the energies of ground state molecular orbitals and the energies and rank in energy of the excited states have been calculated using density functional theory and time-dependent density functional theory methods. Experimentally, the steady-state absorption and fluorescence spectra have been measured. Temporal fluorescence profiles have been measured using a time correlated single photon counting system for the S1 state and a fluorescence upconversion system for the S2 state.<p> The decay mechanisms of highly electronically excited states are governed by the nonradiative S2 S1 internal conversion. The possible existence of any excited state (such as S2' or dark state) lying close to the S2 state and its participation in the nonradiative decay processes of the S2 state has been discussed. The ultrafast nonradiative decay rates of the S2 S1 internal conversion were interpreted on the basis of the energy gap law of radiationless transition theory. For magnesium tetraphenylporphyrin (MgTPP), the radiationless rates (knr)of its S2 state follows the prediction of the energy gap law for the weak coupling statistical limit case. However, the S2 S1 electronic coupling energies of the other metalloporphyrins investigated fall within the inermediate to strong coupling range. The difference of knr relative to the weak coupling limit can be rationalized by the different magnitudes of electronic coupling energies. The magnitude of electronic coupling energies is the major factor in determining the radiationless depopulation rate constants of the S2 states in metallated tetrapyrroles which have S2 S1 electronic coupling energies exceeding the weak coupling limit. In some cases, such as ZnOEP, the magnitude of Frack-Condon factor has only minor effect.<p> The photophysics of Soret-excited metallated corroles have also been investigated in this study. Primary work has shown that two metallated corroles examined have similar S2 S1 interstate electronic coupling energies to that of CdTPP and thus the radiationless decay rates of Soret-excited S2 state are also determined by the magnitude of electronic coupling energies.

The photophysics of highly electronically excited states of a set of d0 and d10 metallated tetrapyrroles, which have different peripheral substituents and central metal atoms, macrocycle substitution patterns and macrocycle conformations, have been investigated both theoretically and experimentally. Theoretically, the energies of ground state molecular orbitals and the energies and rank in energy of the excited states have been calculated using density functional theory and time-dependent density functional theory methods. Experimentally, the steady-state absorption and fluorescence spectra have been measured. Temporal fluorescence profiles have been measured using a time correlated single photon counting system for the S1 state and a fluorescence upconversion system for the S2 state.<p> The decay mechanisms of highly electronically excited states are governed by the nonradiative S2 S1 internal conversion. The possible existence of any excited state (such as S2' or dark state) lying close to the S2 state and its participation in the nonradiative decay processes of the S2 state has been discussed. The ultrafast nonradiative decay rates of the S2 S1 internal conversion were interpreted on the basis of the energy gap law of radiationless transition theory. For magnesium tetraphenylporphyrin (MgTPP), the radiationless rates (knr)of its S2 state follows the prediction of the energy gap law for the weak coupling statistical limit case. However, the S2 S1 electronic coupling energies of the other metalloporphyrins investigated fall within the inermediate to strong coupling range. The difference of knr relative to the weak coupling limit can be rationalized by the different magnitudes of electronic coupling energies. The magnitude of electronic coupling energies is the major factor in determining the radiationless depopulation rate constants of the S2 states in metallated tetrapyrroles which have S2 S1 electronic coupling energies exceeding the weak coupling limit. In some cases, such as ZnOEP, the magnitude of Frack-Condon factor has only minor effect.<p> The photophysics of Soret-excited metallated corroles have also been investigated in this study. Primary work has shown that two metallated corroles examined have similar S2 S1 interstate electronic coupling energies to that of CdTPP and thus the radiationless decay rates of Soret-excited S2 state are also determined by the magnitude of electronic coupling energies.

Thesis (Ph. D.)--University of Florida, 1981. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 76-79).

Thesis (Ph. D.)--University of Wisconsin, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

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This thesis presents the results of a series of experiments in which electrons are superelastically scattered from various laser excited states of sodium. The atoms, once in the optically prepared state, are forced to relax via the superelastic collision with an electron. The rate of detection of superelastically scattered electrons was measured as a function of the laser polarisation which enabled pseudo Stokes parameters to be determined. These pseudo Stokes parameters are functions of both optical pumping parameters and atomic collision parameters. The optical pumping parameters describe the laser-atom interaction and the atomic collision parameters describe the electron-atom collision process. Three different laser excitation mechanisms were used to optically pump the atoms into various excited states. The first of these used a single laser tuned to the 32S 112(F'=2 hyperfine state)-~32P312 transition. The excited atoms underwent a superelastic collision with an electron leaving the atom in the ground state and pseudo Stokes parameters were measured as a function of both scattering angle and incident electron energy. The second superelastic experiment, utilised a folded step excitation mechanism which employed two lasers tuned from the two hypethne states of the 32S112 ground state respectively to the 32P312 excited state. Power broadening effects in the single laser experiment cause the atoms to be optically pumped into the F= 1 hyperfine ground state. The laser powers used were not great enough to power broaden the hyperfine ground states and as such the F'= 1 sublevel effectively acted as a sink. The folded step excitation method enabled the excited state population to be increased so that data at larger scattering angles could be obtained. Stokes parameters from both of these experiments which had an incident energy range of 10eV to 30eV and an angular range of 5°-25° were compared to three current electron-atom scattering theories and previous experimental data. Overall, fair to good agreement was found between theory and experiments for the individual Stokes parameters. Losses of coherence was observed at small scattering angles (50.200) at 20eV and 25eV incident electron energies which were poorly modelled by the three different theories. The third superelastic experiment involved the use of two lasers of specified polarisation to stepwise excite the atoms to the 32D512 excited state. Superelastic collisions with incident electron energies of 20eV from the 32D512-*32P312~312 collision were studied at three different scattering angles and pseudo Stokes parameters for the case where the polarisations of the radiation from the lasers were parallel were measured. The single step and folded step laser-atom interactions for it excitation were modelled using a full quantum electrodynamical treatment so that the optical pumping parameters from the single and folded step experiments could be investigated. Equations of motion were derived in the Heisenberg picture and it is shown that for the single laser case 59 equations of motion are required to fully model the interaction and for the folded step ease 78 equations of motion are required. The results of calculations demonstrated that the optical pumping parameters were sensitive to laser intensity, laser detuning and the Doppler width of the atomic beam. The theoretical quantum electrodynamical calculation results were in good agreement with the experimental results.

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