The ground state properties and excited-state dynamics of two complex molecules of biological significance have been investigated experimentally by steady-state and picosecond transient absorption spectroscopy, and theoretically by molecular orbital calculations. Lumichrome (7,8-dimethylalloxazine), has been found to form a ground-state anion in p-dioxane and certain alcohol solvents. Picosecond transient absorption studies of lumichrome in acetic acid, pyridine, p-dioxane, methanol, and water at pH 9.8, as well as 1,3-dimethyllumichrome and lumiflavin in methanol solvents are reported. The picosecond transient absorption measurements of lumichrome in p-dioxane solvent revealed the presence of a ground-state and possibly excited-state anion, as well as a rapid risetime of $\rm T\sb{\rm n}\gets\rm T\sb1$ absorption of the normal molecule. Studies of lumichrome in methanol solvent indicate the occurrence of excited-state proton-ejection. Picosecond transient absorption experiments of lumichrome in acetic acid and in pyridine solvents suggested that excited-state proton transfer may be preceded by excited-state proton ejection. The absence of observed $\rm T\sb{\rm n}\gets\rm T\sb1$ absorption of the tautomer form of lumichrome in these solvents suggested that the triplet population of the isoalloxazine form may be rapidly depleted by semiquinone radical formation. / Possible radiationless deactivation pathways of the non-fluorescent molecule, 5-hydroxyflavone, have been investigated by steady-state and picosecond transient absorption spectroscopy, as well as by molecular orbital calculations. The specific solvent dependence of the steady-state absorption spectra of 5-hydroxyflavone reflects the previously-proposed strength of the intramolecular H-bond and suggests a strong vibronic coupling. A weakly-absorbing transient was observed beginning at ca. 50 ps in methanol solvent. Ab initio SCF molecular orbital calculations were performed on both the normal and tautomer forms of 5-hydroxyflavone. Ab initio SCF and geometry optimization, and semi-empirical INDO/S-CI calculations were performed on the small analog, 5-hydroxychromone. Results of these calculations, in conjunction with experimental results, suggest that two plausible mechanisms for radiationless pathways in 5-hydroxyflavone are a pseudo-Jahn-Teller effect, and a rapid intersystem crossing, both in the tautomer form of the molecule which is presumed to form via excited-state proton transfer. / Source: Dissertation Abstracts International, Volume: 48-09, Section: B, page: 2659. / Thesis (Ph.D.)--The Florida State University, 1987.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76162 |
| Contributors | MACINNIS, JEAN MARY., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 315 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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