A detailed spectroscopic study was carried out on 3-hydroxyflavone in order to elucidate the mechanism which is responsible for the anomalous fluorescence of flavonols in the green-yellow region. A combination of absorption and luminescence measurements indicated that the green emission in 3-hydroxyflavone is due to excited state tautomerization of the molecule by an intramolecular proton transfer mechanism. Excitation spectra, deuteration studies, and comparison with the luminescence behavior of the corresponding methylated analogue confirmed the proton transfer mechanism. In a rigid hydrocarbon or ether glass at 77 K, the green emission is replaced by a predominant UV-violet fluorescence of the normal molecule, in the usual vibrational envelope inversion relationship with the absorption spectrum. The extraordinary viscosity dependence of the tautomerization process has been explained in terms of the mechanical viscous-flow-barrier model of Dellinger and Kasha. Luminescence measurements were performed at various temperatures between 25 K and ambient temperature. The gradual changes in the ratio of normal vs. tautomer emission appeared to follow the expectations according to the above model. / The studies on 3-hydroxyflavone were extended to other flavonols, having additional hydroxy substituents. The general findings were similar to 3-hydroxyflavone, with characteristic minor differences. The molecules 5-hydroxyflavone and 7-hydroxyflavone were also investigated, in order to compare their luminescence behavior with that of 3-hydroxyflavone. The three molecules were found to exhibit very distinct and contrasting luminescence properties. Both ground and excited state ionization were indicated in 7-hydroxyflavone, while in 5-hydroxyflavone a non-adiabatic proton tranfer mechanism, leading to rapid radiationless deactivation of the excited state, seems very probable. / A study was undertaken on the pigment contents of near-white cultivars of Hemerocallis in order to provide guidelines on hybridization programs directed toward production of blue cultivars. The cultivars were divided into four classes, chiefly on the basis of absorption profiles of their methanolic extracts. Flavonols were found in one class only, while carotenoids and hydroxycinnamic acids were present in all classes. / Finally, an attempt was made to characterize synthetic anthocyanin- copigment complexes on the basis of absorption and luminescence measurements. / Source: Dissertation Abstracts International, Volume: 41-12, Section: B, page: 4363. / Thesis (Ph.D.)--The Florida State University, 1980.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74369 |
| Contributors | SENGUPTA, PRADEEP KUMAR., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 172 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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