Dokument: Fluorescence Quantum Yields and Anisotropies of Short-Lived Chromophores
| Titel: | Fluorescence Quantum Yields and Anisotropies of Short-Lived Chromophores | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=67562 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20241129-083544-3 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Morshedi Mian Abad, Mahbobeh [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Gilch, Peter [Betreuer/Doktorvater] Prof. Dr. Schmitt Michael [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | In fluorescence spectroscopy, the fluorescence quantum yield Фfl serves as an important metric that quantifies the efficiency with which a fluorophore converts absorbed photons into emitted light. The relative method, commonly employed for determining fluorescence quantum yield, involves comparing the yield Фfl of a compound to that of a reference material with a known yield. In the first study of this thesis, three new reference compounds with emission spectra covering the UV/Vis range have been identified for determining low fluorescence quantum yields, with yields ranging from 10-5 to 10-4. These include thymidine in water for the blue, dibenzoylmethane in ethanol for the green, and malachite green chloride in water for the red region of the spectrum. These substances are chosen for their ease of handling, photostability, commercial availability, and the mirror-image symmetry observed between their absorption and fluorescence spectra. This symmetry suggests that the same electronic states are involved in both the absorption and emission processes, justifying the use of the Strickler-Berg relationship. Additionally, the fluorescence excitation spectra of these compounds closely match their absorption spectra, ensuring that the emissions measured are indeed from the compounds being studied. The fluorescence quantum yields Фfl of the compounds were first determined using the relative method and then compared with the one according to the Strickler-Berg analysis in conjunction with time resolved fluorescence spectroscopy. The fluorescence quantum yield values obtained from both methods show agreement within their respective error margins.
The second study of this thesis investigates the photophysical properties of a specific copper(I) carbene complex, [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]-(2-picoline)copper(I) tetrafluoroborate (abbreviated as NHCCuPy), by femtosecond spectroscopy and quantum chemistry across various solvents. Copper(I) complexes, with intriguing luminescent properties, are increasingly emerging as viable alternatives to heavy metal-based complexes like iridium and platinum, which are commonly used in organic light-emitting diodes (OLEDs). NHCCuPy exhibits significant sensitivity to environmental conditions, as evidenced by its performance in different media. While embedded in a poly(methyl methacrylate) (PMMA) matrix or processed as a powder, the complex shows a high fluorescence quantum yield. Conversely, this yield dramatically decreases when the complex is in the form of single crystals or in solution. Employing the fluorescence Kerr gate setup with high sensitivity allowed for a detailed comparative analysis of the small emissions from NHCCuPy and 2-picoline (the ligand). The third study of this thesis is concerned with femtosecond fluorescence and transient absorption experiments on the photophysics of 2-cyanoindole in solution. The chromophore of the naturally occurring fluorescent amino acid tryptophane is indole. Therefore, unnatural amino acid derivatives with functionalized indoles are of great interest as fluorescent probes in protein studies. For instance, the fluorescence quantum yield of 2-cyanoindole is strongly sensitive to the solvent. Its fluorescence quantum yield in water is as small as 4.4⋅10-4 and increases to a value of 0.057 in tetrahydrofuran. 2-Cyanoindole can, thus, represent a promising fluorescence probe in hydration studies of proteins. In water, its fluorescence decays within 8 ps, irrespective of the excitation wavelength. For short wavelength excitation (266 nm) the initial fluorescence anisotropy is close to zero. For excitation with 300 nm, it amounts to ~ 0.2. This is in accordance with the energetic proximity of two singlet states (La and Lb). The transition from the La to Lb state occurs in less than 100 fs. For all solvents studied in this work, a bi-exponential decay was observed. In water, femtosecond transient absorption reveals that the fluorescence decay is solely due to internal conversion to the ground state. In aprotic solvents such as acetonitrile and tetrahydrofuran, the fluorescence decay is prolonged, with time constants of ~900 ps and ~2.6 ns respectively, where intersystem crossing to the triplet state contributes to the decay. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät | |||||||
| Dokument erstellt am: | 29.11.2024 | |||||||
| Dateien geändert am: | 29.11.2024 | |||||||
| Promotionsantrag am: | 23.07.2024 | |||||||
| Datum der Promotion: | 19.09.2024 |
