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Excited state processes in linear conjugated systems
ŠEBELÍK, Václav
The main topics of this thesis are the excited states of carotenoids in solvents and in light-harvesting antennas. The first two chapters provide an introduction into the topic, while the later ones are the research chapters, based on published papers. In the research section, the different methods of ultrafast spectroscopy were used. Transient absorption spectroscopy, two-photon excitation, and pump-dump-probe experiments were used to explore the so-called dark states of carotenoids in solvents. The femtosecond dynamics of long polyenes was also studied by the transient absorption spectroscopy. In addition to the exploration of the nature of carotenoids and polyenes in solvents, the energy transfer in the CAC antenna of Rhodomonas salina was studied by transient absorption spectroscopy.
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Carotenoid Excited State Processes by Femtosecond Time-Resolved Pump-Probe and Multi-Pulse Spectroscopies
WEST, Robert G.
This Ph.D. thesis is an exploration of carotenoids by ultrafast, time-resolved absorption spectroscopy to investigate their complicated relaxation processes, means of energy transfer, and dependence on structure. The introduction begins with an overview of carotenoids, intended for the reader to appreciate their importance and their complexity as revealed by decades of research in carotenoid photophysics. To understand the primary concerns of this research field, the reader is guided through basic theory of energetic processes, the experimental method, and methods of analysis. The main body of the text is the Research Chapter, containing four sections, each describing research using varied ultrafast transient absorption spectroscopies on carotenoids in solution and when bound to a host protein. Section 2.1 concerns an equilibration phenomenon in the lowest excited state of the carotenoid fucoxanthin in various solutions and temperatures by a multi-pulse transient absorption method. The same method is applied to fucoxanthin in a host antennae protein of the pennate diatom Phaeodactylum tricornutum to investigate the function of the equilibration in energy transfer to Chlorophyll a in Section 2.2. The next two sections regard the effect of carotenoid structure on its relaxation dynamics. Section 2.3 investigates the effect of the non-conjugated acyloxy group of two fucoxanthin derivatives in various solvents. Here, one of the energetic states involved in the equilibrium mentioned above is seen drastically affected. Lastly, Section 2.4 investigates alloxanthin, a carotenoid with an unusual pair of carbon-carbon triple bonds. Their effect on the conjugation is evaluated based upon the molecules' decay dynamics. A general summary and conclusion is provided at the end.
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