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Photodissociation of small polyatomic molecules investigated via molecular beam and velocity map imaging techniques
Vinklárek, Ivo ; Fárník, Michal (advisor) ; Wester, Roland (referee) ; Klán, Petr (referee)
Velocity map imaging (VMI) combined with supersonically expanded molecules pro- vides molecular-level insight into many fundamental natural phenomena. This compre- hensive work delivers an introduction to the photodissociation theory and applied VMI and mass spectrometric experimental techniques, followed by an overview of our achieve- ments in the investigation of photodissociation and clustering on the selected molecular systems. Also, new implementations of the centroiding mode and the current status of the apparatus for imaging are commented on for future measurements. The first part of the experimental results focuses on fundamental research of photodissociation of isolated molecules. We demonstrate an efficient coupling between the stretching vibration and ejection of hydrogen radical in pyrrole and, furthermore, describe the impact of singlet- triplet dynamics and molecular frame on energy redistribution during the fragmentation of selected chloroalkanes. The second part revolves around chloroalkane clusters in the perspective of atmospheric chemistry, which is represented by the observations of differ- ent dynamics for CH3 and Cl fragments in (CH3Cl)n cluster photodissociation. Finally, the clustering research is extended by our recent pickup experiments with clusters of polyaromatic hydrocarbons...
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Temperature dependence of the triplet-triplet energy transfer in photosynthetic light-harvesting complexes
Vinklárek, Ivo ; Pšenčík, Jakub (advisor)
Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...
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Temperature dependence of the triplet-triplet energy transfer in photosynthetic light-harvesting complexes
Vinklárek, Ivo ; Pšenčík, Jakub (advisor) ; Polívka, Tomáš (referee)
Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...
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Delayed fluorescence of Protoporphyrin IX for medical diagnosis
Vinklárek, Ivo ; Scholz, Marek (advisor) ; Alster, Jan (referee)
The aim of this work is to analyse mechanisms of delayed fluorescence in solutions of protoporphyrin IX mainly through measurements of time-resolved spectroscopy. Delayed fluorescence is a type of fluorescence in which luminophore undergoes reversed intersystem crossing from triplet state to singlet state which is subsequently brought to the ground state by emission of photon. One of the applications of delayed fluorescence is a measurement of oxygen partial tension in mitochondria in vivo. For the right interpretation of the data it is necessary to understand the processes of generation of delayed fluorescence. A new experimental setup for simultaneous time-resolved measurements in infra-red and visible spectral regions was developed and tested as a part of the work. Absorption and fluorescence spectra of protoporphyrin IX were measured under different conditions in dimethylformamide and ethylenglycol solutions. The influence of photodegradation was regarded as well. Then we measured kinetics of protoporphyrin IX with the main focus on the influence of singlet oxygen-sensitized delayed fluorescence. Our research indicates that it participates together with thermal delayed fluorescence, which could be helpful in further interpretation and analysis of the experimental data. The research was carried out in...
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