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Study of excitonic interactions in light harvesting complexes
Bouda, Karel ; Alster, Jan (advisor) ; Dostál, Jakub (referee)
The thesis explores the possible presence of exciton interaction in phycobilisomes, the large pigment-protein light-harvesting complexes occurring mainly in cyanobacteria. The technique of two-dimensional electron spectroscopy, which provides a resolution on the femtosecond scale and is sensitive to exciton interactions, was used to study phycobiliso- mes of cyanobacteria thermosynechococcus elongatus. A possible model of energy levels of phycobilisomes and the flow of excitatory energy between them was constructed from the obtained data measured on the spectral range of approximately 590 to 700 nm. The data indicate the likely presence of exciton interaction between 3 pairs of electron states. 1
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Fluorescence excitation spectra of photosynthetic antennae
Materna, Filip ; Mančal, Tomáš (advisor) ; Alster, Jan (referee)
The aim of this thesis is to offer a brief overview of energetic transfer taking place in photosynthetic antenna systems by studying an example antenna and trying to simulate its behavior. Utilising modern literature, we describe the structure of photosynthetic antenna systems, their properties and the methods used to study them. We follow this by proposing a model of the kinetics of ener- getic states in the studied system. The theoretical section is followed by analysis of measured absorption and fluorescence excitation spectra of the actual chloro- phyll + carotenoid dimers with use of OriginPro2020 and Python3. With this knowledge, we have developed a simulation to fit our model to the experimental values. We utilize the Quantarhei Python3 package to calculate the absorption spectra and the FES spectrum is constructed by solving a system of differential equations proposed from the kinetics model and fitting the measured data. From there, we extract the efficiency of energy transfer in the dimer.
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Optimization of the signal from pigment triplet states in photosystem I
Charvátová, Kateřina ; Pšenčík, Jakub (advisor) ; Alster, Jan (referee)
The main objective of the thesis is to improve signal-to-noise ratio for pigments' triplet states in photosystem I. The sample was purified from cyanobacterium Thermosynecho- coccus elongatus. Based on the measurements we could deduce that the sample with optimal concentration has an absorbance about 0,7. It is beneficial to remove oxygen for example by nitrogen bubbling. Anaerobic conditions help to increase the lifetime of ca- rotenoid triplet states and to protect the sample from damage. Depending on the time of measurement we choose the maximal energy of the excitation pulse, which does not cause any significant damage to the photosystem. For the measurement, which takes about two hours, we find it is optimal to use the excitation energy from 1,5 mJ to 2 mJ. The re- laxation processes in the photosystem are fast during the first 100 ns. It is, therefore, necessary to use the shortest detection time, which is in our case a gate of 2 ns. At the later delays, it is possible to increase the gate to about 10 ns and at the same time to decrease the amplification of the measurement light (gain) so the final intensity of the signal would not change. This will contribute to a significant reduction of noise for the later delays. 1
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Signatures of vibronic modulation of small molecular aggregates in two-dimensional electronic spectra
Perlík, Václav ; Šanda, František (advisor) ; Alster, Jan (referee) ; Gelin, Maxim (referee)
We studied the effects of underdamped vibrational modes on excitonic energy transfer in small molecular aggregates by means of ultrafast nonlinear spectroscopy. We developed a vibronic dynamical model to account for the interplay of electronic and vibrational coherence during excitation transport. Our model was aimed to simulate signals of a broad class of linear and third order spectroscopies (absorption, fluorescence, transient absorption (TA), transient grating (TG), two-dimensional spectroscopy (2D)) in the visible domain andaccounts for anharmonic vibrations, sub-exponential relaxation and nonlinear electron-vibrational coupling. We subsequently applied the model for several case studies, such as carotenoid to bacteriochlorophyll excitation transfer in light-harvesting 2 complex (LH2) of purple bacteria, excitation transfer in perylene dyads or vibrational dynamics in hypericin. We have paid particular attention for detailed interpretation of lineshapes of 2D spectrograms employing, e.g. phase analysis and center line (CL) slopes with emphasis to study interplay of electronic, vibrational modulations, or finite excitation pulse durations.
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Interaction of bacteriochlorophyll c and its derivative with titanium dioxide
Ridzoňová, Katarína ; Pšenčík, Jakub (advisor) ; Alster, Jan (referee)
Dye-sensitized solar cells (DSSC) are promising low-cost molecular photovoltaic devices that have a good chance to become a competitor for solar cells based on technology of p-n junction. One of the key components of DSSC is a dye, which is responsible for the capture of light. The main goal of this bachelor thesis is to compare adsorption properties of bacteriochlorophyll c (BChl c) and its modified version referred as bacteriochlorophyllide c (BChlide c) on titanium dioxide (TiO2). In the experimental part of this work interaction of these two sensitizing dyes with TiO2 were investigated by several different methods, including absorption spectroscopy and measuring photo-induced current and current-voltage characteristics of the fabricated DSSC. It has been shown, that BChlide c adsorbs better on the TiO2 layer presumably due to the presence of a carboxylate group. Also the performance of the DSSC based on BChlide c was better than with BChl c.
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Measurement of two-dimensional electronic spectroscopy response of solvents
Bouda, Karel ; Alster, Jan (advisor) ; Dostál, Jakub (referee)
Two-dimensional electronic spectroscopy is a technique used mainly for the study of energy transfer in organic systems. Nevertheless, it seems to be a good choice for studying plenty of other complexes, for example nanocrystals. However, these complexes require different solvents, not only water which is used for organic systems and has a known behaviour in this analysis. These solvents are mainly organic, such as benzene, toluene, xylene and others. The behaviour of these solvents during the 2DES measurements is unknown, therefore it is possible that the obtained data would be contaminated by signals from the solvent. This thesis provides a detailed description of the behaviour of 11 different solvents during the 2DES analysis. 1
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Signatures of vibronic modulation of small molecular aggregates in two-dimensional electronic spectra
Perlík, Václav ; Šanda, František (advisor) ; Alster, Jan (referee) ; Gelin, Maxim (referee)
We studied the effects of underdamped vibrational modes on excitonic energy transfer in small molecular aggregates by means of ultrafast nonlinear spectroscopy. We developed a vibronic dynamical model to account for the interplay of electronic and vibrational coherence during excitation transport. Our model was aimed to simulate signals of a broad class of linear and third order spectroscopies (absorption, fluorescence, transient absorption (TA), transient grating (TG), two-dimensional spectroscopy (2D)) in the visible domain andaccounts for anharmonic vibrations, sub-exponential relaxation and nonlinear electron-vibrational coupling. We subsequently applied the model for several case studies, such as carotenoid to bacteriochlorophyll excitation transfer in light-harvesting 2 complex (LH2) of purple bacteria, excitation transfer in perylene dyads or vibrational dynamics in hypericin. We have paid particular attention for detailed interpretation of lineshapes of 2D spectrograms employing, e.g. phase analysis and center line (CL) slopes with emphasis to study interplay of electronic, vibrational modulations, or finite excitation pulse durations.
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Preparation and characterization of photovoltaic cells based on photosystem I
Kuižová, Alžbeta ; Pšenčík, Jakub (advisor) ; Alster, Jan (referee)
Photosystem I is increasingly used for new types of photovoltaic devices because of high stability. The goal of this thesis was to characterize organic photovoltaic cells based on photosystem I. Our task was to compare three electron mediators, namely TMPD, DCIP and cytochome c, and to choose the best one. In the experimental part of thesis, TMPD was selected as the most effective electron mediator. Subsequent measurements were performed to optimize the thickness of the cell and the concentration of photosystem I and TMPD in a final solution. Solar cells have been characterized by absorption and action spectra, and current-voltage characteristics were used to determine the overall power. It was found out that thinner photovoltaic cells work better and that the use of more concentrated solutions of photosystem I and TMPD leads to more efficient cells.
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