|
|
Preparation and characterization of solar cells sensitized by bacteriochlorophyll a
Johanovská, Zuzana ; Pšenčík, Jakub (advisor) ; Dostál, Jakub (referee)
In this work, we explored the potential of bacteriochlorophyll a for its use in dye-sensitized solar cells. Bacteriochlorophyll a absorbs in the near-infrared spectral region where most of the pigments tested in dye-sensitized solar cells absorb poorly. It turned out that bacteriochlorophyll a rapidly oxidize to chlorophyl-like molecule at aerobic conditions, what is connected with an undesirable shift of the main absorption band to the shorter wavelengths. Therefore we prepared also several derivatives of bacteriochlorophyll a with similar absorption and tested their stability. We also studied a performance of solar cells with bacteriochlorophyll a and those derivatives, namely bacteriopurpurin, bacteriochlorophyllin and bacteriochlorin. It turned out that bacteriochlorin is the most stable of all the tested pigments. Moreover, it exhibits the best performance when used in the dye-sensitize solar cell.
|
|
|
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
|
|
| |
|
|
Nelineární optická spektroskopie molekulárních komplexů
Linhart, Jan ; Mančal, Tomáš (advisor) ; Pšenčík, Jakub (referee)
Práce se zabývá teorií nelineární spektroskopie a projevy kvantové koherentní dynamiky v nelineární spektroskopii. Poskytuje stručný přehled spektroskopických metod se zaměřením na metodu pump-probe. Dále rozví- jíme teorii nelineární odezvy, přičemž vycházíme z obecného N-wave mixing experimentu, a dospíváme ke tvaru odezvové funkce třetího řádu vyjádřené pomocí Liouvillových drah. Pro vybrané modelové systémy sledujeme koher- entní efekty, které se projevují v 2D a pump-probe spektrech, a provádíme jejich porovnání. D·raz je kladen na objasnění jev· relaxace a excitonové koherence mezi dvěma excitovanými stavy molekulárního dimeru. 1
|
|
|
The effect of oxygen on the triplet state lifetime of carotenoids in photosynthetic complexes
Vahalová, Petra ; Pšenčík, Jakub (advisor) ; Bína, David (referee)
The aim of this study was to find a suitable method of preparation of anaerobic conditions in or- der to determine intrinsic lifetimes of carotenoid triplet states in photosynthetic light-harvesting complexes. We have compared the following three methods: (1) blowing an inert gas (nitrogen) above the surface of a liquid sample, (2) removing oxygen by means of chemical reactions catalyzed by glucose oxidase and catalase and (3) use of sodium dithionite. Each method was first tested on meso-tetra (4-sulfonatophenyl) porphine and then applied on the main light-harvesting complex of Amphidinium carterae. The lifetimes of the triplet states of carotenoids in the light-harvesting complex were determined from kinetics measured directly by a photomultiplier tube and from transient absorption spectra measured at different delays after the excitation pulse by an intensi- fied CCD camera. The effects of the used substances on the sample stability were evaluated by measuring steady-state absorption spectra and pH. Blowing the sample with nitrogen was time- consuming and less efficient in attaining anaerobic conditions compared to the other two methods. In contrast, anaerobic conditions were obtained in a relatively short time after the application of so- dium dithionite; however, it caused acidification of the sample ralated...
|
|
| |
|
| |
|
|
Quenching of chlorophyll triplet states by carotenoids in thylakoid membranes
Vahalová, Petra ; Pšenčík, Jakub (advisor) ; Vácha, František (referee)
Photosynthesis is one of the most important biological processes. The photosynthetic apparatus is protected against formation of reactive singlet oxygen by carotenoids. In this work, thylakoid membranes from spinach were studied, and the main aim was to explore the effect of a partial carotenoid removal on the protective function. Carotenes, which are nonpolar carotenoids, were removed from a part of the sample by hexane. About 90 % of carotenes were removed, as revealed by liquid chromatography. However, the high efficiency of chlorophyll triplet state quenching was not affected by the carotene removal. Therefore, it was concluded that the remaining carotenes are probably localized around reaction centres, where they are not accessible to hexane and where their protective function is the most important. At the same time, changes in optical spectra were observed, which were ascribed to structural modifications caused by the carotene removal from the outer parts of the complexes. The carotenoids removal probably caused detachment of outer light-harvesting complexes. This interpretation is supported by the fact that similar changes were observed in experiments with a detergent dodecyl maltoside. 1
|
|
| |
|
|
Srovnání poruchových a neporuchových přístupů k teorii optické spektroskopie
Malý, Pavel ; Mančal, Tomáš (advisor) ; Pšenčík, Jakub (referee)
This thesis focuses on the comparison of perturbative and non-perturba-tive calculation of the third order polarization in two dimensional (2D) optical spec- troscopy. A two-level molecule and a coupled dimer are chosen as simple systems for which the 2D spectrum is calculated using explicit equations of motion for the reduced density matrix and integrating the response functions. The two approaches are compared qualitatively and quantitatively using obtained re- sults. The main difference found is the presence of higher order polarization contributions in non-perturbatively calculated spectrum. 1
|
guest ::
RSS feed.