| Abstract [eng] |
Concentration quenching occurs when fluorescence intensity decreases with increasing molecular concentration. However, it is not fully understood how this phenomenon works. It has also been observed in in vitro studies with chlorophyll. Zinc phthalocyanine molecules were used as a model system to elucidate the processes of concentration quenching of chlorophyll a molecules. The aim of this master 's thesis is to investigate and compare the concentration quenching of chlorophyll a and zinc phthalocyanine in different molecular environments - solutions and thin films. Tasks: to investigate the light absorption of different concentrations of chlorophyll a and zinc phthalocyanine in solutions and thin films; to investigate the fluorescence spectra of different concentrations of chlorophyll a and zinc phthalocyanine in solutions and thin films; to investigate the fluorescence kinetics of different concentrations of chlorophyll a and zinc phthalocyanine in solutions and thin films. The systems used for the concentration quenching of molecules are solutions and thin films. Solutions were prepared in a toluene solvent and samples of different concentrations were measured using a 0.1 mm optical path disc cuvette. Thin films were made on a glass plate using a spin coating method, where the solution consists of polystyrene, toluene, and different concentrations of the molecules under study. The light absorption spectra did not show any significant differences between the samples at different concentrations, except for the zinc phthalocyanine 2.5 mM thin film, where the spectrum shows a relative increase in light absorption at the ~ 615 nm and ~ 650 nm bands, demonstrating some degree of aggregation at higher concentrations. The fluorescence spectra of the solutions differ very slightly, however a significant decrease of fluorescence intensity is observed in the thin films with increasing concentration of the molecules, which demonstrates concentration quenching in the samples. Fluorescence kinetics of solutions and lower concentration thin films show a mono-exponential decay, while higher concentration films show a multi-exponential decay kinetics, which is described by the stretched exponential function. |
