The possibility of application of natural photosynthetic pigments and their derivatives in photodynamic therapy and photodynamic diagnosis has been investigated. The triplet states of dyes are highly photochemically active, therefore, the dyes exhibiting high efficiency of triplet states generation are usually efficient photosensitizers in photodynamic therapy. Generation of triplet states has been estimated by means of the laser induced optoacoustic spectroscopy. The type of the photoreaction was established by comparing the yield of triplet generation with and without the oxygen presence. The intersystem crossing transition from excited singlet state S1 to triplet state T1 is competing with fluorescence emission, therefore, the dyes with efficient triplet generation usually are not suitable for diagnosis which requires a high yield of fluorescence.
The chlorophyll-like pigments of prospective applications in medicine have been studied. Preliminary selection of dye-sensitizers has been made on the basis of investigation of the same dyes in model systems (solutions) and their complexes with macromolecules. The final study has been performed for resting (healthy) and stimulated (cancerous cells models) lymphocytes. Of course, the properties of sensitizers in cells and in models are not the same, but the measurements have enabled a selection (from a set of similar molecules) of the most promising dyes, tested later in the cells. The results obtained for chlorophyll-like pigments are compared with those obtained for the synthetic dyes (porphyrins, stilbazolium merocyanines and phthalocyanines) earlier investigated in our laboratory and with literature data.
The delayed luminescence of the various glass and quartz plates as well as of deposited semiconducting and orientating layers was investigated. The shape of emitted delayed luminescence spectrum was different for various samples, but the intensity of this emission can not be neglected in the case of optical systems in which low intensity emission is investigated. Through the proper choice of the material and thickness of the plates, these perturbing effects can be diminished. The lowest delayed luminescence from investigated samples exhibits the quartz Suprasil SQ1. The delay luminescence is practically not diminished and the decrease in temperature from 295 K to 8 K shows that this emission is not generated with the participation of thermal energy.
Chlorophyll a (Chl) in most model systems (monolayers, fluid solvents, adsorbed layers, and polymer films) occurs in three forms: `dry monomers' (isolated from interaction with water), hydrated dimers and oligomers built from such dimers; but in nematic liquid crystal (LC) cell `dry monomers' are predominant. It is a competition between the various paths of deactivation of excited Chl. Excitation energy can be emitted as fluorescence, or delayed luminescence, transferred to other forms of Chl (ET), thermally deactivated or used for photochemical reactions. In order to compare the efficiency of these various paths the following measurements were done and analyzed: absorption, fluorescence, fluorescence excitation, photoacoustic spectra, and lifetime of fluorescence in ps range. There are some important differences between Chl in LC cell and polymer films: Chl in LC cell has a much lower concentration of aggregated forms and the pigment molecules are more uniformly distributed as compared to the Chl in polymer samples. To explain ET in polymer films the fractals model has to be used, whereas mean distances between solvated Chl molecules in LC can be obtained from dye concentration. In order to establish the interaction between Chl a and (beta) -carotene the LC cell with both pigments were also investigated.
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