We present a theoretical and experimental study of the fluorescent ability of new coumarin sensitizers. Using the INDO method, we have drawn the level diagram for the photophysical processes in the coumarin molecules. We have calculated the rate constants for internal conversion and intersystem crossing and the radiative rate constants. We have determined the experimental and theoretical fluorescence yields of the test compounds.Introduction. Coumarins are a group of organic dyes in the blue-green range. These compounds are widely used in different fields of science and technology. For example, many coumarins exhibit intense fluorescence, which is used to design fluorescent labels, optical brighteners, laser active media, and organic light-emitting diodes [1,2]. At the same time, a change in structure can lead to creation of coumarins having good photosensitizing properties.Furocoumarins (psoralenes) are heterocyclic aromatic compounds having photosensitizer properties in the UV radiation range, 320-400 nm [3]. Usually photosensitization is an undesirable phenomenon [4,5], leading to light-induced burns on the skin and eyes for low exposure doses which, under ordinary conditions, do not have a damaging effect. However, sometimes the combined action of light and the photosensitizer causes positive therapeutic effects. Photochemotherapy methods have been devised based on such combination effects of light and dyes on the human body.A number of substances from this group of compounds have properties enabling their use in photochemotherapy of various skin diseases (psoriasis, atopic dermatitis, rheumatoid arthritis, vitiligo) [6,7]. Many substituted coumarins display anticoagulant activity, which is used for therapy of thromboses. In recent years, compounds in this class have also begun to be used for photoinduced modification of nucleic acids, for phototherapy of cancer and viral infections (including HIV infections), and also in transplantology to prevent rejection of transplanted tissues. Despite their widespread popularity, this class of compounds still remains poorly studied.Some compounds in the substituted coumarin series act as bifunctional photoreagents, capable of crosslinking both DNA strands [5,8]. Besides photoreactions of furocoumarins with DNA to form adducts (type III reactions), other types of photochemical reactions are possible [9]. For structurally different furocoumarins, the ratio of the contributions of the different types of photoreactions may vary significantly. The increasingly expanding use of furocoumarins as photosensitizers and photoreagents urgently requires determining the relationship between their structure, spectral luminescence properties, and the primary photoprocesses occurring in them. We may hypothesize that it is specifically the spectral luminescence and photophysical properties and their dependence on the structure of the compound that to a significant extent will determine the later course of both photochemical and photobiological processes, since they all occur with partici...
