Fluorescent characteristics of coumarin photosensitizers

Abstract

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...

Luminescence characteristics of new substituted coumarins

“…The more fluorescent compounds were identified. The calculations [14] found that triplet states of these compounds are efficiently populated because of the proximity of levels of different orbital nature (ππ * -type and nπ * -type) as a result of spin-orbit coupling. As a result, the fluorescence quantum yields in such systems are low (≈0.007-0.080); phosphorescence yields, high (≈0.25-0.72).…”

“…The calculation was carried out directly by the INDO method with spectroscopic (triplet) parametrization [11][12][13]. Theoretical and experimental fluorescence quantum yields at room temperature have been previously compared [14]. Therefore, we include (Table 2) only experimental and calculated wavelengths of phosphorescence maxima.…”

Site Covalent Modification of Methionyl Peptides for the Production of FRET Complexes

“…The samples were excited at 354 nm, and emission spectra were recorded. Coumarin 120 (7‐amino‐4‐methyl‐1, 2‐benzopyrone) was used as a reference 34…”

“…Coumarin 120 (7-amino-4-methyl-1, 2-benzopyrone) was used as ar eference. [34] 7-Methoxycoumarin-3-carboxylic acid was used as at ag in which the methoxy group acts as an electron donor and carbonyl asa na cceptor. The fluorescencei ntensity of this coumarin dye is solvent-dependent and it increases with solvent polarity with negligible emission shift.…”

Kinetics of catalyzed hydrolysis of 4-methylumbelliferyl caprylate (MUCAP) salmonella reagent

“…Coumarin derivatives possess a wide range of applications as anticoagulants [1], antitumor [2], photosensitizers [3], anti-HIV [4], antimicrobial [5], chemosensor [6] and anti inflammatory agents [7]. Coumarin derivatives have been linked to other molecules in gene expression studies [8] as well as in salmonella detection [9].…”