Features of emission and absorption of indotricarbocyanine dyes on extitation to higher electronic states

The manifestation of ion pairs in the absorption and emission of fluorescence by symmetric indotricarbocyanine dyes with the same cation and anions Br, I, and BF4 in ethanol, methylene chloride, and dichlorobenzene has been investigated. It is shown that the formation of ion pairs on passing to low-polarity solvents, along with the changes in the electronic absorption and emission spectra, manifests itself in the polarization and fluorescence excitation spectra. We were the first to establish that the presence of an equilibrium mixture of contact ion pairs and free ions in solutions has an effect on the position and probabilities of transitions not only for the first but also for higher excited singlet states of the molecules of polymethine dyes. The formation of ion pairs manifests itself more clearly when the spectral-luminescence properties of compounds in the shortwave spectral region are analyzed. It has been established that marked changes arise in the absorption, excitation, emission, and polarization fluorescence spectra, as well as in the lifetime and quantum yield of fluorescence in this spectral region when the solvent is changed

Generation of singlet oxygen by indotricarbocyanine dyes in low-polarity media

We present the results of a study of the spectral luminescence properties of three groups of indotricarbocyanine dyes, each of which is formed from compounds with the same cation and different anions. In high-polarity solvents, in the absorption and emission spectra of the dyes we see one type of center; in low-polarity solvents, due to the presence of different ionic forms of the dyes (free ions, contact ion pairs), we observe either one type or two types of centers. By analysis of the luminescence of molecular oxygen in the 1.27 µm spectral region, we determined the efficiency of photosensitization of 1O2 formation by dyes in deuterated solvents. We have shown that in low-polarity solvents, the yield for singlet oxygen generation is higher for indotricarbocyanine dyes which are found in the contact ion pair state and which also contain a heavy atom (I) in the anion. We have observed that an increase in the fraction of contact ion pairs in solution as the dye concentration increases or when an additional salt is introduced leads to an increase in the quantum yield for generation of singlet oxygen. In polar deuterated acetonitrile, the counterion has no effect on the efficiency of photosensitization of oxygen by the dyes

Spectral-luminescent properties of cationic indotricarbocyanine dyes in cancerous cells and solutions

The spectral-luminescent properties of symmetrical indotricarbocyanine dyes with the same cation and different anions (Br−, BF4−) in cancerous HeLa cells, an isotonic solution of NaCl, and organic solvents have been investigated. It is shown that when these dyes are present in cells in nontoxic concentrations, they are in a monomeric state, they are localized in the region with a low dielectric permeability, bonded to biological macromolecules, and do not make contact with an aqueous medium. It has been established for the first time that the molecules of the polymeric dyes are present in cells predominantly in the form of contact ion pairs, and in a dye with the Br− anion the presence of free cations or solvately separated ionic pairs is revealed. It is shown that the shift of the ion equilibrium toward contact ion pairs for the dyes in the cells (as compared to the low-polarity organic solvents) can be due to the fairly high concentration of salts in the biosystem

Spectral Properties of Thioflavin T and Its Complexes with Amyloid Fibrils

Comparative analysis of the absorption and fluorescence spectra and fluorescence excitation spectra of thioflavin T (ThT) in various solvents and in the composition of amyloid fibrils has shown that ThT, when excited in the region of the long-wavelength absorption band, fluoresces in the spectral region with a maximum at 478–484 nm. The appearance in aqueous and alcohol solutions of a fluorescence band with a maximum near 440 nm has been attributed to the presence in the composition of the ThT preparations of an impurity with an absorption band in the 340–350-nm range. The literature data showing that in glycerol ThT has a wide fluorescence spectrum with two maxima are due to the artifact connected with the use of a high concentration of the dye. It has been suggested that the cause of the low quantum yield of ThT aqueous and alcohol solutions is the breakage of the system of conjugated bonds due to the reorientation of the benzothiozole and benzaminic rings of ThT in the excited state with respect to one another. The main factor determining the high quantum yield of fluorescence of ThT incorporated in fibrils is the steric restriction of the rotation of the rings about one another under these conditions. The suggestions made have been verified by the quantum-chemical calculation of the ThT molecule geometry in the ground and excited states

Extrinsic Fluorescent Dyes as Tools for Protein Characterization

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization

Spectral-luminescent properties of cationic indotricarbocyanine dyes in cancerous cells and solutions

The spectral-luminescent properties of symmetrical indotricarbocyanine dyes with the same cation and different anions (Br−, BF4−) in cancerous HeLa cells, an isotonic solution of NaCl, and organic solvents have been investigated. It is shown that when these dyes are present in cells in nontoxic concentrations, they are in a monomeric state, they are localized in the region with a low dielectric permeability, bonded to biological macromolecules, and do not make contact with an aqueous medium. It has been established for the first time that the molecules of the polymeric dyes are present in cells predominantly in the form of contact ion pairs, and in a dye with the Br− anion the presence of free cations or solvately separated ionic pairs is revealed. It is shown that the shift of the ion equilibrium toward contact ion pairs for the dyes in the cells (as compared to the low-polarity organic solvents) can be due to the fairly high concentration of salts in the biosystem