Features of Emission and Absorption of Indotricarbocyanine Dyes on Excitation 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.     

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.     

关于PDT光敏剂敏化效应光谱及其量子产率的研究

从实验的角度研究了HA光敏剂激发态的敏化特性,建立了单态氧量子产率在近红外区的荧光光谱测量系统,测定了HA光敏剂的单态氧量子产率为0．78。结果表明,该类光敏剂具有较强的敏化效应,是一类有前途的光动力治疗(PDT)候选光敏剂。     

Fluorescence and Time-Resolved Delayed Luminescence of Porphyrins in Organic Solvents and Polymer Matrices

Porphyrin dyes fulfill an essential function in photosynthesis and are important in photodynamic therapy and in a range of electronic devices. Their spectroscopic characteristics may play a crucial role in these processes. The spectral properties of two porphyrin dyes: tetraphenylporphyrin and tetraphenysulfporphyrin in organic solvents (acetone, chloroform, methyl alcohol, and dimethyl-sulfoxide) and in polyvinyl alcohol and poly(methylmethacrylate) films have been investigated. Absorption, fluorescence, and microsecond time-resolved delayed luminescence spectra have been measured at room temperature. The existence of different aggregated dye forms in the ground and excited states has been demonstrated. The manifold of dye species depends on the solvent/polymer. In the case of the polymers, it also depends on the solvent used to coat the polymer film. Delayed luminescence spectra and decay times of the two porphyrins in the different solutions and in polymeric matrices suggest that different mechanisms of deexcitation of the singlet excited states may be responsible for their generation in these and other porphyrin dyes.     

Determination of the rate constant of oxygen quenching of the excited states of molecules from the singlet oxygen luminescence

We have pioneered a method of determining the rate constant of quenching of the excited electronic states of molecules by molecular oxygen from measurements of the kinetics of photosensitized luminescence of singlet molecular oxygen (^lδ_g). The method can be used in the case where the lifetime of the excited electronic state in an air-saturated solution is comparable with or larger than the luminescence time of the singlet molecular oxygen in the given solvent. It is shown that this situation is implemented on quenching, by molecular oxygen, of the excited triplet states associated with the biopolymers of tetrapyrrole molecules in aqueous (H₂O and D₂O) solutions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 401–404, May–June, 2000.     

Dynamics of photosensitized singlet oxygen generation and photophysical characteristics of chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> in photolon ointment

We have used luminescence and absorption spectroscopy to study the dynamics of photosensitized singlet oxygen generation and the photophysical characteristics of chlorin e ₆ in Photolon ointment. We have shown that dimethylsulfoxide and polyethylene glycol 400, in concentrations comparable with their content in the ointment form of the drug Photolon, do not lead to appreciable changes in the spectral characteristics of chlorin e ₆. Substantial changes in the photophysical characteristics of the photosensitizer are observed at significantly higher concentrations of the excipients in the ointment. We have shown that in buffer solution, chlorin e ₆ forms a complex with polyethylene glycol 1500. For the first time, we have detected luminescence of singlet oxygen from the surface of biological tissue treated with Photolon ointment.     

Mechanism for quenching of the luminescence of 9,10-anthraquinone vapor by oxygen

The fluorescence of 9,10-anthraquinone, 1-aminoanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone is not quenched by oxygen because the singlet-triplet energy difference in these compounds is less than the energy needed for excitation of the triplet state of oxygen to the singlet state. Luminescence of 9,10-anthraquinone is quenched because it is mainly phosphorescence, for which the singlet-triplet difference is sufficient for quenching by a mechanism involving singlet oxygen formation. The weak fluorescence of 9,10-anthraquinone is not quenched. The resistance of the fluorescence of 9,10-anthraquinone vapor to quenching by oxygen and the quenching of its phosphorescence explain the different effects of oxygen on the luminescence of α-substituted and β-substituted anthraquinones known from the literature, and indicate that their singlet excited state cannot convert triplet oxygen to singlet oxygen. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 79–4, January–February, 2008.     

Long-term luminescence of sensibilizers in tissues at the conditions of oxygen deficiency due to photodynamic effect

Long-term luminescence of organic dyes (xanthene dyes, halogen substituted fluoroscein) was used for an in vitro study of the photodynamic effect of exogenic probes in malignant tumors and healthy tissues of mice. It is shown that the photodynamic activity of oxygen and the dynamics of its concentration in tissues can be estimated from the delayed fluorescence of exogenic probes caused by singlet–triplet annihilation of singlet oxygen and excited triplet states of the molecules of photosensitizer dyes. It is found that quenching of long-term luminescence of photosensitizers significantly differs in tumors and normal tissues.

     

Luminescence-spectrum and strength properties of rhodamine 6G-doped silica gel films

Silica gel films dyed with rhodamine 6G in the sol stage are prepared and investigated. It is shown that the host matrix of the film loosens structurally as a result of intensification of the formation of dye molecular associates, lowering of the luminescence photon yield, and enhancement of the luminescence spectral sensitivity of such films to vapors of highly volatile organic solvents. Fiz. Tverd. Tela (St. Petersburg) 40, 466–471 (March 1998)     

Luminescence diagnostics of malignant tumors in the IR spectral range using Yb-porphyrin metallocomplexes

The creation and application of new low-toxic photosensitizers for the luminescence diagnostics of cancer are considered. The new photosensitizers weakly generate singlet oxygen, exhibit developed luminescence, and retain the tumor-tropic properties of the therapeutic photosensitizers. Twenty one ytterbium complexes of porphyrin compounds that differ by the substituents at the periphery of the porphyrin ring are synthesized. The absorption and luminescence spectra and the luminescence decay curves of these substances are studied. The primary toxicological and pharmacokinetic investigations are performed for the most promising compounds in the organisms of experimental animals. The experimental data prove that the Yb-porphyrin complexes are promising as low-toxic markers for the luminescence diagnostics of malignant tumors in the IR spectral range (975–985 nm) that are free of the phototoxicity typical of the conventional porphyrins at a relatively high luminescence contrast and the selective accumulation in tissue.     

Indole photodissociation in the gas phase

Kinetic characteristics of the growth in delayed luminescence intensity of indole in the gas phase have been measured with excitation of the molecules in the spectral region 250–287 nm. The luminescence build-up kinetics show two components with characteristic lifetimes of about 1 and 10 μs that are associated with the formation of free radicals due to N–H bond dissociation. Two basic mechanisms for photodissociation of indole in the gas phase have been identified based on an analysis of the dependence of the kinetic characteristics for these components on the excitation radiation wavelength/intensity and the vapor pressures of indole and foreign gases. The fast component results from the dissociation of an N–H bond of vibrationally excited molecules in the ground state that is populated through internal conversion. The slow component is associated with the generation of free radicals because of annihilation of two triplet indole molecules. A dependence of the quantum yield of intersystem crossing on the excitation wavelength in the spectral region 260–287 nm has been found. It is shown that the fluorescence quantum yield drop with a decrease of the excitation radiation wavelength is caused by an increase in the internal conversion quantum yield to the electronic ground state.     

White luminescence of a system based on poly(9,9-di(ethylhexyl)fluorene) activated by fluorescent dyes

Luminescence has been studied for poly(9,9-di(ethylhexyl)fluorene) containing laser dyes which fluoresce in the green and red spectral regions. It has been shown that white luminescence can be obtained as a result of singlet-singlet energy transfer from the polymer matrix to the dyes at certain concentrations of the latter. Two systems are proposed that make it possible to obtain equi-energy white emission and white emission, taking into account the characteristics of the spectral sensitivity of the human eye. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 37–41, January–February, 2007.     

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ_F?≈?0.002–0.004), and short singlet state lifetime (τ_expt?≈?20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ_??≈?0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M^?1 cm^?1). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ_max?≈?640–650 nm, and a ?≈?0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

     

Dual-band lasing of benzopyran dyes in the red region of the spectrum

We have studied the spectral and energy characteristics of lasing for two benzopyran dyes in a dispersive cavity with a diffraction grating when the dyes are excited at several different wavelengths using an additional flashlamp-pumped dye laser. These dyes have high fluorescence quantum yield and lase efficiently in the red region of the spectrum. The tuning range of their lasing spectrum is greater than 100 nm. We discuss the characteristic features of conversion of the selective excitation energy by these dye molecules. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 401–404, May–June, 2006.     

A mathematical model of the photodynamic fullerene-oxygen action on biological tissues

A kinetic model of the photodynamic fullerene-oxygen action on biological tissues is developed. The efficiency of generation of singlet oxygen is studied in relation to the intensity of exciting radiation and the concentrations of fullerene and oxygen. The spectral efficiencies of singlet oxygen generation upon irradiation of a biological tissue by a lamp and different lasers are studied and compared with each other. The power of luminescence of singlet oxygen is calculated. The spatial distributions of singlet oxygen in allantoic fluid and in murine sarcoma are studied. The oxidation of lipids of external membranes is assumed to be the basic mechanism of cell damage. The characteristic time of this oxidation is calculated. The dose curve of cell survival is estimated. The results of modeling are compared with experimental data in the literature.     

Color and Luminescence Centers in LuAG and Pr:LuAG Crystals Before and After <Superscript>60</Superscript>Co γ-Irradiation

Entire luminescence spectrum of a commercial photosensitizer Radachlorin in aqueous solution has been recorded under laser excitation at 660 nm and analyzed. The peak of singlet oxygen phosphorescence at 1274 nm has been observed. The results obtained were compared with those recorded with laser excitation at 405 nm and reported earlier. The comparison showed the similarity of relaxation and luminescence processes occurring in both cases. Effective absorption cross sections were determined at each excitation wavelength, it was also shown that the singlet oxygen quantum yield is independent of photosensitizer concentration. The lifetime of the first excited triplet state in Radachlorin was determined. The results obtained can be used for optimization of the conditions of singlet oxygen generation and detection in solutions and biological samples.     

Specific features of the radiative relaxation of excited states of polymethine dyes of different ionicity in films of photoconductive and nonphotoconductive polymers

The spectral and luminescent properties of film composites based on photoconductive poly-N-epoxipropylcarbazole and nonphotoconductive polyvinylbutyral with admixtures of cationic and anionic polymethine dyes, as well as the effect of an external magnetic field on these properties, are studied. It is found that the magnetic field affects the intensity and kinetics of the delayed fluorescence and recombination luminescence of the cationic dye in photoconductive films. This is explained by specific features of photogeneration of charge pairs, namely, by the participation of the singlet and triplet excited states of dye molecules in this process, as well as by the singlet-triplet conversion in dye molecules and photogenerated charge pairs.     

Electron impact excitation of luminescence of uracil

We have measured the luminescence spectra of isolated uracil molecules in the wavelength range of 200–500 nm that were excited by slow electrons. The spectrum contains more than 20 spectral bands and lines. We show that the luminescence spectrum of uracil is formed by processes of dissociative excitation of molecules, dissociative excitation with ionization, and excitation of electronic states of the initial molecule and molecular ion.     

Spectroscopic characteristics of activated tungsten phosphate glasses in the VUV region

Absorption, reflection, excitation, and quantum yield spectra of the luminescence of Eu³⁺-activated tungsten phosphate glasses were investigated within the range 30,000–95,000 cm⁻¹. It is shown that the differences between the ligands in the first coordination sphere of tungsten and the effects of their mutual influence are responsible for the appearance of tungsten groups WO ₂ ²⁺ with an increased multiplicity of the tungsten—oxygen bond. The spectroscopic properties of tungsten complexes are associated with electron transitions from three completed orbitals that have the character of transitions with charge transfer from the ligands to the coordinating center. This leads to a kind of localization of excitation in the WO ₂ ²⁺ group and ensures constancy of the quantum yield of luminescence in a wide spectral range. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 433–435, July–August, 2000.     

Synthesis and luminescence of a folic acid-europium chelate conjugate

We have synthesized a folic acid–europium complex conjugate which shows promise for biomedical applications. We have studied the absorption spectra, the luminescence spectra, and the luminescence excitation spectra of folic acid–spacer–amino-substituted phenanthroline and folic acid–spacer–europium chelate conjugates, and also of the individual components of the synthesized triads. All the spectral luminescence data obtained confirm that a folic acid–europium complex conjugate is fogrmed. Binding of the synthesized conjugate to a folate receptor on HeLa tumor cells is demonstrated.