Influence of Vibrational Excitation of Triplet Molecules of Anthraquinone on the Photochemical Processes in Gas Mixtures with Amines

By the quenching of the delayed fluorescence (DF) of anthraquinone vapors by aliphatic amines (diethylamine, dibutylamine, cyclohexylamine) and pyridine the photoinduced processes proceeding with the participation of vibrationally excited triplet molecules of anthraquinone have been investigated. The DF quenchingrate constants K _q varying from 1·10⁶ sec^–1·torr^–1 in mixtures with diethylamine to 7·10³ sec^–1·torr^–1 in mixtures with pyridine have been estimated. A correlation between the values of K _q and the ionization potentials of foreign gases confirming the important role of interactions with charge transfer in the quenching of triplet molecules in the gas phase has been established. The influence of other relaxation processes on the DF quenching is considered. It is shown that the intermolecular vibrational relaxation in the T ₁ triplet state leading to the establishment of relaxation equilibrium at a vibrational temperature T _vib considerably increasing the medium temperature is the fastest process among the biomolecular processes (rate constants K _col ^V > 10⁶ sec^–1·torr^–1 > K _q). The values of T _vib and the vibrational energies E _vib of the triplet molecules after the energy exchange in the collisional complex have been estimated. It has been concluded that the photochemical reaction yield is determined by the intermolecular processes proceeding in the T ₁ state at a vibrational equilibrium characterized by high values of T _vib. The influence of E _vib of triplet molecules on the DF quenching rates at a photoinduced electron transfer is considered.     

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.

     

Role of charge-transfer complexes in oxygen quenching of excited states of anthracene derivatives in the gas phase

Oxygen quenching of excited triplet and singlet states of gas-phase anthracene and its derivatives that have similar energies of the lower triplet levels but widely different oxidation potentials (0.44 < E_ox < 1.89 V) was studied. Quenching rate constants for singlet (k_S^O2) and triplet (k_T^O2) states in addition to the fraction of oxygen-quenched singlet and triplet states q_{S 1}(T₁^O2 were determined from the decay rates, fluorescence intensities, and delayed fluorescence as functions of oxygen pressure. It was found that k_S^O2 values vary from 2·10⁴ (9,10-dicyanoanthracene) to 1.2·10⁷ sec⁻¹·torr⁻¹ (anthracene, 9-methylanthracene, 2-aminoanthracene) and k_S^O2 values from 5·10² to 1·10⁵ sec⁻¹·torr⁻¹. The k_S^O2 values for anthracene, 9-methylanthracene, and 2-aminoanthracene, which have fast rates of interconversion from S₁ to T₁, are close to the rate constants for gas-kinetic collisions and are independent of the oxidation potentials (E_ox). The quenching rate constants k_S^O2 for the other anthracene derivatives and k_T^O2 for all studied compounds decrease with increasing free energy of electron transfer ΔG_ET, which indicates the important role of charge-transfer interactions in the oxygen quenching of singlet S_1- and triplet T₁ states. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 36–42, January–February, 2008.     

Induced Intersystem Crossing at the Fluorescence Quenching of Laser Dye 7-Amino-1,3-Naphthalenedisulfonic Acid by Paramagnetic Metal Ions

The fluorescence and triplet state quenching of 7-amino-1,3-naphthalenesulfonic acid by paramagnetic metal ions have been investigated in an aqueous medium. The basic mechanism of the fluorescence quenching involves the static and dynamic electron transfer to the paramagnetic cation. The induced S₁→T₁ intersystem crossing at fluorescence quenching of the fluorophore by Cu²⁺ cation has been found. There is a correlation between triplet state quenching rate constants and values of the efficient paramagnetic susceptibility and spin of the cations. The rate constants for the quenching pathways have been calculated.     

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.

     

Interaction of triplet excitons with excited naphthalene and deuteronaphthalene molecules in benzophenone crystals

An increase in the intensity of the exciting light is shown to cause a significant decrease in the quantum yield and rise time of the sensitized phosphorescence of impurity C₁₀H₈ and C₁₀D₈ in benzophenone crystals. Nonlinear quenching of the impurity phosphorescence occurs because one or two excitations are quenched in the interaction of triplet excitons with impurity molecules in the excited state in which they are left after the first exciton capture. Experiments show the nature of the changes in the quantum yield and the rise time of the impurity phosphorescence as the exciting-light intensity is varied from 3.6 · 10¹² to 6 · 10¹⁶ photons/cm² · sec depends strongly on the impurity concentration, the crystal thickness, and the lifetime of the triplet state of the impurity molecules. The experimental results are in good agreement with a proposed theory for the kinetics of the interaction of triplet excitons with impurity molecules in the ground and triplet states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 12–16, August, 1969.     

Study of the interaction of Na9[SbW9O33]·19.5H2O with bovine serum albumin: Spectroscopic and voltammetric methods

The interaction of Na₉[SbW₉O₃₃]·19.5H₂O (SbW) with bovine serum albumin (BSA) is studied by spectroscopic and voltammetric methods. Absorption spectroscopy of BSA and the linear sweep voltammetry of SbW proved the formation of ground-state SbW–BSA complex. Fluorescence quenching of serum albumin by SbW is also found to be a static quenching process. The binding constant K_a is 4.13×10⁴ L mol⁻¹ for SbW–BSA at pH 7.40 Tris–HCl buffer at 295 K. The number of binding sites and the apparent binding constants at different temperatures are obtained from the analysis of the fluorescence quenching data. The thermodynamic parameters determined by the Van’t Hoff analysis of the binding constants (ΔH=−80.01 kJ mol⁻¹ and ΔS=−182.85 J mol⁻¹ K⁻¹) clearly show that the binding is absolutely entropy driven. Hydrogen bonding and van der Waals interaction force play major role in stabilizing the complex. The effect of SbW on the conformation of BSA is analyzed using synchronous fluorescence spectroscopy.     

Photoinduced Electron Transfer From Carbazole to Halomethanes in a Gas Phase

Intermolecular photoinduced electron transfer (PET) in a gas phase was studied using carbazole vapor fluorescence quenching by halomethanes (CHCl₃, CH₂Br₂, CCl₄, CHBr₃). The fluorescence quenching rate constants k _q changing from 2.3·10⁵ sec^–1·torr^–1 in mixtures with CHCl₃ to 4.6·10⁶ sec^–1·torr^–1 in mixtures with CHBr₃ at a constant temperature of 403 K were estimated. The dependence of the carbazole fluorescence decay rates in the presence of halomethanes on the free energy change G during transfer of the electron from carbazole to halomethanes is considered. It is suggested to take into account the influence of the vibrational energy of the carbazole molecule E _vib and its temperature changes in estimation of the G values. The differences between PET in the gas and liquid phases were analyzed. It is found that for mixtures with CCl₄ and CHBr₃ the negative temperature dependence of k _q is observed, when the decay rates and efficiencies of the intermolecular PET decreased with temperature increase in the range 403–573 K, i.e. these mixtures the electron transfer is not a barrier-restricted process.     

Fluorescence and Laser Emission from Coumarin-Acridine Orange Mixtures

The sensitized fluorescence and laser emissions of dye mixtures; (I) coumarin 102 (donor) and acridine orange (acceptor) and (II) coumarin 47 (donor) and acridine orange (acceptor) with Hg-lamp and N₂ laser, have been measured as a function of dye concentration and of the pump power (N₂ laser). Acridine orange which does not lase by itself on excitation with N₂ laser, lases efficiently in the presence of 7-amino-coumarins via singlet-singlet energy transfer. Energy transfer rate constants and critical distances have been estimated from fluorescence intensity and lifetime measurements. The performance of energy transfer dye lasers (ETDLs) are discussed in terms of spectral characteristics of the dyes and their penetration depths.     

Study on the interaction between theasinesin and human serum albumin by fluorescence spectroscopy

The binding properties on theasinesin to human serum albumin (HSA) have been studied for the first time using fluorescence spectroscopy in combination with UV–vis absorbance spectroscopy. The results showed that theasinesin strongly quenched the intrinsic fluorescence of HSA through a static quenching procedure, and non-radiation energy transfer happened within molecules. The number of binding site was 1, and the efficiency of Förster energy transfer provided a distance of 4.64 nm between tryptophan and theasinesin binding site. At 298, 310 and 323 K, the quenching constants of HSA–theasinesin system were 2.55×10³, 2.16×10³ and 1.75×10³ mol L⁻¹. ΔH^θ, ΔS^θ and ΔG^θ were obtained based on the quenching constants and thermodynamic theory (ΔH^θ<0, ΔS^θ>0 and ΔG^θ<0). These results indicated that hydrophobic and electrostatic interactions are the mainly binding forces in the theasinesin–HSA system. In addition, the results obtained from synchronous fluorescence spectra showed that the binding of theasinesin with HSA could induce conformational changes in HSA.     

Fluorescence resonance energy transfer between acridine orange and rhodamine 6G and analytical application in micelles of dodecyl benzene sodium sulfonate

A new method for the determination of erythromycin by energy transfer fluorescence quenching of acridine orange (AO)—rhodamine 6G (R6G) in micelles solution studied and established. It was found that the effective energy transfer could occur between AO and R6G in the dodecyl benzene sodium sulfonate at and Britton-Robinson buffer (BR, pH=5.72). The fluorescence intensity of R6G had been increased sharply. Erythromycin diminished the fluorescence intensity of R6G. The detection limit was up to 0.316 mg l⁻¹. The range of determining concentration of erythromycin was 0.75-15 mg l⁻¹. The relative standards deviation were 0.66-1.38% for six parallel determinations of erythromycin. The recoveries of erythromycin were 96.95-101.41%. The measurement was applied to the determination of capsules of erythromycin with good results.     

Combined Quenching Mechanism of Anthracene Fluorescence by Cetylpyridinium Chloride in Sodium Dodecyl Sulfate Micelles

The Stern-Volmer quenching constant (K_SV) for quenching of anthracene fluorescence in sodium dodecyl sulfate (SDS) micelles by pyridinium chloride has been reported previously to be 520 M^?1 based on steady state fluorescence measurements. However, such measurements cannot distinguish static versus dynamic contributions to the overall quenching. In the work reported here, the quenching dynamics of anthracene in SDS micelles by cetylpyridinium chloride (CPC), an analogue of pyridinium chloride, were investigated using both steady state and time resolved fluorescence quenching. Concurrent measurement of the decrease in fluorescence intensity and lifetime of anthracene provide a quantitative evaluation of collision induced (i.e. dynamic) versus complex formation (i.e. static) quenching of the anthracene fluorophore. The results reveal that a combined quenching mechanism is operative with approximately equal constants of 249?±?6 M^?1 and 225?±?12 M^?1 for dynamic and static quenching, respectively.     

Fluorescence of Acridine Orange in inorganic glass matrices

Steady-state, time-resolved and polarization-resolved fluorescence studies of glasses doped with acridine orange with concentrations near 10^–3 M/L are reported. It was found that at this concentration a noticeable part of dye molecules exists in the form of dimers. By means of a polarization-resolved spectroscopic technique the structure of dimers was found to be consistent with the simple exciton theory.     

Study of the Interaction Between Apis mellifera Venom and Micro-Heterogeneous Systems

The bee venom, used in treatment of inflammatory and articular diseases, is a complex mixture of peptides and enzymes and the presence of tryptophan allows the investigation by fluorescence techniques. Steady state and time-resolved fluorescence spectroscopy were used to study the interaction between bee venom extracted from Apis mellifera and three micro heterogeneous systems: sodium dodecylsulphate (SDS) micelles, sodium dodecylsulphate-poly(ethylene oxide) (SDS-PEO) aggregates, and the polymeric micelles LUTROL^® F127, formed by poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide). Fluorescence parameters in buffer solution were typical of peptides containing tryptophan exposed to the aqueous medium, and they gradually changed upon the addition of surfactant and polymeric micelles, demonstrating the interaction of the peptides with the micro heterogeneous systems. Quenching experiments were carried out using the N-alkylpyridinium ions (ethyl, hexyl, and dodecyl) as quenchers. In buffer solution the quenching has low efficiency and is independent of the alkyl chain length of the quencher. In the presence of the micro heterogeneous systems the extent of static and dynamic quenching enhanced, showing that both fluorophore and quenchers reside in the microvolume of the aggregates. The more hydrophobic quencher (dodecyl pyridinium ion) provides higher values for K _SV and dynamic quenching constants, and SDS-PEO aggregates are most efficient to promote interaction between peptides and alkyl pyridinium ions. The results proved that bee venon interacts with drug delivery micelles of the copolymer LUTROL^® F127.     

Determination of the Probability of Intermolecular Energy Transfer of the Triplet State of a Number of Tetrapyrrole Molecules in Liquid Solutions

The quenching of the triplet state of a number of Pd porphyrins and chlorophyll a by other complexes of porphyrins with Pd and Fe in liquid solutions was investigated with the use of pulsed photoexcitation. It is shown that the experimental data are consistent with the results of a kinetic analysis of the mechanism of quenching of the triplet state through the formation of excited complexes of interacting molecules. On the basis of analytical and experimental data, the probability values of intermolecular tripletstate energy transfer have been determined: K _ET = 2·10⁴3·10⁵ sec^–1. A conclusion about the character of the excited complexes has been drawn; in particular, the distance between the molecules in the complexes has been estimated to be 5 .     

Method for determining rate constants of processes in atoms and molecules

A variant method is proposed for determination of rate constants of elementary processes occurring within a plasma, including irradiation of the plasma by resonant radiation. In the proposed variant the radiant power is varied during experiment, but remains less than the value which causes saturation of fluorescence. It is shown that this method permits simultaneous determination of several constants. The technique is demonstrated for a C₂ molecule. The effective section for thermal excitation of the level d³_g from states (X¹ _g ⁺ + a³_u) is determined, equal to 3·10^–18 cm²±80%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 19–23, October, 1988.     

Oxygen fluorescence quenching studies with single tryptophan-containing proteins

The work of Lakowicz and Weber [Biochemistry 12, 4161 (1973)] demonstrated that molecular oxygen is a powerful quencher of tryptophan fluorescence in proteins. Here we report studies of the oxygen quenching of several proteins that have a single, internal tryptophan residue. Among these are apoazurin (Pseudomonas aeruginosa), asparaginase (Escherichia coli), ribonuclease T₁ (Aspergillus oryzae), and cod parvalbumin. Both fluorescence intensity and phase lifetime quenching data are reported. By comparison of these data we find that there is a significant degree of apparent static quenching in these proteins. The dynamic quenching rate constants,k _q, that we find are low compared to those for tryptophan residues in other proteins. For example, for apoazurin we find an apparentk _q of 0.59×10⁹ M ^–1 s^–1 at 25°C. This value is the lowest that has been reported for the oxygen quenching of tryptophan fluorescence.     

Production and Application of the Langmuir Aggregates of Eosine with Cetyl Trimethyl Ammonium Bromide

The procedure of microphase adsorption–spectral correction is applied to the interaction of eosine Y (EO) to the micelles of cetyl trimethyl ammonium bromide (CTAB). The Langmuir aggregation of EO on CTAB occurs owing to microelectrostatic attraction. The results have shown that at pH 3.8, monomeric and micellar aggregates have the structure EO₅·CTAB₂ and (EO₅·CTAB₂)₃₉. The adsorption constant of an aggregate is 7.01·10⁵, its molar absorption coefficient is = 8.8·10⁴ liters·mole^–1·cm^–1 at 550 nm. Application of the aggregation of EO on CTAB gives satisfactory results for quantitative determination of cation surfaceactive agents (surfactants).     

Photodegradation and aggregation of acridine dyes adsorbed on the surface of mesoporous TiO<Subscript>2</Subscript> films

Electronic spectroscopy and laser desorption/ionization (LDI) mass spectrometry have been used to study the effects of UV exposure on acridine dyes such as acridine orange (AO) and acridine yellow (AY) adsorbed on the surface of mesoporous TiO₂ films. The main stages of the photodegradation process have been identified. The first one is photooxidative N-demethylation of the dimethylamino group in AO and deamination in AY. The following stages are photodimerization and photoaggregation on the superhydrophilic TiO₂ surface and further photocatalytic decomposition to the completely mineralized dyes.     

Elastic constants of the alloys Cd1−x Zn x (x<0.3%) and their temperature dependence

The temperature dependence of elastic constants of Cd_1–x Zn _x alloys, havingx=0.021, 0·042 and 0·233 at.%, has been measured in the temperature range from 4·2 to 300 K by the pulse-echo-overlap ultrasonic method. The adiabatic compressibilities and the Debye temperatures have been calculated. All elastic constants with the exception ofc ₄₄ increase slightly with the growing concentration of Zn.The summary of this paper was presented on the 7^th Conference on Ultrasonic Methods in ilina, September 11^th–13^th, 1980.