Inductive-resonant triplet-triplet annihilation in solid solutions of erythrosine

Experimental investigations of annihilation-induced delayed fluorescence and phosphorescence of frozen ethylene glycol solutions activated by erythrosine were carried out. It is found that the kinetics of the annihilation-induced delayed fluorescence is nonexponential in the initial stage, and approaches an exponential decay at later stages with the lifetime equal to half the triplet-state lifetime. It is shown that experimental data agree well with the theory proposed to describe triplet-triplet annihilation by an inductive-resonant mechanism in solid solutions of complex organic molecules. Belarusian State University, 4, F. Skorina Ave., Minsk, 2200050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 629–632, September–October, 1997.     

Heterogeneous triplet-triplet annihilation of erythrosine and anthracene molecules on a fractal anodized aluminum surface

We have studied exchange resonance processes of homogeneous triplet-triplet annihilation and heterogeneous triplet-triplet annihilation for erythrosine and anthracene molecules on an anodized aluminum surface over a broad temperature range. We have shown that the kinetics of the considered processes are determined by the dimensionality of the molecular clusters on the porous anodized aluminum surface. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 205–210, March–April, 2007.     

Kinetics of triplet-triplet absorption of anionic water-soluble porphyrins

It was established that in aqueous solutions of anionic porphyrins the processes of triplet-triplet (T-T) annihilation are absent (K₂<2.5·10⁵ M⁻¹ sec⁻¹), while a delayed annihilation fluorescence can be detected for these porphyrins in methanol (K₂≊3.5·10⁷ M⁻¹ sec⁻¹) and for their lipophilic analogs in organic solutions (K ₂≊2.5·10⁹ M⁻¹ sec⁻¹), and the kinetics of absorption of the latter porphyrins in triplet states is dependent on the intensity of the exciting radiation. The extremely small constant of T-T annihilation of anionic porphyrins can be due to the formation of a relatively dense solvate shell consisting of water molecules around the charged groups of the porphyrin molecules, which increases steric barriers and thus prevents an exchange-resonance transfer of energy between triplet excited molecules in aqueous solutions. It is also shown that porphyrin molecules can electrostatically repel one another when in their structure there are charged groups. To whom correspondence should be addressed. Deceased. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus; e-mail: llum@imaph.bas-net.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 791–795, November–December, 1999.     

Homo- and Heteroannihilation of Triplet-Excited Bengali Rose and Anthracene Molecules on Silica in a Wide Temperature Range

The processes of triplet-triplet annihilation of the triplet-energy donor of Bengali rose dye and anthracene acceptor adsorbed on the surface of wide-pore silica have been investigated in the temperature range 150–290 K. The rate constants of homo- and heteroannihilation of the molecules of luminophors have been determined in a wide temperature range. It has been established that the processes of energy transfer in the initial (after photoexcitation) periods of phosphorescence decay are described by the Inokuti–Hirayama equations modified in the present work for a two-dimensional problem, whereas in the mean-time and long-time periods the kinetics of phosphorescence decay becomes similar to the fractal one.     

Regularities of triplet-triplet annihilation of aromatic hydrocarbons in aqueous micellar solutions of sodium dodecyl sulfate

Investigation of deactivation processes in triplet states of a series of aromatic hydrocarbon molecules (antracene, 1,2-benzantracene, and 3,4-benzpyrene) made it possible to reveal the presence of triplet-triplet annihilation of the molecules in aqueous micellar solutions of sodium dodecyl sulfate. It is shown that the effect of microheterogeneous solutions on the process of triplet-triplet annihilation manifests itself in an increase in the probability of excimerization upon dissociation of triplet pairs of 1,2-benzantracene and 3,4-benpyrene molecules compared to one-component solutions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 626–628, September–October, 1997.     

Determination of the rate constants of excited-complex formation and the diffusion rate constants for triplet-triplet annihilation kinetics for tetrapyrrole molecules in liquid solutions

With the flash-photolysis method, the kinetis of triplet-triplet annihilation (TTA) is investigated for a number of tetrapyrrole molecules in liquid solutions. Based on the analysis of the kinetic scheme of TTA through the formation of excited complexes (TT) a procedure for determining the constant of the rate of (TT) formation from two molecules in the triplet state (k₁) is proposed. The k₁ values obtained are equal to the rate constants for the processes controlled by molecular diffusion in the solution (K_d), which are calculated by a modified Vavilov-Debye formula. The values of K_d can be determined experimentally by the proposed procedure for processing the data on TTA. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 521–527, July–August, 1998.     

Long-lived luminescence of complex molecules

Results of investigations of all types of long-lived luminescence of organic molecules in the gas phase and condensed media are presented. Methods for identification and separation of contributions of phosphorescence and thermally activated fluorescence in long-lived luminescence of organic-molecule vapors are proposed. Energy transfer and migration processes in the case of the inductive-resonant mechanism of intermolecular interaction leading to the appearance of sensitized phosphorescence and annihilation-induced delayed fluorescence are considered. Experimental results on energy migration obtained for solid solutions of organic compounds are analyzed within the framework of the concepts of percolation theory with account for the microscopic inhomogeneity of the systems under investigation and the fractal properties of the clusters of activator molecules. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, F. Skorina Ave., 70, Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 662–674, September–October, 1998.     

Mechanism of singlet-oxygen induced delayed fluorescence of bacteriopheophytin in laser excitation

The relative intensity of photosensitized phosphorescence of singlet oxygen (¹O₂) at 1270 nm (L₁₂₇₀) and¹O₂-induced delayed fluorescence (L_df) of bacteriopheophytin a (BPh) (770 nm) in air-saturated solutions of BPh in hexafluorobenzene in excitation by 337-nm pulses of a nitrogen laso is investigated. It is established that L_df≪L₁₂₇₀. The ratio of the initial intensity of delayed fluorescence and phosphorescence of¹O₂(L_df)₀/(L₁₂₇₀)₀ changed from 0.02 to 0.30 as a function of the energies of laser pulses (2.5–5.0 mJ/cm¹) and the BPh concentration (6–18 μM). As the index of quantum efficiency of the delayed fluorescence, the authors used the coefficient

Phenylalanine fluorescence and phosphorescence used as a probe of conformation for cod parvalbumin

The fluorescence emission and triplet absorption properties of phenylalanine in cod fish parvalbumin type II, a protein that contains no Trp or Tyr, was examined in the time scale ranging from nanoseconds to microseconds at 25°C in aqueous buffer (pH 7.0). In the presence of Ca(II), the decay of fluorescence gave two lifetimes (5.9 and 53 ns) and the triplet lifetime was 425 s. Upon removal of Ca, the fluorescence intensity decreased to values approaching that for free Phe, while the longest fluorescence decay component was 17 ns. At the same time, the decay of triplet showed complex nonexponential kinetics with decay rates faster than in the presence of Ca. Quenching and denaturation analyses suggest that the Phe's are present in a hydrophobic environment in the Ca-bound protein but that the Ca-free protein is relatively unstructured. It is concluded that Phe luminescence in proteins is sensitive to conformation and that the long lifetime of Phe excited states needs to be considered when studying its photochemistry in proteins.     

利用磁致发光曲线研究Rubrene器件中激子分裂和湮没过程

为了研究Rubrene分子中激发态的能量共振和分子间π-π共轭的特性对有机磁效应的影响, 本文制备了基于不同浓度和厚度的Rubrene有机发光器件, 并在不同温度下测量了器件的电致发光磁效应(magneto-electroluminescence, MEL). 实验发现, 发光层中Rubrene的厚度和浓度均可以对器件中的MEL产生较大的影响, 室温下MEL的高场值随Rubrene层厚度的增加而增加, 并在30 nm之后逐步趋于饱和; 随着Rubrene分子的浓度和测量温度的降低, MEL高场增加的幅度逐渐减小, 甚至在低温时出现高场下降. 通过对实验曲线进行数值拟合, 认为Rubrene分子之间形成的π-π共轭结构有助于双分子相互作用的发生, 单重态激子分裂、三重态激子之间的湮没和单-三重态极化子对的系间窜越三种过程在器件中相互竞争导致了所得MEL的变化. 本工作有助于加深对有机光电子器件内部机理的认识.     

Characteristic features of carbazole phosphorescence quenching by benzophenone molecules in toluene at 77 K

We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 554–556, July–August, 2006.     

Quenching of fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules

We have studied the mechanisms for quenching of the fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules. We have shown that molecules in the diketone series are quenching agents for the fluorescence of the indicated polymers, and can serve as singlet-triplet converters capable of populating the triplet state of the polymer. We have observed that the efficiency of quenching of the fluorescence of the studied polymers depends considerably on the presence of bulky side groups in the polymer or in the activator molecules. Based on analysis of the data obtained, we conclude that in the case of a rigid planar structure for the polymer, a significant contribution to quenching of its fluorescence comes from not only singlet-singlet energy transfer but also charge transfer, leading to formation of intermolecular complexes (exciplexes). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 756–762, November–December, 2006.     

Delayed Luminescence of 8-Aza-D-Homogone-1,3,5(10),13-Tetraene-12,17a-Dione in the Gas Phase and Solid Solutions

It is shown that the delayed-luminescence spectrum of 8-aza-D-homogone-1,3,5(10),13-tetraene-12,17a-dione (8-aza-D-homogonane) in the gas phase comprises a band of thermally activated delayed fluorescence and a band of annihilation delayed fluorescence that are respectively due to the C- and D-centers representing products of photo-and thermotransformations of the initial steroid for which we failed to detect delayed luminescence. The triplet-triplet energy transfer from the C-centers to the D-centers has been detected and its efficiency has been determined. It has been established that, in a frozen hexane solution (T = 77 K) of the substance taken from a vacuum cuvette after the investigation of initial 8-aza-D-homogonane in the gas phase, only the C- and D-centers phosphoresce. For a frozen solution of the initial steroid in a vitrifying mixture of tetrahydrofuran and toluene, a phosphorescence of both the steroid itself (λ _max ^phos = 415 nm) and the C- and D-centers (λ _max ^phos = 498 and 532 nm, respectively) was detected. This indicates that even the initial steroid kept at room temperature contains products of its transformation whose concentration increases on irradiation and heating. The C- and D-centers are stable molecules.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 192–197, March–April, 2005.     

Steady-state fluorescence and phosphorescence spectroscopic studies of bacterial luciferase tryptophan mutants

Bacterial luciferase, which catalyzes the bioluminescence reaction in luminous bacteria, consists of two nonidentical polypeptides, and . Eight mutants of luciferase with each of the tryptophans replaced by tyrosine were generated by site-directed mutagenesis and purified to homogeneity. The steady-state tryptophan fluorescence and low-temperature phosphorescence spectroscopic properties of these mutants were characterized. In some instances, mutation of only a single tryptophan residue resulted in large spectral changes. The tryptophan residues conserved in both the and the subunits exhibited distinct fluorescence emission properties, suggesting that these tryptophans have different local enviroments. The low-temperature phosphorescence data suggest that the tryptophans conserved in bot the and the subunits are not located at the subunit interface and/or involved in subunit interactions. The differences in the spectral properties of the mutants have provided useful information on the local environment of the individual tryptophan residues as well as on the quaternary structure of the protein.     

Features of sensitized phosphorescence and delayed annihilation fluorescence spectra of coronene in frozen solutions

We have studied the sensitized phosphorescence spectra of coronene in toluene and its delayed annihilation fluorescence spectra in n-decane at 77 K. We show that as a result of perturbation of electronic states by exchange interactions, intensity redistribution occurs in both the sensitized phosphorescence spectrum and the delayed annihilation fluorescence spectrum. The nonzero probability of the symmetry-forbidden radiative 0–0 transition is explained by the lower symmetry of the bimolecular system compared with the symmetry of the coronene molecule.     

B-type delayed fluorescence of rubreneperoxide in solution.

B-type of delayed fluorescence was observed for the first time for rubreneperoxide. Rubreneperoxide molecules were excited in a two step process. In the first step an excited singlet S₁ is created, which undergoes intersystem crossing to T₁; then T-T absorption creates an excited triplet rubreneperoxide molecule, which returns to the first excited singlet level by intersystem crossing. The recreated first excited singlet of rubreneperoxide decays back to the ground state by emitting B-type of delayed fluorescence.     

Excited state dynamics of new-type thermally activated delayed fluorescence emitters: theoretical view of light-emitting mechanism

Excited state dynamics of two new-type thermally activated delayed fluorescence emitters (DABNA-1 and DABNA-2) synthesised based on multiple resonance effect is studied based on first-principles calculation, and their light-emitting mechanism is explored. The excited state dynamics combing with the adiabatic energy structure of several low-lying excited states indicates that three lowest triplet states are involved in the light-emitting process. The analysis of reorganisation energy indicates different performances for two molecules in solvent and in film. Our theoretical work provides rational explanation for experimental results, and also gives clear picture for light-emitting mechanism of these new-type molecules.     

Quenching of excited complexes by Fe-octaethylporphin in triplet-triplet annihilation of Mg-phthalocyanine in liquid solutions

The effect of triplet-state quenchers on the kinetics of triplet-triplet annihilation (TTA) of Mg-phthalocyanine (Mg-Phc) is studied. It is found that the rate constant of triplet-state quenching caused by TTA increases with increasing concentration [Q] of quenchers. The maximum values of the relaxation parameter of triplet states are proportional to [Q]². The experimental data correspond to TTA with the formation of TT complexes from molecules in triplet states. The proportionality of the decay rate of TT complexes into molecules in the ground state to [Q]² suggests that two quenching molecules are required for quenching one TT complex. It seems that the complex contains two locally excited triplet states of individual molecules. The spin correlation time in the triplet state seems to be longer than the average lifetime of complexes (≤10^?4 s). The quenching probability of triplet states in complexes (caused, in particular, by the energy of charge transfer) is lower than the probability of intermolecular triplet energy transfer to the quencher levels.     

Quenching of the triplet state of tetrapyrrole molecules by Ni-, Ag-, and Fe-porphyrins and formation of excited complexes and photoproducts

Using the method of pulse photolysis, we studied the quenching of the triplet state (TS) of a number of tetrapyrrole molecules by complexes of Ni-, Ag-, and Fe-porphyrins in liquid solutions at a temperature of ∼298 K under the conditions where the kinetics are markedly affected by the triplet-triplet annihilation of the molecules of energy donors. In the analysis of experimental data, derivatives for the time dependences of the optical density of the triplet-triplet absorption were determined. The triple-triplet annihilation process was considered for the case of the formation of excited a triplet-triplet complexes of two molecules in the triplet state. A procedure of determining the rate constant for the quenching of the triplet state by foreign molecules (K_q) under the effect of such triplet-triplet annihilation process is proposed and the values of K_q are obtained. For some donor-quencher pairs it is found that the kinetics of the triplet-state deactivation are affected by the formation of short-lived particles with lifetimes both shorter and longer than the triplet-state lifetimes. The conclusion is drawn that such particles are respectively the excited complexes of interacting molecules or ion radicals formed from such complexes in polar solvents. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 296–300, May–June, 2000.     

乙醇-水团簇分子形成激基缔合物及荧光发射机理研究

紫外光照射具有特殊结构的长链式乙醇-水团簇分子时,处于激发态和基态的分子形成了分子间激基缔合物,并发射荧光.根据实验结果分析和能量转移理论可知,激发态单分子和激基缔合物间形成了电子迁移洛合物并发生了能量转移.根据Mulliken理论对电子迁移洛合物进行量子力学处理,得出了团簇分子在基态和激发态能量E^b_N和E^b_E以及由于电子迁移而引起的静电相互作用能E^s;根 关键词： 荧光光谱 激基缔合物 电子迁移 乙醇-水团簇