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.     

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.     

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.     

Spectroscopic study of the interaction between porphyrin and chlorin molecules of opposite charge in solutions

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, Minsk, 220072, 70, F. Skorina Ave., Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 152–163, March–April, 1995.     

Photoinduced electron transfer in solutions of A Pd-porphyrin-quinone complex

Photoinduced electron transfer (PET) in a Pd-porphyrin-quinone complex (Pd-P-Q) was investigated using the flash photolysis method in microsecond and picosecond range and by luminescence. The investigations were performed for toluene solutions. Intramolecular PETs in the lower excited singlet state (k_CT=1.7·10¹⁰ sec⁻¹) and in the triplet state (k_CT=2.5·10⁸sec⁻¹) were observed. For a quantum yield of the triplet state that is close to 1 in Pd-porphyrin (Pd-P) this yield is equal to 0.4 in Pd-P-Q. This decrease is the result of PET in the excited state and, possibly, in an unrelaxed triplet state. Triplet Pd-P-Q molecules were efficiently quenched by unexcited molecules, and this process is related to intermolecular charge transfer. This electron transfer is likely to occur from the Pd-P protion of an excited molecule to the quinone protion of an unexcited molecule in the collisional complex (Pd-P-Q)₂. Charged radicals, formed once the collisional complex is transferred and separated, have a wide absorption band with a maximum of about 960 nm. The average lifetime of the radicals was about 2 msec. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No 1 pp. 61–70, January–February, 1997.     

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.     

Mechanism of formation and spectral characteristics of triplet excimers of Pd-porphyrins in liquid solutions

Concentration quenching of the triplet state (CQTS) of a number of Pd-porphyrins in toluene is investigated. Based on an analysis of experimental results, a conclusion is drawn that such quenching proceeds via formation of exciting complexes from molecules in the ground and triplet states (TS). From a small value of decay rate constants of the complexes it follows that these complexes are triplet excimers but not complexes due to collision. It is established that by increasing the concentration of porphyrins the maxima of their phosphorescence bands shift toward large wavelengths by a value of up to 3 nm and the bands, as a consequence, broaden by 5–7 nm. The formation of excimers is explained by enhancement of solvophobic dispersion interactions of molecules in the TS. Relatively small changes in the phosphorescence spectra upon formation of excimers are attributable to these interactions. The magnitude of dipole-dipole interaction of molecules in the TS is insignificant since the dipole moment of the T↭S transition is small. On the basis of consideration of the oxidation-reduction and energy characteristics of the compounds, it is shown that the interaction with charge transfer in the case of the CQTS of Pd-porphyrins is inefficient. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 857–863, November–December, 1998.     

Kinetics of Triplet-Triplet Annihilation of Mg-Phthalocyanine in Methanol and Deuteromethanol

Using the method of flash photolysis, the effect of deuteration of a solvent on the kinetics of triplet-triplet annihilation is studied on the example of Mg-phthalocyanine (Mg-Phc) in methanol-h ₄ and methanol-d ₄ at 298 K. The time and concentration kinetic dependences are different in different solvents, which cannot be explained only by the difference in the viscosity of the latter. The experimental data are analyzed based on consideration of the triplet-triplet annihilation mechanism via the formation of triplet-triplet complexes from molecules in a triplet state. It is established that in methanol-d ₄ the constants of the rates of monomolecular deactivation of the triplet state and of the decomposition of the complexes is 1.5–2 times smaller than in methanol-h ₄. The effect of deuteration is explained by the decrease in the rate of dipole-dipole energy transfer from the triplet state of the pigment to the solvent molecules in deuteration.     

Positron annihilation study for cadmium (electronic structure and enhancement effect)

The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.     

Reasons for the difference between the rate constant of quenching of the triplet state and the diffusion rate constant of chlorophyll-like molecules

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 1, pp. 110–116, January, 1989.     

Intermolecular hydrogen bonds in acetic acid and its solutions

The band at 896 cm⁻¹ in the Raman spectrum of acetic acid consists of at least two lines (873 and 896 cm⁻¹) whose intensities and depolarization factors differ strongly. A temperature increase leads to an increase in the intensity of the 873-cm⁻¹ line as compared to the intensity of the 896-cm⁻¹ line. Dilution of the acid with acetonitrile leads to a similar but much more pronounced effect. In solutions with CCl₄ and water, the relative intensity of the low-frequency line decreases; in aqueous solutions, the width of the 896-cm⁻¹ line passes through a maximum with 0.4 mol. fractions of the acid (for this concentration, the line width is larger by a factor of 2.5 than in a pure liquid), while in the solutions with CCl₄ it decreases smoothly (almost twofold with strong dilution: 0.05 mol. fractions). Experimental data are in agreement with the assumption that the 873- and 896-cm⁻¹ lines refer to the vibrations of the same atoms in a molecule and to associates with a free and an H-bonded atom of the oxygen of a C=O group, respectively. The difference in the frequencies and depolarization factors of the lines causes the differences in the distribution of an electron cloud in the molecule. To whom correspondence should be addressed. Alisher Navoi Samarkand State University, 15, Universitetskaya Str., Samarkand, 703004, Uzbekistan. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 467–470, July–August, 1999.     

Effect of the reabsorption or radiation in the lines on the rate of ionization and recombination processes in a nonequilibrium plasma

To whom correspondence should be addressd.     

Specific features of the generation of aqueous solutions of Rhodamine 6G in laser pumping

M. V. Lomonosov Moscow State University, Vorob'yovy Gory, Moscow, 119899, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 63, No. 2, pp. 236–241, March–April, 1996.