Dynamic relaxation of the triplet states of mono- and dimesoaryl derivatives of porphyrins and their chemical dimers

For the first time it is discovered that the mono- and dimesoaryl substitution in porphyrins (free bases and their Zn-complexes) as well as the formation of chemical dimers with a phenyl spacer are manifested in the abrupt reduction (300–500 times less) of the lifetime of T₁-states at 295 K and are not accompanied by enhancement of the nonradiative deactivation of the S₁-state. These effects are associated with the nonlinear dynamic deformations of the π-conjugate macrocycle in the T₁-state due to torsional oscillations of a phenyl ring about a single C–C-bond in sterically complicated porphyrins. To whom correspondece should be addressed. 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. 4, pp. 471–475, July–August, 1998.     

Influence of laser heating on the optical properties of a superhigh-modulus organoplastic material

The degree and azimuth of polarization and the indicatrix of the intensity of radiation (λ=0.63 μm) reflected by the surface of a monodirectional superhigh-modulus organoplastic material after structural transformations induced in it by CO₂-laser radiation are measured. It is shown that the space-polarization characteristics of the radiation reflected by the organoplastic material charred as a result of laser heating correspond to the parameters of radiation scattered by a nontransparent material with an isotropic surface in the approximation of geometrical optics. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 635–639, September–October, 1999.     

New feature of the phosphorescence of copper complexes ofmeso-tetraarylporphyrins

Introduction of methyl groups in orthopositions of phenyl rings of a Cu-meso-tetraphenylporphin (Cu-TPhP) molecule is shown to lead to a substantial decrease in the diffusivity of the spectrum of low-temperature (77 K) phosphorescence. It is found that the long-lived (580 μsec) and short-lived (0.7 μsec) components of Cu-TPhP phosphorescence differ in emission and absorption (phosphorescence-excitation) spectra and belong to two forms of molecules. The phosphorescence spectrum of the predominant form with small τ_p is diffuse, while its absorption spectrum is shifted slightly in a bathochromic manner. The phosphorescence spectrum with large τ_p is structural and is similar to the spectrum of Cu-meso-tetrakis-(ortho-tolyl)porphin. The difference is attributed to the nonplanarity (saddle distortion) of a Cu-TPhP molecule in the lower triplet state in the case of the form with small τ_p. 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. 743–747, November–December, 1999.     

Role of highly efficient collisions in collisional transfer of vibrational energy in benzophenone-foreign gas mixtures

Collisional losses of vibrational energy in mixtures of benzophenone excited by nitrogen laser radiation (λ=337 nm) and foreign gases (Ar, Kr, SF₆, C₅H₁₂) were studied by time-resolved delayed luminescence. It is established that the intensities and rates of decay of the fast and slow components of delayed luminescence can be used to evaluate the characteristics of V–V– and V–T–transfer of vibrational energy. For the V-V-process, the efficiencies and mean energies transferred in a collision are determined. It is shown that in the mixture with multiatomic gases, vibrational equilibrium is reached after a few collisions, the number of which decreases as the molecule of the foreign gas becomes more complicated. The V–V–process is characterized by high efficiencies of collisions typical for “supercollisions”. The experimental characteristics of V-V-transfer correlate well with ergodic transfer of vibrational energy predicted by statistical theories. 0120 0126 V 3 Institute of Molecular and Atomic Physics of the National Academy of Science of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 340–345, May–June, 1998.     

Photoelectric properties ofp-CuInSe2 thin films obtained by pulsed laser vaporization

Using the method of phase-sensitive detection, we investigated the photoconductivity spectra of polycrystalline p-CuInSe₂ films obtained in vacuum by the method of pulsed laser vaporization of initial single crystals. We show that, in contrast to single crystals, films are characterized by monopolar photoconductivity in the extrinsic and intrinsic regions of optical absorption and by a linear mechanism of recombination of nonequilibrium charge carriers at the intensities of illumination 0–100 mW/cm² in the temperature range 80–300 K. Institute of the Solid-State and Semiconductor Physics, National Academy of Sciences of Belarus, 17, P. Brovka St., Minsk 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii. Vol. 66, No. 1, pp. 138–141, January–February, 1999.     

A two-frequency He−Ne laser at the 3S 2→3P 4 transition in mutually orthogonal transverse magnetic fields

By taking as an example a He−Ne laser that operates at the 3S₂−3P₄ transition (λ=3.39 μm), we studied the specific features of nonlinear interaction of the waves of linear orthogonal polarizations in a transverse magnetic field. Using mutually orthogonal transverse magnetic fields on the neighboring portions of an active medium, we implemented a regime of two-frequency generation, which was investigated theoretically and experimentally. To whom correspondence should be addressed. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 568–573, July–August, 1999.     

Infrared filters and analyzers of the composition of substances based on them

Results of investigations on designing band dispersion and dispersion-interference filters for the 4–30 μm IR range and cutoff filters for the 50–300 μm region are presented. Analyzers of the composition of a substance that are designed on the basis of band IR filters and analysis procedures are described. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 734–744, September–October, 1998.     

Photophysics ofβ-carotene and related compounds (review)

A review of data on the photophysics of carotenoids is presented. Results of investigations of spectroscopic, temporal, and energy parameters of excited S₁ and S₂ singlet states of β-carotene and related compounds are critically examined. These states give rise to extremely high probabilities (10¹¹–10¹³ sec⁻¹) of radiationless deactivation of the electronic excitation energy in carotenoids. Results of investigations of photophysical properties of triplet states of carotenoids are considered mainly from the standpoint of quenching of singlet oxygen and triplet states of organic molecules by carotenoids. 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. 5–19, January–February, 1997.     

Spectra of the action of photoinduced NH(ND)-rearrangement of cyanosubstituted isobacteriochlorin

Based on the measured spectra of the action of the process of cis-trans-NH(ND)-isomerization of 5-cyano-2,2,8,8,12,13,17, 18-octamethylisobacteriochlorin (H₂-COMiBCh) and its deuteroderivative (D₂-COMiBCh) in polycrystalline matrices of n-octane and r hexale at 4.2 K, it is established that the character of embedding of COMiBCh in the matrices of n-alkanes has a substantial effect on the barrier of dark rearrangement and the rate of photoinduced NH(ND)-rearrangement, while deuteration of the center of a molecule shifts the dynamic equilibrium toward a trans-form in photoexcitation. To whom correspondence should be addressed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina, Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 555–559, July–August, 1999     

The nature of empirical constants in the equation relating the frequency of the stretching vibration of oh-groups to parameters of the [MO n ]-polyhedrons coordinating these groups

Institute of Physicoorganic Chemistry, Academy of Sciences of Belarus, 220603, Minsk, Ul. Surganova, 13, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 1, pp. 104–107, January–February, 1995.     

Fine fluorescence and absorption spectra of hypericin in a polymer matrix at a temperature of 4.2 K

Monochromatic photoexcitation and selective registration in bands of purely electronic S₁↔S₀ transitions resulted in fine fluorescence and absorption (fluorescence excitation) spectra of hypericin in polyvinylbutyral at a temperature of 4.2 K. Vibration analysis of the spectra is done and conclusions are made about the form of many normal vibrations. It is found that the formation of intramolecular hydrogen bonds in the hypericin structure has a substantial effect on the relative position of the electronic vibrational levels of the pigment molecule. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina ave., Minsk 200072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 539–545, July–August, 1998.     

Photophysical properties of mesonitrophenyl-substituted porphyrins and their dimers at 295 K

It is shown that at 295 K in meso-orthonitrophenyl-substituted octaethylporphyrins and their chemical dimers the steric interactions of the nitro-group and the volume substituents at β-positions of the pyrrole rings favor direct overlapping of molecular orbitals in a donor-acceptor pair. The efficient quenching of fluorescence of the nitroporphyrins in toluene is attributed to direct nonadiabatic electron transfer from the S₁-level of a porphyrin to the lower-lying state with charge transfer by the “through-space” mechanism. Quenching of the T₁-states is related with heat-stimulated transmission to the higher-lying states with charge transfer of the ion-radical pair as well as with enhancement of the probability of the nonradiative T₁→S₀-transition. To whom correspondence should be addressed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 531–535, July–August, 1999.     

Molecular complexes based on tetrapyrrole compounds. Quantum-chemical investigation of the properties of excited states and conformational dynamics

On the basis of quantum-chemical calculations of the properties of excited states and comparison with the experimental data, we show that at room temperature unliganded dimers of Zn-porphyrins and Zn-chlorins, bonded through a CH₂−CH₂-group, are in a conformation close to an eclipsed one, while their dipyridine complexes are in an unchanged conformation. For triad and pentad complexes, formed as a result of extraliganding of dimers of Zn-porphyrins with di- and tetrapyridyl-substituted free bases of porphyrins, the calculations predict the presence of states with transfer of a charge from dimers onto a free porphyrin base that are manifested in the region between the Q- and B-transitions in electron absorption spectra. To whom correspondence should be addressed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 535–537, July–August, 1999.     

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.     

Temperature dependence of the width of spectral holes: Octaethylporphin in polymer matrices

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 2, pp. 145–150, March–April, 1995.     

Fluorescence assay of tyrosine in blood plasma

A more simple and sensitive assay for the quantitative determination of tyrosine in blood plasma is developed on the basis of a modification of the method of S. Udenfriend (1962). A volume of 0.2 ml of plasma is used in the analysis; after its deproteinization with trichloroacetic acid, it is reacted with sodium nitride, nitrous acid, and 1-nitroso-2-naphthol at 65°C, and the content of the reaction product is measured by the fluorescence at λ_ex/λ_em=460/570 nm. The consumption of plasma and reagents is reduced by a factor of 5–10 compared to the original method; in addition, the stage of extraction with an organic solvent is excluded. The linear dependence of the fluorescence signal on the tyrosine concentration within the range of 2–60 μg/ml, high specificity, accuracy, and reproducibility of the assay are shown. The importance of tyrosine determination in monitoring of glucocorticoid therapy and protein catabolism is discussed. Institute of Photobiology, National Academy of Sciences of Belarus, 27, Akademicheskaya St., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 366–371, May–June, 1998.     

Optoacoustic determination of low concentrations of gases by the use of commercial CO2-lasers

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Specktroskopii, Vol. 62, No. 6, pp. 81–86, November–December, 1995.     

Relationship between the diffusion rate constant and rate constant of triplet-triplet annihilation for porphyrins in liquid solutions

Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70. F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 63, No. 4, pp. 613–621, July–August, 1996.     

Induced quasicrystallinity of solutions of organic compounds

Using the method of optical probing, we investigated the effect exerted by the concentration of the substance and the temperature of the solution on the spectral behavior of the difference in the refractive indices of ordinary and extraordinary waves Δn=n_o−n_e of excited solutions of Rhodamine 6G and 3,6-tetramethyldiaminophthalimide in glycerin. We established that laser-excitation-induced quasicrystallinity of the indicated solutions in probing in the fluorescence band, which is characterized by the magnitude of the difference between the refractive indices Δn, increases with increase in the concentration of the substance. This increase in the crystallinity of the system with increase in the concentration of the substance (the activator) is possible up to the instant of the appearance of intermolecular interaction of the molecules. To whom correspondence should be addressed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 672–674, September–October, 1999.     

Energy transfer in chemical dimers of porphyrins and chlorins by the methods of selective laser spectroscopy at 1.8–10 K

The methods of selective laser spectroscopy applied at 1.8–10 K to a glass-forming tetrahydrofuran-toluene (3∶1) mixture have revealed that in the dimers of tetrapyrrole compounds (ethane-bis-octaethylporphyrins, ethane-bis-Zn-octaethylchlorins, heterodimers of Zn-cyclopentane porphyrins) the exciton interactions (V₁₂≈118 cm⁻¹) and S-S-transfer of energy (of probability F≈11 sec⁻¹) are implemented under conditions of substantial inhomogeneous broadening (δF_1/2≈50 cm⁻¹). Upon excitation of a donor component in the dimers, one observes a strong quenching of its emission, the disappearance of the fine structure in the fluorescence spectra, a decrease in the efficiency of spectral hole burning by, approximately, an order of magnitude, and a 12-fold increase in their halfwidth. To whom correspondence should be addressed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 500–504, July–August, 1999.