Transformation of radiation-induced defects responsible for theF-band of absorption in NaF crystals subjected to irradiation with light and annealing

It has been found that the F-band of optical absorption which is observed in ψ-irradiated NaF crystals consists of three overlapping bands. The band at 345 nm of width 40 nm is independent of the impurity composition of the crystals; it disappears upon exposure to radiation at 345 nm and appears again upon annealing at 460±15 K for 15 min. This band is correlatable in intensity with the superfine structure of an EPR spectrum. The width (65–110 nm) and the spectral position (355–375 nm) of the second band depend on the impurity composition of the crystal. The band of width 90–110 nm at 320–325 nm disappears upon annealing and appears after exposure to light simultaneously with the disappearance of an EPR signal. It is established that the band at 345 nm is caused by quasimolecules based on fluorine atoms, that at 355–375 nm is triggered by F-centers with a different impurity composition near the haloid vacancy, and the band at 320–325 nm owes its appearance to F-centers in a negatively charged state (F′). 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. 6, pp. 849–853, November–December, 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.     

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.     

Spectral-luminescence properties of a norbornene-substituted tetraazachlorin and its metal complexes

The spectral-luminescence properties of a tetraazachlorin derivative with a norbornene fragment annelated to a reduced pyrrole ring and its complexes with zinc and palladium have been studied at 293 and 77 K. For the norbornene-substituted free base, differences in fluorescence from unsubstituted tetraazachlroin and its dibenzobarrelene-substituted analog are found. The fluorescence lifetime is observed to rise by ∼7 times for the free base and by ∼1.6 ties for the Zn complex on going from 293 to 77 K. An essential dependence of the photophysical parameters on the nature of the solvent is noted. The fluorescence polarization spectrum of the norbornene-substituted tetraazachlorin reveals in the Soret band region at least four electronic transitions. For the Pd complex, weak phosphorescence in the near IR region has been detected; the 0–0 band maximum is at 990 nm and the singlet–triplet interval amounts to 5800 cm^–1, which is larger by 400 cm^–1 than for Pd tetraazaporphine. The quantum yields of the photosensitized formation of singlet oxygen have been determined using a relative luminescence method.     

Interpretation of the soret band of porphyrins based on the polarization spectrum of N-methyltetraphenylporphin fluorescence

Low-temperature (77 K) absorption, fluorescence, and fluorescence-excitation spectra and the fluorescence polarization spectrum for N-methyl-meso-tetraphenylporphin (N-methyl-TPP) are measured. Based on the polarization spectrum the absorption spectrum in the visible region (a “generic” porphyrin spectrum) is interpreted. In particular, it is shown that the fifth absorption band (the “Longo band”) that manifests itself in some porphyrins is a Q_y(0–2) band and does not belong to the individual electron transition. Emphasis is placed on the region of the Soret band. It is inferred that at least two allowed electron transitions (G →B_x and G→B_y) polarized mutually perpendicularly manifect themselves in this region. The interpretation of the Soret band of porphyrins [2] that attributes this band to one electron transition G→B_x is thereby rejected. This interpretation is confirmed by computer modeling of the polarization spectrum. Special features of the experimental polarization spectrum are explained by a more developed vibrational structure and, possibly, a larger half-width of the B_x band than the half-width of the B_y band. The contribution of the states of intramolecular charge transfer to the formation of the Soret band is discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 65–72, January–February, 1999.     

Intramolecular charge transfer and formation of luminescence centers of 4-nitro-4-dimethylaminobutadiene in binary solvents

Absorption and luminescence spectra of a 4-nitro-4-dimethylaminobutadiene molecule in binary solvents have been experimentally obtained and investigated. Formation of the absorption spectra is associated with a chromophore grouping of the molecule in a bent state, while the bathochromic shift of the band in the absorption spectrum is consistent with the theory of dipole-dipole interaction of a bipolar molecule with solvent molecules. The fluorescence spectrum and its form and bathochromic shift depend not only on the solvent polarity but also on the proportion and kind of binary mixture of solvents. For a certain proportion of the binary solvent, radiation has been generated at λ=610 nm in pumping by a nitrogen laser. Reported at the International Conference on Luminescence, November, 22–24, 1994, Moscow. Belarusian State University, 4, F. Skorina Ave., Minsk, 220080, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 119–121, January–February, 1997.     

Structure of excited electronic states of Mg-chlorin and Mg-bacteriochlorin dimers

Within the framework of a procedure proposed previously for fragment-by-fragment quantum-chemical calculation of aggregates of molecules with π-electronic chromophore groups, account is taken of hyperconjugation, which allows practically exact reproduction of results obtained by the all-valence CNDO/S method. Calculations of excited electronic states of sandwichlike Mg-chlorin (Mg-Ch)₂ and Mg-bacteriochlorin (Mg-BCh)₂ dimers with variation of the interplanar distance between monomers are made. It is shown that on passing from a Mg-porphin dimer to the (Mg-Ch)₂ and (Mg-BCh)₂ dimers there is a considerable decrease in the energies of charge-transfer states, which are resonant in nature (CR-states). Moreover, (Mg-BCh)₂ has a considerably reduced energy interval between the lower CR-state and the forbidden component of the lower Q-state, which is indicative of easier charge separation in the lower excited electronic singlet states under the action of the field of the environment of tetrahydroporphyrin dimers than of dimers of porphyrins and hydroporphyrins, which can be of biological importance. 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. 2, pp. 166–175, March–April, 1998.     

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.     

Association of mono- and dimethyl ethers of chlorine 6 in ethanol-water solutions

The association of γ-mono- and 6,γ-dimethyl ethers of chlorin e₆ (I and II) in mixtures of a phosphate buffer and ethanol is studied. The number of molecules in associates and the dimerization constants are determined. The formation of the dimers of compound I and dimers and associates of a higher order for II is established. It is found that, unlike I, the shift of the Q absorption band of the dimer toward larger wavelengths is rather great as compared to the monomer band for II; it exceeds 30 nm, which is uncommon for porphyrins. This difference of spectral changes in association of I and II is attributed to the dissimilar character of interaction of their molecules with each other and with the molecules of the surroundings, and also to the structural features of the dimers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 440–444, July–August, 2000.     

Band structure of electronic levels and the formation of the fluorescence spectra of polar compounds in polar media

The paper sets out a statistical theory of the effect exerted by interactions of constant dipoles in solutions on the fluorescence spectra of polar compounds. The theory is based on the concept of band structure of the electronic levels of a polar impurity (dissolved) molecule in polar media. 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. 2, pp. 209–216, March–April, 1997.     

Spectroscopic Detection of Tetracationic Porphyrin H-Aggregation on Polyanionic Matrix of Inorganic Polyphosphate

Self-assembly of tetracationic porphyrin TMPyP⁴⁺ onto polyanionic matrix of inorganic polyphosphate (PPS) in aqueous solutions has been studied in a wide range of molar phosphate-to-dye ratios using techniques of polarized fluorescence, absorption, resonance Raman spectroscopy and static light scattering. The binding of TMPyP⁴⁺ to PPS is characterized by the binding constant of 3 × 10⁵ M⁻¹ and the cooperativity parameter of about 150. The fluorescence quenching of the bound TMPyP⁴⁺ evidences the stacking of the porphyrine chromophores. Under the stoichiometric binding ratio TMPyP⁴⁺ forms extended continuous face-to-face aggregates (so-called H-aggregates) which manifest themselves by a blue shift (12 nm) and a large hypochromisity (51%) of the Soret absorption band. Each face-to-face TMPyP⁴⁺ stack is formed with participation of four PPS chains. Formation of such columnar aggregates is promoted by the ability of PPS chains to take a helix conformation where negative charges are arranged along two oppositely situated rows with intercharge distance of 0.36 nm which corresponds to the thickness of the porphyrin π-electronic system. The ability of each PPS strand to be template for formation of two porphyrin stacks results in the integration of the adjacent stacks into higher-order aggregates which dimension was estimated from the fluorescence polarization data.     

Effect of the mode composition of laser radiation on the intracavity formation of periodic surface structures

We investigated the effect of the mode composition (longitudinal and transverse modes) of laser radiation on the basic parameters of the stroke pattern formed on a treated surface placed inside a laser cavity. We found that the contrast of the stroke pattern formed by a laser beam with a complex set of longitudinal modes depends, in the first place, on the width of the laser radiation spectrum and the laser cavity length and is virtually independent of the angle of rotation of the beam. In the region of small rotation angles the broadening of strokes caused by the effect of transverse modes becomes predominant. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikaladnoi Spektroskopii, Vol. 64, No. 1, pp. 50–54, January–February, 1997.     

Stability of the conditions for excitation of atomic spectra in plasma produced on exposure of copper alloys to laser radiation

We show that the temperature of plasma produced by exposure of copper-zinc alloy specimens to laser radiation changes little (within the limits of random errors) with a change in the conditions of the laser effect and chemical composition of the specimens. With use of electric discharges (a low-voltage spark), systematic changes in the temperature of the plasma are observed when the chemical composition of copper-zinc alloys changes. 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. 3, pp. 319–321, May–June, 1998.     

Optical properties of heated air, carbon dioxide, and argon

Stable-plasma generators, spectroscopic measuring equipment, and methods for determining the optical properties of an extremely heated medium with a given composition have been developed. The spectral coefficients of absorption and emission of heated air, carbon dioxide, and argon were studied. A comparison with the data of other theoretical and experimental investigations has been performed. Deceased. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 818–826, November–December, 1997.     

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.     

Spectral studies of the structure of copper phthalocyanin-polyimide composites produced by vacuum deposition

Visible and IR absorption spectra are studied for copper phthalocyanin (CuPc)-polyyimide composites. The composite films are obtained by vacuum codeposition of CuPc, pyromellitedianhydride, and diaminodiphenyloxide followed by temperature-induced imidization. On the basis of IR spectra it is shown that in the prepared composites imidization occurs over the whole CuPc concentration range (10–90%). From the visible spectra it is found that CuPc is deposited mainly in the form of a-microcrystals, which are destroyed during imidization to produce noncrystalline molecular aggregates. Subsequent heat treatment (320–350°C) gives rise to CuPc β-microscrystals. A. N. Sevchenko Research Institute of Applied Physical Problems, 7, Kurchatov St., 220064, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 502–506, July–August, 1997.     

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.     

Luminescence of human blood serum in the longwave spectral region

An investigation is made of the absorption, fluorescence, and fluorescence excitation spectra of human blood serum whole and diluted with a sodium-phosphate buffer solution. Time characteristics of the longwave serum luminescence are obtained. The quantum yield of background fluorescence upon excitation by radiation with λexc=500 is found to be 0.5%. 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. 66, No. 3, pp. 433–436, May–June, 1999.     

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.