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.     

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.     

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.     

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.     

Infrared multiphoton excitation of polyatomic molecules

Results of investigations of the process of multiphoton excitation of polyatomic molecules by CO₂-laser radiation are presented. The mechanism of formation of the profiles of IR absorption bands of polyatomic molecules is discussed. New experimental methods of investigation of relaxation processes at high levels of vibrational excitation of molecules in the ground and triplet states are considered. For vapors of polyatomic molecules and their mixtures with foreign gases, the quantitative characteristics of the collisional exchange and the vibrational-energy transfer as well as the rates of intercombinational conversion ⇛ and triplet-triplet transfer are presented and their dependences on the vibrational-excitation level are discussed. 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. 5, pp. 675–693, September–October, 1998.     

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.     

Quasiline fluorescence and absorption spectra of NH-isomers of octamethylisobacteriochlorin

Quasiline fluoresence and fluorescence excitation spectra of NH-isomers of 2,2,7,7,12,13,17,18-octamethylisobacteriochlorin (cis- and trans-) in polycrystalline matrices in n-hexane and n-octane at 4.2 K are obtained. A vibration analysis of the spectra in combination with the data of quasiline spectra of cyano-substituted octaethylisobacteriochlorin and octamethylporphin permitted a qualitative interpretation of the vibronic spectra of NH-isomers. It is inferred that for a trans-isomer, the 0–0 transition S₂⇃S₀ is localized in the region of electron-vibrational S₁⇃S₀ transitions; the interval S₂-S₁ has a magnitude of about 1300 cm⁻¹. Reported at the VIIIth International Conference on the Spectroscopy and Chemsitry of Poprhyrins and Their Analogs, Belarus, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 79–85, January–February, 2000.     

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.     

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.     

Vibrational spectra of In2S3, CuIn5S8 and AgIn5S8 compounds with a spinel structure

The IR reflection spectra of In₂S₃, CuIn₅S₈, AgIn₅S₈ compounds with a spinel structure are investigated. Using the DA-K-K method, we determined the frequencies of longitudinal and transverse phonons, attenuation coefficients of phonons, and IR intensities, as well as the dielectric constants ε₀ and ε_∞. Belarusian State University of Information Science and Radioelectronics, 6, P. Brovka St., Minsk 220600, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 263–265, March–April, 1997.     

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.     

Optical properties of new indotricarbocyanine dye as a limiter of laser radiation power

We present results of experimental and theoretical studies of the optical characteristics of a new indotricarbocyanine dye that is capable of effectively limiting the power of laser radiation in the visible spectral range. The spectral-luminescent and energy characteristics of the dye molecules and their absorption spectra from the excited state with nanosecond resolution are investigated experimentally. Quantum-chemical methods are used to calculate electronic absorption spectra from the ground (S₀ → S_n) and excited (S₁ → S_n) states and to determine the nature of electronic states of the molecule and the rate constants of intramolecular photophysical processes. The results of the theoretical research agree with experimental data. It is shown that the investigated dye has singlet-singlet absorption at 400–600 nm. Nonlinear absorption of the dye upon excitation by radiation of the second harmonic of a Nd:YAG laser is studied by z-scanning with an open diaphragm. The ratio of dye absorption cross sections from the excited and ground states at 532 nm is determined in the framework of a three-level model. The results are compared with those for previously studied compounds. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 473–480, July–August, 2007.     

Absorption and fluorescence of 9,10-diiodoanthracene in undegassed solutions

A procedure for producing 9,10-diiodoanthracene that is an alternative to the known procedure is described. The spectra of absorption and fluorescence in hexane, carbon tetrachloride, and polymethylmethacrylate are measured at 22°C. The quantum yield of undegassed liquid solutions in hexane and carbon tetrachloride in excitation at the maximum of the 0←0 band is practically the same and is equal to 0.018. In excitation in shorter-wave vibrational bands, it is different for different solvents and decreases noticeably as the frequency of the exciting light increases. The decrease in the yields is explained by the existence of a fast nonradiative process from hot (Franck-Condon) vibrational S₁-states capable of competing with vibrational relaxation. A possible scenario of this approach is discussed. Institute of Molecular Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 197–200, March–April, 1999.     

Spectropolarization investigations of the region of the cathode drop in the potential of a helium glow discharge at atmospheric pressure

The dimensions of the region of the cathode drop in potential in a helium glow discharge at atmospheric pressure (in Kiselevskii’s plasma source) are determined. Using Stark spectroscopy of the Balmer-series hydrogen line H_β the spatial distribution of the constant and variable components of the electric-field strength is measured. 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. 3, pp. 362–368, May–June, 1999.     

Spectral-time characteristics of combined-target laser plasma

From the analysis of the contours of the spectral lines of target-material atoms, the electron and atomic concentrations and their variation with time are determined in the laser plasma of a combined Cu–Al–Cu target. The time dependences for the concentrations of electrons and atoms in the ground and excited states are explained within the framework of a model that allows for plasma decay being determined by processes of three-particle recombination and ionization as well as by the variation in the particle concentration in plasma expansion. 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. 3, pp. 426–432, May–June, 1998.     

A resonance-reman-scattering multifrequency spectrometer for investigating excited states of molecules and photoinduced high-rate processes

A resonance-Raman-scattering multifrequency laser spectrometer operating in a wide spectral range (355–750 nm) and making possible the recording of both stationary Raman spectra and spectra with a time resolution of up to 100 psec in the time interval of 0–50 nsec has been developed. The spectrometer has been used with advantage for the study of the excited states of molecules of metalloporphyrins in solutions and processes of interaction of model metalloporphyrins with DNA and DNA-modeling polynucleotides. To whom correspondence should be addressed. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus 68, F. Skorina Ave., Minsk, 210072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 726–733, September–October, 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.     

Optoacoustic gas analyzer based on a13C16O2 laser for multicomponent pollution of air

A computer-aided optoacoustic gas analyzer based on a continuous¹³C¹⁶C₂ laser for multicomponent pollution of atmospheric air is described. The analyzer has the ability to detect absorption of radiation by detected substances at the level of ∼1·10⁻⁹ cm⁻¹ at a time resolution of 30 sec. Results of an experiment on simultaneous detection of H₂O, CO₂, NO₂, NH₃, HNO₃, OCS, and C₂H₄ in the atmospheric air using 40 laser lines are presented. 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. 3, pp. 345–350, May–June, 1999.     

Formation of chemical compounds in a laser plasma

Using the methods of laser-induced fluorescence and emissive spectroscopy, we carried out investigations of the formation of TiO molecules in a laser plasma produced by focusing the radiation of an AYG:Nd³⁺ laser on the surface of a titanium target in air. The radiation flux density varied within the range 10⁸–10¹⁰ W/cm². We investigated the distribution of molecules over internal states and the space-time distributions of Ti atoms in the ground, metastable, and excited states, as well as of TiO molecules in the ground and excited states. We found that gas-phase reactions with participation of Ti atoms in the ground state provide the most probable channel for the formation of TiO molecules; the role of reagents in ionized, excited, and metastable states is of secondary 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. 66, No. 1, pp. 109–115, January–February, 1999.     

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.