Constraints on transmission, dispersion, and density of states in dielectric multilayers and stepwise potential barriers with an arbitrary layer arrangement.

Normal-incidence transmission and dispersion properties of optical multilayers and one-dimensional stepwise potential barriers in the nontunneling regime are analytically investigated. The optical paths of every constituent layer in a multilayer structure, as well as the parameters of every step of the stepwise potential barrier, are constrained by a generalized quarter-wave condition. No other restrictions on the structure geometry are imposed, i.

Spectral-luminescent properties of 12-oximino derivatives of 8-AZA-D-homogona-12,17a-diones and their concentration dependence.

This paper presents the results of the investigation of the spectral-luminescent characteristics of 12-oximino derivative of 8-aza-D-homogona-12,17a-dion, its hydrochloride, and their dependences on the concentration. It has been shown that the form and position of the absorption spectrums of 16,16-dimethyl-12-oximino-8-aza-D-homogona-1,3,5(10),13-tetraene-17a-one in all solvents used are independent of its concentration. At the same time, for its hydrochloride in ethanol and water, a strong dependence of the absorption spectrum on its concentration has been revealed.

Interaction of low-energy electrons with linear diphenylethynyl derivatives in the gas phase.

The gas phase electron impact spectroscopy has been used to study the relative efficiency of excitation into singlet states and energies of singlet-triplet transitions for two electroactive organic materials, anthracene and biphenyl-containing diphenylethynyl derivatives. The probability of the lowest singlet-triplet transition in anthracene-containing molecule was found to be much higher than that in anthracene which is connected with triple bonds. No noticeable contribution of the triple bonds into singlet spectra of the studied molecules was observed.

Delayed fluorescence and phosphorescence of 8-aza-D-homogonane in the gas and condensed phases.

The delayed fluorescence spectrum for 8-aza-D-homogonane in the gas phase consists of a band of E-type delayed fluorescence of M-centers and a band of P-type delayed fluorescence of L-centers being the products of photo- and thermotransformations of a basic steroid. Triplet-triplet energy transfer from the M-centers to the L-centers is established and its efficiency is determined. For 8-aza-D-homogonane in frozen hexane solutions at T=77 K only the phosphorescence of the M- and L-centers is revealed.

Spectral and luminescent properties and electroluminescence of polyvinylcarbazole with 1,8-naphthalimide in the side chain.

A novel copolymer with moieties capable of charge transport and light emission on the basis of polyvinylcarbazole and 1,8-naphthalimide is synthesized. A bright and stable electroluminescence from single layered structure is observed. White light emission can be easily realized by tuning the content of naphthalimide moieties or a number of naphthalimide derivatives.

Acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin: Role of conformational flexibility.

The acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin were studied in aqueous solution and compared with the respective data for the corresponding porphyrin. The reduction of the pyrrole ring in the tetrapyrrolic macrocycle noticeably influences both free base/monoprotonated and mono-/diprotonated species equilibria. In strong acidic solutions protonation of 4-sulfonatophenyl groups takes place in addition to protonation of the macrocycle core.

Solvent polarity effect on excited-state lifetime of carotenoids and some dyes.

The theory demonstrating the role of medium at the fluorescence quenching of polar compounds in solutions is briefly presented. It has been shown, that the rate of S(1) --> X(n) nonradiative conversion between the intramolecular charge transfer states depends on the permanent dipole moments in the ground (S(0)) and excited (S(1), X(n)) states as well as on solvent polarity. A relation for the rate of nonradiative excited-state energy conversion has been obtained and employed to test the known literature data for solvent effect on the S(1)-state lifetime of some biologically significant carotenoids and dyes (phthalimides).

Mutual effects of proton and sodium chloride on oxygenation of liganded human hemoglobin.

The different effects of pH and NaCl on individual O2-binding properties of alpha and beta subunits within liganded tetramer and dimer of human hemoglobin (HbA) were examined in a number of laser time-resolved spectroscopic measurements. A previously proposed approach [Dzhagarov BM & Lepeshkevich SV (2004) Chem Phys Lett390, 59-64] was used to determine the extent of subunit dissociation rate constant difference and subunit affinity difference from a single flash photolysis experiment. To investigate the effect of NaCl concentration on the association and dissociation rate constants we carried out a series of experiments at four different concentrations (0.

Continuous-wave Raman generation in a diode-pumped Nd3+:KGd(WO4)2 laser.

Continuous-wave Raman generation in a compact solid-state laser system pumped by a multimode diode laser is demonstrated. The Stokes radiation of stimulated Raman scattering at 1.181 microm is generated as a result of self-frequency conversion of the 1.

Phosphorescence of 8-azasteroids and related compounds.

We have investigated the electron absorption, fluorescence and phosphorescence spectra of 8-azasteroids and model compounds containing enaminodicarbonyl fragment. It has been shown that the investigated compounds have absorption and phosphorescence spectra similar in form and position. The results obtained permit the conclusion that the main deactivation channel of the excited singlet state is the intersystem crossing.

Photoinduced gas-phase electron transfer reactions.

The electron transfer quenching process, when a reactive excited state is singlet or triplet, for gas-phase systems (benzophenone and anthraquinone with amines and pyridine as well as carbazole with halomethanes) was systematically investigated using time-resolved fluorescence. Bimolecular rate constants were obtained. Variable-temperature measurements were performed for eight donor-acceptor pairs.

Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene).

The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP.

A kinetic description of dioxygen motion within alpha- and beta-subunits of human hemoglobin in the R-state: geminate and bimolecular stages of the oxygenation reaction.

Laser flash photolysis technique is used to study human hemoglobin (HbA) oxygenation. Monomolecular geminate oxygenation of triliganded R-state HbA molecules is described by a function of three exponentials. Geminate oxygenation of the alpha-subunit within R-state HbA is characterized by two components with time constants of 0.

Laser kinetic spectroscopy studies of the bimolecular oxygenation of alpha- and beta-subunits within the R-state of human hemoglobin.

Bimolecular oxygenation of tri-liganded R-state human hemoglobin (HbA) is described by bi-exponential kinetics with association rate constants k(alpha) = 27.2 +/- 1.3 (micro M*sec)(-1) and k(beta) = 62.

[Effect of ethanol on functional properties of the human hemoglobin molecule].

The effect of ethanol on the oxygenation of hemoglobin was studied by kinetic absorption spectroscopy. It was found that the efficiency of oxygen geminate rebinding decreased upon ethanol addition. At ethanol concentrations up to 4.

Photophysics of the cationic 5,10,15,20-tetrakis (4-N-methylpyridyl) porphyrin bound to DNA, [poly (dA-dT)]2 and [poly (dG-dC)]2: interaction with molecular oxygen studied by porphyrin triplet-triplet absorption and singlet oxygen luminescence.

Interaction between molecular oxygen and the cationic free-base 5,10,15,20-tetrakis (4-N-methylpyridyl) porphyrin (H2TMpyP4+) complexed with [poly (dA-dT)]2, [poly (dG-dC)]2 and calf thymus DNA, has been monitored in air-saturated heavy water solutions through porphyrin triplet-triplet absorption and singlet oxygen luminescence. Three different rate constants of porphyrin triplet state quenching have been found which correspond to different accessibilities of molecular oxygen to porphyrins embedded in the duplexes. The longest triplet state lifetime (30 microseconds), found for porphyrin bound to [poly (dG-dC)]2, corresponds to molecules well protected from oxygen.

Luminescence and structure of the protonated forms of meso-tetraarylporphyrins in solution.

A comparative study of the spectral-luminescent properties (at 293 K and 77 K) of meso-tetrakis(o-tolyl)porphyrin (o-TTP) and meso-tetraphenylporphyrin (TPP), and also meso-tetrakis(n-propyl)porphyrin (TPrP) in nonaqueous acid media has been carried out with the aim to reveal effects associated with the influence of methyl groups which hinder sterically the twist of the phenyl rings enhancing their conjugation with the macrocycle in acid medium. On the basis of the spectral data it is concluded that although the introduction of the methyl groups diminishes this twist of phenyls it does not eliminate it completely (the absorption spectra of protonated o-TTP are intermediate between those of TTP and TPrP). The fluorescence spectra of the protonated forms of o-TTP and TPP at 77 K are approximately mirror-symmetrical to the Q(0-0) and Q(0-1) absorption bands; on the elevation of the temperature up to 293 K the fluorescence and absorption bands broaden, the Stokes shift largely increases, and the mirror symmetry of the spectra disappears, which is indicative of changes in solute-solvent interactions in the S1 state.

Optimization of detection of atomic absorption lines in intracavity laser spectroscopy.

An intracavity laser spectrometer equipped with a graphite furnace electrothermal atomizer and two alternative types of narrow atomic lines detection schemes (high resolution diffraction spectrograph with optical multichannel analyzer or a resonant detector based on a hollow-cathode lamp) is described. Such system was used to determine ultra-trace amounts of lithium and strontium in aqueous solutions. A significant reduction in the measurable absorbance was demonstrated for both elements.

Intracavity laser polarization spectrometer for biomolecule traces.

A polarization variant of an intracavity laser spectrometer based on the competition of beams in an argon ion laser, radiating a number of narrow lines in the 275 to 529 nm spectral range, is proposed and described for the spectral analysis of liquid samples, having broad absorption bands, mainly biomolecules in solutions. By careful optimization of the operating conditions, a procedure has been established that results in a minimal measurable absorbance decreased up to 10(-5) units of optical density. The examined spectrometer provides a wide dynamic range of analysis.

Intracavity laser atomic absorption spectrometry with graphite furnace atomizer or pulsed laser sampler.

An absorption intracavity laser spectrometer with two types of sample vaporization systems (graphite furnace electrothermal atomizer or laser sampler) is described that can be used for the determination of trace amounts of metals (Al, Cr, Fe and Mn) in liquid samples and at the surface of solid targets. The limits of detection for the elements tested are lower than those obtained by modern conventional spectrometers. The examined technique provides a wide dynamic range of linear standard calibration curves.

Determination of cesium, manganese and terbium by intracavity laser spectroscopy.

The statistical characteristics of the intracavity laser spectrometer are investigated by analysis of cesium in aqueous solutions. The error distribution of measurements is normal. The relative standard deviation of the analysis in the middle of the dynamic range is equal to 9.