Preparation and Photophysics of 2-(1-Pyrenyl)acrylic Acid and Its Methyl and 2′,2′,6′,6′-Tetramethyl-4′-Piperidyl Esters

Novel probes represented connection of pyrene as chromophore and sterically hindered amine stabilizers (HAS) in the form of esters of 2-(1-pyrenyl)acrylic acid were synthesized. HAS was in the form of parent amine (PAP) as well as stable nitroxyl radical form (PAP-NO^.). Photophysics of these probes were compared with their precursor as 2-(1-pyrenyl)acrylic acid (PAA) and its methyl ester (PAM). The fluorescence spectrum of PAA strongly depends on the acidity of the solution. The spectrum in neutral methanol indicates that it originates from the anionic form –COO⁻. Changes of acidity or basicity of methanol solution resulted in the changes of shape, position as well as the intensity of fluorescence band. This is due to the presence of protolytic equilibria, either in the ground state or in the singlet excited state, leading to the formation of molecular form –COOH and the cationic form –COOH₂⁺. The ester analogues did not show any changes in various pH conditions. Fluorescence of all probes depends on the polarity of solvents and the presence of oxygen. Intermolecular quenching was studied with external quenchers TEMPO and oxygen and the data were compared with the intramolecular quenching using 1′-oxo-2′,2′,6′,6′-tetramethyl-4′-piperidinyl-2-(1-pyrenyl)acrylate (PAP-NO^.).     

Fluorescent analysis of photoinduced biodegradation of cresol isomers

We have used fluorescence spectroscopy to study photoinduced biodegradation of ortho-cresol, para-cresol and mixture of them in water when excited by different UV radiation sources. We show that the efficiency of photolysis for both the individual isomers and the mixture of cresols is higher for excitation by radiation at λ ∼ 222 nm. Pre-irradiation of aqueous cresol solutions slows down subsequent biodegradation. Using a combination of UV irradiation and the strain Penicillium tardum H-2 for utilization of the cresol mixture led to complete degradation of para-cresol and partial degradation of ortho-cresol. Spectral and chromatographic study of the qualitative composition of the metabolites formed during biodegradation of para-cresol showed that preparatory metabolism of such compounds occurs both through oxidation of the methyl group with formation of 4-hydroxybenzoic acid and through hydroxylation with formation of 4-methylcatechol. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 250–255, March–April, 2008.     

Spectrophotometric Study of Luminol in Dimethyl Sulfoxide–Potassium Hydroxide

The spectrophotometric study of luminol (LH₂) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH₂ absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L^2–) formation at 3 × 10^–4 – 2.4 × 10^–3 M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH₂-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10^–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH₂-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH⁺ ₃ cation formation. In LH₂-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH₂-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed.     

Comparison of the Optoelectronic Performance of Neutral and Cationic Forms of Riboflavin

The riboflavin dye 2,3,4,5-tetra-O-acetyl-1-[3-(6-bromohexyl)-7,8-dimethyl-2,4-dioxo-3,4-dihydrobenzo[g]pteridin-10(2H)-yl]-1-deoxypentitol and its pyridinium salt were synthesized, and studied by absorption and fluorescence spectroscopy in solutions and on thin film states. The first absorption band of riboflavin-pyridinium salt derivative is red-shifted by 10 nm compared to neutral one on film. Cationic riboflavin derivative shows significant wavelength changes on its fluorescence emission spectrum in the excited state depending on the solvent polarity and the electronic environment. The fluorescence quantum yields of cationic riboflavin gave much higher values as compared to that of its neutral form. The fluorescence lifetimes were found to be in the range of 5.5–6.6 ns with mono ? exponential behavior. These dyes possess low-lying HOMO energy levels which are suitable to be able to inject holes to donor polymers so that they can be used as acceptor component in the active layer of bulk heterojunction solar cells (BHJ-SCs). Photovoltaic responses are reported for P3HT:riboflavin active layer wherein the synthesized dyes are used as acceptor component. Also, neutral riboflavin shows greater electron mobility value of 1.3 × 10^?3 cm²/V?s compared to its cationic derivative.     

Cluster emission under ion bombardment of metallic targets

Mass spectroscopic studies of the neutral particles sputtered by Ar⁺ ions at 8 keV from polycrystaline samples have been performed, using non-resonant laser ionization and subsequent time-of-flight mass spectroscopy. Besides sputtered atoms, also dimer and trimer contributions in the order of 10^–1 to 10^–2 and 10^–3 to 10^–4, respectively, are found in the sputtered flux. The data obtained here together with previously published data by other groups for different bombarding energies provide strong support for the validity of the recombination model.     

Estimation of the energy spectrum of cosmic ray electrons at the atmospheric depth (3.8–7.4)g.cm−2

Analytical calculations have been done to estimate the energy spectra of the secondary electrons originated from the decay of charged and neutral pions initiated on the upper atmosphere from the primary nucleon–air interactions in the energy range (4–100) GeV. The calculations are valid up to an atmospheric depth of about (3.8–7.4) g.cm^–2. The derived results are compared with the observed electron fluxes available from the balloon flight experiments of MASS2, HEAT, magnetic spectrometer system of Golden et al., instrument using scintillating fibers of Nishimura et al., and BETS.     

Bromoacyl Analogs of Pyrene–Containing Phosphatidylcholine as New Fluorescent Lipid Probes with Intramolecular Quenching

Two new derivatives of phosphatidylcholine with an intramolecularly quenched fluorescence, namely, 1––bromoundecanoyl–2–[4–(pyren–1–yl)butyroyl]–sn–glycero–3–phosphocholine (BPPhC) and 1–(9,10–dibromostearoyl)–2–[4–(pyren–1–yl)butyroyl]–sn–glycero–3–phosphocholine (DBPPhC), have been obtained by replacing acyl chains by residual pyrenebutyric and bromine–labeled fatty acids. Their structure has been verified by the ¹H–NMR method and the spectral properties have been characterized in media of different polarity with the aid of absorption and fluorescent spectroscopy. It has been established that when BPPhC and DBPPhC are included in liposomes, the intensity of their fluorescence changes markedly as a function of the physical state of the bilayer, which makes it possible to use the compounds obtained as lipid probes for investigating the properties of biological and artificial membranes.     

Studies of vibrational relaxation in CDF3 following intense laser excitation

The V-T/R relaxation time of CDF₃ was measured studying the laser-induced infrared fluorescence emitted by vibrationally excited CDF₃. Following excitation by the 10R(12) line of a TEA CO₂ laser infrared fluorescence has been detected without spectral resolution in the 1100–700 cm^–1 range. A decay rate of 28.8 ms^–1 Torr^–1 was obtained for pure CDF₃ when it is excited with a fluence of 390 mJ/cm². Measurements have also been made in the presence of different bath gases (He, Ne, Ar, Xe, and CHF₃).     

XeCl-laser-generated ablation products from a nitrogen-rich polymer studied by laser-ionization mass spectrometry

Laser-ionization time-of-flight mass spectrometry has been used to probe laser-ablation products from a nitrogen-rich polymer at a wavelength of 308 nm. The ablation products at a laser fluence of 150 mJ/cm² showed, similar to 532 nm ablation studied previously [18], two strong peaks due to neutral species that were assigned to C⁺ and CN⁺, as well as several weak peaks that were assigned to CH⁺, HCN⁺, HCNH⁺, H_nN–CN⁺ (n=1–3), and H₂N–C=N–CN⁺ or H₂N–C=N–CN⁺. The ablation products at 870 mJ/cm² revealed, in addition to a broad signal due to ionic products generated directly by the ablation laser, several peaks due to neutral products that were assigned to C⁺, C ₂ ⁺ , C ₃ ⁺ , CN⁺, HCN⁺, HCNH⁺, and NCCN⁺. The most probable flight velocities for major neutral products are 5.7×10⁴ cm/s at 150 mJ/cm² and 2.3–2.7×10⁴ cm/s at 870 mJ/cm². The results at a laser fluence of 150 mJ/cm² support the finding that the translational energy of the tragments has importance for the collision-induced product generation in the laser plume, as suggested earlier [18]. Furthermore, the product generation at 870 mJ/cm² is interpreted by the ejection of small neutral and ionic fragments, and subsequent reactions among the fragments.     

Determination of the Gamow–Teller strength function for the neutron-deficient isotopes In

The Gamow–Teller β decays of the neutron-deficient indium isotopes ^104–107In have been investigated by using total absorption γ-ray spectrometry on mass-separated sources. The experimental Gamow–Teller strength, deduced as a function of the excitation energy in the daughter nuclei ^104–107Cd, is compared to shell-model predictions.     

Enhancement of the Fluorescence Quenching Efficiency of DPPH<Superscript>•</Superscript> on Colloidal Nanocrystalline Quantum Dots in Aqueous Micelles

Luminescent CdS quantum dots capped with thioglycolic acid (CdS-TGA QDs) were demonstrated to serve as a fluorescence probe for a model organic radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•), employing the quenching of the CdS-TGA QDs emission signal by the radical. Under the optimum conditions, the quenching efficiency of DPPH^• on CdS-TGA QDs was proportional to the concentration of DPPH^•, following Stern-Volmer relationship. Different types of surfactants (cationic, anionic and neutral surfactants) were introduced to CdS-TGA QDs in order to increase the detection sensitivity. The fluorescence intensity of CdS-TGA QDs was greatly enhanced by cationic and neutral surfactants. Moreover, the quenching efficiency of DPPH^• on the QDs in the presence of micelles was remarkably ca. 13 times higher than that in the system without micelles. Effects of pH and concentration of surfactants on the fluorescence quenching of CdS-TGA QDs were investigated. Electron spin resonance (ESR) spectroscopy was also used to monitor the DPPH radical species in CdS-TGA QDs mixtures with and without micelles. Fluorescence quenching mechanisms of CdS-TGA QDs by DPPH^• in the presence and in the absence of CTAB were proposed.     

Environmental influence on the IR fluorescence of Xe<Subscript>2</Subscript><Superscript>*</Superscript> molecules in electron beam excited Ar–Xe mixture at high density

We report new measurements of the near infrared (NIR) Xe₂^* excimer fluorescence in an electron–beam–excited Ar (90%)–Xe (10 %) mixture at room temperature. Previous measurements up to a density N≈2×10²⁶ m^-3 discovered a broad excimer fluorescence band at ≈7800 cm^-1, whose center is red–shifted by increasing N [A.F. Borghesani, G. Bressi, G. Carugno, E. Conti, D. Iannuzzi, J. Chem. Phys. 115, 6042 (2001)]. The shift has been explained by assuming that the energy of the optical active electron in the molecule is shifted by the density–dependent Fermi shift and by accounting for the solvation effect due to the environment. We have extended the density range up to N≈6×10²⁶ m^-3, confirming the previous measurements and extending the validity of the interpretative model. A detailed analysis of the width of the fluorescence band gives a value of 2.85 nm for the size of the investigated excimer state. Such a large value lends credibility to the validity of the proposed explanation of the experimental findings.     

A turn-on fluorescent chemosensor for Hg based on phenanthroline fluorophore

Dipyrido[3,2-a:2′,3′-c]-phenazine (L) was employed as a selectively fluorescent chemosensor for Hg²⁺ in DMF solution under buffered conditions with its fluorescence being strongly increased. The fluorescence increasing was attributed to the formation of L–Hg²⁺ by 1:1 complex ratio (K=3.7×10⁵ M⁻¹), which constitutes the basis for the determination of Hg²⁺ with the prepared chemosensor. The experiment results also show that the response behavior of L to Hg²⁺ is pH independent in the range of pH 6.0–9.0 and show excellent sensitivity and selectivity for Hg²⁺ over other examined metal ions.     

Molecular Dynamics of Biological Probes by Fluorescence Correlation Microscopy with Two-Photon Excitation

We report on the application of fluorescence correlation microscopy under two-photon excitation of fluorophores of biological interest: FITC–dextran (MW, from 20 to 150 kDa), green fluorescent protein (MW, 27 kDa), and fluorescein (MW, 330 Da). Under these experimental conditions, the translational diffusion coefficients of these molecules in aqueous solutions derived from the fluorescence intensity autocorrelation function were determined for the first time and were found to be 24 × 10^–7, 8.2 × 10^–7, and 3 × 10^–7 cm² s^–1 for 150-kDa FITC–dextran, green fluorescent protein, and fluorescein, respectively. These results are discussed in connection with previously reported results obtained by different methods. The great sensibility of the system has been applied to single-molecule detection of the smaller fluorophore, fluorescein.     

Non-ideal behavior of mixed micelles of cationic gemini surfactants with varying spacer length and anionic surfactants: A conductimetric study

Mixtures of cationic and anionic surfactants (catanionic mixtures) are often highly non-ideal, exhibiting strong synergism in their interfacial properties, manifested for instance in significant reduction of the mixture critical micelle concentration (cmc) and enhanced adsorption onto surfaces. The magnitude of such effects is of fundamental interest and has important application-related uses (e.g. in detergent formulation). In this work, the micellization process of mixtures of cationic gemini surfactants of the alkanediyl-α,ω-bis(alkyl dimethylammonium bromide) type, denoted by 12–n–12 (where n is the spacer length), with several common anionic surfactants has been investigated by electric conductivity. For the purpose of comparison, cationic–cationic mixtures, where dodecyltrimethylammonium bromide is the second cationic surfactant, have also been investigated. The cationic/anionic mixtures show relatively significant deviations from ideal behavior, depending on the structure of the gemini surfactant and the anionic surfactant. The interaction parameter β₁₂, within Rubingh's non-ideal model for mixed micelles, has been calculated for each mixture, as well as the mixed micelle composition as a function of mixture composition. The observed synergism in the different mixtures is interpreted in terms of the molecular structure of the surfactants and corresponding head–head and chain–chain interactions.     

Cation-Responsive Fluorescence Of Dansyl-Labeled Polyanions Bearing Crown Ether Units

Anionic polymers bearing both crown ether units and Dansyl units were prepared by radical terpolymerization of the corresponding monomers, and the effect of cations on the fluorescence properties of the polymers was studied in aqueous media. The fluorescence peaks of the polymers are observed at 500–527 nm. The fluorescence quantum yields () of the polymers were found to be 6.3 × 10^–3–4.0 × 10^–1, depending on the polymer structure. On the addition of alkali metal cations, the fluorescence intensity increases in the order LiCl < NaCl < KCl < RbCl < CsCl. The polymer which has almost-equimolar amounts of crown ether groups and–COOH groups shows the highest responsiveness to the cations added. The structure of the anionic moieties in polymers strongly affects the cation-responsive fluorescence. The mechanism for the cation-induced changes in fluorescence is discussed.     

Plasma in open magnetic trap injected from independent UHF source

The properties of plasma injected into the open magnetic trap of uniform field from an independent UHF source have been investigated. It is established that a rather quiescent plasma with control density within the range of 2×10⁸–2×10¹² cm^–3 and temperature 2–3 eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it is not practically changed with the variation of neutral gas pressure and reaches the maximum value 4×10^–3 s at magnetic field strength in the trap equal 1600 Oe. Besides, the experimental data are analyzed on the basis of balance equations.     

Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence

Nitrogen atoms have been detected in stoichiometric flat premixed H₂/O₂/N₂ flames at 33 and 96 mbar doped with small amounts of NH₃, HCN, and (CN)₂ using two-photon laser excitation at 211 nm and fluorescence detection around 870 nm. The shape of the fluorescence intensity profiles versus height above the burner surface is markedly different for the different additives. Using measured quenching rate coefficients and calibrating with the aid of known N-atom concentrations in a discharge flow reactor, peak N-atom concentrations in these flames are estimated to be on the order of 10¹²–5×10¹³ cm^–3; the detection limit is about 1×10¹¹ cm^–3.     

High-Resolution Laser Spectroscopy of YbCl: The AΠ–XΣ Transition

The A²Π–X²Σ⁺ transition of ¹⁷⁴Yb³⁵Cl and ¹⁷²Yb³⁵Cl has been rotationally analyzed for the first time. Doppler-limited laser excitation spectroscopy with selective detection of fluorescence was used to obtain spectra of the 0–0 and 1–0 bands with a measurement accuracy of approximately 0.0035 cm⁻¹. Resolved fluorescence was used to record the 0–1, 0–2, and 0–3 bands and to unequivocally assign the rotational numbering, N, to the laser excitation spectra. In total, over 1300 line positions have been measured and assigned for each of the two isotopomers and employed in least-squares fits of molecular parameters. The principal results for the A²Π state are A_e = 1491.494(2) cm⁻¹ and R_e = 2.4433(1) Å, and for the X²Σ⁺ state, R_e = 2.4883(2) Å and γ_e = 4.59(2) × 10⁻³ cm⁻¹. The interaction between the X²Σ⁺ and A²Π states has been investigated and is shown to be the main contributor to the spin–rotation splitting in the ground state.     

Microhardness of crystals of KBr-KI solid solutions with Sr2+ and OH− impurities

The microhardness, conductivity, and dielectric-loss angle have been studied in KBr and KI single crystals and in their solid solutions with Sr²⁺ and OH^– impurities. It is shown that the Sr²⁺ impurity dissolves only slightly in KI crystals and in KBr-KI solid solutions having a large KI content. Addition of the anionic OH^– impurity to the molten salts reduces the micro-hardness of KBr but it does not affect that of KI crystals or KBr-KI solid solutions having a large KI content. The composition dependence of the microhardness for KBr-KI solid solutions is constructed on the basis of the microhardness values for the corresponding crystals purified of cationic impurities of different valence.Translated from Izvestiya VUZ. Fizika, No. 10, pp. 18–21, October, 1969.