Laser Spectra and Efficiencies of Pyrazolo Derivatives of Coumarins

Abstract

Of the new laser dyes of coumarin series reported earlier, pyrazolo derivatives have been further studied. The paper reports their laser spectra and efficiencies in various solvents compared to a standard coumarin laser dye C₅₁₅. One of the derivatives shows comparable output under optimum concentration conditions as compared to the standard.     

Factors affecting the low-dose gamma irradiation of hydrocarbons

The effect of differing conditions on the extent and nature of the damage produced in organic substances by γ-irradiation at low dose rates has been examined by a new chromatographic method which makes detection possible in a region where all other standard techniques fail. Use is made of the fact that certain surface active dyes profoundly affect the shape of a chromatographic band in a manner related to the composition of the material undergoing chromatography.

Taking length of outline per unit area as a measure of the shape of the band on paper impregnated with such dyes, a method of chromatography has been evolved, having a completely standardized development technique for all mixtures which does not require the separation of the components of the mixture.

This outline/area index varies with the temperature according to the nature of the polar groups of the compounds present in the mixture under investigation and with the concentration of the individual components.

It is thus possible to construct a three dimensional diagram having as axes, temperature, concentration and index. The diagram obtained is absolutely characteristic of the composition of a given mixture.     

Comparative study on the process behavior and reaction kinetics in sonocatalytic degradation of organic dyes by powder and nanotubes TiO2

Sonocatalytic degradation of various organic dyes (Congo Red, Reactive Blue 4, Methyl Orange, Rhodamine B and Methylene Blue) catalyzed by powder and nanotubes TiO₂ was studied. Both catalysts were characterized using transmission electron microscope (TEM), surface analyzer, Raman spectroscope and thermal gravimetric analyzer (TGA). Sonocatalytic activity of powder and nanotubes TiO₂ was elucidated based on the degradation of various organic dyes. The former catalyst was favorable for treatment of anionic dyes, while the latter was more beneficial for cationic dyes. Sonocatalytic activity of TiO₂ nanotubes could be up to four times as compared to TiO₂ powder under an ultrasonic power of 100 W and a frequency of 42 kHz. This was associated with the higher surface area and the electrostatic attraction between dye molecules and TiO₂ nanotubes. Fourier transform-infrared spectrometer (FT-IR) was used to identify changes that occurred on the functional group in Rhodamine B molecules and TiO₂ nanotubes after the reaction. Sonocatalytic degradation of Rhodamine B by TiO₂ nanotubes apparently followed the Langmuir-Hinshelwood adsorption kinetic model with surface reaction rate of 1.75 mg/L min. TiO₂ nanotubes were proven for their high potential to be applied in sonocatalytic degradation of organic dyes.     

Long-term luminescence of sensibilizers in tissues at the conditions of oxygen deficiency due to photodynamic effect

Long-term luminescence of organic dyes (xanthene dyes, halogen substituted fluoroscein) was used for an in vitro study of the photodynamic effect of exogenic probes in malignant tumors and healthy tissues of mice. It is shown that the photodynamic activity of oxygen and the dynamics of its concentration in tissues can be estimated from the delayed fluorescence of exogenic probes caused by singlet–triplet annihilation of singlet oxygen and excited triplet states of the molecules of photosensitizer dyes. It is found that quenching of long-term luminescence of photosensitizers significantly differs in tumors and normal tissues.

     

Degradation of reactive,acid and basic textile dyes in the presence of ultrasound and rare earths [Lanthanum and Praseodymium]

Degradation of five textile dyes, namely Reactive Red 141 (RR 141), Reactive Blue 21 (RB 21), Acid Red 114 (AR 114), Acid Blue 113 (AB 113) and Basic Violet 16 (BV 16) in aqueous solution has been carried out with ultrasound (US) and in combination with rare earth ions (La³⁺ and Pr³⁺). Kinetic analysis of the data showed a pseudo-first order degradation reaction for all the dyes. The rate constant (k), half life (t_1/2) and the process efficiency (φ) for various processes in degradation of dyes under different experimental conditions have been calculated. The influence of concentrations of dyes (16–40 mg/L), pH (5, 7 and 9) and rare earth ion concentration (4, 12 and 20 mg/L) on the degradation of dyes have also been studied. The degradation percentage increased with increasing rare earth amount and decreased with increasing concentration of dyes. Both horn and bath type sonicators were used at 20 kHz and 250 W for degradation. The sonochemical degradation rate of dyes in the presence of rare earths was related to the type of chromophoric groups in the dye molecule. Degradation sequence of dyes was further examined through LCMS and Raman spectroscopic techniques, which confirmed the sonochemical degradation of dyes to non-toxic end products.     

Photoquenching parameters for commonly used laser dyes

Laser dyes which are commonly used in pulsed laser pumped dye laser (PLPDL) systems have been investigated. It is shown that photoquenching plays an important role in the pumping process of all laser dyes, determining the efficiency of the PLPDL. Molecular parameters, such as absorption cross sections at various pumping wavelengths and fluorescence lifetimes of theS _n (n>1) excited electronic states of laser dyes, have been determined utilizing the photoquenching technique.     

Laser dye stability

Lasing characteristics and bleaching of four Eastman Kodak ir dyes have been examined in dimethyl sulfoxide. These ir dyes are shown to improve in performance in the absence of oxygen. Their photochemical stability was found to be comparable to the quinolone laser dyes when exposed to flashlamp excitation. Photodecomposition of the ir dyes under lasing conditions was found to vary between 1.6 and 6×10⁻¹⁰ moles of dye for each joule (electrical) of input energy; in comparison, the photodecomposition values for the better coumarin dyes was 0.2 to 1.0×10⁻¹⁰ moles/J at a concentration of 1.0×10⁻⁴ M in ethanol. It was also found that increasing the concentration of these tricarbocyanine dyes gives a marked improvement in the useful lifetime of these solutions as lasing media in the absence of oxygen.     

Dual fluorescence and laser emissions from fluorescein-Na and eosin-B

Dual laser emissions were observed from fluorescein-Na and eosin-B in ethanolic solutions individually in the concentration range from 10⁻² to 10⁻³ mol dm⁻³ under N₂ laser excitation. The first compound was found to lase at two distinct regions with wavelength maxima around 540, 550 nm, while the second one around 558, 574 nm. Steady-state absorption, fluorescence excitation, fluorescence polarization, fluorescence emission and decays of the dyes in various solvents under varying conditions of excitation and detection systems were carried out to identify the nature of the emitting species responsible for laser emissions in two distinct regions. Both the dyes exhibited concentration and excitation wavelength dependence of fluorescence and the effects were found to be more pronounced in binary solution. The fluorescence decays of dyes were monoexponential in ethanol, while in some other solvents used, the decays showed biexponential behavior. The absorption and excitation studies using thin layers of solutions revealed the formation of dimers with the dye concentration around 1×10⁻³ mol dm⁻³. Fluorescence polarization and decay studies confirmed the presence of dimers. The two laser bands observed in the shorter and longer wavelengths were respectively ascribed to monomeric and dimeric species.     

Computational study of new azo dyes with different anchoring groups for dye-sensitised solar cells

Some of new azo dyes with different anchoring groups, such as biscarbodithiolic acid, hydroxamic acid, phosphonic acid, carboxcylic acid and sulfonic acid have been investigated theoretically to evaluate the effects of various anchoring groups on the optical and electronic properties of the dyes in dye-sensitised solar cells. Optical and electronic properties, UV–Vis absorption spectra, light-harvesting efficiency, lifetime of the excited state, chemical hardness and lowest unoccupied molecular orbital (LUMO) orbital weight of the dyes on the anchoring groups, have been studied to shed light on how the various anchoring groups influence the properties of the dyes. The biscarbodithiolic acid-based dye shows the longest maximum absorption wavelength and the widest absorption spectra together with the highest light-harvesting efficiency, the longest lifetime of the excited state and the highest the LUMO orbital weight of the dye on the atoms of the anchoring group, suggesting the good ability in electron injection. Theoretical calculations have been also performed on the adsorption of these dyes on the TiO₂ anatase (101) surface. These results show that the biscarbodithiolic acid-based dye has the highest adsorption energy and the largest negative shift of the conduction band of TiO₂ due to the adsorption of the dye onto the TiO₂.     

Interaction between flavin mononucleotide-containing azoreductase and azo dyes

ABSTRACT

Azoreductase, a flavin mononucleotide-containing oxidoreductase from Escherichia coli, can catalyze the reduction of azo dyes to form aromatic amine compounds. Few spectroscopic studies have explored the binding mode of azo dyes or the role of the arginine at site 59 in Azoreductase. In this article, protein engineering strategy has been used to construct one mutant in which the arginine residue at site 59 was mutated to glycine. Fluorescence spectroscopic data showed that the addition of Methyl Red and Methyl Orange resulted in the fluorescence quenching of the cofactor flavin mononucleotide bound to Azoreductase. The association constant was fitted using the standard binding equation instead of the Stern-Volmer equation. The results showed that the mutation from the arginine to glycine at site 59 weakened the association constant from 2.21?×?10⁵?L.mol^?1 to 4.55?×?10⁴?L.mol^?1 at 25°C. A similar phenomenon was also observed when Methyl Orange was used as a substrate. In each case, the association constant tended to decrease as the temperature increased from 25°C to 37°C. Thermodynamic parameter analysis revealed that the interaction type changed from a van der Waals interaction (between Azoreductase and the dyes) to a hydrogen bonding interaction (between the mutant and the dyes). Moleculcar docking was also performed in this work to provide some support for the binding mode and binding stability between Azoreductase/mutant and azo dyes.     

Additive-free controllable fabrication of bismuth vanadates and their photocatalytic activity toward dye degradation

Bismuth vanadates (BiVO₄) with various crystal structures (tetragonal scheelite, monoclinic scheelite, and tetragonal zircon) and morphologies (sphere-, nanosheet-, dendrite-, and flower-like) were controllably fabricated by using a mild additive-free hydrothermal treatment process under the different preparation conditions. The crystal structures, morphologies, and photophysical properties of the products were well-characterized. Subsequently, their UV- as well as visible-light photocatalytic performance was evaluated via dyes rhodamine B (RB) and methylene blue (MB) degradation. Special attention was paid to evaluate the correlation of the reactivity with crystal structure, morphology, and electronic structure of as-prepared BiVO₄ samples.     

Effect of γ-Irradiation on the Absorption Spectra of the Solutions of Acid Dyes

The absorption spectra of -irradiated solutions of some acid dyes in various solvents are investigated. The characteristic times of radiation-induced destruction of dyes in the solutions are determined. It is shown that irreversible radiative discoloration of solutions occurs as a result of the interaction of the dye molecules with the oxygen-containing radicals formed in radiolysis of solvents. Practical recommendations for increasing the radiation stability of the solutions of acid dyes and for using them as detectors of a dose of hard radiation are given.     

Singlet and Triplet State Properties and Singlet Oxygen Yield of an Amino-Acyl-Quinoxalinone Yellow Dye

Amino-acyl-quinoxalinone yellow dyes are cyclised analogues of the yellow azomethine dyes developed for, and still used in, silver halide colour photography. Unlike image azomethine dyes, which are rapidly deactivated in their excited states by torsion about the azomethine bond, amino-acyl-quinoxalinone dyes have an interesting photophysics because torsion is not possible due to their cyclised structure. We report results from studies on singlet and triplet state properties, and singlet oxygen yields, of the yellow dye, 7-diethylamino-3-(2,2-dimethyl-propionyl)-5-methyl-1-phenyl-1H-quinoxalin-2-one, in polar and nonpolar solvents. The dye photophysics is characterised by a weak fluorescence, with a solvent dependent emission yield (Φ_F?≈?0.002–0.004), and short singlet state lifetime (τ_expt?≈?20–50 ps), both increasing by a factor of ≈2 in going from polar acetonitrile to non-polar dioxane as solvent. DFT ZINDO calculations show a transition involving significant electron transfer from the diethyl-amino group into the carbonyl region of the molecule. In solution, in the presence of oxygen, the triplet state decays almost exclusively by oxygen quenching, and singlet oxygen is produced in high yield (Φ_??≈?0.5–0.55). The triplet state absorbs across the 450–750 nm region with maxima around 480 and 650 nm, and moderate molar absorption coefficients (ca. 6000–8000 M^?1 cm^?1). In a glass at 77 K, triplet decay gives a red phosphorescence, with λ_max?≈?640–650 nm, and a ?≈?0.25 s lifetime. If singlet oxygen yields are a good indication of triplet yields, then internal conversion and intersystem crossing occur with roughly equal efficiency.

     

Synthesis of BODIPY Derivatives Substituted with Various Bioconjugatable Linker Groups: A Construction Kit for Fluorescent Labeling of Receptor Ligands

The goal of the present study was to design small, functionalized green-emitting BODIPY dyes, which can readily be coupled to target molecules such as receptor ligands, or even be integrated into their pharmacophores. A simple two-step one-pot procedure starting from 2,4-dimethylpyrrole and ω-bromoalkylcarboxylic acid chlorides was used to obtain new ω-bromoalkyl-substituted BODIPY fluorophores (1a–1f) connected via alkyl spacers of different length to the 8-position of the fluorescent dye. The addition of radical inhibitors reduced the amount of side products. The ω-bromoalkyl-substituted BODIPYs were further converted to introduce various functional groups: iodo-substituted dyes were obtained by Finkelstein reaction in excellent yields; microwave-assisted reaction with methanolic ammonia led to fast and clean conversion to the amino-substituted dyes; a hydroxyl-substituted derivative was prepared by reaction with sodium ethylate, and thiol-substituted BODIPYs were obtained by reaction of 1a–1f with potassium thioacetate followed by alkaline cleavage of the thioesters. Water-soluble derivatives were prepared by introducing sulfonate groups into the 2- and 6-position of the BODIPY core. The synthesized BODIPY derivatives showed high fluorescent yields and appeared to be stable under basic, reducing and oxidative conditions. As a proof of concept, 2-thioadenosine was alkylated with bromoethyl-BODIPY 1b. The resulting fluorescent 2-substituted adenosine derivative 15 displayed selectivity for the A₃ adenosine receptor (ARs) over the other AR subtypes, showed agonistic activity, and may thus become a useful tool for studying A₃ARs, or a lead structure for further optimization. The new functionalized dyes may be widely used for fluorescent labeling allowing the investigation of biological targets and processes.     

Detection of Genuine Multipartite Entanglement in Multipartite Systems

We investigate genuine multipartite entanglement in general multipartite systems. Based on the norms of the correlation tensors of a multipartite state under various partitions, we present an analytical and sufficient criterion for detecting the genuine four-partite entanglement. The results are generalized to arbitrary multipartite systems.

     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.     

Pseudo first ordered adsorption of noxious textile dyes by low-temperature synthesized amorphous carbon nanotubes

Amorphous carbon nanotubes (a-CNTs) were synthesized by solid state reaction. The as prepared a-CNTs were characterized by X-ray diffraction, field emission scanning and high resolution transmission electron microscope and Raman spectroscopy. As-synthesized a-CNTs were used for, the first time, for removing different organic dyes from water. The dyes mainly include Rhodamine B and Methyl Orange and systematic batch mode studies of a-CNTs assisted adsorption have been executed in detail. The removing efficiency of a-CNTs has also been investigated for various sorption parameters like contact time, dosage, pH, initial dye concentration, contact time etc.It is seen that a-CNTs can be material of potential for removal of dyes. In case of Rhodamine B, the maximum time for removal was 45 min whereas for Methyl orange rapid removal was plausible in about 30 min even in ambient condition. The experimental data have been well correlated with classical Langmuir-Freundlich and Temkin adsorption models.     

Tunable,narrow bandwidth, 2 MW dye laser pumped by a KrF1 discharge laser

Characteristics of p-terphenyl and PBD, the most efficient uv dyes, have been investigated under high intensity pumping by a multi-atmosphere KrF¹ discharge laser at 248 nm wavelength. Energy conversion efficiencies, spectral features and temporal behaviour of the dyes were studied parametrically. A maximum powerof 2 MW uv emission with a bandwidth of ～2×10^-2 nm was obtained for PBD. It was found that a mixture of both dyes provided higher (by a factor of 1.3) output in the range 348–366 nm than either of the dyes alone. Significant pump intensity dependent conversion efficiency and pulse shape variations were observed for the most efficient uv dye, p-terphenyl and were related to triplet-triplet adsorption processes in the dye.     

Decoupling Parameter for Rotational Bands Based on Mixed-Symmetry States

The energy as determined experimentally for the first excited 2⁺ state of the ¹⁵⁶Gd rotational band based on the mixed-symmetry state is extremely small in relation to characteristic values of this energy in deformed nuclei. The possibility of explaining this experimental fact by a large value of the decoupling parameter is explored. The result is that the decoupling-parameter values obtained under various assumptions on the structure of the mixed-symmetry state are too small for explaining the experimental excitation energy of the state in question.

     

Water Soluble Metallo-Phthalocyanines: The Role of the Functional Groups on the Spectral and Photophysical Properties

Strategies are reported that produce symmetrical metal-free and metallo-phthalocyanine dyes, Pc and MPc, respectively, containing various numbers of water solubilizing carboxylic acid groups on their periphery that provide a dual role by also serving as functional groups to covalently link primary amine-containing targets to these dyes. In order to induce water compatibility and to minimize the degree of aggregation, the periphery of the macrocycle was decorated with various numbers of water-solubilizing groups and/or altering the identity of the metal center. The influence of the number of solubilizing groups and metal center on the spectral and photophysical properties were evaluated. MPc dyes containing 4, 8, or 16 carboxylic acid groups exhibited similar absorption and emission maxima (677 and 686 nm, respectively) with the molar absorptivity of the Q-band ∼10⁵ M⁻¹ cm⁻¹. Results indicated that the fluorescence lifetimes and quantum yields varied as a function of the metal center; the degree of carboxylation did not significantly alter these properties in DMSO, but did mediate the solubility and aggregation states when placed in aqueous solvents. The water solubilizing groups could also serve as labeling moieties for targets bearing primary amines. Results showed that the conjugate, produced by covalently linking an MPc to streptavidin through one of its carboxylate groups, generated a red-shift in the emission maximum with a fluorescence lifetime shorter than that of the native MPc dye.