Two-photon laser photochemistry of a coumarin laser dye

Irradiation of 7-dimethylamino-4-methylcoumarin (1), a commercially available laser dye, in ethanol solution with the focused output of an XeCl excimer laser at 308 nm resulted in the formation of yellow oligomeric material derived from the ethanol solvent. The efficiency of formation of the yellow material was shown to be dependent on the intensity of the laser light, indicating that the photochemistry involved absorption of two photons. The oligomeric material is proposed to be a substance which interferes with stimulated emission in coumarin dye lasers. In addition, acetaldehyde and several gaseous products, principally hydrogen and butane, were formed. A product resulting from the coupling of 1 with the ethanol solvent was also isolated and characterized. Excimer laser irradiation of 1 in methanol yielded formaldehyde, hydrogen and solvent oligomers, while irradiation of 1 in benzene resulted in the formation of a black precipitate. The non-oligomeric products are similar to those observed from the direct irradiation of the solvent in the vacuum-UV region. A mechanism is proposed for the observed photochemistry in which 1 absorbs, sequentially, two photons from the laser pulse, resulting in the formation of a highly excited state which then transfers energy to the solvent.     

Transient absorptions in a polymethine laser dye

Transient absorptions in HITC are investigated in the range 650-950 nm by a conventional flash photolysis technique and “picosecond” spectroscopy with a train of 6 to 7 pulses. This study gives evidence for S₁-S_n absorption, photoisomer and triplet generation. The comparison between experimental data and computer solutions allows the determination of the rate constants of these processes and molar extinction coefficients of the absorption spectra. Taking into account these results, we discuss the limitations of the performances of the flashlamp excited HITC dye laser.     

Dimerization of thymol blue in solution: Theoretical evidence

The possibility of dimerization of thymol blue was addressed by ab initio and force field calculations. In agreement with experimental information, a dimer forming symmetrical chemical environments for hydrogen bond formation was determined. This dimer is stable in vacuum and aqueous media and corresponds to the same protonated state proposed by the experiment. A comparison of the CVFF and MM3 force fields and ab initio results shows the suitability of CVFF to qualitatively describe this system.     

Titanium dioxide sensitization with a biscyanine dye in the photocatalytic reduction of methylene blue

Kinetics and Catalysis - Photosensitive heterostructures containing titanium dioxide and a sensitizer, viz., a cyanine dye with two conjugated chromophores have been obtained. Their absorption...     

Colorimetric assay for lysozyme using Micrococcus luteus labeled with a blue dye, Remazol brilliant blue R, as a substrate.

Micrococcus luteus (M. lysodeikticus) labeled with Remazol brilliant blue R (blue ML) was prepared as a novel substrate for the colorimetric assay of lysozyme. The treatment of the labeled substrate with lysozyme resulted in the release of soluble blue products which can be easily measured spectrophotometrically at 600 nm. The blue color was most efficiently released at pH 7 and ionic strength of 0.2 on incubation with hen lysozyme at 40 degrees C. A new colorimetric method for the assay of lysozyme using this substrate was developed. The assay system gave a linear dose-response curve, and as little as 0.1 microgram of human lysozyme (1 microgram/ml, 100 microliters) can be detected. The present method is more convenient and reproducible than the conventional lysozyme assay with bacterial cells. Application of the system to the determination of lysozyme in human serum is described.     

Supramolecular organization of toluidine blue dye in solid amorphous phases

Toluidine blue (TB) dye molecules are intensively utilized for large-area photophysics applications such as carcinoma detection, photoinactivation of bacteria, biosensors, and photovoltaic cells. Understanding the nature of the TB aggregation state becomes an essential point of the research process in order to know the structure-function relationship and to foresee technological applications of this class of metachromatic-dye molecules. However, no structural information on toluidine blue is available in the literature, maybe because of the poor crystalline character of the aggregate. Here, we present the first structural determination of TB organic molecules using the energy dispersive X-ray diffraction technique. The investigation highlights dimeric arrangements of stacked molecules in antiparallel fashion, forming a superstructure of two dimers in a transverse arrangement. The behavior of the TB higher aggregates indicates that these dye molecules, in spite of repulsion due to similar charge (cationic dyes), undergo self-aggregation to form helical conformations.     

Phase control of the competition between electronic transitions in a solvated laser dye

Excited state population can be manipulated by resonant chirped laser pulses through pump–dump processes. We investigate these processes in the laser dye LD690 as a function of wavelength by monitoring the saturated absorption of chirped ultrafast pulses. The resulting nonlinear absorption spectrum becomes increasingly complex as the pulse is tuned to shorter wavelengths. However, fluorescence measurements indicate that the excited state population depends weakly on chirp when the pump wavelength is far from the lowest order electronic transition. Using a learning algorithm and closed-loop control, we find nonlinear chirp parameters that optimize features in the transmission spectrum. The results are discussed in terms of competition between excited state absorption and stimulated resonant Raman scattering.     

Optimization and mass transfer simulation of remazol brilliant blue R dye adsorption onto meranti wood based activated carbon

Remazol brilliant blue R dye (RBBR) brings toxicity to living organisms once it enters the environment. This study utilized response surface methodology (RSM) and Polymath software for optimization and mass transfer simulation purposes, respectively. RSM revealed that the optimum preparation conditions of meranti wood-based activated carbon (MWAC) were 441 W, 5.76 min, and 1.35 g/g for radiation power, radiation time, and KOH:char impregnation ratio (IR), respectively, which translated into 86.39 mg/g of RBBR uptakes and 31.94 % of MWAC’s yield. The simulation study predicted the mass transfer rate, r_m to be 112.20 to 1007.50 s^?1 and the adsorption rate, k₁ to be 3.96 to 4.34 h^?1. The developed model predicted the adsorption surface area, a_m to be 790.04 m²/g and this value is highly accurate as compared to the actual mesopores surface area of 825.58 m²/g. Mechanism analysis divulged that the interaction that occurred between RBBR molecules and MWAC’s surface were hydrogen bond (methylene and alkyne), dipole–dipole force (alkyl carbonate, terminal alkyne, and methoxy), and ion–dipole force (primary amine). The isotherm and kinetic studies found that the adsorption data obeyed the Freundlich model and pseudo-first-order (PFO) model the best, respectively. The Langmuir maximum adsorption capacity, Q_m was computed to be 327.33 mg/g. Thermodynamic parameters were calculated to be ?4.06 kJ mol^?1, 0.06 kJ mol^?1 K^?1, –22.69 kJ mol^?1, and 16.03 kJ mol^?1 for ΔH°, ΔS°, ΔG°, and E_a, respectively, which signified the adsorption process studied was exothermic, spontaneous and governed by physisorption.     

A tunable picosecond dye laser for use in dioxin analysis.

A distributed-feedback dye laser with a quenching cavity was designed and constructed for generating a tunable picosecond pulse with a narrow spectral linewidth. This nearly transform-limited pulse was succeedingly amplified by a triple-pass off-axis amplifier. The pulse duration and the spectral linewidth were 60 ps and 9.4 pm, respectively. The amplified pulse was frequency-doubled by second-harmonic generation, producing a 0.5-mJ pulse with no background emission. The potential advantage of this laser in the analysis of dioxin based on supersonic jet/resonance-enhanced multiphoton ionization/mass spectrometry is discussed.     

HCO radical kinetics: Conjunction of laser photolysis and intracavity dye laser spectroscopy

HCO radical at a concentration of about 10¹⁴ cm^?3 is produced by monochromatic laser photolysis of H₂CO with a 0.6 mJ frequency-doubled, flashlamp-pumped dye laser pulse. Intracavity dye laser spectroscopy quantitatively monitors HCO absorbance near 614 nm as a function of delay time between photolysis and probing pulses. Rate constants for HCO + O₂ and HCO + NO are found to be 4.0 ± 0.8 × 10^?12 and 1.45 ± 0.2 × 10^?11 cm³ molecule^?1 sec^?1.     

Saturation spectroscopy of NH2 using a CW dye laser

Hyperfine structure in the electronic spectrum of NH₂ has been resolved using the technique of intermodulated fluorescence with CW dye laser excitation. From the observed spacings values for the ¹⁴N Fermi contact and dipole-dipole coupling terms have been estimated for both the ground state and the Π(0,10,0) vibrational level of the à ²A₁ excited electronic state.     

Efficient thiocyanate-free sensitizer: a viable alternative to N719 dye for dye-sensitized solar cells

We have designed and synthesized a new thiocyanate-free sensitizer coded as SPS-01 and used it as the sensitizer in a TiO(2) based nanocrystalline dye-sensitized solar cell (DSSC). SPS-01 exhibits strong visible absorption properties with maximum peak around at 532 nm. The overall power conversion efficiency (PCE) of a DSSC sensitized with SPS-01 (7.96%) is higher than that of N719 (7.30%) under identical experimental conditions. This high PCE is attributed mainly due to the improvement in the short circuit current.     

Photoluminescent mechanism of a proton-transfer laser dye in highly doped polymer films

Photoluminescent properties in thin films of the proton-transfer laser dye, 2-(2-hydroxyphenyl)benzothiazole (HBT) were investigated, when it was doped into hole-transport polymer, poly(N-vinylcarbazole) and when it was codoped with hole-transport small molecule, N,N′-di(m-tolyl)-N,N′-diphenylbenzidine (TPD) into polystyrene. The more the doping concentration of HBT was raised up to about 40 wt%, the more its photoluminescent intensity was enhanced without showing excimer or exciplex emissions. The mechanism for such phenomena was discussed in connection with the excited-state intramolecular proton-transfer reaction of HBT.     

Melting in two-dimensional Yukawa systems: a Brownian dynamics simulation

We studied the melting behavior of two-dimensional colloidal crystals with a Yukawa pair potential by Brownian dynamics simulations. The melting follows the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario with two continuous phase transitions and a middle hexatic phase. The two phase-transition points were accurately identified from the divergence of the translational and orientational susceptibilities. Configurational temperatures were employed to monitor the equilibrium of the overdamped system and the strongest temperature fluctuation was observed in the hexatic phase. The inherent structure obtained by rapid quenching exhibits three different behaviors in the solid, hexatic, and liquid phases. The measured core energy of the free dislocations, E(c) = 7.81 ± 0.91 k(B)T, is larger than the critical value of 2.84 k(B)T, which consistently supports the KTHNY melting scenario.     

New laser dye based on the 3-styryl analog of the BODIPY dye PM567

We report the synthesis, photophysical properties and evaluation of laser dye of a new BODIPY dye with a 3-styryl substituent, PMS, and with the rest of the substituents as in the commercial dye PM567. PMS shows an emission band at 584 nm in methanol, i.e. displaced ca. 50 nm to longer wavelengths with regard to the green-emission band of PM567, as well as a high-fluorescence quantum yield (0.82) and also a high-molar absorption coefficient (10⁵ M⁻¹ cm⁻¹) in the same solvent. The laser action of the new dye has been analyzed under transversal pumping at 532 nm, 5.5 mJ pulse⁻¹ and up to 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices of methyl methacrylate copolymerized with crosslinking or fluorinated monomers. Lasing emission at 602–610 nm, with maximum efficiencies of 18%, were reached in these media. In solid-fluorinated matrices, good lasing photostabilities were established, with 30% of the initial laser output remaining after 100,000 pump pulses at 10 Hz.     

Catalytic properties of Fe-Cu-Al-montmorillonites in the oxidation of acid chrome dark blue azo dye

Interlayer cations in the sodium form of the aluminosilicate montmorillonite (Mt) have been exchanged by mixed, bulky, polynuclear hydroxo cations (Al: (Fe + Cu) = 10, Cu: Fe = 0–1, OH: (Fe + Cu + Al) = 2), and the product has been heat-treated to obtain Fe-, Fe-Al-, and Fe-Cu-Al-containing materials (Fe-Cu-Al-Mt). The chemical composition and textural characteristics of the materials depend on the Cu: Fe molar ratio. The catalytic properties of the materials in the oxidation of acid chrome dark blue (ACDB) azo dye with hydrogen peroxide have been investigated. The activity and stability of the Fe-Cu-Al-Mt systems are determined by the quantity of copper and iron atoms introduced into the structure of the material. As the iron ion content is increased, the specific catalytic activity of the system increases and the system becomes less resistant to the leaching of iron ions into the solution. Raising the copper content of the system above 0.07 wt % reduces its activity and stability. The effects of the catalyst content, pH of the solution being oxidized, and reactant ratio (H₂O₂: ACDB) on the reaction rate have been studied. The ACDB oxidation conditions have been optimized.     

Photo-induced decolorization of dimethylmethylene blue with selenious acid: a novel method to examine selective monomer-dimer distribution of the dye in micelle

In this report, selenious acid (H2SeO3) has been exploited to study the decolorization of a cationic dye, dimethylmethylene blue (DMMB) with UV-light. Micelles have effectively been employed as organized media to promote the rate of decolorization of the dye molecules. Micellar catalysis has been explained as a consequence of electrostatic, hydrophobic and charge transfer interactions. It has also been shown that strong charge transfer and electrostatic interaction lead to an appreciable enhancement of the reaction rate in micelle, whereas, weak hydrophobic interaction is of marginal importance. Existence of monomer-dimer equilibrium for the dye molecules under certain selective environments has been identified spectrophotometrically. Then the shift of dimer-monomer equilibrium of the dye has been successfully studied in aqueous and micellar environments exploiting photodecolorization process for the dye in solution. 'Salting-in' and 'salting-out' agents were introduced into the reaction mixture to examine the viability of the dye decolorization process for dye contaminated water samples.