Organic Dye Solutions Research Articles

On the mechanism of photosensitized luminescence of singlet oxygen dimols in air-saturated pigment solutions

Luminescence of singlet oxygen dimols (1O2)2 was studied in aerobic solutions of a nonfluorescent photosensitizer phenalenone in CCl4 and C6F6 using a setup with a mechanical phosphoroscope and relatively low rates of photosensitizer excitation. The luminescence spectrum was found to resemble those reported in our previous papers dealing with dimol luminescence in solutions of porphyrins and other organic dyes. The main maximum was located at 703–706 nm, and two much weaker bands at 640 and 770–780 nm. These data suggest that dimol luminescence arises owing to interaction of two 1O2 molecules and one ground-state pigment molecule. Light is emitted by the dimol-pigment contact complexes, which are formed as a result of 1O2 collisions with metastable, probably triplet, intermediates appearing in 1O2 reaction with pigment molecules. It is proposed that this mechanism of dimol luminescence might be of general importance for photochemical, chemical, and biological systems where singlet oxygen is generated. However, the luminescence of this type dominates at relatively low rates of 1O2 generation. According to the literature data, at high 1O2 generation rates the prevalent type of dimol luminescence has the main maximum at 635–637 nm and is caused by direct collisions of two 1O2 molecules.

Theoretical multilevel approach for studying the photophysical properties of organic dyes in solution

Classical all-atom molecular dynamics (MD) simulations and quantum mechanical time-dependent density functional theory (TD-DFT) calculations are employed to study the conformational and photophysical properties of tetramethylrhodamine iso-thiocyanate (TRITC) in solution. The potential energy surface (PES) is explored and the minimum energy structure is identified both in water and ethanol. An accurate force-field is parameterized on the computed quantum mechanical data and used in the classical dynamics to take into account solute vibrations and solvent effects. Several configurations, extracted from the MD trajectories, are employed to investigate absorbance spectra in a time dependent approach, considering solvation models of increasing complexity. Explicit- and implicit-solvent approaches, as well as combinations of them are used to predict and explain the absorption properties and the electronic structure of the dye. The defined theoretical methodology succeeds in reproducing correctly the available experimental data.

Influence of absorption from excited singlet states on the lasing parameters of polymethine dyes

The influence of absorption from excited singlet states (singlet—singlet absorption) on the lasing parameters of ionic (symmetric and asymmetric cationic) and intraionic (merocyanine) polymethine dyes excited by nanosecond 532-nm second-harmonic pulses from a Nd:YAG laser and 308-nm pulses from a XeCl laser is studied. It is shown that singlet—singlet absorption at the pump and lasing wavelengths affects the spectral and energy lasing parameters of organic dye solutions.

Investigation of electrochemical degradation and application of e-paper dyes in organic solvents

To avoid environmental pollution due to organic dye solutions, the electrophoresis and degradation of dye in organic solvents such as alcohol were investigated. Many dyes were tested in the Indium tin oxide (ITO) electrode driving cell, and about 15 dyes moved under voltage driving. Both the curves of ultraviolet-visible (UV-Vis) and infrared (IR) spectra of the electrophoresis samples showed that the metal complexes Red 04 and Acid Black 1 were degradable in alcohol solution by electrochemical reaction. The cyclic volt-ampere curves of the samples from the electrochemical working station proved that electrochemical reactions took place. Based on the analysis of UV-Vis and IR spectra, the electrochemical degradation products of azo and metal complex azo dyes at lower voltage driving (1-5 V) in organic solvents are oxidized azobenzene, not hydrazine, which was found in the electrochemical degradation of dye water solutions. When the ITOelectrode is modified by a polyimide (PI) film to a thickness less than 4 μm, the electrochemical degradation of the dye in alcohol solution will not appear in the cyclic volt-ampere curves. A dye electrophoresis in organic solution flexible prototype e-paper display was formed and the display picture is shown.

Stimulated Rayleigh–Bragg Scattering From a Two-Photon Absorbing CdSe–CdS–ZnS Quantum-Rods System: Optical Power Limiting and Phase-Conjugation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This work reports the properties of stimulated Rayleigh–Bragg scattering (SRBS) from a two-photon absorbing CdSe–Cds–ZnS quantum-rods (QRs) solution in chloroform, excited by 1064-nm and <formula formulatype="inline"> <tex>$\sim$</tex></formula>13-ns laser pulses. The two-photon absorbing capability of the scattering medium, as well as the pump threshold, spectral structure, and pulse waveforms of the backward stimulated scattering were measured. Comparing to a pure solvent or an organic dye-solution, the semiconductor QR system has many advantages such as the lower pump threshold, higher energy transfer efficiency, and better photo-physical and photo-chemical stability. The measured output/input characteristic curve shows that the backward SRBS can enhance the optical power limiting performance that is based on two-photon absorption, backward stimulated scattering, and other nonlinear absorption mechanisms. In addition, the backward SRBS beam from our sample medium exhibits a fairly good optical phase-conjugation capability, so that the distortion influence from an inserted aberrator can be automatically removed. </para>

Adsorption and catalytic properties of SiO 2/Bi 2S 3 nanocomposites on the methylene blue photodecolorization process

The decolorization of aqueous solutions methylene blue (C.I. Basic Blue 9), due to the presence of nanocrystalline Bi 2S 3, supported on SiO 2 submicron particles, was investigated here. For this decolorization process, two distinct characteristics, though related, associated to the role of SiO 2/Bi 2S 3 were identified: (i) high methylene blue adsorption capability and (ii) photocatalytic activity to methylene blue photodecolorization. Effects of experimental parameters on the decolorization process, such as methylene blue and nanocomposite concentrations, pH and Bi 2S 3 particle size were investigated. The maximum adsorption ability of the SiO 2/Bi 2S 3 was approximately 15.6 mg methylene blue per gram. The complete decolorization of a 16 ppm organic dye solution can be achieved, by an adsorption process, in an extremely short time (less than 5 min), using 1.6 g/L of SiO 2/Bi 2S 3 nanocomposite. The study of the decolorization of the dye by an adsorption–photoassisted decolorization process was carried out by irradiation of a suspension prepared with 100 mL of methylene blue solution (8 ppm) and 50 mg of SiO 2/Bi 2S 3. In these conditions the complete decolorization of the dye, adsorbed and in the solution, was achieved in 40 min.

Porous Barium Strontium Titanate-Titania Nanocomposites for Photocatalytic Applications

Porous barium strontium titanate−titania (BST−TiO2) nanocomposite was developed by the combination of electrochemical anodization and hydrothermal synthesis. Self organized titania nanotube arrays were first fabricated by electrochemical anodization of titanium foil in 0.2 wt.% HF. The as-anodized titania was then used as a template and was subject to a hydrothermal treatment in the solution mixture of barium hydroxide and strontium hydroxide with different molar ratios. Well crystallized barium strontium titanate was developed directly from the titania nanotubes. Annealing was carried out to transform residual amorphous titania to crystallized anatase, resulting in the porous BST−TiO2 nanocomposite. The surface morphology and structure of the nanocomposite were characterized. The photoelectrochemical response of the BST−TiO2 composite was investigated and the photocatalytic property was evaluated through the photo-decomposition of an organic dye solution. The effect of hydrothermal parameters on the surface morphology and the photocatalytic activity of the nanocomposite was studied.

Optical properties of organic-dye-doped spherical particles of polyorganosiloxane derived from methyltrimethoxysilane using a reaction field of W/O emulsion

Polyorganosiloxane spherical particles were synthesized by a sol-gel method from methyltrimethoxysilane (MTMS) using a reaction field of W/O emulsion consisting of sorbitantrioleate (SPAN85), n-octane, and aqueous solutions of basic, acid, and oil-soluble organic dyes. The investigation focused on the types of dyes suitable for incorporation into the spherical particles by using this method. The morphology of the particles was observed with scanning electron microscopy (SEM). Fluorescence and ultraviolet-visible (UV-vis) reflectance spectra of dye-doped spherical particles were measured. Basic dyes [Rhodamine B (RB), Rhodamine 6G (R6G), Crystal Violet (CV), Malachite Green (MG), and Thioflavin T (TT)] were doped into the spherical particles. Spherical particles obtained from aqueous solutions of RB, R6G, and CV were colored deeply. However, the MG- and TT-doped particles were scarcely colored. The reason for this color difference was discussed based on the comparison of UV-vis reflectance spectra of dye-doped spherical particles with absorption spectra of starting solutions of the dyes. It is found that the dye that tends to form dimers in aqueous solution was doped more easily than the dyes that tend to form monomers only. On the other hand, spherical particles obtained from acid dyes [Fluorescein Sodium Salt (FSS), Orange G (OG), Naphthol Green B (NGB), and Erythrosin B (EB)] and oil-soluble dye [Fluorescein (FLU)] were all white, confirming that these dyes were not doped in the particles. The reason was discussed in terms of the nature of the dyes and the formation mechanism of the spherical particles.

Metallic Micropatterns on Anodic Alumina: Laser-Assisted Exposure of Trapped Seeds for Metallization

Microscale metallic patterns are fabricated on the anodic alumina by demonstrating a novel technique. The porous anodic alumina was colored in organic dye solution containing small amounts of palladium acetate and then hydro-thermally sealed. Such coloring and pore-sealing of porous anodic alumina enhanced the absorption of laser beam by the film, facilitating the laser ablation on the film surface. The palladium ions, impregnated during coloring, were trapped underneath the crystalline hydroxide layer that had formed during the hydrothermal treatment. Removing the surface layer with the help of laser beam exposed the palladium on the surface, which acts as seeds for the subsequent electroless plating. Various metallic micro-patterns with thickness of about 2μm were fabricated on the anodic alumina. The metallic patterns were free from cracks or defects, and can be fabricate with high precision.

Femtosecond filament and supercontinuum generated in cobalt phthalocyanine chloroform solution

Filamentation and supercontinuum generation in cobalt phthalocyanine chloroform solution by 800 nm 50-fs Ti: sapphire laser pulse is investigated for the first time to the best of our knowledge. It is found that filamentation is triggered by self-focusing and defocusing. The main mechanism of supercontinuum and conical emission generation is self-phase modulation (SPM) enhanced by self-steepening of the pulse and group velocity dispersion (GVD). This investigation of organic dye solutions by fs laser is a good complementarity to study the propagation of powerful ultrashort laser pulses in liquid media.

Optimum methodology for the quantitative analysis of large arrays of solvatochromic and solvatofluorochromic data

A new approach is formulated to the solution of the crucial problem associated with developing the optimum methodology for quantitatively analyzing large arrays of experimental data relating to the optical spectra of solutions of polar organic dyes in a wide set of individual solvents of various chemical natures. The approach is based on the analytical relations of the semi-empirical theory proposed earlier by one of the authors and makes it possible for the first time to calculate all the main components of the absolute solvation shift of the absorption and fluorescence spectra of solutions during a gas-solution transition. This approach makes it possible to propose extremely simple working formulas that are convenient in practice for finding the collection of electric, optical, and structural characteristics of the dye molecule in the excited electronic state from the spectroluminescence data.

Compact dye laser on a chip fabricated by ultraviolet nanoimprint lithography

High aspect ratio and high resolution distributed feed back (DFB) gratings have been patterned on a fused silica plate by ultraviolet nanoimprint lithography and reactive ion etch techniques. Then, they were integrated into a microfluidic chip for optofluidic operations. The authors observed laser emission from organic dye solutions flowing through an optical resonator formed between two third order DFB gratings. Such a dye layer can operate with a picoliter dye solution. With rhodamine 6G dye molecules dissolved in ethanol and pumped by a frequency-doubled Nd:YAG pulsed laser, a laser emission of threshold of 12μJ∕mm2 has been found.

Advanced Oxidation Processes in Azo Dye Wastewater Treatment

The chemical degradation of synthetic azo dyes color index (C.I.) Acid Orange 7, C.I. Direct Orange 39, and C.I. Mordant Yellow 10 has been studied by the following advanced oxidation processes: Fenton, Fenton-like, ozonation, peroxone without or with addition of solid particles, zeolites HY, and NH4ZSM5. Spectrophotometric (UV/visible light spectrum) and total organic carbon measurements were used for determination of process efficiency and reaction kinetics. The degradation rates are evaluated by determining their rate constants. The different hydroxyl radical generation processes were comparatively studied, and the most efficient experimental conditions for the degradation of organic azo dyes solutions were determined.

Single mode optofluidic distributed feedback dye laser

Single frequency lasing from organic dye solutions on a monolithic poly(dimethylsiloxane) (PDMS) elastomer chip is demonstrated. The laser cavity consists of a single mode liquid core/PDMS cladding channel waveguide and a phase shifted 15th order distributed feedback (DFB) structure. A 1mM solution of Rhodamine 6G in a methanol and ethylene glycol mixture was used as the gain medium. Using 6 nanosecond 532nm Nd:YAG laser pulses as the pump light, we achieved threshold pump fluence of ~0.8mJ/cm(2) and single-mode operation at pump levels up to ten times the threshold. This microfabricated dye laser provides a compact and inexpensive coherent light source for microfluidics and integrated optics covering from near UV to near IR spectral region.

Femtosecond laser photoelectron projection microscopy of organic nanocomplexes

Organic nanocomplexes obtained by applying an organic dye (Coumarin 153) solution onto the surface of a metal nanotip were studied by femtosecond laser photoelectron projection microscopy. The tip was a 100-nm-diameter capillary covered with a thin nickel layer. The image of a through hole of the capillary was a convenient reference for interpretation of the results. The spatial resolution achieved in these experiments was equal to about 5 nm.

Light-resistant dyes based on organic and inorganic nanocrystals for optical polymers

This paper shows that nanocomposites consisting of nanocrystals of organic semiconductors (the dyes Mg phthalocyanine and thioindigo red) and inorganic semiconductors (CdS), introduced in high concentrations into a polymeric matrix (polycarbonate), possess substantially higher photostability than molecular solutions of organic dyes in a polymeric matrix and are therefore promising materials for colored optical filters.

Specific Features of XeCl*-Laser Radiation Absorption by Concentrated Solutions of Organic Dyes

The transmission of focused laser radiation with power densities in the range (1–250) MW/cm2 through solutions of laser dyes (substituted paraterphenyls and rhodamine 6G) is investigated. The dependence of the transmission on the exciting radiation power density is measured, and numerical modeling is used to estimate the lifetime of the fluorescent state of molecules and the influence of stimulated emission on the lifetime of the S1 state. The effect of scattering on the transmission of highly absorbing media is demonstrated under nanosecond excitation.

Study of nonlinear optical characteristics of various media by the methods of z-scan and third harmonic generation of laser radiation

The nonlinear optical parameters of colloidal solutions of metals, semiconductor chalcogenide films, vapours and solutions of organic dyes, as well as of fullerene-doped polyimide films are studied by the methods of z-scan and third harmonic generation (THG). The nonlinear refractive indices, nonlinear susceptibilities, and nonlinear absorption coefficients of these materials are measured at the fundamental 1064-nm emission wavelength of a 35-ps pulsed Nd:YAG laser and its second harmonic at 532 nm. The study of the optical limitation of picosecond and nanosecond light pulses in these media showed that the appearance of the long-wavelength absorption band at the final stage of aggregation of colloidal metals resulted in nonlinear absorption of picosecond pulses. The nonlinear susceptibilities χ(3)(—3ω,ω,ω,ω) of colloidal metals, fullerenes, and dye vapours are measured by the picosecond THG method, and the effect of self-action on THG in these media is analysed.

Two-photon spectroscopy and analysis with a white-light continuum probe

We present a powerful experimental tool and analysis for characterization of two-photon absorption (2PA) spectra. We demonstrate this method with ZnS and then apply it to organic dyes in solution. We also compare the results with those from other methods such as two-photon fluorescence spectroscopy. This femtosecond pump-probe method uses a white-light continuum (WLC) as the probe to produce a nondegenerate 2PA spectrum. The extreme chirp of the WLC requires that transmittance data be collected over a range of temporal delays between pump and probe pulses. These data then need to be corrected for the effects of this chirp as well as for the temporal walk-off of the pulses in the sample that result from the frequency nondegenerate nature of the experiment. We present a simple analytic solution for the transmitted fluence through the sample, which is applicable for most practical cases.

Resonance absorber based on thin films of pseudoisocyanine J-aggregates

Nanometre films of pseudoisocyanine N-alkyl-substituted J-aggregates are obtained on glass substrates by spin-coating from organic dye solutions. The optical and non-linear optical properties of these films are investigated. These films are shown to possess a high optical quality over the area of size more than 30 × 30 mm and a high photochemical stability. These films feature strong absorption saturation at the maximum of excitonic absorption of the aggregates. The radiative damage threshold of the films at the maximum of the excitonic absorption was measured to be 5 MW cm-2. The dispersion of optical nonlinearity of the films within the J-band is measured by the Z-scan and probe field methods. The films can be used as two-dimensional optical light-controlled switches.