Nonlinear optical characteristics of polymethine dyes

Nonlinear refraction, nonlinear absorption, and saturated absorption of a number of polymethine dyes are studied and their nonlinear optical parameters are measured by the Z-scan method (λ=1064 nm). Simultaneous occurrence of several nonlinear optical processes in the case of excitation of dye solutions by picosecond pulses is analyzed. Saturated absorption of dye solutions is considered in terms of different models.     

Photophysical studies of PET based acridinedione dyes with globular protein: Bovine serum albumin

Interaction of acridinedione dyes with model transport proteins, bovine serum albumin (BSA) in aqueous solution were investigated by fluorescence spectral studies. A fluorescence enhancement was observed on the addition of BSA to photoinduced electron transfer (PET) based acridinedione dyes, which posses C₆H₄(p-OCH₃) in the 9th position of the basic acridinedione ring. On the contrary, the addition of BSA to non-PET based acridinedione dyes with methyl or phenyl substitution in the 9th position does not result in any fluorescence enhancement. The enhancement in the fluorescence intensity is attributed to the suppression of PET process through space between -OCH₃ group and the acridinedione moiety is elucidated by steady state fluorescence measurements. The fluorescence anisotropy value (r) of 0.40 reveals that the motion of the dye molecule is highly constrained and is largely confined to the rigid microenvironment of the protein molecule. The binding constant (K) was found to be in the order of 6.0×10³ [M]⁻¹, which implies the existence of hydrophobic interaction between the PET based dye and BSA. Time resolved fluorescence lifetime measurements reveal that the PET based acridinedione dye preferably binds in the hydrophobic interior of BSA.     

Optical bistability in fluorescein dyes

Optical bistability has been observed in highly concentrated fluorescein dye solutions and in thin (1 m) doped polymeric films. At concentrations larger than 10^–5 mole/l dye dimers are formed. For fluorescein dye, the dimer-monomer equilibrium constant is 10⁵ l/mole so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10^–18 cm²/molecule, while that for the dye monomer molecule is 7.6×10^–17 cm²/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. This high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system.Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry-Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10^–4 mole/l fluorescein than in 10^–6 mole/l fluorescein in which dimer formation is not that efficient.In disodium fluorescein no significant dimer formation is observed even at 10^–3 mole/l dye concentration. The observed bistability both in solution and in thin films can be explained in terms of recent models for optical bistability in nonlinearly absorbing molecular systems.     

The mechanism of sensitized anti-stokes luminescence in crystals with adsorbed dyes

We have analyzed regular features of sensitization processes of crystals AgCl, AgCl_0.95I_0.05, and Zn_0.6Cd_0.4S to processes of a low-threshold (10^?3–10^?4 W/cm²) two-quantum excitation of anti-Stokes luminescence by adsorbed molecules and by J and H aggregates of dyes of different classes. The excitation centers of this luminescence are complex and consist of dye molecules and few-atom silver clusters adsorbed nearby. Luminescence-excitation processes involve stages of photoexcitation of adsorbed dye molecules; resonance transfer of electronic excitation energy to adsorbed atoms and few-atom silver clusters, levels of which lie near the middle of the band gap; and their subsequent photoionization.     

Interaction of dyes with nanoclusters adsorbed on the surface of AgBr microcrystals

We have performed a comparative luminescence investigation into spectral sensitization with dyes of holographic emulsions that contain AgBr microcrystals and are subjected to chemical sulfur or reducing sensitization. We show that, upon spectral sensitization of silver sulfide (Ag₂S) _n nanoclusters located on AgBr microcrystals, the polylayer adsorption of dyes on the surface of nanoclusters is observed, which is caused by van der Waals forces in the J-aggregated state. For silver oxide (Ag₂O) _m nanoclusters located on AgBr micro-crystals, the adsorption of dyes on their surface occurs only if chlorine atoms of heterocyclic residues of the dye interact with the nanocluster surface, which determines the adsorption of the dye as its chemisorption. In the remaining investigated cases, the polylayer adsorption of dyes during the spectral sensitization occurs not on the surface of nanoclusters but rather on the surface of AgBr microcrystals, initially in the J-aggregated state and then in the molecular- and H-aggregated states.     

Fluorescent properties of novel dendrimer dyes based on thiazole orange

In this paper, polyamidoamine (PAMAM) dendrimers with active amino group of some generations (G=0.5-2) were prepared from commercial aminoacetaldehyde diethyl acetal by the divergent method. After that, thiazole orange (TO) with -COOH was incorporated with dendrimers of G=1 and 2 to afford novel dendrimer-TO dyes. The fluorescent properties studies showed that the fluorescent intensity of the same concentration of dendrimer-TO (G=2) was higher than that of the dendrimer-TO (G=1), and both of them were much stronger than free TO with -COOH. There was a fluorescent enhancement of the dendrimer dyes compared with free dye. The dendrimer dyes were of well-defined chemical structure,with little aggregation and self-quenching as well as good fluorescence properties of good stability, high intensity and sensitivity, which could be used in labeling cancer cells and further in diagnosis and detection of early-stage tumors.     

Effect of electric field on the optical absorption of amorphous molecular semiconductors doped with polymethine dyes

The effect of a dc electric field on the evolution of the electronic absorption spectra of poly(N-epoxypropylcarbazole) (PEPC), poly(styrene) (PS), and poly(vinyl butyral) (PVB) films doped with methine dyes is investigated. It is revealed that these spectra in the absorption range of the dye undergo transformations depending on the dipole moment and the symmetry of the π-electron structure of dye molecules. The inference is made that the electron density in the dye molecule is redistributed in an external electric field. This redistribution gives rise to the electric field-induced anisotropy in the spatial distribution function of photogenerated electron-hole pairs in amorphous molecular semiconductors.     

Energy transfer from Eu(III) and Tb(III) complexes to dyes in their mixed nanostructures. I

The formation of nanostructures that consist of complexes of β-diketones with 1,10-phenanthroline and involve dyes of the polymethine, triphenylmethane, oxazine, and xanthene series is observed in aqueous solutions. It is found that nanostructures of complexes of Ln(III) ions and dyes are reliably observed at concentrations of Ln complexes from 0.5 to 5 μM and at dye concentrations above 5 nM. Nanostructures of complexes Eu(MBTA)₃phen, Eu(NTA)₃phen, Eu(PTA)₃phen, Tb(PTA)₃phen, Gd(MBTA)₃phen, and Lu(MBTA)₃phen with dyes are studied, where MBTA is n-methoxybenzoyltrifluoroacetone, NTA is naphthoyltrifluoroacetone, PTA is pivaloyltrifluoroacetone, and phen is 1,10-phenanthroline. It is shown that nanostructures formed can contain dye molecules not only inside a nanostructure of Ln complexes but also on its outer shell. It is proved that, at a dye concentration in the solution of the order of nanomole or higher, the formation of mixed nanostructures of Eu complexes and dyes whose S ₁ level is below the ⁵ D ₀ level of Eu(III) leads to the quenching of the luminescence of Eu(III) and gives rise to the sensitized luminescence of dyes. The energy transfer efficiency from Eu(III) ions to dye molecules is determined by the ability of these molecules to incorporate into nanostructures of Eu complexes. The effect of the formation of nanostructures on the shape and position of the spectra of luminescence and absorption of dyes is studied. Comparison of the sensitized luminescence intensities of Nile blue in structures of Eu, Lu, and Gd complexes shows that the greater part of the excitation energy of Eu complexes is transferred directly from ions to dye molecules according to the inductive-resonance energy transfer mechanism rather than by means of energy migration over singlet levels of organic ligands in complexes of a nanostructure.     

Specific features of the two-photon absorption of cationic symmetric polymethine dyes

The two-photon absorption of a number of cationic symmetric polymethine dyes based on 3H-indolium and benzothiazolium is experimentally studied upon excitation by nanosecond radiation from a Nd:YAG laser (1064 nm, 12 ns). The two-photon absorption cross section of dye molecules is determined by the two-quantum standard method. The influence of the spectral-luminescent properties and structure of the polymethine dyes on the two-photon absorption cross section is discussed. It is shown that, upon excitation in the range of the long-wavelength band of the dyes studied (the S ₀ → S ₁ transition), the maximum of their two-photon absorption is blue shifted. The reasons for a considerable increase in the two-photon absorption of symmetric polymethine dyes upon their excitation in the range of the S ₂ state are discussed. Using the data of quantum-chemical calculations, it is shown that, along with changes in the selection rules for two-photon transitions, this increase is connected with an increase in the size of the delocalized π electron cloud of HOMOs involved in the S ₀ → S ₂ transition.     

Spectral sensitization of the fullerene photoconductivity by organic dyes

The sensitization of the photoconductivity of C₆₀ fullerene polycrystals by adsorbed molecules of organic dyes with the long-wavelength edge at up to 1300 nm is established. It is shown that the adsorption of dye molecules causes the sensitization associated with the formation of charge transfer complexes fullerene-sensitizer (in the region near 700 nm) and with the adsorbed dye (in the region from 800 to 1300 nm).     

High-efficiency degradation catalytic performance of a novel Angelica sinensis polysaccharide-silver nanomaterial for dyes by ultrasonic cavitation

Currently, the polluted wastewater discharged by industry accounts for the major part of polluted bodies of water. As one of the industrial wastewaters, dye wastewater is characterized by high toxicity, wide pollution, and difficulty in decolorization degradation. In this paper, a novel composite nanomaterial catalyst of silver was prepared by using Angelica sinensis polysaccharide (ASP) as a reducing and stabilizing agent. And the optimum reaction conditions explored are V_AgNO3 = 5 mL (300 mM) and v_ASP = 7% (w/v) for 6 h at 90 °C. In addition, the ASP-Ag nanocatalyst was characterized by several techniques. The results demonstrated that ASP-Ag nanoparticles were successfully synthesized. Degradation rate, which provides a numerical visualization of the percentage reduction in pollutant concentration. With the wrapping of ASP, the ultrasonic catalytic degradation rates of different organic dyes including rhodamine B (RB), methylene blue (MB), and methyl orange (MO) were from 88.2%, 88.7%, and 85.2% to 96.1%, 95.2% and 93.5% at room temperature, respectively. After the experiments, when c_dyes = 10 mg/L, the highest degradation rate can be observed under c_APS-AgNPs = 10 mg/L with the most powerful cavitation frequency f = 59 kHz. The effect of ultrasonic frequency on the acoustic pressure distribution in the reactor was investigated by using COMSOL Multiphysis^@ software to propose the mechanism of ultrasonic degradation and the mechanism was confirmed by OH radical trapping experiments. It indicates that OH produced by the ultrasonic cavitation effect plays a determinant role in the degradation. And then, the intermediate products of the dye degradation process were analyzed by gas chromatography and mass spectrometry (GC–MS), and the possible degradation processes of dyes were proposed. The resulting products of degradation are SO₄²⁻, NH₄⁺, NO₃⁻, N₂, CO₂ and H₂O. Finally, the recycling degradation experiments showed that catalyst maintains a high degradation rate within reusing 5 cycles. Thus, this catalyst is highly efficient and recyclable.     

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S₁-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S₁-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.     

Adsorption of cyanine dyes on AgCl crystals studied by XPS

Adsorption of 3,3'-dimethyl-9-ethylthiacarbocyanine dyes with iodide or bromide counter ions showed two energy states of sulfur in the dye molecule, one is the adsorption state to AgCl substrate and the other occurs when dye molecules aggregated. Though iodide conversion occurred on KI adsorption on AgCl, the counter ion of the dye molecule did not cause halide conversion on adsorption. The counter ion was observed only after the first dye monolayer on AgCl was completed, and increased parallel with adsorbed dye amounts. On Ag-deposited quartz plate monolayer formation occurred only by dye adsorption compared by its counter ion, while only iodine adsorbed in KI adsorption.     

Effect of the layer charge on the interaction of porphyrin dyes in layered silicates dispersions

Interaction between tetracationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP), and layered silicates in aqueous dispersions was studied using absorption, steady-state and time-resolved fluorescence spectroscopies. The charge density of silicates increases in order synthetic laponite (LAP)<Kunipia F montmorillonite (KF)<synthetic fluorohectorite (FHT). Interpretations of the spectra of layered silicate-porphyrin (LSP) systems considered models of dye adsorption on clay mineral colloid particles, analyzing phenomena occurring in similar systems such as structural changes of TMPyP and the formation of dye molecular assemblies. Structural changes of TMPyP, including flattening of the porphyrin molecule, do not fully explain all the spectral observations. One should mention variations of the Q-bands and fluorescence spectra in dependence on the layer charge. The molecular association of the TMPyP molecules is expected to occur to a certain extent in dependence on the layer charge of a clay mineral template. H-aggregates were not observed in any system. Only FHT colloids induced the formation of at least two components with significantly different spectral properties.     

The mutual influence of two different dyes on their sensitized fluorescence (cofluorescence) in nanoparticles from complexes

We have studied the fluorescence sensitization and quenching for pairs of different dyes simultaneously incorporated into nanoparticles from complexes M(diketone)₃phen, where M(III) is La(III), Lu(III), or Sc(III); diketone is p-phenylbenzoyltrifluoroacetone (PhBTA) or naphthoyltrifluoroacetone (NTA); and phen is 1,10-phenanthroline. We have shown that, upon formation of nanoparticles in the solution in the presence of two dyes the concentrations of which are either comparable with or lower than the concentration of nanoparticles (<20 nM), the intensities of the sensitized fluorescence of dyes in nanoparticles in binary solutions and in solutions of either of the dyes coincide. We have found that the intensity of sensitized fluorescence of small (<20 nM) concentrations of rhodamine 6G (R6G) or Nile blue (NB) increases by an order of magnitude upon simultaneous introduction into nanoparticles of 1 μM of coumarin 30 (C30), while the intensity of fluorescence of C30 sensitized by complexes decreases by an order of magnitude. The same effect is observed as 1 μM of R6G are introduced into nanoparticles with NB ([NB] ≤ 20 nM). The increase in the fluorescence of dye molecules upon their incorporation from the solution into nanoparticles from complexes is noticeably lower than that expected from the proposed ratio of concentrations of complexes and dyes in nanoparticles. Analysis of the obtained data indicates that the introduction of large concentrations of C30 or R6G dyes into nanoparticles makes it possible to prevent large energy losses due to impurities or upon transition to a triplet state that arises during the migration of the excitation energy over S ₁ levels of complexes. Energy accumulated by these dyes is efficiently transferred to another dye that is present in the solution at lower concentrations and that has a lower-lying S ₁ level, which makes it possible to increase its fluorescence by an order of magnitude upon its incorporation into nanoparticles.     

X-ray photoelectron spectroscopy of merocyanine dyes: III. Structure of the O1s line in the merocyanine 540 dye

The structure of the 01s spectrum for the MC 540 merocyanine dye is resolved using data obtained from XPS analysis of a series of merocyanine dyes displaying less complex O1s signals.The 01s binding energy (BE) of the carbonyl group in these molecules is unusually low and the photoionization peak is accompanied in most cases by a satellite on the high BE side.The data obtained in this study permit a reconstruction of the 01s profile of the MC 540 molecule. The 01s binding energy thus obtained for the carbonyl groups in MC 540 is 531.2 eV. This BE is low when compared to those usually observed for such groups and indicates that, in the MC 540 molecule, they predominantly exist in the ⩾C-O⁻³ form.     

Preparation of MgTi2O5 nanoparticles for sonophotocatalytic degradation of triphenylmethane dyes

MgTi₂O₅ (magnesium dititanate) nanoparticles were prepared by a simple hydrothermal assisted post-annealing method and characterized with various analytical techniques. The catalytic properties (sonocatalytic, photocatalytic and sonophotocatalytic activity) were evaluated using the degradation of triphenylmethane dyes (crystal violet, basic fuchsin, and acid fuchsin). The sonophotocatalytic activity of MgTi₂O₅ nanoparticles towards crystal violet was found to be ~2.9 times higher than the photocatalytic activity and ~20 times higher than that of the sonocatalytic processes. In addition, the sonophotocatalytic efficiency of MgTi₂O₅ nanoparticles was found to be remarkable for the degradation of basic fuchsin (cationic dye) and acid fuchsin (anionic dye). The mechanism of these catalytic activities has been discussed in detail.     

Excited singlet-state absorption in laser dyes at the XeCl wavelength

The transmission properties of the laser dyes BBQ, PBD, BPBD, -NPO,p-Quarterphenyl and PPO have been measured using a XeCl (308 nm) excimer laser. A model for the dye saturation which incorporates excited-state absorption was used to estimate the lifetime and the absorption cross section of the first excited singlet-state for each dye.     

Photoelectric, nonlinear optical, and photorefractive properties of polymer composites including carbon nanotubes and cyanine dyes

The effect of cyanine dye additives on the photoelectric, nonlinear optical, and photorefractive properties of polyvinyl carbazole composites based on closed single-walled carbon nanotubes has been investigated. It has been found that these characteristics are affected by the dye in which the lowest unoccupied molecular orbital (LUMO) lies below the level of the photoexcited nanotube. The addition of this dye to the composite leads to a 14-fold increase in the quantum efficiency of the generation of mobile charge carriers under irradiation by a laser (1064 nm) in the absorption region of the nanotubes. Moreover, the addition of the dye to the composite decreases the third-order susceptibility χ⁽³⁾, presumably, due to the opposite orientations of dipoles of the dye and the nanotube upon adsorption of the dye on the nanotube. The addition of the dye to the composite also provides a twofold increase in the two-beam photorefractive amplification factor of the laser beam with a wavelength of 1064 nm. The obtained values of the two-beam photorefractive amplification factor reach 120 cm^?1.