Increasing Dye Content Research Articles

Photocatalytic reduction of methylene blue by the heterostructure of Titanium (IV) oxide and symmetric cationic polymethine dye

The results of the spectral, electrochemical and energy characteristics of symmetric cationic polymethine dye 2 - [(1E) -1,3,5-hexatrienyl -] - 1- (phenylmethyl)-benzindolium boron fluoride (D) indicate the possibility of its use as an effective titanium(IV) sensitizer oxide. Comparison of the absorption spectra of the dye solution and the reflectance spectra of the D/TiO2 heterostructures showed that the deposition of the dye on the TiO2 surface leads to bathochrome and hypochromic shifts of the absorption bands, the value of which depends on the content of this component in the heterostructure (HS). The obtained changes in the spectra of heterostructures indicate the possibility of formation of both J- and H-aggregates. Cyclic voltammetry determines the oxidation and reduction potentials of the investigated polymethine dye and calculates their redox potentials in the excited state. They have been found to be sufficient for sensitization by electron transfer to the TiO2 conduction band. The photocatalytic activity of HS D/TiO2 in the model reaction of methylene blue reduction depending on irradiation conditions and dye concentration has been determined. It is shown that, when irradiated with D/TiO2 heterostructures with light with λ <400 nm, their photocatalytic activity decreases with increasing dye content in the whole concentration range of the studied concentrations. When irradiated with heterostructures by light absorbed by the dye (λ = 872 nm), the photocatalytic activity increases to a maximum value at a concentration of the dye equal to 0,20 mg/g, and then decreases with increasing concentration. The energy of possible electronic processes caused by the action of light absorbed by a semiconductor and a dye-sensitizer is considered. The possibility of using created heterostructures as functional materials with a given level of photocatalytic activity and extended range of light sensitivity is shown.

Quantitative Assessment of Nanoparticle Biodistribution by Fluorescence Imaging, Revisited.

Fluorescence-based whole-body imaging is widely used in the evaluation of nanoparticles (NPs) in small animals, often combined with quantitative analysis to indicate their spatiotemporal distribution following systemic administration. An underlying assumption is that the fluorescence label represents NPs and the intensity increases with the amount of NPs and/or the labeling dyes accumulated in the region of interest. We prepare DiR-loaded poly(lactic- co-glycolic acid) (PLGA) NPs with different surface layers (polyethylene glycol with and without folate terminus) and compare the distribution of fluorescence signals in a mouse model of folate-receptor-expressing tumors by near-infrared fluorescence whole-body imaging. Unexpectedly, we observe that fluorescence distribution patterns differ far more dramatically with DiR loading than with the surface ligand, reaching opposite conclusions with the same type of NPs (tumor-specific delivery vs predominant liver accumulation). Analysis of DiR-loaded PLGA NPs reveals that fluorescence quenching, dequenching, and signal saturation, which occur with the increasing dye content and local NP concentration, are responsible for the conflicting interpretations. This study highlights the critical need for validating fluorescence labeling of NPs in the quantitative analysis of whole-body imaging. In light of our observation, we make suggestions for future whole-body fluorescence imaging in the in vivo evaluation of NP behaviors.

Light absorption engineering of a hybrid (Sn3S72\u2212)n based semiconductor \u2013 from violet to red light absorption

The crystalline two-dimensional thiostannate Sn3S7(trenH)2 [tren = tris(2-aminoethyl)amine] consists of negatively charged (Sn3S72−)n polymeric sheets with trenH+ molecular species embedded in-between. The semiconducting compound is a violet light absorber with a band gap of 3.0 eV. In this study the compound was synthesized and functionalized by introducing the cationic dyes Methylene Blue (MB) or Safranin T (ST) into the crystal structure by ion exchange. Dye capacities up to approximately 45 mg/g were obtained, leading to major changes of the light absorption properties of the dye stained material. Light absorption was observed in the entire visible light region from red to violet, the red light absorption becoming more substantial with increasing dye content. The ion exchange reaction was followed in detail by variation of solvent, temperature and dye concentration. Time-resolved studies show that the ion exchange follows pseudo-second order kinetics and a Langmuir adsorption mechanism. The pristine and dye stained compounds were characterized by powder X-ray diffraction and scanning electron microscopy revealing that the honeycomb hexagonal pore structure of the host material was maintained by performing the ion exchange in the polar organic solvent acetonitrile, while reactions in water caused a break-down of the long-range ordered structure.

Characterization of electrodeposited zinc oxide/tetrasulphonatedcopper phthalocyanines (ZnO/Ts-CuPc) hybrid films and their photoelectrochemical properties

Hybrid films of zinc oxide (ZnO) and tetrasulphonatedcopper phthalocyanine (Ts-CuPc) have been prepared by cathodic electro-deposition from aqueous O2-saturated solutions of ZnCl2 and Ts-CuPc. The Ts-CuPc content of the films can be varied in a wide range by variation of dye concentration in the electro-deposition bath – from single Ts-CuPc molecules embedded in compact crystalline ZnO to films based on an amorphous Ts-CuPc framework. With increasing dye content the colour of the films changes from light blue to deep blue. All films were characterized by XRD, SEM and AFM. Photoelectro-chemical characteristics of the electrodes were studied by photocurrent spectra and by time-resolved photocurrent measurements in 0.1M KCl electrolyte. At the same time, changes in the electrical and photoelectrical properties of the films are observed, enabling the tuning of these properties in view of optoelectronic applications. Theoretical calculations based on density functional theory (DFT) models were made to understand the optoelectronic properties of the hybrid films. Different parallel and perpendicular orientations were tested. For the most stable hybrid structure, total and projected densities of states of the system were obtained and the alignment of the levels observed.

Electrodeposited Zinc Oxide/Phthalocyanine Films – An Inorganic/Organic Hybrid System with Highly Variable Composition

AbstractHybrid films of zinc oxide (ZnO) and tetrasulfonated nickel phthalocyanine (TSPcNi) have been electrodeposited by cathodic electrodeposition from aqueous O2‐saturated solutions of ZnCl2 and TSPcNi. The TSPcNi content of the films can be varied in a wide range by variation of dye concentration in the electrodeposition bath – from single TSPcNi molecules embedded in compact crystalline ZnO to films based on an amorphous TSPcNi framework. With increasing dye content the colour of the films changes from green, indicating the presence of the TSPcNi monomers, to blue, caused by TSPcNi aggregates. At the same time, changes in the electrical and photoelectrical properties of the films are observed, enabling the tuning of these properties in view of optoelectronic applications.

Morphology and switching of holographic gratings containing an azo dye

The effects of an azo dye on the diffraction efficiency, morphology and electro‐optic properties of the transmission mode of a holographic polymer dispersed liquid crystal (LC) have been studied. The azo dye induced an induction period which otherwise does not exist, followed by a gradual increase of the diffraction efficiency to a saturation value which increased with increasing azo dye content, as a result of the azo dye reorientating LC molecules within the droplet. The increased diffraction efficiency was caused by the decreased droplet coalescence which was due to the hindered migration of the LC by the dye molecules, and to LC orientation induced by azo dye molecules giving a high refractive index contrast. The droplet size decreased with increasing dye content. The dye also lowered the threshold voltage due to the high dielectric anisotropy caused by the presence of a strong on‐axis dipole moment and decreased the response time.

Effects of blending with fluorescing molecules on the dynamics of the β, α, and α′ relaxations observed in poly(methyl methacrylate)

Perturbations in typical dielectric or calorimetric features of the molecular relaxation dynamics in amorphous poly(methyl methacrylate) and two blends with a neutral/apolar brominated perylene dye were analyzed to explore guest-host nanoscale interactions and their role on lasing properties. Aside from a gradual increase of the relaxation strength Δεβ (plasticization), the local β relaxation is nearly independent of the presence of dye. By contrast, segmental dynamics are moderately hampered: both the dielectric (Tα) and calorimetric (Tg) estimates of the glass transition temperature rise with increasing dye content, probably as a result of modifications in the free volume (antiplasticization). Analogous shifts are observed in the peak temperature of the space-charge relaxation (Tρ) and the α′ (liquid-liquid) transition (TLL), with Tρ∕Tα=1.04±0.01 and TLL∕Tα=1.10±0.01.

Acid-sensitivity and physical properties of polymethylmethacrylate and polyurethane films containing polymeric styryl dye

Solution-cast films of polymethylmethacrylate (PMMA) and polyurethane (PU) containing polymeric styryl dye up to 5% by weight were prepared to investigate their acid-sensitivity and mechanical and thermal properties. Original red samples due to styryl dye turned out yellow very rapidly as they were exposed to acid vapor of hydrochloric acid or p-toluenesulfonic acid. According to UV/VIS spectroscopic measurements, characteristic peak intensities near 430 nm and 520 nm increased or decreased relatively with exposed amounts of acid, respectively. Both PMMA and PU samples showed uniform color distribution due to a good miscibility between polymer and dye which can be evidenced by measurements of glass transition temperature. No significant difference in acid-sensitivity was found between PU and PMMA except relative absorbance. However, dependence of their mechanical properties on dye content was somewhat different with PU or PMMA. In case of PMMA, modulus and breaking stress increased up to about 50% with increasing dye content, whereas those of PU samples showed only slight increase. It was ascribed to whether the matrix polymer was in the glassy or rubbery state.

Electrical conduction and dielectric properties of poly(methyl methacrylate)/perylene solar concentrators

AbstractPoly(methyl methacrylate) doped with fluorescent perylene dye was prepared by both radical polymerization of methyl methacrylate and solvent casting from polymer solutions. The samples were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, electrical conductivity, and dielectric properties. Both conductivity and dielectric properties were measured in the temperature range 303–433 K and the frequency range 103 to 5 × 106 Hz. The results show that the direct‐current electrical conductivity increased by increasing dye content in solvent‐cast samples, whereas it decreased radically polymerized samples. The results of alternating‐current conductivity suggest electron hopping between filled and empty localized states. The study of dielectric properties showed two relaxation peaks corresponding to the dipole segmental and dipole group losses. Explanations based on the polymer free volume and acid–base interactions were proposed to examine the influence of the sample preparation and perylene dye concentration on the glass‐transition temperature and dielectric relaxation of the samples. The obtained results recommend the thermal and molecular stability of luminescent solar concentrator (LSC) matrices prepared by radical polymerization over those prepared by solvent casting. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 793–805, 2003

Host–Guest Interactions and Laser Activity in AlPO 4-5/Laser Dye Composites

In situ inclusion of the laser dyes coumarin 466, coumarin 7, pyridine 2 and DCM has been conducted successfully in AlPO 4-5 crystals. The charged molecule pyridine 2 interacts with the framework and leads to bundle-like morphologies with increasing dye content. Uncharged molecules (DCM, coumarin 7, coumarin 466) are included, although corresponding molecular dimensions are exceeding pore size. These dyes probably induce local defects in the pore walls of AlPO 4-5 which are healed during crystal growth leading to well-developed hexagonal prisms. Spectroscopic studies show interactions of the dyes with the solid-state matrix which are reflected by shifts of absorption and emission maxima of the dyes. For the first time, laser activity is demonstrated on a perfect hexagonal single AlPO 4-5/DCM crystal.

Host–Guest Interactions and Laser Activity in AlPO4-5/Laser Dye Composites

In situ inclusion of the laser dyes coumarin 466, coumarin 7, pyridine 2 and DCM has been conducted successfully in AlPO4-5 crystals. The charged molecule pyridine 2 interacts with the framework and leads to bundle-like morphologies with increasing dye content. Uncharged molecules (DCM, coumarin 7, coumarin 466) are included, although corresponding molecular dimensions are exceeding pore size. These dyes probably induce local defects in the pore walls of AlPO4-5 which are healed during crystal growth leading to well-developed hexagonal prisms. Spectroscopic studies show interactions of the dyes with the solid-state matrix which are reflected by shifts of absorption and emission maxima of the dyes. For the first time, laser activity is demonstrated on a perfect hexagonal single AlPO4-5/DCM crystal.

Effects of dye doping on ferroelectricity in vinylidene fluoride and trifluoroethylene copolymers

The effects of dye doping on ferroelectricity in vinylidene fluoride and trifluoroethylene copolymers have been investigated mainly through dielectric and switching measurements. Large dielectric relaxation, which cannot be explained by dipole fluctuations of individual chain molecules around their axes, was observed in the dye-doped copolymer films. With increasing dye content in copolymers, the relaxation times increase, and the dielectric relaxation strength becomes large. However, the switching times and the switching curve are nearly independent of dye content. These results can be explained if we assume that dye is doped into noncrystalline regions but not into crystalline regions, and forms a long and slender phase boundary in which the dye content is high.

Dyeing Properties of a Polyamide–Epichlorohydrin Resin

The dyeing behaviour of cured films prepared from a polyamide–epichlorohydrin resin (Hercosett) was examined in orderto obtain a better understanding of the dyeing beha viour of Hercosett–treated wool. The polymer films swell by 500–1000%. The swelling decreases with increasing dye content in the polymer and with increasing temperature. The diffusion of acid dyes into the polymer is extremely fast (D =10‐7 cm2/s), and can be accelerated by the addition of salt. The sorption of the dye is described in terms of a Langmuir isotherm, indicating that an ion–exchange mechanism is operative. The concentration of cationic groups in the polymer is very high (2. 4mo//kg) and does not depend on the curing conditions. The addition of salt reduces the exhaustion of the dyebath. Reactive dyes were found to be bound covalently to the resin. During industrial resin treatment it has been shown that the molecular weight distribution of the Hercosett in the resin bath changes markedly, molecular weight increasing with running time and the spread of values being much narrower. This may explain the variation in the dyeing behaviour of wool fibres that have been treated at different times in the same resin bath.

SPHERULITIC STRUCTURES OF 1, 4-DIAMINOANTHRAQUINONE CRYSTALLIZED IN POLYSTYRENE

The polystyrene films containing 1, 4-diaminoanthraquinone dye were examined with an optical microscope during heating and cooling at constant rates. Spherulitic structures were observed which were composed of needle-like crystallites of the dye in the cooling process. Size of these spherulites increased with increasing dye content and with decreasing cooling rate. Size of crystallites formed in cooling process was larger than that formed in heating process.

CONCENTRATION DEPENDENCE OF DIFFUSION COEFFICIENT OF DISPERSE DYE IN POLYVINYLACETATE

A sublimative desorption study of model disperse dyes, p-nitroaniline (PNA), p-amino-azobenzene (PAAB) in polyvinylacetate has been carried out with dye content from 0.01 to 0.25 in g-dye/g-polymer. The desorption temperature ranged from 80 to 130°C. The apparent diffusion coefficients of these dyes increased linearly with an increase in dye concentration; diffusion of PNA showed much stronger concentration dependence than that of PAAB. These features of dye diffusivity could be explained quantitatively in terms of Fujita's free volume theory of diffusion. On the other hand, increasing dye concentration had an effect on lowering the glass transition temperature (Tg) of the colored polymer. Both depression of Tg and increase in dye diffusivity with dye concentration were considered as resulting from the same functional increase in fractional free volume in polymer-dye mixture with increasing dye content.