Modeling of organic light-emitting diodes with graded concentration in the emissive multilayer

We model the electrical behavior of organic light-emitting diodes whose emissive multilayer is formed by blends of an electron transporting material, tris-(8-hydroxyquinoline) aluminum (Alq(3)) and a hole transporting material, N,N-'-diphenyl-N,N-'-bis(1,1(')-biphenyl)-4,4-diamine. The multilayer is composed of layers of different concentration. The Alq(3) concentration gradually decreases from the cathode to the anode. We demonstrate that these graded devices have higher efficiency and operate at lower applied voltages than devices whose emissive layer is made of nominally homogeneous blends. Our results show an important advantage of graded devices, namely, the low values of the recombination rate distribution near the cathode and the anode, so that electrode quenching is expected to be significantly suppressed in these devices.

Concentration effects of Er3+ ion in YAG : Er laser crystals

Laser crystals of (Y1-xErx)(3)Al5O12, (YAG:Er) have been grown by the Czochralski method and the spectral properties have been studied for different Er3+ concentrations. The effects of various Er3+ concentrations on the structural distortions, luminescence quenching Of F-4(9/2), H-2(11/2), S-4(3/2) and red shift in laser wavelength have been discussed for the YAG:Er laser crystals. By using absorption spectra and Judd-Ofelt theory the experimental oscillator strengths, Omega(lambda), parameters and the excited state integrated absorption cross sections of Er3+ ion are reported and some variation regularities of these parameters have been observed. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Dengue Envelope Domain III-Peptide Binding Analysis via Tryptophan Fluorescence Quenching Assay

In the efforts to find an anti-viral treatment for dengue, a simple tryptophan fluorescence-screening assay aimed at identifying dengue domain III envelope (EIII) protein inhibitors was developed. Residue Trp391 of EIII was used as an intrinsic probe to monitor the change in fluorescence of the tryptophan residue upon binding to a peptide. The analysis was based on the electron excitation at 280 nm and fluorescence emission at 300–400 nm of EIII, followed by quenching of fluorescence in the presence of potential peptidic inhibitors coded DS36wt, DS36opt, DN58wt and DN58opt. The present study found that the fluorescence of the recombinant EIII was quenched following the binding of DS36opt, DN58wt and DN58opt ina concentration-dependent manner. Since the λmax for emission remained unchanged, the effect was not dueto a change in the environment of the tryptophan side chain. In contrast, a minimal fluorescence-quenching effect of DS36wt at 20 and 40 µM suggested that the DS36wt does not have any binding ability to EIII. This was supported by a simple native-page gel retardation assay that showed a band shift of EIII domain whenincubated with DS36opt, DN58wt and DN58opt but not with DS36wt. We thus developed a low-cost and convenientspectrophotometric binding assay for the analysis of EIII–peptide interactions in a drug screening application.

Interaction of flavonoids with bovine serum albumin: a fluorescence quenching study

The interaction between four flavonoids (catechin, epicatechin, rutin and quercetin) and bovine serum albumin (BSA) was investigated using tryptophan fluorescence quenching. Quenching constants were determined using the Stern-Volmer equation to provide a measure of the binding affinity between the flavonoids and BSA. The binding affinity was found to be strongest for quercetin, and ranked in the order quercetin>rutin>epicatechin=catechin. The pH in the range of 5 to 7.4 does not affect significantly (p<0.05) the association of rutin, epicatechin and catechin with BSA, but quercetin exhibited a stronger affinity at pH 7.4 than at lower pH (p<0.05). Quercetin has a total quenching effect on BSA tryptophan fluorescence at a molar ratio of 10:1 and rutin at approximately 25:1. However, epicatechin and catechin did not fully quench tryptophan fluorescence over the concentration range studied. Furthermore, the data suggested that the association between flavonoids and BSA did not change molecular conformation of BSA and that hydrogen bonding, ionic and hydrophobic interaction are equally important driving forces for protein-flavonoid association.

Control of excitation and quenching in multi-colour electrogenerated chemiluminescence systems through choice of co-reactant

We demonstrate a new approach to manipulate the selective emission in mixed electrogenerated chemiluminescence (ECL) systems, where subtle changes in co-reactant properties are exploited to control the relative electron-transfer processes of excitation and quenching. Two closely related tertiary-amine co-reactants, tri-n-propylamine and N,N-diisopropylethylamine, generate remarkably different emission profiles: one provides distinct green and red ECL from [Ir(ppy)3] (ppy=2-phenylpyridinato-C2,N) and a [Ru(bpy)3](2+) (bpy=2,2'-bipyridine) derivative at different applied potentials, whereas the other generates both emissions simultaneously across a wide potential range. These phenomena can be rationalized through the relative exergonicities of electron-transfer quenching of the excited states, in conjunction with the change in concentration of the quenchers over the applied potential range.

The effect of Eu3+ concentration on the Y2O3 host lattice obtained from citrate precursors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Modeling of organic light-emitting diodes with graded concentration in the emissive multilayer

We model the electrical behavior of organic light-emitting diodes whose emissive multilayer is formed by blends of an electron transporting material, tris-(8-hydroxyquinoline) aluminum (Alq(3)) and a hole transporting material, N,N-'-diphenyl-N,N-'-bis(1,1(')-biphenyl)-4,4-diamine. The multilayer is composed of layers of different concentration. The Alq(3) concentration gradually decreases from the cathode to the anode. We demonstrate that these graded devices have higher efficiency and operate at lower applied voltages than devices whose emissive layer is made of nominally homogeneous blends. Our results show an important advantage of graded devices, namely, the low values of the recombination rate distribution near the cathode and the anode, so that electrode quenching is expected to be significantly suppressed in these devices. (C) 2004 American Institute of Physics.

Luminescence quenching by iron in barium aluminoborate glasses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interactions between the non-ionic surfactant C(12)E(5) and poly(ethylene oxide) studied using dynamic light scattering and fluorescence quenching

Dynamic light scattering measurements have been made to elucidate changes in the coil conformation of a high molecular weight poly(ethylene oxide) (PEG) fraction when the non-ionic surfactant C(12)E(5) is present in dilute solutions. The measurements were made at 20 degrees C as functions of(a) the C(12)E(5) concentration at constant PEO concentration, (b) the PEO concentration at constant C(12)E(5) concentration, and (c) the C(12)E(5)/PEO concentration ratio. The influence of temperature on the interactions in terms of the relaxation time distributions was also examined up to the cloud point. It was found that when the C(12)E(5)/PEO weight ratio was >2 and when the temperature was >14 degrees C, the correlation functions became bimodal with well-separated components. The fast mode derives fi om individual surfactant micelles which are present in the solution at high number density. The appearance of the slow mode, which dominates the scattering, is interpreted as resulting from the formation of micellar clusters due to an excluded-volume effect when the high molar mass (M = 6 x 10(5)) PEO is added to the surfactant solution. It is shown that the micellar clusters form within the PEO coils and lead to a progressive swelling of the latter for steric reasons. The dimensions of the PEO/C(12)E(5) complex increase with increasing surfactant concentration to a value of R(H) approximate to 94 nm (R(g) approximate to 208 nm) at C-C12E5 = 3.5%. Fluorescence quenching measurements show that the average aggregation number of C(12)E(5) increases significantly on addition of the high molar mass PEG. With increasing temperature toward the cloud point the clusters increase in number density and/or become larger. The cloud point is substantially lower than that for C12E5 in water solution and is strongly dependent on the PEO concentration.

Interaction between poly(ethylene glycol) and C12E8 investigated by dynamic light scattering, time-resolved fluorescence quenching, and calorimetry

Dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry have been used to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene glycol n-dodecyl monoether, C12E8, to form a complex. Whereas the relaxation time distributions for the binary C12E8/water and PEG/water systems are unimodal, in the ternary mixtures they may be either uni- or bimodal depending on the relative concentrations of the components. At low concentrations of PEG or surfactant, the components of the relaxation time distribution are unresolvable, but the distribution becomes bimodal at higher concentrations of either polymer or surfactant. For the ternary system in excess surfactant, we ascribe, on the basis of the changes in apparent hydrodynamic radii and the scattered intensities, the fast mode to a single micelle, the surface of which is associated with the polymer and the slow mode to a similar complex but containing two or three micelles per PEG chain. Titration microcalorimetry results show that the interaction between C12E8, and PEG is exothermic and about 1 kJ mol(-1) at concentrations higher than the CMC of C12E8. The aggregation number, obtained by TRFQ, is roughly constant when either the PEG or the C12E8 concentration is increased at a given concentration of the second component, owing to the increasing amount of surfactant micelles inside the complex.

Effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys

In this work the effect of Ag concentration on the thermal behavior of the Cu-10 mass% Al and Cu-11 mass% Al alloys with additions of 4, 6, 8 and 10 mass% Ag was studied using differential scanning calorimetry (DSC), in situ X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that for the Cu-10 mass% Al alloy Ag addition induce the beta'(1) phase formation and for the Cu-11 mass% Al alloy these additions increase the amount of martensite formed on quenching and decrease the stability range of this phase on heating.

Interaction of the nonionic surfactant C12E8 with high molar mass poly(ethylene oxide) studied by dynamic light scattering and fluorescence quenching methods

Dynamic light scattering has been used to investigate ternary aqueous solutions of n-dodecyl octaoxyethylene glycol monoetber (C12E8) with high molar mass poly(ethylene oxide) (PEO). The measurements were made at 20 °C, always below the cloud point temperature (Tc) of the mixed solutions. The relaxation time distributions are bimodal at higher PEO and surfactant concentrations, owing to the preacute of free surfactant micelles, which coexist with the slower component, representing the polymer coil/micellar cluster comptex. As the surfactant concentration is increased, the apparent hydrodynamic radius (RH) of the coil becomes progressively larger. It is suggested that the complex structure consists of clusters of micelles sited within the polymer coil, as previously concluded for the PEO-C12E8-water system. However. C12E8 interacts less strongly than C12E8 with PEO; at low concentrations of surfactant the complex does not contribute significantly to the total scattered intensity. The perturbation of the PEO coil radius with C12E8 is also smaller than that in the C12E8 system. The addition of PEO strongly decreases the clouding temperature of the system, as previously observed for C12E8/PEO mixtures in solution Addition of PEO up to 0.2% to C12E8 (10 wt %) solutions doss not alter the aggregation number (Nagg) of the micelles probably because the surfactant monomers are equally partitioned as bound and unbound micelles. The critical micelle concentration (cmc), obtained from the I1/I3 ratio (a measure of the dependence of the vibronic band intensities on the pyrene probe environment), does not change when PEO is added, suggesting that for neutral polymer/surfactant systems the trends in Nagg and the cmc do not unambiguously reflect the strength of interaction.

Numerical investigation of effects of addition of ethanol to gasoline on Laminar Flame Speed (LFS), autoignition, and wall quenching

Since the advent of automobiles, alcohol has been considered a possible engine fuel1,2. With the recent increased concern about the high price of crude oil due to fluctuating supply and demand and environmental issues, interest in alcohol based fuels has increased2,3. However, using pure alcohols or blends with conventional fuels in high percentages requires changes to the engine and fuel system design2. This leads to the need for a simple and accurate conventional fuels-alcohol blends combustion models that can be used in developing parametric burn rate and knock combustion models for designing more efficient Spark Ignited (SI) engines. To contribute to this understanding, numerical simulations were performed to obtain detailed characteristics of Gasoline-Ethanol blends with respect to Laminar Flame Speed (LFS), autoignition and Flame-Wall interactions. The one-dimensional premixed flame code CHEMKIN® was applied to simulate the burning velocity and autoignition characteristics using the freely propagating model and closed homogeneous reactor model respectively. Computational Fluid Dynamics (CFD) was used to obtain detailed flow, temperature, and species fields for Flame-wall interactions. A semi-detailed validated chemical kinetic model for a gasoline surrogate fuel developed by Andrae and Head4 was used for the study of LFS and Autoignition. For the quenching study, a skeletal chemical kinetic mechanism of gasoline surrogate, having 50 species and 174 reactions was used. The surrogate fuel was defined as a mixture of pure n-heptane, isooctane, and toluene. For LFS study, the ethanol volume fraction was varied from 0 to 85%, initial pressure from 4 to 8 bar, initial temperature from 300 to 900K, and dilution from 0 to 32%. Whereas for Autoignition study, the ethanol volume fraction was varied between 0 to 85%, initial pressure was varied between 20 to 60 bar, initial temperature was varied between 800 to 1200K, and the dilution was varied between 0 to 32% at equivalence ratios of 0.5, 1.0 and 1.5 to represent the in-cylinder conditions of a SI engine. For quenching study three Ethanol blends, namely E0, E25 and E85 are described in detail at an initial pressure of 8 atm and 17 atm. Initial wall temperature was taken to be 400 K. Quenching thicknesses and heat fluxes to the wall were computed. The laminar flame speed was found to increase with ethanol concentration and temperature but decrease with pressure and dilution. The autoignition time was found to increase with ethanol concentration at lower temperatures but was found to decrease marginally at higher temperatures. The autoignition time was also found to decrease with pressure and equivalence ratio but increase with dilution. The average quenching thickness was found to decrease with an increase in Ethanol concentration in the blend. Heat flux to the wall increased with increase in ethanol percentage in the blend and at higher initial pressures. Whereas the wall heat flux decreased with an increase in dilution. Unburned Hydrocarbon (UHC) and CO % was also found to decrease with ethanol concentration in the blend.

A Steep Dependence of Inward-Rectifying Potassium Channels on Cytosolic Free Calcium Concentration Increase Evoked by Hyperpolarization in Guard Cells1

Inactivation of inward-rectifying K+ channels (IK,in) by a rise in cytosolic free [Ca2+] ([Ca2+]i) is a key event leading to solute loss from guard cells and stomatal closure. However, [Ca2+]i action on IK,in has never been quantified, nor are its origins well understood. We used membrane voltage to manipulate [Ca2+]i (A. Grabov and M.R. Blatt [1998] Proc Natl Acad Sci USA 95: 4778–4783) while recording IK,in under a voltage clamp and [Ca2+]i by Fura-2 fluorescence ratiophotometry. IK,in inactivation correlated positively with [Ca2+]i and indicated a Ki of 329 ± 31 nm with cooperative binding of four Ca2+ ions per channel. IK,in was promoted by the Ca2+ channel antagonists Gd3+ and calcicludine, both of which suppressed the [Ca2+]i rise, but the [Ca2+]i rise was unaffected by the K+ channel blocker Cs+. We also found that ryanodine, an antagonist of intracellular Ca2+ channels that mediate Ca2+-induced Ca2+ release, blocked the [Ca2+]i rise, and Mn2+ quenching of Fura-2 fluorescence showed that membrane hyperpolarization triggered divalent release from intracellular stores. These and additional results point to a high signal gain in [Ca2+]i control of IK,in and to roles for discrete Ca2+ flux pathways in feedback control of the K+ channels by membrane voltage.

Aluminum Induces a Decrease in Cytosolic Calcium Concentration in BY-2 Tobacco Cell Cultures1

Al toxicity is a major problem that limits crop productivity on acid soils. It has been suggested that Al toxicity is linked to changes in cellular Ca homeostasis and the blockage of plasma membrane Ca2+-permeable channels. BY-2 suspension-cultured cells of tobacco (Nicotiana tabacum L.) exhibit rapid cell expansion that is sensitive to Al. Therefore, the effect of Al on changes in cytoplasmic free Ca concentration ([Ca2+]cyt) was followed in BY-2 cells to assess whether Al perturbed cellular Ca homeostasis. Al exposure resulted in a prolonged reduction in [Ca2+]cyt and inhibition of growth that was similar to the effect of the Ca2+ channel blocker La3+ and the Ca2+ chelator ethyleneglycol-bis(β-aminoethyl ether)-N,N′-tetraacetic acid. The Ca2+ channel blockers verapamil and nifedipine did not induce a decrease in [Ca2+]cyt in these cells and also failed to inhibit growth. Al and La3+, but not verapamil or nifedipine, reduced the rate of Mn2+ quenching of Indo-1 fluorescence, which is consistent with the blockage of Ca2+- and Mn2+-permeable channels. These results suggest that Al may act to block Ca2+ channels at the plasma membrane of plant cells and this action may play a crucial role in the phytotoxic activity of the Al ion.