Home About us Contact
|
Home About us Contact | ||
|
|
||
Emission Spectra (emission + spectrum)
Kinds of Emission Spectra Selected AbstractsEffect of PCBM Concentration on Photoluminescence Properties of Composite MEH-PPV/PCBM Nanoparticles Investigated by a Franck,Condon Analysis of Single-Particle Emission SpectraCHEMPHYSCHEM, Issue 14 2009Daeri Tenery Dr. Abstract The emission of composite conjugated polymer (MEH-PPV)/fullerene (PCBM) nanoparticles is investigated by single particle spectroscopy (SPS), and changes in vibronic structure with nanoparticle composition are evaluated by means of a detailed Franck,Condon analysis. Consistent with previous reports we find that the emission spectra can be modeled as the superposition of two types of emitters, one with aggregate character and one with molecular character. Major findings from the fitting of the SPS data to a Franck,Condon model are that 1) the occurrence of each of the two types of emitters changes with nanoparticle composition to the point that no aggregate emitters are detected (at 50 wt,% PCBM), 2) at the highest PCBM doping levels (75 wt,% PCBM) aggregate emitters reappear due to nanoscale phase separation in the composite nanoparticles, 3) the molecular emitters show small Huang,Rhys factors that increase with PCBM doping, indicative of extensive delocalization and exciton migration that is reduced by the disorder introduced in the polymer material by PCBM doping and 4) the aggregate emitters show large Huang,Rhys factors, indicative of the localized nature of these energy trap sites, with a broad distribution of values of these Huang,Rhys factors. The latter observation suggests a broad heterogeneous distribution of aggregate morphologies in blended conducting polymer materials, which can be attributed to variations in polymer chain folding and stacking at the aggregate sites. The reported results obtained by the SPS approach show how blending conjugated polymers with fullerenes at various doping levels induces changes in interchain interactions and aggregate site density even at length scales below a few tens of nanometers that affect conjugated polymer material properties, an observation that has gone unnoticed in bulk studies of blended conjugated polymer films. [source] Paradoxical Solvent Effects on the Absorption and Emission Spectra of Amino-Substituted Perylene Monoimides,CHEMPHYSCHEM, Issue 8 2005Peter D. Zoon Abstract In N -(2,5-di- tert -butylphenyl)-9-pyrrolidinoperylene-3,4-dicarboximide (5PI) the absorption and emission spectra display large solvatochromic shifts, but, remarkably, the Stokes shift is practically independent of solvent polarity. This unique behavior is caused by the extraordinarily large ground-state dipole moment of 5PI, which further increases upon increasing the solvent polarity, whereas the excited-state dipole moment is less solvent dependent. In the corresponding piperidine compound, 6PI, this effect is much less important owing to the weaker coupling between the amino group and the aromatic imide moiety, and in the corresponding naphthalimide, 5NI, it is absent. The latter shows the conventional solvatochromic behavior of a push,pull substituted conjugated system, that is, minor shifts in absorption and a larger change in the emission energy with solvent polarity. [source] Changes in the Room-temperature Emission Spectrum of Chlorophyll During Fast and Slow Phases of the Kautsky Effect in Intact Leaves,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Fabrice Franck ABSTRACT Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves, the comparison of Fo (basal level of fluorescence yield at transient O) and FM (maximum level of fluorescence yield at transient M) spectra showed that the relative amplitude of total variable fluorescence was maximal for the 684 nm Photosystem II (PSII) band and minimal for the 725 nm Photosystem I band. During the increase from Fo to FM a progressive redshift of the spectrum of variable fluorescence occurred. This shift reflected the different fluorescence rise kinetics of different layers of chloroplasts inside the leaf. This was verified by simulating the effect of screening on the emission spectrum of isolated chloroplasts and by experiments on greening leaves with low Chl content. In addition, experiments performed at different greening stages showed that the presence of uncoupled Chl at early-greening stages and lightharvesting complex II (LHCII) at later stages have detectable but minor effects on the shape of room-temperature emission spectra. When strong actinic light was applied to mature green leaves, the slow fluorescence yield, which declined from FM to FT (steady-state level of fluorescence yield at transient T), was accompanied by a slight redshift of the 684 nm PSII band because of nonphotochemical quenching of short-wavelengthemitting Chl ascribed to LHCII. [source] Photoluminescence of Ho3+:YVO4 crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007S. Polosan Abstract Emission spectra of Ho3+ -doped YVO4 crystals are studied in the visible and infrared spectral regions. Besides the emission bands at 544 nm and at about 1950 and 2017 nm due to Ho3+, we observed a broad emission band at 610 nm at low temperatures like 15 K in the highly doped crystals with the Ho3+ concentrations of more than 0.5 mol%. The excitation band for this broad emission is located at 390 nm which is near the edge of band gap of the crystal. It is suggested that the 610 nm band is attributed to defects related to oxygen vacancies around V4+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescent properties of PP and LDPE films and rods doped with the Eu(III)-La(III) complexPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2006Roman Pogreb Abstract The work is devoted to luminescent properties of trivalent lanthanide complexes dispersed in thermoplastic host matrices. Polyethylene films and polypropylene-rods, both doped with these complexes, were manufactured using an extrusion technique. Two kinds of dopants were used: Eu(III)-thenoyltrifluoroacetone-1,10-phenanthroline complex (1) and Eu(III)-La(III)-1,10-phenanthroline complex (2). Absorption, excitation, emission spectra and lifetime of luminescence were studied. The impact of the polymer matrix on the emission spectra was investigated. Emission spectra of the films were studied at room and helium temperatures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) surface mapping showed that in the Eu(III)-La(III) complex europium forms islands (clusters) with a dimension of 1,µm, whereas lanthanum was dispersed more uniformly in the polymer matrix. Dependence of emission intensity on the excitation was determined. Copyright © 2006 John Wiley & Sons, Ltd. [source] Combustion Measurements of Fuel-Rich Aluminum and Molybdenum Oxide Nano-Composite MixturesPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 2 2010Tim Bazyn Abstract Fuel rich nano-composite powders of aluminum and molybdenum oxide were tested for ignition and combustion behind the incident and reflected shock waves in a shock tube. The powders consisted of approximately 10,,m particles, each of which contained Al and MoO3 mixed by mechanical alloying on the nano-scale. These powders were aluminum rich with composition ratios of 4,:,1, 8,:,1, and 16,:,1 Al,:,MoO3 by mass. Ignition tests were performed behind incident shocks for temperatures in the range of 900 to 1500,K. From these tests, ignition delay times were obtained, and some information on combustion duration was also derived. Samples were tested in air at 0.2,MPa, and compared against nano-Al, 2.7,,m Al, and 10,,m Al baselines. Ignition results for the baseline Al cases were as expected: 10,,m Al not igniting until 2000,K, 2,,m Al igniting down to ,1400,K, and n-Al igniting as low as 1150,K. The thermite samples showed considerable improvement in ignition characteristics. At the lowest temperature tested (900,K), both the 8,:,1 and 4,:,1 samples ignited within 250,,s. The 16,:,1 sample (94% Al) ignited down to 1050,K , which represents an improvement of roughly 1000,K over baseline Al with only a small energetic penalty. In all cases, the ignition delay increased as the amount of MoO3 in the composite was reduced. The 4,:,1 nano-composite material ignited as fast or faster than the n-Al samples. Ignition delay increased with decreasing temperature, as expected. Emission spectra and temperature data were also taken for all samples using high-speed pyrometry and time-integrated spectroscopy. In these cases, measurements were made behind the reflected shock using end-wall loading, though the conditions (temperature, pressure, and gas composition) were identical to the incident shock tests. Spectroscopy showed strong AlO features in all the samples, and the spectra fit well to an equilibrium temperature. Broadband, low resolution spectra were also fit to continuum, gray body temperatures. In general, the observed temperatures were reasonably close to 3500,K, which is similar to the combustion temperatures of pure aluminum under these conditions. [source] Comparison of basis set effects and the performance of ab initio and DFT methods for probing equilibrium fluctuationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2007Ross C. Walker Abstract The electronic absorption and emission spectra of large molecules reflect the extent and timescale of electron-vibration coupling and therefore the extent and timescale of relaxation/reorganization in response to a perturbation. In this paper, we present a comparison of the calculated absorption and emission spectra of NADH in liver alcohol dehydrogenase (LADH), using quantum mechanical/molecular mechanical methods, in which we vary the QM component. Specifically, we have looked at the influence of basis set (STO-3G, 3-21G*, 6-31G*, CC-pVDZ, and 6-311G**), as well as the influence of applying the DFT TD-B3LYP and ab initio TD-HF and CIS methods to the calculation of absorption/emission spectra and the reorganization energy (Stokes shift). The ab initio TD-HF and CIS methods reproduce the experimentally determined Stokes shift and spectral profiles to a high level of agreement, while the TD-B3LYP method significantly underestimates the Stokes shift, by 45%. We comment on the origin of this problem and suggest that ab initio methods may be naturally more suited to predicting molecular behavior away from equilibrium geometries. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 478,490, 2007 [source] Detection and Analysis of Strong Oscillating Electric Fields in a Picosecond Laser Plasma with the Help of Plasma Satellites of X-ray Spectral LinesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2005V. S. Belyaev Abstract X-ray lines of ions in a solid target interacting with picosecond laser pulses of the intensity ,3 × 1017 W/cm2 were studied on the "Neodim" laser facility. We observed X-ray Ly, emission spectra of hydrogen-like fluorine ions. Satellite lines were also recorded, evidencing the presence of intense plasma oscillations with an amplitude of the electric field larger than 108 V/cm and a frequency of about 1015 s,1. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cr3+ -doped LiNbO3 crystals grown by the Bridgman methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005Haiping Xia Abstract The growth of LiNbO3 crystals doped with Cr3+ ions in 0.1, 0.2, and 0.5 mol % concentrations by Bridgman method were reported. The Cr3+ ion concentrations in crystals were measured by inductively coupled plasma spectrometry. Electron paramagnetic resonance had been used to investigate the sites occupied by the Cr3+ ions. Two Cr3+ ion centers located at Li+ and Nb5+ sites (CrLi3+ and CrNb3+ centers, respectively) were observed. Optical absorption and temperature-dependence emission spectra of the Cr3+ ions were reported. The crystal-field parameters and Racah parameters of the Cr3+ ion defect sites were reported and compared with those grown by Czochralski technique. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimized green fluorescent protein variants provide improved single cell resolution of transgene expression in ascidian embryosDEVELOPMENTAL DYNAMICS, Issue 2 2006Robert W. Zeller Abstract The green fluorescent protein (GFP) is used extensively to monitor gene expression and protein localization in living cells, particularly in developing embryos from a variety of species. Several GFP mutations have been characterized that improve protein expression and alter the emission spectra to produce proteins that emit green, blue, cyan, and yellow wavelengths. DsRed and its variants encode proteins that emit in the orange to red wavelengths. Many of these commercially available fluorescent proteins have been "codon optimized" for maximal levels of expression in mammalian cells. We have generated several fluorescent protein color variants that have been codon optimized for maximal expression in the ascidian Ciona intestinalis. By analyzing quantitative time-lapse recordings of transgenic embryos, we demonstrate that, in general, our Ciona optimized variants are detected and expressed at higher levels than commercially available fluorescent proteins. We show that three of these proteins, expressed simultaneously in different spatial domains within the same transgenic embryo are easily detectable using optimized fluorescent filter sets for epifluorescent microscopy. Coupled with recently developed quantitative imaging techniques, our GFP variants should provide useful reagents for monitoring the simultaneous expression of multiple genes in transgenic ascidian embryos. Developmental Dynamics 235:456,467, 2006. © 2005 Wiley-Liss, Inc. [source] Synthesis, Characterisation and Optical Properties of Silica Nanoparticles Coated with Anthracene Fluorophore and Thiourea Hydrogen-Bonding SubunitsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 36 2008Pilar Calero Abstract Bifunctionalised hybrid silica nanoparticles have been synthesised and characterised, and their optical emission properties in the presence of certain anions in acetonitrile solutions have been studied. The alkoxysilane derivatives N -butyl- N, -[3-(trimethoxysilyl)propyl]thiourea (1), N -phenyl- N, -[3-(trimethoxysilyl)propyl]thiourea (2) and 3-[(anthracen-10-yl)methylthio]propyltriethoxysilane (3) were prepared and used to functionalise uncoated LUDOX silica nanoparticles with a mean diameter of 18,±,2 nm. The functionalisation of the nanoparticle surfaces was carried out by two different approaches. The first approach relies on the consecutive grafting of the two subunits. In this protocol, the nanoparticles were first functionalised with anthracene derivative 3 (solid NA), and then treated with the corresponding binding sites 1 or 2 to result in the NA-Pt3 and NA-Bt3 solids. The second approach deals with the simultaneous grafting of 1 or 2 and the signalling subunit 3 in different ratios. This method was used for the preparation of the NA1Pt1, NA1Bt1, NA1Pt3 and NA1Bt3 nanoparticles. The bifunctionalised silica nanoparticles were characterised by using standard techniques. Acetonitrile suspensions of NA nanoparticles (5 mg in 20 mL) showed anthracene bands centred at ca. 350, 370 and 390 nm. Upon excitation at 365 nm, a typical emission band with fine structure in the 390,450 nm range was observed. Similar absorption and emission spectra were found for the bifunctionalised nanoparticles. The work is completed with a prospective study of the fluorescence of the prepared nanoparticles in the presence of organic (acetate, benzoate) and inorganic (F,, Cl,, Br,, CN,, HSO4, and H2PO4,) anions. The apparent binding constants (adsorption constants) for the interaction of NA-Pt3 with anions in acetonitrile were determined by performing a Langmuir-type analysis of fluorescence titration data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Structure Variation and Luminescence Properties of Lanthanide Complexes Incorporating a Naphthalene-Derived Chromophore Featuring Salicylamide Pendant ArmsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2008Xue-Qin Song Abstract A new potentially bridging ligand containing two salicylamide pendant arms separated by a 2,3-dimethoxynaphthalene spacer has been prepared and its coordination chemistry with LnIII ions has been investigated. An analysis of the presented crystal structures indicates that the diversity of these supramolecular structures is mainly dictated by the nature of the metal ions. These compounds represent good examples of tuning crystal structures arising from the flexibility of the ligands and the Ln contraction effect. Luminescence studies showed that the introduction of the methoxyl substituents on the naphthalene backbone lowers the triplet energy and considerably changes the luminescent behaviors of the EuIII and TbIII complexes, which is very different from the literature data on similar compounds. In the emission spectra of the Tb complex the ligand fluorescence remains relatively important because of the back-energy transfer from the TbIII ion to the ligand, which to the best of our knowledge, may be the first example of salicylamide lanthanide complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Nickel-Organic Coordination Layers with Different Directional CavitiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006Youfu Zhou Abstract The two new metal-organic coordination frameworks [Ni2(pydc)2(4,4,-bpy)(H2O)4]n·0.5n(4,4,-bpy)2H2O (1) and [Ni2(pydc)2(2,2,-bpy)2(H2O)2]n·2nH2O (2) (H2pydc = pyridine-3,4-dicarboxylic acid; bpy = bipyridine) have been synthesised under hydrothermal conditions and characterised by single-crystal X-ray diffraction analysis. The structure of 1 contains parallel rectangular channels that accommodate large 4,4,-bpy guests while that of 2 contains vertical channels coordinated to 2,2,-bpy ligands. Their magnetic analyses show that they exhibit different magnetic interactions. The red shifts of the peak in their emission spectra relative to those of the the free ligands could be attributable to the metal,ligand coordination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Theoretical Studies on Metal,Metal Interaction and Intrinsic 1,3[,*(d),(s/p)] Excited States of Dinuclear d10 Complexes with Bridging Phosphane LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2006Qing-Jiang Pan Abstract To explore the metal,metal interaction and spectroscopic properties, the ground- and excited-state structures of [M2(dpm)2]2+ [M = Ag (2), Cu (3), dpm = bis(diphosphanyl)methane] and their solvated species [M2(dpm)2]2+·(MeCN)2 were optimized by the MP2 and CIS methods, respectively. In the ground states, the calculated M,M distances and their corresponding M,M stretching frequencies for 2 and 3 indicate the presence of metallophilic attraction; there is strong N,Cu/Ag coordination in acetonitrile, which is different from the case in previous studies of [Au2(dpm)2]2+ (1). CIS calculations show that 2 and 3 have 1,3[,*(d),(s/p)] as their lowest-energy excited state, as is also the case for 1, confirmed by unrestricted MP2 calculations. On the basis of the CIS-optimized structures, the TD-DFT (B3LYP) method was employed to calculate the emission spectra of such complexes. For 3, the phosphorescent emissions were calculated at 424 and 514 nm in the solid state and acetonitrile, which is comparable to the experimental data of 475 and 480 nm, respectively. The comparison between the gas-phase and solution emissions for 1,3 reveals that the N,M coordination results in a large red-shift of the emission wavelength. Taking previous studies into account , we found that the M,M distances are linearly correlated with the M,M stretching frequencies for the dinuclear d10 complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Metal-Directed Self-Assembly: Two New Metal-Binicotinate Grid Polymeric Networks and Their Fluorescence Emission Tuned by Ligand ConfigurationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2004Benlai Wu Abstract Two new 2-D metal-binicotinate coordination polymers, namely, [CdII(bpdc)]n (1) and {[ZnII8(bpdc)8(H2O)8](H2O)8}n (2) (H2bpdc = binicotinic acid) have been synthesized using hydrothermal and three-layer diffusion methods, respectively. Single-crystal X-ray analyses revealed that both are extended grid networks of the (4,4) topology. Their structures alter with the configuration and function of bpdc. The achiral, free H2bpdc has axial chirality induced by metal coordination in 1, and bpdc connects to four metal centers forming a 2-D (4,4) net with three kinds of apertures generated through self-assembly. In 2, however, bpdc connects to three metal centers, fabricating a microporous framework containing hydrophilic channels. Studies on the solid emission spectra of the free ligand, 1, and 2 confirmed, that the configuration of bpdc resulting from metal-directed coordination has a profound effect on the fluorescence emissions of 1 and 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Influence of light energy and power density on the microhardness of two nanohybrid compositesEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2008Kerstin Gritsch The purpose of this study was to investigate the role of light parameters on nanohybrid composite curing. Two nanohybrid resins were cured by two light-emitting diode (LED) devices and by one quartz-tungsten-halogen (QTH) device using different combinations of energy density and power density (8 J cm,2 and 400 mW cm,2; 8 J cm,2 and 1,000 mW cm,2; 16 J cm,2 and 400 mW cm,2; and 16 J cm,2,1,000 mW cm,2). The effects of these combinations on polymerization were assessed by measuring the Vickers microhardness. Data differed for the two composites and varied according to the light parameters and the nature of the curing device. For both resins, an energy density of 16 J cm,2 yielded the best microhardness values at both the top and the bottom of the sample, independently of the power density. When using a lower energy density of 8 J cm,2, a modulated power density was required to achieve proper curing at the bottom of the sample: 8 J cm,2 and 400 mW cm,2 induced greater values at the bottom surface. At an energy density of 16 J cm,2, the power density was not relevant (no significant differences were found between 400 and 1,000 mW cm,2), except when the emission spectra of the light-curing units (LCUs) did not match exactly with the absorption spectra of the photoinitators included in the resins (greatest values with 16 J cm,2 and1,000 mW cm,2). These results suggest that above a certain energy density threshold, the power density may not significantly influence the polymerization kinetics. [source] Toward Highly Efficient Solid-State White Light-Emitting Electrochemical Cells: Blue-Green to Red Emitting Cationic Iridium Complexes with Imidazole-Type Ancillary LigandsADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Lei He Abstract Using imidazole-type ancillary ligands, a new class of cationic iridium complexes (1,6) is prepared, and photophysical and electrochemical studies and theoretical calculations are performed. Compared with the widely used bpy (2,2,-bipyridine)-type ancillary ligands, imidazole-type ancillary ligands can be prepared and modified with ease, and are capable of blueshifting the emission spectra of cationic iridium complexes. By tuning the conjugation length of the ancillary ligands, blue-green to red emitting cationic iridium complexes are obtained. Single-layer light-emitting electrochemical cells (LECs) based on cationic iridium complexes show blue-green to red electroluminescence. High efficiencies of 8.4, 18.6, and 13.2,cd A,1 are achieved for the blue-green-emitting, yellow-emitting, and orange-emitting devices, respectively. By doping the red-emitting complex into the blue-green LEC, white LECs are realized, which give warm-white light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.42, 0.44) and color-rendering indexes (CRI) of up to 81. The peak external quantum efficiency, current efficiency, and power efficiency of the white LECs reach 5.2%, 11.2,cd,A,1, and 10,lm,W,1, respectively, which are the highest for white LECs reported so far, and indicate the great potential for the use of these cationic iridium complexes in white LECs. [source] The Influence of Alkyl-Chain Length on Beta-Phase Formation in PolyfluorenesADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Daniel W. Bright Abstract Di- n -alkyl substituted polyfluorenes with alkyl chain lengths of 6, 7, 8, 9, and 10 carbon atoms (PF6, PF7, PF8, PF9, and PF10) are studied in dilute solution in MCH using optical spectroscopy. Beta-phase is formed upon cooling in solutions (, 7,µg mL,1) of PF7, PF8, and PF9 only, which is observed as an equilibrium absorption peak at , 437,nm and strong changes in the emission spectra. Beta-phase is formed upon thermal cycling to low temperature in solutions (,7,µg mL,1) of PF7, PF8, and PF9, which is observed as an equilibrium absorption peak at , 437,nm and strong changes in the emission spectra. Beta phase is found to occur more favorably in PF8 than in PF7 or PF9, which is attributed to a balance between two factors. The first is the dimer/aggregate formation efficiency, which is poorer for longer (more disordered) alkyl chain lengths, and the second is the Van der Waals bond energy available to overcome the steric repulsion and planarize the conjugated backbone, which is insufficient in the PF6 with a shorter alkyl chain. Beta phase formation is shown to be a result of aggregation, not a precursor to it. A tentative value of the energy required to planarize the fluorene backbone of (15.6,±,2.5) kJ mol,1 monomer is suggested. Excitation spectra of PF6, PF7, PF8, and PF9 in extremely dilute (, 10,ng mL,1) solution show that beta phase can form reversibly in dilute solutions of PF7, PF8 and PF9, which is believed to be a result of chain collapse or well dispersed aggregates being present in solution from dilution of more concentrated solutions. PF7, PF8, and PF9 also form beta phase in thermally cycled solid films spin-cast from MCH. However, in the films the PF7 formed a larger fraction of beta phase than the PF9, in contrast to the case in solutions, because it is less likely that the close-packed chains in the solid state will allow the formation of planarized chains with the longer PF9 side chains. [source] Tuning the Energy Level and Photophysical and Electroluminescent Properties of Heavy Metal Complexes by Controlling the Ligation of the Metal with the Carbon of the Carbazole Unit,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2007L. Yang Abstract Four novel IrIII and PtII complexes with cyclometalated ligands bearing a carbazole framework are prepared and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction studies of complexes 1, 3, and 4 reveal that the 3- or 2-position C atom of the carbazole unit coordinates to the metal center. The difference in the ligation position results in significant shifts in the emission spectra with the changes in wavelength being 84,nm for the Ir complexes and 63,nm for the Pt complexes. The electrochemical behavior and photophysical properties of the complexes are investigated, and correlate well with the results of density functional theory (DFT) calculations. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ3/LiF/Al can attain very high efficiencies. [source] The Synthesis, Photophysical Characterization, and X-Ray Structure Analysis of Two Polymorphs of 4,4,-DiacetylstilbeneHELVETICA CHIMICA ACTA, Issue 6 2010Cameron Pye Abstract A palladium(II) acetate-catalyzed synthesis of 1 that utilizes the novel triazene 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a ,,,* transition in the range of 330,350,nm. Compound 1 was observed to be luminescent, with room-temperature solution and solid-state emission spectra that exhibited maxima in the range 400,500,nm. All room-temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77,K in propanenitrile glass was broad and featureless with a maximum at 447,nm. Compound 1 crystallized as a yellow and colorless polymorph. X-Ray structure analyses of both of these polymorphs and 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone are presented. [source] Solution-Processable Red Phosphorescent Dendrimers for Light-Emitting Device Applications,ADVANCED MATERIALS, Issue 6 2004D. Anthopoulos High efficiency, solution-processed electroluminescent devices are realized using two new red-light-emitting phosphorescent dendrimers (see Figure). By modulating the dendrimer architecture (changing the structure of the luminescent core), tuning of the emission spectra is demonstrated. Processability in organic solvents is achieved by incorporating the red-emitting cores into dendrimers with suitable surface groups and dendrons. [source] Theoretical electronic spectra of 2-aminopurine in vapor and in waterINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006Antonio Carlos Borin Abstract The accurate quantum chemical CASSCF and CASPT2 methods combined with a Monte Carlo procedure to mimic solvation effects have been used in the calculation of the spectroscopic properties of two tautomers of 2-aminopurine (2AP). Absorption and emission spectra have been simulated both in vacuum and in aqueous environment. State and transition energies and properties have been obtained with high accuracy, leading to the assignment of the most important spectroscopic features. The lowest-lying 1(,,,*) (1La) state has been determined as responsible for the first band in the absorption spectrum and also for the strong fluorescence observed for the system in water. The combined approach used in the present work gives quantitatively accurate results. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Examples for the importance of radiophysical measurements in clinical phototherapyJOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 5 2007Lars Alexander Schneider Summary Background: Optimal UV therapy requires regular surveillance of the variables that influence therapeutic success. In daily practice, phototherapy equipment is often operated with an attitude of "autocontrol." This implies that thorough control measurements of the emission spectra and calibration of UV fluences are not routinely performed. For both quality control and patient safety, it is essential to regularly check whether a UV source is providing the right target spectrum with the correct dose to the skin. Methods: We have exemplarily taken three UV sources currently used in clinical practice and performed radiophysical measurements, i. e. determined emission spectra, radiation output and correctness of dose calculation. Results: All three sources revealed either a largely inhomogeneous distribution pattern of radiation intensity, variation of radiation intensity over time or insufficient filtering of the UV lamp emission spectrum. Furthermore the dose calculation procedures had to be revised because of significant differences between the estimated and the administered UV doses. Conclusions: Radiophysical measurement of all UV-equipment in clinical use is a simple and effective way to improve the safety and reliability of phototherapy. Such measurements help to uncover technical flaws in radiation sources and prevent unnecessary side effects and UV exposure risks for the patient. [source] Synthesis and characterization of high thermally-stable and good soluble PVK-based polymers with perylene moietyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Jianli Hua Abstract Three new poly(N -vinylcarbazole) (PVK)-based copolymers containing N -(n -butyl)- N -ethyl-1,6,7,12-tetra-(4- tert -butyl-phenoxy)-3,4,9,10-perylene tetracarboxylic bisimides were successfully synthesized by partially formylated by the standard Vilsmeier reaction, and the formyl groups of high reactivity are condensed with cyanoacetylated perylene to afford PVK-based polymers. The copolymers containing different percentage of perylene were obtained through the percentage of cyanoacetylated perylene unit being controlled by the initial feed ratio. The structures and properties of three copolymers were characterized and evaluated by FT-IR, NMR, UV,vis, FL spectroscopy, gel permeation chromatography, and thermogravimetric analysis measurements. The polymers were highly soluble in conventional solvents such as toluene, CHCl3, THF, DMF etc., and they were thermally stable up to 442,445°C. Three copolymers have emission spectra with characteristic features of the perylene unit, and fluorescence quantum yields of polymers are higher than that of perylene bisimide, which may be caused by singlet,singlet energy transfer from PVK backbone to perylene in the polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Weighting hyperspectral image data for improved multivariate curve resolution resultsJOURNAL OF CHEMOMETRICS, Issue 9 2008Howland D. T. Jones Abstract The combination of hyperspectral confocal fluorescence microscopy and multivariate curve resolution (MCR) provides an ideal system for improved quantitative imaging when multiple fluorophores are present. However, the presence of multiple noise sources limits the ability of MCR to accurately extract pure-component spectra when there is high spectral and/or spatial overlap between multiple fluorophores. Previously, MCR results were improved by weighting the spectral images for Poisson-distributed noise, but additional noise sources are often present. We have identified and quantified all the major noise sources in hyperspectral fluorescence images. Two primary noise sources were found: Poisson-distributed noise and detector-read noise. We present methods to quantify detector-read noise variance and to empirically determine the electron multiplying CCD (EMCCD) gain factor required to compute the Poisson noise variance. We have found that properly weighting spectral image data to account for both noise sources improved MCR accuracy. In this paper, we demonstrate three weighting schemes applied to a real hyperspectral corn leaf image and to simulated data based upon this same image. MCR applied to both real and simulated hyperspectral images weighted to compensate for the two major noise sources greatly improved the extracted pure emission spectra and their concentrations relative to MCR with either unweighted or Poisson-only weighted data. Thus, properly identifying and accounting for the major noise sources in hyperspectral images can serve to improve the MCR results. These methods are very general and can be applied to the multivariate analysis of spectral images whenever CCD or EMCCD detectors are used. Copyright © 2008 John Wiley & Sons, Ltd. [source] High-level ab initio calculations on HGeCl and the equilibrium geometry of the Ã1A, state derived from Franck-Condon analysis of the single-vibronic-level emission spectra of HGeCl and DGeClJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Daniel K. W. Mok Abstract CCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X,1A, and Ã1A, states of HGeCl. The fully relativistic effective core potential, ECP10MDF, and associated standard valence basis sets of up to the aug-cc-pV5Z quality were employed for Ge. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HGeCl. Based on the currently, most systematic CCSD(T) calculations performed in this study, the best theoretical geometrical parameters of the X,1A, state are re(HGe) = 1.580 ± 0.001 Å, ,e = 93.88 ± 0.01° and re(GeCl) = 2.170 ± 0.001 Å. In addition, Franck-Condon factors including allowance for anharmonicity and Duschinsky rotation between these two states of HGeCl and DGeCl were calculated employing CCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate Ã1A, , X,1A, SVL emission spectra of HGeCl and DGeCl. The iterative Franck-Condon analysis (IFCA) procedure was carried out to determine the equilibrium geometrical parameters of the Ã1A, state of HGeCl by matching the simulated, and available experimental SVL emission spectra of HGeCl and DGeCl of Tackett et al., J Chem Phys 2006, 124, 124320, using the available, estimated experimental equilibrium (r) structure for the X,1A, state, while varying the equilibrium geometrical parameters of the Ã1A, state systematically. Employing the derived IFCA geometry of re(HGe) = 1.590 Å, re(GeCl) = 2.155 Å and ,e(HGeCl) = 112.7° for the Ã1A, state of HGeCl in the spectral simulation, the simulated absorption and SVL emission spectra of HGeCl and DGeCl agree very well with the available experimental LIF and SVL emission spectra, respectively. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Comparison of basis set effects and the performance of ab initio and DFT methods for probing equilibrium fluctuationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2007Ross C. Walker Abstract The electronic absorption and emission spectra of large molecules reflect the extent and timescale of electron-vibration coupling and therefore the extent and timescale of relaxation/reorganization in response to a perturbation. In this paper, we present a comparison of the calculated absorption and emission spectra of NADH in liver alcohol dehydrogenase (LADH), using quantum mechanical/molecular mechanical methods, in which we vary the QM component. Specifically, we have looked at the influence of basis set (STO-3G, 3-21G*, 6-31G*, CC-pVDZ, and 6-311G**), as well as the influence of applying the DFT TD-B3LYP and ab initio TD-HF and CIS methods to the calculation of absorption/emission spectra and the reorganization energy (Stokes shift). The ab initio TD-HF and CIS methods reproduce the experimentally determined Stokes shift and spectral profiles to a high level of agreement, while the TD-B3LYP method significantly underestimates the Stokes shift, by 45%. We comment on the origin of this problem and suggest that ab initio methods may be naturally more suited to predicting molecular behavior away from equilibrium geometries. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 478,490, 2007 [source] Reconstitution of Photosystem II Reaction Center with Cu-Chlorophyll aJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 11 2006Shuang Liu Abstract An isolated photosystem (PS) II reaction center (RC) with altered pigment content was obtained by chemical exchange of native chlorophyll a (Chl) with externally added Cu-Chl a (Cu-Chl). Pigment composition and spectroscopic properties of the RC exchanged with Cu-Chl were compared with native RC and RC treated with Chl in the same way. High-performance liquid chromatography analysis showed approximately 0.5 Cu-Chl per two pheophytin in the Cu-Chl-reconstituted RC preparation. Insertion of Cu-Chl resulted in a decrease in absorption at 670 nm and an increase at 660 nm, suggesting that the peripheral Chl may have been displaced. Fluorescence emission spectra of the Cu-Chl-reconstituted RC displayed a marked decrease in fluorescence yield and a blue shift of the band maximum, accompanied by the appearance of a broad peak at a shorter wavelength, indicating that energy transfer in the modified RC was disturbed by Cu-Chl, a quencher of the excited state. However, there were few differences in the circular dichroism (CD) spectra, suggesting that the arrangement of pigments and proteins responsible for the CD signal was not significantly affected. In addition, no obvious change in peptide components was found after the exchange procedure. (Managing editor: Ping He) [source] A white light confocal microscope for spectrally resolved multidimensional imagingJOURNAL OF MICROSCOPY, Issue 3 2007J. H. FRANK Summary Spectrofluorometric imaging microscopy is demonstrated in a confocal microscope using a supercontinuum laser as an excitation source and a custom-built prism spectrometer for detection. This microscope system provides confocal imaging with spectrally resolved fluorescence excitation and detection from 450 to 700 nm. The supercontinuum laser provides a broad spectrum light source and is coupled with an acousto-optic tunable filter to provide continuously tunable fluorescence excitation with a 1-nm bandwidth. Eight different excitation wavelengths can be simultaneously selected. The prism spectrometer provides spectrally resolved detection with sensitivity comparable to a standard confocal system. This new microscope system enables optimal access to a multitude of fluorophores and provides fluorescence excitation and emission spectra for each location in a 3D confocal image. The speed of the spectral scans is suitable for spectrofluorometric imaging of live cells. Effects of chromatic aberration are modest and do not significantly limit the spatial resolution of the confocal measurements. [source] Broadly distributed nucleophilic reactivity of proteins coordinated with specific ligand binding activityJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2005Yasuhiro Nishiyama Abstract Covalent nucleophile,electrophile interactions have been established to be important for recognition of substrates by several enzymes. Here, we employed an electrophilic amidino phosphonate ester (EP1) to study the nucleophilic reactivity of the following proteins: albumin, soluble epidermal growth factor receptor (sEGFR), soluble CD4 (sCD4), calmodulin, casein, ,-lactalbumin, ovalbumin, soybean trypsin inhibitor and HIV-1 gp120. Except for soybean trypsin inhibitor and ,-lactalbumin, these proteins formed adducts with EP1 that were not dissociated by denaturing treatments. Despite their negligible proteolytic activity, gp120, sEGFR and albumin reacted irreversibly with EP1 at rates comparable to the serine protease trypsin. The neutral counterpart of EP1 reacted marginally with the proteins, indicating the requirement for a positive charge close to the electrophilic group. Prior heating resulted in altered rates of formation of the EP1,protein adducts accompanied by discrete changes in the fluorescence emission spectra of the proteins, suggesting that the three-dimensional protein structure governs the nucleophilic reactivity. sCD4 and vasoactive intestinal peptide (VIP) containing phosphonate groups (EP3 and EP4, respectively) reacted with their cognate high-affinity binding proteins gp120 and calmodulin, respectively, at rates exceeding the corresponding reactions with EP1. Reduced formation of EP3,gp120 adducts and EP4,calmodulin adducts in the presence of sCD4 and VIP devoid of the phosphonate groups was evident, suggesting that the nucleophilic reactivity is expressed in coordination with non-covalent recognition of peptide determinants. These observations suggest the potential of EPs for specific and covalent targeting of proteins, and raise the possibility of nucleophile,electrophile pairing as a novel mechanism stabilizing protein,protein complexes. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||