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Quenching Efficiency (quenching + efficiency)
Selected AbstractsWater-soluble conjugated polymers: Synthesis and optical propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Baohan Xie Abstract Two sets of water-soluble poly(phenylene vinylene)s were synthesized and their optical properties were studied. The aqueous solubility of all these polymers is rendered by pendant sulfonate groups. One set of polymers (polymer I series) contains, in addition to the sulfonate pendants, dimethoxy substituents, while the other (polymer II series) contains oligo(ethylene oxide) side chains. Within each set, polymers containing lithium (Ia and IIa), sodium (Ib and IIb), and potassium (Ic and IIc) counter ions were prepared. The two sets of polymers showed different properties from physical appearance (fiber vs film) to thermal properties and to optical properties. It was found that set I polymers, with shorter side chains, exhibit stronger aggregation in aqueous solutions than set II polymers, which led to their lower fluorescence quantum yields and lower polymer-to-MV2+ quenching efficiencies. Within each set, the effect of counter ions on optical properties was noted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5123,5135, 2007 [source] Fast transient fluorescence technique for studying swelling of gels made at various crosslinker contents and exposed to organic vapourPOLYMER INTERNATIONAL, Issue 9 2002M Erdo Abstract Fast transient fluorescence technique (FTRF) was employed for studying swelling of disc-shaped poly(methyl methacrylate) (PMMA) gels, which were prepared by free radical copolymerization of methyl methacrylate (MMA) using various ethylene glycol dimethacrylate (EGDM) contents at 60,°C. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P-doped PMMA gels under chloroform vapor. Decay curves of P were measured during in situ swelling experiments. Exponential fits were performed to measure pyrene lifetimes, ,, inside the PMMA gels. It was observed that , values decreased as swelling proceeded. An equation is derived for low quenching efficiencies to interpret the behaviour of P lifetimes during swelling. The Li,Tanaka equation was used to determine the cooperative diffusion coefficients, Dc, for the gels made at various crosslinker contents. It is observed that Dc values decrease as the crosslinker content is increased. © 2002 Society of Chemical Industry [source] Numerical simulation of thermal interaction between polymer and argon induction thermal plasmaELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 1 2009Yoshitaka Takeuchi Abstract Influence of polymer powder injection into Ar thermal plasmas was investigated by numerical approaches. Thermal plasma,polymer solid coupling phenomena such as melting and evaporation were considered to study plasma-quenching effect of polymer injection. Dominant process for decay of plasma temperature was examined by changing thermodynamic parameters such as melting, boiling temperatures and their latent heats of solid and liquid polymers. As a result, thermodynamic properties of evaporated polymer vapor directly affect plasma-quenching phenomena more markedly than the properties of liquid and solid which influence plasma quenching efficiency through the amount of evaporation. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(1): 24,33, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10226 [source] Solar Cell Blends: High-Resolution Spectroscopic Mapping of the Chemical Contrast from Nanometer Domains in P3HT:PCBM Organic Blend Films for Solar-Cell Applications (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Mater. The inside cover image presents a near-field spectroscopic map of a P3HT:PCBM solar cell blend film obtaining using a parabolic-mirror-assisted optical microscope. This technique allows for simultaneous recording of both morphological and spectroscopic information, and on page 492 Xiao Wang et al. use it to investigate local molecular distribution, photoluminescence quenching efficiency, and other key properties of the P3HT:PCBM blend film. [source] A Graphene Nanoprobe for Rapid, Sensitive, and Multicolor Fluorescent DNA AnalysisADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Shijiang He Abstract Coupling nanomaterials with biomolecular recognition events represents a new direction in nanotechnology toward the development of novel molecular diagnostic tools. Here a graphene oxide (GO)-based multicolor fluorescent DNA nanoprobe that allows rapid, sensitive, and selective detection of DNA targets in homogeneous solution by exploiting interactions between GO and DNA molecules is reported. Because of the extraordinarily high quenching efficiency of GO, the fluorescent ssDNA probe exhibits minimal background fluorescence, while strong emission is observed when it forms a double helix with the specific targets, leading to a high signal-to-background ratio. Importantly, the large planar surface of GO allows simultaneous quenching of multiple DNA probes labeled with different dyes, leading to a multicolor sensor for the detection of multiple DNA targets in the same solution. It is also demonstrated that this GO-based sensing platform is suitable for the detection of a range of analytes when complemented with the use of functional DNA structures. [source] High-Resolution Spectroscopic Mapping of the Chemical Contrast from Nanometer Domains in P3HT:PCBM Organic Blend Films for Solar-Cell ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Xiao Wang Abstract A high-resolution near-field spectroscopic mapping technique is successfully applied to investigate the influence of thermal annealing on the morphology of a poly(3-hexylthiophene) and [6,6]-penyl-C61 butyric acid methyl ester (P3HT:PCBM) blend film. Based on the simultaneously recorded morphological and spectroscopic information, the interplay among the blend film morphology, the local P3HT:PCBM molecular distribution, and the P3HT photoluminescence (PL) quenching efficiency are systematically discussed. The PL and Raman signals of the electron donor (P3HT) and acceptor (PCBM) are probed at an optical resolution of approximately 10,nm, which allows the chemical nature of the different domains to be identified directly. In addition, the local PL quenching efficiency, which is related to the electron transfer from P3HT to PCBM, is quantitatively revealed. From these experimental results, it is proposed that high-resolution near-field spectroscopic imaging is capable of mapping the local chemical composition and photophysics of the P3HT:PCBM blends on a scale of a few nanometers. [source] The UV properties of E+A galaxies: constraints on feedback-driven quenching of star formationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007S. Kaviraj ABSTRACT We present the first large-scale study of E+A galaxies that incorporates photometry in the ultraviolet (UV) wavelengths. E+A galaxies are ,post-starburst' systems, with strong Balmer absorption lines indicating significant recent star formation, but without [O ii] and H, emission lines which are characteristic of ongoing star formation. The starburst that creates the E+A galaxy typically takes place within the last Gyr and creates a high fraction (20,60 per cent) of the stellar mass in the remnant over a short time-scale (<0.1 Gyr). We find a tight correlation between the luminosity of our E+A galaxies and the implied star formation rate (SFR) during the starburst. While low-luminosity E+As [M(z) > ,20] exhibit implied SFRs of less than 50 M, yr,1, their luminous counterparts [M(z) < ,22] show SFRs greater than 300 and as high as 2000 M, yr,1, suggesting that luminous and ultra-luminous infrared galaxies in the low-redshift Universe could be the progenitors of massive nearby E+A galaxies. We perform a comprehensive study of the characteristics of the quenching that truncates the starburst in E+A systems. We find that, for galaxies less massive than 1010 M,, the quenching efficiency decreases as the galaxy mass increases. However, for galaxies more massive than 1010 M,, this trend is reversed and the quenching efficiency increases with galaxy mass. Noting that the mass threshold at which this reversal occurs is in excellent agreement with the mass above which active galactic nuclei (AGN) become significantly more abundant in nearby galaxies, we use simple energetic arguments to show that the bimodal behaviour of the quenching efficiency is consistent with AGN and supernovae (SN) being the principal sources of negative feedback above and below M, 1010 M,, respectively. The arguments assume that quenching occurs through the mechanical ejection or dispersal of the gas reservoir and that, in the high-mass regime (M > 1010 M,), the Eddington ratios in this sample of galaxies scale as M,, where 1 < , < 3. Finally, we use our E+A sample to estimate the time it takes for galaxies to migrate from the blue cloud to the red sequence. We find migration times between 1 and 5 Gyr, with a median value of 1.5 Gyr. [source] Polymeric Photosensitizer Prodrugs for Photodynamic TherapyPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Marino A. Campo ABSTRACT A targeting strategy based on the selective enzyme-mediated activation of polymeric photosensitizer prodrugs (PPP) within pathological tissue has led to the development of agents with the dual ability to detect and treat cancer. Herein, a detailed study of a simple model system for these prodrugs is described. We prepared "first-generation" PPP by directly tethering the photosensitizer (PS) pheophorbide a to poly-(l)-lysine via epsilon amide links and observed that by increasing the number of PS on a polymer chain, energy transfer between PS units improved leading to better quenching efficiency. Fragmentation of the PPP backbone by trypsin digestion gave rise to a pronounced fluorescence increase and to more efficient generation of reactive oxygen species upon light irradiation. In vitro tests using the T-24 bladder carcinoma cell line and ex vivo experiments using mouse intestines illustrated the remarkable and selective ability of these PPP to fluoresce and induce phototoxicity upon enzymatic activation. This work elucidated the basic physicochemical parameters, such as water solubility and quenching/activation behavior, required for the future elaboration of more adaptable "second-generation" PPP, in which the PS is tethered to a proteolytically stable polymer backbone via enzyme-specific peptide linkers. This polymer architecture offers great flexibility to tailor make the PPP to target any pathological tissue known to over-express a specific enzyme. [source] The Effect of pH on the Topography of Porphyrins in Lipid Membranes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Irena Bronshtein ABSTRACT The effect of the acidity of the environment on the topography and photophysics of sensitizer molecules in homogeneous solutions, and when embedded in a lipid microenvironment, was studied. Four hematoporphyrin (HP) analogs were studied, which have chemical "spacers" of varying lengths between the chromophoric tetrapyrrole and the carboxylate moiety. These derivatives have essentially the same chemical attributes and reactivity as the parent compound, HP IX, which is used in clinical procedures of photodynamic therapy. The binding constants of these HP derivatives to membrane model systems increase with the length of carboxylate chain in the pH range 3.0,6.6. This effect of chain length is attributed to an increase in the hydrophobicity of the molecule on elongation of the alkyl chains. A strong pH dependence of the quenching efficiency of the porphyrins' fluorescence by iodide ions was observed in aqueous solution and is attributed to a unique electrostatic interaction between the fluorophore and the quencher. The quenching efficiency in liposomes, relative to the quenching in buffer, as a function of pH, shows that porphyrins in the neutral form penetrate deeper inside the lipid bilayer and are less exposed to external quenching than when negatively charged at the carboxylic moiety. This vertical displacement in the membrane is also evidenced in the effect of pH on the photosensitized oxidation efficiency of a membrane-bound chemical target. Increasing the pH causes a significant decrease in the sensitization efficiency in liposomes. This trend is attributed to the vertical localization, and protonation of the carboxylic groups on lowering the pH leads to sinking of the sensitizer into the lipid bilayer and to a consequent generation of singlet oxygen at a deeper point. This increases the dwell time of singlet oxygen within the bilayer, which results in greater photodamage to a membrane-residing singlet oxygen target. [source] Two mechanisms of 1D2 fluorescence quenching of Pr3+ -doped Y2SiO5 crystalPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003Yu. V. Malyukin Abstract In Y2SiO5:Pr3+ crystals (0.1 at%, 0.3 at%, 0.6 at% , and 1.8 at% Pr3+) characterized by the existence of two types of Pr3+ optical centers, the energy transfer has been investigated using time-resolved site-selective spectroscopy techniques. The results obtained show that at certain conditions there are two different mechanisms of fluorescence quenching of the excited 1D2 states of Pr3+ ions. At 0.3 at% Pr3+ and under the excitation of 1D2 states as the result of 3P0 , 1D2 nonradiative relaxation, the phonon-assisted energy transfer from 1D2 states of the I-type Pr3+ ions to the II-type ones has been found. The nonexponential part of donor fluorescence decay was described by the law t0.5. and the transfer efficiency exhibits a strong temperature dependence in the range of 1.5,80 K. At the direct selective excitation of the 1D2 states of one type Pr3+ optical centers it was possible to observe only their own fluorescence which quenched at a concentration above 0.6 at% Pr3+. The donor fluorescence decay was not fit by the law t0.5 and the quenching efficiency was characterized by the square-loaw dependence on the concentration and a very poor dependency on the temperature. The analysis of some models allows us to assume, that in this case, the cooperative quenching of the 1D2 states of both type Pr3+ optical centers can take place. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Discrimination of Single-Nucleotide Alterations by G-Specific Fluorescence QuenchingCHEMBIOCHEM, Issue 6 2005Chikara Dohno Dr. Abstract A new strategy for the detection of single-base alterations through fluorescence quenching by guanine (G) is described. We have devised a novel base-discriminating fluorescent (BDF) nucleoside, 4,PyT, that contains a pyrenecarboxamide fluorophore at the thymidine sugar's C4,-position. 4,PyT-containing oligodeoxynucleotides only exhibited enhanced fluorescence in response to the presence of a complementary adenine base. In contrast, the fluorescence of mismatched duplexes containing 4,PyT/N base pairs (N=C, G, or T) was considerably weaker. This highly A-selective fluorescence was a product of guanine-specific quenching efficiency; when the complementary base to 4,PyT was a mismatch, the pyrenecarboxamide fluorophore was able to interact intimately with neighboring G bases (the most likely interaction in the case of intercalation), so effective quenching by the G bases occurred in the mismatched duplexes. In contrast, duplexes containing 4,PyT/A base pairs exhibited strong emission, since in this case the fluorophores were positioned in the minor groove and able to escape fluorescence quenching by the G bases. [source] | |||||||||||||