Ultrafast study of inter‐ and intrachain energy transfer in a core–polymer

Interchain interactions can play a positive role in reaching amplified spontaneous emission in an interesting core–polymer system where the donor (side chains) and the acceptor (core) are chemically linked together. Different degree of interchain interactions modifies the photophysical characteristics of the polymer. By means of transient absorption spectroscopy we show that the stimulated emission from the core decreases passing from solid state to concentrated solution and it is almost absent in the diluted solution. The conformational rearrangements of the core–polymer chain in solution limits the efficiency of the intrachain Förster energy transfer mechanism. The free chain rotations decrease the exciton hopping along the conjugated chains, the ratio between donor and acceptor moieties in the polymer, and change the relative orientation of the transition dipoles of the donor and acceptor causing a strong decrease of energy transfer efficiency and subsequently of the gain. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 965–969     

Two- and three-dimensional restricted geometry case of luminescence quenching

We present general analytical expression for two and three-dimensional cases of static energy transfer kinetics in doped nanoparticles (of round, spherical and cylindrical shape). A series of numerical experiments has been performed using Monte-Carlo simulation. The analytical expressions have shown very good coincidence with the computer simulation.     

殖民主义的仆从——《基姆》和《印度之行》中殖民主义者的比较研究

吉卜林和福斯特是有关印度书写的殖民与后殖民文学的两位重要作家。本文通过比较吉卜林和福斯特对印度不同时期殖民官员的描述,从后殖民角度揭示文化霸权指引下的文学活动,尤其是小说在形成帝国主义态度和参照系的重要作用,以及西方作家本身存在着的种族与阶级意识歧视与偏见。由此看来,这些参与殖民建构的作家们才是帝国的真正仆从。     

Peripatetic Highlights in Bern

This tour of significant scientific sites in Bern uses the local legacy of its most illustrious scientists, Albert Einstein (1879–1955) and Fritz Houtermans (1903–1966), as its guiding thread through the old town and the university district.Ann M.Hentschel is translator of the correspondence volumes of The Collected Papers of Albert Einstein and is currently employed by the Institute for the History and Philosophy of Science at the University of Bern to write the guide for a city tour of Einsteins old haunts in Bern for the coming jubilee of special relativity in 2005. For the historical companion guidebook, see Hentschel and Grasshoff, Albert Einstein (ref. 4) and the website <.     

Hydrophobicity effect on interactions between organic molecules in nanocages of surfactant micelle

Interactions between the cationic polymethine dyes 3,3′-diethyloxacarbocyanaine iodide (DiOC₂), 3,3′-dioctadecyloxacarbocyanine iodide (DiOC₁₈), and 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in the nano-scale volume of anionic sodium dodecylsulfate (SDS) micelles have been studied using optical spectroscopy techniques. The solubilization of pairs of dye molecules (DiOC₁₈/DiI or DiOC₂/DiI) within SDS micelles was monitored by Forster resonance energy transfer (FRET) between the dyes in each pair. The influence of the hydrophobicity of the dyes DiOC₂ and DiOC₁₈ on the efficiency of their binding to SDS micelles and, consequently, on the efficiency of FRET between DiOC₁₈ and DiI or DiOC₂ and DiI fluorophors has been analyzed. It has been shown that hydrophobic interactions in addition to electrostatic interactions are of key importance for the binding between the positively charged dyes and negatively charged surfactant micelles. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 646–652, September–October, 2008.     

Micellar Sensitization in Benzyldimethylhexadecylammonium Chloride/Naphthacene and Triton X-405/Pyrene Systems

Abstract

Excitation energy transfer from micellar BDHC and TX-405 to micellized naphthacene and pyrene. respectively, has been shown to occur. In the case of pyrene, the variation of the I₁/I₃ ratio indicates that sensitization also occurs in premicelar aggregates. In micelles, an energy transfer efficiency of 0.50 was found for BDHC/naphthacene and 0.24 for TX-405/pyrene. the respective donor/acceptor separations are 61.6 A? and 78.6 A?.     

Flexibility of the aldolase molecule measured using quenching-induced variations of the Forster distance for fluorescence energy transfer

The range of flexibility of the rabbit muscle aldolase molecule was studied using fluorescent labelled aldolase. The protein molecule was specifically labelled on the opposite sites of the enzyme subunit with the fluorescence energy donor and acceptor residues. Labelled aldolase with full enzymatic activity was used as a tool in the FRET studies between IAEDANS — donor or Cys-289 and IAF — acceptor on Cys-239. A range of Forster distance (R) was obtained by collisional quenching of the donor emission. The experiments of donor fluorescence quenching with wide range of acrylamide concentrations have shown the changes of donor-acceptor distances. In the absence of quencher the D-A distance distribution in characterized by an average value of 40.4 ?, and a half-width of 0.13 ?. A dramatic increase in half-width to 17.7? is observed after expositions of the enzyme to high acrylamide concentrations (0.13 M-0.68 M).     

Renewable resource‐based poly (m‐phenylenevinylene)s and their statistical copolymers: Synthesis,characterization, and probing of molecular aggregation and Forster energy transfer processes

We report a novel poly (m‐phenylenevinylene)s and their copolymers based on renewable resource starting material 3‐pentadecylphenol to trace the Forster energy transfer process and molecular aggregation in the π‐conjugated polymers. The new bisylide monomer was polymerized with bisaldehyde (or benzaldehyde) under Wittig‐Horner reaction conditions to prepare poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 3‐phenylenevinylene)] (m‐PPV) and its para‐counterpart poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 4‐phenylenevinylene)] (p‐PPV) and oligo‐phenylenevinylene model compound 4‐methoxy‐6‐pentadecyl‐1, 3‐distyrylbenzene (OPV). A series of with m‐ or p‐conjugated segments were also prepared by varying the m‐ and p‐content from 0 to 100% in the feed. The selective excitation of m‐conjugated segments in the copolymer by 310 nm light showed emission properties of pure p‐conjugated segments indicating the efficient Forster energy transfer process in segmented copolymers. Both solution quantum yields and the emission intensities increase up to 75% of para‐content in the copolymers. In the solid state, the increase in the p‐incorporation in the copolymer decreases the photoluminescent intensity almost by four times as compared to that of pure meta‐substituted PPV. The excitation spectra of the polymers confirmed a new peak at 400 nm corresponding to the aggregated polymer chains in the film, which is absent in the solution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3241–3256, 2008     

Synthesizing a nano-composite of BSA-capped Au nanoclusters/graphitic carbon nitride nanosheets as a new fluorescent probe for dopamine detection

A strong red fluorescent nanocomposite, consisting of graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) and serum albumin-capped Au nanoclusters (AuNCs), was synthesized. Dopamine (DA) can quench the red fluorescence of the nanocomposite, based on the Forster resonance energy transfer (FRET) mechanism. In this quenching process, the energy is transferred from the fluorescent g-C₃N₄ NSs-AuNCs to the oxidized DA quinine molecules (DA is easily oxidated to form DA quinine in air). The red fluorescence emission at 420 nm decreases dramatically and the quenching ratio (F₀ – F)/F₀ is linearly related to the concentration of DA in the range of 0.05–8.0 μmol L⁻¹ with a detection limit of 0.018 μmol L⁻¹ (S/N = 3). Additionally, this sensor has a potential of application to assay the DA in the real samples, such as human serum and human urine.     

纵向通风隧道正常运营CO浓度限值计算

我国《公路隧道通风照明设计规范》与国外标准对隧道内CO浓度限值的设定在计算方法和取值上都存在差异.针对射流风机式及竖井送排与射流风机组合式纵向通风隧道CO浓度分布特性,基于差分形式的Coburn-Forster-Kane方程(CFK方程),拟合了两类典型纵向通风隧道正常运营CO浓度限值计算式.结果表明:尽管两类隧道具有不同的CO浓度分布特性,工程中可按相同的限值设计;对于长隧道,我国应设定更严格的限值标准.