Multiple switching behaviors of poly(N-isopropylacrylamide) hydrogel with spironaphthoxazine and D-π-A type dye

A multi-switchable poly(NIPAM-co-SPO-co-D-π-A dye) hydrogel with a photochromic spironaphthoxazine and an electron donor-π-conjugated-electron acceptor (D-π-A) type dye was prepared by typical radical copolymerization. The low critical solution temperature (LCST) behavior was investigated by UV–vis spectroscopy, which allows the measurement of the phase transition from 20 to 40 °C in aqueous solution. The fluorescence intensity of the poly(NIPAM-co-SPO-co-D-π-A dye) was temperature-dependent. Reversible modulation of fluorescence intensity was achieved using alternating irradiation with UV and visible light. Prepared polymer hydrogel also exhibited spectra change when not only used Cu²⁺ cation but also an acid unit.     

Solvent effects on structure and optical properties of a D- π-A azobenzene dye

Time-dependent hybrid density functional theory in combination with Onsager reaction field model and super-molecular model has been applied to study solvent effects on the geometrical and electronic structures, as well as one/two-photon absorption properties, of 4-（N-（2-hydroxyethyl）-N-methyl）-amino-4＇-nitroazobenzene. It is found that the short-range interaction has a large effect on the electronic structure of the solute molecule, namely, large red-shift of the maximum one-photon absorption is induced by hydrogen bonding. The solute molecule has a large two-photon absorption cross section, which is enhanced by the solvent effect. The computational results are in good agreement with measurements.[第一段]     

Position of Biphenyl Group Turning the Structure and Photophysical Property of D-π- π -A Prototype Fluorescent Material

Three novel D-π-π-A prototype compounds, namely, (E)-2-(3-([1,1'-biphenyl]-2-yl)-1-(9H-fluoren-2-yl)allylidene)malononitri-le (2-BAM), (E)-2-(3-([1,1'-biphenyl]-3-yl)-1-(9H-fluoren-2-yl)allylidene)malononitri-le (3-BAM), and (E)-2-(3-([1,1'-biphenyl]-4-yl)-1-(9H-fluoren-2-yl)allylidene)malononitri-le (4-BAM) were synthesized. Furthermore, the structures and photophysical properties of three compounds were compared. Molecules of 2-BAM were packed into a 1D column structure with H-aggregation. However, both of 3-BAM and 4-BAM were packed into 3D layer structures with J-aggregation, respectively. Although all three compounds showed highly twisted molecular geometries, their respective molecular packing and intermolecular interactions were different. Because of the differences in electronic structures of molecules, three compounds displayed different emission behaviors in solid and dilute solution states. This study indicated that changing the position of biphenyl groups is an effective way for turning the structures and photophysical properties of such D-π-π-A prototype fluorescent materials.

     

Theoretical study of fluorescence resonant energy transfer dynamics in individual semiconductor nanocrystal–DNA–dye conjugates

Motivated by recent experimental studies of fluorescence resonant energy transfer (FRET), we consider the influence of the temperature-dependent microscopic spectral overlap and relative orientation of the transition dipoles of fluorophores on the nanosecond dynamics of photon statistics and energy transfer efficiency in semiconductor nanocrystal–DNA–organic dye conjugates using Monte-Carlo simulations. Our calculated mean energy transfer efficiencies are found to be well consistent with those measured in experiment at low temperatures. For the higher temperatures, our results demonstrate that the use of Förster radius estimated from the isotropic dynamic average value of 2/3 for the orientation parameter term may lead to overestimation of energy transfer efficiency for the cases of the rigid arrangement of fluorophore transition moments, and thereby deteriorate the precision of the analysis of donor–acceptor distances. Our theoretical results here underline the importance of a detailed understanding of the microscopic picture of FRET for exploiting this spectroscopic technique in various nano- and bio-applications.     

Temperature-induced phase transition and intramolecular charge-transfer process based on poly(N-isopropylacrylamide) hydrogel with covalently attached D-π-A type dye

A thermoresponsive poly(NIPAM-co-dye) copolymer with covalently attached D-π-A type dye was prepared by typical radical copolymerization. Software was used to calculate the electron density distribution of the push-pull, intramolecular charge transfer (ICT) operating in donor-π-conjugation-acceptor (D-π-A) configurations of dye monomer 3. It can be constructed an acid/base-induced molecular switch by modulation of intramolecular charge transfer with protonation/deprotonation. The lower critical solution temperature (LCST) behavior was investigated by means of UV-vis spectroscopy that allows the measurement of the phase transition from 25 to 40 °C in aqueous solution. The poly(NIPAM-co-dye) copolymer also exhibited color change when used an acid/base-induced molecular switch via control of intramolecular charge transfer (ICT). The morphology of the internal microstructure of the poly(NIPAM-co-dye) hydrogel was observed by scanning electron microscopy (SEM). The reversible switch could be obtained by thermal and acid/base stimuli.     

Charge transfer and charge transfer with excitation of a target ion in slow collisions of α particles with helium atoms. II

The cross sections of single- and double-electron capture in ³He²⁺-He collisions in the energy interval of incident α particles of 3–120 keV were obtained. The cross sections were calculated for the Coulomb trajectory of motion of nuclei in the context of the close-coupling equation method using the basis set of two-electron adiabatic molecular states. Introduction of additional requirements that must be satisfied by the numerical solutions of the system of coupled differential equations made it possible to obtain a good correspondence between the calculated values of total cross sections of single- and double-electron capture and the experimental data in the whole range of the considered collision energies.     

Enhancement of stimulated Raman scattering of acetone and the generation of three-color laser by using fluorescence dye RB

The enhancement of stimulated Raman scattering (SRS) of acetone (C3H6O) and the generation of three color lasers in lasing dye rhodamine B (RB) were reported. The first-order Stokes wave (629.9 nm) of SRS of C3H6O was amplified by 2.83 times than that of pure C3H6O. At the same time, a dye laser of RB at the wavelength from 575 to 598 nm can be generated in a suitable concentration of RB between 3×10-5 and 2×10-4 mol/L. Thus the green pump laser, yellow dve laser, and red Stokes wave concurred.     

Calculation and interpretation of vibronic absorption and fluorescence spectra of the first electronic nπ* transitions of pyridine and pyrimidine

We have calculated vibronic spectra of the first electronic nπ* transitions of pyridine and pyrimidine in the isolated state using the DFT method in the Franck-Condon approximation. Vibrational spectra for the ground and excited states have been calculated in the anharmonic approximation, which allowed us to refine the assignment of normal vibrations of pyridine and pyrimidine. We have done a complete interpretation of the vibrational structure of the absorption and fluorescence spectra of pyridine and pyrimidine. It has been shown that Fermi resonances between fundamental and combination vibrations and overtones 12 and 16b + 4, 6a and 2 × 16b affect the formation of the vibrational structure of electronic spectra of pyrimidine. Good agreement between calculated and experimental spectra confirms the correctness of the models of the two molecules in their ground and excited states, which makes it possible to use the models in further investigations of various properties of these molecules in electronically excited states, e.g., tautomerism of pyrimidine bases of nucleic acids.     

Single- and double-electron charge transfer in collisions of α-particles with hydrogen molecules. II

Dependences of single-electron charge transfer cross sections on the molecule orientation are studied in collisions between α-particles and H₂ molecules in the ground state at collision energies E _c from 1 to 23 keV/u. Probabilities of single-electron capture were calculated in the independent electron approximation in the context of the close coupling equation method under the assumption that the hydrogen molecule consists of two independent hydrogen pseudoatoms. The total and partial single-electron capture cross sections averaged over all orientations of the molecule well agree with available experimental data at E _c > 5 keV/u.     

Room-temperature fluorescence of a charge-transfer complex of reserpine in aqueous and aqueous–ethanol media

The room-temperature fluorescence of a charge-transfer (CT) complex different from those of the component donor/acceptor in polar organic solvent is not very common. The phenomenon is even rarer in aqueous medium. The present work demonstrates that a CT complex formed between reserpine (Res) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in aqueous and aqueous–ethanol media exhibits fluorescence at room temperature that is entirely different from those of the components, Res and DDQ. With decreasing polarity of the medium on the addition of ethanol, the fluorescence intensity and also the fluorimetrically determined formation constant of the complex increase, but the fluorescence emission wavelength does not change significantly. The quantum yield of fluorescence of the CT complex systematically decreases with increasing ethanol content of the medium. That the observed fluorescence is due to the CT complex is established by the constancy of the assumed proportionality constant (β) between the fluorescence intensity and the complex concentration measured using different equilibrium concentrations of the complex and also by demonstrating the mirror image relationship between its excitation and emission spectra in aqueous medium. To our knowledge, this is the first report on the room-temperature fluorescence of a CT complex in aqueous solution.     

Orbital Electron Capture Rate and Time Modulation of H- and He-like Ions in a Storage-Ring

We have studied in a heavy ion storage ring the orbital electron capture decays of H- and He-like ¹⁴⁰Pr and ¹⁴²Pm ions and found that the H-like ions with one electron in the K-shell decay 1.49(8) and 1.44(6) times faster, than the corresponding He-like ions with two electrons in the K-shell. This result is explained by spin statistics due to the hyperfine structure of the H-like ions.     

Energy transfer between dimeric chlorophyll a and all trans β- carotene in vitro as resolved by fluorescence photoquenching

The fluorescence properties of 10^-4 M Chl a solutions in dry, de-oxygenated hexane in the presence and absence of all trans β-carotene (10^-3 M) are studied using nanosecond pulsed laser radiation. It is shown that under these irradiation conditions the excitation of monomeric and dimeric Chl a nearly always is carried out under effective population conditions in the excited states which makes the determination of fluorescence quantum yields difficult at best. It is also observed that the intensity of the 625 nm fluorescence band of the cofacial Chl a dimer increases in the presence of all trans β-carotene and follows the latter's absorption profile in the 436–452 nm spectral range. These observations are interpreted in terms of energy transfer from the β-carotene to the cofacial dimer which cannot be satisfactorily explained by Förster's long-range dipole-dipole interaction mechanism.     

Study of X(5568) in a unitary coupled-channel approximation of BK and B_sπ

The potential of the B meson and the pseudoscalar meson is constructed up to the next-to-leading order Lagrangian, and then the BK and B_sπ interaction is studied in the unitary coupled-channel approximation. A resonant state with a mass about 5568 MeV and J~P= 0~+is generated dynamically, which can be associated with the X(5568) state announced by the D0 Collaboration recently. The mass and the decay width of this resonant state depend on the regularization scale in the dimensional regularization scheme, or the maximum momentum in the momentum cutoff regularization scheme. The scattering amplitude of the vector B meson and the pseudoscalar meson is calculated, and an axial-vector state with a mass near 5620 MeV and J~P= 1~+is produced. Their partners in the charm sector are also discussed.     

Solution of the equation of radiative transfer using a Newton–Krylov approach and adaptive mesh refinement

The discrete ordinates method (DOM) and finite-volume method (FVM) are used extensively to solve the radiative transfer equation (RTE) in furnaces and combusting mixtures due to their balance between numerical efficiency and accuracy. These methods produce a system of coupled partial differential equations which are typically solved using space-marching techniques since they converge rapidly for constant coefficient spatial discretization schemes and non-scattering media. However, space-marching methods lose their effectiveness when applied to scattering media because the intensities in different directions become tightly coupled. When these methods are used in combination with high-resolution limited total-variation-diminishing (TVD) schemes, the additional non-linearities introduced by the flux limiting process can result in excessive iterations for most cases or even convergence failure for scattering media. Space-marching techniques may also not be quite as well-suited for the solution of problems involving complex three-dimensional geometries and/or for use in highly-scalable parallel algorithms. A novel pseudo-time marching algorithm is therefore proposed herein to solve the DOM or FVM equations on multi-block body-fitted meshes using a highly scalable parallel-implicit solution approach in conjunction with high-resolution TVD spatial discretization. Adaptive mesh refinement (AMR) is also employed to properly capture disparate solution scales with a reduced number of grid points. The scheme is assessed in terms of discontinuity-capturing capabilities, spatial and angular solution accuracy, scalability, and serial performance through comparisons to other commonly employed solution techniques. The proposed algorithm is shown to possess excellent parallel scaling characteristics and can be readily applied to problems involving complex geometries. In particular, greater than 85% parallel efficiency is demonstrated for a strong scaling problem on up to 256 processors. Furthermore, a speedup of a factor of at least two was observed over a standard space-marching algorithm using a limited scheme for optically thick scattering media. Although the time-marching approach is approximately four times slower for absorbing media, it vastly outperforms standard solvers when parallel speedup is taken into account. The latter is particularly true for geometrically complex computational domains.     

Single-electron charge transfer in collisions of CF 2 ++ with Ar and Ne at collision energies 3–5 eV

Non-dissociative, single-electron charge transfer processes between the dication CF ₂ ⁺⁺ and Ar and Ne were investigated in crossed beam scattering experiments at collision energies of 3.0 and 4.55eV (c.m.). The reaction with Ar produces CF ₂ ⁺ in its ground state and, to a smaller extent, in the excited CF ₂ ⁺ (²_u) state. The reaction with Ne occurs only with an excited state of CF ₂ ⁺⁺ lying about 4.4 eV above the ground state and present in a small amount in the reactant dication beam; its molecular product is CF ₂ ⁺ in the ground state.     

Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4＋ charge transfer transition

Ce^4＋-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4＋ ions doped in Ca2SnO4 occupy the Sn^4＋ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime （-83μs） for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4＋ charge transfer （CT）. The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4＋ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration （x - 0.03） is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%.     

Investigation of electrostatic charge distribution within the reactor wall fouling and bulk regions of a gas–solid fluidized bed

The distribution of charge within the wall fouling region and bulk of a fluidized bed reactor was investigated. Experiments were conducted in a 0.1 m in diameter carbon steel fluidization column under atmospheric conditions. Polyethylene particles were fluidized with extra dry air at 1.5 the minimum fluidization velocity (bubbling flow regime) for 1 h. Using an online Faraday cup measurement technique, the net charge-to-mass ratio (q/m), as well as the size distribution of all particles adhered to the column wall and those in the bulk of the bed was determined. The wall particles were found to be predominantly negatively charged while those which did not adhere to the wall were predominantly positively charged. The charge distribution within each region was then investigated by a custom made charged particle separator that separated the particles according to their charge magnitude and polarity. It was determined that although the net charge of the wall layer particles was negative, a significant amount of positively charged particles existed within each sample and therefore the entire wall particle layer. This suggests that the wall layer was formed through layering between positively and negatively charged particles. Particles in the bulk of the bed also consisted of bipolarly charged particles.