2012 Vol. 25, No. 6

Special Issue
Content
2012, 25(6): 0-0. doi: 10.1088/1674-0068/25/6/0-0
Laser-induced fluorescence excitation spectra of jet-cooled NiCl molecules were recorded in the energy range of 12900-15000 cm-1. Six vibronic bands with rotational structure have been observed and assigned to the [13.0]2П3/2(v'=0-5)-X2П3/2(v"=0) transition progres-sion. The relevant rotational constants, significant isotopic shifts, and (equilibrium) molecu-lar parameters have been determined. In addition, the lifetimes of the observed bands have also been measured.
The interacting patterns and mechanism of the catechin and thymine have been investigated with the density functional theory Becke's three-parameter nonlocal exchange functional and the Lee, Yang, and Parr nonlocal correlation functional (B3LYP) method by 6-31+G*basis set. Thirteen stable structures for the catechin-thymine complexes have been found which form two hydrogen bonds at least. The vibrational frequencies are also studied at the same level to analyze these complexes. The results indicated that catechin interactedwith thymine by three different hydrogen bonds as N-H…O、C-H…O、O-H…O and the complexes are mainly stabilized by the hydrogen bonding interactions. Theories of atoms in molecules and natural bond orbital have been adopted to investigate the hydrogen bondsinvolved in all systems. The interaction energies of all complexes have been corrected for basis set superposition error, which are from -18.15 kJ/mol to -32.99 kJ/mol. The results showed that the hydrogen bonding contribute to the interaction energies dominantly. The corresponding bonds stretching motions in all complexes are red-shifted relative to that of the monomer, which is in agreement with experimental results.
The properties of C-H vibration softening for CH2 and CH3 radicals absorbed on Cun(n=1-6) clusters have been investigated, using the density functional theory with hybrid functional. The results indicate that the absorption of CH2 on Cu clusters is stronger than the case of CH3. The vibrational frequencies of C-H bonding agree with the experimental results obtained for CH2 and CH3 absorbed on Cu(111). With the increase of cluster size, the softening (Einstein shift) of C-H vibrational modes become stronger.
Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophe-none (DMABP) and its hydrogen-bonded DMABP-MeOH dimer. It is found that, in non-polar aprotic solvent, the transitions from S0 to S1 and S2 states of DMABP have both n→π* and π→π* characters, with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group. But when the intermolecular hydrogen bond C=O…H-O is formed, the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two low-lying electronically excited states increases. To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state, the potential energy curves for con-formational relaxation are calculated. The formation of twisted intramolecular charge trans-fer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process. In addition, the decay of the S1 state of DMABP-MeOH dimer to the ground state, through nonradiative intermolecular hydrogen bond stretching vibrations, is facilitated by the formation of the hydrogen bond between DMABP and alcohols.
The structural properties, heats of formation, elastic properties, and electronic structures of four compositions of binary Al-Li intermetallics, Al3Li, AlLi, Al2Li3, and Al4Li9, are ana-lyzed in detail by using density functional theory. The calculated formation heats indicate a strong chemical interaction between Al and Li for all the Al-Li intermetallics. In partic-ular, in the Li-rich Al-Li compounds, the thermodynamic stability of intermetallics linearly decreases with increasing concentration of Li. According to the computational single crystal elastic constants, all the four Al-Li intermetallic compounds considered here are mechani-cally stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill approximations, and the calculated ratios of bulk modulus to shear modulus indicate that the four compositions of binary Al-Li intermetallics are brittle materials. With the increase of Li concentration, the bulk modulus of Al-Li intermetallics decreases in a linear manner.
The protonation effects on one- and two-photon absorption properties of an octupolar molecule TA with 1,3,5-triazine core and pyrrole electron-donating end-groups have been studied at hybrid density functional theory level. A computational scheme is developed tosimulate a proton attached to an atom. The numerical results show that large changes in both one- and two-photon absorption properties are observed when the compound is transformed from neutral to threefold protonated states. When the compound is protonated, more charge transfer states appear and the absorption band has a red-shift. Furthermore, the two-photon absorption cross-section is largely enhanced. The theoretical calculations demonstrate the protonation effect on promoting the intramolecular charge transfer strength. The results present qualitative agreement with the experimental observations. A two-photon absorption switch with the compound TA based on the protonation effect is proposed.
Encapsulation of alkali metals (Li, Na, K, and Rb) into Zn12O12 nanocage has been inves-tigated using density functional theory. Encapsulation of Li and Na atoms is found to be thermodynamically favorable at 298 K and 100 kPa, with negative Gibbs free energy change ΔG of about -130.12 and -68.43 kJ/mol, respectively. By increasing the size of encapsu-lated atom the process become less favorable so that in the cases of K and Rb encapsulations the ΔG values are positive. The results indicate that the LUMO, Fermi level, and specially HOMO of the cluster are shifted to higher energies so that the HOMO-LUMO gap of the cluster is significantly narrowed in all the cases. After encapsulation of the alkali metals the work function of cluster is decreased due to the shift of the Fermi level to higher energies. Therefore, the emitted electron current density from the Zn12O12 cluster will be increased.
Borohydrides have been recently hightlighted as prospective new materials due to their high gravimetric capacities for hydrogen storage. It is, therefore, important to under-stand the underlying dehydrogenation mechanisms for further development of these ma-terials. We present a systematic theoretical investigation on the dehydrogenation mecha-nisms of theMg2(BH4)2(NH2)2 compounds. We found that dehydrogenation takes place most likely via the intermolecular process, which is favorable both kinetically and thermo-dynamically in comparison with that of the intramolecular process. The dehydrogenation of Mg2(BH4)2(NH2)2 initially takes place via the direct combination of the hydridic H in BH4- and the protic H in NH2-, followed by the formation of Mg-H and subsequent ionic recombination of Mg-Hδ- …Hδ+N.
The potential energy surface of gaseous deprotonated arginine has been systematically in- vestigated by first principles calculations. At the B3LYP/6-31G(d) level, apart from the identification of several stable local structures, a new global minimum is located which is about 6.56 kJ/mol more stable than what has been reported. The deprotonated arginine molecule has two distinct forms with the deprotonation at the carboxylate group (COO-). These two forms are bridged by a very high energy barrier and possess very different IR spectral profiles. Our calculated proton dissociation energy and gas-phase acidity of argi-nine molecule are found to be in good agreement with the corresponding experimental results. The predicted geometries, dipole moments, rotational constants, vertical ionization energies and IR spectra of low energy conformers will be useful for future experimental measurements.
We report on the ability to create complex 3D flower-like SiO2 in vitro via CaCO3 micropar-icles supported by polyethyleneimine mediated biosilicification under experimentally altered chemical influences. The morphology, structure, composition of the product have been inves-tigated with the X-ray photoelectron spectrum, scanning electron microscope, transmission electron microscope, and energy-dispersive spectroscopy. The overall morphologies could be controlled to shift from a characteristic network of flower-like silica sphere to a sheet-like structure by adjusting physical adsorption of different amount of polyethyleneimine onto the surface of the CaCO3 microparticles.
Lipid rafts are a dynamic microdomain structure found in recent years, enriched in sphin-golipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer miscibility behavior of mixed systems of Egg-Sphingomyelin (ESM) with 1, 2-dioleoyl-sn-glycero-3-phosphocholine was in-vestigated in terms of mean surface area per molecule and excess molecular area ΔAex at certain surface pressure, surface pressure and excess surface pressure Δπex at certain mean molecular area. The stability and compressibility of the mixed monolayers was assessed by the parameters of surface excess Gibbs free energy ΔGex, excess Helmholtz energy ΔHex and elasticity. Thermodynamic analysis indicates ΔAex and Δπeex in the binary systems with positive deviations from the ideal behavior, suggesting repulsive interaction. The max-imum of ΔGex and ΔHex was at the molar fraction of ESM of 0.6, demonstrating the mixed monolayer was more unstable. The repulsive interaction induced phase separation in the monolayer
A new Eu(III) complex, EuL3(phen), was synthesized, where L is the abbreviation of de-protonated 1-(7-(tert-butyl)-9-ethyl-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione (HL), phen is the abbreviation of 1,10-phenanthroline. The Eu(III) complex was characterized by element analysis, IR, 1H NMR, UV-visible absorption spectroscopy, thermogravimetric anal-ysis (TGA), and photoluminescence measurements (PL). TGA shows that thermal stability of the complex is up to 325 oC. PL measurement indicates that the Eu(III) complex exhibits intense red-emission and extends their excitation bands to visible region. LEDs device was successfully fabricated by precoating complex EuL3(phen) onto 460 nm blue-emitting InGaN chip. The emission of device shows that the complex can act as red phosphor in combination with 460 nm blue-emitting chips. This europium complex based on 1-(7-(tert-butyl)-9-ethyl-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione is a kind of interesting red-emitting material excited by blue light, which could avoid the damage of excitation by UV light.
Lithium-ion conductor Li1.3Al0.3Ti1.7(PO4)3 with an ultrapure NASICON-type phase is syn-thesized by a 1,2-propylene glycol (1,2-PG)-assisted sol-gel method and characterized by differential thermal analysis-thermo gravimetric analysis, X-ray diffraction, scanning elec-tron microscopy, electrochemical impedance spectroscopy, and chronoamperometry test.Due to the use of 1,2-PG, a homogeneous and light yellow transparent precursor solu-tion is obtained without the precipitation of Ti4+ and Al3+ with PO43-. Well crystallizedLi1.3Al0.3Ti1.7(PO4)3 can be prepared at much lower temperatures from 850 oC to 950 oC within a shorter synthesis time compared with that prepared at a temperature above 1000 oC by a conventional solid-state reaction method. The lithium ionic conductivity of the sintered pellets is up to 0.3 mS/cm at 50 oC with an activation energy as low as 36.6 kJ/mol for the specimen pre-sintered at 700 oC and sintered at 850 oC. The high conductivity, good chemi-cal stability and easy fabrication of the Li1.3Al0.3Ti1.7(PO4)3 provide a promising candidate as solid electrolyte for all-solid-state Li-ion rechargeable batteries.
A solvent-non-solvent method invented in our laboratory for preparing non-covalently con-nected micelles (NCCM) was used to intercalate melamine (MA) molecules into stearic acid (SA) bilayers to form the composite nanoparticles with an intercalated nanostructure in which a melamine bilayer is sandwiched between two stearic acid bilayers, NCCM method helps to sufficiently mix the two components in nanospace and meanwhile inhibits the strong tendency of self-crystallization of MA, leading to the intercalation. Although the nanopar-ticles have a regular inner structure, the primary MA/SA nanoparticles have an irregular morphology. Regular nanoparticles were obtained through annealing the suspension of the primary nanoparticles. Through annealing at different temperatures, the MA/SA compos-ite nanowires and vesicles with an intercalated structure were prepared respectively. It is proposed that the morphological change results from the change in the intercalated structure.
Ag nanoparticles grown on reduced CeO2-x thin films have been studied by X-ray photoelec-tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in the CeO2-x thin films on the growth and interfacial elec-tronic properties of Ag. Ag grows as three-dimensional particles on the CeO2-x(111) surface at 300 K. Compared to the fully oxidized ceria substrate surface, Ag favors the growth of smaller particles with a larger particle density on the reduced ceria substrate surface, which can be attributed to the nucleation of Ag on oxygen vacancies. The binding energy of Ag3d increases when the Ag particle size decreases, which is mainly attributed to the final-state screening. The interfacial interaction between Ag and CeO2-x(111) is weak. The resonant enhancement of the 4f level of Ce3+ species in RPES indicates a partial Ce4+→Ce3+ re-duction after Ag deposited on reduced ceria surface. The sintering temperature of Ag on CeO1.85(111) surface during annealing is a little higher than that of Ag on CeO2(111) surface, indicating that Ag nanoparticles are more stable on the reduced ceria surface.
ZnO nanoparticles were first encapsulated in submicron PS hollow microspheres through two-step swelling process of core-shell structured PMMA/PS (PMMA: polymethyl methao-rylate) microspheres in acid-alkali solution, and the ZnO precursors, i.e. the ethanol solu-tions of (CH3COO)2Zn and LiOH. The transmission electron microscope, X-ray diffraction, and thermogravimetric analysis results show that the feeding order of ethanol solutions of (CH3COO)2Zn and LiOH in the second swelling step has great influence on the loading efficiency and the size of ZnO nanoparticles, but little on their crystal form. The photolumi-nescence and UV-Vis absorption behavior of ZnO/PS microspheres show that the PS shell can effectively avoid the fluorescence quenching effect.
We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza-tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 cells with different capacities and electrode materials are evalu-ated by measuring input and output energy which change with charge-discharge time and current. Based on the results of these tests, we build a model of energy loss in cells' charge-discharge process, which include Joule heat and polarization heat impact factors. It was reported that Joule heat was caused by cell resistance, which included DC-resistance and reaction resistance, and reaction resistance could not be easily obtained through routine test method. Using this new method, we can get the total resistance R and the polarization parameter η. The relationship between R, η, and temperature is also investigated in orderto build a general model for series of different Li-ion batteries, and the research can be used in the performance evaluation, state of charge prediction and the measuring of consistency of the batteries.
A flat thin TiO2 film was employed as the photo-electrode of a dye sensitized solar cell (DSSC), on which only a geometrical mono-layer of dye was attached. The effect of sur-face protonation by HCl chemical treatment on the performance of DSSCs was studied. The results showed that the short-circuit current Jsc increased significantly upon the HCl treatment, while the open-circuit voltage Voc decreased slightly. Compared to the untreated DSSC, the Jsc and energy conversion efficiency was increased by 31% and 25%, respectively, for the 1 mol/L HCl treated cell. TiO2 surface protonation improved electronic coupling between the chemisorbed dye and the TiO2 surface, resulting in an enhanced electron in-jection. The decreased open-circuit voltage after TiO2 surface protonation was mainly due to the TiO2 conduction band edge downshift and was partially caused by increased electron recombination with the electrolyte. In situ Raman degradation study showed that the dye stability was improved after the TiO2 surface protonation. The increased dye stability was contributed by the increased electron injection and electron back reaction with the electrolyte under the open-circuit condition.
Huaibei is an energy city. Coal as the primary energy consumption brings a large number of regional pollution in Huaibei area. Differential optical absorption spectroscopy (DOAS) as optical remote sensing technology has been applied to monitor regional average concen-trations and inventory of nitrogen dioxide, sulfur dioxide and ozone. DOAS system was set up and applied to monitor the main air pollutants in Huaibei area. Monitoring data were obtained from 7 to 28 August, 2011. Monitoring results show measurements in controlling pollution are effective, and emissions of pollutants are up to the national standard in Huaibei area. Prediction model was also created to track changing trend of pollutions. These will provide raw data support for effective evaluation of environmental quality in Huaibei area.
Letter
We investigate the fluorene-vinylene unit dependent photo-physical properties of multi-branched truxene based oligomers (Tr-OFVn, n=1-4) employing steady-state absorption and emission spectroscopy, transient absorption spectroscopy, two-photon fluorescence, and z-scan technique. The results show that the increasing of fluorene-vinylene unit leads to a red-shift in the spectra of absorption and fluorescence, and shortens the excited state lifetime. Meanwhile, two-photon fluorescence efficiency and two-photon absorption cross section of truxene based oligomers gradually enhance in company with the extension of π-conjugated length. In addition, the values of two-photon absorption cross section modeled on the sum-over-state approach agree well with the experimental ones. The results indicate multi-branched truxene based oligomers bearing oligo(fluorene-vinylene) arms are promisingorganic materials for two-photon applications.