Showing papers by "Zhen Li published in 2005"

One‐Pot Reaction to Synthesize Biocompatible Magnetite Nanoparticles

Abstract: Biocompatible magnetite nanocrystals (see Figure) are prepared by thermal decomposition of ferric triacetylacetonate in 2-pyrrolidone in the presence of monocarboxyl-terminated poly(ethylene glycol) (MPEG-COOH). The results reveal that MPEG is covalently bound to the nanocrystal surface by COOH groups. Magnetic resonance imaging (MRI) experiments indicate that the coated nanocrystals are potential MRI contrast agents due to their excellent water solubility and biocompatibility.

Structural control of the photoluminescence of silole regioisomers and their utility as sensitive regiodiscriminating chemosensors and efficient electroluminescent materials.

Abstract: We synthesized a group of silole regioisomers 1x,y, whose photoluminescence varied dramatically with its regiostructure. By internally hindering the intramolecular rotation, we succeeded in creating a novel silole (13,4) that is strongly luminescent in solutions and whose fluorescence quantum yield in acetone is as high as 83%. We revealed that 13,4 was a sensitive chemosensor capable of optically discriminating nitroaromatic regioisomers of p-, o-, and m-nitroanilines. Against general belief, crystal formation of 12,4 blue-shifted its emission color and boosted its emission efficiency. The light-emitting diode based on the crystal of 12,4 emitted a strong blue light (464 nm) in a high current efficiency (5.86 cd/A).

Functional Disubstituted Polyacetylenes and Soluble Cross-Linked Polyenes: Effects of Pendant Groups or Side Chains on Liquid Crystallinity and Light Emission of Poly(1-phenyl-1-undecyne)s

Abstract: A group of new poly(1-phenyl-1-undecyne)s with different mesogenic and chromophoric pendant groups or side chains were successfully synthesized and the structural variations were found to greatly affect the mesomorphic and luminescent properties of the polymers. The 1-phenyl-1-undecyne monomers (C6H5)C⋮C(CH2)9OCOR with R = C6H4−C6H10−C5H11 (1), C6H4−OCO−C6H4−OC6H13 (2), and C6H4−C⋮C−C6H4−OC7H15 (3) were prepared by simple esterification and/or coupling reactions. The polymerizations of 1−3 were effected by WCl6−Ph4Sn in toluene at 60−80 °C, giving polymers with high molecular weights in good isolation yields. The structures and properties of the polymers were characterized and evaluated by GPC, IR, NMR, TGA, DSC, POM, XRD, UV, and PL analyses. The polymerizations of 1 and 2 yield linear poly(1-phenyl-1-alkyne)s P1 and P2, respectively, while that of 3 gives a nonlinear macromolecule with its poly(1-phenyl-1-alkyne) main chain cross-linked by the oligo(diphenylacetylene) side chains resulted from the parti...

Structures and properties of the hydrogen-bond complexes : Theoretical studies for the coupling modes of the pyrazole-imidazole system

Abstract: The calculations at the B3LYP/6-311+G* level have been performed for Pyrazole–Imidazole (Py–Im) system. Eight Py–Im complexes are found and their calculated geometric structures, relative energies, IR spectra and stabilization energies are presented. Those Py–Im complexes can be classified into single H-bond mode and double H-bond mode. The single H-bond complexes can be subdivided into N–Hcdots, three dots, centeredN mode and C–Hcdots, three dots, centeredN mode. The four single H-bond complexes are defined as SA, SB, SC, and SD and the four double H-bond complexes are defined as DA, DB, DC, and DD. SA and SB belong to the N–Hcdots, three dots, centeredN coupling mode while SC and SD belong to the C–Hcdots, three dots, centeredN coupling mode, respectively. The double H-bond coupling mode complexes can be further divided into two types. DA and DB have a N–Hcdots, three dots, centeredN type H-bond and a C–Hcdots, three dots, centeredN type H-bond and DC and DD have two C–Hcdots, three dots, centeredN type H-bonds. For the single H-bond modes and double H-bond modes, the complexes with N–Hcdots, three dots, centeredN type H-bond have stronger interactions than those with C–Hcdots, three dots, centeredN type H-bond. DB is the most stable isomer among the eight complexes. With corrections for the zero-point vibrational energies (ZPE) and basis set superposition errors (BSSE), the stabilization energy of DB is 7.60 kcal/mol at the B3LYP/6-311+G* level. The stability order of the eight Py–Im complexes is DB>DA>SB>SA>SC=SD>DD>DC. Moreover, this result is in close agreement with that of the natural bond orbital (NBO) analysis.

Synthesis and properties of new two-photon absorption chromophores containing 3,5-dicyano-2,4,6-tristyrylpyridine as the core

Abstract: This paper reports the synthesis of a series of donor-substituted 3,5-dicyano-2,4,6-tristyrylpyridine derivatives, having two-dimensional branched D-π-A structures, as new two-photon absorption (TPA) chromophores. These chromophores are stilbene-type chromophores containing the same acceptor group but end-capped with different aromatic groups as the donors. Measured as the two-photon-induced fluorescence in chloroform solvent, using a femtosecond multipass Ti∶sapphire amplifier as the irradiation source, the TPA cross section values of some compounds are on the order of 10−48 cm4 s photon−1. These chromophores also have relatively high two-photon-excited fluorescence (TPEF) action cross sections. Pumped by the laser at 800 nm, these chromophores show efficient two-photon-induced orange-red fluorescence emission. The experimental results indicate that the different end-capped functional electronic donors and the number of branches of these chromophores affect their one-photon properties, two-photon up-conversion emission behavior and TPA cross section values. Especially, with increasing numbers of branches, λabsmax and λspfmax exhibit bathochromic shifts, while their two-photon absorption cross sections also increase. Compared with the two-branched chromophore 6, the tribranched chromophore 4 shows a larger TPA cross section, and the cooperative enhancement of the TPA cross section from 6 to 4 is 1.2-fold at 800 nm.

Synthesis and properties of new orange red light‐emitting hyperbranched and linear polymers derived from 3,5‐dicyano‐2,4,6‐tristyrylpyridine

Abstract: Two new orange red light-emitting hyperbranched and linear polymers, poly(pyridine phenylene)s P1 and P2, were prepared by the Heck coupling reaction. In particular, an A2 + B3 approach was developed to synthesize conjugated hyperbranched polymer P2 via one-pot polycondensation. The polymers were characterized by NMR, Fourier transform infrared, ultraviolet–visible, and elemental analysis. They showed excellent solubility in common solvents such as tetrahydrofuran, CH2Cl2, CHCl3, and N,N-dimethylformamide and had high molecular weights (up to 6.1 × 105 and 5.8 × 105). Cyclic voltammetry studies revealed that P2 had a low-lying lowest unoccupied molecular orbital energy level of −3.22 eV and a highest occupied molecular orbital energy level of −5.43 eV. The thin film of P2 emitted strong orange-red photoluminescence at 595 nm. A double-layer light-emitting diode fabricated with the configuration of indium tin oxide/P2/tris(8-hydroxy-quinoline)aluminum/Al emitted orange-red light at 599 nm, with a brightness of 662 cd/m2 at 7 V and a turn-on voltage of 4.0 V; its external quantum efficiency was calculated to be 0.19% at 130.61 mA/cm2. This indicated that this new electroluminescent polymer (P2) based on 3,5-dicyano-2,4,6-tristyrylpyridine could possibly be used as an orange-red emitter in polymer light-emitting displays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 493–504, 2005

Synthesis and second‐order nonlinear optical properties of multifunctional polysiloxanes with sulfonyl‐based chromophores

Abstract: Two new polysiloxanes (P1 and P2) with a high density of sulfonyl-based chromophores were prepared by a new two-step method. Poly[methyl-3-(9-carbazolyl) propyl siloxane] was partially formulated by the standard Vilsmeier reaction, and formyl groups of high reactivity were condensed with cyanoacetylated chromophores; this yielded polysiloxanes P1 and P2 in almost complete conversions. Their structures were verified with 1 H NMR, IR, and ultraviolet-visible spectra. P1 and P2 exhibited good solubility in common organic solvents and were thermally stable. The maximum absorptions appeared at about 452 and 390 nm for P1 and P2, respectively, in tetrahydrofuran; they were blueshifted about 42 and 8 nm, respectively, in comparison with those of the corresponding chromophores with a nitro acceptor and resulted in a wider transparency window. The P1 values of the nonlinear optical coefficient (d 33 ), measured by in situ second harmonic generation, was 16.2 pm/V.

Studies on the structural properties of iodine-containing complexes: DFT calculations for IO–H2O and HOI–H2O systems

Abstract: The calculations of geometric structures, relative energies, vibrational frequencies, infrared intensities and binding energies of six IO–H2O and three HOI–H2O complexes have been performed using the B3LYP, B3P86, B3PW91 methods at the 6-311++G(3df,3pd) basis set level. The corrections for zero-point energy (ZPE) and basis set superposition error (BSSE) of these complexes have also been considered in order to obtain accurate binding energies of these complexes. The analysis of the Natural Bond Orbital (NBO) second-order interaction energies has also been used to illuminate the binding energies and the stability of these IO–H2O and HOI–H2O complexes.

Synthesis and photoluminescence of an anthracene-containing hyperbranched poly(aryleneethynylene)

Abstract: A hyperbranched poly(aryleneethynylene) containing anthracene chromophore was synthesized by palladium-catalyzed cross-coupling reaction of 2,4,6-triiodophenyl 9-anthracenylcarboxylate with 9,9-bis[4-(2-propynyloxy)phenyl]-9H-fluorene. The structure and properties of the polymer are characterized and evaluated by NMR, IR, UV, PL and TGA analyses. The polymer is soluble in common organic solvents, possesses high thermal stability (Td > 330°C), and emits a strong blue light of 465 nm in both solution and solid states.

Ocean wave spectrum from sar image using 2D-ARMA model

Abstract: For more than two decades, SAR images have been evaluated as a means to ocean wave spectrum in oceanographic remote sensing. To fulfill the role, Hasselmann and Hasselmann's SAR imaging theory of ocean surface and Lyzenga and Monaldo's method to evaluate ocean spectrum from SAR image are jointly the attractive ways. In this present paper, a two-dimensional ARMA (auto regressive moving average) model is addressed to extract ocean spectrum information from ENVISAT-ASAR image of South-China Seas. The relation between the parameters of a 2-D ARMA model and ENVISAT-ASAR image is investigated and a new algorithm is proposed based on this relation. Example is given with using ENVISAT-ASAR image. As a result of this example, it is shown that the ARMA parameters and the corresponding power spectrum estimated by the proposed model are practical way to gain the ocean spectrum.

Electrical Properties of Laser‐Synthesized Aluminum Oxide‐Tungsten Oxide Ceramics

Abstract: Electronic ceramics of the Al 2 O 3 -WO 3 system were synthesized by using a high-powered CO 2 laser. It was shown that these ceramics can be used as linear thermistor materials. The linear temperature range of the Al 2 O 3 -WO 3 system was ∼200°C, the nonlinear deviation ∈ was <2%, the thermistor constant B was <10 3 , and the temperature coefficient was between -0.2%/°C and -0.8%/°C. These parameters could be adjusted by changing the composition of the samples and the laser-synthesis parameters. The present study showed that the materials should be encapsulated if they are to be used in an oxidizing atmosphere. The current-voltage curves of the present materials were symmetrical around the coordinate origin, which also is a necessary condition for judging whether or not a thermistor is linear.

[The application of a systematic-dynamic model to study the computer simulation of severe acute respiratory syndrome transmission and the impact of control measures].

Abstract: OBJECTIVE (1) Building a macroscopical systematic-dynamic model of severe acute respiratory syndrome (SARS) transmission and disease control process. (2) To determine key variables on the control of SARS epidemic through computer simulation methodology, especially to analyze the effect of "screening for fever" practice during the epidemics. (3) To provide evidence for related decision-making. METHODS Parameters in the model were collected from local hospitals and municapal CDC through interview, questionnaire survey, literature review and case analysis. A systematic-dynamic model was built under similar studies. 'What-if' analysis was used during the simulation process. RESULTS (1) The mean duration between disease onset and hospital admission, rate of contacts of each infectious individual as well as the rate of contacts in hospital of each infectious individual appeared to be the key variables in the process of SARS transmission. (2) Physician's alertness/sense and practice of self-protection on SARS, measures on quarantine and isolation to the patients, ventilation and disinfection process in the wards appeared to be the key variables for the control of epidemics. (3) "Screening for fever" practice on each patient at the entrance of the hospital did not seem to act as an important factor to the control of the epidemics. CONCLUSION The health system in Beijing can control SARS epidemic rapidly based on current applied disease control measures and plan.

A hybrid vegetation height estimation method using SIR-C polarimetric SAR interferometry data

Abstract: From the repeat pass polarimetric SAR interferometric (Pol-InSAR) data of SIR-C L and C band on October 9 and 10, 1994, a new hybrid inversion method, combining three-stage inversion and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) algorithm, of vegetation height using dual frequency Pol-InSAR data is proposed. The estimated vegetation height is compared with the field measurement data, the result indicates that the new proposed method can estimate the vegetation height with enough accuracy, if the P and X band Pol-InSAR data can be obtained, the accuracy of inversion method will significantly increase.

Land-surface parameters estimation from ERS Wind Scatterometer: a case study in China

Abstract: The ERS-1/2 Wind Scatterometer (WSC) operates at a frequency of 5.3 GHz (C-Band) with vertically like-polarised antennas both in transmission and reception (W-polarization). It continuously provides global measurement of radar cross-section from August 1991 to December 2000. WSC has a resolution cell of about 50 km but provides a high repetition rate (less than four days) and makes measurements at multiple incidence angles. The method presented in this paper combines a theoretical model and an empirical algorithm developed by previous authors to estimate land-surface parameters. The method is implemented using 15 days WSC data in China, a good agreement is observed between retrieved fractional vegetation and NDVI, and the temporal-spatial distribution of soil moisture is reasonable, too.

A Convenient Synthetic Route to 2,5-Dialkoxyterephthalaldehyde

Abstract: A convenient method for synthesizing 2,5‐dialkoxyterephthalaldehyde by oxidation of 1,4‐dialkoxy‐2,5‐bis(halogenomethyl)benzene with dimethyl sulfoxide in one step is described.

Estimating the vegetation coverage with MPDI

Abstract: Surface soil moisture and the overlying vegetation both influence microwave emission from land surface. Estimating and eliminating the vegetation effect to the upwelling microwave radiation is an important part during the process retrieving soil moisture and other land surface parameters with radiometer data. Two recognized methods to estimate vegetation opacity are to compute vegetation opacity with ancillary data about vegetation and to estimate vegetation opacity with some remote sensed data (such as NDVI). The retrieval of soil moisture will be significant simplified, if the vegetation opacity can be computed by MPDI instead of the ancillary data or NDVI. Some researches show that there is some correlation between c τ and NDVI. We take the AMSR/E and MODIS data to analyze the relationship between MPDI and NDVI, and a linear function relationship are built and show good relationship between MPDI