Low threshold amplified spontaneous emission based on coumarin 151 encapsulated in mesoporous SBA-15

Amplified spontaneous emission (ASE) characteristics of a blue dye coumarin 151 encapsulated in a highly ordered mesoporous SBA-15 were studied. The spectra narrowing was observed and found that the threshold and loss were greatly reduced, and the gain is significantly increased compared with spin-coated coumarin 151 doped poly(4-vinylphenol) film. The ASE threshold, gain, and loss, respectively, reached 0.55 mJ pulse(-1) cm(-2), 44.78 cm(-1), and 8.9 cm(-1) for the coumarin 151 encapsulated in mesoporous SBA-15 film. The optimized lasing action owes much to the effects of the better spatial confinement of the molecules in the ordered mesoporous structure of the host SBA-15.

Memory devices based on lanthanide (SM3+, EU3+, Gd3+) complexes

Memory effects in single-layer organic light-emitting devices based on Sm3+, Gd3+, and Eu3+ rare earth complexes were realized. The device structure was indium-tin-oxide (ITO)/3,4-poly(ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT)/Poly(N-vinyl carbazole) (PVK): rare earth complex/LiF/Ca/Ag. It was found experimentally that all the devices exhibited two distinctive bistable conductivity states in current-voltage characteristics by applying negative starting voltage, and more than 10(6) write-read-erase-reread cycles were achieved without degradation. Our results indicate that the rare earth organic complexes are promising materials for high-density, low-cost memory application besides the potential application as organic light-emitting materials in display devices.

Synthesis and characterization of new carbazole/fluorene-based derivatives for blue-light-emitting devices

2,7-Bis(9-ethylcarbazol-3-yl)-9,9-di(2-ethylhexyl)fluorene and a segmented copolymer composed of the same chromophores alternated with hexamethylene fragments were synthesized. The obtained materials possess good solubility in common organic solvents, high thermal stability with 1% weight loss temperature of 350-370 degrees C, and suitable glass transition temperatures. Both derivatives show blue fluorescence in dilute solutions as well as in solid state, demonstrating that excimers are not formed in the thin films. The fluorescence spectra of the materials do not show any peaks in the long-wavelength region even after annealing at 200 degrees C in air. An organic LED with the configuration of ITO/copolymer/Al generates blue electroluminescence with the maximum peak at 416 nm, rather low turn-on voltage (4.0 V), and brightness of about 400 cd/m(2). The heterostructure device based on model derivative emitted stable blue light with low operation voltage (100 cd/m(2) at similar to 11 V) and demonstrated luminescence efficiency of 0.8 cd/A.

Phenylene vinylene-based electroluminescent polymers with electron transport block in the main chain

We report a new route for the design of soluble phenylene vinylene (PV) based electroluminescent polymers bearing electron-deficient oxadizole (OXD) and triazole (TZ) moieties in the main chains with the aryloxy linkage. Both series of the PV-based polymers were prepared by Wittig reaction. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole- and electron injections, such that the device efficiency is significantly improved. Light-emitting diodes fabricated from P1, P2, P3, P4, P5, P6, and P7 with the configuration of Indium-Tin Oxide (ITO)/Poly (styrene sulfonic acid) doped poly (ethylenedioxythiophene) (PEDOT)/polymer/Ca/Al, emit bright green light with the maximum peak around 500 nm. For the device using the optimal polymer (P4) as emitting layer, a maximum brightness of 1300 cd/m(2) at 20 V and a maximum luminance efficiency of 0.325 cd/A can be obtained.

Synthesis and properties of soluble polyimides based on isomeric ditrifluoromethyl substituted 1,4-bis(4-aminophenoxy)benzene

A new fluorinated diamine monomer, [1,4-bis(4-amino-3-trifluoromethylphenoxy)benzene (2)], and a known isomeric analog 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (3) were synthesized. A series of organosoluble polyimides Ia-d and IIa were prepared from the diamines (2, 3) and dianhydrides (a-d) by a high-temperature one-step method. The effects of the trifluoromethyl substituents on the properties of polyimides were evaluated through the study of their soluble, thermal, optical, and gas permeability properties. Polyimides (Ia-d) had glass transition temperatures between 229 and 279 degrees C, and the temperatures at 5% weight loss ranged from 510 to 533 degrees C under nitrogen. These polyimides could be cast into flexible and tough membranes from DMAc solutions. The membranes had tensile strengths in the range of 137-169 MPa, tensile modulus in the range of 1.6-2.2 GPa and elongations at break from 11% to 14%. The polyimide la with trifluoromethyl groups ortho to the imide nitrogen exhibited enhanced gas permeability, solubility, transparency, and thermal stability compared with the isomeric polyimide IIa with the CF3 group meta to the imide nitrogen.

Double propagation based on diepoxide, a facile route to high molecular weight poly(propylene carbonate)

Poly(propylene carbonate) (PPC) with number average molecular weight (M-n) higher than 200 kg/mol was prepared via the terpolymerization of carbon dioxide, propylene oxide and diepoxide using Y(CCl3OO)(3)-ZnEt2-glycerine coordination catalyst. When equimolar ZnEt2 and diepoxide were used, double propagation active species were generated in situ by nucleophilic attack of metal alkoxide on diepoxide, leading to PPC of doubled M-n value. The molecular weight of PPC has dramatic influence on its thermal and mechanical performances. PPC with M of 227 kg/mol showed modulus of 6900 MPa, while the modulus of PPC with M-n of 109 kg/mol was only 4300 MPa. Moreover, when M-n increased from 109 to 227 kg/mol, a 37 degrees C increase of the onset degradation temperature was observed.

High-efficiency spin-coated organic light-emitting diodes based on a europium complex

An organic light-emitting diode fabricated by doping a europium, complex tris(dibiphenoylmethane)-mono (phenanthroline)-europium (Eu(DBPM)(3) (Phen)) into polymer poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene) and poly(N-carbazole) was realized by spin coating. Comparison with other europium complexes, due to the existence of a larger spectral overlap between Eu(DBPM)(3)(Phen) and poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4phenylene), a high efficiency red emission was achieved. The device showed a turn-on voltage of 5.2 V The maximum efficiency reached 0.47 cd/A at luminance of 50 cd/m(2). The maximum luminance can reach 150 cd/m(2) at 95 mA/cm(2). To the best of our knowledge, this is one of the best results based on europium complexes by spin-casting method.

Stress transfer and damage evolution simulations of fiber-reinforced polymer-matrix composites

The stress transfer from broken fibers to unbroken fibers in fiber-reinforced thermosetting polymer-matrix composites and thermoplastic polymer-matrix composites was studied using a detailed finite element model. In order to check the validity of this approach, an epoxy-matrix monolayer composite was used as thermosetting polymer-matrix composite and a polypropylene (PP)-matrix monolayer composite was used as thermoplastic polymer-matrix composite, respectively. It is found that the stress concentrations near the broken fiber element cause damage to the neighboring epoxy matrix prior to the breakage of other fibers, whereas in the case of PP-matrix composites the fibers nearest to the broken fiber break prior to the PP matrix damage, because the PP matrix around the broken fiber element yields. In order to simulate composite damage evolution, a Monte Carlo technique based on a finite element method has been developed in the paper. The finite element code coupled with statistical model of fiber strength specifically written for this problem was used to determine the stress redistribution. Five hundred samples of numerical simulation were carried out to obtain statistical deformation and failure process of composites with fixed fiber volume fraction.

One-step polyelectrolyte-based route to well-dispersed gold nanoparticles: Synthesis and insight

Polyelectrolytes have been widely used as building blocks for the creation of thickness-controllable multilayer thin films in a layer-by-layer fashion, and also been used as flocculants or stabilizer of colloids. This paper reports novel finding that a kind of polyelectrolyte, polyamines, can facilely induce HAuCl4 to spontaneously form well-stabilized gold nanoparticles without the additional step of introducing a reducing reagent during the elevation of temperature, even at room temperature in some cases. The polymer chain-confined microenvironment and the acid-induced evolution of amide of such kind of polyelectrolyte solution play an important role in the nucleation and growth of gold nanoparticles. This method would not only be helpful to gain an insight into the formation of gold nanoparticles in polyelectrolyte systems, but also provide a novel and facile one-step polyelectrolyte-based synthetic route to polyelectrolyte protected gold nanoparticles in aqueous media for potential applications. More importantly, this strategy will be general to the preparation of other nanoparticles.

Medicated wound dressings based on poly(vinyl alcohol)/poly(N-vinyl pyrrolidone)/chitosan hydrogels

Poly(vinyl alcohol) /poly(N-vinyl pyrrolidone) (PVP)/chitosan hydrogels were prepared by a low-temperature treatment and subsequent Co-60 -gamma-ray irradiation and then were medicated with ciprofloxacin lactate (an antibiotic) and chitosan oligomer (molecular weight = 3000 g/mol). The gel content, swelling ratio, tensile strength, and crystallinity of the hydrogels were determined. The effects of the chitosan molecular weight, the low-temperature treatment procedure, and the radiation dosage on the hydrogel properties were examined. The molecular weight of chitosan was lowered by the irradiation, but its basic polysaccharide structure was not destroyed. Repeating the low-temperature treatment and gamma-ray irradiation caused effective physical crosslinking and chemical crosslinking, respectively, and contributed to the mechanical strength of the final hydrogels. The incorporation of PVP and chitosan resulted in a significant improvement in the equilibrium swelling ratio. and elongation ratio of the prepared hydrogels. The ciprofloxacin lactate and chitosan oligomer were soaked into the hydrogels. Their in vitro release behaviors were examined, and they were found to follow diffusion-controlled kinetics.

Polylactide-based polyurethane and its shape-memory behavior

A series of polylactide polyurethanes (PLAUs) were synthesized from poly(L-lactide) diols, hexamethylene diisocyanate (HDI), and 1,4-butanediol (BDO). Their thermal and mechanical properties and shape-memory behavior were studied by infrared spectroscopy (IR), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXID), tensile testing, and thermal mechanical analysis (TMA). The T(g)s of these polymers were in the range of 33-53 degrees C, and influenced by the Mn of the PLA diol and the ratio of the soft-segment to the hard-segment. These materials can restore their shapes almost completely after 150% elongation or twofold compression. By changing the M-n of the PLA diol and the ratio of the hard-to-soft-segment, their Ts and shape-recovery temperatures can be adjusted to the neighborhood of the body temperature. Therefore, these PLAUs are expected to find practical medical applications.

A wide-bandgap semiconducting polymer for ultraviolet and blue light emitting diodes

A novel wide-bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene-based copolymer composed of rigid twisting segments in the main-chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd.m(-2) was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm, and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain-aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors.

Novel polyoxometalate-templated, 3-D supramolecular networks based on lanthanide dimers: Synthesis, structure, and fluorescent properties of [Ln(2)(DNBA)(4)(DMF)(8)][Mo6O19] (DNBA=3,5-dinitrobenzoate)

The spherical Lindquist type polyoxometalate, Mo6O192-, has been used as a noncoordinating anionic template for the construction of novel three-dimensional lanthanide-aromatic monocarboxylate dimer supramolecular networks [Ln(2)(DNBA)(4)(DMF)(8)][Mo6O19] (Ln = La 1, Ce 2, and Eu 3, DNBA = 3,5-dinitrobenzoate, DMF = dimethylformamide). The title compounds are characterized by elemental analyses, IR, and single-crystal X-ray diffractions. X-ray diffraction experiments reveal that two Ln(III) ions are bridged by four 3,5-dinitrobenzoate anions as asymmetrically bridging ligands, leading to dimeric cores, [Ln(2)(DNBA)(4)(DMF)(8)](2+); [Ln(2)(DNBA)(4)(DMF)(8)](2+) groups are joined together by pi-pi stacking interactions between the aromatic groups to form a two-dimensional grid-like network; the 2-D supramolecular layers are further extended into 3-D supramolecular networks with 1-D box-like channels by hydrogen-bonding interactions, in which hexamolybdate polyanions reside. The compounds represent the first examples of 3-D carboxylate-bridged lanthanide dimer supramolecular "host" networks formed by pi-pi stacking and hydrogen-bonding interactions encapsulating noncoordinating "guest" polyoxoanion species. The fluorescent activity of compound 3 is reported.

Copolymerization of carbon dioxide and propylene oxide with neodymium trichloroacetate-based coordination catalyst

The copolymerizations of carbon dioxide (CO2) and propylene oxide (PO) were performed using new ternary rare-earth catalyst, It was found that the rare-earth coordination catalyst consisting of Nd(CCl3COO)(3), ZnEt2 and glycerine was very effective for the copolymerization of PO with CO2. The effects of the relative molar ratio and addition order of the catalyst components, copolymerization reaction time, and operating pressure as well as temperature on the copolymerization were systematically investigated. At an appropriate combination of all variables, the yield could be as high as 6875 g/mol Nd per hour at 90 degreesC in a 8 h reaction period.

Strontium-based initiator system for ring-opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr-PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring-opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA). The Sr-PO initiator demonstrated an effective initiating activity for the ROP of epsilon-caprolactone (epsilon-CL) and L-lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr-PO initiator. Block copolymer PCL-b-PLLA was prepared by sequential polymerization of epsilon-CL and LLA, which was demonstrated by H-1 NMR, C-13 NMR, and gel permeation chromatography. The chemical structure of Sr-PO initiator was confirmed by elemental analysis of Sr and N, H-1 NMR analysis of the end groups in epsilon-CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr-PO initiator and model monomer gamma-butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination-insertion mechanism, and cyclic esters exclusively inserted into the Sr-O bond.