Synthesis and characterization of poly(epsilon-caprolactone)-poly(L-lactide) diblock copolymers with an organic amino calcium catalyst

The quasiliving characteristics of the ringopening polymerization of epsilon-caprolactone (CL) catalyzed by an organic amino calcium were demonstrated. Taking advantage of this feature, we synthesized a series of poly (F-caprolactone) (PCL)-poly(L-lactide) (PLA) cliblock copolymers with the sequential addition of the monomers CL and L-lactide. The block structure was confirmed by H-1-NMR, C-13-NMR, and gel permeation chromatography analysis. The crystalline structure of the copolymers was investigated by differential scanning calorimetry and wide-angle X-ray diffraction analysis. When the molecular weight of the PLA block was high enough, phase separation took place in the block copolymer to form PCL and PLA domains, respectively.

Poly[di-mu(3)-chloro-mu(2)-trans-1,2-di-4-pyridylethylene-dicopper(I)]: a two-dimensional organic-inorganic hybrid constructed from linear CuCl clusters and bridging ligands

The structure of the title compound, [Cu2Cl2(C12H10N2)](n), contains infinite CuCl staircase-like chains, which lie about inversion centres. The trans-1,2-di-4-pyrid-ylethyl-ene mol-ecules also lie about inversion centres and connect the CuCl chains through Cu-N coordination bonds into a two-dimensional organic-inorganic hybrid network. The planar sheets are stacked along the c axis and associated through weak C-H center dot center dot center dot Cl inter-actions. The results show a reliable structural motif with controllable separation of the CuCl chains by variation of the length of the ligand.

Dependence of performance of organic light-emitting devices on sheet resistance of indium-tin-oxide anodes

The dependence of the performance of organic light-emitting devices(OLEDs) on the sheet resistance of indium-tin-oxide(ITO) anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence(EL) efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

Improved performance by a double-insulator layer in organic thin-flim transistors

Organic thin film transistors based on pentacene are fabricated by the method of full evaporation. The thickness of insulator film can be controlled accurately, which influences the device operation voltage markedly. Compared to the devices with a single-insulator layer, the electric performance of devices by using a double-insulator as the gate dielectric has good improvement. It is found that the gate leakage current can be reduced over one order of magnitude, and the on-state current can be enhanced over one order of magnitude. The devices with double-insulator layer exhibit field-effect mobility as large as 0.14 cm(2)/Vs and near the zero threshold voltage. The results demonstrate that using proper double insulator as the gate dielectrics is an effective method to fabricate OTFTs with high electrical performance.

White organic electroluminescence based on a new boron complex

A bright blue boron complex BPh2(pybm) containing 2-(2-pyridyl)benzimidazole ligand was designed and synthesized by using N, N-bidentate ligand instead of N, O-bidentate one such as 8-quinolinol. For three-layer LED devices with the configuration of ITO/NPB/BPh2(pybm)/Alq(3)/LiF/Al, the white light emission covering the whole visible region from 400 to 750 nm with the maximum brightness of 110 cd/m(2) and the luminous efficiency of 0.8 cd/A was observed.

Patterning and photolumine scent properties of perovskite-type organic/inorganic hybrid luminescent films by soft lithography

Perovskite-type organic/inorganic hybrid layered compound (C6H5C2H4NH3)(2)PbI4 was synthesized. The patterning Of (C6H5C2H4NH3)(2)PbI4 thin films on silicon substrate was realized by the micromolding in capillaries (MIMIC) process, a kind of soft lithography. Bright green luminescent stripes with different widths (50, 15, 0.8 mum) have been obtained. The structure and optical properties Of (C6H5C2H4NH3)(2)PbI4 films were characterized by X-ray diffraction (XRD), UV/Vis absorption and photoluminescence excitation and emission spectra, respectively. It is shown that the organic-inorganic layered (C6H5C2H4NH3)(2)PbI4 film was c-axis oriented, paralleling to the substrate plane. Green exciton emission at 525 nm was observed in the film, and the explanations for it were given.

Patterning and optical properties rhodamine B-doped organic-inorganic silica films fabricated by sol-gel soft lithography

Rhodamine B (RB)-doped organic-inorganic silica films and their patterning were fabricated by a sol-gel process combined with a soft lithography. The resulted film samples were characterized by atomic force microscope (AFM), optical microscope and UV/Vis absorption and photoluminescence excitation and emission spectra. The effects of the concentration of the RB dye and heat treatment temperature on the optical properties of the hybrid silica films have been studied. Four kinds of patterning structures with film line widths of 5, 10, 20 and 50 mum have been obtained by micromolding in capillaries by a soft lithography technique. The RB-doped hybrid silica films present a red color, with an excitation and emission bands around 564 and 585 mum, respectively. With increasing the RB concentration, the emission intensity of the RB-doped hybrid silica films increases and the emission maximum presents a red shift. The emission intensity of the films decreases with increasing the heat treatment temperatures.

Selective penetration of liquid-phase organic probe molecules into SAM of 2-mercapto-3-n-octylthiophene

An inherently disorganized self-assembled monolayer (SAM) of 2-mercapto-3-n-octylthiophene (MOT) has been formed on a gold bead electrode from its dilute ethanolic solution. The disorganization of the monolayer is attributed to the loose packing of the aliphatic chains of the MOT adsorbates, which results from a large difference in dimension/or cross-sectional area between the head (thiophene thiolate) and the tail (alkane chain) groups. Electrochemical measurements including ac impedance spectroscopy and metal underpotential deposition have shown that the monolayer is almost pinhole free. However, the MOT SAM can be penetrated by an organic probe molecule with affinity for the alkane chain part of the monolayer. Some typical probe molecules with different size and hydrophilicity have been employed to assess the permselectivity of the monolayer. Measurement results demonstrate that the ability of the employed probe molecules to penetrate into the monoalyer is mainly dominated by their hydrophilicity/or hydrophobicity. The results presented here suggest the potential application of MOT monoalyer to effectively modify the electrode surface for several research areas such as electrochemical sensors, electrocatalysis, electroanalysis, and supported hybrid bilayer membranes.

Multifunctional organic-inorganic multilayer films of tris(2,2 '-bipyridine)ruthenium and decatungstate

A new multifunctional multilayer films consisting of tris(2,2'-bipyridyl)ruthenium(II) (Rubpy) and sodium decatungstate (W-10) have been prepared by the layer-by-layer (LbL) self-assembly method on ITO substrate. X-ray photoelectron spectra (XPS) confirmed the existence of W10 and Rubpy. Cyclic voltammetry (CV) and UV-Vis spectroscopy demonstrated the uniform assembly of (W-10/Rubpy) multilayer films. The multilayer films possess electrocatalytic activities on the reduction of iodate and oxidation of oxalate. Moreover, the films exhibited electrochemiluminescence (ECL) with tripropylamine (abbreviated as TPA) as the coreactant and the ECL response was proportional to the number of (W-10/Rubpy) layers. These characteristics of the multilayer films might find potential applications in the field of sensors and materials fields.

Metal transfer printing and its application in organic field-effect transisitor fabrication

The fabrication of multilayer microstructures, for example for organic field-effect transistors, using metal transfer printing (MTP) is demonstrated. The Figure shows a two-layer gold structure produced by MTP. Since MTP is a purely additive technique, in which mechanical adhesion acts as the patterning driving force, it is considered an attractive approach to reel-to-reel processing.

Efficient red organic light-emitting devices based on a europium complex

An efficient organic light-emitting device using a trivalent europium (Eu) complex Eu(Tmphen)(TTA)(3) (TTA=thenoyltrifluoroacetone, Tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) as the dopant emitter was fabricated. The devices were a multilayer structure of indium tin oxide/N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl-4,4-diamine (40 nm)/ Eu complex:4,4-N,N-dicarbazole-biphenyl (1%, 30 nm)/2,9-dimethyl,4,7-diphenyl-1,10phenanthroline (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm). A pure red light with a peak of 612 nm and a half bandwidth of 3 nm, which is the characteristic emission of trivalent europium ion, was observed. The devices show the maximum luminance up to 800 cd/m(2), an external quantum efficiency of 4.3%, current efficiency of 4.7 cd/A, and power efficiency of 1.6 lm/W. At the brightness of 100 cd/m(2), the quantum efficiency reaches 2.2% (2.3 cd/A).

A dinuclear aluminum 8-hydroxyquinoline complex with high electron mobility for organic light-emitting diodes

A dinuclear aluminum 8-hydroxyquinoline complex (DAlq(3)) with improved electron mobility was designed for organic light-emitting diodes. The electron mobility in DAlq(3) was determined via transient electroluminescence (EL) from bilayer devices with structure of indium tin oxide (ITO)/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidine (NPB)/DAlq(3)/Mg:Ag. It was found that the electron mobility in DAlq(3) is between 3.7-8.4x10(-6) cm(2)/Vs at electric fields ranging between 1.2x10(6) and 4.0x10(6) V/cm, which is a factor of two higher than that in Alq(3). The DAlq(3) also shows a higher EL efficiency of 2.2 cd/A (1.2 Lm/W), as compared to Alq(3) with an EL efficiency of 2.0 cd/A (1.0 Lm/W), which is attributed to more balanced electron and hole recombination due to the improved electron mobility of DAlq(3).

Blue organic light-emitting diodes based on an oxadiazole-containing organic molecule exhibiting excited state intramolecular proton transfer

A blue organic light-emitting device based on an emissive layer of 2-(2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazole (HOXD), which exhibits excited state intramolecular proton transfer (ESIPT), was presented. The device had a luminance efficiency of 0.8 cd/A and a maximum brightness of 870 cd/m(2). Our studies indicate that some EL may originate from the triplet excitation state of the enol form of HOXD.