Electropolyrnerization of polypyrrole on PFIL-PSS-modified electrodes without added support electrolytes

A novel polyelectrolyte-functionalized ionic liquid (PFIL)/poly(4-styrene sulfonate sodium) (PSS) modified electrode composed of the coaxial and coplanar working, reference and counter electrodes, was used to electropolymerize the polypyrrole. The PFIL/PSS was modified on the integrated electrode (IE) and connected by the working, reference and counter electrodes, resulting in an available charge transfer and lower Ohmic potential drop between the working and counter electrodes. Then polypyrrole (PPy) film was successfully prepared electrochemically without any participation of supporting electrolytes, only in a pyrrole monomer solution. The resulting PPy film in PFIL/PSS matrix exhibited a preferable electroactivity. Subsequently, influence of the modifications on the formation of PPy was further discussed. The results indicated that the synergetic cooperation of PFIL and PSS components accomplished such a successful electropolymerization of PPy.

Synthesis, structure, electrochemistry, photophysics and electroluminescence of 1,3,4-oxadiazole-based ortho-metalated iridium(III) complexes

Four new iridium(III) complexes 1-4, with 1,3,4-oxadiazole derivative as cyclometalated ligand for the first time, have been synthesized and structurally characterized by NMR, EA, MS and X-ray diffraction analysis (except 1). The stronger ligand field strength of the dithiolate ancillary ligands results in higher oxidation potentials and lower HOMO energy levels of complexes than acetylacetone. The absorption spectra of these complexes display low-energy metal-to-ligand charge transfer transition ranging from 350 to 500 nm. Complexes with dithiolate ancillary ligand emit at maximum wavelengths of ca. 500 nm, blue shifting 17 and 11 nm with respect to their counterpart with acetylacetone ligand. The electrophosphorescent devices with 2-4 as phosphorescent dopant in emitting layer have been fabricated. All devices have a low turn-on voltage in the range of 4.5 and 4.9 V. A high-efficiency green emission with maximum luminous efficiency of 5.28 cd/A at current density of 1.37 mA/cm(2) and a maximum brightness of 2592 cd/m(2) at 15.2 V has been achieved in device using 2 as emitter.

Synthesis and characterization of spherical Sr2CeO4 phosphors by spray pyrolysis for field emission displays

A blue emitting Sr2CeO4 phosphor with a one-dimensional structure has been prepared by a two-step spray pyrolysis (SP) method, starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives. The material is ultimately designed for field emission displays (FEDs). X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), field emission scanning electron microscope pictures (FE-SEM) as well as photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and lifetime measurements have been employed to characterize the samples. The morphology, PL and low voltage CL properties of Sr2CeO4 phosphors as-prepared using the SP method have been investigated by changing the concentration of the precursor solution, concentration of PEG, annealing temperature, acceleration voltage and filament current. The obtained Sr2CeO4 phosphor particles are spherical and of submicron size, 0.5-2 mu m. The emission spectrum of the phosphors shows a broad band with maximum at 467 nm (lifetime = 37.4 mu s; CIE chromaticity coordinates: x = 0.15 and y = 0.21), presumably due to a ligand-to-metal charge-transfer transition.

Luminescence properties of LB films based on heteropolytungstate of rare earth

In this work, the LB films based on heteropolytungstate of Dy and Sm have been prepared. The X-ray diffraction shows the LB films have a highly ordered lamella structure. The luminescence characteristics of the LB films were studied. The charge transfer bands of LB films are in higher energies than those of the corresponding solids. It is noticed that the yellow to blue intensity ratio (Y:B) of Dy3+ in the LB films is different from that of the solid. The differences in the spectra show that the Dy3+ site symmetry in LB film was changed due to the interaction between the surfactant and the polyanions. The differences could also be found in the luminescence spectra of the LB films of Sm complex.

Effect of alkyl group length on the conductivity in the 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins and redox properties of the metallooctakis(hexyl-thio)tetraazaporphyrins

A series of 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins (H(2)OATTAP) with different alkyl chain lengths have been synthesized. Cyclic voltammetry and differential pulse voltammetry have been used to investigate the effect of the controlled lengths of the eight peripheral thioether tails on the redox behavior of the molecules. The electrochemical reduction of octakis(hexyl-thio)tetraazaporphyrins, MOHTTAP (where M = Cu, Ni), was studied in 1,2-dichloroethane at a platinum electrode. The Cu derivative was oxidized in one single-electron-transfer step to yield a pi-cation radical and reduced in three single-electron-transfer steps to yield a pi-anion radical, dianion and trianion, respectively. For the Ni derivative, electron transfer reactions involving both the central metal atom and the macrocyclic ring were observed. Electron transfer pathways are proposed based upon voltammetric and in situ spectroelectrochemical results.

VUV-UV photoluminescence spectra of strontium orthophosphate doped with rare earth ions

The measurements of VUV-UV photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra of rare earth ions activated strontium orthophosphate [Sr-3(PO4)(2):RE, RE = Ce, Sm, Eu, Tb] are performed. Whenever the samples are excited by VUV or UV light, the typical emission of Ce-3+,Ce- Sm3+, Eu3+, Eu2+ and Tb3+ ions can be observed in PL spectra, respectively. The charge transfer bands (CTBs) of Sm3+ and Eu3+ are found, respectively, peaking at 206 and 230nm. The absorption bands peaking in the region of 150-160 nm are assigned to the host lattice sensitization bands, i.e., the band-to-band transitions of PO43- grouping in Sr-3(PO4)(2). It is speculated that the first f-d transitions of Sm3+ (Eu3+), and the CTB of Tb3+ are, respectively, located around 165 (14 3) and 167 urn by means of VUV-UV PLE spectra and relational empirical formula, these f-d transitions or CT bands are included in the bands with the maxima at 150-160 nm, respectively. The valence change of europium from trivalent to divalent in strontium orthophosphate prepared in air is observe by VUV-UV PL and PLE spectra.

Vacuum ultraviolet optical properties of (La,Gd)PO4 : RE3+ (RE = Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO4:RE3+ (RE = Eu or Tb) and X-ray photoelectron spectra of LaPO4 and GdPO4 are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO4:RE3+ is enhanced with the increasing of Gd3+ content, which implies that Gd3+ plays an intermediate role in energy transfer from host absorption band to RE3+. When Gd3+ is doped into LaPO4:Eu, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd3+ doped into LaPO4. These results suggest that the dopant (Gd3+) gives an important influence on energy transfer efficiency. The top of LaPO4 valance band is formed by the 2p level of O2-, whereas that of GdPO4 valance band is formed by the 2p level of O2- and the 4f level of Gd3+, showing the differences in band structures between LaPO4 and GdPO4.

Preparation of Y3Al5O12 : Eu phosphors by citric-gel method and their luminescent properties

By using metal nitrates as starting materials and citric acid as complexing agent, Y3Al5O12 (YAG) and Y3Al5O12:Eu (1 mol%) (YAG:Eu) powder phosphors were prepared by a citrate-gel method. The formation process of YAG and YAG:Eu were investigated by means of XRD, TG-DTA and FT-IR spectra. The purified crystalline phases of YAG and YAG:Eu were obtained at 800 degreesC. The crystalline YAG:Eu phosphors showed an orange-red emission with D-5(0)-F-7(1) (591 nm) as the most prominent group, whose intensity was dependent on the pH value of the starting solution, citric acid content and firing temperature. It has been found that the suitable pH and citric acid/metal ratio are 3 and 2 for obtaining the highest emission intensity, respectively. The emission intensity increases steadily with increasing the annealing temperature from 800 to 1200 degreesC, and nearly remains constant after 1200 degreesC. Furthermore, great differences were observed for the lifetimes and the charge transfer band of Eu3+ in crystalline and amorphous states of YAG.

Hydrothermal synthesis and crystal structure of a hybrid material based on [Co-4(phen)(8)(H2O)(2)(HPO3)(2)](4+) and a highly reduced polyoxoanion

An unusual composite hybrid material [Co-4 (phen)(8) (H2O)(2) (HPO3)(2)](H3O)(3) [PMo8VI V-4(IV) O-40 ((VO)-O-IV) 2] 1 (phen = 1,10-phenanthroline) has been hydrothermally synthesized from a mixture of NH4VO3, Na2MoO4.2H(2)O, CoCl2.6H(2)O, phen, H3PO3 and water. It was characterized by elemental analysis, IR, UV-vis, XPS, EPR, TG and single crystal X-ray diffraction. The title compound is constructed from the organic-inorganic hybrid [Co-4(phen)(8)(H2O)(2) (HPO3)(2)](4+) and highly reduced bi-capped pseudo-Keggin [(PMo8V4O40)-V-VI-O-IV ((VO)-O-IV)(2)](7-) polyoxoanions The structure exhibits an extended 2D network through hydrogen bonds among cations, anions and H2O, combining polyoxometalates with metal phosphonates for the first time.

Formation of a supported hybrid bilayer membrane on gold: A sterically enhanced hydrophobic effect

Adsorption of a monolayer of didecanoyl-L-alpha-phosphatidylcholine (DDPC) from dispersions of small unilamellar vesicles onto hydrophobic surfaces was investigated by mean of cyclic voltammetry and impedance spectroscopy. The hydrophobic surfaces were self-assembled monolayers of 2-mereapto-3-n-octylthiophene (MOT) on gold. One characteristic of the MOT monolayer is its permeability to organic molecules in aqueous solution, thus providing a more energetically favorable hydrophobic surface for the addition of phospholipid vesicles. The kinetics of the lipid monolayer formation were followed by measuring the time-dependent interfacial capacitance. Unusual values of thickness and capacitance of the MOT/ DDPC bilayers were observed. An interdigitating conformation of the bilayer structure was proposed to interpret the experimental results, The horseradish peroxidase reconstituted into the bilayer demonstrated the expected protein activity, showing practical use in research and in biosensor application.

Aggregation behavior of amphiphilic D-pi-A molecules bearing recognition group

Aggregation behavior of two amphiphilic D-pi -A molecules bearing barbituric acid as both recogniton group and electron-drawing substituent, 5-(4-dodecyl oxybenzylidene)-(1H, 3H)-2,4,6-pyrimidine trione (PB12) and 5-(4-N,N-didodecyl aminobenzylidene)-(1H,3H)-2,4,6-pyrimidine trione (AB(12)) was studied by UV-visible, fluorescence, and surface voltaic spectroscopies (SPS). The experimental results indicate that PB12 tends to form J-aggregate and AB(12) tends to form H-aggregate under increasing concentration. An intramolecular twisted charge transfer (TICT) emission around 500 nm is observed when J-aggregate is formed between PB12 molecules, and an excimer emission around 600 nm is observed when H-aggregate is formed between AB(12) molecules.

Photosensitization of TiO2 nanoparticulate thin film electrodes by CdS nanoparticles

Surface photovoltage spectra (SPS) measurements of TiO2 show that a large surface state density is present on the TiO2 nanoparticles and these surface states can be efficiently decreased by sensitization using US nanoparticles as well as by suitable heat treatment. The photoelectrochemical behavior of the bare TiO2 thin film indicates that the mechanism of photoelectron transport is controlled by the trapping/detrapping properties of surface states within the thin films, The slow photocurrent response upon the illumination can be explained by the trap saturation effect. For a TiO2 nanoparticulate thin film sensitized using US nanoparticles, the slow photocurrent response disappears and the steady-state photocurrent increases drastically, which suggests that photosensitization can decrease the effect of surface states on photocurrent response.

Infrared spectra and VUV excitation properties of BaLnB(9)O(16): Re (Ln = La, Gd; Re = Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

Electrochemical and in situ spectroelectrochemical behavior of 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and (Zn(II)OHTTAP)

The characterization of free base porphyrin 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and its zinc(II) complexes [Zn(II)OHTTAP] containing eight thioether groups at the beta -pyrrole positions of the macrocycle was reported. Results obtained by cyclic voltammetry and differential pulse voltammetry indicated a five-electron reduction in five steps for each complex. They were oxidized in two single-electron-transfer steps to yield pi -cation radicals and dications and reduced in three single-electron-transfer steps to yield pi -anion radicals, dianions and trianions, respectively. The redox property of H(2)OHTTAP was unusual as compared to porphyrins (PPs) and phthalocyanines (Pcs). Each process was monitored by in situ thin-layer spectroelectrochemistry, which indicated that only the Ligand was electroactive. The existence of the eight hexylthio groups was responsible for the intrastack interactions and enhanced intracolumnar and intercolumnar electron motions, resulting in improved conductivity. Copyright (C) 2001 John Wiley & Sons, Ltd.