Synthetic Metals (v.158, #12)

The electrorheological (ER) behavior of polypyrrole (PPy)–SBS composite suspensions was investigated. The PPy–SBS composites were prepared to improve mechanical and electrical properties, and thereby enhance the ER response of their suspensions. Various PPy–SBS composites were synthesized by emulsion polymerization controlling the amount of SBS. The ER response initially decreased and then increased with increasing amount of SBS. The dielectric constant and conductivity of the PPy–SBS composite particles and the dielectric constant of the PPy–SBS composite suspensions were not consistent with the ER behavior, but the particle size did. A power-law dependence, τ  = 0.207βd 2 E 3/2, shows a good fit to the ER behavior of PPy–SBS composite suspensions with various amounts of SBS. The dependence of E 1.5 is consistent with the conduction model and the dependence of d 2 is consistent with the polarization model, but the dependence of β is not consistent with the either model. A surfactant, Brij®30, was added to the PPy–SBS composite suspension to reduce the non-linear conduction and thereby enhance the ER response. It was observed that the ER response was enhanced by adding the surfactant.
Keywords: Conducting polymer composite; Conducting polymer; Electrorheology; Suspension;

Synthesis and near-infrared luminescent properties of some ruthenium complexes by Shidi Xun; Jidong Zhang; Xianzhen Li; Dongge Ma; Zhi Yuan Wang (484-488).
A series of seven ruthenium complexes with different ligands were synthesized and their optical, electrochemical and photoluminescent properties were characterized. Electroluminescent properties of these complexes were further evaluated using a light-emitting electrochemical cell with a configuration of indium tin oxide (ITO)/complex (100 nm)/Au (100 nm). Tunable photoluminescence (PL) and electroluminescence (EL) from 630 to 1040 nm have been achieved by adjusting the LUMO and HOMO levels of ruthenium complexes.
Keywords: Ruthenium complexes; Light-emitting diodes; Near-infrared emission;

Photoluminescence (PL) changes in cyano-substituted poly p-phenylene vinylene (PPV) derivatives caused by photooxidation are discussed.PL blue shift of ordinary PPVs due to photooxidation is usually known to involve a significant quenching of PL intensity. In the case of cyano-substituted poly p-phenylene vinylene (CN-PPVs), we found that photooxidation at higher temperature results in blue shift without a significant PL quenching, and that photooxidation at lower temperature results in quenching with little blue shift.Our results indicated that photooxidation of CN-PPVs at an appropriate temperature can attach PL blue shift without a quenching of PL intensity, from the PL peak wavelength of solid film state to the PL peak wavelength of solution state. The appropriate temperature is different for each of the CN-PPVs.It is demonstrated that the PL peak wavelength of MEH-CN-PPV solid film can be changed with little significant PL quenching, from the 594 nm, which is the PL peak wavelength of bulk MEH-CN-PPV, to the blue limit of the PL peak wavelength of 547 nm, which is the PL peak wavelength of a well-dispersed state of MEH-CN-PPV. The changed PL properties can be preserved under a reduced pressure atmosphere, even if samples are irradiated by a light source.The dominant factor of the blue shift to the PL peak wavelength of solution state is considered to be expanding of distance between planes (d-space) of the CN-PPV-layered structure, which determines the intermolecular interaction. Controlling d-space of cyano-PPV derivatives by photoirradiation is suggested to be a useful method of creating various PL or EL color patterns of CN-PPVs.
Keywords: Cyano-substituted p-phenylene vinylene; p-Phenylene vinylene; Photooxidation; Photoluminescence;

New dioxo- and aminooxo-pyrimido-fused tetrathiafulvalene (TTF) derivatives, whose pyrimido-rings are substituted by methyl group, were synthesized. In the crystal structures of their tetrabutylammonium salts, complementary hydrogen-bonds inherent in pyrimido-fused TTF derivatives were inhibited by the methyl substitution, and the crystals were constructed by the segregated motifs of cations and anions. Betainic radicals prepared by one-electron oxidation of tetrabutylammonium salts exhibited relatively high conductivities (ca. 10−4  S cm−1 at room temperature) as single-component organic molecules. The optical measurement of betainic radicals showed considerably low-energy charge-transfer absorption between radical molecules compared to those of conventional TTF systems, indicating the reduction of on-site Coulomb repulsion.
Keywords: Pyrimido-fused TTF; Neutral betainic radical; Nucleobase; Single-component organic conductor;

Effective electrical conductivity of functional single-wall carbon nanotubes in aqueous fluids by Brian Glover; Keith W. Whites; Haiping Hong; Arnab Mukherjee; W. Edward Billups (506-508).
In this paper, for the first time, we have used a coaxial fixture to successfully obtain the relatively low and precise electrical conductivity values of nanofluids based on functional sulfonated carbon nanotubes. From 0 to 0.5 wt.% nanotube loading, the conductivity increased approximately 13 times. However, no percolation threshold phenomenon is observed. The linear conductivity increase versus the weight percentage indicates that the dominant conduction mechanism might be the ionic conduction, which is in agreement with the chemical structure of functional SWNT (anion SO3 group).
Keywords: Electrical conductivity; Functional single-wall carbon nanotubes;

We have studied the optical and photoelectrical properties of liquid state photoelectrochemical cells (PECs) based on photoactive electrodes based on poly (phenyl azo methane thiophene) (PPAT) and a composite film of nano-crystalline titanium dioxide (nc-TiO2) and PPAT. The device fabricated with nc-TiO2/PPAT photoactive electrode shows better performance with an open circuit voltage (V oc) 0.56 V, short circuit photocurrent (J sc) = 0.87 mA/cm2 and fill factor (FF) = 0.58 under illumination with white light intensity of 10 mW/cm2. We have analyzed the experimental results by comparing the IPCE spectra of both devices. It is observed that the device with nc-TiO2/PPAT photoactive electrode shows better photovoltaic response as compared to the device based on PPAT photoactive electrode. This indicates that PPAT shows its p-type semiconducting behavior in the device based on PPAT, while in the device based on nc-TiO2/PPAT photoactive electrode, the PPAT acts as a sensitizer to nano-crystalline TiO2. The PEC based on TiO2/PPAT photoelectrode exhibit an exponential increase of low frequency device capacitance due to the diffusion of electrons along TiO2 network. Effect of iodine doping in PPAT on the photovoltaic performance of PEC have been also studied.
Keywords: Photovoltaic properties; Dye sensitization; Photoelectrochemical cells;

In this communication we describe the unprecedented ruthenium(II)-mediated synthesis of polyaniline. The synthesis enroutes via formation of a simple ruthenium(II)–tetraaniline complex which on chemical oxidation with hydrogen peroxide in the presence of hydrochloric acid gives conducting polyaniline–RuO2 composite. The reaction is novel in the way that both the metal center Ru(II) and the coordinated aniline molecules of the intermediate complex 1 take part in the oxidation reaction to yield polyaniline–ruthenium oxide hybrid.
Keywords: Organic–inorganic hybrid; Polyaniline; Ruthenium oxide; Aniline complex;