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In this paper, poly(p-phenylene vinylene) block copolymers (PPV) were immobilised in stearic acid (HSt) Langmuir–Blodgett (LB) films, and their conducting and luminescent properties were enhanced by the incorporation of palladium nanoparticles stabilised by glucose oxidase (GOx-PdNPs). The nanobiocomposite, based on HSt, PPV, and GOx-PdNPs, was transferred from the air-water interface onto solid supports using the LB technique. The films were characterised by surface pressure–area isotherms, polarisation modulation infrared reflection–absorption spectroscopy, fluorescence spectroscopy, and conductivity measurements. The results indicated that the incorporation of GOx-PdNPs in PPV-HSt LB films enhances the luminescence and conducting properties of the PPV. Based on the higher conductivity and emission obtained with the hybrid LB films and the ability to tune the molecular-level interactions between the film components by changing the experimental conditions, thus allowing for further optimisation, one may envisage applications for these films in optical and electronic devices, such as organic light-emitting diodes.

Two cyano oligo-phenylene-vinylenes [α-CNOPV and β-CNOPV] distinguished by the position of cyano (CN) group at the vinylic double bond were synthesized. The acceptor oligomer CNOPVs were blended with poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene) MEH-PPV to achieve α and β blends. The pronounced influence of cyano position on the photophysical and morphological properties of blends was observed through UV–vis absorption, photoluminescence and atomic force microscopy. The optical characterization suggests wider spectral photon harvesting in α blends and more planar conformation of molecules in β blends. The steady-state and time-resolved photoluminescence study provides evidence for efficient energy transfer from α-CNOPV to MEH-PPV. On the other hand, the 3:1 β blend exhibits quenching of PL intensity indicative of charge transfer. In addition, the feasibility of MEH-PPV:CNOPV blends in organic photovoltaic devices have been investigated. The initial device parameters show that power conversion efficiency is as high as 0.05% in β 1:1 devices. The photovoltaic efficiencies were limited by weak exciton dissociation in α blends while poor morphology restricted the efficiency in β blends.

Dopings of vaporized cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethane (CMTE) into poly(methyl methacrylate) (PMMA), polystyrene, and polycarbonate were performed by a vacuum process, and the doping behaviors of CMTE were evaluated. Among the matrix polymers, PMMA was dispersed CMTE densely in its surface region. By using the CMTE-doped PMMA, we could fabricate a novel rewritable medium: a multi-layered film was prepared from over-coating of CMTE-doped PMMA onto poly(p-phenylene vinylene) (PPV) film, which set on a transparent substrate. Image storage could be performed upon irradiation at 365 nm at the side of CMTE/PMMA layer: color of the irradiated area changed a light yellow to a red due to photo-isomerization of CMTE. Next, upon irradiation at 365 nm at the side of the transparent substrate, PPV emitted a green fluorescence at around 530 nm, and the CMTE absorbed the emission from PPV causing image-erasure based on back-isomerization of CMTE.

Semiconducting polymer thin film devices were prepared from three novel 2,5-substituted poly(p-phenylene vinylene) (PPV) derivatives and OC1C10–PPV. The novel PPV-derivatives, namely poly[2-methoxy-5-(triethoxymethoxy)-1,4-phenylene vinylene] (PEO-PPV), poly(2,5-bis-(triethoxymethoxy)-1,4-phenylene vinylene) (diPEO-PPV) and poly[2-(n-nonyloxy)-5-(triethoxymethoxy)-1,4-phenylene vinylene] ((PEO–OC9)–PPV), were obtained through the “sulfinyl precursor route”. The electrical properties of the new materials, i.e. permittivity, conductivity, charge carrier mobility, and solar cell parameters, were compared to the results obtained with the well-known OC1C10–PPV, showing that the introduction of PEO-side chains yielded a systematic increase of the relative permittivity, while the mobility remained unchanged.

Functional dyes could be dispersed into non-substituted poly(p-phenylene vinylene) (PPV), which shows a poor processability due to its insolubility and infusibility, by the vacuum process. Using this methods, it was possible to change the color of PPV from yellow to green with the blue dye, 1,4-(N,N′-diethylamino)anthraquinone (SV59). The fluorescence color of PPV could be changed from green to red by 2 min doping of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM). Furthermore, a pattern doping with DCM could be carried out resulting in production of multicolored luminescent medium.

This paper describes the oxidation process (chemical doping) of the poly( p -phenine vinylene) (PPV) by using iodine vapor, sulfuric acid and ferric chloride to determine the vibrational and electronics modifications caused by the polymer backbone oxidation. The vibrational spectroscopy indicates that a quinoid structure is formed upon oxidation, coexisting with the original benzoid structure, independent of the doping agent. Only the intensity of the bands changes with the nature of the dopant used. From the electronic spectra, three subgap transitions were identified, indicating the formation of polaronic charge carriers. However, by following different doping levels with I 2 doping, bipolaron formation is identified as well showing that polaron and bipolaron coexist as charge carriers in the oxidized polymer. The subgap transitions were peaked at 688, 1724 and 2292 nm for I 2 ; 600, 1360 and 1999 nm for FeCl 3 ; and 603, 1337, 2082 nm for H 2 SO 4 doping.

Composites made by incorporation of silicon oxide (SiO 2 ) or titanium (TiO 2 ) nanoparticles into poly( p -phenylene vinylene) (PPV) have been fabricated and their electrical and optical properties have been investigated. The UV-vis absorption and Raman spectra showed that SiO 2 nanoparticles reduced the conjugation lengths of PPV chains, while TiO 2 nanoparticles did not. In the case of SiO 2 nanoparticles, the reduction of conjugation length was more noticeable on increasing the oxide concentration or on decreasing the particle size. Fourier transform infrared (FT-IR) spectra showed that both types of nanoparticles also reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in the indium tin oxide (ITO)–composite–MgAg diodes exhibit different electrical behavior to the composites depending on the particle size and the nature of the used oxide. The composite–electrode contact morphology, the polymer–dielectric particle contact, and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes.

The frequency dependent conductivity, σ(ω), of the blend containing two different charge carrying material, a conjugated polymer, poly(p-phenylene vinylene), PPV and an ionomer, waterborne polyurethane ionomer, WPUI, was investigated in the frequency (ω) range from 0.1 to 1000 kHz by impedance spectroscopy and compared with the individual materials, PPV and WPUI, respectively. Clear differences could be seen in the dependence of ω on both real and imaginary parts of impedance between WPUI, PPV and the blend film. At high frequencies (>200 kHz), all the three materials, exhibit a power law dependence between σ(ω) and ω as σ(ω)∝ωs. Simulation of s value through theoretical fitting reveals that the s value of the blend (1.108) is in between PPV (1.289) and WPUI (1.035) and signifies the mixed contribution of carrier transport of PPV and WPUI in the blend. The morphology of the blend as observed from atomic force microscopy (AFM) imaging reveals that WPUI connects the islanded parts of PPV and provides a path for carrier conduction. Results observed indicate that carrier transport operates through barrier hopping in these materials and the difference in the dependence of ω on σ in the blend is attributed from the influence of SO3− group in WPUI on the carrier transport of PPV.

We have prepared ultrathin multilayer nanostructural films by a layer-by-layer spin self-assembly method using poly (p-phenylene vinylene) (PPV)/layered silicate and characterized them by contact angle measurement, surface dying technique, UV/Vis spectroscopy, photoluminescent (PL) spectroscopy, X-ray reflectivity (XRR), and model-fitting. The hybrid ultrathin multilayer film was stepwisely deposited using the electrostatic forces between the cationic PPV precursor and the negatively charged surface of layered silicate, and finally thermally converted to (PPV/Laponite RD)n film. The surface coverage of the PPV precursor onto layered silicate and vice versa could be clearly observed using the contact angle measurement and surface dying technique. The continuous increase of UV/Vis absorbance and PL intensity of the films with each bilayer demonstrated the regular and reproducible deposition of this system, and the Kiessig fringes and Bragg peaks in XRR spectra indicated the well-ordered internal structure.

The electroluminescence and photoluminescence of poly( m -phenylenevinylene)-alt-( p -phenylenevinylene) green light emitting copolymers have been studied. The effect of alkoxy substitutions (–OC 4 H 9 and –OC 6 H 13 ) in single and double layer device configurations was also investigated. In double layer devices, poly( p -phenylene vinylene), PPV (60 nm) was used as a hole transport layer and substantial increase in the longevity, stability and electroluminescence efficiency of the devices was observed. Blending of green light emitting copolymers with poly( N -vinylcarbazole), PVK and [2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (butyl-PBD)] gives further promising results, namely an increase in brightness and EL efficiency of the LEDs.

The optical and electroluminescent properties of a novel soluble derivative of poly(p-phenylene vinylene), poly(2-methoxy-5-butoxy-p-phenylene-vinylene) (MBPPV), and its polyblends were studied. We have fabricated a single-layer and double-layer structure of light-emitting devices (LEDs), with polyblends as the active layer. The turn-on voltage and maximum external quantum efficiency of the double-layered structure LEDs were 3.5 V and 1.35%.

The degradation of conjugated polymer poly(p-phenylene vinylene) (PPV) in the atmosphere upon exposure to ultraviolet light limits its applications as the emitting layer in organic light emitting diodes. In this paper we show that a thin layer of aluminum oxide around 10 nm in thickness prevents photoluminescence degradation of PPV during exposure to blue light in the atmosphere but not at lower excitation wavelengths. This oxide film is free of cracks and pinholes from transmission electron microscopy analysis.

Polymer light-emitting diodes (LEDs) based on the structure ITO conducting glass /poly(p-phenylene vinylene)/metal (Al, In, Mg) have been investigated with particular emphasis on some anomalous and poorly understood features of the conduction mechanisms. At large forward bias (above 3 V, where electroluminescence is seen) the DC current is dominated by hole injection at the bottom ITO electrode and is not very sensitive to the top electrode metal or the fabrication conditions. It always increases exponentially with voltage at 20 degrees C, but studies on operating voltages and apparent ideality factors as a function of thickness indicate that the conduction mechanism probably involves thermally assisted tunnelling rather than a simple Schottky diode mechanism. In contrast, the current at low forward bias (0.1-3 V) is exceptionally sensitive to the top electrode material, fabrication conditions, and operating history of the device. Anomalous behaviour is often seen, particularly with new devices and with Mg or In electrodes. With Al electrodes, particularly after a top electrode annealing step, the behaviour becomes much more stable and resistive, and logJ increases linearly with V-1/4 over 3 orders of magnitude of current. The overall behaviour at low bias is controlled by the barrier to holes at the top electrode, but the role of filamentary defects, dopants, and the insulating interfacial layer is also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

We have studied the interface formed on a poly(p-phenylene vinylene) (PPV) thin film by deposition of a thermally evaporated aluminum layer. The cross-section of Al-coated PPV films was analysed by analytical transmission electron microscopy and complemented by X-ray photoelectron spectroscopy. The subsequent presence of oxygen was detected at the polymer-metal boundary accompanied by modified aluminum and carbon bonding states indicating chemical interaction between the metal and the polymer has occurred. The PPV structure was also affected by the evaporation process by the formation of a sublayer in the polymer bulk beneath the interface which reveals the presence of carbonyl groups and possible reticulation of carbon. It was suggested that the interaction between aluminum and carbon was initiated from the binding of the metal atoms to the oxygen of the observed sublayer.

Processible conjugated polymers can be used to fabricate a range of thin-film diodes which can be designed to show good characteristics both as electroluminescent diodes and also as photoconductive diodes. We consider the present understanding of the operation of light-emitting diodes which use conjugated polymers for both charge transport and emission. We highlight the improvement to the electroluminescence efficiency that can be produced by the use of two polymer layers selected so that the heterojunction between the two layers is able to confine charge and thus bring about electron-hole capture to generate excitons at this interface. Photon absorption produces excitons which are considered to be bound at room temperature. Charge penetration requires ionisation of these excitons, which can be achieved efficiently at heterojunctions between layers with different electronegativities, and we report how this can be achieved at the interfaces between interpenetrating networks of electron- and hole-accepting polymers.

The electrical and electroluminescent (EL) properties of poly(p-phenylene vinylene) (PPV) Langmuir-Blodgett (LB) film based light emitting diodes, i.e. ITO/PPV/A1 and ITO/HTL/PPV/A1 devices, were investigated, and found to depend strongly on the thickness of the PPV LB film. The electrical conductivity of the PPV LB film was in the range of 10 −12 to 10 −15 S cm −1 . Under a forward bias, the light emission reached more than 100 cd m −2 in an ITO/PPV(80L) /Al device. Since the EL spectrum was similar to the photoluminescent (PL) spectrum, it was concluded that EL resulted from the recombination of injected charges in the PPV layer.