A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Stability/degradation of polymer solar cells

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

Concepts for the incorporation of inorganic building blocks into organic polymers on a nanoscale

Silicone containing copolymers: Synthesis, properties and applications

The ac complex conductivity σ*(f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1–100 KHz frequency range, are reported The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies In order to interpret both the real and the imaginary components of σ*(f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites

Alternating electrical conductivity of polyaniline

In this work, the effect of gamma radiation on the optical properties of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is studied. The samples were irradiated at room temperature with different doses from 0Gyto152Gy using a Co60 gamma ray source. For thin films, significant changes in the UV-visible spectra were only observed at high doses (>1kGy). In solution, shifts in absorption peaks are observed at low doses (<10Gy), linearly dependent on dose. The shifts are explained by conjugation reduction, and possible causes are discussed. Our results indicate that MEH-PPV solution can be used as a dosimeter adequate for medical applications.

Low dose ionizing radiation detection using conjugated polymers

Hybrid organic−inorganic ionic conductors, also called ormolytes (organically modified electrolytes), were obtained by dissolution of LiClO4 in siloxane−poly(propylene glycol) matrixes. The dynamic features of these nanocomposites were studied and correlated to their electrical properties. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the effects of the temperature and nanocomposite composition on the dynamic behaviors of both the ionic species (7Li) and the polymer chains (13C). NMR, dc ionic conductivity, and DSC results demonstrate that the Li+ mobility is strongly assisted by the segmental motion of the polymer chain above its glass transition temperature. The ac ionic conductivity in such composites is explained by use of the random free energy barrier (RFEB) model, which is in agreement with their disordered and heterogeneous structures. These solid ormolytes are transparent and flexible, and they exhibit good ionic conductivity at room temperature (up to 10-4 S/cm). Co...

Solid-State NMR, Ionic Conductivity, and Thermal Studies of Lithium-doped Siloxane−Poly(propylene glycol) Organic−Inorganic Nanocomposites

Complex impedance measurements were used to analyze the influence of ultraviolet and ozone gas on the electronic behaviour of ZnO films grown by rf magnetron sputtering. The data show that UV exposure strongly increases the ac conductivity of the film at very low frequencies, and that after ozone exposure it recovers the original value. At high frequencies, however, UV-light exposure it does not change the conductivity but the ozone acts in the sense to decrease it. Two distinct mechanisms, related to two relaxation time distributions are clearly observed: they are superimposed in the virgin sample, but they split forming two semicircles in the z ″( f ) −  z ′( f ) diagrams when the samples are treated with UV and/or ozone gas. A combination of the bruggeman effective medium approximation (BEMA) with the random free energy barrier model is used to fit the data and to explain the ac conductivity variation phenomena observed.

/pdf/uv-and-ozone-influence-on-the-conductivity-of-zno-thin-films-305hawx3wz.pdf

UV and ozone influence on the conductivity of ZnO thin films

Poly(p-phenylenevinylene) (PPV) and its derivatives exhibit strong luminescence, being serious candidates to be used as active layers in organic light-emitting diodes. However, the structural degradation caused by photo-oxidation is an obstacle for commercial applications of such materials. Here, we show that spectroscopy ellipsometry is a useful technique to investigate the photo-oxidation of poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] (MH-PPV), a PPV derivative, which emits a red color light. Spectroscopy ellipsometry enables determination of the complex dielectric function ∈ * (E) of MH-PPV thin-layer films exposed to air, in the 2.1-4.2 eV energy range, as a function of the light exposure time (t e ). By using the Lorentz model to fit the experimental ∈*(E) curves, it was inferred that the interactions among polymeric chains increase with t e . From ∈*(E), it is also possible to obtain the complex refractive index, N*(E) = n + ik. At higher energies (where k << n), n increases from 1.32 to 1.40 with the photo-oxidation progress. The behavior of n was investigated by using the Lorenz-Lorentz equation, taking into account the contribution for n by the chromophores of MH-PPV. The effect of photo-oxidation, mainly due to the replacement of vinyl C=C by the ketone C=O bonds, is confirmed by Fourier transform infrared measurements, an effect that reduces the average effective polymer conjugation length.

Rodrigo Fernando Bianchi

Papers

Alternating electrical conductivity of polyaniline

Low dose ionizing radiation detection using conjugated polymers

Solid-State NMR, Ionic Conductivity, and Thermal Studies of Lithium-doped Siloxane−Poly(propylene glycol) Organic−Inorganic Nanocomposites

UV and ozone influence on the conductivity of ZnO thin films

Ellipsometry study of the photo-oxidation of poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene]