Electron spin resonance (ESR) investigations on blends of polyaniline (PANI) and polyvinylchloride (PVC), containing different amounts of PANI, ranging from 0 to 40% (in weight), are reported. The temperature dependence of resonance line parameters, in the temperature range 150 K to 500K is analyzed. It is proved that the high spins bipolarons are not contributed to the ESR spectrum and that the resonance spectrum does not contain contributions due to extremely high conducting islands, with lengths of the order of at least 1micron. From the temperature dependence of the double integral of the resonance line, it is concluded that, the blends exhibit an almost pure paramagnetic behavior and that at short times physical processes control the behavior of these blends. At long times (102 to103 hours), the resonance spectrum is drastically reduced due to the consumption of free electrons in the chemical reactions involved by the degradation processes occurring mainly in PVC. A stationary value is reached for storage times of about 2500 hours, in air, at room temperature.

Organic semiconductors are of continued interest for low-cost display drivers and logic elements. Field-effect transistors (FETs) with organic semiconductor channels have been fabricated in arrays to drive electrophoretic display pixels[1] and polymer dispersed liquid crystals (http://www.research.philips.com/pressmedia/releases/000901a.html). Complementary logic elements and shift registers containing hundreds of organic-based FETs have been produced[2], and high-speed organic circuits have been fabricated on polyester substrates.[3] The source and drain electrodes of individual FETs have been patterned using microcontact printing and inkjet methods[4] to give extraordinary aspect ratios. Inorganic[5] and hybrid[6] materials have been deposited as FET semiconductors using the methods of “organic electronics”. Organic FET channels have been harnessed to demonstrate ambipolar transport[7], chemical sensitivity[8], superconductivity[9], and electrically pumped lasers[10].

We report on the realization and optical properties of a fully evaporated organic microcavity based on LiF-TeOx Distributed Bragg Reflectors and a substituted quinquethiophene as active material. The PL spectrum shows a strong line-width reduction, down to 10 nm, with respect to the bulk spectrum, which is about 110 nm broad. The emission at the mode wavelength shows an enhancement due to the light matter coupling in the optical resonator. The cavity mode shows a splitting for emission angles higher than about 30 degrees which continuously increases with angle up to 99 meV. This feature is observed both in angle resolved PL spectra and in angle resolved reflectance with unpolarized light. A study of angle resolved reflectance with polarized light allows us to attribute this splitting to a polarization effect, rather than to Rabi splitting due to strong coupling in the cavity.

Laser scanning confocal microscopy (LSCM) has been applied to examine the filler particles and their distribution in BaTiO3-polymer composite films. We have measured thin-slice images of the composite films at various depths from the film surface and visualized the submicron size particles and the polymer between them nondestructively. We have found that, although BaTiO3 particles appear to be uniformly dispersed in the composite films when observed under conventional microscope, the particles form clusters at low BaTiO3 concentrations. The lower the concentration the larger the cluster size. The particles appear to be better dispersed in the high concentration composites than at low concentrations.

To develop novel nonlinear dyes for photonic applications, we synthesized a series of transition metal-containing phenylacetylene oligomers and polymers. The optical properties of these compounds were measured by UV/Vis, fluorescence, and flash photolysis experiments. As the number of oligomer units increased, the transition energies decreased. A solvatochromism experiment suggested the fluorescing state was different from the absorbing state. As a group, the spectra of the polymeric versions of these complexes were red shifted from the spectra of the oligomers. The polymeric complexes had less clear trends relating the number of oligomer units to transition energies. A comparison of a low molecular weight and a high molecular weight polymer showed the degree of polymerization caused spectroscopic shifts comparable to the number of phenylacetylene units in the monomer unit.

The methylation of polybenzobisthiazole in dimethylsulfate produces an ndopable polymer which has previously been shown to have high electrical conductivity. The reaction conditions have been shown to chemically degrade the polymer chains, decreasing the molecular weight to about 20% of the original value. A methylationdemethylation scheme has been used to clarify the degree of chain scission.

Non-dispersive and fast electron transport was realized for an amorphous, vapor deposited film of 2,5-bis(2',2''-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene in ambient and inert atmospheres. An electron mobility of 2×10−4 cm2/Vs was measured by time-of-flight at an electric field of 6×105 V/cm. This mobility is more than two orders of magnitude larger than that of the most widely used electron transporter, tris(quinolin-8-olato) aluminum (III), in molecular organic light-emitting devices (MOLEDs). Another silole derivative, namely 1,2-bis (1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl)ethane, exhibits bright fluorescent blue-green light with an absolute quantum yield close to 100 % in the solid state. MOLEDs composed of stacked neat films of these two silole derivatives and a hole transporter show a significantly low operating voltage and an external quantum efficiency of 4.8 %, close to the theoretical limit.

The electrophilic substitution of regioregular poly(3-hexylthiophene) (P3HT) at the 4- position was investigated to produce structurally well defined 3,4-disubstituted poly(thiophene)s. When P3HT was treated with N-bromosuccinimide (NBS) in chloroform at 25 to 50 °C, the 4-hydrogen atom in P3HT is completely substituted by bromine, as indicated by the 1H NMR, 13C NMR and elemental analysis. Similarly, the chlorinated product was obtained using N- chlorosuccinimide (NCS) at room temperature. However, only 85% of the 4-hydrogen atoms were replaced by chlorine and ∼15% of the α-hydrogen atoms on the hexyl side chain were chlorinated. P3HT readily reacts with fuming nitric acid in chloroform at 0 °C to generate a nitrated product with almost 100% substitution at the 4-position. Our preliminary study on the futher functionalizaton of these polymers was conducted on the brominated product. Our results showed that the bromine atom in this polymer could be further substituted with other groups.

We have developed a method for fabricating polymer microstructures based on electric field induced self assembly and pattern formation. A dielectric fluid placed in between to conductive plates experiences a force in an applied electric field gradient across the plates, which can induce a diffusive surface instability and self construction of the fluid surface. This process is exploited for the fabrication of self assembled polymer microstructures as well as replicated patterns through the use of pre-patterned plates or electrodes. We have used silicon wafers and transparent ITO (Indium-Tin Oxide) coated quartz substrates to fabricate the capacitor structures. The bottom silicon plate is spin coated with a 100-200 nm thick polystyrene film. The ITO substrate was placed over the polymer surface at a distance to leave a thin air gap using spacers. For directed pattern transfer, patterned ITO substrates were used. The capacitor setup was heated above the glass transition temperature of the polymer and a voltage was applied across the plates (50-150 Volts), which induces electric fields on the order of 107–108 V/m. The capacitor structure was quenched to observe the structures using optical microscopy and atomic force microscopy. The method described can be used to fabricate a variety of structures in the micron and nanometer scales including bio-fluidic MEMS, polymer optoelectronic devices and patterned templates for nanolithography.

Functionalized aromatic-bis(benzothiazoles) have been synthesized by our group and have shown promise as conductive n-dopable polymers and oligomers. When reduced (n-doped) these materials typically exhibit conductivity on the order of tens of S/cm. Here we examine the material properties of this family of derivatized, conductive aromatic-bis(benzothiazoles). A variety of synthetic approaches have been examined to produce these polymers and oligomers, and will be discussed. Material characterization has been accomplished by spectro-electrochemistry, nuclear magnetic resonance (NMR), electron spin resonance (ESR), Fourier Transform Infrared (FTIR) spectroscopy, and direct current (DC) conductivity.

Two-dimensional image sensor arrays incorporating an organic light sensor are reported, with potential application to digital cameras and x-ray imaging. The 512×512 element array has pixel size of 100 micron, and operates with active matrix addressing using amorphous silicon thin film transistors. The array design allows the use of a continuous layer of the organic sensor material without the need for pixel-level patterning. The sensor is a bilayer comprising a thin generator layer and a thicker hole transport layer. Generator materials benzimidazole perylene (BZP) and hydroxy gallium phthalocyanine (HOGaPc) have been studied, with a tetraphenyldiamine (TPD) transport layer. Both sensors give excellent imaging properties with low leakage current, good charge collection and high spatial resolution.

The charge transport properties in polycrystalline pentacene thin film transistors is investigated. A potential barrier is formed at grain boundaries due charged trapping states. The influence of such grain boundaries on the hole mobility of the devices is analyzed for different grain sizes, trap concentrations, and carrier densities. The results reveal that room temperature mobilities exceeding 0.5 cm2/Vs can be obtained in thin films with large grains as well as in nanocrystalline material. Consequently, single crystal device limits can be reached also by polycrystalline pentacene thin film transistors.

Tunable optical gain is demonstrated, through pump and probe measurements, in spin coated neat films of soluble S,S-dioxide oligothiophenes with different functionalization pattern. The molecular functionalization with alkyl and aryl groups allows us to obtain photoluminescence efficiency up to 70%, good chemical stability, high solubility and tunable gain along the visible range from 470 nm to 660 nm. The gain cross section is up to 9*10-18 cm2. The gain relaxation dynamic is studied through time resolved pump and probe measurements. A comparison with some of the best organic materials for laser application is presented. From these results we conclude that thienyl-S,S-dioxide oligothiophenes are interesting materials for applications to organic lasers and amplifiers.

A very large enhancement of the photoconductivity in pentacene transistors at negative gate voltages is observed. The enhancement is attributed to the separation of electron-hole pairs by the gate field and the consequent slow recombination. The ratio of photoconductivity to dark conductivity is approximately independent of mobility, for samples with a wide range of microstructure. The pentacene films were thermally deposited at different deposition rates and temperatures on silicon thermal oxide. The structure and the morphology of the films were studied by x-ray diffraction measurements and atomic force microscopy, and the influence of the deposition temperature on the morphology and structural properties is discussed. The size of the crystals is correlated with the crystalline bulk phase of the material, which increases with the deposition temperature and the film thickness. The mobility of the transistors increases with the size of the crystallites.

In this paper, 5,5' –bis [ 4'– methyl- ( 2,2'– bipyridin– 4- yl)- ethyl ]- 2,2'– bipyridine (BMBPYBPY), a partially conjugated derivative of oligobipyridine, has been synthesized and found to show strong photoluminescence (PL). Compared with the pyridine-based conjugated polymers, the shortened conjugation length shifts the emission color from green to violet-blue. The effects of morphology on its PL properties have been studied. From its as-precipitated powder state, an emission peak at 418 nm can be observed. However the emission spectra from its diffused states such as doped in KBr, or dissolved in CHCl3, as well as from its amorphous film state fabricated by vacuum evaporation are more complex. Also carried out are preliminary electroluminescent studies. Single layer devices ITO/BMBPYBPY/Al do not emit although current can be observed prominently. Double layer devices ITO/TPD/ BMBPYBPY/Al show emissions both from TPD and BMBPYBPY.

We compare two basic organic FET structures both experimentally and theoretically. By using time resolved analysis we gain insight into the mechanisms affecting the performance of these structures. Using a two dimensional numerical model we focus on the top contact structure and demonstrate the difference between the two structures.

Molecular crystals based on conjugated aromatic molecules have attracted a lot of interest, since their combined electrical and optical properties enable them many technical applicatins. The optical features and the anisotropic electron mobility strongly depend on the crystalline structure of such materials, which itself is determined by the inter-and intramolecular interactions. We investigate those interactions by performing full potential linearized augmented plane wave (FP-LAPW) band structure calculcations accompanied by X-ray [powder diffraction experiments imder hydrpstatoc [ressure up to 50 κbar. In this work we focus on the compounds anthracene and para-terphenyl and report their internal geometry, electronic structure and optical spectra as a functionof pressure.