A series of substituted phenylene ethynylene diazonium salts were prepared from the corresponding anilines by the action of nitrosonium tetrafluoroborate in sulfolane-acetonitrile solvent. Formation of self-assembled layers of the diazonium salts in acetonitrile solution was demonstrated on Au, Cu and Pt surfaces. The self-assembly rate of the diazonium salts was found to be markedly dependent on the electron withdrawing character of the substituents attached to the aromatic rings.

On the subphase, which contains Cd2+ and Mg2+ ions, two-dimensional (2D) J-aggregate crystallites of merocyanine dye molecules exhibit a thermochromic transition. The J-aggregate absorption band of the low (LT) and high temperature (HT) phases are located at 620 and 595 nm, respectively. In order to clarify the in-plane structure of the 2D J-aggregate crystallites, grazing incident X-ray diffraction measurements were performed on the Langmuir-Blodgett multi-layers which consisted of the monolayers of LT and HT phases. It was revealed that the in-plane arrangement of the dye molecules is slightly different in the J-aggregate crystallites of LT and HT phases.

We report synthesis, and optical properties, of dihexyl-fluorene-co-3,4-ethylene- dioxythiophene (DHF-co-EDOT) random copolymers obtained from mixture, in various ratios, of the two corresponding dibrominated monomers. Infra-red studies coupled with 1H NMR clearly indicate, as expected, that the amount of each monomer unit in the materials is strongly connected to the feed composition. It clearly appears that even a low 3,4-ethylene- dioxythiophene (EDOT) content, i.e. 15 %, within a poly(dihexyl fluorene) main chain induces significant changes in the electronic properties of the corresponding material, denoted COPO1, compared with the fluorene-based homopolymer. Higher EDOT contents lead to less soluble copolymers which are not or only to a slight extent suitable to investigate their use as luminescent semiconducting ∼-conjugated materials in Organic Light-Emitting Diodes (OLEDs). Green organic light emitting devices based on COPO1, exhibiting no significant spectral evolution, have been demonstrated and showed improved hole-injection properties when compared to the ones using poly(dihexyl fluorene). The use of an additional PEDOT- PSS layer on the ITO anode has also been investigated leading to improved operating lifetime.

We present an exact classical solution to the problem of dipole emission in a planar multilayer organic light-emitting diode (OLED) device. The inputs to the model are the photoluminescence and quantum yield of the emitter material, and the device layer thicknesses and indices of refraction. The results of the model are applied to predicting the radiant intensity of OLEDs as a function of varying device layer thickness. It is shown that the calculated radiances are in excellent agreement with the data; this suggests that at constant current the variation in electroluminescence caused by modifications of the layer thicknesses can be completely accounted for by optical effects. Finally, we present results (for positions both internal and external to the diodes) for the Poynting power distribution from a randomly aligned dipole in the emission layer.

In this paper, the vibrational FT-Raman spectra obtained at different anodic potentials chosen in the oxidation and reduction branches of the voltamperometric waves of two α,α'-sexithiophenes end capped with n-hexyl and n-thiohexyl groups are investigated. In order to analyze the evolution of the atomic charges and bonth lengths on going from the neutral to the doped species some theoretical calculations have been carried out.

Tris(8-hydroxyquinoline) aluminum (Alq3) based organic light emission diodes (OLED) have been a focus of material research in recent years. One of the key issues in searching for a better device performance and fabricating conditions is suitable electron-injection materials. We have investigated the energy alignment and the interface formation between different metals and Alq3 using X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). The interface is formed by depositing the target cathode material, such as Ca, Al or Al/LiF, onto an Alq3 film in a stepwise fashion in an ultrahigh vacuum environment. While the UPS results show the work function and vacuum level changes during interfaces formation, implying a possible surface dipole layer, XPS results show a more detailed and complex behavior. When a low work function metal such as Ca is deposited onto an Alq3 surface, a gap state is observed in UPS. At the same time, a new peak can be observed in the N 1s core level at a lower binding energy. These results can be characterized as charge transfer from the low work function metal to Alq3. The shifting of core levels are also observed, which may be explained by doping from metal atoms or charge diffusion. These interfaces are drastically different than the Al/Alq3 interface, which has very poor electron injection. At the Al/Alq3 interface there is a destructive chemical reaction and much smaller core level shifts are observed. Based on detailed analysis, energy level diagrams at the interface are proposed.

In this work, the fabrication and performance of thin film optical chemical sensors based on the fluorescence quenching of indicator molecules by several analytes such as organic nitro compounds or metal ions are described. To fabricate the sensors, a fluorescent molecule, 1- hydroxypyrene-3,6,8-trisulfonate or pyrene methanol, was covalently incorporated into poly(acrylic acid) (PAA) and subsequently the polymers were assembled with a polycation employing electrostatic layer-by-layer self-assembly into thin film structures. Fluorescence intensities decreased with increasing concentration of analytes. Quenching behavior follows Stern-Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness and emission intensity was observed with increase in number of bilayers deposited in all multilayer films.

This paper illustrates the use of a high resolution form of rubber stamping, known as microcontact printing (μCP), for patterning plastic active matrix drive circuitry designed for electronic paper. The high resolution (∼1 [.mu]m) of the printed elements, the large area coverage (∼1 sq. ft.) and the good electrical performance of these systems suggest that the methods, materials and processing sequences may be attractive for realistic applications of plastic electronics.

We report the interface formation between silver (Ag) and pentacene, an organic material used as an active material in organic thin-film transistors, using x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). XPS results indicate that silver does not chemically react with pentacene regardless of the deposition order. We see that neither pentacene nor silver exhibited simple layer by layer growth when deposited on the other. UPS results show that a dipole forms as pentacene is deposited on silver.

Enhanced electroluminescence (EL) from vapor deposited p-sexiphenyl (6p) layer has been observed utilizing heterostructure of p-sexiphenyl emissive layer and N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) hole transporting layer. The EL device consists of an indium-tin oxide (ITO) anode, a hole transporting layer, an emissive layer, and a magnesium containing silver cathode. A heterostructure device with 50 nm-thick p-sexiphenyl and 60 nm-thick TPD shows the enhanced emission from the p-sexiphenyl emissive layer. The electroluminescence from the device shows the emission peak centered at 420 nm. The p-sexiphenyl/TPD heterostructure device emits 2 orders of magnitude higher intensity than the conventional single layer of p-sexiphenyl device. The mechanism of enhanced emission from the heterostructure device has been discussed utilizing energy band diagrams of these materials.

Cyclic voltammetry (CV) was used to study the reduction potentials of 2,5- di(ethynylphenyl)-4-nitroaniline and 2,5-di(ethynylphenyl)nitrobenzene. Although no absolute reduction potentials can be used in the correlation between solution (CV) and solid state (nanopore) embodiments, each CV plot showed two reductions. The first and second reduction might correspond to switching events of recently reported molecular electronic devices in a nanopore. Cyclic voltammetry results are also reported for other potential molecular scale electronic devices.

Silica aerogels prepared by sol-gel methods with supercritical drying process have transparency and extremely low refractive index which is not available in any other materials. This extraordinary refractivity is expected to present some new features as an optical material. Ordinarily, coupling-out efficiency of surface-emissive light sources has been assumed to be low. It is due to the losses organized from internal reflection of emitted light at the air-glass interface and dissipation during wave-guiding propagation within the substrate.

However, when material that has extremely low refractive index is inserted between a thin luminescence layer and glass substrate, almost all the light from the luminescence layer can efficiently couple out to air passing through the glass substrate. In this report, we introduce a silica aerogel film as a low refractive index material for surface-emissive devices, such as photoluminescent and electroluminescent device. In the experiments, the photoluminescence intensity of Alq3 through the silica aerogel layer was twice as large as that of the glass substrate without the silica aerogel film. Moreover, we formed a new substrate which contained a transparent electrode on the silica aerogel film. Using this substrate, we fabricated the OLED and observed the disappearance of wave-guiding propagation within the glass substrate.

The semiconducting-polymer/injecting-electrode heterojunction plays a crucial part in the operation of organic solid state devices. In polymer light-emitting diodes (LEDs), a common fundamental structure employed is Indium-Tin-Oxide/Polymer/Al. However, in order to fabricate efficient devices, alterations to this basic structure have to be carried out. The insertion of thin layers, between the electrodes and the emitting polymer, has been shown to greatly enhance LED performance, although the physical mechanisms underlying this effect remain unclear. Here, we use electro-absorption measurements of the built-in potential to monitor shifts in the barrier height at the electrode/polymer interface. We demonstrate that the main advantage brought about by inter-layers, such as poly(ethylenedioxythiophene)/poly(styrene sulphonic acid) (PEDOT:PSS) at the anode and Ca, LiF and CsF at the cathode, is a marked reduction of the barrier to carrier injection. The electro- absorption results also correlate with the electroluminescent characteristics of the LEDs.

The preparation of double-cable polymers, which consist of a hole conducting conjugated chain carrying pendant electron accepting/conducting moieties, is a promising strategy to prevent donor/acceptor phase segregation and to achieve defined microscopic structure in organic bulk heterojunction solar cells. In this paper we report the electrochemical synthesis and the investigation of a double-cable consisting of a polythiophene backbone bearing, via covalent bonds, electron accepting tetracyanoanthraquinodimethane (TCAQ) type moieties. Electrochemical studies and UV- VIS absorption spectroscopy reveal, that in dark, the polythiophene chain and the TCAQ moieties retain their individual ground-state properties. Upon illumination photoinduced electron transfer occurs, which is studied by photoinduced VIS-NIR absorption spectroscopy.

Unimolecular rectification, previously reported between oxide-bearing electrodes, was detected between oxide-free Au electrodes for a Langmuir-Blodgett monolayer of the zwitterionic D+∼-A- molecule hexadecylquinolinium tricyanoquinodimethanide, C16H33Q-3CNQ. The top gold electrode was deposited from a Au vapor pre-cooled by multiple collisions with Ar atoms. The maximum rectification ratio is 27.5 at 2.2 Volts (the average rectification ratio is 7.55). The currents are as large as 9.04 × 104 electrons molecule-1 s-1. The result reinforces previous work with oxide-bearing Al electrodes, but the currents with Au electrodes are larger by three to five orders of magnitude.

Solid-state light-emitting devices have been fabricated by using blends of a binuclear complex of ruthenium(II), with both 1,6-bis[4-(4'-methyl-2,2'-bipyridyl)]hexane and regular 2,2'-bipyridine ligands and lithium trifluorosulfonate/18-crown-6 ether complex. Orange light is emitted for low turn on voltage, i.e. ranging from 2.5-3V, close to the electrochemical gap of the binuclear Ru-based complex. However, the device performances decrease upon operation within few hours. We report that the main degradation process involved in the decrease of the light emission intensity during device operation is based on an electrochemical degradation of the ruthenium complex, mainly a loss of capacity on the reduction side.

Carrier dynamics properties in swollen poly(octylthiophene) gels are investigated via their radiative and non-radiative recombination rates (Wr and Wnr respectively) as a function of their swelling ratio (Q). Photoluminescence decay time (τ, in the picosecond range) and luminescence quantum efficiency (QE) are found to strongly increase with Q. This implies that Wr increases and Wnr decreases as Q increases; such a result cannot be understood if one accounts only for the well-known dilution effect observed for organic dyes. Our interpretation is that the enhanced carrier transport due to the increase of interchain interactions observed upon deswelling induces a separation of carriers. Then, these latter present an increased probability to find non-radiative traps. Variation of the conductivity versus Q in doped gels is also discussed.

Multilayer nanocomposite films have been prepared from exfoliated aluminosilicate/coumarin dye complex through layer-by-layer self-assembly using cationic polyelectrolytes. Coumarin dye molecules were intercalated into the layered aluminosilicate by an ion exchange reaction. Particles of the hectorite/dye complex were delaminated by extensive shaking and sonication of their water suspension into 2∼3 nm-thin silicate layers with molecules of the dye adsorbed on their surface. Atomic force microscopy and transmission electron microscopy data are in agreement with such a model. Ultrathin multilayered films were prepared using layer-by-layer self-assembly from the aluminosilicate platelets and a cationic polyelectrolyte polydiallyldimethylammonium chloride (PDAC). Linear build-up of the films up to 20 cycles was demonstrated and investigated using absorption spectroscopy and spectrofluorometer. The resulting transparent films have exhibited strong characteristic blue-green fluorescence due to coumarin dye molecules adhered to the exfoliated hectorite platelets.

Ionically self-assembled monolayers (ISAMs) have recently been shown to spontaneously exhibit a polar ordering that gives rise to a substantial second order nonlinear optical (NLO) response. Here, the deposition of ISAMs has been studied in situ via second harmonic generation (SHG). We show that the adsorption and ordering of a noncentrosymmetric nonlinear optical polymer is constant over a wide range of concentrations. Upon immersion in the NLO-active polyelectrolyte solution, the SHG rises sharply over the first minute. Immersion in the NLO-inactive partner polyelectrolyte leads to a reduction in the SHG signal. Furthermore, when the film is removed from the NLO-active solution and allowed to dry, the SHG increases rapidly as the water evaporates. These studies provide greater understanding of the processes by which noncentrosymmetric order is formed in ISAM films and allows design of improved self- assembled nonlinear optical materials.

We developed a method to predict the charge transport (CT) type (hole or electron) in molecular materials that uses molecular orbital calculations. The hole-and-electron-mobility ratios of molecular materials were calculated based on molecular structural reorganization energies in a charge hopping process. The CT types predicted from the calculated mobility ratios agreed with those experimentally obtained in seven of the eight model molecules.