New linear conjugated porphyrin polymers were synthesized by a palladium-catalyzed cross-coupling reaction of [5,15-bis(ethynyl)-10,20-bis (mesityl)porphyrin]zinc and diiodobenzene derivatives. Enhanced solubility of the conjugated porphyrin polymers was achieved by attachment of long alkyl ether or dialkyl amide groups to the aryl moiety, resulting in unambiguous characterization by 1H NMRLR, GPC, UV-Vis and fluorescence spectroscopies. The introduction of alkyl ether (electron donor) or dialkyl amide (electron acceptor) results in significant modulation of the electronic properties of the conjugated porphyrin polymers due to strong electronic coupling. The spectroscopic and electronic characterization of these materials provides for comparison to earlier preparations of ethynyl bridged conjugated copolymers in which electronic coupling was substantially weaker.

In order to realize a high-sensitivity, low temperature operable NO2 gas sensor, thin films of at-form copper phthalocyanine (α-CuPc) have been deposited by vacuum sublimation. In this study, we have attempted to improve the gas-sensing characteristics through a modification of the film microstructure. Firstly, the gas sensitivity is remarkably increased by an insertion of higher-sensitive layer (vanadyl Pc film) between the α-CuPc film and the glass substrate in the low gas concentration range. Secondly, a reversibility in cycles of gas doping and dedoping is improved by film deposition on hydrofluoric acid-treated substrate. It is found from atomic force microscope analyses that this phenomenon may be closely related to a modification of the film microstructure.

The asymmetrical forward versus reverse - bias DC electrical conductivity (macroscopic and also nanoscopic) through Langmuir-Blodgett multilayers and monolayers of γ-(nhexadecyl) quinolinum tricyanoquinodimethanide, C16H33Q-3CNQ (1) is attributable to rectification of electrical current by a single molecule.

Stable, conductive films of poly(3-alkylthiophenes) (P3ATs) can be obtained from a single chloroform based solution containing polymer, oxidant (silver triflate), and an oxidantcoordinating ligand (pyridine). Casting of this solution, followed by evaporation of the ligand, results in an electronically conductive film which is more stable and, notably, in the case of thick films, is free of the cracking which often results from swelling of the films during the doping process. This technique, coined solvato-controlled oxidative doping, results in films possessing enhanced stability compared to those oxidized by conventional dopants such as ferric chloride. Also, these silver-containing films are much more stable than those electrochemically doped with the triflate anion. Thus, the presence of metallic silver in the doped film has a profound effect on the stability of the conducting form.

The synthesis of poly(2,5-thienylene vinylene) and poly(4,7-thianaphthene) by vapor deposition polymerization is presented. 2,5-Di(bromomethyl)thiophene was subjected to vapor phase pyrolysis at 550°C to form a reactive intermediate. Upon condensation, the reactive intermediate polymerized spontaneously at a temperature higher than -25°C to produce poly(2,5-thienylene vinylene). The obtained poly(2,5-thienylene vinylene)s were fractionated into THF soluble and insoluble fractions. The number average molecular weights of the THF soluble fractions range from 1500 to 4000 as determined by GPC measurements. The obtained polymer shows no glass transition and melting point on the DSC scans. Doping of a poly(2,5-thienylene vinylene) film with I2 vapor led to a conductivity of 1 × 10−4 S c−1. In the second part of this study, 2,3-diethynylthiophene was subjected to vapor phase pyrolysis at 300°C to yield a reactive intermediate, 4,7- dehydrothianaphthene. Upon condensation, the obtained 4,7-dehydrothianaphthenene was polymerized spontaneously at a temperature higher than -25°C to produce poly(4,7-thianaphthene). The obtained poly(4,7-thianaphthene) was insoluble in common laboratory solvents and shows also no melting point and glass transition on the DSC scans.

Although it is well known that the oxidation state of polyaniline is an important characteristic, there are few reports of its influence on the development of morphology and electrical properties in fibers and films. In this work, differential scanning calorimentry is used in conjunction with measurements of temperature dependence of conductivity and thermoelectric power to elucidate the intimate relationship between structure and properties. By increasing the amount of chemical reduction of polyaniline solutions, films are prepared which exhibit a thermal transition between 300 and 385 °C, indicative of melting. Increasing the chemical reduction also increases the conductivity of iodine doped films. The most reduced film exhibited a semiconductor transport mechanism, while the other films could be modeled with a quasi-one dimensional variable range hopping mechanism. The temperature dependence of conductivity also showed increasing order for increasing reduction, consistent with the DSC results.

In the present study, conductive binary and ternary blends of PANI with thermoplastic polymers were prepared by melt processing.

The binary blends' investigation focused on the morphology and on the resulting electrical conductivity. Generally, the level of interaction between the doped PANI and the matrix polymer determines the blend morphology, and thus, its electrical conductivity. The morphology of a conductive network is described by a primary structure of small dispersed polyaniline particles, interconnected by secondary short range fine fibrillar structure. In blends containing a semicrystalline matrix the doped PANI network locates within the amorphous regions, leading to a reduction of the percolation concentration.

The ternary blends' investigation focused on a system containing two co-continuous immiscible thermoplastic polymers and PANI. The PANI is preferably located in one of the matrix polymers. This concentration effect enables high electrical conductivities at low PANI contents.

We demonstrate that polyaniline (PANI) dissolved in dodecyl benzene sulphonic acid (DBSA) shows thermoreversible gelation. The dissolution has been performed in formic acid which allows particle-free complexes according to optical microscopy. Below the gelation temperature the materials are rubber-elastic in compression experiments, the storage modulus G' does not essentially depend on frequency, and the samples are electronically conductive. Above the gelation temperature, G' indicates flow-like behavior and drastically lower ionic conductivity is observed. These results suggest reversible, i.e. fusible, network formation. The properties are compared with gels consisting of camphor sulphonic acid (CSA) doped PANI dissolved in m-cresol which are poorly thermoreversible.

This contribution describes the use of layer-by-layer self-limiting siloxane chemisorption processes to self-assemble structurally regular multilayer organic LED (OLED) devices. Topics discussed include: 1) the synthesis of silyl-functionalized precursor molecules for hole transport layer (HTL), emissive layer (EML), and electron transport layer (ETL) self-assembly, 2) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron balancing in a vapor-deposited device, 3) the microstructure/chemical characterization of HTL self-assembly using a prototype triarylamine precursor, 4) fabrication and properties of a hybrid self-assembled + vapor deposited two-layer LED, 4) fabrication and properties of a fully self-assembled two-layer OLED.

Atomic Force Microscopy (AFM) and related techniques are used to investigate the morphology of diblock copolymers. We focus on compounds containing a conjugated segment, polyparaphenylene, associated to a polymethylmethacrylate or a polystyrene block. The influence of the presence of the conjugated segment on the microdomain morphology is analyzed as a function of chain composition. Separate microdomains are observed on the surface of thin films by means of phase-detection imaging tapping-mode AFM. Their shape and size are interpreted in terms of molecular aggregation, with the help of molecular dynamics calculations.

The layer-by-layer growth of film structures consisting of sequential depositions of oppositely charged polymers and macrocycles (ring-shaped molecules) have been constructed using molecular self-assembly techniques. These self-assembled thin films were characterized with X-ray reflectometry, which yielded (1) the average electron density, (2) the average thicknesses, and (3) the roughness of the growth surface of the self-assembled multilayer of macrocycles and polymers. These observations suggest that inorganic-organic interactions play an important role during the initial stages of thin-film growth, but less so as the thin film becomes thicker. Optical absorption techniques were also used to characterize the self-assembled multilayers. Phorphyrin and phthalocyanine derivatives were chosen as the building blocks of the self-assembled multilayers because of their interesting optical properties.

High performance thin-film transistors (TFT) made of conducting oligomers are obtained when the organic films are well ordered at a molecular level. Highly ordered films are obtained provided that oligomers have a sufficient mobility on the substrate surface during film formation. One possible way to fulfill such a condition is to evaporate oligomers on heated substrates [1,2]. In this work, we suggest that a high surface mobility is obtained by a chemical functionalization of the silicon dioxide surface, and the corresponding improvements of the TFT performances are evidenced. A self-assembled monolayer of octadecyltrichlorosilane (OTS) was deposited on the SiO2 by chemisorption from solution before the evaporation of sexithiophene film. Room temperature current-voltage measurements indicate that the presence of the OTS monolayer improves TFT performances : threshold voltage is decreased, subthreshold slope is decreased, a high current ratio Ion/Ioff is obtained for a reduced gate voltage excursion, the fieldeffect mobility is slightly increased. We have also fabricated and characterized a nanometer scale organic FET (gate length = 50 nm) made of 6T films and only with a self-assembled monolayer as the insulating film between the degenerated silicon substrate (gate) and the conducting channel (no thick SiO2, we call it « oxide-free » organic FET). Performances of this nanometer size organic FETs are the following : subthreshold slope of 0.35V/dec, threshold voltage of −1.3V, effective mobility of 2×10−4 cm2/V.s.

We report on a method to investigate the inhomogeneous distribution of an electric dc field in multilayer polymer stacks. In situ electroabsorption (EA) measurements are applied in order to estimate the local electric fields in double layer polymer films. The observed time dependent behaviour is compared with a model equivalent circuit. The results indicate that besides the relation of ohmic resistivities and capacities of the different polymer layers in the investigated systems also the influence of the electric properties of polymer/electrode and polymer/polymer interfaces must be considered.

We have developed a general strategy for the construction of ordered nanocomposites with hexagonal symmetry, using polymerizable lyotropic (i.e., amphiphilic) liquid crystals. In this approach, self-organizing lyotropic liquid-crystalline monomers are used to form an ordered template matrix in the presence of a reactive hydrophilic solution. Subsequent photopolymerization to lock-in the matrix architecture, followed by initiation of chemistry within the ordered hydrophilic domains to afford solid-state fillers, yields the anisotropic nanocomposites. Composites have been synthesized that have a regular hexagonal arrangement of extended poly(p-phenylenevinylene) (PPV) domains, with a regular interchannel spacing of 4 nm. The photoluminescence of these materials is significantly altered from that of bulk PPV. The dimensions of these nanocomposites can be tuned by varying the size of the hydrophobic tails and/or the nature of the counterion associated with the hydrophilic headgroup of the monomer.

New thiophene oligomers and fused ring compounds have been designed and synthesized with the aim of maximizing semiconductor mobility in thin film transistors (TFTs) while allowing for liquid phase processability. Thiophene hexamers with alkyl side chains of various lengths, some with an ether oxygen embedded in the chain, were synthesized, as were derivatives of the novel heterocycle anthradithiophene. Mobilities of the vaporphase-deposited films ranged from 0.01 cm2/Vs for the hexamers to 0.15 cm2/Vs for dihexylanthradithiophene. The latter is the highest mobility yet reported for a polycrystalline film. Cast films of some of these compounds from solution gave mobilities within factors of 2–10 of the corresponding values from gas-phase-deposited films.

Extremely thin, single crystals of sexithiophene (6T), 2–14 nm thick and 2–5 μm in length and width, can be grown an flat gold substrates by thermal evaporation. The thickness dimension corresponds to 1–6 monolayers (ML) of 6T molecules arranged with their long axes nearly perpendicular to the substrate. We have measured the current-voltage (I-V) characteristics through the thickness of these crystallites, after doping them with iodine, using conducting probe atomic force microscopy (CPAFM). The I-V traces are linear in the ±50 mV regime. The conductance (I/V) of the doped 6T crystals does not decrease monotonically with increasing thickness as might be expected, but instead has a maximum at 3 ML thickness, and we discuss several possible explanations for this observation.

Since the early 90's, much research has focused on the photoluminescence (PL) and electroluminescence (EL) properties of conjugated polymers, because of their potential application as emitting layer in EL devices. The introduction of uniaxial molecular orientation into films of luminescent polymers was naturally found to yield structures that emit polarized light. Rather surprisingly, the photoluminescence properties of oriented, conjugated polymers have attracted substantially less attention, especially from an application point of view. In this paper we report the fabrication of highly-polarized photoluminescent polymer films based on poly(2,5- dialkoxy-p-phenyleneethynylene)s (PPE), and their use in a new family of liquid crystal displays (LCDs). As one relevant example, a back-lit twisted-nematic configuration of an LCD was built, in which one of the absorbing polarizers was replaced by a polarized PL film, characterized by a dichroic ratio in excess of 70. Such devices can exhibit a substantial improvement in brightness, contrast and viewing angle, since the polarized photoluminescent films can combine two separate features, i.e. the functions of a polarizer and an efficient color filter.

Research into electro-optic effects in nanophase polymer dispersed liquid crystal (PDLC) materials has highlighted their potential as materials for a new class of tuneable filters. The structures, based on UV cured phase separated composites, contain liquid crystal both as discrete nano-scale droplets, and as material dissolved in the polymeric host. The essential difference between these materials and more conventional PDLC's is the scale of the refractive index inhomogeneity which is considerably smaller than the wavelength of visible light. Based upon effective medium approximations, the composite thus acts as a single isotropic medium, whose average refractive index is dependant on the level of applied electric field. Tuneable filters have been fabricated using the composite material for use in the visible spectral band.

Thin films of self-assembled supramolecular grid structures were prepared by electrochemical deposition. The surface structure of the films was determined by electrochemical insitu scanning tunneling microscopy (STM), revealing ordered monolayers of the grid molecules on a Au( 111) surface. The electronic structure of the films was studied by photoelectron spectroscopy. The thin films show semiconducting behavior with an insulating gap of ca. 2.5 eV. The size of insulating gap can be reduced to 0.5 eV by doping the films with additional Cd2+ ions, which is in agreement with molecular orbital calculations. Additionally, conductivity measurements were performed. By doping of the thin films, their conductivity could be increased by several orders of magnitude. This is due to additional electronic states in the insulating HOMO-LUMO gap, which is confirmed by UPS measurements.

The goal of this project is to develop, fabricate, and test advanced optical materials for potential applications to real-time holography based on liquid crystalline polymer hydrogels. In this project, we are investigating the feasibility of increasing holographic capacity and lifetime by coupling a photochromic spyropyran dye to in a liquid crystalline polymer in which cholesteric order has been ‘captured.’ ‘Capture’ is being approached using a unique in-plane poling process with the helical polypeptide poly(α-benzyl-L-glutamate), PBLG, a biopolymer which is capable of maintaining cholesteric order in a liquid crystalline state. Subsequent in situ crosslinking of this aligned biopolymer is projected to offer increased birefringence of the host in the writing of a hologram. Given that a key issue is the magnitude of the real component of the refractive index, increasing the bireflingence may be a useful approach. In writing the hologram, the liquid crystals (LC's) go from isotropic to an ordered dispersion, a property which can be captured via crosslinking to improve holographic lifetime. In the following, the characterization of an aligned host LC system based on the biopolymer poly(α-benzyl-L-glutamate), PBLG, is presented. Inplane alignment is shown to depend on a number of variables, most notably the choice of solvent, polymer molecular weight, and field strength. The results show that optimal alignment of the PBLG LC is achieved with a 2.5% (w/w) concentration of a 118kD biopolymer in methylene chloride in an applied field of 10 kV/cm. Subsequent work will exploit this system as a host for a spiropyran dye for improved holographics.