We report the fabrication and properties of three-, four-, and five-layer electroluminescent devices fabricated from light emissive N-based heterocyclic novel polymeric derivatives of PPP and PPV with which they are isoelectronic. They include poly(pyridine vinylene), (PPyV), and poly(2,5-dihexadecanoxy phenylene vinylene pyridyl vinylene), (PPV.PPyV). Some of the devices operate in both forward and reverse bias modes thus enabling operation in an ac mode. One type of device has the general construction: M/I/polymer/I/ITO where M equals Cu or Al, I equals polyaniline (emeraldine base, EB) or poly(3-hexylthiophene), (P3HT), and polymer equals PPV.PPyV. Under low frequency ac (sinusoidal) driving, light pulses with twice the driving frequency were observed in a device where M equals Al or Cu, I equals EB and polymer equals PPV.PPyV; and in a device where M equals Al, I equals P3HT and polymer equals PPV.PPyV. In the latter device the electroluminescence spectrum in the reverse bias mode differed from that in the forward bias mode. It was also shown that blends of PPyV in Nylon 6,6 exhibit a lower operating voltage than the pure polymer.

We have studied the photoresponse and electroresponse of light emitting diodes (LEDs) made from a variety of soluble conducting polymers sandwiched between indium tin oxide (ITO) and metals including calcium, aluminum and copper. Under illumination all freshly prepared LEDs exhibit relatively large photoconductive current-voltage (I-V) responses which cross the dark I-V curve at a forward-bias voltage V₀ that scales with the difference in the work functions between the ITO and metal electrodes. This causes the open-circuit voltage to easily saturate at V₀ and consequently to be temperature independent, in contrast to the properties of the photovoltaic effect exhibited by conventional Schottky-barrier type photodiodes. Some LEDs, prepared under less ideal conditions exhibit I-V curve, electroluminescence (EL) intensity-voltage (I_EL-V) curve, an EL spectra identical in forward and reverse bias. The I-V curves were also symmetric under illumination, with I approximately equal to 0 at V equals 0, suggesting a negligibly small internal electric field. These diodes are discussed in relation to Fermi-level pinning at defect states in the interfaces between the polymer and the electrodes.

Mobility of positive polarons in poly(phenylene vinylene), PPV, measured by time of flight methods, rages from approximately 10^-3 to 10^-7 cm²/Vs at room temperature. The large range indicates that the materials are disordered. Both disorder and polaronic effects contribute to the activation energy for hopping, but in PPV the polaronic effects are less important and to first approximation may be neglected. Comparison of the observed field dependence of mobility for two sets of samples with the results of Monte Carlo simulations leads to the conclusion that the contribution of site energy disorder is predominant in one case, but comparable to that of orientational disorder in the other. We suggest that the most important factor leading to the wide range of mobility values is different distributions of conjugation lengths, resulting from different choices of precursor polymer and conversion protocol.

The photoluminescence (PL)-, electroluminescence (EL)- and conductivity ((sigma) )-detected magnetic resonance of poly(p-phenylene vinylene) (PPV), poly(p-phenylene ethynylene) (PPE), and PPV/CN-PPV LEDs is reviewed and discussed. In the PPV- and PPE-based LEDs the polaron resonance is EL-quenching, but in the PPV/CN-PPV bilayer diodes it contains both EL-quenching and enhancing components. While the (sigma) -detecting polaron resonance is invariably quenching in the PPV devices, in some of the PPE-based LEDs it is (sigma) -enhancing. The PL-enhancing resonance is attributed to nonradiative recombination of trapped polaron pairs, which reduces their population and consequently the rate at which they nonradiatively quench singlet excitons; the EL-enhancing resonance is tentatively assigned to the same mechanism in the CN-PPV layer, but other mechanisms are not ruled out. Interchain coupling, some defects induced by structural disorder, and sites adjacent to dopant molecules (e.g., C₆₀) apparently enhance the generation of these trapped polarons as well as intersystem crossing from the singlet to the triplet manifold. The EL- and (sigma) - quenching resonances are attributed to the fusion of like-charged free polarons to bipolarons, which is also suspected to be induced by disorder and/or impurities. The LEDs also exhibit half-field EL- and (sigma) -detected triplet exciton resonances. Triplet-triplet fusion to singlets and the role of triplets as quenching sites for singlet excitons are discussed as possible mechanisms leading to the triplet resonances.

During the past five years, (pi) -conjugated organic polymers, such as poly[p-phenylene vinylene] (PPV) and polythiophenes, have become attractive alternatives to semiconducting materials as light-emitting diodes. Various approaches to tuning emission wavelength have been proposed, such as controlling the conjugation length by employing polymer oligomers or via steric effects in the fully conjugated polymers, or by using substituent effects to fine-tune the band gap. In the present study, we demonstrate that these features can be designed into copolymeric structures in which (pi) -conjugated emitters of carefully controlled length alternate with various non-emitting flexible spacers which improve solubility and thus processibility. These copolymers display predictable emission characteristics which can also be fine-tuned by incorporation of electronic substituent effects.

Symmetrically configured ac light-emitting (SCALE) devices based on conjugated polymers utilizing indium-tin oxide (ITO) and aluminum as electrodes have been demonstrated recently. Here we report the fabrication of SCALE devices using a more stable high workfunction metal, such as gold, as a charge (both electron and hole) injection electrode. Also, a variation of such devices in which the electroluminescent polymer, instead of being separated from the insulating polymer, is dispersed in the insulating polymer to form a unified emitter-insulator is reported. These devices emit light in both forward and reverse dc bias with symmetric current- voltage characteristics. Under low frequency ac (sinusoidal) driving voltage, light pulses with double the driving frequency are observed. A model is proposed to account for the device operation.

Electroluminescence efficiency and current-voltage characteristics of conjugated polymer poly(3-octylthiophene) (P3OT) light emitting diodes (LEDs) are discussed in terms of the presently popular band model. Devices were studied in forward and reverse mode of operation, with different types of top contacts to show the dominance of the top electrode workfunction on device properties. Changing the workfunction of the top contact with only 0.9 eV (from Au to Al) results in a change in the preferred current direction, corresponding to a change in the rectification ratio of the diodes of effectively 6 orders of magnitude. When Au is used as a top electrode, no electroluminescence was observed, because the barrier for electron injection is too high. The observation of light emission in the reverse mode of operation for ITO/P3OT/Al is a result of direct carrier tunneling into the transport bands at high electric fields.

Three complementary approaches to the construction of electric field polable high-Tg (glass transition temperature) polyimides and polyureas as second-order NLO materials are discussed. In the first approach, copolymerization of bismaleimides with o,o'- diallylbisphenol A followed by functionalization with high-(beta) NLO chromophores using a Mitsunobu procedure yields, after poling and curing, a series of heavily crosslinked chromophoric polyimides with Tg values as high as approximately 260 degree(s)C and (chi) ⁽²) responses as high as 1.0 X 10^-7 esu (42 pm/V at (lambda) _o equals 1064 nm, 1.17 eV). In the second two approaches, copolymerization of the chromophore 4,5-bis(4'aminophenyl)-2-(4'-nitrophenyl)imidazole with bismaleimides or diisocyanates yields polyimides and polyureas with Tg values as high as 292 degree(s)C and partially resonant (chi) ⁽²) values as high as 0.62 X 10^-7 esu (25 pm/V at (lambda) _o equals 1064 nm). It is found that careful attention to the details of curing and crosslinking during poling results in NLO-active matrices exhibiting negligible decay in (chi) ⁽²) on aging in air at 100 degree(s)C for periods of 1000 - 4000 h. The imidazole- based materials exhibit only approximately 10% (chi) ⁽²) decay on aging for 100 h at 200 degree(s)C under N₂.

A joint analysis of recent NLO spectra of polydiacetylene films and crystals is presented, using vibronic contributions in the Condon approximation and (pi) -electronic states from Pariser-Parr-Pople theory. Raman resonances are shown to be corrections to average excitations. An even-parity state above the photoconduction edge is found in two-photon absorption of PDA-PTS crystals and nondegenerate four-wave-mixing spectra of PDA- 4BCMU films. We incorporate linear and resonance Raman spectra in the joint NLO analysis and emphasize the different roles of electronic and vibrational contributions.

We observe a new electroluminescent (EL) peak from a two-layer polymer device, which does not appear in EL spectra of each layer. The polymers of both layers are poly(p- phenylenevinylene) derivative with monoalkoxy substituents, poly(2-methoxy-1,4-phenylene- vinylene, abbreviated as PMPV), but dialyzed for different periods respectively. A new peak is located at 590 nm and has comparable intensity. The origin of this peak is discussed. Absorption and photoluminescence spectra are also measured and device properties show typical diode characteristics.

A major requirement for polymeric electro-optic materials is that they must possess noncentrosymmetric (roughly uniaxial) order of chromophores in the bulk material. Thermodynamic relaxation of this chromophore alignment is prevented by raising the glass- transition temperature of the polymeric materials during the electric-field poling process. This is accomplished by (1) thermal imidization of a poly(amic acid) prepolymer, (2) thermally induced chemical crosslinking of an acrylate-type prepolymer, prepared from chromophores containing differing reactive functionalities, (3) sol-gel processing of alkoxysilane- incorporated chromophores, and (4) thermosetting polyurethane/polyurea materials. Analogs of these chromophores that contain reversible photoactive moieties are attached to the surface of functionalized polystyrene and polyacrolein beads permitting the realization of room temperature persistent spectral hole burning exploiting morphology-dependent resonances. Such resonances provide the basis of wavelength coding for the development of three and four-dimensional high-density optical memories.

Poled guest-host polyquinoline thin films are shown to demonstrate both exceptionally large electro-optic activity and long-term thermal stability. After an initial drop from 45 pm/V to 26 pm/V in the first 100 hours, the electro-optic coefficient r₃₃ at 26 pm/V remained for more than 2000 hours.

The redox switching of some conducting polymers was investigated. Poly(3,4- ethylenedioxythiophene) and two of its alkyl derivatives were investigated in a liquid electrolyte to probe its usefulness as a visible electrochromic device. The other type of device is based upon actively changing the surface conductivity of one active layer of the device using conducting polymer: in one state the surface conductivity is high, in the other state the surface conductivity is low. Switching speed, contrast ratio, and overall lifetime for both devices were determined and discussed.

Materials which possess transparency, coupled with active controllability of this transparency in the infrared (IR), are today an increasingly important requirement, for varied applications. These applications include windows for IR sensors, IR-region flat panel displays used in camouflage as well as in communication and sight through night-vision goggles, coatings with dynamically controllable IR-emissivity, and thermal conservation coatings. Among stringent requirements for these applications are large dynamic ranges (color contrast), 'multi-color' or broad-band characteristics, extended cyclability, long memory retention, matrix addressability, small area fabricability, low power consumption, and environmental stability. Among materials possessing the requirements for variation of IR signature, conducting polymers (CPs) appear to be the only materials with dynamic, actively controllable signature and acceptable dynamic range. Conventional CPs such as poly(alkyl thiophene), poly(pyrrole) or poly(aniline) show very limited dynamic range, especially in the far-IR, while also showing poor transparency. We have developed a number of novel CP systems ('system' implying the CP, the selected dopant, the synthesis method, and the electrolyte) with very wide dynamic range (up to 90% in both important IR regions, 3 - 5 (mu) and 8 - 12 (mu) ), high cyclability (to 10⁵ cycles with less than 10% optical degradation), nearly indefinite optical memory retention, matrix addressability of multi-pixel displays, very wide operating temperature and excellent environmental stability, low charge capacity, and processability into areas from less than 1 mm² to more than 100 cm². The criteria used to design and arrive at these CP systems, together with representative IR signature data, are presented in this paper.

The degradation mechanisms in polyaniline (PANI) thin films polymerized on SnO₂ after a large number of coloration/bleaching voltammetric cycles were investigated using optical and spectroscopic techniques, allowing us to follow the chemical changes related to the degradation. HCl solutions with different pH (0 and 3) were used and the role of the coloration potential was studied. The number and the nature of the polarons in the colored form play a leading part in the polymer stability, and they are modified by the cycling. This point was particularly emphasized here.

An important current need exists for materials that have dynamically controllable signature in the visible through far-IR spectral regions, for applications ranging from signaling, camouflage, and miniature flat panel displays to shutters and wide-spectral electrochromics. Conducting polymers (CPs) are one of the few materials that can afford such dynamic, wide- spectral signature control, while also affording properties such as stability and in many cases, easy fabricability for complex displays. Common CPs such as poly(pyrrole) and poly(aniline) however show poor multicolor capability, and poor transparency and dynamic range (color contrast), together with less than acceptable environmental stability. Besides proper selection of the CP, the key to obtaining controllable, wide-spectral (visible-IR) electrochromism as well as high dynamic range appears to be proper selection and application of dopants. Ashwin- Ushas Corp. has developed a series of poly(aromatic amines) in combination with several novel dopants and dopant combinations to obtain displays and other hardware with very wide multicolor capability, high dynamic range in the IR, and very high cyclability. Colors in the visible range from glass-clear through the rainbow colors to black. Dynamic ranges in the IR are up to 95% for specular and diffuse reflectance. Other properties of interest, such as extended cyclability and optical memory retention, are also excellent.

The electrochromism of polyaniline in the near infrared spectral range is studied. Spectroelectrochemical data are used to construct optically monitored cyclic voltamograms (o- CV). Details of the electrochromic effects are clarified by comparing o-CV with the ordinary current monitored cyclic voltamograms (i-CV). Components of Faradaic currents to the cyclic voltamogram can be resolved by comparing o-CV with i-CV. We discuss molecular designs for modifying the properties of polyaniline. By a template-guided polymerization scheme, we synthesize the double strand polymeric complex of polyaniline. The first strand is a conducting polymer and the second strand is a polyelectrolyte. This molecular complex has the advantage of being more stable, more processable than the conventional polyaniline. The double strand molecular complex offers increased flexibility in molecular design of electrochromic and electroactive polymers.

In this communication we report results obtained in our laboratory on the design, the synthesis, and the characterization of new light-emitting copolymers. We are interested in block copolymers containing well defined conjugated sequences, which give rise to luminescence. Those chromophores, which are (pi) -conjugated oligomers like oligo(phenylenevinylene)s, are linked to each other by non (pi) -conjugated oligomers, for example oligo(silanylene)s, or directly in a non-coplanar way. In such systems color tuning of the luminescence is achieved through precise control of the length of the conjugated blocks and by changing the chemical structure of those blocks. Variations of the chemical structures of both the luminescent and interrupting blocks also give control over properties like flexibility and solubility of the polymers, which are relevant for device fabrication and optimization.

Oriented films of poly((gamma) -benzyl-L-glutamate), PBLG, were prepared by evaporation of solvent from solutions held in electric fields applied parallel to the film surface. Films thus aligned showed non-linear optical (NLO) activity, i.e., second harmonic generation (SHG). Order parameters calculated from FTIR spectra were correlated with second order susceptibility, and the effects of field strength, solution concentration, and molecular weight on these parameters were investigated. Alignment was observed at field strengths as low as 0.8 kV/cm, as indicated by polarized IR spectra. However, the extent of alignment as measured by IR spectra and values of the second order nonlinear susceptibility, X⁽²), depend not only on field strength but also on solution concentration and the polymer molecular weight. Optimum conditions for alignment appear to be with a molecular weight of 118,000 D and a solution concentration of 2.5% (w/w). Dried films show the typical banded structures reported for polymer films oriented by mechanical shearing stresses. We have shown that these structures extend through the dried film as laminae perpendicular to both the film surface and to the field direction.

Extensive gel permeation chromatography coupled with surface structure and mechanical property measurements clearly indicate that polyaniline in the base form has a tendency to aggregate or agglomerate as a result of intermolecular hydrogen-bonding. The aggregation is present in the solid state powder. The degree of aggregation is found to be dependent on the prior history of the base powder material. In solution, the degree of aggregation is found to be dependent on the solvent, concentration, and temperature. As the solvent becomes a better solvent for the base material, the less aggregated is the structure. LiCl complexes the polymer via a 'pseudo-doping' process, thereby disrupting the internal polyaniline hydrogen-bonding and as a result, deaggregates the structure. As the polymer is deaggregated to different levels by a solvent or by LiCl, the individual chains can better be solvated and thus a conformational change occurs. The chains adapt a more expanded coil type of conformation. The degree of expansion depends on the solvation power of the solvent. These morphological changes have a dramatic effect on the surface structure properties of polyaniline as well as on bulk properties such as mechanical properties and UV/visible/near IR absorbance. As the level of deaggregation and subsequent chain extension increases, the surface structure becomes smoother, the glass transition temperature decreases and a significant red shift is observed in the (lambda) maximum of the absorbance. It is also found that the LiCl induced morphological changes result in increased conductivity upon doping polyaniline base with protonic acid.

Conjugated polymers are of great interest due to their unique structure, interesting physical properties, and potential applications in electronic or opto-electronic devices. Recently, the synthesis of soluble and processable conjugated polymers with different functionalities has become an active research area. We have been exploring palladium-catalyzed reactions (the Stille and the Heck reactions) for preparing functionalized, conjugated polymers. These palladium catalyzed reactions have the advantage of mild reaction conditions and high yields. Different types of conjugated polymers with different properties and applications, such as liquid crystalline conjugated polymers, photoactive metalloporphyrin-containing polymers, and conjugated photorefractive polymers have been synthesized.

Polyaniline has been used as the transducer for an optical sensor by monitoring its evanescent wave spectrum in the near- and mid-IR regions as a function of pH. Cladding on silica and chalcogenide fiber optic cores was replaced with thin films of polyaniline. A low energy electronic transition in the near-IR and vibrational transitions in the mid-IR can be used to predict pH. The near-IR transitions have higher signal-to-noise ratios and are more useful for sensing pH. However, changes in the vibrational transitions observed in the evanescent wave spectra suggest extensive changes in chemical groups as a function of pH. The near-IR evanescent wave sensor was converted into a glucose sensor by immobilizing glucose oxidase on the surface of the polymer. The enzyme converted glucose to gluconic acid and the resulting pH change was used to predict glucose concentrations. Standard errors of prediction for the concentration range of 0 to 20 mM were 0.25 mM for distilled water and 0.8 mM for buffer solutions.

We studied conductive polymers as an anti-corrosion coating on 7075-T6 aluminum alloys. A double strand polyaniline molecular complex was used as the coating material. The new double strand polyaniline complex is advantageous compared with the traditional polyaniline by improvements in processability and stability. Potentiodynamic tests show that the coating is effective for protection against corrosion. The results are consistent with a passive film formation protection mechanism. Further data shows the coating provides additional corrosion protection for the metal surface when a scratch is present on the surface, suggesting the coatings have damage resistant properties.

Thiophene oligomers ((alpha) -(alpha) ' linkages) have been intensively studied in past years. In particular, sexithiophenes have been synthesized with a high degree of purity and good crystallinity allowing the fabrication of reliable field effect transistors. When donor- acceptor terminal groups are attached to thiophene oligomers, an anomalous behavior of the fluorescence as a function of the number of rings has been reported. There are experimental evidences of charge transfer suppression for oligomers containing more than four rings. In this work, we investigate the electronic structure of these systems. Geometrical optimizations and spectroscopic features of both ground and excited states are obtained through the use of sophisticated semi-empirical methods. Our results show that charge transfer suppression can be explained in terms of the evolution of the electronic spectrum.

The nonlinear wave equation an be derived from a principle of extreme physical information (EPI) K. This is for a scenario where a probe electron moves through a medium in a weak magnetic field. The field is caused by a probabilistic line current source. Assume that the probability current density S of the electron is approximately constant, and directed parallel to the current source. Both the source probability amplitudes (rho) and the electron probability amplitudes (phi) are unknowns (called 'modes') of the problem. The net physical information K here consists of two components: functional K₁[(phi) ] due to modes (phi) and K₂[(rho) ] due to modes (rho) , respectively. To form K₁[(phi) ], the Fisher information functional I₁[(phi) ] for the electron modes is first constructed. This is of a fixed mathematical form. Then, a unitary transformation on (phi) to a physical space is sought that leaves I₁ invariant, as form J₁. This is, of course, the Fourier transformation, where the transform coordinates are momenta and I₁ is essentially the mean-square electron momentum. Information K₁[(phi) ] is then defined as (I₁ - J₁). Information K₂ is formed similarly. The total information K is formed as the sum of the two components K₁[(phi) ] and K₂[(rho) ], by the additivity of Fisher information, and is then extremized in both (phi) and (rho) . Extremizing first in (rho) gives a Taylor series in powers of (phi) _n*(phi) _n, which is cut off at the quadratic term. Back-substituting this into the total Lagrangian gives one that is quadratic in (phi) _n*(phi) _n. Now varying (phi) * gives the required cubic wave equation in (phi) .

We show that optical absorption spectra of polyphenylenes can be explained only within theoretical models that explicitly include the Coulomb interaction among the (pi) -electrons. We also show that the dominant effect of substitution on the electronic structure of polyphenylenes within Coulomb correlated models is broken spatial symmetry, while broken charge conjugation symmetry plays a rather weak role. The broken spatial symmetry has a subtle, and weak, effect on the optical absorption spectrum. Consequently, optical absorption spectra of unsubstituted polyphenylenes and the substituted derivatives are nearly identical. Comparison of theoretical and experimental absorption spectra leads to the conclusion that the exciton binding energy in a long chain of poly(para-phenylenevinylene) is about 0.9 eV. Such a large binding energy would be in agreement with nonlinear spectroscopic measurements and pump-probe experiments. However, the present work also indicates that the experimental polymers actually consist of short chains with the chain length distribution peaking at about 10 phenylene units. The gaps between the energy levels above the calculated continuum threshold are much too large for transport to be an intrachain process. Photoconductivity may be predominantly an interchain process, and probably measures the dissociation energy of the exciton which is different from the exciton binding energy.

A series of alkyl-substituted bithiophenes, terthiophenes, and sexithiophenes is theoretically investigated in the framework of semi-empirical quantum chemical calculations. Full geometry optimizations are performed to obtain the torsion energies of thiophene rings around the inter- ring bonds. Comparison among several semi-empirical techniques is presented. A dramatic dependence of torsion barriers as a function of substitution position is observed. These geometrical data are used to interpret the properties of the newly synthesized polymers, based on terthiophenes substituted in the edge rings as well as in the inner ring, that are reported in the literature. The influence of inter-chain coupling and solvent effects on the thermo- and solvatochromic properties of these materials also is investigated.

We report on the synthesis and characterization of an asymmetrically substituted oligothiophene, 2-cyano-5-octylquarterthiophene (CN-4T-Oct), which is shown below. The preliminary work to characterize this molecule indicates that it exhibits a complex liquid crystalline behavior which may lead to the ability to modulate the optical and electrical properties as a function of molecular order. Solution based electrochemical and optical characterization indicates that this material is readily doped to form electronic states required for charge carrier formation and modulation of the optical properties.