Charge transfer complexes, their inherent electrical conductivity, magnetic properties and donor-acceptor redox relationships have been a focus of much research in the last several years. One direction has been in the design of memory devices and applications in molecular electronics.1,2 Our work has focused on analysis of such processes in a polymeric medium. Polycarbonate films of 7,7’,8,8’-Tetracyanoquinodimethane (TCNQ) and o-tolidine (o-T) complexes were studied by EPR spectroscopy from 100-300K. EPR spectra and magnetic susceptibility of the dispersed charge-transfer complexes are presented and compared with the pristine materials. These studies were carried out as a function of donor/acceptor stoichiometry and concentration within the polymer matrix. Saturation studies show significant differences as the composition varies. In addition the g-tensor and linewidth are strongly dependent on temperature and composition.

Electrochemical measurements have been employed to study the formation process of the charge-transfer complexes Cu+TCNQ−,a switching and memory material, in a saturated TCNQ/CH3CN solution. These studies show that the Cu/Cu+TCNQ−(s), TCNQo(CH3CN) system is an active-passive system corroding under diffusion control. A possible mechanism of localized corrosion-crystallization is proposed for the formation of a Cu+TCNQ− film in an acetonitrile solution

A low-field (0.6 Gauss, 2 MHz) EPR spectrometer providing quantitative parameters is described. It gives informations such as frequency dependence of the linewidth, anisotropy of inhomogeneous line and also the values of T1, T2 and the magnetic susceptibility using simple hypothesis.

The behaviour of different typical π-systems, as well metallic as semiconducting is compared to a radical anion salt, quinolinium bis tetracyano-quinodinemethane Qn(TCNQ)2 considered as a reference.

The materials physical characteristics will be provided by a new variable field (0.6–60 Gauss, 2–200 MHz) which is under realization, for an extended family of organic radicals.

Electrochemical oxidation of the metal-organic complex, nickel(II)–bis(1,3-dithiole-2-thione-4,5-diselenolate) or simply [Ni(dsit)2]2−, yields highly conducting salts, in which the stoichiometry and packing arrangement depends critically on the size of the counter-cations incorporated. Smaller counter-cations, e.g., tetramethylammonium and tetramethylphosphonium ions, yield salts with a 1:2 cation:[Ni(dsit)2] stoichiometry, while the larger tetraethylammonium ion yields a salt with 2:2 stoichiometry. In both these salts, the [Ni(dsit)2] units occur as tightly bound dimers, in which the coordination geometry of nickel is a unique, but not unprecedented square-pyramidal type. Moreover, the packing arrangement of [Ni(dsit)2]2 dimer units in both (Me4N)[Ni(dsit)2]2 and (Me4P) [Ni (dsit)2]2 is κ-type, similar to that found in the organic superconductor with the highest-known Tc (10.4 K), κ-(BEDT-TTF)2Cu(NCS)2. Both these salts possess good room temperature conductivities (σrt = 36 and 19 S.cm−1 respectively), but the temperature dependance of their conductivities is characteristic of semiconductors with small bandgaps (Eg = 0.11 and 0.13 eV, respectively). The 2:2 salt (Et4N)2[Ni(dsit)2]2, on the other hand, has a substantially lower room temperature conductivity, about six orders of magnitude smaller than that of the 1:2 salts. Its structure is characterized by [Ni(dsit)2]2 dimer units which are separated from each other by the tetraethylammonium cations, with no effective interaction between [Ni(dsit)2]2 dimers. It is suggested that dimeric metal-dithiolene and metal-diselenolene complexes may be potential building blocks in the structural design of κ-type organic conductors and superconductors.

Bridged quasi onedimensional macrocyclic transition metal complexes [MacM(L)]n using phthalocyanine (Pc), tetrabenzoporphyrine (TBP), 1,2 -and 2,3-naphthalocyanines (1,2-; 2,3-Nc) as macrocycles (Mac) with M = e.g. Fe, Ru, Co and L = e.g. pyrazine (pyz), 1,4-diisocyanobenzene (dib), tetrazine (tz) exhibit interesting electrical properties. Regardless of the size of the bridging ligand after either chemical or electrochemical doping stable semiconducting compounds [MacM(L)Xy]n (X = e.g. I, BF4-, CIO4-…) are formed. For the first time the complete characterization of a soluble oligomer [MacM(L)]n (Mac = R4PC, M = Ru, L = dib) by 1H-NMR spectroscopy is reported. Some of these shish kebab complexes e.g. [PcM(tz)]n, (M = Fe, Ru) or [MacMCN]n; (Mac = Pc, TBP; M = Co, Fe) exhibit good semiconducting properties without additional external doping. Whether or not these compounds are intrinsic semiconductors will be discussed. The synthesis of oligomeric bridged mixed valence compounds [PcM3+LPсM2+L]n (M = e.g. Fe) is another target of our work. We report here about first attempts to synthesize these oligomers.

Porphyrins exhibiting discotic liquid crystalline phases have been developed in order to prepare thin, large-area, crystalline films of molecular conductors. A series of octaalkylporphyrins bearing different side chains have been synthesized including some with electron-withdrawing substituents at the meso positions. The photophysical properties of thin films of these compounds are a strong function of the film order (crystallinity). A substantial and persistent photovoltaic effect was achieved (e.g., Voc = 0.3 V, jsc = 0.4 mA/cm2 under white light, 150 mW/cm2) in capillary-filled symmetrical cells with indium-tin oxide electrodes. A model based on kinetically-controlled asymmetric exciton dissociation leading to photoinjection at the illuminated interface is presented to explain these results. This appears to be the first unambiguous example of a photovoltaic cell controlled entirely by interfacial kinetics. The predominance of the photoinjection process in these cells is attributed to the single-crystal-like character of the porphyrin films.

In low-dimensional conductors, the instability of the metallic state can lead to the formation at low temperature of a spin density wave induced by the magnetic field (FISDW). The transition results from the complex interplay between the one dimensional instability of the electronic gas and the quantization of the magnetic field’s flux. This second-order phase-transition line has been investigated by measuring both specific heat and thermal conductivity along the c* direction. The mean-field jump and the gap value have been deduced respectively from the anomaly and the exponential decay of the electronic specific heat. The coupling strength λ has been evaluated, and the λ > 0.3 value indicates clearly a strong coupling behavior at high field. Below 8 teslas, the specific heat displays a double anomaly in relation with the competition between subphases. Above the second-order transition line, critical fluctuations are observed on both specific heat and lattice thermal conductivity. Along this line, one-dimensional fluctuations increase with increasing magnetic field. It is proposed that the very high field reentrance of the metal is to be related to enhancement of the 1D fluctuations.

The purpose of this talk is to discuss the physical properties of the (TMTSF)2X charge transfer salts in high magnetic fields. This class of materials is of great interest since the effective lower dimensionality and the various ground states are magnetic field dependent at low temperatures. At present, the so-called “standard model” provides a good theoretical description of the low field field induced spin density wave transitions (FISDW). However the reentrance from the last FISDW back to a high field metallic state, and the coexistence of “fast oscillations” in all measured properties, is yet to be accurately described theoretically. The emphasis of this paper is on recent specific heat results which have been obtained on (TMTSF)2ClO4 in magnetic fields as high as 30 T. Here we observe both the reentrant phase transition and the fast oscillations in the specific heat. A main conclusion we draw from our measurements is that the density of states in the reentrant phase is less than it is in the low field metallic state at low temperatures.

High magnetic field (to 31T) d.c. magnetization measurements on the quasi-one dimensional organic conductor (TMTSF) 2ClO4 yield thermodynamic evidence for the reentrance of a metallic phase from the magnetic field-induced spin density wave state. The H-T phase diagram developed previously from magnetotransport measurements is reproduced from 8 to 26 tesla. The reentrance occurs as a sharp collapse of M(H) to (near) zero magnetization in the high field metal phase. For fields above 27 tesla, deHaas-van Alphen-like oscillations appear, similar to earlier resistance data, as well as other features possibly signifying multiple transitions in the very high field regime.

We present a microscopic theory of the sound propagation in quasi one dimensional charge density wave (CDW), spin density wave (SDW) and field induced spin density wave (FISDW). First, we consider the ideal situation that the phase correlation length in the CDW or the SDW is infinite. In this limit due to the diffusion pole at iω = Dq2 in a variety of correlation functions the sound propagation depends on a) what is the ratio ω/Dq2 and b) if the CDW (or the SDW) is pinned or unpinned where D is the diffusion constant. Second, when the CDW (or the SDW) is unpinned, the phason starts to participate in the screening of the ionic potential. However, since the unpinned part is strongly inhomogeneous, the contribution of the phason term depends on the wave vector of q of the sound wave like (1 + (Lq)2)−1 where L is the Fukuyama-Lee-Rice coherence length. The present theory accounts for a variety of features observed in sound propagation in quasi-one dimensional CDW systems like NbSe3 and TaS3.

We have studied the elastic properties of the Bechgaard salts (TMTSF)2PF6 and (TMTSF)2C104 through their Spin Density Wave (SDW) and anion ordering transitions. Using a vibrating reed technique to measure the sound velocity and attenuation, we observed a large softening of sound velocity immediately above the SDW transition temperature, 12K, of (TMTSF)2PF6 followed by a large hardening below the transition. The softening results from a strong dependence of Tc on stress in the most conducting direction, while the hardening results from the loss of screening from the conduction electrons and yields a value for the long wavelength electron-phonon coupling constant. The anion ordering transition at 24K in (TMTSF)2ClO4 is marked by a hardening of the lattice that is considerably larger than expected from the lattice constant changes. Our most interesting finding, however, is the observation of a series of steps in the sound velocity as the Field Induced Spin Density Wave (FISDW) transitions are crossed by increasing the magnetic field at low temperatures. The fact that the sound velocity steps are small at the beginning of the cascade of transitions and increase with field, even as extrapolated to low temperature, is an unexpected result from present theory and may indicate a more direct coupling of the lattice stiffness to the SDW order parameter.

Young’s modulus E measurements using the vibrating reed technique are reported for salts of the (TMTTF)2X series, where X = ReO4, SbF6, AsF6. All three exhibit softening of the modulus at the structureless transition, with the largest effect in the material with the non–centrosymmetric anion ReO4. The behavior is typical of quadratic coupling to an order parameter plus effects from fluctuations. There is a large stiffening of E below the anion ordering temperature of (TMTTF)2ReO4.

We present magnetotransport data and the phase diagram derived from them for (TMTSF)2PF6 under sufficient pressure that the zero field Spin Density Wave (SDW) is suppressed and the material is superconducting. Application of a large magnetic field perpendicular to the conducting plane then leads to the cascade of Field Induced Spin Density Wave (FISDW) transitions. The transitions are in good agreement with the Standard model for these transitions and in contrast to the more complicated behavior seen in the ClO4 salt. In addition Hall and longitudinal resistivity indicates a behavior much closer to that observed in conventional Quantum Hall devices than in the ClO4 salt or previous studies of PF6. We do observe the “rapid” Schubnikov de Haas like oscillations in magnetoresistance at high field similar to those seen in ClO4, even though in the present case there is no evidence for anion ordering as some theories would require.

Methyl and ethyl ring-substituted polyaniline derivatives have been synthesized and characterized by UV-visible-near IR spectroscopy. Optical spectra of the base forms in DMF solution suggest that the torsion angle between adjacent rings is increased by steric hindrance due to the alkyl groups in the substituted polymers, leading to blue shifts in the ∼4 eV (“bandgap”) and ∼2 eV (“exciton”) absorptions and an accompanying decrease in the relative intensity of the “exciton” band.

The methyl ring-substituted derivative, poly(o-toluidine), is shown to exhibit solvatochromism. The “exciton” absorption shifts from 2.03 eV in pure NMP to 2.19 eV in CH2CI2, accompanied by a loss in intensity relative to the “exciton” absorption.The phenomenon is attributed to the presence of a more “rod-like” state in NMP as compared to a more “coil-like” state in CH2CI2.

The effects of alkyl substituents on acetic acid solution spectra of “emeraldine” salt will be discussed with respect to polaron band formation in these systems.

We discuss recent low temperature results on the magnetoresistance of (TMTSF)2C104 in the low field metallic and the moderate field FISDW phases. From constant field rotations in a plane perpendicular to the highest conducting a-axis, we observe oscillatory resistance behavior along certain orientations at al. fields measured. While at odds with usual considerations of resistance anisotropy due to the crystal structure, this feature may be consistent with the recent predictions of Lebed and Bak[1,2], wherein the oscillatory electron trajectories along the b* and c* directions become commensurate near particular “magic” orientations in the magnetic field. We compare our preliminary data with the Lebed-Bak model, finding some qualitative agreement.

First we calculate the tunneling density of states of quasi-two dimensional charge density waves (CDW) or spin density waves (SDW) in the presence of impurity scattering. Second, we consider the tunneling current between two CDWs or two SDWs. We point out the existence of new contribution, which gives rise to the a.c. current when one CDW is sliding relative to the other one.

We present a summary of our recent results on the electrical and mechanical properties of fibers made from poly(2,5-dimethoxy-p-phenylene vinylene), PDMPV and poly(2,5-thienylene vinylene), PTV, using the precursor polymer methodology, and from polyaniline, PANI, using the method of processing as polyblends with poly-(p-phenylene terephthalamide), PPTA, from sulfuric acid. The solubility of both PANI and PPTA in H2SO4 presents a unique opportunity for co-dissolving and blending PANI and PPTA to exploit the excellent mechanical properties of PPTA and the electrical conductivity of PANI; we summarize the electrical and mechanical properties of such composite fibers. For PDMPV and PTV fibers, we find a strong correlation between the conductivity and the tensile strength (and/or modulus), and we show from basic theoretical concepts that this relationship is an intrinsic feature of conducting polymers.

The synthesis of polyaniline in its fully oxidized, fully reduced and selected average intermediate oxidation states is described together with the synthesis of a self-protonic acid doped polyaniline. The processing of polyaniline films and fibers by thermal stretching to give conductivities up to ∼100 S/cm is reported. Both doped and undoped polyaniline fibers have tensile strengths approaching those of commercial polymers.

Polyanilines have been known for over one hundred years. Recent studies of this chemically flexible polymer have demonstrated unusual electronic phenomena in both the insulating forms and the conducting forms. Studies of both forms show that the origins of the electronic phenomena are substantially different than those observed in polyacetylene and related earlier studied conjugated carbon backbone polymers. Unusual aspects include the formation of massive polarons upon photoexcitation in the insulating forms. These polarons have unusual time dynamics associated with the roles of ring-flipping and ring-conformation in the polymer system. A new model for the effects of electron lattice coupling via ring rotation has been introduced. The “metallic” form of the polymer shows that the metallic state is associated with the ordered regions of the doped polymer. The roles of localization are important in leading to the formation of a textured, granular metal. At low temperatures for emeraldine salt, and at higher temperatures for derivatized polyanilines, localization is important. Potential new technologies based on the polyanilines, including optical information storage, controlled microwave absorption, and use of a self-protonating derivative that is soluble in aqueous media are noted.

The optical absorption spectra of polyaniline in the visible and UV spectral regions have been characterized before. The electrically conductive form has a band gap absorption at 3.8 eV and polaron absorptions at 2.9 and 1.5 eV [1,2] . An additional electronic absorption band at 0.9 eV was found to be also related to the existence of polaron. The assignment of this transition has yet to be made. Epstein and co-workers [31 have found a photo-induced absorption band at 0.9 eV by photo-exciting emeraldine base (insulator) with 2.0 eV light. It is not known yet whether these two 0.9 eV transitions belong to the same set of electronic energy levels of polaron, or they belong to two different electronic systems but are coincidentally have the same transition energy.