Characterization of conducting copolymers of 2,2′-bithiophene and pyrrole by cyclic voltammetry and UV/visible spectroscopy

Several polymers have been prepared by electropolymerization of mixtures of pyrrole (PY) and 2,2′-bithiophene (BT). Cyclic voltammetry on prepared polymer films shows three anodic oxidation peaks, two of which match the oxidation potentials of homopolymeric PY and BT, and a third which is intermediate. UV/visible spectroscopy displays a unique spectrum for each of the reduced and oxidized forms of these polymers. Nernstian plots from UV/visible data exhibit three well-defined redox couples in polymer films produced at 1.3 V. Overall, the data strongly support the formation of a copolymer, consisting of three distinct oxidizable units. Two of these can be attributed to short blocks of either PY or BT, and a third to random and alternate groupings of PY and BT. The polymers produced are electrically conductive, but the conductivity drops rapidly as BT units are introduced into a homopolymer of PY. © 1992 John Wiley & Sons, Inc.     

Conjugate polymer-based membranes for gas separation applications: current status and future prospects

Conjugate polymers provide the possibility of exploiting both the chemical and physical attributes of the polymers for membrane-based gas separation. The presence of delocalized π electrons provides high chain stiffness with low packing density, thus making the membrane a rigid structure that favors facilitated transport. Historically, the polymeric membranes were constrained by the tradeoff relationship between gas permeability and gas selectivity. So, different methods were investigated to prepare the membranes that can overcome the limitation. In recent years, electroconductive polymeric membranes have gained attention with their enhanced transportation properties combining the separation behavior depending on both molecular size discrimination as well as the facilitated transport. They offer better selectivity toward polar gases such as CO₂ because of the increased solubility. This review is aimed to provide a literature survey on gas separation using conjugate polymers such as polyaniline, polypyrrole, and some derivatives of polythiophenes. It contains various methods used by different researchers to enhance the gas separation properties of the membranes with improved mechanical and thermal stability such as changing the morphology and membrane preparation methods. In addition, it provides the pros and cons of various factors affecting the conjugate polymer membrane performance. The major challenges and future work that can be done in improving the transportation properties through the membrane to achieve viable membranes are also discussed so that they can be used for commercial and practical applications in the future.     

Some Properties of the (TMTSF)2X Superconductors

Measurements of the anisotropy of the critical field in (TMTSF)₂X superconductors are presented. The results show that the a axis H_c2 is Pauli limited based on a T_c near 1K. The large energy gap obtained from tunneling data is therefore thermodynamically untenable in terms of the present critical field studies and the superconductivity is singlet rather than triplet. Moreover, we find that low levels of irradiation induced defects eliminate the superconductivity in the ClO₄ and PF₆ salts and leave the thermopower of the ClO₄ salt below 100K unchanged. These results are incompatible with the proposal for 1D superconducting fluctuations below 40K. A discussion of the arguments for and against the occurance of superconducting fluctuations in the (TMTSF)₂X salts is given with emphasis on the role of interchain interactions and other possible interpretations of the tunneling data.     

EQCM study of the p- and n-doping processes of a poly[4,4-bis(butylsulphanyl)-2,2-bithiophene]

Electrogenerated deposits of poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] have been characterised in the presence of different supporting electrolytes, by coupling current (charge) to microgravimetric measurements from the electrochemical quartz crystal microbalance (EQCM). The simultaneous collection of voltammetric measurements and of data relative to mass changes shows the influence exerted by the nature of the supporting electrolyte on the charge-discharge steps of both p- and n-doping processes. Interestingly, the microgravimetric data collected corresponding to the pre-peaks of both doping processes suggest the occurrence of two opposite motions of ions (ingress into and exit out from the polymer) in the relevant potential region, giving a contribution to the study of the `residual charge' phenomenon.     

Influence of the nature of contacts on the dark and photovoltaic characteristics of the Schottky junction between n-doped silicon and poly(4,4′-dipentoxy-2,2′-bithiophene)

The dark and photovoltaic characteristics of the Schottky junction between n-doped silicon and a conducting polymer in its oxidised form, poly(4,4′-dipentoxy-2,2′-bithiophene), have been determined as a function of the nature of the electrical contact on the polymer side. It was found that the dark and photovoltaic performances of the device depended strongly on this contact. An aluminium contact is oxidised by the polymer and an aluminium oxide film forms between the polymer and the contact through which the forward current is controlled by charge injection. The devices assembled with indium tin oxide, platinum and gold contacts show better characteristics than the ones with aluminium contact; in the last three cases, however, a faradic charge transfer reaction on the contact, probably the oxidation of some amount of water contained in the polymer, affects the characteristics of the junction. Received: 27 December 1997 / Accepted: 24 April 1998     

Extended conjugated mesogens: synthesis and mesomorphic properties of H-shaped mesogens based on 3,3ʹ,5,5ʹ-tetrasubstituted 2,2ʹ-bithiophene with oligo(1,4-phenyleneethynylene) arms

A new class of extended conjugated mesogens, namely H-shaped mesogens based on 3,3?,5,5?-tetrasubstituted 2,2?-bithiophene with oligo(1,4-phenyleneethynylene) arms, have been synthesised, and the relationships between molecular structures and mesomorphic properties investigated. Tetraalkyl, tetraalkoxy and dialkyldialkoxy derivatives, [R¹C₆H₄CCC₆H₂(C₂H₅)₂CC]₂[R²C₆H₄CCC₆H₂(C₂H₅)₂CC]₂C₈H₂S₂ where R¹ and R² = alkyl and alkoxy chains of different lengths, exhibit nematic phases. The length, number and position of the terminal chains strongly affect the mesomorphic properties. The tetraalkyl derivatives in which R¹ = R² = pentyl to heptyl exhibit enantiotropic mesophases, whereas the derivatives with octyl or nonyl chains exhibit monotropic mesophases. The tetraalkoxy derivatives in which R¹ = R² = pentyloxy to nonyloxy all exhibit enantiotropic nematic phases. The mesophase range increases with increasing alkoxy chain length, except that the octyloxy and nonyloxy derivatives have almost the same temperature range. The dialkyldialkoxy derivatives in which R¹ = alkyl; R² = alkoxy and in which R¹ = alkoxy; R² = alkyl (R¹ and R² = heptyl, nonyl, hexyloxy or nonyloxy) exhibit enantiotropic mesophases. The derivatives in which R¹ = alkoxy have a significantly lower crystal–nematic transition temperature than the corresponding derivatives (R² = alkoxy), although the two types of derivatives have a similar nematic–isotropic transition temperature.     

5′-Alkoxy-2,2′-bithiophene azo dyes: a novel promising series of NLO-chromophores

A series of bithienyl azo dyes have been prepared from their corresponding coupling components, 5-alkoxy-2,2′-bithiophenes. The solvatochromic behaviour of the compounds was investigated. The hyperpolarizabilities β of derivatives 3-5 were measured using hyper-Rayleigh scattering and thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that good nonlinearity-thermal stability is well balanced for azo-bithiophene NLO-chromophores 3-5 making them good candidates for NLO applications.     

Poly(3,3′-dimethoxy-2,2′-bithiophene): Synthesis and comparison with poly(3-methoxythiophene)

A new electroactive polymer, namely poly(3,3′-dimethoxy-2,2′-bithiophene) has been prepared by voltammetric polymerization of 3,3′-dimethoxy-2,2′-bithiophene. Due to a different coupling pattern (equivalent to “head-to-head,” and “tail-to-tail” coupled alkoxythiophene rings), poly(3,3′-dimethoxy-2,2′-bithiophene) exhibits different voltammetric properties than the corresponding “head-to-tail” coupled polymer, i.e., poly(3-methoxythiophene). Poly(3,3′-dimethoxy-2,2′-bithiophene) gives very sharp oxidation and reduction peaks indicating an abrupt insulator to conductor transition. This hypothesis was corroborated by the studies of relative resistance as a function of electrode potential. Sharper and better-defined redox peaks may indicate better stereoregularity of poly(3,3′-dimethoxy-2,2′-bithiophene) as compared to poly(3-methoxythiophene) since in this compound the 5,5′-coupling positions are geometrically equivalent and no coupling defects are expected. © 1992 John Wiley & Sons, Inc.