New low-gap thiophene-based regular copolymers are produced by anodic coupling of 3,4ethylenedioxythiophene-2,5-substituted thieno [3,4-b]pyrazine (TP), cyclopenta[2,1-b;3,4-b′]dithiophen-4-one (CO), and 4-dicyanomethylene-4H-cyclopenta [2,1-b;3,4-b′]dithiophene (CN). The copolymers are characterized by cyclic voltammetry, FTIR reflection-absorption and UV-vis spectroscopy, electrochemical quartz crystal microbalance analysis, and in situ pand n-conductivity measurement. The copolymers show low optical gaps (measured at the maximum absorption) and electrochemical gaps (measured from redox potentials) in the range 0.8-1.3 eV. The CN-based polymer displays the lowest reported electrochemical gap (0.8 V). Random copolymers of CO and 3,4-ethylenedioxythiophene (EDT) have also been produced and compared with the relevant regular copolymer. Copolymerization of CO with increasing amounts of EDT decreases the gap. From an analysis of redox potential as a function of EDT fraction, it is found that the gap is limited by the redox potentials of the individual homopolymers. Localization of n-doping carriers in the polythiophene chains is progressively increased by donor-acceptor alternation and then by copolymerization till the expected intrinsic conductivity is made completely p-type.

The adsorption of some substituted ferrocene molecules (Fc-R) on indium−tin-oxide electrodes has been investigated by cyclic voltammetry in acetonitrile. Adsorption occurs with carboxyl-substituted (R = −COOH and −(CH2)6COOH) and to a lesser extent with amino-substituted (R = −CH2N(CH3)2) ferrocenes. Adsorption from the neutral (ferrocene) carboxyl-substituted molecule produces layers with a coverage of 1 × 10-10 mol cm-2 which increases to 4 × 10-10 mol cm-2 from the oxidized (ferrocenium) molecule in air-saturated solution. In the latter case, adsorption occurs on a thin layer of amorphous iron oxide produced by oxidative decomposition of the ferrocenium. Electrodes modified by amorphous iron oxide layers are able to give stable monolayers from the carboxyl-terminated molecules, particularly with R = −(CH2)6COOH due to self-assembly. The layer structures are discussed on the basis of the adsorbate structure and the electrochemical parameters.

Hexylferrocene phosphonic acid was adsorbed on indium-tin oxide (ITO) and amino-primed ITO electrodes from ethanol. The obtained monolayers are stable in acetonitrile where cyclic voltammetry shows the formation of domains of self-interacting and free ferrocene molecules. Distinct phases are observed on bare ITO, whereas a single Frumkin isotherm is obtained on amino-primed ITO. Dilution experiments with alkylphosphonic acids CnH2n+1PO(OH)2 (n ) 3, 6, and 12) have shown that only the dodecyl chain may compete with the hexylferrocene chain, which remains 50 times more strongly bound to the surface. The free energy of self-interaction of the ferrocene moieties in the layers is ca. 40 kJ mol -1 ; that is, it is equivalent to that of a 15 carbon atom alkyl chain. Lateral interactions among hexylferrocene and dodecyl chains form isolated domains of the components, ruling out a real dilution of ferrocenes to single isolated molecules.

The in situ conductivity vs p-doping charge of low-defect polypyrroles, N-substituted polypyrroles, and polythiophenes has been investigated in acetonitrile in the presence of the weakly coordinating perchlorate ion as supporting electrolyte. In-situ ESR and EQCM measurements have given supporting information on polymer structure and conduction carriers. The structures of the polymers cover a wide range of conjugative, geometrical, and solvation conditions, but the conductive pattern follows simply the polymer ring type (pyrrole, N-substituted pyrrole, or thiophene). In polythiophenes an initial region of low conductivity, due to strongly spin-dimerized polarons, is followed by an increase of conduction to a plateau of high conductivity. N-substituted polypyrroles display a linear increase of conductivity with charge followed by a plateau of conductivity. Polypyrroles without N-substitution show an increase of conductivity to a maximum followed by a symmetrical decrease to zero at a charge corresponding to one bipolaron per tetrapyrrole unit. A redox-type bipolaron model of conduction, based on stabilization of the bipolaron positive charge by H-bonding with the counteranion, is suggested. The parent polypyrrole shows the uncomplicated conductivity pattern (increase of conductivity to a plateau) due to a uniquely strong stabilization of the π-stacked polymer chains.

A conveniently assembled electrochemical cell, exploiting a porous electrode supported on a moist perfluorinated ion-exchange polymer, is proposed for profitable electrochemical detection in supercritical fluid chromatography. It consists of a porous Pt working electrode, contacted by the mobile phase from the chromatographic column, which is chemically deposited onto one side of a Nafion membrane. The rear uncoated side of this membrane, acting as a solid polymer electrolyte, is contacted by an electrolyte solution (1 M NaCl) contained in an internal compartment equipped with a Pt counter electrode and a Ag/AgCl, Cl(-) 1 M reference electrode. Ferrocene, eluted with supercritical carbon dioxide through a Spherisorb column installed in a supercritical fluid chromatographic system, was used as electroactive prototype analyte to test the performance of this detector, which turned out to be quite better than that provided by a conventional on-line UV absorbance detector. The recorded peaks were characterized by both a good reproducibility (4.5%) and a linear dependence of their height and area, which extended over a wide concentration range ( approximately 3 orders of magnitude). Moreover, they were not interfered by possible solvent front, unlike peaks recorded by the UV detector. The detection limit, estimated for a signal-to-noise ratio of 3 (4.2 x 10(-11) mol), was lower by approximately 1 order of magnitude than that found for the UV detector. Finally, the long-term stability of this detector was satisfactory in that only a approximately 6% decrease in the current responses was observed after a rather long period (2 months) of continuous use.