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New thiophenes carrying 18-crown-6-ether ring directly linked to the 3- and 4-positions of the thiophene ring were synthesized and polymerized by anodic coupling in acetonitrile. The polymers were characterized by cyclic voltammetry (CV), UV-Vis and FTIR spectroscopy, matrix-assisted laser desorption ionization (MALDI) mass spectroscopy and in situ conductivity. Electrochemical quartz crystal microbalance (EQCM) analysis of the alkali metal coordination ability of the 18-crown-6-ether polymer films in acetonitrile has evidenced that the coordination constants (e.g. 20–80 M−1 for Na+) are ca. two orders of magnitude lower than those of polythiophenes bearing the crown substituents pendant from the polythiophene backbone. The result has been ascribed both to electronic and solid-state effects of the conjugated polythiophene chains.

3,4-Ethylenedioxythiophene (EDT) and thieno-(3,4-b)-2,3-dihydro-2-tetradecyl-1,4-dioxane (EDT-C14) were electrochemically deposited onto Pt using different electrolytes in acetonitrile. The resulting PEDT films containing different counter ions were subsequently characterized and their in situ conductivity values were measured using a two band electrode. The latter showed that the highest conductivities were obtained with ClO4− and BF4− as counter ions. Furthermore, the morphology, and thus the conductive properties, of the films seem to be strongly dependent on the applied polymerization potential.

Several alkylated 3,4-ethylenedioxythiophene (EDT-C n H 2 n +1 ; n =1,6,10,14) derivatives were electrochemically polymerized in acetonitrile, after which the corresponding polymers were characterized and their properties were studied (cyclic voltammetry, UV–VIS, in situ conductivity and in situ ESR). With increasing alkyl chain length (i) the electronic spectra show an increased coplanar disposition of the thiophene rings; (ii) the conductivity initially decreases and then increases again, and (iii) injected polarons are dimerized to the same level, independently of the alkyl chain length. An exceptionally high conductivity (850 S/cm) is found for the tetradecyl-substituted polymer.

Anodic coupling of bisdithienylethylene is reported. The resulting material, which has been characterized by cyclic voltammetry, UV–vis, Fourier transform infrared (FTIR) and matrix-assisted laser desorption ionization (MALDI) mass spectroscopies and in situ conductivity, results to be mainly constituted by the dimer coupled through the α-thiophene positions. In situ (solid state) polymerization increases the degree of polymerization from 2 to ca. 5. The conjugation ( λ max =490 nm) and conductivity (5 S cm −1 ) of the polymer are slightly lower than those of poly(dithienylethylene) (505 nm and 40 S cm −1 ).

Anodic coupling of thiophene- (1) and cyclopentadithiophene- (2) hexyl acrylates in acetonitrile to polythiophenes is reported. The resulting polymers have been characterized by cyclic voltammetry, UV–vis and FTIR spectroscopy and in-situ conductivity. The produced polythiophene films, for which FTIR analysis show that the acrylate moiety is kept unchanged, display high conjugation lengths (λmax=520 (1) and 600 (2) nm) and conductivities (20 (1) and 100 (2) S cm−1).

Anodic coupling of dithienylacetylene and dithienylacetylenes substituted with alkyl and alkoxy groups has been investigated in acetonitrile. The resulting polymers have been characterized by cyclic voltammetry, UV-Vis spectroscopy, electrochemical quartz crystal microbalance, in situ ESR and in situ conductivity. The degree of conjugation of the polymers is increased as the monomer oxidation potential is lowered, which occurs with alkyl-substitution and even more with alkoxy-substitution. Alkoxy-substitution in position 3 of the thiophene ring produces the dimer, whereas 4-substitution yields an extensively crosslinked polymer. A regularly coupled polymer is obtained by 3,4-disubstitution with the ethylenedioxy group. The low conductivity (1 × 10 −3 S cm −1 ) and the high unpaired spin density in the oxidized state of this polymer are explained by localization of charge and spin operated in the dithienyl moieties by the triple bonds.

In situ conductivity of some selected polypyrroles (polypyrrole and poly(N-methylpyrrole)) and polythiophenes (poly(4,4′-dipentoxydithiophene), poly(dithienylethylene) and two crown-5-substituted poly(cyclopentadithiophenes)) as a function of oxidative doping level is reported. The relationship is in general composed of three segments (threshold, linear increase and plateau). Doping-charge thresholds of conductivity are explained on the basis of charge pinning of polarons and bipolarons by anions and (in polythiophenes) by π-dimerization of polarons.

In situ ESR measurements have shown that polarons generated in polybithiophene by electrochemical oxidation in acetonitrile decay to bipolarons. The decay follows a first-order kinetic law with half-life times which increase as the oxidation level is increased. This phenomenon is attributed to electrostatic crosslinking which makes the material progressively stiff. Absence of polaron decay has been observed in alkoxy- and alkyl-substituted polythiophenes and attributed to polaron stabilization in the solvent-swollen materials. The structural factors (polymer matrix stiffening or swelling) are shown to be critical parameters in the long-debated stability of polarons in non-degenerate polyconjugated conducting polymers.

The reversible hydroxide-anion doping of polypyrrole (PPy) has been investigated by FT-IR, cyclic voltammetry, in situ conductivity and ESR techniques. FT-IR confirmed that the hydroxide anion substitutes the counteranion reversibly in doped PPy. The dopant hydroxide anion produces a strong negative shift of the oxidation potential of PPy and doubling of the reversible charge. No similar effects are displayed in N -substituted PPys. In situ conductivity shows that the material becomes conducting (up to 2 S cm −1 ) only after about 50% of the doping charge is passed. Similarly, the ESR signal is absent during the initial stages of charging, developing just before the onset of conductivity. The results indicate that the hydroxide anion stabilizes the positive charges in PPy by NH bonding. The interaction is so strong that fixed bipolarons are formed without the intermediate formation of polarons. Polarons are produced only at higher charges with subsequent injection of mobile bipolarons and setting in of conductivity.

Anodic coupling of 2,2′-azopyrrole, N,N′-dimethyl-2,2′-azopyrrole and pyrrolyl-2-aldazine has been performed in acetonitrile. The resulting polymer films were investigated by cyclic voltammetry (CV), UV-Vis-NIR spectroscopy, FT-IR reflection-absorption spectroscopy and in situ conductivity. Polyazopyrrole is the first reported narrow-bandgap pyrrole-based polymer (Eg ≈ 1.0 eV). It undergoes reversible oxidation without significant changes in the visible region but with strongly enhanced absorption in the NIR region. The CV of polyazopyrrole displays a two-step oxidation process with a finite potential window of conductivity (maximum conductivity 2 × 10−2 S cm−1). In the oxidized form polyazopyrrole easily dissociates its NH protons. Its acidic properties are no longer displayed in its N,N′-dimethyl-substituted homologue and in poly (pyrrolyl-2-aldazine).

We present FT-Raman and FT-IR spectra of neutral α,α′-dimethyl end-capped oligothiophenes (to six thiophene units) as solid samples and in solution. Gas-phase potential to internal rotation of α,α′-dimethylbithiophene has been predicted by ab initio calculations at the RHF/ 6-31G** level, as a model for the theoretical study of the conformational flexibility of these molecules.

The in situ conductivity of some poly(cyclopentadithiophenes) modified at the 4 position with reducible ( p -nitrophenyl and p-N -methylpyridyl) or oxidizable (ferrocene) redox groups was investigated in acetonitrile. In the nitrophenyl- and pyridyl-functionalized polymers the reduction, which is confined to the pendant redox group, makes the polymer mixed-valence conductive. The conductivity ((3–6) × 10 −3 S cm −1 ), which is the highest reported for a redox polymer, remains within the limits expected for a direct intersite electron hopping. In the ferrocene-functionalized polymers the oxidation involves both the redox group and the backbone. Redox conduction at the ferrocene group is enhanced by hopping through the conductive polymer backbone. The hopping rate is increased by a decrease of the ferrocene-backbone distance and by conjugation of ferrocene with the backbone itself making conductivity increase up to 1 S cm −1 .

Electrochemical polymerization of thiophene oligomers ( n = 2−4) bearing pentoxy groups in regiochemically defined positions (3 or 4 of the terminal thiophene rings) was performed in acetonitrile. Cyclic voltammetry and UV-Vis spectroscopy showed that the degree of polymerization decreases as the monomer length increases and this result is accounted for by the corresponding decrease of the coupling rate constant, measured by cyclic voltammetry for the less reactive 3-substituted series. Compared with alkyl substitution, alkoxy substitution induces a smaller bandgap and lowers the oxidation potential, therefore giving the polymer a higher stability of the doped state. However, no variation in the effective conjugation length was found when alkoxy groups were present in head-to-head or tail-to-tail linkages. It is suggested that the presence of the oxygen atom not only minimizes the steric hindrance but also plays a role in planarizing the polymer chain.

Irreversible changes occurring in the electrochemical reduction of some polythiophenes in acetonitrile have been investigated by cyclic voltammetry (CV), UV-Vis and IR spectroscopy and the electrochemical quartz crystal microbalance (EQCM). Reduction in the presence of alkali metal cations (Li + , Na + , K + and Cs + ) does not result in n-doping but in hydrogenation of the alkene moieties. The promotion of double-bond saturation by alkali metal cations following the order Li + , Na + > K + > Cs + is attributed to their charge-pinning action which decreases as the ion radius is increased. Reversible reduction in tetralkylammonium electrolyte (n-doping) is accompanied by production of hydroxide ions within the polymer which are thereby inserted by subsequent oxidation. The resulting quinone-like groups are responsible for the CV pre-peaks usually observed in conducting polymers after n-doping and previously assigned to trapped charges.

The characteristics of the products of the anodic copolymerization of thionaphtheneindole (TNI) and dithienopyrrole (DTP) in acetonitrile with tetrabutylammonium perchlorate as supporting electrolyte depend on the relative concentrations of the monomers. When the concentrations are comparable, electrochromic conducting copolymers are obtained; at TNI concentrations much higher than those of DTP, an insulating adherent film of copolymer is deposited at the electrode. An explanation of these findings is given, based on the different lengths of the conjugation segments in the two types of oxidized copolymers.

A series of cyclopentadithiophenes, substituted at the 4-position with the ylidene groups = CHR (R = Ph, p -PhOBut, 4-pyridyl), were synthesized and polymerized by anodic coupling in acetonitrile and the polymers were characterized. Reduction of the polymers does not result in n-doping but is followed by dimerization of the resulting radical anion to cross-coupled anionic polymers linked at carbon atoms α to the substituent R. The process may be electrochemically reversed. The anionic polymers are irreversibly quenched by water (hydrodimerization). The mechanism of electrohydrodimerization was also investigated on the monomers.

Electrochemical n-doping of poly(dithienylvinylene) has been performed in AN + 0.1 M N(CnH2n+1)4+ClO4− (n = 1,2,3,4 and 6) and compared with p-doping. Cyclic voltammetry, in situ ESR and UV-Vis spectroelectrochemistry show that radical anions produced in n-doping are moderately unstable towards disproportionation whereas, in p-doping, radical cations are stabilized by π-dimerization. In situ conductivity of n-doped polymer decreases as the size of the dopant cation increases, suggesting charge transport control by interchain hopping. The different conductivities of n- and p-doped polymers are due to the different sizes of the counterions.

The kinetics of anodic coupling to dimers of thiophene oligomers ( n = 3–5), methyl protected at one α-terminal position, is second order in oligomer concentration and evidences high activation enthalpies and negative activation entropies. Activation free energies are linearly related to the inverse of the oligomer length n (the dimerization rate decreases as n is increased). Thin films of methyl end-capped thiophene oligomers ( n = 4, 6, 8 and 10) display reversible oxidations from a single one-electron step (tetramer) to a single two-electron step (octamer and decamer) through two separate one-electron steps (hexamer). ESR indicates strong magnetic dimerization for the one-electron-oxidized hexamer. The close resemblance of the electrochemical and ESR behaviour of the hexamer with that of polythiophene suggests that oxidation of the latter occurs via hexameric spin-dimerized polarons. The conductive and capacitive properties of the end-capped oligomers ( n = 6, 8 and 10) were investigated by in situ conductivity and chronopotentiometry. While conductivity of octamer and decamer is displayed at the two-electron (bipolaron) state, the hexamer, insulating at this state, is conducting at the mixed-valence polaron-bipolaron state; capacitive responses are evidenced at the bipolaron state for the octamer and decamer only. The difference of conductive and capacitive behaviour between the hexamer and the higher oligomers is explained by charge localization in hexameric segments.

The oxidative polymerization of thionaphtheneindole is investigated. It is found that the nature of the resulting polymer depends on the reaction medium: in particular with perchlorate as electrolyte, the conducting polymer is the product of the thionaptheneindole oxidation; on the contrary, in the presence of p -toluenesulfonate, the same oxidation gives rise to the neutral polymer.

Reaction of poly(dithienylvinylene) as thin film with bromine occurs in two subsequent stages, i.e., doping to the conductive state and addition to an insulating material. Electrochemistry and spectroelectrochemistry show that both 1esses may be electrochemically reversed. Possible applications to gas sensors are proposed.

Monomers constituted of two bithienyl or terthienyl moieties end-bridged by one ethylene fragment were prepared and the possibility of obtaining the corresponding polymers by anodic coupling were evaluated. Different results are obtained by varying the number of the thiophene rings in the monomeric unit.

With the aim of improving the processability of some electrochromic polymers, dithienopyrrole and dithienthiophene were polymerized by a potentiodynamic technique on platinum electrode coated by poly(vinylchloride). A composite was obtained in both cases, characterized by a good processability, typical for poly(vinylchloride), and by electrochromic features very similar to those of the conducting polymers.

Well-defined oligo(2,5pyrrole)s and the corresponding polymer with a DP≈20 have been prepared by a Pd-catalyzed coupling reaction between N-protected activated monomers and subsequent removal of the protecting group. The results of structural, electrochemical and spectroscopical characterizations on these previously unknown materials are described.

Different alkyl and alkoxy-substituted polyanilines were electropolymerized in acidic conditions. The steric and electronic effects of the substituents on the electrical and optical properties of the resulting polymers, were principally investigated. It has been found that alkyl-substituted anilines give less planar polymers than the alkoxy derivatives. However, alkoxy mono-substituted anilines exhibit lower conductivities than those obtained with the alkyl derivatives, because the selectivity of the head-to-tail couplings is reduced by the incorporation of a methoxy group at the ortho position. Nevertheless, more regular and processable materials have been obtained with poly(2,5-dialkoxyanilines): for instance, poly(2,5-dimethoxyaniline) exhibits a high conjugation length and a good conductivity (ca. 0.3 S/cm).

Electrochemical doping of poly( p -phenylenesulfide) (pPPS) in concentrated sulfuring acid offers a promising way for studying electrical properties of this material because an accurate control of the doping level is possible. We have performed an extensive investigation of the electrochemical behaviour of pPPS in 96% H 2 SO 4 and, hence, measured in situ optical spectra, conductivity and ESR data of samples at different values of the injected charge; in this paper the results are presented and discussed in relation to data of pPPS and oligomers chemically doped.

An overview of the applications of polyconjugated conducting polymers to electrochemical sensors is given. Gas sensors, ion sensors, and biosensors (non-enzyme and enzyme sensors) are presented and discussed. The role of the polymer as enzyme host and mediator of charge transfer is particularly emphasized in the light of recent results.

Polypyrenes from anodic coupling of pyrene in acetonitrile and 1,2-dichloroethane have been identified as the 1,1′-coupled dimer and tetramer, respectively, on the basis of electrochemical analysis and IR, UV-Vis and mass spectroscopies. Bipyrene and tetrapyrene are reversibly reduced at −2.27 and −2.15 V versus Ag/Ag + , respectively. Their electrochemical oxidation (at 0.96 and 0.87 V) is followed by further polymerization and ultimate degradation whereas iodine doping of tetrapyrene leads reversibly to a conducting adduct (6 × 10 −3 S/cm).

Monomers constituted by two terminal pyrrolic units fused onto a central electron-poor heterocycle, dipyrrolopyrazine ( 1 ) and dipyrroloquinoxaline ( 2 ), have been prepared and polymerized by electrochemical way. The properties of the resulting polymers are discussed. Preliminary results are also offered concerning the dihydro-compound ( 3 ) which is a true N,N′-dipyrrol-2-yl.

In-situ conductivity of polypyrrole (as tosylate) as a function of oxidative doping level attains a maximum at 3/4 the total oxidation charge and the relevant in-situ ESR signal corresponds to an equal concentration of spin-carrying (polaron) and spinless (bipolaron) species. Results are explained on the basis of mixed-valence conduction.

Anion dependence of conductivity in well-ordered polypyrrole tosylate deposits was determined by anion exchange in aqueous medium with several inorganic (NO 3 − , ClO 4 − , F − , Cl − , Br − , BF 4 − , HSO 4 − , OH − ) and organic (CF 3 COO − , CH 3 COO − , CH 3 CH 2 COO − , PhCOO − , PhO − , p -CH 3 C 6 H 4 SO 3 − ) anions. Conductivity was found to be high (80–100 S cm −1 ) and almost independent of anion size and (for anions of strong acids) of anion type, but it decreased with increasing anion basicity (70 S cm −1 for carboxylate, 25 S cm −1 for phenoxide and 3 × 10 −2 S cm −1 for hydroxide anion). Quenching of conductivity by nucleophilic anions is explained by pinning of positive charges in the polypyrrole backbone with a pinning energy as high as 0.4 eV for OH − , as determined by E 0 shifts in the cyclic voltammograms of the polymer.

Conductivity σ and redox potential E 0 for 20 pyrrole- and seven thiophene-based polymers reported in the literature are correlated. A linear relationship between ln σ and E 0 is obeyed with slope −16 V −1 for both classes and x -axis intercept 0.05 V and 0.7 V versus SCE for pyrrole- and thiophene-based polymers, respectively. The relationship is explained according to simple theoretical arguments and analysed on the basis of existing models for conducting polymers. Experimental and predicted conductivities for new pyrrole- and thiophene-based polymers agree within one order of magnitude.

A new conducting polymer was obtained by electrooxidation of N -methyl-10,10-dimethyl-phenazasiline (SIN). The electrochromic properties of poly(SIN) have been investigated. It was found that this material presents a good chemical stability and a reversible behaviour during many subsequent redox cycles.

In situ conductivity of polythiophene (PT) deposits from anodic coupling of thiophene (T), bithiophene (BT) and terthiophene (TT) increases with redox switching to an extent which depends on the monomer. Changes are considerable with TT, minor with BT and negligible with T, involving extra oxidative charges with the same trend, and are paralleled by evolution of electronic and infrared spectra and cyclic voltammograms. Results are explained by the occurrence of solid-state polymerization of oligomers leading ultimately to the same polymer with a conductivity of 1–3 S cm−1. PT from thiophene is much less conducting (0.06 S cm−1), because of oxidative degradation during deposition.

Polyconjugated polyfuran (PF) was produced by electroreduction of 2,5-dibromofuran in acetonitrile using Ni(bipy)32+ as catalyst. Polymerization occurs only in the presence of excess Ni(bipy)32+ at potentials in the range −1.7 to −2.0 V versus Ag/Ag+ via binuclear organonickel complex. IR spectroscopy, elemental analysis and mass spectroscopy confirm that PF is constituted by 2,5-linked furan units and indicate a degree of polymerization > 100. Red PF films (λmax = 420 nm, Eg = 2.2 eV) are reversibly oxidized at 0.45 V and reduced at −2.5 V. Doping with AsF5 gives PF a conductivity of 10−3 S/cm. Polymers produced by anodic coupling of furan were also investigated for comparison. IR spectroscopy and elemental analysis indicate that they display a lower degree of conjugation due to the concomitant acidcatalyzed polymerization.

Potentials for the first reversible oxidation and optical bandgaps of phenyl- N -capped aniline oligomers ( n = 1,2 and 4) are linearly related with 1/ n . The comparison of the values extrapolated for the infinitely long polymer and those of electrochemically synthesized polymer samples indicates for the latter an average equivalent length of 6–10 monomeric units.

Polycationic polythiophenes with high conjugation length, conductivity, and solubility have been obtained by anodic coupling of 4-(4H-cyclopentadithien-4-yl)ammonium perchlorates. One of these polymers can be reversibly reduced (n-doped) showing the characteristics of self-doped materials. The n-doping process is fast and does not show any dependence on the cation size.

Polythiophene-based polyelectrolyte multilayers have been layer-by-layer deposited on ITO/glass and characterized by UV-vis spectroscopy, cyclic voltammetry and conductivity. Multilayers in which both polycation and polyanion are based on the same polythiophene backbone are reported for the first time. Uv-vis spectroscopy and cyclic voltammetry indicate a linear dependence of the amount of deposited polymer on the number of deposition cycles. The amount of deposition depends on the oxidation state of the polythiophene. The sheet and perpendicular conductivities of the multilayers and their photoluminescence properties are reported.

Transmittance and reflectance spectra as a function of the electrode potential are reported for the title polymer, an electrochemically prepared thiophenic polymer with extremely good chemical stability and mechanical properties of its conductive state. An electrochromic effect both for the transmitted and for the reflected light is shown. The “reflection electrochromism” here reported, besides its relevant implications in the analysis of the electronic states of conducting polymers, is certainly an interesting effect for its possible application in energy saving systems.

Carboxyalkyl-substituted bithiophenes and terthiophenes, bearing the oligothiophene tail either perpendicularly or linearly linked to the tethering hexanoyl chain, have been adsorbed on ITO electrodes. The monolayers of perpendicular adsorbates are anodically oxidized to polymer layers. The linear terthiophene may be coupled with itself in solution to produce a one-end surface-grafted sexithiophene monolayer.

We have analyzed the size dependence of the infrared and Raman active modes of two neutral thiophene-based oligomers in the solid state. The compounds have a well-barrier-well structure, where the well parts are two bithiophene or terthiophene end-moieties and the barrier part is a non-conjugating ethylene spacer. Relevant features are correlated with the vibrational data previously collected on a series of medium-size α,α'-dimethyl end-capped oligothienyls. Experiments indicate the existence of a rather effective conjugation in the case of 1,2-Di-[5-(2,2′:5′,2″-terthienyl)]-ethane, in spite of the introduction of sp 3 defects into the oligomer backbone

Self-assembly (SA) of molecules constituted of hexyl-bridged pyrrole or cyclopentadithiophene heads and ferrocene tails on ITO electrodes was investigated in acetonitrile. SA layers are formed from both the ferrocene and the ferrocenium forms. Anodic coupling of SA layers produces polythiophene layers contacting directly the electrode surface.

Low band-gap pyrrole-based polymers showing narrow potential windows of conductivity have been obtained by alternation of electron rich and electron poor moieties.

Summary form only given. Recently, neutral polyfuran (PFu) has been prepared following the cathodic routo by electroreduction of 2,5-dibromofuran using Ni(biPY)/sub 3/ /sup 2+/. The spectroscopic analysis of the PFu samples in the pristine and iodine-doped states indicated that polyconjugation may exist in the polymer. Here, we extend our study of polyconjugation in PFu to the photoinduced infrared absorption spectrum. The formalism of the Effective Conjugation Coordinate which was used in the analysis of pristine and doped material will be used to understand the photoinduced infrared spectrum.