Electrically conducting poly[3-(ω-hydroxyalkyl)thiophenes]

A series of poly[3-(ω-hydroxyalkyl)thiophenes] was synthesized by chemical oxidative polymerization using FeCl₃ and characterized by FT-IR, thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Upon doping with iodine the polymers attained electrical conductivities of between 0.5 and 38 S cm⁻¹. Electrical conductivities of doped samples were found to increase with alkyl chain lengths, being optimum for the octyl pendant moiety. Thereafter, the conductivity decreased, as the doping and dedoping for the polymers became more difficult. Increasing the hydrocarbon chain length of the pendant substituent also resulted in decreased thermal stability of the polymers. XPS results showed that some C–OH groups in the polymers were oxidized to CO in the polymerization process.     

Electrical properties of Cu(II)-N,N′-dimethyldithiooxamide polymers

Cu(II)-dithiooxamide polymers were prepared by a direct deprotonation of the ligand with a Cu(II) salt. The polymers had a chain length of about 13 units. The undoped polymers showed low electrical conductivity with an Arrhenius-type temperature dependence. Doping of Cu(II)-N,N′-dimethyldithiooxamide was performed by iodine in the vapour phase and by FeCl₃ in solution. In both cases, the oxidative doping resulted in highly increased conductivities. A thermopower measurement indicated p-type conduction. The infrared spectra of the undoped material and the one doped with FeCl₃ were completely identical, indicating that charge transfer from the ligand to the dopant is small. The conductivity curves of the doped polymer did not show an Arrhenius-type behaviour. In order to find an explanation for the conduction mechanism different models were tested. The best fit of the experimental conductivity data of the FeCl₃-doped polymers was obtained with the theoretical prediction of a variable-range hopping model.     

Electrically conductive and fluorescent poly[1,4-bis(3-alkyl-2- thienyl)phenylenes]: syntheses and preliminary characterization aspects

A series of polymers containing alternating phenylene and symmetrically substituted bithiophene repeat units have been synthesized and characterized using UV-Vis absorption spectroscopy, fluorescence emission spectroscopy, conductivity measurement and thermal analyses. The results reveal that the polymers have a bandgap energy of 2.5 eV and a fluorescence quantum yield of up to 26% with respect to quinine sulfate. The polymers show a maximum conductivity of 0.2 S cm⁻¹ upon doping with I₂ and display good thermal stability in both neutral and doped states. The influence of alkyl chain size on conductivity, spectral behavior and thermal stability is discussed.     

X-ray photoelectron spectroscopy of iodine-doped polyethynylferrocene

Iodine-doped polyethynylferrocene, prepared from a solution of iodine in tetrahydrofuran, has been studied by X-ray photoelectron spectroscopy. We find that in the range of doping contents in which the electrical conductivity shows a maximum, iodine is distributed homogeneously in the bulk and in the surface region. These measurements, together with the data from the literature, are indicative of the presence of iodine as a relatively stable I₅⁻ possibly in equilibrium with I₂ and I₃⁻. Iron in the Fe³⁺ form is formed upon doping and increases in content as the iodine content increases.     

Polarization properties of the Raman spectra in neutral and iodine doped cis-trans (CH)x

Polarized resonant Raman spectra of oriented cis-trans -(CH)_x are presented for undoped and iodine doped samples. For undoped films the depolarization ratios of cis lines are consistent with a fibrils misorientation of about 20°. Similar values of depolarization ratios have been measured in iodine doped films as well as for the cis and trans lines than for I₃⁻ mode. These results mean that doping does not destroy the orientational ordering of polymer chains and that under doping the iodine takes the orientation of these chains.     

Electrical conductivity of organosilicon polymers II: Synthesis and electrical conductivities of iodine-doped polysilanes containing amino groups

A series of polysilanes containing an N,N-dimethylaminophenyl group and N-pyrrolyalkyl group as in the side chain were prepared by the Wurtz coupling polymerization. The polymerization of N-pyrrolylbutyl or N-pyrrolylhexyl-substituted dichlorosilane with sodium gave successfully the polysilanes with higher molecular weight than 10⁵. The electrical conductivities of I₂-doped polysilanes were dependent on the chemical structure of the amino side chain. Moreover, by use of excess iodine, the conductivity of the polymer was enhanced. The electrical conductivity of poly[bis(6-(N-pyrrolyl)hexyl]silane] (7a) increased to a maximum value of 8 × 10⁻² S/cm.     

The FeCl3-doped poly(3-alkyithiophenes) in solid state

The FeCl₃-doped three poly(3-alkylthiophenes) (P3ATs) in solid state, i.e. poly(3-octylthiophene) (P3OT), poly(3-dodecylthiophene) (P3ODT) and poly(3-octadecylthiophene) (P3ODT), were investigated in this paper. In X-ray diffraction results, there are obvious variations of the interlayer and interlayer spacings in the layered structures of P3ATs. In addition, it is found that some orientations of the side-chain groups occur after the doping process. The infrared spectra have also shown the microstructural changes arising from the readjustments of the polymer chains due to the intervention of the dopant. The presence of dopant leads to the formation of bipolarons and polarons at the same time. The conductivity measurements reveal that the conductivity decreases with the increase of the length of side-chain group. We have also observed the relaxation behaviors in the conductivities of the doped polymers.     

The synthesis of low crystallinity polyacetylene from the precursor polymer polybenzvalene

The synthesis and properties of the conductive polymer precursor polybenzvalene (PBV) and its conversion to polyacetylene (PA) are presented. PBV was synthesized by ring-opening metathesis polymerization (ROMP) of benzvalene (BV) with non-Lewis acidic tungsten alkylidene catalysts. Treatment of PBV with solutions of HgCl₂, HgBr₂, ZnI₂ and AgBF₄ results in a CC bond rearrangement, and produces polyacetylene PA. The PA films produced with HgCl₂ displayed the highest conductivities and the best mechanical properties. The PA produced was of low crystallinity and upon treatment with I₂ exhibited conductivities of 1 Ω⁻¹cm⁻¹. Oriented PA was produced by stretching the PBV and converting it to PA. With I₂ doping, the oriented PA (l/l₀=6) displayed a conductivity of 49 Ω⁻¹cm⁻¹.     

Preparation and electrical–magnetic properties of polyaniline doped with ionic ferrocenesulfonic acid

Conducting polyaniline with electrical conductivity of 2.34 × 10⁻¹ S cm⁻¹ was obtained using ferrocenesulfonic acid as dopant. After the ferrocenesulfonic acid was oxidized with FeCl₃, though the electrical conductivity of the doped polyaniline decreased by 1–2 orders of magnitude, the magnetic susceptibility (χ) increased with the increase of the oxidation degree of ferrocenesulfonic acid. EPR spectra showed not only a signal with a g value of around 2, but also a so-called half-field signal with a g value of about 4 even at room temperature. Coexistence of ferromagnetic intrachain interactions and antiferromagnetic interchain interactions in the materials has been suggested.     

E.S.R. of BF4−-doped polythiophene

We have studied poly(3-methylthiophene) doped electrochemically with BF₄⁻ by electron spin resonance. The spin concentration increases linearly by about one spin per injected charge up to quite high doping levels (≈ 10 mol% at room temperature). The magnetic susceptibility χ_m(T) gradually changes from a Curie- to a Pauli-type behaviour with increasing doping concentration. Simultaneously, an increasing degree of delocalization of the corresponding spin centres is inferred from linewidths, line shape analysis and spin-lattice relaxation rates. The metallic behaviour observed by e.s.r. at high doping levels is attributed to a microscopic electrical conductivity, which is higher than the macroscopic one observed by transport measurements by a factor of about 50. The present results demonstrate that polarons are the dominant charge states in poly(3-methylthiophene) doped with BF₄⁻.     

One-step chemical synthesis of doped polythiophene by use of copper(II) perchlorate as an oxidant

A reaction of 2,2′-bithiophene with copper(II) perchlorate in acetonitrile achieved polymerization and doping in one step, and yielded polythiophenes, [(C₄H₂S)(ClO₄)_x·yH₂O]_n. The polymers with x ∼ 0.17 and y ∼ 0.3 exhibited a high electrical conductivity in the range 3 – 8 S cm⁻¹ at 300 K and a small activation energy of 0.04 eV. The i.r. and e.s.r. spectra showed the characteristics of doped polythiophenes.     

Polymers synthesized from (3-alkylthio)thiophenes by the FeCl3 oxidation method

Thiophenes substituted by alkylthio (hexylthio and dodecylthio) pedant groups were polymerized using the FeCl₃ oxidation method. The polymers were characterized using microanalyses, conductivity measurements, thermogravimetry (TG) and ${}^1\text{H}$ NMR, UV-Vis, FTIR and XPS. The polymers are regiorandom in structure as expected and have a head-to-tail (HT) content of about 80% based on the ${}^1\text{H}$ NMR spectrum. Poly[(3-hexylthio)thiophenes] (PHTT), which carries the shorter side chain, exhibits a higher solubility in common organic solvents and is more thermally stable than the polymers with the longer dodecylthio poly[(3-dodecylthio)thiophenes] (PDDTT) chains. The polymers are moderately conductive after being doped by FeCl₃ or I₂. The high concentration of covalently bonded chlorine found from XPS and microanalysis and supported by ${}^1\text{H}$ NMR spectra suggests chlorination of the backbone occurred during the polymerization process. The influence of chlorination on the absorption spectra and conductivity were noted and discussed.     

Poly(2,5-dialkoxy-p-phenylenebutadiynylene)s—Novel rigid conjugated polymers with liquid crystalline property

Novel rigid conjugated poly(p-phenylenebutadiynylene)s having long alkoxy side chains, octyloxy (C8), decyloxy (C10), and dodecyloxy (C12) at 2,5-positions of a phenylene unit, are synthesized by oxidative polycondensation of corresponding 2,5-dialkoxy-1,4-diethynylbenzenes with Hay catalyst. The polymers are soluble in hot solvents such as CHCl₃ and fusible upon heating. UV–Vis spectra of the polymers show an absorption maximum (λ_max) around 420 nm due to the π-conjugation along the main chain. An intense fluorescence exhibiting the λ_max around 475 nm is observed in all of the polymers. Cyclic voltammetry of the polymer shows two Li ion-participated redox reactions occurred at the dialkoxyphenylene moiety and in the conjugated polymer chain due to an n-doping process. Electrical conductivity is an order of 10⁻⁸ S cm⁻¹ which increases to an order of 10⁻⁴ S cm⁻¹ upon vapor phase doping by H₂SO₄. Thermochemical investigations by DSC and polarized optical microscopy suggest that the polymers have a nematic liquid crystalline phase. The molecular arrangements in the phase is evaluated by XRD and a molecular dynamics simulation. A nematic phase is shown to arise from a side-by-side accretion of the rigid rodlike main chains. A lamellar structure is suggested in the crystalline phase.     

Tetra(9,10-phenanthro)tetraazaporphyrin - phthalocyanine: Comparative electrical conductivities

Tetra(9,10-phenanthro)tetraazaporphyrin, H₂TPTAP, has been synthesized and characterized for comparative electrical conductivity measurements with phthalocyanine, H₂Pc, before and after iodine doping. The objective is to determine the effect on conductivity of fusing eight additional benzo rings to the periphery of the phthalocyanine ring. H₂Pc doped to a (H₂Pc)I_2.5 composition with a resistivity decreases from 10¹⁵ to 1 ω cm, while H₂TPTAP doped to a (H₂TPTAP)I_0.26 composition with a corresponding resistivity change from 10¹¹ to 10⁸ ω cm. Experimental data and the literature indicate that benzene rings fused to the periphery of the tetraazaporphyrin ring have little π-electron interaction. Similarly, the structure-conductivity correlation of data is interpreted as indicating that fusion of additional benzo rings has an insulating substituent group effect on oxidation of and charge transport between the tetraazaporphyrin rings in the polycrystalline solid.     

Novel `synthetic metals' based on symmetrically tetrasubstituted nickel phthalocyanines

Nickel(II) 2,9,16,23-tetrasubstituted phthalocyanines, NiPTX (where X=–OH, –NO₂, –NH₂ and –SO₃H) were synthesized in pure state and doped with iodine. Elemental analysis, UV-Vis, infrared, X-ray diffraction, magnetic susceptibility and TGA studies were used to investigate the effects of iodine doping as well as substituents on the properties of the complexes. The electrical conductivity of nickel phthalocyanine derivatives found to depend on the nature of the substituents and showed ∼10³–10⁵ times increased electrical conductivity in comparison to parent nickel phthalocyanine. Further, the substitution and iodine doping show remarkably very high improved electrical conductivity nearly 10¹¹ times the electrical conductivity of nickel phthalocyanine.     

Poly(3′,4′-dibutyl-α-terthiophene-phenylene-vinylene): a new soluble and dopable phenylene-vinylene-based conjugated polymer

A new soluble and dopable copolymer consisting of 3′,4′-dibutyl-2,2′:5′,2″-terthiophene and phenylene-vinylene units has been designed and prepared via a Wittig reaction. This title copolymer is soluble in common organic solvents such as THF and CHCl₃, and can be doped with iodine achieving an electrical conductivity of about 3.2 × 10⁻² S/cm at room temperature. Films of this copolymer are electroactive and turn reversibly and rapidly from red to green-blue upon doping and undoping electrochemically.     

Electric properties of iodine-doped polyacetylene

Results of d.c. and microwave conductivities and dielectric constant measurements on iodine-doped (CH)_x are reported. The gradual variation of the transport properties as a function of the iodine concentration indicates that no sharp phase transition occurs with increasing doping levels. Charged π-phase kinks localized around I₃^? qualitatively describe the dielectric properties in the lightly doped range.     

Polyaniline with ω-hydroxyalkoxy pendant substituent on the meta-position

A series of meta-substituted polyaniline derivatives, poly[3-(ω-hydroxyhexoxy)aniline], poly[3-(ω-hydroxyoctoxy)aniline], poly[3-(ω-hydroxydecoxy)aniline] and poly[3-(ω-hydroxydodecoxy)aniline] have been synthesized via chemical oxidative polymerization. The resulting polymers show enhanced solubility in organic solvent. The polymerization yield is increased and the reaction is accelerated by the addition of aniline. The homopolymers can attain conductivity in the range of 10⁻⁶ to 10⁻⁴ S cm⁻¹ after protonic doping with HCl. Upon doping oxidatively with iodine, the conductivity is ca. 10⁻⁵ to 10⁻³ S cm⁻¹. For the copolymers with aniline (15 mol%), the corresponding conductivity is higher, 10⁻⁵ to 10⁻³ S cm⁻¹ upon HCl doping and 10⁻⁴ to 10⁻² S cm⁻¹ upon iodine doping. Thermogravimetry (TG) of the polymer depicts two major weight loss steps corresponding to the degradation of side chain and the thermal breakdown of the backbone, respectively. The polymers are largely amorphous but show an increase in crystallinity with increasing pendant chain length. The polymers were also subjected to FT-IR, UV–VIS and X-ray photoelectron spectroscopy (XPS) studies.     

New π-conjugated polymers constituted of dialkoxybenzodithiophene units: synthesis and electronic properties

New stable and conductive polymers constituted of a new fused thiophene unit, 4,8-dialkoxybenzodithiophene, and related copolymers with thiophene were prepared by organometallic polycondensation in high yields. They showed electrical conductivity of 10⁻²–5 S cm⁻¹ on doping with iodine. Homopolymers were prepared by Ni-promoted dehalogenation polycondensation, and their molecular structures were confirmed by data from IR spectroscopy and elemental analysis. They were partly soluble in organic solvents, and the soluble part gave number average molecular weights, M_n, of 3000–3600 with M_w/M_n value (M_w=weight average molecular weight) of 1.1–2.4 in the GPC analysis; the M_n value corresponds to a degree of polymerization of about eight. Alternative copolymers consisting of the 4,8-dimethoxybenzodithiophene and thiophene or bithiophene units were synthesized by a Pd catalyzed polycondensation.Soluble organic model compounds for the homopolymer and copolymers were synthesized via analogous organometallic coupling reaction, and optical and electrochemical properties of the model compounds were compared with those of the polymers. UV–VIS spectrum of the oligomeric model compounds showed a large bathochromic shift by >50 nm from the monomeric compound. The p-doping of the polymers was reversible, and the iodine-doped polymers were neutralized by hydrazine. Packing structures of the polymers are discussed based on their XRD patterns and density.     

X-ray diffraction study of regioregular poly(3-alkylthiophenes)

X-ray diffraction studies carried out for regioregular poly(3-octylthiophene) and poly(3-hexylthiophene) are presented. The diffraction data are supported by computer modelling of the structure. The comparison of the results obtained in this work with the results reported for the ‘common’, non-regioregular poly(3-alkylthiophenes) gives evidence of better chain planarity and higher crystallinity of the regioregular polymers. In addition, structural aspects of poly(3-alkylthiophenes) doped with FeCl₄⁻ are investigated.