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X-band electron spin resonance was employed to study the structural anisotropy in several polythiophene derivatives. Because of the dominating homoge- neous width, the obtained absorption spectra were Lorentzian-shaped. Information about the structural anisotropy was obtained from the position and width of the absorption peak. Qualitatively, the anisotropy was in full agreement with earlier results from X-ray diffraction, including a flip in molecular orientation with respect to the film substrate between solution-cast and spin-cast films. With the Monte Carlo technique, the spectra were fitted with a biaxial g tensor, an anisotropy parameter S, and an intrinsic width . The simulations showed that g could be treated as pseudo- uniaxial, with the unique axis along the side chains rather than along the ring normal. Closed-form analytical expressions relating g to the anisotropy were obtained and used for a quantitative assessment of the molecular anisotropy. Because the molecular g tensor for these materials was not known, a known value of S for one of the samples obtained by X-ray diffraction was used for normalization. Fairly consistent values were obtained for both g and S. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3011-3025, 2003

The varying degree of preferential orientation observed in films of poly(al- kylthiophene)s obtained by solution casting from different solvents has been studied quantitatively with X-ray diffraction. The (uniaxial) orientational distribution function is obtained after some important instrumental corrections that are described in detail. Orientational distribution functions of an exponential type are found to give an ade- quate description with only a few fitted parameters, unlike Legendre series fits, which require longer series. An attempt has been made to relate the anisotropy to the chemical and physical properties of the solvents used. The anisotropy seems to be higher for samples cast from solvents with low boiling points and, correspondingly, high vapor pressures. Also, the average crystallite size is solvent-dependent. The character- istic dimension of the crystallites in the a-axis direction appears to be longest for crystallites with the a axis parallel to the film normal. Along the b axis, that is, the -stacking direction, the crystallite dimension is shorter than along the a axis. Also, the amorphous regions of the films exhibit anisotropy. © 2003 Wiley Periodicals, Inc. J Polym

The drying process of poly(octyl-thiophene) (POT) from chloroform and tetrahydrofuran (THF) solutions has been studied using grazing incidence diffraction (GID). Concentrated solutions combined with high ventilation rates in the sample cell promote the formation of a solid skin at the solution–air interface. This skin has a swollen unit cell and restricted correlation length compared with the dry films. The early skin formation could be reversed by switching off the ventilation. Conversely, dilute concentrations and low ventilation rates tend to give drying from the edges, i.e. solidification directly onto the substrate. It appears that the anisotropy of the films produced by low ventilation rates, especially those resulting from ‘edge drying’, is slightly higher than for the other films. A three-stage model of drying is appropriate for most of the cases studied. After an initial period of constant rate volume loss, the thickness reduction obeys exponential decay in a falling rate period. In the final third stage, the minute residual amounts of solvent leave the sample accompanied with an increasing internal order in the sample. However, both the ‘edge drying’ for dilute solutions and the skin formation for concentrated solutions modify this three-stage description.

Sub-micrometer layers of electrochemically prepared methyl- and decylsubstituted poly(3,4-ethylenedioxythiophene) (PEDOT) carrying perchlorate counterions have been examined with grazing incidence X-ray diffraction with synchrotron radiation. The materials were found to be partially crystalline, and the data could be ascribed to a model of sheets of π-π stacked polymer chains with a smectic ordering of these sheets. An unsubstituted PEDOT sample with the polymeric polystyrenesulfonic acid as a counterion was also investigated and turned out to be essentially amorphous.

X-ray diffraction on samples in the form of a deposited thin layer, a crushed powder and a flake were used to deduce models for the crystalline structure of polypyridine (-(C5H3N)n-), a conjugated polymer of great interest for applications. A monoclinic unit cell with lattice parameters a = 7.47 A, b = 5.83 A, c = 4.25 A, ? = 108.7° containing two chains running along the c-axis and with the molecular plane normal to the a-axis gives a good fit with the observations. The interchain packing distance is about 3.6 A, i.e. in the same range as intermolecular distances found in conductive charge transfer salts. The deposited layer is highly anisotropic, with the a-c-plane parallel to the substrate. © 2001 Elsevier Science B.V. All rights reserved.

The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ by grazing incidence diffraction of synchrotron X-rays from the solution surface, with the solvent evaporation rate being controlled by a flow of dry nitrogen gas. It was found that a solid, partially crystalline film is formed on the upper surface while the interior is still fluid. The initially formed film is swollen and of restricted correlation length, but the swelling disappears gradually on further drying. A considerable fraction (>20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state only during the removal of the last 5% of the solvent.

A series of 2,2-di(alkylthien-2-yl)propanes has been synthesized by chloroalkylation of the thiophene ring in the presence of zinc chloride. The products were obtaines as mixtures of regio isomers which were not separated. These monomers were oxidatively polymerized with iron(III) chloride to yield the respective broken π -conjugated poly(2,2-di(alkylthien-2-yl)propane)s. The new polymers are broken π -conjugated due to the blocking of the bridge carbon with two methyl groups. Due to the limited conjugated segments, these polymers show conductivity on the order of 10 −7 S/cm.

Various substituted poly(phenylthiophene)s have been studied by X-ray diffraction. They are semicrystalline, with very different degrees of crystallinity. Those with para-substituted phenyl groups have a low degree of crystallinity, whereas those with ortho-substituted phenyl groups are more crystalline. The most crystalline materials in this study have two equally long substituents on the phenyl ring, one at the ortho position and the other at the ortho or meta position on the opposite side of the phenyl ring. Poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) was most thoroughly studied, and a structural model is proposed. The structure of PDOPT is quite different from previously studied substituted polythiophenes in that the octyl side chains are directed normal to the thiophene planes. In this way, the conjugated polymer chains are kept separated from each other. Solution-cast and spin-cast PDOPT films are anisotropic, with the octyl side chains oriented normal to the film surface in both cases. This is con...

A series of 3,3′-dialkyl-2,2′-bithiophenes (DAT2s) has been synthesized by the nickel-catalyzed Kumada coupling of 2-bromo-3-alkylthiophene with 2-(3-alkylthienyl) magnesium bromide. These monomers were analyzed by NMR and UV–Vis spectroscopies. The monomers were oxidatively polymerized with iron(III) chloride to yield the respective π-conjugated poly(3,3′-dialkyl-2,2′-bithiophene)s. The new polymers were characterized with 1 H NMR and UV–Vis spectroscopies. Conductivity was in the order of 10–10 2 S/cm, depending upon the length of the alkyl chain.

Electrochemical dedoping and redoping of p-toluene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been studied with in situ grazing incidence diffraction with water used as an electrolyte. The diffraction peak positions and integrated intensities do not change significantly during doping and dedoping, while the peak widths increase upon dedoping and decrease upon doping. This implies that the lattice parameters and the relative positions of the polymer chains and the p-toluene sulfonate ions remain unchanged, the redox processes being carried out by the motion of smaller ions between the polymer and the electrolyte, and that the structural order decreases upon dedoping and increases upon doping in a reversible manner.

Polyalkylthiophenes with alternating head-to-head and tail-to-tail couplings (poly(3,3′-dialkyl-2,2′-bithiophene)s) have been synthesized with methyl, butyl, hexyl and octyl sidechains. The materials have been studied by X-ray diffraction, and structural models have been proposed. The structure of the methyl-substituted polymer is found to be similar to that of poly(3-methylthiophene), with planar polymer chains, whereas the polymers with longer sidechains are found to have twisted main chains. The material with octyl sidechains has been studied during heating and during doping with iodine. This polymer is found to possess a negative thermal expansion coefficient. Iodine-doping leads to a transition to a phase with planar backbones, accompanied by an observed increase in conductivity.

A series of 2,2′-di(alkylthienyl)methanes has been synthesized by chloroalkylation of 3-alkylthiophenes in the presence of zinc chloride. These monomers were oxidatively polymerized with iron(III) chloride to yield the respective partially broken π-conjugated poly(2,2′-di(alkylthienyl)methane)s. Solubility and processability properties of the polymers were dependent on the alkyl groups attached to the thiophene ring. The new polymers contain quinoidal segments due to dehydrogenation of the bridge carbon during polymerization, which can be seen by UV–Vis and 1H NMR spectroscopy. Due to the quinoidal segments, these polymers show conductivity in the range from 10−6 to 10−4 S/cm.

Di(thien-2-yl) methanol and di(thien-2-yl) methyl octyl ether have been synthesized and oxidatively polymerized to yield quinoidal poly(di(thien-2-yl) methane). The polymers are quinoidal due to the removal of the oxygen-containing group on the bridge carbon. The solubility and processability properties of the polymers matched the previously synthesized poly(di(thien-2-yl) methane) made by polymerizing di(thien-2-yl) methane.

The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast ...

Thin films (50–400 nm) of tosylate-doped poly(3,4-ethylene-dioxy-thiophene) (PEDOT) on various substrates have been studied by grazing incidence X-ray diffraction, using synchrotron radiation. The material was found to be highly anisotropic. This is correlated with a strong anisotropy observed in its optical and electronic properties. The crystalline order is limited, and evidence is found for a paracrystalline structure. A structural model is presented, which corroborates with the optical anisotropy. The effect of heating the material to 200 °C was studied. Unlike the situation for other substituted polythiophenes, heating PEDOT increases the crystalline order.

Synchrotron x-ray diffraction from poly(3-octylthiophene) and revealed that the structures of these two polymers remain different under hydrostatic pressure despite their similar chain configuration. The a-axis of poly(octyl-thiophene) is considerably more compressible than its b-axis, and poly(octyl-thiophene) is more compressible along both these directions than poly(dioctyl-bithiophene). The differences in compressibility corroborate with the planar chain model of poly(octyl-thiophene) and the chain twist model of poly(dioctyl-bithiophene), but with a reduction in the chain twist angle under pressure for the latter. The spectral shift caused by variation of temperature (thermochromism) is compared with the spectral shift caused by pressure. From the shifts of the band edge and the behaviour of the overall peak shape it is argued that these two effects are associated with different structural aspects: whereas thermochromism is related to a two phase situation, the shift caused by pressure is related to an increased interchain wave function overlap.

Polyaniline (PANI) (in the form of emeraldine) protonated with (±) camphorsulfonic acid (CSA) was subjected to computer modelling of its crystalline structure. Diffraction patterns were calculated for some modelled structures with the aim of obtaining the best agreement with observed X-ray diffraction patterns (recorded on films cast from m-cresol solutions) and with measured density. The model structures consist of layers of parallel PANI chains intercalated by CSA molecules, that do not contain m-cresol. Two particular models are presented and their features are discussed.

Thin, spin-cast layers of poly(octylthiophene) were shown to be partially crystalline. For thin samples, the crystalline part is orientated with both the alkyl side chains and the polymer main chains parallel to the substrate surface. The orientation effect disappears irreversibly upon heat treatment of the polymer layer. For poly(dioctylbithiophene), no orientation effect was found.

The structural properties of poly(3-(4-octylphenyl)thiophene) (POPT) in bulk solution-cast films and in ultra-thin spin-cast films were studied by X-ray diffraction. The structural aspects associated with an induced colour change of the spin-cast films are highlighted. In bulk form POPT is partial crystalline and is characterized by a lamellar structure in which stacks of planar thiophene main chains are uniformly spaced by the octylphenyl side chains. The polymer is preferentially oriented with the side chains normal to the substrate surface. The crystal structure resembles that of poly(3-octylthiophene), although the lattice parameters along the side chains (α-axis) and along the stacking direction (b-axis) are larger in POPT. The ultra-thin (sub-micron) spin-cast films, on the contrary, are essentially amorphous, but exposure to chloroform vapour and/or heat leads to an increase of crystallinity, paralleling a red shift of the absorption spectrum.

Sub-micron layers of poly(3-octylthiophene) and poly(3-hexylthiophene) deposited by spin-casting on glass substrates were for the first time investigated by X-ray diffraction using synchrotron radiation. The polymers have a partial crystalline structure and are, in contrast to bulk materials, oriented with their side chains parallel to the substrate surface. Optical absorption spectra obtained from the same samples show that the conjugation length is related to the crystalline order.

X-ray diffraction has been used to study the structures of two oriented hexylthiophene-octylthiophene copolymers as functions of the hexylthiophene-to-octylthiophene ratio. The results show that the samples are partially crystalline with structures intermediate between those of the homopolymers poly(3-hexylthiophene) and poly(3-octylthiophene). In the crystalline part, stacks of thiophene chains, equally spaced by the side chains, form a lamellar structure. The distance between adjacent stacks is found to vary linearly with the mole fraction of octylthiophene.

The structure of poly(octylthiophene)s and alternating octylthiophene-thiophene-copolymers with a varying degree of intrachain regularity was studied by means of X-ray diffraction and optical absorption measurements. Although these polymers show a varying degree of crystallinity, evidence is found that they all tend to pack as relatively straight parallel chains. The lateral packing distance depends strongly on the regularity and the relative amount of alkyl side chains. Generally poly(thiophene)s with a larger relative amount and higher stereoregularity of the octyl side chains tend to pack more ordered. On the other hand, a large conjugation length (high degree of chain planarity), as revealed by optical absorption spectroscopy, and a crystalline packing of the polymer chains are not found to be interdependent. For the polymer with highest degree of crystallinity two surprisingly different crystalline structures were found for the two versions with different regularity, viz. poly(3-octylthiophene) and poly(3,3′-dioctyl-2,2′ bithiophene). For the latter we find evidence of a polymer chain twist between adjacent head-to-head coupled thiophene rings, and we propose a structural model for its crystalline packing. Our new model can explain previously measured differences in spectroscopic and transport-related properties for these two stoichiometrically identical polymers.

Layered crystalline materials like K3Me(CN)6 with Me=Cr, Mn, Fe, Co may often exist in various polytypic forms, due to a variety of choices of layer stacking modes. For cases where the interlayer constellations can be limited to only two energetically almost equivalent ways, the buildup of the crystal may be described by a spin-1/2 Ising-like model. For the system presently being studied one can rationalize the layer stacking to a four-valued choice (i.e., a 1D 4-state Potts case), or use an Ising-like two-sublattice model. Previous diffraction studies of K3Me(CN)6 indicated that two long-range ordered structures prevailed, an orthohombic one named MDO1, with one double layer per repetition unit, and a monoclinic one, MDO2, with two double-layer units. Our studies reveal a more complex situation: The Fe material is for the most part of the MDO2 type. But in addition, in some crystal samples, a hitherto unobserved phase also appears, with six double-layer repetition units, in fact a hybrid of MDO1 and MDO2. The Co material is for the most part of the MDO2 type, but contains in addition a considerable contribution of stacking disorder, as evidenced by the presence of diffuse X-ray scattering lines. The lines do, however, contain distinct maxima, indicating the presence of several layer stacking modes with preference of two, three, four, five, and seven double-layer correlations. The findings can be qualitatively discussed in terms of the ANNNI model.

For the first time, the structural and thermochromic properties of mixtures of poly(3-hexylthiophene) (PHT) and poly(3-octylthiophene) (POT) have been studied. X-ray diffraction and optical absorption spectroscopy were employed, the latter on spin-cast films in the temperature range 20–210 °C. The results show that the mixtures are single-phase materials that are structurally intermediate between PHT and POT. It was found that the longest interchain distance a in the crystalline part of the polymer and the thermochromic transition temperature Tt both vary nonlinearly with composition in such a way that Tt and a are approximately linear to each other. This indicates that the side chains act primarily as spacers between main chains, rather than being directly involved indicates that the side chains act primarily as spacers between main chains, rather than being directly involved in the thermochromic transition. This transition may instead be induced by a melting of the polymer backbone.

Homogeneous and flexible films of polythiophene are known to be difficult to obtain electrochemically on indium tin oxide (ITO) glass electrodes using normal 1,6–1,7 V applied voltage. The situation is greatly improved by using higher voltage. 0,1–10 μm thick films of polythiophene (PT) and various poly(3-alkylthiophene)s (P3AT's) (alkyl = methyl (P3MT), hexyl (P3HT) and octyl (P3OT)) were electropolymerized on ITO-covered glass anodes under an applied voltage of 8 V vs. an Ag/AgCl reference electrode. In this paper we report upon the properties of these films compared to their chemically and at low-voltage electrochemically polymerized equivalents. Generally, the films have all the properties known for PT and P3AT's. Characteristics such as thermo- and solvatochromism, conductivity and electronic band structure as studied by ultraviolet photoemission spectroscopy and optical absorption were comparable to the properties shown by the reference samples. However, the structure of high-voltage films differs considerably from those reported for chemically polymerized samples. The high-voltage films contain a higher amorphous fraction, and the polymer is more cross-linked and branched.

Gas phase electron diffraction was performed at 97–98°C on 2,2′-bithiophene and the experimental data show the existence of two conformations, anti -like and syn -like, with torsional angles of 148(3) and 36(5)° and conformational weights 56(4) and 44(4)%, respectively, which are in agreement with ab initio calculations using standard 3-21G ∗ and 6-31G ∗ basis sets.

Soluble poly(3-alkylthiophenes) with alkyl side chains longer than butyl precipitate from solution to suspension during cooling from solvents with strong temperature dependent solubility (marginal solvents). The precipitation is accompanied by a colour change from yellow to red, which is in accordance with the thermochromic- and solvachromic shifts previously reported. Optical absorption measurements were used to monitor the precipitation process. The measurements showed an energy shift for the absorption edge and a growth of some sharper (fine structure) peaks. These peaks can be interpreted as a vibronic combination of the π - π ∗ electronic transition and the 1460 cm −1 vibrational mode, the latter known to occur in well ordered poly(3-alkylthiophenes). The fine structure peaks were used to monitor the crystallization process, and indicated a high degree of polymer ordering in the precipitants. Mats of the precipitated materials were studied by x-ray diffraction. The amount of crystallinity were high compared to ordinary solution cast samples, whereas the crystal structure itself was the same, i.e. straight polymer chains with an alternating “up-down” conformation of the thiophene rings. The polymer mats were found to be anisotropic with the alkyl side chains oriented perpendicular to the mat surface.

With the aaim of obtaining information on the state of the alkyl side chains in polyalkylthiophenes neutron scattering studies were undertaken on deuterated and hydrogenated polyhexythiphenes. Both materials were prepared from bromohexanes and magnesium thiophenes, using FeCl3 as the oxidizing agent for the polymerization. Pronounced isotope effects were observed in the neutron scattering, showing clear orientation effects with stretched film samples. The data corroborate qualitatively with a previous model involving partial side chain disorder. Indication was found of possible “side chain pairing”.

Grignard coupling of 2-bromo-3-methylthiophene and 5,5′-dibromo-2,2′-dithiophene, and chemical polymerization of the resulting tetramer using FeCl3 as coupling agent gave a new type of substituted polythiophene, namely Poly(3,3‴-dimethyl-(2,2′:5′,2′:5′,2‴)tetrathiophene)) (PDMTT), with two new and interesting features compared to conventional polythiophenes. Firstly, we have a polythiophene with exact methyl side group positioning, eliminating the possibility of side group position disorder. Secondly, and especially interesting from a structural point of view, we obtained a polymer which is intermediate between the unsubstituted polythiophene (PT) and poly(3-methylthiophene) (P3MT). The polymer was obtained as a black insoluble powder which turned out to be amorphous. X-ray diffraction profiles were measured and compared to the profiles of PT and P3MT. We were able to follow the intensity and position variation of the diffraction peaks as a function of the methyl substitution.

Neutron diffraction studies, which constitute the first neutron structure work on solid polythiophenes, were performed on as-prepared powders of polyhexylthiophene (PHT) with the hexyl side chains deuterated (PHT-d) and hydrogenated (PHT-h). Although still preliminary in character, the diffraction profiles revealed two important features: (1) the strongest diffraction peak is weaker in PHT-d than in PHT-h, and (2) the diffuse scattering component is considerably stronger in PHT-d, both facts pointing to a considerable degree of side-chain disorder.

Solution-cast films of poly(3-hexylthiophene) (P3HT) and poly(3-octylthiophene) (P3OT) were oriented by stretching to obtain more detailed information about their crystalline structure. For the first time reflections associated with the stretch direction l = 1–7 were revealed using a combination of X-ray film exposures and detailed intensity mapping by various detector scans. The reflections were located at finite angles to the stretch axis indicating a monoclinic (or triclinic) unit cell. The equatorial diffraction patterns (l = 0) of P3HT and P3OT show that the two structures are equal only with one differing lattice dimension caused by the length of the alkyl side chains. The crystalline structure for the unstretched (isotropic) and the stretched sample is found to be the sa me. Existence of h00 and absence of hk0, h0l and hkl reflections, all with finite integers h, k and l, indicate layer stacking disorder between bc-planes. Intensity calculations based upon this model corroborate well with the measured diffraction pattern on the assumption of disordered alkyl side chains.