N-doped Polymer Research Articles

Optical Amplification at 1.5µm in ErIII Coordination Polymer-Doped Waveguides Based on Intramolecular Energy Transfer.

9,9-bis (diphenylphosphorylphenyl) fluorene (FDPO) and dibenzotetrathienoacene (DBTTA), are synthesized as the neutral and anionic ligands, respectively, to prepare the ErIII coordination polymer [Er(DBTTA)3(FDPO)]n. Based on the intramolecular energy transfer, optical gains at 1.5µm are demonstrated in [Er(DBTTA)3(FDPO)]n-doped polymer waveguides under excitations of low-power light-emitting diodes (LEDs) instead of laser pumping. A ligand-sensitization scheme between organic ligands and Er3+ ions under an excitation of an ultraviolet (UV) LED is established. Relative gains of 10.5 and 8.5dBcm-1 are achieved at 1.53 and 1.55µm, respectively, on a 1-cm-long SU-8 channel waveguide with a cross-section of 2×3µm2 and a 1.5-µm-thick [Er(DBTTA)3(FDPO)]n-doped polymethylmethacrylate (PMMA) as upper cladding. The ErIII coordination polymer [Er(DBTTA)3(FDPO)]n can be conveniently integrated with various low-loss inorganic waveguides to compensate for optical losses in the C-band window. Moreover, by relying on the intramolecular energy transfer and UV LED top-pumping technology, it is easy to achieve coupling packaging of erbium-doped waveguide amplifiers (EDWAs) with pump sources in planar photonic integrated chips, effectively reducing the commercial costs.

Pore engineering of ultramicroporous carbon from an N-doped polymer for CO2 adsorption and conversion

Microporous carbon materials are widely used in CO2 adsorption because of their unique structure and excellent stability. In this work, N-doped porous carbon (NPC) with an ultramicroporous structure was prepared through the carbonization of an N-doped polymer and KOH at 600 °C, 700 °C, and 800 °C, respectively. The prepared NPC exhibited excellent CO2 adsorption properties of up to 6.95 mmol·g−1 at 1 bar and 0 °C, and this value is considerably higher than that of the parent N-doped polymer. The excellent CO2 adsorption performance is due to the well-defined ultramicroporous structure and high specific surface area of NPC. Moreover, these porous carbons can be combined with tetrabutylammonium bromide (TBAB) to fix CO2 into various cyclic carbonates, with a yield of up to 99% without any solvent. Whether the cause is the adsorption or catalytic conversion of CO2, NPC-700 exhibits excellent stability and can be cycled multiple times without significant reduction in its performance.

Customized poly (aniline-co-o-aminobenzoic acid) by functionalizing with n/p dopants and its application in symmetrical redox supercapacitor

The chemically synthesized poly (aniline-co-o-aminobenzoic acid) copolymer was functionalized electrochemically by cationic and anionic doping and tailored its property for suitable redox behavior. The mechanism during this process has been proposed using cyclic voltammetry studies, and the doping was confirmed in FTIR and UV studies. In the electrochemical impedance spectroscopy, undoped and doped behavior revealed the possibility of fine-tuning of conditions that are required for redox supercapacitor. A symmetrical supercapacitor was fabricated with an optimized doped co-polymer-based electrode and the specific capacitance values were 107 Fg−1 for n-doped polymer and 140 Fg−1 for p-doped polymer. The electrochemical characterization of n/p 1 cm2 cells in terms of specific power, specific energy, specific capacitance, columbic efficiency, IR drop, and ESR was calculated from charge/discharge studies. Data were analyzed in terms of complex power versus complex capacitance, and hence, active region of n/p supercapacitor was obtained. This concept paves way for future tailoring of dopants during the synthesis of conducting polymer and its copolymers.Graphical abstract

Highly Conductive and Solution-Processable n-Doped Transparent Organic Conductor

Transparent conductors (TCs) play a vital role in displays, solar cells, and emerging printed electronics. Here, we report a solution-processable n-doped organic conductor from copper-catalyzed cascade reactions in the air, which involves oxidative polymerization and reductive doping in one pot. The formed polymer ink is shelf-stable over 20 days and can endure storage temperatures from -20 to 65 °C. The optimized n-doped thin-film TC exhibits a low sheet resistance of 45 Ω/sq and a high transmittance (T550 > 80%), which can rival indium tin oxide. The transparent organic conductor exhibits excellent durability under accelerated weathering tests (85 °C/85% RH). Furthermore, the n-doped polymer film can also function as an electrode material with a high volumetric capacity. When it is paired with p-doped PEDOT:PSS, a record-high coloration efficiency is obtained in a dual-polymer electrochromic device.

Cr-N bridged MIL-101@tubular calcined N-doped polymer enhanced adsorption of vaporous toluene under high humidity

High capacity adsorption of volatile organic compounds (VOCs) in high humidity environment is a crux but challenge for atmospheric VOCs governance. In this work, tubular carbonized N-doped polymers (TCNP) were implanted into MIL-101 via N-Cr-O interface self-assembly, enabling high adsorption for vapor toluene in high humidity. Through mechanical ball milling and carbonization, Cr ions were preloaded on TCNP to form highly dispersed 3–5 nm Cr-N crystallite as anchors for growing MIL-101(Cr/Cu). Newly constructed smaller micropores of 6.8 Å with aromatic rings/N sites at the interface and doped Cu ions in MOF framework synergistically enhanced π-π conjugation and electrostatic interaction for C7H8 molecules. This endowed [TCNP5/MIL(Cr/Cu)]N-Cr 2.9 times higher toluene uptake (6.34 mmol/g) at low vapor pressure (P/P0 = 0.02) and 1.9 times diffusivity under high humidity (60% RH) than that of MIL-101(Cr) at 298 K. The adsorption breakthrough curves for vaporous toluene showed that TCNP@MIL-101(Cr/Cu) exhibited outstandingly higher adsorption equilibrium capacity (2.7 mmol/g) under 80% RH, corresponding to approximately 2–10 times than those of reported state-of-the-art adsorbents under similar conditions. This study provided a novel interface construction strategy for hydrophobic MOF composites, which supplied deeper understanding for VOCs adsorption and promoted MOFs practical application in VOCs capture under humid environment.

Use of a Multiple Hydride Donor To Achieve an n-Doped Polymer with High Solvent Resistance.

The ability to insolubilize doped semiconducting polymer layers can help enable the fabrication of efficient multilayer solution-processed electronic and optoelectronic devices. Here, we present a promising approach to simultaneously n-dope and largely insolubilize conjugated polymer films using tetrakis[{4-(1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazol-2-yl)phenoxy}methyl]methane (tetrakis-O-DMBI-H), which consists of four 2,3-dihydro-1H-benzoimidazole (DMBI-H) n-dopant moieties covalently linked to one another. Doping a thiophene-fused benzodifurandione-based oligo(p-phenylenevinylene)-co-thiophene polymer (TBDOPV-T) with tetrakis-O-DMBI-H results in a highly n-doped film with bulk conductivity of 15 S cm-1. Optical absorption spectra provide evidence for film retention of ∼93% after immersion in o-dichlorobenzene for 5 min. The optical absorption signature of the charge carriers in the n-doped polymer decreases only slightly more than that of the neutral polymer under these conditions, indicating that the exposure to solvent also results in negligible dedoping of the film. Moreover, thermal treatment studies on a tetrakis-O-DMBI-H-doped TBDOPV-T film in contact with another undoped polymer film indicate immobilization of the molecular dopant in TBDOPV-T. This is attributed to the multiple electrostatic interactions between each dopant tetracation and up to four nearby anionic doped polymer segments.

Additive-Free Aqueous Phase Synthesis of Formic Acid by Direct CO2 Hydrogenation over a PdAg Catalyst on a Hydrophilic N-Doped Polymer–Silica Composite Support with High CO2 Affinity

A series of N-doped polymer containing silica (NPS) materials were synthesized via condensation reactions of 3-aminopropyltriethoxysilane (APT) and various aldehydes. These materials were assessed ...

Reduction Treatment of Molecular-Doped Polymer Semiconductors for High-Performance N-Channel Organic Field-Effect Transistors

Here, we study an efficient reduction treatment for improving the electron transport properties in n-type organic field-effect transistors (OFETs) based on solution-processed polymer semiconductors. If complementary-type printed electronic circuits are to be enabled, equivalently high-performance p-type and n-type organic semiconductors have to develop. Most organic semiconductors have p-type performance superior to the n-type performance. Therefore, high-performance n-type organic semiconductors and their doping process are essential. Reduced-state viologen is known to be a powerful molecular dopant via donating electrons to the conjugated polymer semiconductors. However, the reduced-state viologen readily converts to its initial ionic species under ambient conditions, which leads to insufficient n-doping performance, especially for low electron affinity organic semiconductors. N-doped polymer semiconductors using pristine viologen molecular dopants show inadequate n-channel OFET behavior. For enhancing the electron transfer doping process, solution-based reduction treatment is used to improve remarkably the performance of n-channel OFETs based on initially p-type dominant donor-acceptor-type ambipolar polymer semiconductors. This solution-processed organic active channel layer can be produced at low cost and can be applied to flexible electronic and optoelectronic devices by using various graphic art printing techniques.

The dynamic bipolar electrode in polymer light-emitting electrochemical cells

The redox doping reactions in polymer light-emitting electrochemical cells (PLECs) have been analyzed to gain insight into a new type of bipolar electrode (BPE) formed within the cells. Planar (lateral) PLECs are constructed on a glass substrate with an exposed active polymer layer contacted by two aluminum (Al) driving electrodes at 11 mm apart. A horizontal array of 13 silver (Ag) microdiscus is deposited in-between the driving electrodes. When a 200 V bias is applied between the driving electrodes, the electrically floating Ag discs functioned as BPEs to induce redox p- and n-doping reactions in polymer layer that initially occur at the extremities of the BPEs. The doping reactions are visualized as strong photoluminescence quenching of the luminescent polymer. Over time, the doped regions grow in size, and the silver disc BPEs transform into dynamic, composite BPEs consisting of a p- and n-doped polymer conductor connected by the initial BPE disc. Unlike a homogenous BPE, the dynamic BPE is not a quasi-equipotential body under operation. Moreover, the n/p area ratios of all 13 BPEs in the array converge to a single value which is strongly affected by the composition of the PLEC layer. The n/p ratios ranging from 0.24 to 2.19 have been observed in PLECs made with Li, Na, and K triflate salts as well as two different luminescent polymers. The dynamic BPE array thus presents a novel essay to evaluate and screen the mixed luminescent conductor for device applications.

Dynamic Bipolar Electrode Array for Visualized Screening of Electrode Materials in Light-Emitting Electrochemical Cells.

Charge injection at a metal/semiconductor interface is of paramount importance for many chemical and physical processes. The dual injection of electrons and holes, for example, is necessary for electroluminescence in organic light-emitting devices. In an electrochemical cell, charge transfer across the electrode interface is responsible for redox reactions and Faradic current flow. In this work, we use polymer light-emitting electrochemical cells (PLECs) to visually assess the ability of metals to inject electronic charges into a luminescent polymer. Silver, aluminum, and gold microdisks are deposited between the two driving electrodes of the PLEC in the form of a horizontal array. When the PLEC is polarized, the individual disks functioned as bipolar electrodes (BPEs) to induce redox p- and n-doping reactions at their extremities, which are visualized as strongly photoluminescence-quenched growth in the luminescent polymer. The three metals initially generate highly distinct doping patterns that are consistent with differences in their work function. Over time, the doped regions continue to grow in size. Quantitative analysis of the n/p area ratio reveals an amazing convergence to a single value for all 39 BPEs, regardless of their metal type and large variation in the size of individual doped areas. We introduce the concept of a dynamic BPE, which transforms from an initial metal disk of a fixed size to one that is a composite of p- and n-doped polymer joined by the initial metallic BPE. The internal structure of the dynamic BPE, as measured by the n/p area ratio, reflects the properties of only the mixed conductor of the PLEC active layer itself when the area ratio converges.

Electron Injection on Metal/n-Doped Semiconducting Polymer

Efficient n-type doping was not established since the dopants dose not dissolve in same organic solutions of polymer semiconductors. Evaporative Spray Deposition using Ultra-dilute Solution (ESDUS) method enabled it recently. We have already reported efficient n-type doping of poly(2-methoxy-5-(2’-methyl-hexyloxy)-p- phenylenevinylene) (MEH-PPV: LUMO: 3.1 eV, HOMO: 5.2 eV). The high doping efficiency as much as 15% was realized. In organic devices composed of non-doped organic semiconductors, electron injection barrier is basically equal to the gap between LUMO of the organic semiconductor and work function of the el ectrode. It is still open question how the barrier is formed in the n-doped polymer/electrode. The metal/semiconductor junction of n-doped polymer has not been studied yet. In this research, we have fabricated electron only devices (EOD) of an n-doped polymer semiconductor using electrodes of Al and Ca. The electron injection from Al or Ca was examined.MEH-PPV (Mw = 40,000-70,000 Aldrich) and Cesium carbonate were used as a host polymer and an n-type dopant, respectively. The asymmetric EOD using Al for bottom and top electrodes and and a top Ca electrode having a lower work function (3.0 eV) were fabricated. The current-voltage (J-V) characteristics were measured in vacuum without breaking vacuum after the top electrode deposition. J-V characteristics of asymmetric EOD (Fig. 1), Al(50nm)/MEH-PPV:Cs2CO3 (110nm)/Ca(50nm) are fabricated. The current density was drastically increased as the doping concentration increased. The asymmetric EODs, current density in the forward bias was about 1 order of magnitude larger than that in reverse bias at low doping concentration at 0, 0.2, 2.0 wt%.However, the current density was almost overlapped in forward and reverse bias at the doping concentration of 10wt%. The disappearance of the rectification property suggests that the quantum tunneling takes place due to the very thin depletion layer at Al/MEH-PPV junction at the high doping concentration. In order to evaluate depletion layer width on Al/MEH-PPV junction, C-F measurement was carried out. As a result of the calculation, the depletion layer width of the 0.2 wt% doped device was 16.3 nm, the 2.0 wt% doped device was 9.3 nm, and the 10.0 wt% doped device was 3.3 nm. These results suggest that the depletion layer narrows as the doping concentration increases and the rectification property disappears in the 10 wt% doped device by quantum tunneling. The depletion layer width when quantum tunneling was observed in the p-type organic device, Au/ZnPc:0.3%F4-TCNQ/Au, was 5.2nm. Compared with this depletion layer width of 5.2 nm at metal/p-type organic semiconductor junction, it can be said that the value of 3.3 nm calculated this time is sufficiently narrow to observe quantum tunneling.

Improved Electron Transport with Reduced Contact Resistance in N-Doped Polymer Field-Effect Transistors with a Dimeric Dopant.

Attaining control on charge injection properties is significant for meaningful applications of organic field-effect transistors (OFETs). Here, molecular electron-doping is applied with an air-stable dimer dopant for n-type OFETs based on (naphthalene diimide-diketopyrrolopyrrole) polymer hosts. Through investigating the doping effect on contact and transport properties, it is found that the electron transport increases in n-doped OFETs at low doping regime with remaining large on/off ratios. These favorable meliorations are reconciled by the mitigated impacts of contact resistance and interfacial traps, as well as the surface morphology exhibiting features of increased ordering. The occurrence of doping in the presence of dimer dopants is evidenced by the observed shift of Fermi level toward vacuum level coupled with compositional analysis. Without applying vacuum-deposition-based contact doping, charge injection efficiencies are gained without losing OFET characteristics using the solution-based methodology.

P-Type and n-Type Doping for Polymer Semiconductor

Nondoped organic semiconductors are usually used in organic devices such as organic light-emitting diodes (OLEDs) and solar cells, although inorganic semiconductor devices are realized by doping. Carrier doping has been attempted with dispersion of the donor or acceptor molecules in some organic semiconductors. The conductivity of the organic semiconductor can be significantly improved. The doping efficiency is defined as the ratio of increased carrier density to dopant density. The doping efficiency in small-molecule semiconductors fabricated by a coevaporation method has been increased recently. The OLEDs and solar cells with the p-i-n structure consisting of small molecules have been realized by layer-by-layer deposition of p-type doped and n-type doped semiconductors. On the other hand, p-i-n doping in polymer semiconductors has not been realized yet, because there are some problems with the use of n-type molecular dopants. The representative dopants used in coevaporation such as Cs2CO3, FeCl3, and CsF are poorly soluble in organic solvents, which can dissolve polymer semiconductors, and aggregate easily in the polymer matrix during spin coating even when they are dispersed in a polymer solution. Therefore, the doping efficiency in polymer semiconductors has been very low, with 3% as the highest.We have developed a polymer-thin-film preparation method, evaporative spray deposition using an ultradilute solution (ESDUS), which enables the preparation of polymer semiconductor films using a highly diluted solution at 1 ppm. In a previous study, on the basis of using this method of preparing polymer semiconductor films using an ultradilute solution, we have tried to prepare n-type doped polymer semiconductor poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) thin films with Cs2CO3, which is an effective n-type dopant with low solubility in an organic solvent. As a result, the conductivity of the device was significantly improved with a high doping efficiency of 60%. This result is caused by ESDUS, which suppresses aggregation of dopant molecules. Furthermore, we have fabricated pn junctions by layer-by-layer deposition of an n-doped polymer semiconductor film on a p-doped polymer poly(3-hexylthiophene) (P3HT) film. In the present study, we attempted p-type and n-type doping of a polymer semiconductor, poly[2-methoxy-5-(2’-methyl-hexyloxy)-p-phenylenevinylene] (MEH-PPV LUMO, 3.1 eV, HOMO, 5.2 eV). It is one of the most widely used conductive polymers and a bipolar carrier-transporting semiconductor. FeCl3 (work function, 5.52 eV) as a p-type dopant and Cs2CO3(work function, 2.96 eV) as an n-type dopant were chosen for p-type and n-type doping in MEH-PPV, respectively. MEH-PPV was dissolved in THF at 10 ppm. After the optimization of deposition conditions such as temperature, carrier gas flow rate, and solution feed flow rate, a homogeneous and continuous film of 20 nm thickness was obtained. Each dopant molecule was dissolved in dehydrate ethanol at a concentration of 3 mg/ml and the solution was kept in a glove box with stirring overnight at 50 ℃. The dopant solutions were diluted with THF and added to a THF solution of MEH-PPV. The polymer concentration was kept constant at 10 ppm and the dopant concentration was varied at 0.02, 0.2, and 2 wt% against the polymer (0.02 wt% corresponds to FeCl3:0.096 mol% and Cs2CO3:0.047 mol% against the monomer of an MEH-PPV unit). The MEH-PPV solution containing each dopant was supplied to the ESDUS and formed into thin films. Electron-only-device (EOD), Al/MEH-PPV (100 nm)/Ca, and hole-only-device (HOD), ITO/MEH-PPV (100 nm)/Au, were fabricated by vacuum deposition of the top electrode after ESDUS preparation of the MEH-PPV layer with the desired dopant concentration. Current-voltage (I-V) characteristics were measured using a Keithley 238 source meter without breaking vacuum after top electrode deposition. The hole and electron densities of the nondoped MEH-PPV and hole and electron mobilities were calculated from the I-V curves. The Fermi levels of the MEH-PPV films were estimated using a surface potential meter (Kelvin probe, Riken Keiki, FAC-1) in nitrogen without exposing the samples to the ambient atmosphere after ESDUS film deposition. The nondoped and doped MEH-PPV films of 100 nm thickness were fabricated on Al and the Fermi level was estimated with respect to the Au standard (5.03 eV). The current-voltage (I-V) characteristics of hall-only-devices (HOD) with varying FeCl3 (p-dopant) concentration and electron-only-devices (EOD) with varying Cs2CO3 (n-dopant) concentration clearly indicate that the current density increases significantly more than 1000 times as the doping concentration gets higher (Fig. 1). The carrier density increases with dopant concentration linearly and the doping efficiency is as high as 15% at low dopant concentration. The wide dispersion of the dopants in the ultradilute solution leads to high doping efficiency and large charge separation with the host polymer. Figure 1

Dielectric spectroscopy of [P(NID2OD-T2)]n thin films: Effects of UV radiation on charge transport

Poly[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyll-alt-5,5′-(2,2′-bithiophene)]-[P(ND12OD-T2)]n is a n-doped polymer that is stable in air. Low frequency (40Hz–30kHz) dielectric spectroscopy shows that the polymer impedance strength is reduced under ultra-violet (UV) radiation as a result of charge increase in the bulk polymer. Photo-excitation and the creation of electron-hole pairs and subsequent hole recombination with electron trapping species adsorbed by the polymer are suggested as possible doping mechanisms. The relaxation times were also faster in the presence of UV indicating multiple pathways for oscillating dipoles to relax. These results imply increased polymer conductance with corresponding enhancement of charge mobility due to reduced scattering in the presence of UV radiation. A thin film field effect transistor was fabricated using this polymer as the active material and characterized in the presence of UV radiation. As expected, the device exhibited n-type behavior with a charge mobility of 3.0×10−3cm2/V-s. Exposure to UV radiation increased the channel current, shifted the threshold voltage to more negative values and doubled the value of the mobility. These results are consistent with dielectric measurements and suggest an easy method of increasing device currents and charge mobility in this polymer via UV irradiation.

Electrosynthesis of viologen cross-linked polythiophene in ionic liquid and its electrochromic properties

Utilizing electrochemical reduction of pendant cyanopyridinium ions to cross-link polymeric viologens is well known. In this work, we report electrosynthesis of a thiophene monomer bearing a pendant cyanopyridine moiety in its side chain (Th-CN). Its electropolymerization results in the growth of a polythiophene film which is highly cross-linked by the viologen unit (PTh-V). In order to improve adhesion and insolubility of the as-formed polymer film, we choose the ionic liquid 1-butyl-3 methylimidazolium hexafluorophosphate (BmimPF6), as electrolyte. The obtained polymer film was studied by cyclic voltammetry, FTIR spectroscopy, in situ UV-Vis spectroelectrochemistry and electrochemical impedance spectroscopy (EIS). The CV results showed electrochemical activity both of the viologen and polythiophene moieties. FTIR spectra of the polymer film confirm the formation of viologen by disappearance of the–CN stretching band from the polymer spectrum. EIS studies revealed that both resistive as well as capacitive element controls the charge transfer mechanism. In situ spectroelectrochemical studies of the polymer film shows enhanced electrochromic contrast of polythiophene film due to incorporation of viologen pendant group with coloring characteristics both of the viologen and the polythiophene backbone. An n-doped polymer is a dark blue colored film with coloration efficiency being ca. 97 cm2/C at 625nm while the p-doped polymer is transparent violet in color with coloration efficiency of ca. 12 cm2/C at 775nm. The results showed that the PTh-V film can be used as redox active conducting layer to develop dynamic optoelectronic and electrochromic devices.

Charge Injection and Transport in Metal-Containing Conducting Polymers: Spectroelectrochemical Mapping of Redox Activities

Electropolymerization of tris(dioximate) cage complexes furnished metal-containing conducting polymers (MCPs) that deposit directly onto the electrode surface as uniform films. The injection of electrons into, or removal of electrons from, these electroactive materials proceeds via different pathways with different rates, the underlying molecular mechanisms of which were investigated by a combination of electrochemical, spectroscopic, and focused-ion-beam–scanning electron microscopy (FIB-SEM) cross-section analysis studies. For cobalt-containing polymers, both the metal centers and π-conjugated organic backbone work cooperatively as hopping stations for migrating holes, whereas the reduced polymer utilizes less-efficient self-exchange between cobalt(II) and cobalt(I) centers for electron transport. A small molecule model of such reductively doped polymer was prepared independently, which provided compelling electrochemical and spectroelectrochemical evidence to support the structural integrity of the metal centers upon redox switching. A well-defined metal-to-ligand charge transfer (MLCT) band of the n-doped polymer was exploited further as a straightforward spectroscopic tool to quantify the number of redox-active metal centers directly and to estimate the lower distance limit of diffusional charge transport across the bulk material.

UV-Vis-NIR spectroelectrochemical and in situ conductance studies of unusual stability of n- and p-doped poly(dimethyldioctylquaterthiophene-alt-oxadiazole) under high cathodic and anodic polarizations

Combined CV studies and UV-Vis-NIR spectroelectrochemical investigations revealed an unusual stability of the p- and n-doped PMOThOD in the wide potential window of 4 V. The n-doping process occurs in this polymer down to -2.7 V (vs. Ag/Ag+) in a non-destructive way with the characteristic development of the omega3 transition as a function of the doping level. In situ electronic transport studies revealed a high conductivity of the n-doped polymer which implies high mobility of the negatively charged carriers in the freshly doped PMOThOD film electrodes. An increase in the cathodic polarization, long-term cycling of the film electrodes, especially of higher thickness, results in a growing contribution of the negatively charged carriers trapping to the redox properties of the PMOThOD. The trapping of the charged carriers reduces gradually the electronic conductance of the PMOThOD film, but its effect on the redox-capacity of the film (in a typical scan rates range up to 50 mV s(-1)) is only minor.

X-ray photoelectron spectroscopy studies of the electrochemically n-doped state of a conducting polymer

X-ray photoelectron (XPS) and UV photoelectron (UPS) spectroscopies were used to characterize the electrochemically n- and p-doped states of poly (3-(4-fluorophenyl) thiophene), PFPT. The polymer was electrochemically grown on platinum electrode from the corresponding monomer. The polymer was characterized by cyclic voltammetry in an electrochemical cell that was attached to the antechamber of the spectrometer in order to avoid as much as possible exposure to ambiant air since the n-doped state is very air and water sensitive. UPS was used to evaluate the position of the Fermi level of the doped PFPT’s which allows for the determination of their work functions. The work functions of p- and n-doped PFPT are 4.3 and 2.6 eV, respectively. The S 2p core level spectrum of the n-doped polymer shows a main doublet at absolute binding energies of about 167.6 (2p 3/2) and 168.9 (2p 1/2) eV and a second doublet at lower binding energy which disappears upon oxidation to the p-doped state and is only observed for the reduced n-doped polymer. The presence of this low binding energy doublet can be explained by a higher charge localization for the n-doped state relative to the p-doped state and is consistent with the lower conductivity (by a factor of about 10) of the former. XPS was also used to investigate ion-exchange during redox switching of polymers and evaluate the doping levels of polymer. In most cases, the later values were found to be in relatively good agreement with those computed from the electrochemical data.

A theoretical study of the chemical structure of the non-conjugated polymer poly(3,3′-phthalidylidene-4,4′-biphenylene)

The equilibrium geometry of an isolated chain of poly(3,3′-phthalidylidene-4,4′-biphenylene), or PPB, has been studied using quantum chemical calculations based upon the Austin Model 1 (AM1) method. The band structure of an isolated PPB chain has been calculated, using the AM1 geometry as input, with the help of the valence-effective Hamiltonian (VEH) model. From the electronic structure results, the density of valence states has been derived for comparison with experimental data. Both the neutral and the n-doped polymer chains have been simulated. The results are compared with features of the polymer deduced through other measurements reported in the literature.

Electrochemical n-doping of poly(dithienylvinylene). A comparison of cyclovoltammetric and conductive properties in n- and p-doping

Electrochemical n-doping of poly(dithienylvinylene) has been performed in AN + 0.1 M N(C n H 2 n+1 ) 4 +ClO 4 − ( 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.