Nonconjugated Conductive Polymer Research Articles

Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped polyethylene terephthalate

Quadratic electro-optic effect has been measured in the nonconjugated conductive polymer iodine-doped polyethylene terephthalate (PET). Films of PET were doped with iodine in the vapor phase using standard procedure. The optical absorption and FTIR spectroscopic results show that iodine doping causes a charge-transfer from the terephthalic ring to iodine, thus forming a metallic quantum dot of subnanometer dimension. Nonlinear optical measurements were performed on the iodine-doped PET samples using field-induced birefringence method at 633 nm with lock-in detection. The magnitude of the Kerr coefficient for varying doping levels was determined. The magnitudes were shown to increase with doping level. For an iodine molar concentration of 0.28, a Kerr coefficient of ∼1.5 × 10−11 m/V2 was measured. For a molar concentration of iodine of 0.83, the measured Kerr coefficient was ∼5 × 10−11 m/V2. These magnitudes are comparable to (slightly smaller than) the Kerr coefficients measured in other iodine-doped nonconjugated conductive polymers representing metallic quantum dots of subnanometer dimensions.

Electroabsorption in Metallic Nanoparticles within Transparent Dielectric Media

Electroabsorption in metallic nanoparticles within transparent dielectric media has been measured. In particular, gold nanoparticles in glass and subnanometer-size metallic domains in iodine doped nonconjugated conductive polymer have been studied. Measurements have been made for applied ac fields at 4 kHz, at a wavelength close to the onset of the surface plasmon resonance. The measured electroabsorption (imaginary part of χ(3) or Kerr coefficient) has a quadratic dependence on electric field. Its magnitudes were compared for different sizes of the metallic nanoparticles down to the subnanometer-size particles in iodine-doped nonconjugated conductive polymer. As in the case of quadratic electro-optic effect reported earlier, electroabsorption has approximately a 1/d3 dependence, d being the diameter of nanoparticle. This is consistent with existing theories on confined metallic systems.

Quadratic Electro-Optic Effect in Metal Nanoparticles in a Transparent Dielectric Medium

The quadratic electro-optic effect/Kerr coefficients were measured for the first time for metal nanoparticles. In particular, gold nanoparticles in glass were studied. Measurements were made using the field-induced birefringence method at a wavelength near the onset of the surface plasmon resonance. The magnitudes of the Kerr coefficients for different sizes of gold nanoparticles in glass were measured and compared with that of subnanometer size metallic particles in non-conjugated conductive polymers. The magnitude of the Kerr coefficient was found to increase rapidly (about d−3) when the diameter, d, of the nanoparticles was decreased. This is consistent with the existing theories and understanding of nonlinear optics in metal nanoparticles. The results imply a broad range of new applications of metal nanoparticles in electro-optic switching/modulation, low-cost Kerr cells and other uses in optoelectronics.

Photovoltaic cells involving the nonconjugated conductive polymer, iodine-doped cis-poly(isoprene)

ABSTRACTNovel photovoltaic cells involving a nonconjugated conductive polymer have been fabricated using titanium dioxide/doped cis-1,4-poly(isoprene)/carbon on ITO coated PET substrates. Photocurrents and photo-voltages for different intensities of light (emission at 300–700 nm) have been measured. These cells have shown significantly higher photocurrents and photo-voltages compared to previous reports. A photocurrent density of about 0.27 mA/cm2 and a photo-voltage of 0.73 V have been measured for a light intensity of ∼4 mW/cm2.

Photovoltaic Cells Involving the Nonconjugated Conductive Polymer Iodine-Doped Styrene-Butadiene-Rubber (SBR)

Novel photovoltaic cells involving a nonconjugated conductive polymer have been fabricated using titanium dioxide/doped styrene-butadiene-rubber/carbon on ITO coated PET substrates. Photocurrents and photo-voltages for different intensities of light (emission at 300–700 nm) have been measured. These cells have shown significantly higher photocurrents and photo-voltages compared to previous reports. A photocurrent density of about 0.25 mA/cm2 and a photo-voltage of 0.74 V have been measured for a light intensity of ∼4 mW/cm2.

Photovoltaic Cells Involving the Nonconjugated Conductive Polymer, Iodine-Doped Poly(β-pinene)

Novel photovoltaic cells involving a nonconjugated conductive polymer have been fabricated using titanium dioxide/doped poly(β-pinene)/carbon on ITO glass-substrates. Photocurrents and photo-voltages for different intensities of light (emission at 300-700 nm) have been measured. Use of iodine-doped nonconjugated conductive polymer (poly(β-pinene)) film has led to significant enhancement of photocurrent compared to previous reports involving undoped polymer in a different device-structure. A photocurrent density of about 0.03 mA/cm2 and a photo-voltage of 0.65 V have been measured for a light intensity of ∼5 mW/cm2. These cells being the first generation of its kind the results are promising for applications.

Thermal Studies of an Organic Nanometallic based on a Nonconjugated Conductive Polymer, Poly(ß-pinene)

Differential scanning calorimetry (DSC) has been used to measure the thermal properties of the nonconjugated conductive polymer, poly(ß-pinene) before and after doping with iodine. The measurements have been made over the temperature range of −50°C to 110°C. The glass transition temperature of undoped poly(ß-pinene) has been determined to be about 77°C. The specific heat increased by about 16% upon doping, from about 2.03 J/g-°C in the undoped state to about 2.35 J/g-°C in the doped state. The observed increase in specific heat capacity upon doping, along with the reported electrical, linear optical and exceptionally large nonlinear optical characteristics in the doped state, have been attributed to the nanometallic-like structures formed in this polymer upon doping.

Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped trans-polyisoprene, an organic nanometallic system

Thin films of 1,4-trans-polyisoprene have been prepared on various substrates from toluene solution and characterized using Fourier transform infrared (FTIR) spectroscopy, optical absorption spectroscopy and X-ray diffraction before and after doping with iodine. The optical absorption spectrum at low doping shows two peaks: one at 4.2 eV and the other at 3.2 eV. X-ray diffraction indicates an increase of (111) and (122) peak intensities upon doping. Quadratic electro-optic measurements have been made using field-induced birefringence. The Kerr coefficients as measured (3.5×10 −10 m/V 2 at 633 nm and 2.5×10 −10 m/V 2 at 1.55 μm) are exceptionally large, and they have been attributed to the subnanometer-size metallic domains formed upon doping and charge transfer.

Photo-induced Charge-transfer and Photovoltaic Effect in a Composite Involving a Nonconjugated Conductive Polymer and C60

Photo-induced charge-transfer and resulting photovoltaic effect in a composite involving a nonconjugated conductive polymer, poly(β -pinene) and C60 is reported. The photovoltaic cell was fabricated using indium-tin-oxide coated glass as one electrode and aluminum as the other, with poly(β -pinene)-C60 composite film sandwiched in-between. A Nitrogen laser (325 nm) and an illuminant white-light-source (300–700 nm) were used and the photo-voltage produced was found to have a linear dependency on light intensity. The photoluminescence of poly(β -pinene) (at 360 nm) was quenched when C60 was added to form the composite. Therefore, the photovoltaic effect is a result of excited-state electron-transfer from poly(β -pinene) to C60.

Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped poly( [formula omitted]-pinene) measured at longer wavelengths including [formula omitted

The quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped poly( β -pinene), measured at longer wavelengths including 1.55 μm, is reported. The field-induced birefringence technique was used. A modulation depth of 0.1% was observed in a 1 μm thick sample for an applied field of 1 V/μm at 1.55 μm. The corresponding Kerr coefficient obtained is 1.6×10 −10 m/V 2. The Kerr coefficients measured at 790–810 nm are also very large. This exceptionally large (largest known) optical nonlinearity has been attributed to the subnanometer size metallic quantum dots formed in this polymer upon doping with iodine and the optimized film quality recently achieved.

New Additions to Nonconjugated Conductive Polymers; Nonlinear Optical Effects

Recently, new additions to nonconjugated conductive polymers have been made that include: poly(β-pinene), poly(ethylenepyrrolediyl) derivative and polynorbornene. These polymers have different double-bond number fractions per repeat compared to previously reported nonconjugated conductive polymers. Upon doping with electron acceptor (e.g. iodine) the conductivities increase more than ten orders of magnitude to levels consistent with their double-bond number fractions. Radical cations that are formed upon doping have dimensions less than a nanometer leading to unexpectedly large nonlinear optical effects. The measured Kerr coefficient of doped polyisoprene is ∼1.6 × 10-10 m/V2 at 633 nm. For doped poly(β-pinene) the Kerr coefficient is ∼1.2 × 10-10 m/V2 and for poly(ethylenepyrrolediyl) derivative it is ∼1.2 × 10-9m/V2. Exceptionally large two-photon absorption coefficient (∼2.6 cm/MW at 810 nm) has been measured for doped poly(β-pinene). The mechanism of the nonlinear optical effect has been explained using a model of subnanometer size metallic quantum dots. These novel materials with wide transparency are expected to have significant applications in photonics.

Electrical and Optical Properties of a Novel Nonconjugated Conductive Polymer, Polynorbornene

We report electrical and optical properties of a novel nonconjugated conductive polymer, polynorbornene which has an isolated double bond in the repeat. Electrical conductivity of this polymer increases by twelve orders of magnitude to about 0.01 S/cm upon doping with iodine. Optical absorption measurements of the polymer film have been made at different dopant concentrations. For a lightly doped polymer, two absorption peaks: one corresponding to cation radicals and the other corresponding to charge transfer between the double bond and the dopant were observed at 4.20 eV (295 nm) and 3.13 eV (396 nm) respectively. FTIR spectroscopic measurements have shown reduction in the intensities of the C═C stretching and ═C─H bending vibration bands upon doping indicating formation of radical cations. Photoluminescence studies have shown an emission band with a major peak at ∼422 nm when excited at 280 nm. The peaks in the photoluminescence spectrum are consistent with the vibration bands observed in the FTIR spectrum.

EPR Spectroscopic Studies of Radical Cations in a Novel Nonconjugated Conductive Polymer, Poly(β‐pinene)

Electrical conductivity, FTIR spectroscopy and electro‐optic effect in a novel nonconjugated conductive polymer, poly(β‐pinene), have been recently reported. The conductivity increases by more than ten orders of magnitude upon doping with iodine. The double bonds decrease upon doping due to charge‐transfer and formation of radical cations. In this report, electron paramagnetic resonance (EPR) spectroscopic measurements of poly(β‐pinene) before and after iodine doping are discussed. The results show that the EPR signal increases in proportion to the doping level consistent with the formation of radical cations upon doping. Hyperfine splitting has been observed at high doping levels due to reduction in distance between the radical cation and the iodine anion. Such splitting was not observed for a doped conjugated polymer since in that case the radical is delocalized.

Quadratic electro-optic effect in a nano-optical material based on the nonconjugated conductive polymer, poly(ethylenepyrrolediyl) derivative

We report the results of optical absorption, quadratic electro-optic and electroabsorption measurements in a novel nano-optical material based on the nonconjugated conductive polymer, poly(ethylenepyrrolediyl) derivative. Two peaks at about 310 and 420 nm have been observed in the optical absorption spectrum of the polymer at a low doping level of iodine. The Kerr constant as determined at 633 nm, which is close to resonance, is about 1.2×10 −9 m/V 2 which is about 495 times that of nitrobenzene. This exceptionally large Kerr coefficient has been attributed to the special structure and quantum confinement of this electronic system within a subnanometer domain.

Two-photon absorption in quantum dots based on a nonconjugated conductive polymer

Two-photon absorption has been measured in a nano-optical material (quantum dots) based on the nonconjugated conductive polymer, iodine-doped poly(β-pinene). The measurement has been made using open-aperture z scan at 730–860nm with 150fs pulses. Exceptionally large two-photon absorption coefficient has been observed with a peak of magnitude ∼2.6cm∕MW that appeared at ∼1.53eV which is close to half of the optical gap corresponding to the charge-transfer transition involving the isolated double bond. Saturation of absorption was observed at lower intensities and shorter wavelengths. The results have been attributed to the quantum dots (subnanometer size) formed upon doping.

Quadratic electro-optic effect in a nano-optical material based on the nonconjugated conductive polymer, poly(β-pinene)

Large quadratic electro-optic effect has been observed in a nano-optical material based on a nonconjugated conductive polymer, poly(β-pinene). Doping of poly(β-pinene) leads to subnanometer size charge-transfer sites with positive charges (holes). The observed large electro-optic effect has been attributed to these confined systems with special structures. The magnitude of the Kerr constant increases with the concentration of the dopant or charge-transfer sites. The maximum Kerr coefficient at 633nm which is close to resonance is about 50 times that of nitrobenzene.

Electrical and optical properties of a novel nonconjugated conductive polymer, poly(β‐pinene)

AbstractElectrical conductivity in a novel nonconjugated conductive polymer, poly(β‐pinene), has been measured as a function of molar concentration of iodine. The conductivity increases about 10 orders of magnitude to a maximum value ˜8 × 10−3 S/cm. The molar concentration of iodine, corresponding to saturation, is ˜0.85. The optical absorption measurements after light doping have shown two peaks: one at 4.0 eV and the other at 3.1 eV. The first peak is due to the radical cation, and the second due to the charge‐transfer between the double bond and the dopant. As observed in other nonconjugated conductive polymers, the second peak becomes broader and undergoes a red shift, upon higher doping. The FTIR spectroscopic studies have shown that the CC stretching vibration at 1610 cm−1 and the CH bending vibration band at 728 cm−1 decrease upon doping, because of decrease of double bonds. Photoluminescence studies of poly(β‐pinene) show a maximum value at 360 nm for excitation at 280 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3695–3698, 2005

Polyalloocimene, a Novel Nonconjugated Conductive Polymer: The Correct Fundamental Basis for Conductive Polymers

A polymer does not have to be conjugated to become electrically conductive. The correct fundamental basis for a polymer to be conductive is that it must have at least one double bond in the repeat. The magnitude of conductivity increases with the number fraction of the double bonds in the repeat. Polyisoprene, the first known nonconjugated conductive polymer has a double bond number fraction of 1/4 while polyacetylene, the first known conjugated conductive polymer, has a number fraction of 1/2. A new nonconjugated conductive polymer, polyalloocimene, has a double bond number fraction of about 1/3. Consequently, the electrical conductivity, the doping rate and the optical transition energies of polyalloocimene are intermediate between those of polyisoprene and polyacetylene. The magnitude of conductivity has a power law dependence on the number‐fraction of double bonds. The optical absorption peak of the radical cation produced upon doping appears at lower energies as the separation between the double bonds decreases. The general mechanism of conductivity going from a nonconjugated structure involving isolated double bonds to a fully conjugated structure has been established.

NONCONJUGATED CONDUCTIVE POLYMERS

Conjugation is not a prerequisite for a polymer to be conductive. A polymer must have at least one double bond in the repeat to become conductive. Interaction with a dopant (e.g., electron acceptor) causes transfer of an electron from the double bond to the dopant creating a hole at the double bond site. Electrical conduction occurs via intersite hopping of holes. Various spectroscopic methods (FTIR, optical absorption, solid-state 13C NMR, etc.) along with electrical measurements have been used to elucidate the mechanism of conduction in specific nonconjugated conductive polymers. Examples of these polymers include 1,4-polyisoprene which has one double bond and three single bonds in the repeat. The conductivity of polyisoprene increases 100 billion times upon doping with iodine to a maximum value of 10 S/m. Polyisoprene (natural rubber) is used nonconjugated conductive polymers have a wide range of applications in antistatics, various sensors and optoelectronics.

The infrared spectrum of a non conjugated conducting polymer

MNDO calculations are presented on the dimer of butadiene and the derivatives that are conceivably obtained upon its doping with iodine, namely, its polaron (radical cation), its iodonium ion (π complex), and its iodiocation (σ complex). The calculations are aimed at gaining some understanding of nonconjugated conductive polymers of which polybutadiene is a prototype. First a justification of the adopted procedure is given; then, the infrared spectra of the pristine and the doped polymer are examined in view of the results obtained for the dimer. Evidence is found in the spectra of both polaron and the π complex. The charge flow in all systems is evaluated and all of the dimer derivatives are found to have a charge flow larger than the parent species, with the largest one due to the polaron. On the basis of the results, it is argued that the temperature dependence of the electron transport in the two species found in the spectra (π complex and polaron) could be different.