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

The FeCl3-doped three poly(3-alkylthiophenes) (P3ATs) in solid state, i.e. poly( 3-octylthiophenl) (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 sidechain group. We have also observed the relaxation behaviors in the conductivities of the doped polymers. (C) 2001 Elsevier Science B.V. All rights reserved.

Negative differential resistance in doped poly(3-methylthiophene) devices

The current density-voltage (J-V) characteristics of poly(3-methylthiophene) devices show a negative differential resistance (NDR) at room temperature with a large peak to valley current ratio (similar to 507). This NDR can be tuned by two orders of magnitude by controlling the carrier density due to the variation of the space-charge region in the device. The temperature and scan rate dependent J-V measurements infer that the NDR is mainly driven by the trapping and de-trapping of carriers. The photo-generation of carriers is observed to reduce the NDR effect.

NMR relaxation studies in doped poly-3-methylthiophene

NMR relaxation rates (1/T-1), magnetic susceptibility, and electrical conductivity studies in doped poly-3-methylthiophene are reported in this paper. The magnetic susceptibility data show the contributions from both Pauli and Curie spins, with the size of the Pauli term depending strongly on the doping level. Proton and fluorine NMR relaxation rates have been studied as a function of temperature (3-300 K) and field (for protons at 0.9, 9.0, 16.4, and 23.4 T, and for fluorine at 9.0 T). The temperature dependence of T-1 is classified into three regimes: (a) For T < (g mu(B) B/2k(B)), the relaxation mechanism follows a modified Korringa relation due to electron-electron interactions and disorder. H-1-T-1 is due to the electron-nuclear dipolar interaction in addition to the contact term. (b) For the intermediate temperature range (g mu(B) B/2k(B)) < T < T-BPP (the temperature where the contribution from the reorientation motion to the T-1 is insignificant) the relaxation mechanism is via spin diffusion to the paramagnetic centers. (c) In the high-temperature regime and at low Larmor frequency the relaxation follows the modified Bloembergen, Purcell, and Pound model. T-1 data analysis has been carried out in light of these models depending upon the temperature and frequency range of study. Fluorine relaxation data have been analyzed and attributed to the PF6 reorientation. The cross relaxation among the H-1 and F-19 nuclei has been observed in the entire temperature range suggesting the role of magnetic dipolar interaction modulated by the reorientation of the symmetric molecular subgroups. The data analysis shows that the enhancement in the Korringa ratio is greater in a less conducting sample. Intra-and interchain hopping of charge carriers is found to be a dominant relaxation mechanism at low temperature. Frequency dependence of T-1(-1) on temperature shows that at low temperature T < (g mu(B) B/2k(B))] the system shows three dimensions and changes to quasi one dimension at high temperature. Moreover, a good correlation between electrical conductivity, magnetic susceptibility, and NMR T-1 data has been observed.

Injection barrier induced deviations in space charge limited conduction in doped poly(3-methylthiophene) based devices

The carrier density dependent current-voltage (J V) characteristics of electrochemically prepared poly(3-methylthiophene) (P3MeT) have been investigated in Pt/P3MeT/Al devices, as a function of temperature from 280 to 84 K. In these devices, the charge transport is found to be mainly governed by different transport regimes of space charge limited conduction (SCLC). In a lightly doped device, SCLC controlled by exponentially distributed traps (Vl+1 law, l > 1) is observed in the intermediate voltage range (0.5-2 V) at all temperatures. However, at higher bias (> 2 V), the current deviates from the usual Vl+1 law where the slope is found to be less than 2 of the logJ-logV plot, which is attributed to the presence of the injection barrier. These deviations gradually disappear at higher doping level due to reduction in the injection barrier. Numerical simulations of the Vl+1 law by introducing the injection barrier show good agreement with experimental data. The results show that carrier density can tune the charge transport mechanism in Pt/P3MeT/Al devices to understand the non-Ohmic behavior. The plausible reasons for the origin of injection barrier and the transitions in the transport mechanism with carrier density are discussed. (C) 2015 AIP Publishing LLC.

The effects of different alkyl substitution on the structures and properties of poly(3-alkylthiophenes)

In order to investigate the influence of different alkyl side chain substitution on the structures and properties of P3ATs, X-ray diffraction, differential scanning calorimetry (DSC), thermal gravity analysis (TGA), Fourier transform infrared spectra (FTIR) and ultraviolet-visible spectra (W-VIS) were applied to characterizing the samples of ploy(3-octylthiophene) (P3OT), poly(3-dodecylthiophene) (P3DDT) and poly(3-octadecylthiophene) (P3ODT). It is found that the different length of alkyl group substitution leads to great difference in molecular chain packings, according to the room temperature X-ray diffraction results. The temperature dependence of X-ray diffraction experiments were also performed to study the melting processes of P3ATs. With the increase in the number of carbon atoms in alkyl side chains, the melting point decreases, and the thermal stability decreases too. The results of both FTIR and W-VIS spectra indicate that the conjugation length of P3DDT is the longest. among the three P3ATs. (C) 2001 Elsevier Science B.V. All rights reserved.

Non-isothermal crystallization kinetics of the poly(3-alkylthiophenes)

According to the data obtained from Differential Scanning Calorimetry (DSC),the method of Jeziorny, BOPOXOBCKHH and a new approach proposed by our laboratry are applied to study the nonisothermal crystallization behavior of poly( 3-dodecylthiophene) (P3DDT) and poly(3-octadecylthiophene) (P3ODT),and Kissinger method is used to get the value of the crystallization activation energy. The effect of the different alkyl substitution on crystallization is also investigated. In comparison to the methods of Jeziorny and BOPOXOBCKHH in which it can be found that the deviation from the line occurs in the later stage of crystallization, the new approach appears applicable due to the better linear relation. The values of the crystallization activation energy of P3DDT and P3ODT are estimated as 184.78kJ/mol and 246.93kJ/mol, respectivley, which implies that it is easiser to crystallize P3DDT than P3ODT.

Optical VOCs detection using poly(3-alkylthiophenes) with different side-chain lengths

The use of conjugated polymers in the gas and volatile organic compounds (VOCs) detections represents an advance in the development of the electronic noses. Polythiophenes show good thermal and environmental stability, are easily synthesized and they have been studied as gas and VOCs sensors using different principles or transduction techniques. Among these techniques, optical sensing has been attracted attention, mainly due to its versatility. However, conjugated polymer-based optical sensors are still less studied. This paper describes the use of two poly(3-alkylthiophenes) for VOCs optical detection. The sensing measurements were carried out using visible spectroscopy. Both polymers showed good sensitivity to the VOCs, showing fast and reversible responses with some hysteresis, and were unable to detect hydroxylated samples. Furthermore, it was demonstrated that the thickness of polymer films influences the intensity of the optical response. Although there is similarity in the superficial composition of the polymers films, demonstrated by their surface energies, they showed significant differences in their optical properties upon exposure to the VOCs. (c) 2009 Elsevier B.V. All rights reserved.

Evidence of room temperature charge-density wave behavior and glass-like states in pressed pellets of lightly doped poly (3-methyl thiophene)

We show room temperature charge-density wave (CDW) characteristics in d.c. and a.c. electric data in pressed pellets of lightly doped poly(3-methylthiophene). The possibility of a Peierls glass is discussed and metastables states are observed. D.C. and A.C. data also show a state with negative differencial resistance.

Room temperature ferromagnetic behavior in pressed pellets of doped poly (3-methylthiophene)

Room temperature ferromagnetic behavior has been observed in pressed pellets of doped poly(3-methylthiophene). In this work we show that thermoremance data taken in two different ways favours the interpretation of data in terms of the Dzialoshinski-Moriya anisotropic superexchange interaction of the polarons via dopant anions giving rise to weak ferromagnetism.

GIGAHERTZ CONDUCTIVITY OF PRESSED PELLETS OF CLO4--DOPED POLY(3-METHYLTHIOPHENE) OBTAINED FROM ELECTRON-SPIN-RESONANCE MEASUREMENTS

Gigahertz conductivity of pressed pellets of ClO4--doped poly( 3-methylthiophene) can be readily obtained from the asymmetry ratio (A / B) of the electron spin resonance line using Dyson's theory. The measurements were performed in three different frequencies, 1.3, 9.4, and 35 GHz. The temperature dependence of the gigahertz conductivity is sensitive to the heating rate, probably due to the ordering of the randomly assembled anions. (C) 1994 Academic Press, Inc.

Field-dependent conductivity at low electric fields in pressed pellets of doped poly (3-methylthiophene): evidence of charge-density wave depinning

Field-dependent conductivity at low electric fields was observed from low to room temperature in pressed pellets of doped poly(3-methylthiophene). The room temperature data showed good agreement with Bardeen's theory of charge-density wave depinning and the values of the parameters obtained are consistent with a strong electron-phonon interaction as expected for quasi-one dimensional systems. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Two-phase separation observed in thermally treated pellets of ClO4- doped poly(3-methylthiophene) from electron spin resonance measurements

A pressed pellet of CIO (-)(4) poly (3-methylthiophene) (P3MT) was heated for two hours at 85 degrees C and suddenly dropped in liquid nitrogen. A change was observed around 220 K in the Electron Spin Resonance (ESR) spectra when the sample was slowly cooled from room temperature. ESR line asymmetry parameter (A/B) showed two spatially separated phases. One was identified as a small metallic-like phase. The other phase, the larger one, makes a transition to a semiconducting Charge-Density Wave (CDW) state.

THERMAL-HISTORY-DEPENDENT TRANSITION IN PRESSED PELLETS OF CLO4(-)-DOPED POLY(3-METHYLTHIOPHENE)

Electron-spin-resonance and dc conductivity data show a thermal-history-dependent transition at 240 K in pressed pellets of ClO4--doped poly(3-methylthiophene) (P3MT). We discuss the possibility of this transition to be a Peierls transition from a room-temperature-metallic to a charge-density-wave state driven by anions ordering at this temperature. Below 100 K, dc conductivity shows a change from linear to exponential decay. Nonlinear conductivity has also been observed in this system for very low electric fields.

Metal-insulator transitions in pressed pellets of BF4 - doped poly(3-methylthiophene)

From Electron Spin Resonance (ESR) data in pressed pellets of BF4 - doped Poly(3-methylthiophene) (P3MT) we obtained simultaneously the paramagnetic susceptibility and. the microwave conductivity. We observed a transition from a high-temperature insulator state to a room-temperature metallic state. Around 240K. evidence of a Peierls transition is observed, but if the sample is slowly cooled, this transition is partially suppressed. DC conductivity data taken with the sample quenched to 79 K show a non-linear I-V response for very small electric fields, suggesting depinning of Charge-Density Wave (CDW). The data for heating and cooling the system above room temperature, indicate the formation of bipolarons.