ESR in conducting polymers: Oxygen-induced contribution to the linewidth

Abstract

The oxygen-induced ESR line broadening has been investigated in the case of the conducting polymer polyaniline in powder and in film form. Pumping under vacuum results in a narrowing of the ESR linewidth. After initial pumping various oxygen containing gases have been applied to the sample ͑pure O 2 , ambient air, dry air͒ and the linewidth has been measured as a function of time. The residual water in these gases was found to seriously affect the narrowing behavior of the linewidth. A theoretical calculation is proposed showing that the line broadening is proportional to the oxygen concentration and to the polaron mobility. Considering the linewidth dependence upon applied oxygen pressure an evaluation of the polaron mobility is obtained. This value is consistent with the values estimated from previous spin dynamics studies. An evaluation of the exchange integral is also given.

Electrically detected and conventional magnetic resonance investigation of surface and bulk states in polyaniline thin films

“…Figure 1͑a͒ shows the EPR signal of an undoped EB-PANI film at 300 K. The peak-to-peak linewidth ͑⌬H pp ͒ is 2.6 G and the g factor is 2.0031. These values are in agreement with those found in the literature, although the reported values may vary from 4 0.29 to 23 G. 12 These differences are due to magnetic interaction of polarons and the triplet state of oxygen molecules, 13 which broadens the resonance line.…”

“…12 Since the adsorption sites, where the polaron is centered ͑i.e., NH + ͒, are the same for O 2 and H 2 O molecules, the higher water adsorption leads to less free sites for oxygen to be adsorbed. Houzé and Nechtschein 13 proposed that H 2 O molecules are more tightly bound to the polymeric polyaniline chain than O 2 molecules, and that water acts as a shield between polarons and oxygen. Thus, as the doping level is increased, we have more delocalized polarons, and, consequently, more sites for oxygen adsorption, which will broaden the EPR signal due to dipole-dipole interactions with paramagnetic species.…”

“…Peak-to-peak linewidths ͑⌬H pp ͒, equal to 12 2.2 and 2.0 G, 13 have been reported, respectively, to samples in the water vapor atmosphere and ambient atmosphere. These results are very close to the values of ⌬H pp obtained in this work ͑⌬H pp = 2.6 G͒, in which the films were prepared and kept in air.…”

Light-induced EPR study of charge transfer in P3HT/bis-PCBM bulk heterojunctions

“…The n P values obtained are considerably lower than that, n p ≈ 0.05, estimated for polarons excited in doped polyaniline. 39 The fitting of LEPR spectra of the P3HT/bis-PCBM composite allowed us to obtain separately all terms of its effective paramagnetic susceptibility χ as contributions of mobile and localized polarons χ P and methanofullerene anion radicals χ F . Figure 3 illustrates the changes in LEPR spectra of the P3HT/bis-PCBM composite with its heating and temperature dependences of all contributions into sum χ .…”

“…A positive charge of polaron is not required to be recombined with negative charge on first fullerene, it can to recombine with a charge on a subsequent counter-ion. The fullerene molecules can be considered as fast relaxing impurities, and the spin flip-flop probability p during such a collision should depend on the exchange amplitude and the frequency of polaron diffusion ω hop as 39,43 …”