ESCA Analysis of Polymer–Acceptor Interactions in Chemically Synthesized Polypyrrole–Halogen Complexes

Abstract

ABSTRACT:X-Ray photoelectron spectroscopy (XPS) studied have been performed on conductive polypyrrole (PPY)-halogen complexes, such as PPY-I2, PPY-Br2, and PPY-Cl2 complexes, prepared by the simultaneous chemical polymerization and oxidation of pyrrole by the respective halogens. Substantial halogenation of the pyrrole ring was observed in the case of PPY -Cl2 and PPY-Br 2 complexes. In the case of PPY -Br 2 complex, the ratio of covalent to ionic bromide content can be effectively varied over a wide range by varying the bromine to monomer ratio used for polymerization. The increase in covalent bromide content causes a decrease in the electrical conductivity of the complex. The Nls spectra suggest the presence of positively charged nitrogen species and their possible contribution to the electrical conductivity of the complexes. The Cls spectra for all the complexes reveal that close to 1/3 of the carbon atoms may have been associated with structural disorder, as in the case of electrochemically prepared PPY s.KEY WORDS X-Ray Photoelectron Spectroscopy / Polypyrrole-Halogen Complexes / Chemical Synthesis / Structural Disorder / Electrical Conductivity / Electroactive polymers have attracted a great deal of attention during the past decade because of their unusual electrical/electronic properties. A survey of the literature 1 -3 reveals that most of the recent interest on conductive polyheterocycles, polypyrrole (PPY) in particular, are devoted to the materials obtained from electrochemical polymerization and oxidation. For example, most of the Electron Spectroscopy for Chemical Applications (ESCA) studies were centered on electrochemically prepared polypyrrole and related polyheterocycles. 4 -8 These ESCA studies provided information pertaining to the nature of interactions between polymeric cations and their counter anions, and the structural disorder in these polymers arising from these interactions. However, there are still certain discrepancies 4 · 6 between the results reported.Rather conductive PPY complexes have also EXPERIMENTAL Polymer SamplesThe polypyrrole samples used for this study consist of various polypyrrole-halogen complexes, such as PPY-1 2 , PPY-Br 2 , and PPYCl2 complexes. All samples were prepared via the simultaneous chemical polymerization and oxidation of pyrrole by the respective halogen acceptor according to the methods reported earlier. 12 · 13 The PPY-Br2 and PPY-Cl2 complexes were prepared .in acetonitrile while the PPY-1 2 complex was prepared in an aqueous medium. In the case of PPY-Br 2 complexes, and to a lesser extent the PPY-Cl 2 and PPY-12 complexes, the amount of acceptor incorporated in the final complexes can be effectively varied by varying the monomer to halogen ratio used for the polymerization process. The final physicochemical and electrical properties of the PPY complexes are strongly affected by the type of acceptor incorporated and the nature of the polymer-acceptor interactions. ESCA MeasurementsX-Ray photoelectron spectroscopy (XPS) measurements were made on pow...

Iodine doped polyaniline thin film for heterostructure devices via PECVD technique: Morphological, structural, and electrical properties

“…The binding energy at 618.8 eV is associated with I 3d 5/2 XPS spectrum which is attributed to I 3 -anions in I 2 -PANI/TiO 2 thin film. 27,40,41 It is noteworthy that the I 2 dopant is attached interstitially with PANI in the form I 3 -anions by PECVD. Thus, it again affirms the doping of I 2 in I 2 -PANI/TiO 2 thin film by the sophisticated PECVD technique.…”

Characteristics of vibration modes of polypyrrole on surface-enhanced Raman scattering spectra

“…The oxidation level and the corresponding doping level, calculated from the peaks area ratios of Cl 2p existing in the PPy matrix to N 1s in XPS spectra with individual correction using the appropriate instrument sensitivity factor [45,48,[53][54][55], are shown in Table 3. Inspecting the relationship between conductivities and N þ /N ratios of samples 1c, 2c and 5c, it is found that this relationship is consistent with the general concept of a higher N þ /N ratio being responsible for a higher conductivity [45,48,[53][54][55]. However, contrary results are also found on over-oxidized and aged PPy films.…”

XPS Studies of Some Chemically Synthesized Polypyrrole–Organic Acceptor Complexes

“…However, the small peak at about 288.5 eV is as yet unidentified, but the high binding energy suggests the presence of electron-withdraw atoms, possibly as a result of surface oxidation. 8 Finally, at 291.0eV, a shake-up satellite arising from the aromaticity of the polymer and acceptor can be resolved.…”

“…Similar line shape has been observed in other oxidized PPY s prepared electrochemically 6 or chemically. 8 The peak widths (FWHM) for the main component are 2.0eV and 1.8eV, respectively, for the PPY-DDQ and PPY-chloranil complex. The broader peak observed in the former is probably due to the contribution from the cyano group of DDQ.…”

“…[3][4][5][6][7] We reported recently on the XPS technique as a convenient tool for analysing the polymer-acceptor interactions in chemically synthesized PPY-halogen complexes. 8 XPS technique has also been found to be suitable for studying electron donor-acceptor interactions in organic systems because of its ability to elucidate the structure of reaction products and to detect any redistribution of charges within the molecules resulting from charge transfer. 9 Although numerous charge transfer interactions between polymers and various organic electron acceptors have been reported, 10 -13 the application of XPS technique in the studying of polymer-organic acceptor interactions has been limited.…”