Electronic structure and charge transport mechanism in poly[1,4-bis(pyrrol-2-yl)phenylene]

The electrochemical and electronic properties, as well as the redox induced ion and charge transport mechanism in poly[1,4-bis(pyrrol-2-yl)phenylene] (PBPyP), have been studied by electrochemical, optical and electron spin resonance (ESR) spectroscopies, along with electrogravimetric techniques. PBPyP films are obtained by electropolymerization in several solvent/electrolyte systems. Due to the electron-rich and three-ring nature of 1,4-bis(pyrrol-2-yl)benzene (BPyB), polymerization occurs at low potentials (ca. 0.3 V versus Ag/Ag+), and the resulting polymers are stable to multiple redox switching. The ESR and optical spectra of the polymer are consistent with the sequential formation of cation-radical and diamagnetic charge-carriers during the doping process. These results fit the classical polaron/bipolaron model, though the presence of rt-dimers cannot be ruled out. The evolution of the ESR signal during gradual oxidation of the polymer indicates that radical-cations (polarons) are intermediates in the redox mechanism even though the individual redox processes from neutral to polaron and from polaron to bipolaron cannot be observed in the cyclic voltammograms of the polymer. Electrogravimetric studies using the electrochemical quartz microbalance (ECQM) combined with conductance spectra indicates that the electrolyte anions are the dominant mobile species during the redox switching of the polymer. (C) 2001 Elsevier Science B.V. All rights reserved.