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 re sonance (ESR) spectroscopies, along with electrogravimetric techniques. PBP yP films are obtained by electropolymerization in several solvent/electroly te systems. Due to the electron-rich and three-ring nature of 1,4-bis(pyrro l-2-yl)benzene (BPyB), polymerization occurs at low potentials (ca. 0.3 V v ersus Ag/Ag+), and the resulting polymers are stable to multiple redox swit ching. The ESR and optical spectra of the polymer are consistent with the s equential formation of cation-radical and diamagnetic charge-carriers durin g the doping process. These results fit the classical polaron/bipolaron mod el, though the presence of rt-dimers cannot be ruled out. The evolution of the ESR signal during gradual oxidation of the polymer indicates that radic al-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. El ectrogravimetric studies using the electrochemical quartz microbalance (ECQ M) 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.