Phenyl ring rotations, structural order and electronic states in polyaniline

Abstract

Much progress has recently been made in the physics and chemistry of the polyanilines with respect to several central issues, such as the nature of the electron-phonon coupling in these materials, the stability of polarons versus bipolarons, and the role of disorder. The three primary oxidation states of polyaniline (leucoemeraldine, emeraldine and pernigraniline) have been synthesized. Photoinduced absorption studies on these materials reveal long-lived weak induced infrared activity and strong induced electronic transitions, demonstrating the importance of massive polarons (and other related defects) involving distortions of the ground state ring angles in these ring-containing polymers. The properties of recently synthesized ring derivatives of polyaniline, such as poly( o-toluidine), can also be understood by changes in ring-rotational properties. Localization effects are enhanced through chain derivatization, which increases the chain separation and thus reduces interchain interactions. The isolation of partially crystalline forms, fibers and oriented films of the emeraldine oxidation state of polyaniline has allowed not only the determination of structural information via X-ray diffraction, but also a correlation between the microscopic structure and the magnetic properties of the charged defect states of these materials. While a metallic polaron lattice is formed in protonated crystalline regions of emeraldine base, spinless defects form upon protonation of the amorphous regions.