Furthering Our Understanding of the Doping Mechanism in Conjugated Polymers Using Tetraaniline

Polyaniline is known for reversible acidic doping. However, despite extensive work, little experimental evidence exists for the initial doping mechanism mainly due to the difficulty of synthesizing polyaniline with a uniform chain length. In this study, we partially dope aniline tetramers in order to investigate the initial stage of doping in both solution and the solid state. In solution, we discovered a method for visualizing the doping level due to solvent density differences. The optical results in both the liquid and solid state suggest that the partially doped aniline tetramers are physical mixtures of aniline tetramer in the emeraldine base and emeraldine salt forms. Electron paramagnetic resonance confirms the formation of spinless bipolarons as the major carriers. Therefore, we postulate that the doping mechanism proceeds via a continual increase in the number of doubly doped tetraanilines.