Leucoemeraldine

Leucoemeraldine is the most reduced oxidation state of polyaniline (PANI), a conducting polymer. In this state, all nitrogen atoms in the polymer chain are present as amines, and the repeating unit consists of benzenoid rings linked by –NH– groups. Leucoemeraldine is typically colorless to pale yellow and exhibits very low electrical conductivity under ordinary conditions.

Chemical structure and oxidation states: The fully reduced form contains only benzenoid (amine) units, with no imine linkages. Oxidation of leucoemeraldine introduces imine linkages along the chain, producing the emeraldine form, which is partially oxidized and much more conductive. Further oxidation can lead to the fully oxidized pernigraniline state. The emeraldine base and emeraldine salt states are the forms most commonly associated with electrical conductivity.

Preparation and stability: Leucoemeraldine can be generated by strong chemical reduction of polyaniline and is sometimes formed transiently during polymerization under highly reducing conditions. It is generally less stable in air than the emeraldine form and tends to oxidize to emeraldine when exposed to atmospheric oxygen. Leucoemeraldine salts (protonated forms) are even less stable and tend to convert to emeraldine under ambient conditions.

Properties and behavior: As the fully reduced state, leucoemeraldine is insulating. Its electrical properties can change dramatically upon oxidation to emeraldine, which can be doped to become highly conductive. Because of its tendency to oxidize, leucoemeraldine is mainly of interest as a reference state or precursor in studies of polyaniline redox chemistry rather than as a practical conducting material.

Applications: Leucoemeraldine serves as a model for understanding oxidation-state control in polyaniline, and as a precursor in synthesis of other polyaniline oxidation states. Its instability in air limits its direct use in applications, which rely on the conductivity of the emeraldine or pernigraniline forms.