Chiral Polyanilines: Synthesis, Chirality Influencing Parameters and Applications

Recently supramolecular chirality has received increasing interest due to its potential applications in enantioselective sensors and chromatographic separation of enantiomers. The appearance of such chirality results from the helical organization of molecules manifested by H-bonding interactions, weak van der Waals forces, and electrostatic forces. In recent years a lot of interest has been focused towards the synthesis of chiral conjugated polymers such as polyacetylene, polythiophene, polypyrrole, polyaniline (PANI), and poly(p-phenylene vinylene) due to their potential applications in circularly polarized electroluminescence and chiral electrode for asymmetric synthesis. Among these chiral PANI is desirable because it is inexpensive, environmentally stable, and can be readily doped and dedoped using simple acid–base stimuli. Besides PANI does not require any synthetic steps before the polymerization of achiral aniline and totally relies on the preferential formation of either right- or left-handed helix of the polymer backbone due to the presence of a chiral dopant in the reaction medium. Different types of chiral acids have been used for the creation of helical polyaniline using different methods. This review paper presents a detailed discussion of different methods of synthesizing helical/chiral polyaniline, different types of dopants used for chirality induction, chirality measurement by circular dichroism spectroscopy, parameters controlling induction and stabilization of chirality in PANI, and application of chiral polyanilines in diverse areas such as enantiomer separation, enantioselective synthesis, chiral nanocomposites, and microwave absorption.