Liquid-crystalline state of dyes can be easy distinguished from the crystalline one by the appearance of characteristic long-wavelength optical absorption, the so-called J-band. Similarly, long-wavelength absorption of polyaniline is assumed to be the signature of its J-like liquid-crystalline state. When water evaporates from polyaniline adsorbed on a glass support during polymerization, the long-wavelength maximum at about 800 nm disappears, and one at 570 nm appears, characteristic for highly crystalline and strongly oriented thin film. Reversible red shift of long-wavelength absorption upon water adsorption is a significant feature of these films. By analogy with dyes, it is attributed to water-promoted superficial formation of J-like mesophase. Such surprising properties of wet films as propagation of chemical reduction and enhanced exciton transport, reported by us recently, can also be considered as a signature of the J-like liquid-crystalline state of polyaniline.

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The consideration of polyaniline (PANI) as a supramolecular assembly similar to J-aggregates of dyes is proposed. Fibrils with a length of more than 100 nm and a diameter of about 4 nm are formed in water during aniline polymerization, as shown by small-angle X-ray scattering. Long-wavelength absorption of the fi brils, redshifted with respect to highly crystalline PANI fi lm supports the idea about the formation of J-aggregates. Their formation, similar to dyes, is promoted by the addition of a sulfonated polyelectrolyte and becomes more pronounced with an increase of the molar mass of the polyelectrolyte. Self-organization of aniline oligomers in a polar environment is confi rmed by atomistic molecular dynamics simulations.