J-like liquid-crystalline and crystalline states of polyaniline revealed by thin, highly crystalline, and strongly oriented films.

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.