Novel Secondary Dopants for Camphorsulfonic Acid Doped Polyaniline Emeraldine Salts

Abstract

The doping of emeraldine base with (±)-10-camphorsulfonic acid (HCSA) or (+)-HCSA in molten thymol (60°C) or liquid carvacrol (5-isopropyl-2-methylphenol) as solvents provides emeraldine polyaniline (PAn)·HCSA salts (1) with 'expanded coil'-type conformations for their polyaniline chains. Conversion of both racemic PAn·(±)-HCSA (1a) and optically active PAn·(+)-HCSA (1b) films from a 'compact coil' into a partial 'expanded coil' conformation is also facilitated by exposure of the films to either thymol or carvacrol vapours. These conformational changes are supported by modifications to their ultraviolet-visible-near-infrared and circular dichroism spectra and by the marked increase in the electrical conductivity of the films. In the case of carvacrol vapour, treated films of (1a) and (1b) exhibited conductivities of ≥ 130 S/cm, similar to conductivities previously generated by m-cresol. In view of the much lower toxicity of carvacrol compared with m-cresol, it would appear to have considerable promise as an effective 'secondary dopant' for emeraldine salts leading to materials with enhanced electrical conductivity.