Electrochemical synthesis of optically active polyanilines

The synthesis of optically active polyaniline salt films of the type PAn.HCSA (HCSA = camphor-10-sulfonic acid) has been achieved via the enantioselective electropolymerization of aniline on indium-tin-oxide (ITO)-coated glass electrodes in the presence of (+)- or (-)-HCSA. Similar results were obtained under potentiostatic, galvanostatic and potentiodynamic conditions. The chiroptical and electrical properties of these novel materials have been characterized by u.v.-visible and circular dichroism (c.d.) spectroscopy, electrochemical quartz crystal microbalance techniques and resistometry. The intensity of the c.d. spectra of potentiostatically grown PAn.(+)-HCSA films was found to increase with increasing applied potential over the range 0.8-1.1 V (v. Ag/AgCl) and with increasing charge consumed. C.d. spectroscopic studies also showed that the polyaniline chains retained their initial configuration when the (+)-HCSA dopant acid in PAn.(+)-HCSA films was replaced by HCl via potential cycling in 1 mol dm(-3) HCl. Similarly, chemical de-doping of PAn.(+)-HCSA with 0.5 mol dm(-3) NH4OH produced optically active emeraldine base, which upon re-doping with HCl gave optically active PAn.HCl with a c.d. spectrum very similar to that of the original PAn.(+)-HCSA. These results suggest that chiral holes may be formed in the polymer matrix during both redox and chemical de-doping/re-doping cycles with PAn.(+)-HCSA salt films.