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.