Influence of Electrochemical Polymerization Temperature on the Chiroptical Properties of (+)-Camphorsulfonic Acid-Doped Polyaniline

The chiroptical properties of electrochemically deposited emeraldine salt PAn·(+)-HCSA (HCSA = 10-camphorsulfonic acid) films have been found to vary markedly with the temperature employed during polymerization. The circular dichroism spectra of such films grown at >40 °C are inverted compared to the spectra of analogous films deposited at temperatures ≤25 °C, indicating an inversion of conformation for the polyaniline chains. These observations are rationalized in terms of a temperature-induced interconversion between the two diastereomeric emeraldine salt products from the doping of the growing polyaniline chains by the chiral (+)-CSA - anion. The marked temperature dependence of the diastereoselectivity highlights the importance of employing a fixed temperature during the electrosynthesis of optically active polyanilines.