Chiral Induction in the Acid Doping of Poly(o-methoxyaniline)

Abstract

The acid doping of the emeraldine base form of poly(o-methoxyaniline) (POMA) with 0.10 mol dm^–3 (+)-(1S)-camphor-10-sulfonic acid (HCSA) in dimethyl sulfoxide solvent causes the induction of chirality in the poly(o-methoxyaniline) backbone by the chiral (+)-CSA^– dopant anion leading to optically active POMA·(+)-HCSA emeraldine salts. The salts obtained from both high molecular weight (M_w = 144000 Da) and low molecular weight (M_w = 31000 Da) emeraldine base precursors exhibit a well defined high wavelength polaron absorption band consistent with a ‘compact coil’ conformation. In the high molecular weight case, this band undergoes a large red shift (Δ = 130 nm) over 48 h which is attributed to slow de-aggregation of the polymer chains. Chiral induction into the poly(o-methoxyaniline) chains is much slower than for the analogous acid doping of the parent polyaniline emeraldine base, due to steric hindrance to polymer rearrangement by the methoxy ring substituent.