In situ synthesis of optically active poly(o-ethoxyaniline) in organic media and its chiroptical properties

Optically active poly(o-ethoxyaniline) (PEOA) was prepared in situ in organic solvents with (+)- or (-)-camphorsulfonic acid (CSA) as the chiral dopant. This presented an effective facile route to prepare optically active polyaniline derivatives with large ring substituents and to dispel the potential influence of water involved in the classical aqueous media on their chirality. Thin films of PEOA/(+)- and (-)-CSA or their solutions exhibit mirror-imaged circular dichroism spectra in the UN/visible region, indicating diastereoselection in the former in situ polymerization system. The optical activity can be 'memorized' in the solid state during dedoping/redoping cycles indicating that the observed optical activity arises from the macroasymmetry of the polymer backbone and not the (+)-CSA dopant. A strong solvent effect exists on the PEOA's chain conformation and subsequent chiroptical property. Changing the nature of the solvent has a significant influence on the positions of the bipolaron band in the UV/visible spectrum and the bisignate exciton-coupled bands in the circular dichroism spectrum. Moreover, PEOA/(+)-CSA lost its optical activity completely when dissolved in dimethyl sulfoxide despite maintenance of the emeraldine salt character, comfirming that a preferred one-screw is maintained by both the electrostatic bonding of the enantiomeric (+)-CSA(-) anions to HN.+ centers and the hydrogen bonding of (+)-CSA(-) carbonyl groups to NH sites.