Reversible isomerization of a zwitterionic polysquaraine induced by a metal surface

Abstract

The variation of visible and IR absorption spectra and of small-angle X-ray scattering of poly(3-octylpyrrole)squaraine in trichloromethane solution indicates that, for this zwitterionic conducting polymer (CP), a reversible change of conformation is induced by contact of the solution with the surface of an active metal. The structure of the target polymer might switch from being linear to being folded. For a copper surface, the activation energy of isomerization between the two forms, whatever their nature, is 18.9 ± 0.7 kJ mol⁻¹, whereas for the reverse process the activation energy is 38 ± 6 kJ mol⁻¹. In a folding transformation, formation of intramolecular hydrogen bonds might play a key role. This observation of a reversible conformation for a zwitterionic polymer induced by a metallic surface provides an impetus to investigate both such a structural modification of other CP and applications of this phenomenon.