Isomerization and <i>n</i>-type doping of polyacetylene: Pure <i>t</i> <i>r</i> <i>a</i> <i>n</i> <i>s</i>-(CH)<i>x</i> and <i>t</i> <i>r</i> <i>a</i> <i>n</i> <i>s</i>-(CD)<i>x</i>

Abstract

A systematic study of thermal isomerization leads to a definition of standard conditions (5 min at 180 °C) to obtain trans-polyacetylene (CH)x and (CD)x. Light doping with Na derivatives of benzophenone enables the preparation of pure trans-(CH)x and (CD)x. The characteristics of these systems have been determined and, in particular, a peak-to-peak ESR linewidth as small as 0.28 G has been found for both systems. ESR and IR spectroscopic evidences of the inhomogeneity of the doping process have been obtained. The dopant is concentrated at the surface before penetrating inside the fibrils. The doping process is linked to the appearance of additional bands in the IR spectra, the position of which is sensitive to the nature of the polymer [(CH)x or (CD)x] and of the doping agent (Na or I2). Upon ’’compensation’’ by a subsequent doping, the properties of the insulating trans-(CH)x are recovered, but any doping inside the fibers is proved to create a high concentration of magnetic defects. After such compensation, a further doping allows recovery of the metallic state.