SOLID-STATE NMR CHARACTERIZATION OF POLYPYRROLE - THE NATURE OF THE DOPANT IN PF6- DOPED FILMS

P-31 and F-19 solid state NMR have been used to study the nature of the PF6- anion in polypyrrole films at various levels of oxidation. It appears that the symmetric PF6- unit remains undistorted and unchanged throughout, suggesting that it is predominantly acting only as a counterion and not as a true 'dopant', since any distortion in the phosphorous environments would result at the very least in chemical shift anisotropy of the P-31 nucleus. A second set of phosphorous and fluorine resonances, which are consistent with a difluoride phosphorous compound, appeared in the films. Upon electrochemical reduction of the polymer, the undistorted PF6- anion leaves the film whereas the second phosphorous species remains. Re-oxidation of the polymer reverses the processes observed during reduction.