PHOTOCHEMISTRY OF ELECTRONICALLY CONDUCTING POLY(3-ALKYLTHIOPHENES) CONTAINING FECL4- COUNTERIONS

Irradiation of electronically conducting poly(3-alkylthiophenes) doped with the FeCl4- counter ion results in a loss of electronic conductiv ity (6 S/cm --> 10(-5) S/cm). The mechanism proceeds by (i) direct pho tolysis of FeCl4- and (ii) photoreduction of FeCl4- to FeCl42- followe d by (iii) electron transfer to bipolaronic residues. Upon prolonged p hotolysis the products are neutral, nonconductive polymer and octahedr al iron(III) complexes. Photochemical dedoping occurs in vacuo but is greatly accelerated by moisture. The reaction is sufficiently facile t o occur significantly under ambient light. Replacement of FeCl4- with a less photolabile counterion, AuCl4-, results in a several orders of magnitude increase in the longevity of the irradiated conducting polym er. Photochemical mechanisms responsible for these observations are de scribed.