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 conductivity (6 S/cm --> 10(-5) S/cm). The mechanism proceeds by (i) direct photolysis of FeCl4- and (ii) photoreduction of FeCl4- to FeCl42- followed by (iii) electron transfer to bipolaronic residues. Upon prolonged photolysis the products are neutral, nonconductive polymer and octahedral iron(III) complexes. Photochemical dedoping occurs in vacuo but is greatly accelerated by moisture. The reaction is sufficiently facile to 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 polymer. Photochemical mechanisms responsible for these observations are described.