EPR studies of electron transfer processes in composites of substituted sexithiophenes with fullerene derivatives

We have examined by EPR spectroscopy a series of of films of hexamethyl and tetramethylsulfanyl substituted sexithiophenes (T6) with C60 and C60 derivatives. We have found that Photoinduced Electron Transfer (PET) from donor to acceptor molecules occurs in mixed films of C60 and hexamethyl-T6 and in cpmposites of methylsulfanyl substituted T6 with fullerenes derivatives. Persistent electron transfer in the ground state was also observed. Spin polarization of the emissive EPR signal attributed to T6(+) cation in hexamethyl-T6/C60 composite is consistent with the formation of the radicals from a non polarized triplet exciplex which gives rise to a loosa radical pair after the PET process. In the mixed film of tetramethylsulfanyl-T6 and C60 polimerized with methylmethacrylate, time resolved EPR spectra reveal that a tightly bound radical pair is formed in which the partners are coupled by dipolar and exchange interactions.Such pair relaxes into a loose pair at later times