GROUND-STATE CHARGE-TRANSFER IN FULLERENE POLYALKYLTHIOPHENE COMPOSITES - ESR AND IODINE DOPING EFFECT

Charge transfer in the ground state has been observed in poly (3-octad ecylthiophene) (PAT-18), doped by C-60. ESR studies of PAT-18-C-60 com posite reveal for the first time two ESR signals without photoexcitati on. For the detection of two ESR signals an increase of microwave powe r is important. Only then can the two ESR signals be resolved: one wit h g(1) = 2.0022 and Delta H-PP = 3.5 G, corresponding to positive pola ron P+ in PAT-18 chains, and the second with g(2) = 1.9993 and Delta H -PP = 1.5 G, corresponding to the C-60(-) anion. The microwave power d ependence of the intensity of these two ESR signals differs significan tly due to different mechanisms of spin relaxation in C-60 and PAT-18. The ESR study of PAT-18-C-60 composite, additionally doped by I-2, sh ows at the initial stage the disappearance of the C-60(-) anion signal due to the further step of charge transfer (CT) from C-60(-) to I-2 a t a low doping level and then, after heavy doping in I-2 vapor, the in crease of the polaronic P+ polymer signal due to strong CT doping of P AT-18 by I-2.