A high-frequency light-induced electron spin resonance study of conjugated polymer/fullerene composites

Light-induced electron spin resonance (LESR) measurements are reported in composites of MDMO-PPV and PCBM, a soluble derivative of C60. After illumination of the sample, two radicals are formed. One is the remaining positive polaron P+ on the polymer backbone and the other the C61•- radical anion. Using high-frequency (95 GHz) LESR, it was possible to separate these two contributions to the spectrum on the basis of their g-parameters, and to resolve the g-anisotropy of the radicals. The P+-polaron possesses axial symmetry whereas for C61•- a lower, rhombic symmetry was observed.