EPR study of charge transfer in the poly-3-dodecylthiophene-fullerene system

Abstract

The EPR spectra of photoinduced radical pairs excited by a laser with photon energies of 1.88, 2.22, and 2.75 eV in poly-3-dodecylthiophene modified by 6,6-phenyl-C61-butanoic acid methyl ester are measured and identified at 77–320 K for the first time. When the volume heterotransition is irradiated in the system, the simultaneous formation of spin charge carriers, polarons, and anion radicals of fullerene with different magnetic resonance parameters is detected. The number of radical pairs follows the activation law and increases with increasing photon energy. The spin-lattice and spin-spin relaxation times of the charge carriers are separately measured by the continuous saturation method. Dynamic parameters are found, and the mechanism of 1D polaron diffusion along the polymer chains and of the rotational diffusion of fullerene molecules about the distinguished axis is determined. The energy parameters of spin charge carriers differ, which indicates their weak interaction in this system.