Dynamics of photoinduced radical pairs in poly(3-dodecylthiophene)/fullerene composite

Radical pair laser (660 nm) photoinduced in poly(3-dodecylthiophene)/[1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61] (P3DDT/PCBM) composite were investigated by the X-band light-induced EPR method in a wide temperature region. Two lines with different magnetic parameters were attributed to non-interacting polaron and fullerene ion-radical. The susceptibility of these centres follow activation law and decrease drastically at T>180 K due to their geminate recombination. The spin–lattice and spin–spin relaxation times of these paramagnetic centres were determined separately by the steady-state saturation method. It was shown that two independent spin dynamics processes are mainly realized in illuminated P3DDT/PCBM composite, namely polaron diffusion along the polymer chains with activation energy of 0.071 eV and rotation of fullerene ion-radicals with activation energy of 0.024 eV.