Spin relaxation and structure of light-induced spin-correlated PCBM-/P3HT+ radical pairs

The electron spin echo (ESE) technique is applied to determine the spin relaxation times of long-lived light-induced radicals and short-term spin-correlated radical pairs (SCRPs) formed by the laser flash of a composite consisting of [6,6]-phenyl-C-61-butyric acid methyl ether (PCBM) and poly-(3-hexylthiophene) (P3HT) at 80 K. The ESE signal dependences recorded to measure the longitudinal relaxation times of P3HT(+)/PCBM- SCRPs and the free P3HT(+) radical are fitted by the exp(-(t/T (1))(0.6)) dependence with T (1) values lying in the microsecond time scale. The difference in the transverse spin relaxation times of the P3HT(+)/PCBM- radical paira appeared after selective and non-selective echo-detected EPR spectrum excitation is explained by the instantaneous diffusion model. Based on the model, the magnetic interaction energy between the electron spins in P3HT(+)/PCBM- SCRPs is estimated; E/A similar to 10(6) s(-1).