Exciton dynamics in α-sexithienyl films

We present a characterization of the optical dynamics following photoexcitation in T6 films. The relaxation of the excited state, generated by optical transitions at 3.2 eV, is measured using a time-resolved pump-probe technique. The relaxation kinetics consist of two main processes: a fast decay which depends on the excitation density and a slow decay which does not. We show that the fast dynamic is consistent with a time-dependent exciton annihilation model, which provides a value for the bimolecular rate constant of /2~ 3 × 10−13 cm3 s−12. The slow decay is assigned to a monomolecular recombination process via exciton diffusion towards recombination centers. The obtained results are discussed within the wider context of photoexcitation in conducting polymers.