Abstract
The relaxation and transport dynamics of singlet excitons in 100nm-thick, electrochemically prepared polybithiophene films were investigated by monitoring the time evolution of photoinduced bleaching and S1 − Sn absorption with femtosecond transient absorption spectroscopy. The decay dynamics of both bleaching and S 1 − S n absorption between 500 and 800 nm are observed to be independent of the pump pulse wavelength and can be fitted by a biexponential function with the time constants τ1 = 120fs±20fs and τ2 = 2ps±0.3ps. The short time constant τ1 = 120fs was ascribed to the transport dynamics of the initially generated free excitons migrating over parallel aligned polymer segments to structural defects acting as traps. The competing process, occuring predominantly in structurally disordered regions, is structural relaxation of the initially generated free excitons to selftrapped excitons decaying with a lifetime of about 2ps.
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