Ultrafast Excitation Transfer and Trapping in a Thin Polymer Film.

Summary, in English

Transient absorption anisotropy of a polythiophene polymer in a thin film was studied on a femtosecond time scale. The anisotropy has a non-exponential decay on the sub-picosecond time scale, with a fastest component characterized by an ∼40 fs time constant. To simulate the anisotropy decay an incoherent energy migration model has been used. Comparison between the simulated and experimental kinetics enabled us to estimate the nearest-neighbor pair wise hopping time (τh=1±0.1 ps), the fraction of the interchain aggregates (∼10%) and the structural disorder of the polymer. The initial ∼30 fs anisotropy decay does not originate from incoherent hopping energy transfer but from some other relaxation among electronic excited states within a spectroscopic unit.