Ultrafast exciton dynamics in a polymeric heterostructure based on thienylene-phenylene sequences

We have investigated by femtosecond pump-and-probe measurements the exciton dynamics in a novel conjugated polymeric heterostructure consisting of regularly alternated thienylenic and phenylenic segments. A fast initial relaxation followed by a power law decay has been observed. The initial part of the decay is consistent with the self-trapped exciton relaxation process. The power law decay has been interpreted in terms of the modulation of the energy band gap along the polymeric chains. We have also studied the optical properties of a thienylene-based oligomer with the same well-barrier-well structure of the polymer in order to investigate the role of disorder on the polymer relaxation dynamics.