DYNAMICS OF OPTICAL-EXCITATIONS IN A LADDER-TYPE PI-CONJUGATED POLYMER CONTAINING AGGREGATE STATES

The dynamics of optically generated excitations in a poly-(para)-pheny lene-type ladder polymer has been investigated by means of femtosecond pump-probe as well as femtosecond luminescence up-conversion spectros copy. In addition to the bulk emission a low-energy emission band assi gned to physical aggregates is observed. By comparing the photolumines cence (PL) decay of the bulk emission with the time-resolved PL traces of the aggregate emission we show that in the presence of aggregates the dynamics of the initially generated excitons are determined by tra nsfer from bulk to aggregate states. Additionally stimulated emission (SE) as well as photoinduced absorption are observed for different spe ctral regions in the pump-probe experiments. The SE is ascribed to bul k singlet excitons as evidenced by the correspondence of the temporal behavior of SE and the decay of bulk emission, whereas the PA is attri buted to spatially separated excitons.