Origins of aggregation quenching in luminescent phenylenevinylene polymers

We measure transient absorption, gain and bleaching of a model conjugated polymer in solution where aggregation of the polymer has been deliberately controlled. Evidence is presented that photoexcitation of aggregated polymer chains leads to creation of interchain non-emissive polaron pairs in large quantum yield. This is shown to be consistent with film behavior and accounts for low luminescence quantum yields in the solid state. It also explains the recent reports of rapidly formed species with characteristic infrared active vibrations. Our data support a picture where polaron pairs mostly recombine to form the ground state directly, in stark contrast to their presumed recombination mechanism in electroluminescent devices where they have been postulated to form only excited singlet and triplet states.