Fluorescence from conjugated polymer aggregates in dilute poor solution

We examine a PPV derivative, viz. poly(2,5-dioctyloxy p-phenylene vinylene) (DOO-PPV) in poor solution. The solubility of DOO-PPV in toluene solution exhibits dramatic variation when cooled below room temperature. The fluores cence exhibits a characteristic red-shift emission spectrum during the cool ing process. This fluorescence spectrum and the accompanying red-shift abso rption spectrum suggest that the polymer forms dimer-like aggregates in dil ute poor solution. The reduction in solubility also introduces a quenching effect. In comparing the photophysics of the film and the solutions, we can see that the films are comprised of individual polymer and interchain aggr egates, but the fluorescence exhibits only the behavior of aggregates. At l ow temperature, additional light-emitting species result in spectral dynami cs over several nanoseconds in the films. This indicates multiple emission species in polymer films.