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 fluorescence exhibits a characteristic red-shift emission spectrum during the cooling process. This fluorescence spectrum and the accompanying red-shift absorption spectrum suggest that the polymer forms dimer-like aggregates in dilute 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 aggregates, but the fluorescence exhibits only the behavior of aggregates. At low temperature, additional light-emitting species result in spectral dynamics over several nanoseconds in the films. This indicates multiple emission species in polymer films.