Fluorescence Quenching of 1-Pyrenemethanol by Methylviologen in Polystyrene Latex Dispersions

Fluorescence quenching of 1-pyrenemethanol by methylviologen through photoinduced electron transfer is investigated in polystyrene (PS) latex dispersions as well as in aqueous homogeneous solutions. In aqueous homogeneous solutions, the Stern-Volmer plot for the intensity is linear and close to that for the lifetime, indicating a dynamic quenching mechanism. In PS latex dispersions, however, the Stern-Volmer plots for the intensity are downward curving and the decay curves are not so much affected by the quencher as those for aqueous solutions, implying a significant contribution of static quenching. The downward-curving Stern-Volmer plots are well described by a two-site model that assumes accessible and inaccessible sites to the acceptor on latex particles. The Stern-Volmer constants obtained indicate that in the latex dispersions the fluorescence quenching occurs several hundreds times more efficiently than that in an aqueous homogeneous solution. This drastic enhancement of the quenching in latex dispersions is attributed to the increase in the local concentrations of the reactants on the latex surface. We have demonstrated the usefulness of latex surfaces as a new type of reaction field for photoinduced electron transfer.