Photoluminescence quenching of conjugated macromolecules by bipyridinium derivatives in aqueous media: Charge dependence

Quenching of the photoluminescence from a water-soluble conjugated macromolecule, poly[5-methoxy-2-(4-sulfobutoxy)-1,4-phenylenevinylene], by neutral 4,4'-dipyridyl and by six bipyridinium derivatives with different charges was studied. For the neutral quenchers, the linear Stern-Volmer constant (K-sv) was (1-2) x 10(5) M-1. For the charged quenchers, K-sv increases when the charge on the quencher is increased, from (1-3) x 10(6) M-1 for singly charged quenchers to 2 x 10(7) M-1 for bipyridinium derivatives with charge +2 and +4, consistent with static quenching via the formation of a complex between the positively charged polymer and the positively charged quencher. A modified Stern-Volmer equation, including the sphere-of-action contribution, is used to discuss the upward curvature observed in the Stern-Volmer plots at higher concentrations.