Catalysis of ionic reactions by polyelectrolytes. IV. Quenching of the quinine cation fluorescence by Fe++, Ag+, and Br− in solutions of poly(vinylsulfonic acid)

The fluorescence quenching of the doubly charged quinine cation by Fe⁺⁺, Ag⁺, and Br^? was studied in the presence and absence of polyvinylsulfonate (PVS). The quenching by cationic species was greatly enhanced by PVS at low polyion concentrations; at higher concentrations of PVS, the fluorescence intensity increased owing to displacement of the quinine cations from the polyion domain. Quenching of quinine fluorescence by Br^? was repressed by PVS. Interpretation of the data with the use of Fe⁺⁺ as the quenching agent led to “effective concentrations” of counterions in the polyion domain similar to those calculated from the catalysis of the redox reaction of Co(NH₃)₅Cl⁺⁺ with Fe⁺⁺. This may indicate that the reagent ions are not rigidly bound to the polyion chain, since such binding would affect differently processes with high and low activation energies. The Stern-Volmer constant for self-quenching of the quinine fluorescence can also be obtained from fluorescence intensity data in PVS solution.