Steady-state and time-resolved fluorescence quenching experiments were performed on a series of random terpolymers comprising sodium acrylate, acrylamide, and a phenanthrene (Phen) derivative. The polymers in this series had a fixed Phen loading (4 mol %) and differed in the relative composition of the acrylate and acrylamide monomers. Fluorescence quenching by Tl+ and Cs+ was measured as a function of ionic strength in basic aqueous solutions. The apparent bimolecular rate constant for quenching (k(q)) is on the order of 10(12) M(-1) s(-1) at low ionic strength and diminishes by approximately 1 order of magnitude at 14 mM added ionic strength. This behavior is independent of the particular group 1A counterion salt but does depend on the polyelectrolyte linear charge density. At relatively high quencher concentration both Tl+ and Cs+ display negative curvature in their I-0/I Stem-Volmer plots. "Displacement" experiments were carried out in which K+ is added to a solution of the polyelectrolyte with a fixed concentration of Tl+, thereby decreasing the fluorescence quenching. These data and membrane dialysis imply preferential binding of the Tl+ to the polyelectrolyte (compared to Na+ and K+). A restricted geometry model based on Manning condensation theory is presented that captures many of the features of a Poisson-Boltzmann reaction-diffusion calculation of the quenching dynamics.