Fluorescence Quenching Kinetics of Anthracene Covalently Bound to Poly(Methacrylic Acid): Midchain Labeling

Poly(methacrylic acid) labeled by anthracene in the middle of the chain (A-m-PMA) has been synthesized by anionic polymerization of tert -butyl methacrylate followed by introduction of the difunctional terminating agent 9,10-bis(bromomethyl)anthracene. Deprotection to yield the polyacid using trifluoroacetic acid in the presence of thioanisole results in complete removal of the tert -butyl moieties without destruction of the anthracene chromophore. Steady-state and time-resolved fluorescence quenching by Tl + in aqueous solution at pH 11 at different ionic strengths has been measured. The data have been analyzed and compared to data previously obtained for 9-ethanolanthracene pendant-labeled poly(methacrylic acid) (9EA-PMA) using the following kinetic models: Stern−Volmer; hindered-access; combined Stern−Volmer−Perrin model developed by Morishima et al. ( Macromolecules 1993, 26, 4293). These two polymers exhibit very similar quenching behavior, with the most significant difference being that static quenching is more important for A-m-PMA than 9EA-PMA. The Morishima model has been modified to include a preferential binding constant ( K b ) for Tl + in the vicinity of the chromophore. The estimated values of K b are significant, on the order of 12−21, depending on the polymer and ionic strength.