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-Penin 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 Kb are significant, on the order of 12-21, depending on the polymer and ionic strength.