Fluorescence quenching kinetics of anthracene and naphthalene covalently bound to the terminus of poly(methacrylic acid)

Poly(methacrylic acid) (PMA) end-tagged with anthracene, bromoanthracene, and naphthalene fluorescence probes have been prepared by anionic polymerization methods, and the fluorescence quenching by a simple monovalent ion (Tl+) has been studied at pH 11 as a function of ionic strength. Under equivalent conditions the efficiency of fluorescence quenching has been found to be approximately an order of magnitude lower than for an anthracene probe located in the center of the PMA chain (Clements, J. H.; Webber S. E. J. Phys. Chem. A 1999, 103, 2513). This is believed to reflect the relatively low density of condensed ions near the chain ends. The steady-state fluorescence quenching data has been analyzed using several models (Stern-Volmer, hindered access, a modification of a model proposed by Morishima et al. (Morishima, Y.; Ohgi, H.; Kamachi, M. Macromolecules 1993, 26, 4293)). The latter model suggests a preferential binding of the Tl+ ion in the vicinity of the hydrophobic probe. The relation of the fitting parameters of these models to the fluorescent lifetime of the probes is discussed as is the relative importance of static quenching. The pH dependence of the fluorescence spectrum, intensity, and quenching by Tl+ was also measured for the anthracene-tagged PMA, and it was found that at low pH the fluorescence intensity was diminished and the chromophores were almost completely protected from the Tl+ ion.