Study on the interaction between nitroxide free radical and conjugated polyelectrolytes by fluorimetry

In this work, we studied the fluorescence quenching of the anionic conjugated polyelectrolyte PPE-SO3 by the paramagnetic species 2,2,6,6-tetramethylpiperidine-N-oxide free radical (TEMPO) in aqueous solution. At low quencher concentration the Stern-Volmer constant is 94 mol/L; as the quencher concentration increases the Stern-Volmer plots become superlinear. Ascorbic acid is used to reduce TEMPO to the corresponding hydroxylamine and the PPE-SO3 fluorescence is fully recovered. Under a large excess of ascorbic acid over TEMPO, the rise of fluorescence followed pseudo-first-order kinetics. The second-order rate constant calculated from this time course is 0.7 mol/L/s. Copyright (c) 2008 John Wiley & Sons, Ltd.