Radical Scavenging Mediating Reversible Fluorescence Quenching of an Anionic Conjugated Polymer: Highly Sensitive Probe for Antioxidants
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Abstract
The anionic conjugated polymer poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} (PFP-SO3-) can form a complex with cationic quencher 4-(trimethylammonium)-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT1) through electrostatic interactions. The fluorescence of PFP-SO3- is efficiently quenched by CAT1 with a Stern−Volmer constant (Ksv) of 2.3 × 107 M-1. The dynamic quenching rate constant of 8.85 × 1016 M-1 s-1 shows that the static quenching, as supported by PFP-SO3-/CAT1 charge pairing, is the dominant quenching mechanism. Either by hydrogen abstraction, or by reduction, the transformation of the paramagnetic nitroxide radical into diamagnetic hydroxylamine inhibits the quenching, and therefore, the fluorescence of anionic conjugated polymer is recovered. The fluorescence recovery can be used to probe the processes of hydrogen transfer reaction from antioxidants to radicals and the reduction of radical by antioxidants. These assays benefit from the sensitivity of optical signals from conjugated polymers. The PFP-SO3-/CAT1 assembly can also be used as a platform to sense ascorbic acid in water with high selectivity and sensitivity.
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