Steady-state fluorescence quenching kinetics of water-soluble zinc porphyrins in reversed micelles

Abstract

The steady-state kinetics of quenching of the fluorescence of the water-soluble zinc tetramethylpyridylporphyrin tetraiodide (ZnTMePyP4+) by anthraquinone-2-sulphonate (AQS) and methyl viologen (MV2+) has been studied in reversed micelles of benzyldimethyl-n-hexadecylammonium chloride (BHDC). The quenching process is dependent on the water content and size of the water pool when the quencher (AQS) is bound at the micellar interface. The quenching rate constant observed in the system ZnTMePyP4+/MV2+ is kq= 7 × 109 dm3 mol–1 s–1 at water content w0=[H2O]/[surf]4, but at low water content the quenching is static and the quencher follows a Poisson distribution.A dynamic process is observed in the system ZnTSPP4–/DQ where the fluorescent probe is located at the interface and the quencher is in the organic phase. The measured quenching rate constant is kq=(1.7 ± 0.2)× 109 dm3 mol–1 s–1, nearly one order of magnitude smaller than the quenching rate constant kq= 8.5 × 109 dm3 mol–1 s–1 found in the system ZnTPP/DQ in these reversed micelles.