Fluorescence quenching mechanisms in micelles: the effect of high quencher concentration

In this investigation the fluorescence quenching of fluorescent probe molecules situated within surfactant micelles was examined. The hydrophobic polyaromatic hydrocarbon benzo(a)pyrene (B(a)P) and the more polar 6-propionyl-2-(dimethylamino)-naphthalene (PRODAN) were used to assess the effect of high quencher concentration on the quenching process in micelles. Using the surfactant systems sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100), three distinct modalities of quenching were observed. For the TX-100 system, both I− and H2O2 quenching of probe fluorescence reached saturation in efficiency. These data are modeled quite well by assuming a limited number of quenching sites per micelle in conjunction with standard Stern–Volmer quenching dynamics. For the SDS system, similar quenching saturation effects are observed, but the saturation model worked less well. It is suggested that a bimodal distribution of micelle sizes could be responsible. The B(a)P/SDS/I− system is singular in that the quenching does not saturate. The efficiency of quenching here varies approximately with the third power of I− concentration. A resonance energy transfer mechanism is proposed in which B(a)P is quenched by I3−. © 2000 Elsevier Science S.A. All rights reserved.