Time-Resolved Detection of Magnetic Field Effects on Radical Pairs in Micelles: Two-Step Two-Laser Fluorescence Spectroscopy of Transient Radicals

A two-step two-laser fluorescence spectroscopy method was employed to enable time-resolved detection of magnetic field effects (MFEs) on radical pairs (RPs). In the photoinduced hydrogen abstraction reaction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micellar solution, fluorescence from the BP ketyl radical (BPH•) was observed under various magnetic fields; BPH• forms RPs with hydrogen-abstracted SDS radicals (•SDS) in the micelles. Kinetic parameters of the RP dynamics such as the spin relaxation rate, the generation rate, and the escape rate were determined from the simple analysis. The MFEs on BPH• observed from the fluorescence measurements were explained by the spin relaxation mechanism proposed by Hayashi and Nagakura. In this study, we demonstrate that two-step two-laser fluorescence spectroscopy in combination with a magnetic field provides valuable information about photochemical reactions in which RPs play important roles.