Micellized ketyl-phenoxyl radical pairs have been examined by using laser flash photolysis techniques. These radical pairs were generated by reaction of triplet butyrophenone with various phenols, including α-tocopherol. For example, for the α-tocopherol system in sodium dodecyl sulfate micelles at room temperature, the radical pair's lifetime is 360 ns, and it decays by a mixture of geminate reaction with kgem = 2.0 × 106 s-1 and radical escape from the micelle with k- = 7.7 × 105 s-1. In the Earth's magnetic field the ratio of escape to cage reaction is 20:80, but in a 5000-G field 72% of the radical pairs escape. The magnetic field slows down intersystem-crossing processes and reduces the importance of cage reactions. It is concluded that radical pairs involving phenoxyl radicals behave very similarly to their carbon analogues. An important observation in this work is the fact that rather small magnetic fields (e.g., those due to stirring bars) can lead to rather large changes in radical-pair behavior. Photoinitiated processes of this type will therefore produce different consequences in the presence of magnetic fields (e.g., magnetic stirrers or those involved in NMR or EPR spectroscopy) than in the absence of these fields.
The Journal of Physical Chemistry92, no. 5 (1988): 1257–1262.