High magnetic field effects on the lifetimes of radical pairs generated by the photoreduction of anthraquinone and n-alkyl anthraquinone-2-carboxylates in micellar solutions

The magnetic field effects on the lifetimes of radical pairs (RPs) comprising anthrasemiquinone (AQH(.)) and alkyl radicals generated in Brij35, HDTCl, and SDS micellar solutions of anthraquinone (AQ) and n-alkyl anthraquinone-2- carboxylates (AQ-n) were studied by laser flash photolysis in high magnetic fields up to 13 T. The KP lifetimes of AQ and AQ-n in the three surfactants increased along with increasing the magnetic field from 0 to about 2 T. The RP lifetimes of AQ in Brij35 and HDTCl drastically decreased in a magnetic field from 3 to 13 T, whereas the RP lifetimes of AQ in SDS were almost constant in the same range of the magnetic field. The increase in the three surfactants was explained by spin-lattice relaxation (SLR) modulated by anisotropic hyperfine and electron dipole-dipole interactions. The drastic decrease in Brij35 and HDTCl was interpreted by SLR modulated by an anisotropic Zeeman interaction. The parameters of the anisotropic g-value and the rotational correlation time for an anisotropic Zeeman interaction were obtained. The constant RP lifetimes in SDS at a high magnetic field were interpreted referring to an escape process of AQH(.) from the micelle core.