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

The magnetic field effects on the lifetimes of radical pairs (RPs) comprisi ng anthrasemiquinone (AQH(.)) and alkyl radicals generated in Brij35, HDTCl , and SDS micellar solutions of anthraquinone (AQ) and n-alkyl anthraquinon e-2- carboxylates (AQ-n) were studied by laser flash photolysis in high mag netic fields up to 13 T. The KP lifetimes of AQ and AQ-n in the three surfa ctants 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 m agnetic field from 3 to 13 T, whereas the RP lifetimes of AQ in SDS were al most 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 drast ic decrease in Brij35 and HDTCl was interpreted by SLR modulated by an anis otropic Zeeman interaction. The parameters of the anisotropic g-value and t he rotational correlation time for an anisotropic Zeeman interaction were o btained. The constant RP lifetimes in SDS at a high magnetic field were int erpreted referring to an escape process of AQH(.) from the micelle core.