Dynamics of the electron spin polarization of the quinone anion radical generated from the photoinduced electron transfer between duroquinone (DQ) and N,N-dimethylaniline (DMA) as well as its p-halogen substituents (4XDMA) has been investigated by using transient absorption and FTEPR spectroscopies. The radical yield decreased with increasing atomic number of the halogen in the donor. The intrinsic enhancement factors of net absorptive polarization due to the spin-orbit coupling mechanism (SOCM) of V-SOCM = 2, 17, and 25 were determined in the unit of thermal equilibrium polarization at room temperature for the DQ-4ClDMA, DQ-4BrDMA, and DQ-4IDMA systems, respectively. The net absorptive spin polarization observed has been discussed in terms of SOC interaction of the triplet contact radical ion pair (CRIP) state with the ground state, which is coupled with the singlet GRIP states in the solvent coordinate.