Pulsed EPR detection of light-generated nuclear coherences in photosynthetic reaction centers

Light generation of nuclear coherence in spin-correlated radical pairs has been established as a novel mechanism employing a pulsed EPR technique. At the instant of the laser flash, the radical pair intermediates of the primary events of photosynthesis are created in a singlet state, which is not an eigenstate of the corresponding spin Hamiltonian. This implies formation of zero quantum electron and single quantum nuclear coherence between specific eigenstates of the radical pair. Analytical model calculations indicate that light generation of nuclear coherence is associated with high nuclear spin polarization.