  Single magnetic molecules may be the smallest functional magnets. An
electric-field controllable spin state of magnetic molecules is of fundamental
importance for applications while its realization remains challenging. To date
the observed spin-electric interaction based on spin-orbit coupling or spin
dipole coupling is useful to tune fine spin structures but too weak to flip the
spin state. In this work, we propose a new mechanism to realize enhanced
spin-electric coupling and flip the spin states by tuning the spin
superexchange between local spins. Using first-principles calculations and
Heisenberg Hamiltonian, we demonstrate this effect in a family of magnetic
molecules, transition metallic Porphyrins. We show that their d-{\pi} and
{\pi}-{\pi} spin superexchange couplings are determined by the relative
energies of d and {\pi} electronic states, which are sensitive to the applied
electric field. Therefore, applying electric field can tune a wide range of
magnetic ground states, including ferromagnetic, ferrimagnetic, and
antiferromagnetic configurations. This spin-electric coupling may provide a new
approach for designing and controlling molecular spintronics.
