Charge transfer states and super-exchange energy. The exciton states above from state interactions among locally excited monomers do not explicitly account for charge-transfer (CT) delocalization in the full system. Often, the energies of CT states between monomers X and Y are relatively high relative to valent excitations, but they, nevertheless, play an important role in stabilizing the excited complex. If the two monomers are symmetrically equivalent in an excimer, there is no net charge transfer, but the stabilization energy due to the resonance between CT configurations can still be significant. Such a resonance effect is also called super-exchange (SE) interaction in electron transfer theory, which is adopted here. The charge-resonance SE states are given by