In principle, the synergic correlation mechanism involves a donor-acceptor energy transfer (ET) process where the luminophore and the SCO metal center act as donor and acceptor, respectively . The superposition of the luminophore emission and SCO metal center-based absorption (coming from metal-to-ligand charge transfer and d-d electronic transitions) significantly affect the luminescence signal of the luminophore during spin-state switching. The HS state of the SCO complex features very weak absorption in the near-IR (NIR) region, so the spectral overlap with the donor moiety is less. As a result, the luminescence of the donor doesn't quench (Fig. ). The LS state of the SCO complex has a high absorption coefficient in the visible region and has more spectral overlap with the ligand than the HS state. Thus, in this case, energy transfer from the donor to the metal center is much facile leading to quenching of the luminescence intensity of the donor moiety .