A novel fluorescence redox switch based on the formal NiII/NiI couple

The nickel(II) complex of the naphthalene-containing macrocyclic ligand 4 has been synthesized by a template reaction and structurally characterized. [Ni(4)](2+), which in solution displays an emission spectrum typical of naphthalene derivatives, undergoes a reversible one-electron reduction process at a moderately negative potential value to give a formal nickel(I) species. The reduction process induces a distinct decrease of the emission intensity, but fluorescence is recovered after reoxidation to the original nickel(II) species. Thus, fluorescence can be switched OFF and ON through the redox reaction involving the formal Ni-II/Ni-I couple, which can be carried out both chemically (in MeCN : water) and electrochemically (in MeCN).