Molecular movements and translocations controlled by transition metals andsignaled by light emission

Transition metals can play a determining role in promoting oriented movemen ts at the molecular level. Examples include the oscillation of a pendant ar m in Ni(II) and Cu(II) scorpionate complexes (i.e., complexes of a tetraaza macrocycle containing a flexible coordinating side chain), which can be re located either on the metal center or far away from it, by varying pH. More over, a transition metal itself can be reversibly translocated between the two defined compartments of a heteroditopic multidentate ligand, by taking profit (i) of a pH change (which modifies the binding tendencies of one com partment) or (ii) of a variation of the redox potential [which changes the oxidation state of the metal, e.g., Fe(III)/Fe(II), Cu(II)/Cu(I)]. Examples are given in which the molecular motion [the swinging of the pendant arm i n an Ni(Il) scorpionate complex; the pH-driven translocation of an Ni(II) i on within an acid-sensitive two-box system] is signaled to the outside thro ugh a net change of the fluorescent emission of a built-in anthracene fragm ent.