Light-emitting molecular devices based on transition metals

Multicomponent systems have been designed, which are able to perform defined functions related to light emission and quenching. The desired function can be switched ON/OFF by the operator through a chemical input, either a change of pH or a variation of the redox potential. Transition metals (e.g. NiII, CuII) are key constituents within the considered systems, playing a distinctive architectural role and favouring electron transfer processes. Investigated devices include static molecular switches, in which fluorescence can be quenched/restored through an acid–base or an oxidation–reduction reaction directly involving the metal centre, and dynamic switches, in which changes of the light emission intensity follow mechanical motions of the ligating framework. Motions include the oscillation of the pendant arm in scorpionate complexes, the metal ion translocation in a ditopic ligand and the assembling–disassembling of helicates.