Gating the photoactivity of azobenzene-type ligands trapped within a dynamic system of an M4L6 tetrahedral cage, an M2L2 metallocycle and mononuclear MLn complexes

Abstract

Complexation of transition metal ions by a doubly chelating bis(diimine)-type ligand incorporating a photoresponsive azobenzene linker yielded two types of structurally distinct metallosupramolecular architectures, an [M₄L₆]⁸⁺ tetrahedral cage and an [M₂L₂]⁴⁺ metallocycle. In solution, these complexes are open for reversible interconversions between each other by varying the M : L ratio, or switching into a dynamic library of [M(L′/L′′)_n]²⁺ mononuclear species upon addition of a competing monoamine. While the unbound ligand presents the reversible photoactivity of the azo bond, its complexes are photochemically inert, due to the inherent topology of these assemblies resulting from the restrictions of coordinate bond formation.