Self-assembly of new fluorescent Pd(ii) and Pt(ii) 2,7-diazapyrenium-based metallocycles and study of their inclusion complexes and [3]catenanes

Abstract

New fluorescent square-shaped metallocycles were self-assembled from N-monoalkyl-2,7-diazapyrenium derivatives 1 and 4 and Pd^II/Pt^II complexes. Using ligand 1, the metal-directed self-assembly process produced a single metallocycle, while the non-symmetrical salt 4 produced mixtures of regioisomeric Pd^II and Pt^II metallocycles upon complexation with the corresponding square-planar cis-complexes. Due to the improved π-deficient character of 1 and 4 compared to related bipyridinium-based ligands, complexation and catenation of the obtained metallocycles with selected electron-rich aromatic substrates produced the corresponding 1 : 2 inclusion complexes and [3]catenanes in a highly efficient fashion. This is particularly relevant for metallocycles derived from ligand 4, as complexation and catenation occurs in a regioselective fashion, generating only the supramolecules with the appropriate parallel arrangement of the diazapyrenium subunits in order to maximize the host–guest π-stacking interactions. The potential of the new metallocycles for optical signalling applications is illustrated by analyzing their absorption and emission behaviour upon complexation and catenation.