Space-separated 1,10-phenanthroline, 4,5-diazafluorene, or 3,6-di(2-pyridyl)pyridazine units as ligands in diruthenium complexes: Preliminary studies of metal-metal interactions

[Extract] There has been much activity in the field of intramolecular energy transfer and electron transfer in large molecular assemblies, and the next advances will clearly require sophisticated molecular design. Where metal complexes are involved as the light-harvesting chromophore the design and construction of ligands becomes an important component. Studies on intramolecular electron transfer have been reported in which metal complexes have been tethered to redox-active chromophores, but almost all of these systems contain flexible linkages. Elegant syntheses have been reported recently for fully conjugated diad systems incorporating the 1,10-phenanthroline moiety as the bidentate ligand and we have described the first molecular rack (molrac) in which two units of the same ligand are spatially separated. We report here on the preparation of a new set of rigid bis(bidentate ligand) structures in which the individual bidentate ligands (1,10-phenanthroline, 4,5-diazafluorene, or 3,6-di(2-pyridyl)pyridazine) are fused to an alicyclic framework