Nature of the lowest energy excited state of a bis-phenanthroline [2]-catenand and its Cu(I), Ag(I) and Co(II) complexes

The excited state absorption and emission spectra and lifetimes of a [2]-catenand made of two interlocked 30-membered rings (containing 2,9-dianisyl-1,10-phenanthroline-type coordinating moietes) and its Co2+, Cu+, and Ag+ complexes have been investigated in CH2Cl2 solution. The lowest energy excited state is established to be a triplet ligand-centered level for the Ag+ complex and a triplet metal-to-ligand charge-transfer level for the Cu+ complex. For the Co2+ complex, where no emission or transient absorption can be observed, the lowest excited state is most likely to be a distorted triplet metal-centered level. No transient absorption can be observed for the lowest energy triplet excited state of the [2]-catenand in CH2Cl2 solution because of a fast reaction with solvent molecules.